[Torbjorn968]

Are these done by bore or stroke? (both?) Bad idea?

Torbjörn

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[Monstrous4Banger]

Usually bore. 108mm IIRC. Bad idea? Hmmm, depends who you talk to. Whether or not its a bad idea I think has to do with boost levels. Our engines blocks have an open deck, under high boost, the cylinders tend to "wiggle", and lose shape. The thinner the cylinder wall, the more likely it will wiggle. There are ways around this. I plan to go to 3.2 on my 93', with moderate boostg levels, about 17-18 psi most likely. