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- Sep 18, 2002
Why not lower cr via cleaning up the combustion chambers? I'm pretty sure you could lose 0.3-0.5 without too much trouble and/or removal of squish area. Just a thought.
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Building a B21FT from the ground up
- Thread starter The Aspirator
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Matt Dupuis
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- Feb 18, 2004
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- Calgary, Ab
What I meant by "reverse domed" is to mill out a shape that mirrors the shape of the combustion chamber. That leaves the entire squish band intact, similar to a flat top, unlike a cylindrical dish. The ring lands would stay solid, unless you allowed the shape to extend out to the edge of the piston (as does the shape of the combustion chamber.)
Milling off the top of the piston just puts the piston further down the hole, and kills your squish.
Kenny's right, of course: You could take out some volume from the combustion chamber. I'm afraid of how much you'd have to take out, though, and what it would do to the swirl. Flow would probably go up... maybe... possibly... if you do everything right... if you know what you're doing.
The chamber porting would be less expensive but more time consuming, and you'd have to measure your chambers while you're doing it, to make sure that the volumes stay consistent cylinder to cylinder. Getting a CNC to carve up the pistons will be much easier and you'll be sure that they're all the same. However, you'll be weakening the pistons, but lightening them up too. Pros and cons...
Milling off the top of the piston just puts the piston further down the hole, and kills your squish.
Kenny's right, of course: You could take out some volume from the combustion chamber. I'm afraid of how much you'd have to take out, though, and what it would do to the swirl. Flow would probably go up... maybe... possibly... if you do everything right... if you know what you're doing.
The chamber porting would be less expensive but more time consuming, and you'd have to measure your chambers while you're doing it, to make sure that the volumes stay consistent cylinder to cylinder. Getting a CNC to carve up the pistons will be much easier and you'll be sure that they're all the same. However, you'll be weakening the pistons, but lightening them up too. Pros and cons...
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stealthfti
Guest
to lower the SCR...
John,
I can understand your concern on SCR....for your motor and for your brother's motor. The higher the SCR, the lower the total boost level that can be used; and the more precise the ignition timing has to be.
The flattop B21F pistons do not have the thickness of material in the crown to accomodate machining a dish of sufficient depth to lower the compression ratio enough solely by doing that machining. And, as Matt pointed out, removing a layer of material from the entire crown is counterproductive. I would not recommend thinning the crown on those cast pistons. If you determine that dishing the pistons is necessary, then I suggest that the better course of action would be to install B21FT pistons: they have a 6.1mm [0.240in] dish.
As Cappy suggested, opening up the combustion chambers several cc's would be an effective way to lower the SCR. There is material across from the spark plug, on the other side of the valves, that could be removed to increase the CC volume a sufficient amount; and without weakening the head. Removal of material there would not necessarily diminish squish action; it would increase the volume of the CC without making the distances for the flame to travel overly long: you would be widening the combustion chamber.
Basically, it boils down to three choices on the B21FT motor build:
...install B21FT pistons with the 6.1mm [0.240in] dish,
...open up the combustion chamber several cc,
...or do both.
If budgetary constraints are such that obtaining B21FT pistons is not feasible, then combustion chamber enlargement is the direction that you will have to take. Some actual volume measurements of the combustion chambers, and calculations of the static compression ratio will need to be performed in order to establish just where the motor build will be with the flattops deck clearanced for good squish. The Mahle catalog lists the B21F flattops as being 9.3:1 SCR; but that is more of a comparison number than a precise number.
All that said, I still have a feeling that the main issues, and the resulting contradictions, are not being addressed.
The issues: a budget build for the joint purposes of a reliable daily driver and a weekend racer. The contradictions: the cross purposes of reliability and racing on a budget.
How so? A reliable DD on a budget is doable. And to a point, a racer on a budget is also doable. The budget limits the race capabilities. The race use affects the reliability. Because the race use will make the temptation to up the boost for that "little bit more power" irresistable. Enough is never enough; and the easy way to get more is to up the boost. And every time the boost gets upped just a little bit to get just a little bit more, the reliability takes a hit.
For a reliable DD that runs stronger than stock, a tight squish high SCR motor is very good. For the weekend racer, the high SCR is going to be a barrier that will be ignored....sooner or later. The contradictions will be resolved: something will break.
Rather than creating the contradictions, the build should be done to accomodate the reality: do the build with a lower SCR. That way the temptations that are not resisted won't kill the motor as quickly.
I am not saying this as a complaint; but as an acknowledgement of the reality.
TF
John,
I can understand your concern on SCR....for your motor and for your brother's motor. The higher the SCR, the lower the total boost level that can be used; and the more precise the ignition timing has to be.
The flattop B21F pistons do not have the thickness of material in the crown to accomodate machining a dish of sufficient depth to lower the compression ratio enough solely by doing that machining. And, as Matt pointed out, removing a layer of material from the entire crown is counterproductive. I would not recommend thinning the crown on those cast pistons. If you determine that dishing the pistons is necessary, then I suggest that the better course of action would be to install B21FT pistons: they have a 6.1mm [0.240in] dish.
As Cappy suggested, opening up the combustion chambers several cc's would be an effective way to lower the SCR. There is material across from the spark plug, on the other side of the valves, that could be removed to increase the CC volume a sufficient amount; and without weakening the head. Removal of material there would not necessarily diminish squish action; it would increase the volume of the CC without making the distances for the flame to travel overly long: you would be widening the combustion chamber.
Basically, it boils down to three choices on the B21FT motor build:
...install B21FT pistons with the 6.1mm [0.240in] dish,
...open up the combustion chamber several cc,
...or do both.
If budgetary constraints are such that obtaining B21FT pistons is not feasible, then combustion chamber enlargement is the direction that you will have to take. Some actual volume measurements of the combustion chambers, and calculations of the static compression ratio will need to be performed in order to establish just where the motor build will be with the flattops deck clearanced for good squish. The Mahle catalog lists the B21F flattops as being 9.3:1 SCR; but that is more of a comparison number than a precise number.
All that said, I still have a feeling that the main issues, and the resulting contradictions, are not being addressed.
The issues: a budget build for the joint purposes of a reliable daily driver and a weekend racer. The contradictions: the cross purposes of reliability and racing on a budget.
How so? A reliable DD on a budget is doable. And to a point, a racer on a budget is also doable. The budget limits the race capabilities. The race use affects the reliability. Because the race use will make the temptation to up the boost for that "little bit more power" irresistable. Enough is never enough; and the easy way to get more is to up the boost. And every time the boost gets upped just a little bit to get just a little bit more, the reliability takes a hit.
For a reliable DD that runs stronger than stock, a tight squish high SCR motor is very good. For the weekend racer, the high SCR is going to be a barrier that will be ignored....sooner or later. The contradictions will be resolved: something will break.
Rather than creating the contradictions, the build should be done to accomodate the reality: do the build with a lower SCR. That way the temptations that are not resisted won't kill the motor as quickly.
I am not saying this as a complaint; but as an acknowledgement of the reality.
TF
The Aspirator
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Thanks guys, it looks like opening up the combustion chambers will be the easiest and cheapest way of doing things. Below is a picture of my 405 before any work, and I still don't know why the cylinder is so much larger than the combustion chamber....? Wouldn't you benefit from blending down the sidewalls to be a lot smoother of a transition? It's just that when I see pictures of extensive head porting, this is never done. So I'm sure there is a reason.
http://www.j2mediagroup.com/john/405-02.jpg
Stealth, one big reason for the B21F pistons is that they're 1st oversize. And higher compression. We still have Erik's B21FT pistons, and they might do alright with just a hone and new rings. But they're SUPER low compression, is there a way to raise that? What if we milled the tops down a bit, and decked the block alot? Then that would probably screw up the cam timing and such.... But if there were a way to use those pistons and raise compression, we might consider it because that would take off the cost of boring the cylinders. I dunno.
Stealth, you mentioned doing both. Installing the B21FT pistons and porting the combustion chamber, but wouldn't that result in like 7.0:1 compression?????
John
http://www.j2mediagroup.com/john/405-02.jpg
Stealth, one big reason for the B21F pistons is that they're 1st oversize. And higher compression. We still have Erik's B21FT pistons, and they might do alright with just a hone and new rings. But they're SUPER low compression, is there a way to raise that? What if we milled the tops down a bit, and decked the block alot? Then that would probably screw up the cam timing and such.... But if there were a way to use those pistons and raise compression, we might consider it because that would take off the cost of boring the cylinders. I dunno.
Stealth, you mentioned doing both. Installing the B21FT pistons and porting the combustion chamber, but wouldn't that result in like 7.0:1 compression?????
John
Matt Dupuis
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- Calgary, Ab
- The "cylinders" being so much bigger than the chambers - you're looking at the inside diameter of the fire ring there, and the ID of the fire ring is well outside the OD of the cylinder, for obvious reasons. If you want to blend down the chamber to anything, I suggest you bolt it to the block once the block's bored, scribe a line on the head all around the circumference of the cylinder, and port the chamber out to that line.The Aspirator said:
- The B21FT pistons - Brad bought Kolbenschmidt B21FT pistons for his rebuild, but their dishes are similar to B21A piston dimensions - I think that they're reducing cost by spec'ing the same piston for both engines. I don't know if it's equivelant to the reinforced cast construction of Mahle B21FT pistons or not, but you were going to use plain cast pistons in the engine, so what's the big deal? The SCR ends up at about 8.7:1 with those pistons, after boring, decking the block and head, etc., before any porting to the CC is done, and they're reasonably priced. If you want to send me those pistons back, no hard feelings, and you'll save the cost of rings.
*edit* The B21F pistons haven't proven to be too weak yet - in fact, none of the F+T guys have broken/melted a piston yet, have they? If the pistons are still plenty strong at .300" thick, and if a lighter piston with a proper mirrored dome could be created by thinning them by 15%, would it not be unreasonable to try?
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stealthfti
Guest
The Aspirator said:
John,
in my last post, I was listing the options for lowering the SCR; and I did the job poorly. I was not intending to advocate a particular choice. And as I review it all, I may have come across as dissing Matt's autocad suggestion. [A mirror dish would be sweet.] I did not intend that. So: my apologies, Matt.
I am confused: which head is going on your brother's motor? the 398 or the 405?
Actually, as I have thought about this some since, I have decided to be more pro-active, and clearer; and suggest that you go with the flattops; possibly do some combustion chamber enlargement via either a shallow mirror dish and/or some head CC work; go for 37 to 35 squish; and start out with the A or B cam.
Doing some combustion chamber size increases would be good. But, if you do not enlarge the CCs, the SCR will not be unmanageable. You are close to Cappy; discuss the head CC work with him. He can and will advise you well on that. He won't let you kill the squish.
I would suggest that, for the B21FT built with flattops and tight squish, you will notice a considerable power increase offboost, during transition to boost, and in boost.
You will have to start off with boost settings on the conservative side when it is built. And the same goes for the redline. I would suggest that 10 PSI and 5500 are good starting points.
Yeah, that IS conservative. But the reason to start off like that is to allow you time to get used to the tight squish and fast burn. It will be different from what you are used to.
Tight squish/higher SCR does have its drawbacks: it is more sensitive to stupidity. So: don't be stupid. Build the motor carefully; run it in carefully; and get to know what it can do. Starting out with a conservative boost and redline, I would suggest that the way to find the power potential would be to try to optimize the power output at that boost level, and under that redline. Tuning for more power will no longer be just a matter of cranking up the boost. It will take more thought and prep than that. When you have done what you can at 10/5500 to get the most output, you will find that the next level up will be easier to fine tune.
A tight squish/fast burn/higher SCR motor also has its attractions: it will WANT to run and make power. You won't have to force it to make power. Your job will be more of removing the hindrances that hold it back.
An example that would apply to both points: exhaust flow. I am fairly certain that you will find it necessary to improve the exhaust flow with a 90+ manifold and 3in system. That stuff won't be an option; it will be essential. That motor will be demanding it.
In case I don't have time to post more on the motor build before leaving, I wanted to add a couple of things:
...for the main and rod bearing clearances, I would suggest going for 0.002in.
...for the piston to cylinder wall clearances, I would go for 0.002in.
those clearances are on the loose side of how I prefer to set things up; but will lend themselves well to a weekend warrior.
I hope this helps clear up the confusion I may have caused with my last post. I think the 1st OS flattops are the way to go.
TF
The Aspirator
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Thomas, that was wonderful. Clear and concise, I totally understood it.
Sorry I confused you, Erik will be using a 398 head for now. And we have both an A-cam and a B-cam that we could use, I guess they're fairly similar, so it doesn't matter much.
I also agree completely that setting the limits at 10psi and 5500 rpm would be ideal to get things started. With Megasquirt and Spark I'll be able to set a nasty rev limiter on him, that he won't be able to change. And I'll just tell him not to up the boost. There's also an overboost fuel cut option that I haven't tried yet, but I'm sure it'll work wonderfully.
Once we both get a good feel for this engine, and get it broken in, then we can start upping the boost. But I think as it stands, with the 10psi/5500rpm, it'll be pretty damn quick anyways. We're not trying to build a 12 second car right now, just something super reliable and damn quick. I really thing we're on the right track so far. Once things get settled, and numbers start going up, I don't think I'll let the engine rev much more than 6,500 rpm, so I guess we could call that our absolute redline.
As for exhaust, he's already got a 3" system installed, except it's using a B21ft downpipe. Very shortly after getting this motor done and installed we will upgrade that to a 3" mandrel downpipe and cat. The 90+ manifold might have to wait a little bit, but it'll be on the upgrade list. If I have time and energy I might end up trying to port his pre-90 manifold, turbine housing and wastegate hole. We'll see.
As you said, the drawback of a higher compression motor is that it's more sensitive to stupidity. I think we will not O-ring it, but rather use a copper sprayed Elring as Doug suggested. Also, it obviously has Megasquirt and Spark. Soon enough I'll implement a knock sensor with LED, and megasquirt will pull ignition timing whenever it knocks. This will allow some leeway for bad gas or other odd things (stupidity). I'll throw my Wideband O2 sensor on there for a while and get things tuned nice and safe fuel wise.
Thanks for the clearance numbers, I still have to pick up one of those Volvo Green Manuals. I think the project might actually start up this week. First up is to get the parts hot tanked and magnafluxed. I'll be sure to update this thread with tips and tricks that I'm learning along the way.
