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What's the thinnest b230 Cometic you've run?

I have run several .027" Cometic gaskets on redblocks, nothing has collided yet.
B230s? Do you know how much the pistons were sticking up, if any, before reassembly?
Yes again. Rebuilt, as in boring of the cylinders and new pistons. Or 'refreshed' as in measured and bores honed, with pistons cleaned, measured, knurled and fitted to restore piston to wall clearances to ~1.5 thou [0.0015-0.0017"]

Remember, the rule of thumb for squish clearance is a guideline for safely getting into tight squish on a build. The fact that rod stretch is not linear to rpm is accounted for in the guideline.

You might want to review what I wrote on pbase:

www.pbase.com/stealthfti/b230ftshortblock

....where I get into not only the advantages of going tight squish, but also a third corollary about going for optimal squish.

Which was in part the reason I built the 24 thou squish motor. For the purposes for which that motor would be used, I wanted to push the guideline a bit. The car's owner was given the assurance that if there was any problem due to the extra tightness of the squish clearance, my 50,000 mile warranty on the motor would fully cover it. at no charge.

It has over 60K on it, and it still performs excellently.

I would advise for you to shoot for a squish clearance in the low/mid 30s. At 35 thou, you have achieved effective tight squish. And I sure hope that you have an effective and reliable rev limiter on that motor. For those times in the heat of battle that someone misses a shift.....haha

TF
Do you have a write up of what you've experienced on the .024" squish motor and if it's been more beneficial than other tight squish motors you've done? Or any other links to more recent areas of your gallery, it's been a couple years since I went through it. I'm sure it's better, but it's probably by a hair. Then again, a lot of hairs add up, and that's what some of us are here for. A LOT OF HAIR! :rofl: Seriously though, what were your thoughts on that setup? I guess some of the benefit would be from the slightly raised compression ratio, if nothing else.

I know there are a few out there that have slapped on the .027" gaskets on top of untouched b230s, but getting them to comment in here seems a bit harder than a personal message. :-(

To be honest, I think we are going to risk running tighter squish than that. In part to be as efficient as possible, in part to raise compression as far as we feel safe doing, and in part to experiment. It doesn't take too long to do a headgasket, especially if we use Hylomar, and we have a little over a month left to do some testing once re-assembled.

As far as redline goes, it's LH2.4 but raised a little bit. It doesn't hit ignition cut until at least 7500rpm(I don't know if the ignition chip has a rev limit, basically), but the fuel cut, which is what normally kicks in first on an LH car, should be around 6500.

On another note, were you referencing to anything specific when talking about oil pressure? :)
 
piston piston poke/drop measurement done, now which gasket thickness?

Interesting thread...

I'm not sure if I've got the target properly conceived or not...
Let's say I'm going for the tight squish arrangement, which seems at this point to suggest aiming for a figure of 0.035" unless I'm trying to participate in exploring the boundaries and gains therein. My motor is a '92 B230F, original and stock at ~150k mi. I've measured +0.004" of poke on cylinder one, meaning above the block deck by 0.004" on cylinder one, and maybe as much as 0.005" on cylinder four. This was at the indicated (as in with a dial indicator, not with the timing mark which is off by maybe around 2 degrees) TDC.
Does this indicate a theoretical gasket thickness of 0.039" in order to reach the target for tight squish? I see the Cometic 0.040" gasket, which is PFC, and the 0.036" which would seem to result in a squish-tastic 0.032" figure.

1) Am I doing the figgerin' correctly?

2) If I was at a theroretical 0.043" with the stock gasket, and the head is at NAPA awaiting a rebuild and decking, shall I just have them take off 0.008" and plan on a stock ga$ket instead of the Cometic?

Thanks for any remedial attention I may need...
 
I'm running an 0.027 on my B23F+T. Stock bottom end with flattops, stock head with a K-cam. My pistons were about 0.005 in the hole.

I scraped the block & head at home, cleaning them up really well, then just slapped the Cometic in there. No problems, no leaks. This motor runs ~10.7:1 SCR and is happy with 10psi of boost from a 60/48 T3.

I ran an 0.027 on a B230FT for a few months. Again, I cleaned up the head and block surfaces really well before installing the Cometic. It also sealed flawlessly and worked great. As mentioned, you can feel the extra compression. A rod let go before the gasket.
 
Interesting thread...

I see the Cometic 0.040" gasket, which is PFC, and the 0.036" which would seem to result in a squish-tastic 0.032" figure.

1) Am I doing the figgerin' correctly?

