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Back to the drawing board...6-speed options for a Redblock?

Mylesofsmyles

A Member
Joined
Jan 18, 2010
Well, I always learn the hard way... fortunately there wasn't much cost involved, less a couple hundred dollars and a few hours, before I found out the transmission I elected wasn't the best choice. With my M46 slowly starting to show it's age, I've been investing time and research into other options for a custom upgrade.

I know there's been success with the T5 and the Getrag 5-speed options, when mounted behind a turbo Redblock, but I'm interested in narrowing down the 6-speed options to a handful of candidates.

I chose the Aisin AZ6 from a Honda S2000 because the shifter location, output flange configuration, overall size and power handling to be ideal for a 240 with up to 350ish hp. I thought it had a simple removable bell housing, however, now that I've got the transmission in front of me, I see the bell housing is integral with the front cover, and removing it would leave 1.5-2" of transmission open, exposed and loose. It'd require, at least a custom front cover, that'd then accept a Redblock bell housing.

So, here's the riddle, is it economical to assume I can have a custom front cover made for cheap, and have it accept a stock or modified redblock bell housing? Or do I leave the S2000 transmission alone and consider other options?


Other options to consider...

Tremec T56, but I'm worried about gear ratios, cost and size
ZF-whatevs? from a BMW or Nissan 350Z, dunno why I wouldn't consider these.

Anything else to consider?

Anyone able to machine a way to use the Aisin AZ6 for under $1,000?

I know there are some smart people here, and plenty who are creative, so thought I'd ask.

I really like the idea of a close ratio 6 speed...fun for the twisties and auto-x and still one for the open road. My conclusion on the AZ6 might have been a little premature and undereducated, but I'm open to input. I know the Mazda, Toyota and Honda tuners really like the AZ6, as it's light, shifts beautifully and handles an impressive amount of power.

And to satisfy those just jonsing for pictures, here's my AZ6...

DSCF4816.JPG


DSCF4818.JPG
 
you remove a few inches of material from the mating surface (transmission to Honda motor) , weld up a new plate........inside diameter could be an issue, do you have a redblock flywheel or pressure plate to see if it fits?
 
Says who?

should be fine. I know people with boosted turbo miata's and rotary powered miatas with upwards of 450 hp and torques and love this tranny.

the miata version is really no different with regards to the integral front cover/bell housing. it's different on the output side though, it accepts a splined yolk instead of the flange type we have. an easy hurdle to clear, however the lengths of the S2000 unit are so close to the M46, that I'm hoping this swap can be done with an unmodified 240 driveshaft.


you remove a few inches of material from the mating surface (transmission to Honda motor) , weld up a new plate........inside diameter could be an issue, do you have a redblock flywheel or pressure plate to see if it fits?



I considered the option of cutting the front of the Honda flange and welding on the redblock bell housing flange...the machinist liked the idea at first, but ruled it out when he decided there wouldn't be enough surface to do so.

I don't have a flywheel and pressure plate to fit in there, but should.
 
how far does the input shaft stick past the bellhousing is the first question, if it sticks out far enough a simple steel adapter plate may be all that is needed. second option is making a jig that has the bellhousing pattern of the redblock concentric to the input shaft, and fab a new bellhousing around it, one of the ones i saw was basically a bushing around the input shaft into the pilot hole in the crank, a template of the bellhousing attached to the volvo block, and then the engine/tranny is shimmed and measured until they're concentric, with the bellhousing cut off the tranny with some room to attach material, a new one is welded in place (constantly making sure it stays in spec)

shouldn't cost more than a grand, really......

also not sure on the tolerance for an input shaft, but plus or minus a couple thou should be adequate, and not impossible to maintain.
 
how far does the input shaft stick past the bellhousing is the first question, if it sticks out far enough a simple steel adapter plate may be all that is needed. second option is making a jig that has the bellhousing pattern of the redblock concentric to the input shaft, and fab a new bellhousing around it, one of the ones i saw was basically a bushing around the input shaft into the pilot hole in the crank, a template of the bellhousing attached to the volvo block, and then the engine/tranny is shimmed and measured until they're concentric, with the bellhousing cut off the tranny with some room to attach material, a new one is welded in place (constantly making sure it stays in spec)

shouldn't cost more than a grand, really......

also not sure on the tolerance for an input shaft, but plus or minus a couple thou should be adequate, and not impossible to maintain.


the input shaft is about flush with the end of the bell housing. with my quick, vague measurements, the input shaft of the honda is about 0.5" shorter than the volvo. internal diameter of the bellhousings is about the same, but I still need to see how well a volvo clutch and flywheel will clear.

with the shortage in input shaft length, I wonder if I can get away with a slim hydraulic throwout bearing to control the clutch.
 
No personal experience , but the swedes mate the Volvo bellhousing to the ZF box from a BMW all the time. Its even possible to buy a complete welded up ZF box at certain dealers.
What are the ratios like in the Honda box ?
 
Came two ways...

2000-2003, which I think is what I have...


1st: 3.133
2nd: 2.045
3rd: 1.481
4th: 1.161
5th: 0.970
6th: 0.810
Secondary gear reduction: 1.160
Final drive: 4.100
Reverse: 2.800


and 2004-2009....

1st: 3.133
2nd: 2.045
3rd: 1.481
4th: 1.161
5th: 0.943
6th: 0.763
Secondary gear reduction: 1.208
Final drive: 4.100
Reverse: 2.800
 
Them ratios are great for an na car....there to close for a turbo car.....you'll never take advantage of the boost and the power out put....it'll rev out to fast. Id like to see a deeper first gear or a taller 6th gear.
 
Them ratios are great for an na car....there to close for a turbo car.....you'll never take advantage of the boost and the power out put....it'll rev out to fast. Id like to see a deeper first gear or a taller 6th gear.

Or you'll have greater success staying in the boost curve, no?

Close ratio means less drop in revs with each shift, no? so the revs stay up and I stay in the boost, so far as I understand it.

These ratios are fairly close to the T5 ratios, just a little tighter and one final gear.

For reference...

http://www.ttcautomotive.com/english/products/T-5.asp
 
I have a T5 in my car with the 2.95 first.....3.73 rear and 25 inch tall tires. How much tq does your car make? I might be in a differeat league here but, I build 300+ ftlbs from just shy of 4k to over 7k. So my power band is pretty big. My .76 is a little short on the freeway and my 2.95 is a little tall for good take offs. I think for a good 6 speed in a turbo car, either have 2 overdrives like .8 then .6 or so, or have 5th gear 1-1 with a deep 3.50+ first gear and run a taller diff setup.

Auto's only shift 3 times to get to 1-1 and TLAO is pulling some good times with that. To me, just to me, thats one extra gear in my power side to have to use the clutch.....Id rather go for 2 decent overdrives after driving the T5 I have now with a 4.11 rear gear.
 
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