John
Sorry I confused you, Erik will be using a 398 head for now. And we have both an A-cam and a B-cam that we could use, I guess they're fairly similar, so it doesn't matter much.
I also agree completely that setting the limits at 10psi and 5500 rpm would be ideal to get things started. With Megasquirt and Spark I'll be able to set a nasty rev limiter on him, that he won't be able to change. And I'll just tell him not to up the boost. There's also an overboost fuel cut option that I haven't tried yet, but I'm sure it'll work wonderfully.
Once we both get a good feel for this engine, and get it broken in, then we can start upping the boost. But I think as it stands, with the 10psi/5500rpm, it'll be pretty damn quick anyways. We're not trying to build a 12 second car right now, just something super reliable and damn quick. I really thing we're on the right track so far. Once things get settled, and numbers start going up, I don't think I'll let the engine rev much more than 6,500 rpm, so I guess we could call that our absolute redline.
As for exhaust, he's already got a 3" system installed, except it's using a B21ft downpipe. Very shortly after getting this motor done and installed we will upgrade that to a 3" mandrel downpipe and cat. The 90+ manifold might have to wait a little bit, but it'll be on the upgrade list. If I have time and energy I might end up trying to port his pre-90 manifold, turbine housing and wastegate hole. We'll see.
As you said, the drawback of a higher compression motor is that it's more sensitive to stupidity. I think we will not O-ring it, but rather use a copper sprayed Elring as Doug suggested. Also, it obviously has Megasquirt and Spark. Soon enough I'll implement a knock sensor with LED, and megasquirt will pull ignition timing whenever it knocks. This will allow some leeway for bad gas or other odd things (stupidity). I'll throw my Wideband O2 sensor on there for a while and get things tuned nice and safe fuel wise.
Thanks for the clearance numbers, I still have to pick up one of those Volvo Green Manuals. I think the project might actually start up this week. First up is to get the parts hot tanked and magnafluxed. I'll be sure to update this thread with tips and tricks that I'm learning along the way.
John
- Joined
- Nov 12, 2002
The Aspirator said:
Best bet John, install a knocksense on his car. Boris had to picked the worlds brightest LED for it (luckily). I think you can do ok on a true block/head with just a copper sprayed Elring.
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- Rockville, MD
when all is said and done this thread should be consolidated and made into a article
The Aspirator
It's a girl!
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Yup, that's what I meant. I've got one sitting here waiting to go into my car. Can't wait to see how bright this thing really is! Where did you place your LED?Snoop Dougy Doug said:
Boris once told me that if you put this LED anywhere within 30* of your face, it'll poke your eye out!
John
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stealthfti
Guest
John,
Get the 398 head combustion chambers checked for cc's. I ran some numbers; and verified them as best I could. You need to have the CCs to be at least 55cc; and preferably 58-60cc. That will bring the SCR down to about 9.3:1 with 58cc CCs.
The flattops, the 1st OS, and the decking for plus 10 kicks the SCR up real fast.
Talk to Cappy on that before you turn someone loose on that head with a die grinder. The objective is to get to 58cc or more; but without killing the squish area and action. It can be done. And of course, you want all four to be the same size.
This is important: to get the SCR into the lower 9's, and keep the tight squish. There is material opposite the spark plug that can be removed and reshaped to open up the CC without hurting the squish action. The hump next to the spark plug can be blended back a tad as well. I strongly discourage removing any material between the valves; ie, between the cylinders themselves. Some do this calling it radiusing the wall for improved flow. You need the meat there between the cylinders. Don't remove any metal there.
Cappy and I have gone around and around on this in the past. He can explain what you need to do to that 398 head.
TF
Get the 398 head combustion chambers checked for cc's. I ran some numbers; and verified them as best I could. You need to have the CCs to be at least 55cc; and preferably 58-60cc. That will bring the SCR down to about 9.3:1 with 58cc CCs.
The flattops, the 1st OS, and the decking for plus 10 kicks the SCR up real fast.
Talk to Cappy on that before you turn someone loose on that head with a die grinder. The objective is to get to 58cc or more; but without killing the squish area and action. It can be done. And of course, you want all four to be the same size.
This is important: to get the SCR into the lower 9's, and keep the tight squish. There is material opposite the spark plug that can be removed and reshaped to open up the CC without hurting the squish action. The hump next to the spark plug can be blended back a tad as well. I strongly discourage removing any material between the valves; ie, between the cylinders themselves. Some do this calling it radiusing the wall for improved flow. You need the meat there between the cylinders. Don't remove any metal there.
Cappy and I have gone around and around on this in the past. He can explain what you need to do to that 398 head.
TF
The Aspirator
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I talked to Kenny (captain bondo) for a little while today. We kind of came to the conclusion that it would be much better to start with a 405 head rather than a 398. Since we are trying to enlarge the combustion chamber, it would be easier to start with the 405. According to the article on the T-bricks homepage by Mike Aaro...
398: 51.7cc
405: 53.7cc
If my eventual goal is 58cc's, that's a LOT of grinding to the 398. And my inexperienced hands would feel vulnerable to messing up an effective chamber. According to literature, a B23 with a 398 head has 10.3:1 compression ratio, but the same engine with a 405 has just 10:1 SCR. So a rough estimate would conclude that a 2cc bigger chamber would equal .3 less of a compression ratio. So if I brought the 405 head out to 58cc's, I could estimate a drop of .845 in the compression ratio as opposed to using a stock 398 head! Wow, that's PLENTY.
The problem is that I live about an hour's drive away from my brother, so we can't really work on this project each and every day. That's why we haven't really started yet, cause I haven't had the chance to get down there. I'll be heading down there for a few days here soon, so we'll see what I get accomplished.
John
398: 51.7cc
405: 53.7cc
If my eventual goal is 58cc's, that's a LOT of grinding to the 398. And my inexperienced hands would feel vulnerable to messing up an effective chamber. According to literature, a B23 with a 398 head has 10.3:1 compression ratio, but the same engine with a 405 has just 10:1 SCR. So a rough estimate would conclude that a 2cc bigger chamber would equal .3 less of a compression ratio. So if I brought the 405 head out to 58cc's, I could estimate a drop of .845 in the compression ratio as opposed to using a stock 398 head! Wow, that's PLENTY.
The problem is that I live about an hour's drive away from my brother, so we can't really work on this project each and every day. That's why we haven't really started yet, cause I haven't had the chance to get down there. I'll be heading down there for a few days here soon, so we'll see what I get accomplished.
John
andrew_d
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Is it an established fact that B23 had the same pistons in both 10.3:1 and 10:1 verisons?
I wonder how it can be that swapping a head on B230F from 530 to 531 gives a 0.5 CR drop from 9.8:1 to 9.3:1 but doing supposedly the same thing on B23 drops it only 0.3? Do 405/531 heads have different CC size? Do 398/530 heads have different CC size?
I'm 100% sure that B230F(9.8:1) and B230FB/FX (9.3:1) pistons are the same. Actually, entire bottom end is the same ...
Just curiosity.
I wonder how it can be that swapping a head on B230F from 530 to 531 gives a 0.5 CR drop from 9.8:1 to 9.3:1 but doing supposedly the same thing on B23 drops it only 0.3? Do 405/531 heads have different CC size? Do 398/530 heads have different CC size?
I'm 100% sure that B230F(9.8:1) and B230FB/FX (9.3:1) pistons are the same. Actually, entire bottom end is the same ...
Just curiosity.
Matt Dupuis
Active member
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- Feb 18, 2004
- Location
- Calgary, Ab
Yes it's an established fact that both engines you mentioned had flat top pistons. However, what's not clear is the deck height of any of the blocks that were delivered from Volvo. It's of the opinion of some that they machined more or less from the block to change the compression ratio slightly for different markets It may be that the B230F had the same pistons and bottom end, but with a little bit more taken from the top of the block, than the B230FB/FX, and when you combine that volume with the volume in the combustion chamber, you get the 0.5:1 C/R change.andrew_d said:
Not to mention, that's an "advertized" compression ratio. Volkswagen is notorious for over-selling the CR of their motors, to adjust for "used conditions", where carbon builds up on top of the pistons, raising the compression ratio to get the engine up to near the advertized number. It's possible that the B230FB/FX actually had 9.5:1, or the B230F had 9.5:1, or BOTH had 9.5:1.
The Aspirator
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I have quite a few tips to share that I've recently picked up. Now, Matt/Thomas/Kenny already know this stuff in and out, but the rest of us noobs can really benefit from learning this!
Subject: Pre-ignition
I've been talking to all these guys, and reading Corky Bell's book "Maximum Boost", and I'm learning a hell of a lot of neat stuff. There are MANY ways to combat detonation, not just lower compression. Corky says that for example an improperly setup 7.0:1 compression motor might detonate a lot more than a 9.0:1 comp motor with proper squish/etc. So it's all how you set it up.
One thing I just learned about was "hot spots in the combustion chamber".
Here is a picture I took so you can visualize what I'm talking about:
Look between the valve seats, see that little ridge sticking up around the perimiter? Could this be a possible hot spot? Also if the spark plug itself doesn't thread all the way into the head, those extra unengaged thread could be hot spots too.
(notice also how the right valve seat has a dull shine to it, this is what lapping the valves does. It provides a good seal between the valve and the valve seat. A more complicated method is a 3 or 5 angle valve job)
Here is an image from the Stealth's site showing roughly where a spark plug is located, and how far it's threaded in. (Also if you've ever heard talk about "indexing" spark plugs, this means having all 4 heads point the exact same direction in the combustion chamber, further making each cylinder burn just like the rest)
Click here
And here is a big picture of his showing what a nicely smoothed and shaped combustion chamber looks like:
Click here
More later, we'll try to document the entire process with pictures and descriptions.