2) If I was at a theroretical 0.043" with the stock gasket, and the head is at NAPA awaiting a rebuild and decking, shall I just have them take off 0.008" and plan on a stock ga$ket instead of the Cometic?

Thanks for any remedial attention I may need...

1) yes

2) you can go that route: mill the block deck to increase the piston deck height positively to be able to use an OE type composite HG to end up with the squish clearance in the tight squish range....under 35 thou.

BTDT

but using the correct thickness MLS HG is easier.

I would say that the 36 thou MLS HG would be my first choice, given the piston deck height numbers you've given. A 40 thou MLS HG would not do it as well. 2nd choice would be a 30 thou HG, IF the piston rock is not excessive, and you're not going to be hanging out at redline a lot.

Kyle, I meant to respond back when, but got busy elsewhere. Since what you're doing with that motor is intended to hang out in the upper RPM ranges, I would have ASSumed that oiling would have been a high priority. Because the B2XX motors oil the four rods via two mains, making sure of rod oiling IS a priority.

Just what all to do and how far to go in pursuit of priority rod oiling......that's a discussion that I don't care to get into for probably another year. I have some things in R&D that are being worked on and checked out that it will be quite a while before I can show the results on....it's a five point attack. When I do have the results, I will be incorporating the findings, procedures, and parts into motors I build. What I am saying here is that priority rod oiling is something that I have had to address for a few projects on the white board. I'm working on it.

TF
 
2) If I was at a theroretical 0.043" with the stock gasket, and the head is at NAPA awaiting a rebuild and decking, shall I just have them take off 0.008" and plan on a stock ga$ket instead of the Cometic?

Thanks for any remedial attention I may need...

Um, decking the HEAD won't bring it any closer to the pistons...
 
True, but that won't affect the "squish-tastic" figure he's referring to. But your point is well taken- increase your odds of mixing valves and pistons- engine stew!
 
True, but that won't affect the "squish-tastic" figure he's referring to. But your point is well taken- increase your odds of mixing valves and pistons- engine stew!

Wait...why wouldn't it change the squish parameter? In bringing the roof of the combustion chamber closer to the piston crown, why does it matter, at least as far as resultant squish, whether that is achieved via milling the block, milling the head, or changing to a thinner gasket? I can see reasons for choosing one method or the other, some theoretical some practical, but I can't see a squish reason.
 
Wait...why wouldn't it change the squish parameter? In bringing the roof of the combustion chamber closer to the piston crown, why does it matter, at least as far as resultant squish, whether that is achieved via milling the block, milling the head, or changing to a thinner gasket? I can see reasons for choosing one method or the other, some theoretical some practical, but I can't see a squish reason.

Then it is apparent that your understanding of just what "squish clearance" is, and what determines it to be, is SERIOUSLY deficient and uninformed.

There is no way that machining off material from the cylinder head surface will ever do a damn thing to change "squish clearance". period.

YOU have some reading to do.

TF
 
Then it is apparent that your understanding of just what "squish clearance" is, and what determines it to be, is SERIOUSLY deficient and uninformed.

There is no way that machining off material from the cylinder head surface will ever do a damn thing to change "squish clearance". period.

YOU have some reading to do.

TF

TF -

Hey, thanks for the replies, I'm trying to learn what you're talking about here. I've read your page linked in this thread a few times. Maybe you've got another reference link or a dozen words to help explain to this dunderhead "why" bringing down the roof via machining aluminum doesn't bring squish clearance down, but bringing it down via a thinner gasket does. That's what I was trying to ask. It seems like any deficiency in this knowledge could prove to be serious for the person contracting work and putting an engine together. I'm a bit surprised, but willing to believe, how dense I'm being here, help me out...

Thanks again for any help, I'll be over here in the corner with my new awesome pointy-hat!
 
True, but that won't affect the "squish-tastic" figure he's referring to. But your point is well taken- increase your odds of mixing valves and pistons- engine stew!

Well that point is overblown and all people need to do is plot valve lift and crank rotation to see that IF valve lift begins say 25* BTDC and closes say 60* ABDC that max lift is somewhere around 100* ATDC, and that valve lift at TDC is, in the girlie-boy cams that everybody here uses, maybe at max around 1.2 to 1.6mm..
Chamber is ~~~ 12-13mm deep so chopping 1-1,5mm off still means when the piston is at TDC there's 7-8mm between valve and piston---IN A 8V with valves inline with bore.


