92mm Pistons

Birdman Wolfsburg Wizard

428 posts · joined May 2010 · 26 Apr 2013, 4:33 pm

#952958

Hey all,

For some reason I have the opinion that 92mm pistons are a bad idea in a performance engine and 94s would be better.

somthing about thin walls and going oval when they get hot?

I mate a picked a scat engine kit with AA 92's and wants to circuit race it so im a bit worried for him.

Can anyone with actual case machining and or engine building knowledge give me some info about this scenario please?

He is convinced the 92s are a better way to go because he is scared of getting too close to the head studes when machining for 94's????
cheers

Stanley I guess the reward is in the doing of it

4,523 posts · joined Mar 2003 · 26 Apr 2013, 8:48 pm

#953007

There's plenty of guys running 94s circuit and drags.
For what it costs for machining i'd go 94s. In saying that I've had an 1835 and never had an issue but I didn't race it.
My advice would be to unconvince him.

matberry Moderator Go hard or go home

8,114 posts · joined Mar 2006 · 26 Apr 2013, 10:13 pm

#953026

I wouldn't touch the thin wall 92's. One look at the two side by side and it's very obvious, the 92's cylinders are way thinner. Cylinder stability (staying round), head to barrel seal and ring sealing suffer. There are thick wall 92's available but they use the same size hole as 94.

Top engine builders use an even thicker cylinder than the std 94 when possible

Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE

Birdman Wolfsburg Wizard

428 posts · joined May 2010 · 29 Apr 2013, 6:51 pm

#953438

matberry wrote:There are thick wall 92's available but they use the same size hole as 94.

Thanks mate, this is the type of info im after.

So you have to machine a bigger hole for 94's but my mate says that you start cutting into the stud area and this scares him, hence he went for 92's.

Is this true and what do you do about it? case savers and 8mm studs?

matberry Moderator Go hard or go home

8,114 posts · joined Mar 2006 · 29 Apr 2013, 7:37 pm

#953449

Is he worried about the case or the head? Doesn't really matter as his concerns are unfounded. It is a tricky machining proceedure as sometimes the original barrel spiggot location needs to be tweeked to be centred to the studs but nothing an experienced VW machinist isn't used to. Best to get someone like DB (Dangerous) to do the machining.

Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE

Bizarre Moderator The artist formerly known as blue74l

12,785 posts · joined Aug 2002 · 29 Apr 2013, 7:41 pm

#953455

He could always put 90.5's in - the case and heads are cut the same as 92's
Yes - it will only be 1776

The 90.5's will be thicker walled at the heads than the 92's

Or just run the 92's and reasses when/if you develop power loss or problems later

Futue te ipsum!!!