John
Subject: Pre-ignition
I've been talking to all these guys, and reading Corky Bell's book "Maximum Boost", and I'm learning a hell of a lot of neat stuff. There are MANY ways to combat detonation, not just lower compression. Corky says that for example an improperly setup 7.0:1 compression motor might detonate a lot more than a 9.0:1 comp motor with proper squish/etc. So it's all how you set it up.
One thing I just learned about was "hot spots in the combustion chamber".
The way I understand that is that every little sharp edge could get really hot (from lots of boost, lets say) and pre-ignite the mixture before the spark plug lights up. Meaning, detonation. Now what can cause hot spots to get hot in the first place? HOT charge air. A good intercooler will combat this well. As would a water injection system that comes on at say 5psi. Anything to get the intake air colder is an improvement.Maximum Boost said:
Here is a picture I took so you can visualize what I'm talking about:
Look between the valve seats, see that little ridge sticking up around the perimiter? Could this be a possible hot spot? Also if the spark plug itself doesn't thread all the way into the head, those extra unengaged thread could be hot spots too.
(notice also how the right valve seat has a dull shine to it, this is what lapping the valves does. It provides a good seal between the valve and the valve seat. A more complicated method is a 3 or 5 angle valve job)
Here is an image from the Stealth's site showing roughly where a spark plug is located, and how far it's threaded in. (Also if you've ever heard talk about "indexing" spark plugs, this means having all 4 heads point the exact same direction in the combustion chamber, further making each cylinder burn just like the rest)
Click here
And here is a big picture of his showing what a nicely smoothed and shaped combustion chamber looks like:
Click here
More later, we'll try to document the entire process with pictures and descriptions.
John
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dl242gt
The world of the smiling Dogo
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- Jun 21, 2002
- Location
- S NJ, a suburb of Phila.
head and hot spots
One of the interesting things pointed out to me by Pierre is that the metal casting quality is better on the higher output factory heads. He told me that when polishing the combustion chambers the 405 polishes to a brighter, smoother, finish than any of the 160 and 398 heads he has worked on. This may also apply to the 530 vs the 531. So a better finish in the combustion chamber in the first place will also help eliminate potential hot spots.
Best regards,
One of the interesting things pointed out to me by Pierre is that the metal casting quality is better on the higher output factory heads. He told me that when polishing the combustion chambers the 405 polishes to a brighter, smoother, finish than any of the 160 and 398 heads he has worked on. This may also apply to the 530 vs the 531. So a better finish in the combustion chamber in the first place will also help eliminate potential hot spots.
Best regards,
Volv-a-Ratti Man
New member
- Joined
- Oct 8, 2004
- Location
- Prosper, TX
This is a good thread to introduce myself.
Hello, I am new to T-Bricks but not to Volvo's. Been over at Club Volvo for a while, and thought I'd migrate a bit.
I've got a project going to take a super modified B21F that I had a pro shop re-build for my now deceased '78 242GT. It is a high (9.5:1) compression engine with a +.060 overbore and Mahle alloy flat-top pistons and rods with 1" mains. I had originally wanted to make a great rally beast of this 180 hp n/a motor that has an R grind cam on it (not actually sure, but I got it in '87 from IPD and is NLA due to emissions in the US, very high lift and overlap), but has been sitting for almost 10 yrs and only 50 miles on the motor. The guy that did the head for me was a drag race specialist and did his magic on the head, which is a 398 head. He opend up the combustion chamber to the piston diameter and made a swirl around the edge between the intake an exhasut valve with about a 1/4 radius, deepening into a hollow in the middle of the combustion chamber. Behind the intake and exhaust valve, he sculpted the ports to large smooth radius, tapering down to where the valve seats started. When he was done, it had a mirror finish. He then planed .030 off the head to reduce the gap between the piston and combustion chamber and raise the '79 B21F stock compression.
A note to you guys from them old timer that did my motor, scrap those dished out pistons that came on the early 8.7:1 n/a taht came in my 242GT (what POS motor!) or 7:1 Turbo motors. He said the porting and polish will do more than anything to improve combustion and you'd want to bump the compression up anyway. Since he had a Lotus Esprite Turbo apart on the bench next to my motor, I took his word for it.
The 242GT flew for only a short time, but it's time now to resurect the motor. I've got a turbo and manifold along with the Turbo+ kit from an '89 780 Bertone and plan on dropping it into my '89 245. Initially I want to use the LH 2.4 to see how it behaves, but ultimately think I need a secondary system to control fuel at WOT, like plumbing the K-Jet injectors with a valve operated pressure regulator and the fuel distributor in-line with the LH2.4 AMM. That means an 8 injector system, using a low boost and BOV somewhere aroung 5-8 psi.