Gets way more exciting with valves canted over 22-22.5*:omg:
 
TF -

Hey, thanks for the replies, I'm trying to learn what you're talking about here. I've read your page linked in this thread a few times. Maybe you've got another reference link or a dozen words to help explain to this dunderhead "why" bringing down the roof via machining aluminum doesn't bring squish clearance down, but bringing it down via a thinner gasket does. That's what I was trying to ask. It seems like any deficiency in this knowledge could prove to be serious for the person contracting work and putting an engine together. I'm a bit surprised, but willing to believe, how dense I'm being here, help me out...

Thanks again for any help, I'll be over here in the corner with my new awesome pointy-hat!
Quench pads are above the hg. Milling a head doesn't bring the pistons higher than a non milled head

---------|
________|
________|
---------|

That ghetto ASCII representation of the bore and piston should help. See how its slightly below deck. The head is above that. Milling it won't magically move the head closer to the piston, there is still the block deck and hg in the way. Milling the block or thinner hg makes it like

---------|
__________|
__________|
---------|
 
Wait...why wouldn't it change the squish parameter? In bringing the roof of the combustion chamber closer to the piston crown, why does it matter, at least as far as resultant squish, whether that is achieved via milling the block, milling the head, or changing to a thinner gasket? I can see reasons for choosing one method or the other, some theoretical some practical, but I can't see a squish reason.

Forget all the droniing panacea crap and listen, it really is simple...
*look at a piston and notice there's these grooves cut in the side leaving an overhanging shelf above the first groove
* ponder now the strength of nice aluminum alloy as temp rises from all the exciting sheet going on, and the pressure (just think about say 75 bar pressure or in 'Merkanski about 1175 PSI ---there's around 11.33 sq/in in a 96.5mm piston and thats 1175 pounds pressure on each of those 11.33 sq/in
Strength of aluminum gooes down sharply with temp going up.

So IF the edge of the piston all overhanging that ring groove "sees" a bunch of that temp, strength goes down and pressure--normal pressure is going want to deform the thing downward..
SO, bring the piston as close as we dare to the nice relatively cool flat parts of the head---conveniently enough they're called "quench pads"------(note : they don't call them "squish pads") and we do a number of things nice...
1)nearly all the air/fuel mix is shoved into the chamber where it has a better chance of burning in the time we have--which ain't a lot of time. 3000 rpm means the motor turns around 50 times a second a full 360 degrees---
2)and mainly the piston edge doesn't "See" all the exciting fire and pressure and being near the nice cool head---REMEMBER! There water just a few mm away, nice cool water/coolant

so the edge ofthe poor long suffering piston doesn't heat up insanely, get localised insanely hot, and weaken.
(and begin to fail and/or pinch the top ring)

The best engine guys in this country are NASCAR guys--those pushrod things as 'ancient" as the designs, make more BMEP that F1 motors make.
NASCAR guys speak about "bore to quench pad ratios".....If you look at some of the tactic they're doing, then look at the most interesting of the head work being done in Sweden (http://www.topplocksverkstan.se/ )you'll see both are making more and more compact combustion chambers by having--via welding on both 8 and 16v Volvo heads, then reshaping----larger and larger quench pads...
This type of thinking reached local level guys like me way back in 1987, there's nothing new about it..
That's why I say it is firmly established that one can mitigate detonation when piston is somewhere around .036 or 0,9mm from the nice cool head.....and......

there MAY very well be further benefits to bring the piston even closer...I've built some at around .032....

But so far there are only assertions--ya know--claims..And angry bluster, and harumph-ing and cowardly slander, sadly.

The problem with 8vs is relatively small quench pads and i don't anticipate people here welding chambers and reshaping---despite the great benefits to flow ---especially at lower lift--and increased flow at lower lift always makes a car quicker--- so the easiest solution is a better head design---the pent roof 16v head.. Flow AND thermal efficiency..

But they also benefit from increased quench pad area....

Re-reading your post slower:
Milling block pluses: can overcome block variation and get those pistons DEAD FLUSH or out by the hole by (my preferred) .004---and a bit more if you're brave. I ain't brave
Also you get a flat deck, which is usually not the case these days.

004 stick out CAN be done by ordering custom pistons thru someplace that gives a s**t:oogle:, but with stock or off the shelf cheapies, decking kills 2 birds w/one stone.

Leaving pistons down the bore is the worst thing and most B21/B23 motors stock leave the poor pistons .010 to .016 down the bore, accomplishing nothing except exposing the piston to heat, and keeping it away from the succor of the head.


