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Wed Apr 14, 2010 9:06 pm

Ok guys, I hate to do it but I have to show my ignorance here. I don't know the difference between A series and B series pistons. Could someone please explain the difference. Thanks

Clyde

Wed Apr 14, 2010 9:14 pm

B is for stroker engines.

Wed Apr 14, 2010 9:27 pm

wompninja wrote: B is for stroker engines.

The piston hole for the wrist pin is in a different location, to adjust for increased crankshaft stroke.

Wed Apr 14, 2010 9:38 pm

I really like your subject heading! Depending on what motor you are building you can use up to a 78 stroker with shims however your motor gets wider. This means modifying tin and sometimes headers and not to mention engine bays in some vehicles. But I really just wanted to comment on title. It is very appropriate at times. 8)

Thu Apr 15, 2010 6:44 am

C pistons exist too for 86 stroke and up :twisted: .

Thu Apr 15, 2010 12:31 pm

Can someone tell me exactly which series pistons are designed for which stroke? I am thinking about building an engine and I don't want to have to use shims or modify the sheet metal.

A =
B =
C =

Thanks for your help.

Thu Apr 15, 2010 12:34 pm

http://aircooled.net/gnrlsite/resource/articles/t1hpeng.htm

As = 69-76 stroke

Bs = 78-84 stroke

Cs = 86+ stroke.

but as I've said, Bs and 78 stroke are a non-standard combo, and usually require more work. One solution is longer rods to reduce the shimming, but you can avoid this by just using Bs with an 82 crank, and get a bigger engine to boot.

Thu Apr 15, 2010 1:12 pm

John,
Assuming I go with the 82 mm crank, I would like to go with a piston/cylinder set that will give me the thickest cylinder wall. What would you suggest?

Thu Apr 15, 2010 1:18 pm

what car?

Thu Apr 15, 2010 1:32 pm

69 Ghia coupe

Thu Apr 15, 2010 1:40 pm

no brainer; 94s

Thu Apr 15, 2010 1:44 pm

John,
Thanks, I will contact you when I get ready to order my parts. I really enjoyed reading the article in the link you posted.

Thu Apr 15, 2010 2:11 pm

Thanks to all who took the time to answer my question. Hopefully, one day, I will be able to do the same for others.

Clyde

Thu Apr 15, 2010 2:38 pm

I know it's been posted before, but for those that want to know

A : 39,6mm. from center of pin, to piston crown

B : 35 mm. from pin to crown

But this can't be right, now that I think about it. that's only a 4.6 difference, and in fact would make the 78.2 crank a perfect fit. ,,,,But i know from experience the 82mm makes it perfect.

Goin' to the garage and measure, BRB.

Thu Apr 15, 2010 2:46 pm

Can't find a B piston, think I gave them away....dang. Now this is bugging me. Tried to measure pin height on a A piston, looks to be around 40mm....hard to tell with hand held calipers.

Thu Apr 15, 2010 2:58 pm

Ok, the info posted on this site before is WRONG.

A =39.6mm
B =34mm

Which makes the 80.2 crank ideal( no such crank, I know), but if you want a close deck height, and you do, the extra .9 mm( 1/2 stroke increase )upward travel from the 82mm crank allows you set the deck easy with small shims.

Remember if you start trying to figure how much more piston travel you have, it's half the stroke increase. So going from a 69 to a 82, equals 82-69 = 13mm

13mm/2= 6.5.

The B piston gives 5.6mm more Deck, so you need to add shims to the extra .9mm. But, with 94mm pistons, the cylinders are a little longer, so if you build a 2276 it works out perfect.

Which makes a 2276 with chevy journals one the easiest strokers to build, and since all cranks cost about the same, there is no reason to F' with a smaller crank, the machine work to get the deck height right will cost you more.

Thu Apr 15, 2010 5:45 pm

My 1980 something Cima spec sheet says the 94 b was 35mm, while the 90.5 b was 34mm.
I don't have a 94 b to measure, I don't know if they are 35 or 34 now.
This is the likely reason for the mix up.

I think we should compile all the dimensions and make a thread about it.
Update my 1980 cima spec sheet for today, and post it.
It might save a lot of hassle. Good idea?

Fri Apr 16, 2010 12:14 am

Here is what I have as far as Cima/Mahle pistons. All this came from a magazine, All About Performance VW Engines II, from Hot VWs, I had which dates back to '97, so I am not sure if the specs changed from then until now. Hopefully nothing has changed since then. But if it did please post up, I would like to update my spec sheet for future reference.

Cima/Mahle compression height

piston size, A/B
85.5mm 1.551"/no B's ever made
87mm 1.551"/no B's ever made
88mm 1.558"/no B's listed or made in '97
90.5mm 1.558"/1.338"
92mm 1.558"/1.358"
94mm 1.558"/1.378"

Now I don't have anything about AA or QSC pistons. It would be nice to update my current list.

Now I remember back in the 80's Scat used to offer many different pistons with a range of compression heights for the different sizes of stroker crankshafts. One could order up a set pistons for a 76 stroke crankshaft and in theory, no shims needed and it is just as wide as a stock 1600. Same goes with any other stroke up to 82mm. It seems it was not very popular, since everyone had the mentality to just "go big or go home" and went with the 82mm stroke.

Fri Apr 16, 2010 1:49 am

Yes, that matches up perfectly with my old sheet. Now that I look at it, 92b says 34.5mm compression height. Huh.
I will be buying some 92b soon. Will be interesting to see what they really are.
I just bought some AA thickwall 92A, looks like they directly copied mahle. The cylinders are just like mahle 94s on the outside, 101 top, 97 bottom, 114 head to case.
The pistons are just like mahle too, even used the same cam grind on the piston, different alloy though. 39.6 compr height.

Fri Apr 16, 2010 10:56 am

the engine my builder is currently putting together for me is a 74mm Crank with B pistons.

Any Thoughts?