I'm just beginning on the new project, so , I'll be back with more questions and comments as I get farther along.
In the mean time, my new V70 2.5T is nice, but just isn't fast enough either! I had a built '68 144 that was a lot faster than any stock Volvo turbo I've ever had (1/4's in the high 13's), so now it's time to get a built turbo. Maybe some competition for Doug who's probably lurking around here somewhere.
Oh, and Hi Dave!
Peter
Hello, I am new to T-Bricks but not to Volvo's. Been over at Club Volvo for a while, and thought I'd migrate a bit.
I've got a project going to take a super modified B21F that I had a pro shop re-build for my now deceased '78 242GT. It is a high (9.5:1) compression engine with a +.060 overbore and Mahle alloy flat-top pistons and rods with 1" mains. I had originally wanted to make a great rally beast of this 180 hp n/a motor that has an R grind cam on it (not actually sure, but I got it in '87 from IPD and is NLA due to emissions in the US, very high lift and overlap), but has been sitting for almost 10 yrs and only 50 miles on the motor. The guy that did the head for me was a drag race specialist and did his magic on the head, which is a 398 head. He opend up the combustion chamber to the piston diameter and made a swirl around the edge between the intake an exhasut valve with about a 1/4 radius, deepening into a hollow in the middle of the combustion chamber. Behind the intake and exhaust valve, he sculpted the ports to large smooth radius, tapering down to where the valve seats started. When he was done, it had a mirror finish. He then planed .030 off the head to reduce the gap between the piston and combustion chamber and raise the '79 B21F stock compression.
A note to you guys from them old timer that did my motor, scrap those dished out pistons that came on the early 8.7:1 n/a taht came in my 242GT (what POS motor!) or 7:1 Turbo motors. He said the porting and polish will do more than anything to improve combustion and you'd want to bump the compression up anyway. Since he had a Lotus Esprite Turbo apart on the bench next to my motor, I took his word for it.
The 242GT flew for only a short time, but it's time now to resurect the motor. I've got a turbo and manifold along with the Turbo+ kit from an '89 780 Bertone and plan on dropping it into my '89 245. Initially I want to use the LH 2.4 to see how it behaves, but ultimately think I need a secondary system to control fuel at WOT, like plumbing the K-Jet injectors with a valve operated pressure regulator and the fuel distributor in-line with the LH2.4 AMM. That means an 8 injector system, using a low boost and BOV somewhere aroung 5-8 psi.
I'm just beginning on the new project, so , I'll be back with more questions and comments as I get farther along.
In the mean time, my new V70 2.5T is nice, but just isn't fast enough either! I had a built '68 144 that was a lot faster than any stock Volvo turbo I've ever had (1/4's in the high 13's), so now it's time to get a built turbo. Maybe some competition for Doug who's probably lurking around here somewhere.
Oh, and Hi Dave!
Peter
- Joined
- Sep 18, 2002
Hey man, that ridge is exactly the spot I was trying to explain getting rid of when you came by the little shop of horrors the other day. Basically you take all of that "roughness" on the roof of the chamber down so it is flush with the valve seats. Making that all smooth will eliminate hotspots like you just read about.
I was thinking, btw- I have a nice new Blue-Point variable speed 1/8" air pencil (tiny die grinder especially for porting) I bought to port my head, and i also have a portable compressor. Prob is I have no bits yet. If you can track down some bits I could bring that stuff by and we could clean the head up if you're free on a monday. Oh, I have the stuff to cc the chambers too. hit me up on pm if you're interested. I wouldn't mind some practice and if we eff it up I have multiple 398's if need be.
I was thinking, btw- I have a nice new Blue-Point variable speed 1/8" air pencil (tiny die grinder especially for porting) I bought to port my head, and i also have a portable compressor. Prob is I have no bits yet. If you can track down some bits I could bring that stuff by and we could clean the head up if you're free on a monday. Oh, I have the stuff to cc the chambers too. hit me up on pm if you're interested. I wouldn't mind some practice and if we eff it up I have multiple 398's if need be.
S
stealthfti
Guest
John,
I can understand your desire to start with the 405 head because of the larger cc CC to start with.
I suggested the actual cc'ing of the 398 head to confirm the CC volume because I really do think that the footprint of the 398 head would be better than the 405 would be, on a 1st OS B21. I like to have as close to a complete circle of squish area around the piston. To illustrate my point: take a B21 HG, and lay it onto a 398 head and look at the amount of head surface that is inside the fire ring. Then do the same overlay on a 405 head. There will be less of an overlap over the fire rings between the cylinders.