Does this help? Fixating and throwing the word "squish" around endlessly is focusing on the means, not the end...Sometimes it is better to use the terms--representing concepts--that are used by people in the trade...and here at Turbobrick the word "squish" has become what is called a "social marker" used to show one belongs to a social group...... for whatever that's worth in trying to build your motor to make reliable power.:roll:
 
having fun, but still corn-fused

L-A: Thanks for the post, I'm guessing that in your illustration the head is missing, but would be positioned to the right of the illustration? My pistons, if I'm understanding the illustration, have been measured as already being in a position more like your bottom illustration.

Re-reading your post slower:
Milling block pluses: can overcome block variation and get those pistons DEAD FLUSH or out by the hole by (my preferred) .004---and a bit more if you're brave. I ain't brave
Also you get a flat deck, which is usually not the case these days.

004 stick out CAN be done by ordering custom pistons thru someplace that gives a s**t:oogle:, but with stock or off the shelf cheapies, decking kills 2 birds w/one stone.

Leaving pistons down the bore is the worst thing and most B21/B23 motors stock leave the poor pistons .010 to .016 down the bore, accomplishing nothing except exposing the piston to heat, and keeping it away from the succor of the head.


Does this help? Fixating and throwing the word "squish" around endlessly is focusing on the means, not the end...Sometimes it is better to use the terms--representing concepts--that are used by people in the trade...and here at Turbobrick the word "squish" has become what is called a "social marker" used to show one belongs to a social group...... for whatever that's worth in trying to build your motor to make reliable power.:roll:

John,
Thanks for the post. Things like ratio of bore to quench pad area are right up my alley, and fun to talk about. I understand the benefit of getting the piston circumference areas closer to some cooler parts of the head, and the other stuff. Thanks for the background.

There's a little bit more area to fill under my pointy hat, theory-wise.
What we're calling quench pads are 3-dimensional volumes of material within the cylinder head, right? These areas are not in plane with the HG, they're above it, is that right? If that is so, then does removing some of the head not bring these areas downward and therefore closer to the piston? Granted, more than one thing is being changed by doing that, and not all of it is good. I also understand that compared to the piston position, decking the head doesn't change the point at which HG meets head.

One other thing, if you re-read my post slowly again, you'll see that I'm saying my pistons are ALREADY 0.004"-0.005" above the block deck! Above and not below! Stick out! Poke! Whatever you want to call it...I've got that. Given that, I just couldn't devine how using a thinner HG brings the quench pads closer to the piston but milling some head off the areas below the quench pads doesn't. Now if the quench pads are co-planar to the HG mating surface, then I'd get it. That I could understand. Is that it? My head is at the machine shop or else I'd check it myself.

For brevity's sake, here are some multiple choice responses...

[ ] The quench pads in the head are co-planar to the HG mating surface, that's why decking the head doesn't do the squish-tastic stuff we're talking about.

[ ] Yes, milling the head would do the same boundary layer co-mingling that a thinner HG would do in this case.

[ ] Whatever dude, it's my way or the highway.

[ ] Too many words, too many words.
 
Quench pad/area= the area of the cylinder head surface (deck) that is outside of the combustion chamber, but within the cylinder. When the piston is at the top, on our 8V heads, there's a little area opposite the spark plug, and just where the spark plug sits where the piston ALMOST touches the head. This is where the mixture gets SQUISHED at TDC and squeezes into the combustion chamber all turbulent like.

Since the quench pad surface IS the cylinder head surface, machining it won't bring it any closer to the cylinder block. This can only be done by decking the block to have the pistons poke out farther, or using a thinner head gasket.
 
You would have to shave the head quite a bit to change the size of the quench pad.
Take the block and put a staight edge across the bore. Rotate pistones to top dead center and measure gap with a feeler gauge. Then have the block shaved that amount or slightly more.
Dont make it too complicated.
 
Finally folks are beginning to get it and use good useful real words like "poking out"

Quench pads; the flat bits within the gasket area:
K20RadDeck3.jpg



And we're trying to avoid doing this:
DSCN4620.jpg


And this:

detonation_03.jpg


and this is really what we're trying to avoid at all costs, piston to head contact:
2011-09-25_19-54-58_932-1.jpg



I say its hard to really sit down and crunch a bunch of numbers to calculate all the factors that could lead to pistons ramming into the head, too many places that one would be forced to guess, making all the rest of the 'calculating" into a big wank fest...and thus a huge waste of time for a unknown, only theoretical advantage which may only be an advantage under very narrow (imagined--or guesssed at) conditions..

So get the damn thing within say 030 to 040 OR!!! over 3mm and be happy.
 
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