7A vs 3B blocks

[Error404]

I'v got a choice to use either a 3B or a 7A block for my build. Both are good.

Investing in new pistons so will be getting a re-bore either way.
Obviously i will gain about 100 CC using the 7A but are there any downsides i.e. cylinder wall thickness / stability?

Cheers
Alex

[JP]

Stock mls gasket is 82mm 7A is 82.5mm

[20Vcqdriver]

Know several people using the 7A block so must be an easy answer. Hope so as just started stripping a spare 7A to replace my 3B block...... Like you say and instant 100cc extra

[spink]

[QUOTE=20Vcqdriver;579626Know several people using the 7A block so must be an easy answer. Hope so as just started stripping a spare 7A to replace my 3B block...... Like you say and instant 100cc extra[/QUOTE]

still no sign of it then?

[OldKingPole]

Sorry, are we talking just using the 7A block with 3B internals or 7A block and 7A internals? And i'm assuming a 3B or other 20vt head to cap it off right?

[Error404]

Stock mls gasket is 82mm 7A is 82.5mm

Thanks for the info mate, that might be a decider then.
Do you know if they available for the 7A block on the aftermarket?

[andy10v]

Things I have read; gasket as said, thinner walls and also less option too oversize in future due to wear/accidents (don't know if that is a consideration to you though)

That said seem to be a few high hp 7a base motors.

[JP]

If I were doing a 7a block properly I'd run the stock fibre gasket and o-ring the block. It's a cheaper and more effective solution for the 600hp bracket than the overkill copper gasket and o-ring route.

[Rocco]

If you want more power,displacement,torque, use the 3b block with a 92.8 or 95.5 crankshafts.



It is possible of course!

[Error404]

If I were doing a 7a block properly I'd run the stock fibre gasket and o-ring the block. It's a cheaper and more effective solution for the 600hp bracket than the overkill copper gasket and o-ring route.

I'm trying to put together a bulletproof engine capable of a reliable 450-500lbft with as big an area under the curve as poss. So considering the 7A purely from an extra CC point of view, i guess my question should be is it worth going down the 7A route to help me achieve my goal?
Books I have read have stressed bore stability as being critical though, which was my concern about the thinner cylinder walls on the 7A being more suceptible to ovaling, especially if it was rebored to 82.75 for new pistons.

[x6rs]

heard of a guy in sweden with 600hp+ s2 coupe 7a... oem internals(didnt open the engine!), big turbo, NIRA efi, and drove it on e85

[x6rs]

guess i was wrong, he did change rods and bearings, but used oem pistons from 7a and didnt change pistonrings
heres the tread, but only in swedish: http://www.karlstadracing.nu/viewtop...147&hilit=audi

645 hp/764 nm

[20Vcqdriver]

still no sign of it then?

Given up to be honest, but might have done me a favour if I can get this 7A to fit easily which it looks like it will and gain a capacity increase. Looks like 034 do a metal gasket for $95 that suits 82.5 bore.. Just need to source the pistons before i do anything else... Any recommended, Wossner seems to be several peoples preference as no slap when cold apparently

[Jamo]

Re gasket ask Terrybullwon to overbore the standard metal gasket which he can to 83mm, problem solved.

[Jeltuh]

guess i was wrong, he did change rods and bearings, but used oem pistons from 7a and didnt change pistonrings
heres the tread, but only in swedish: http://www.karlstadracing.nu/viewtop...147&hilit=audi

645 hp/764 nm

Did he use the stock head as well? Couldn't find it in the thread.