I realize that I cannot offer 'proof' or 'evidence' that having a squish area all the way around the CC is either a necessity or something that is even important. I can only offer the evidence that 'where' there is a good tight squish clearance over the ringland areas of the piston, those areas of the ringland will run cooler...because of the boundary layer proximity heat transfer that does occur where the squish clearance is tight. And I believe that keeping the ringlands as cool as possible is a very good thing.
The other reason that I would recommend the 398 head as the better one to start with is because of that extra aluminum between the cylinders. The more metal there between the bores, the stronger and more rigid the head casting will be between the bores.
If you can see your way to understand what I am driving at from the squish area and strength of the casting between the bores viewpoint, then I would suggest that you get a disposable syringe or a small beaker that holds 25 cc or 50 cc of liquid, and put 5 or 6 cc of water in it. It actually is not that much of a volume. There is room to remove that much metal on the other side of the CC across from the spark plug. That 'straight' wall over there can be rounded out a bit away from the spark plug.
I understand that such an undertaking of enlarging the CC volume can be quite intimidating; but the benefits of getting the CC volume up to about 58 cc for that tight squish flattop B21FT will be worth it. You will get the SCR down to under 9.4:1, which will enable you to run higher boost levels as time progresses. [whether or not you will HAVE to run higher boost levels is yet to be seen]
Getting the combustion chambers to the needed size and uniformly sized IS worth the effort. And if you have to practice on a junk head, so be it.
For a comparison purpose, and for a reference purpose: I spend about 40 hours assembling the shortblock; and I spend almost that much time on the cylinder head itself. I don't flat rate a motor build: however much time it takes to get it 'right as rain' is how much time it takes......attention to details takes time. I have the time AND take the time to do the job right [or as close to 'right' as I can possibly get it] the first time. Having to redo a job is more than a double loss to me. Fortunately, I don't have to redo a job very often.
What I am trying to get across is this: if you want that motor to live, and if you want it to be durable, it is not going to be a "wham bam thank you ma'am" proposition. "Quickies" are for another area of life's experiences.
****
Pre-ignition is not the same thing as detonation. Pre-ignition can actually have more catastrophic results than detonation because it can occur anytime after the intake valve opens....something to further your research and analysis. And yes, getting rid of sharp edges is a very good thing to do.
TF
I can understand your desire to start with the 405 head because of the larger cc CC to start with.
I suggested the actual cc'ing of the 398 head to confirm the CC volume because I really do think that the footprint of the 398 head would be better than the 405 would be, on a 1st OS B21. I like to have as close to a complete circle of squish area around the piston. To illustrate my point: take a B21 HG, and lay it onto a 398 head and look at the amount of head surface that is inside the fire ring. Then do the same overlay on a 405 head. There will be less of an overlap over the fire rings between the cylinders.
I realize that I cannot offer 'proof' or 'evidence' that having a squish area all the way around the CC is either a necessity or something that is even important. I can only offer the evidence that 'where' there is a good tight squish clearance over the ringland areas of the piston, those areas of the ringland will run cooler...because of the boundary layer proximity heat transfer that does occur where the squish clearance is tight. And I believe that keeping the ringlands as cool as possible is a very good thing.
The other reason that I would recommend the 398 head as the better one to start with is because of that extra aluminum between the cylinders. The more metal there between the bores, the stronger and more rigid the head casting will be between the bores.
If you can see your way to understand what I am driving at from the squish area and strength of the casting between the bores viewpoint, then I would suggest that you get a disposable syringe or a small beaker that holds 25 cc or 50 cc of liquid, and put 5 or 6 cc of water in it. It actually is not that much of a volume. There is room to remove that much metal on the other side of the CC across from the spark plug. That 'straight' wall over there can be rounded out a bit away from the spark plug.
I understand that such an undertaking of enlarging the CC volume can be quite intimidating; but the benefits of getting the CC volume up to about 58 cc for that tight squish flattop B21FT will be worth it. You will get the SCR down to under 9.4:1, which will enable you to run higher boost levels as time progresses. [whether or not you will HAVE to run higher boost levels is yet to be seen]
Getting the combustion chambers to the needed size and uniformly sized IS worth the effort. And if you have to practice on a junk head, so be it.
For a comparison purpose, and for a reference purpose: I spend about 40 hours assembling the shortblock; and I spend almost that much time on the cylinder head itself. I don't flat rate a motor build: however much time it takes to get it 'right as rain' is how much time it takes......attention to details takes time. I have the time AND take the time to do the job right [or as close to 'right' as I can possibly get it] the first time. Having to redo a job is more than a double loss to me. Fortunately, I don't have to redo a job very often.
What I am trying to get across is this: if you want that motor to live, and if you want it to be durable, it is not going to be a "wham bam thank you ma'am" proposition. "Quickies" are for another area of life's experiences.
****
Pre-ignition is not the same thing as detonation. Pre-ignition can actually have more catastrophic results than detonation because it can occur anytime after the intake valve opens....something to further your research and analysis. And yes, getting rid of sharp edges is a very good thing to do.
TF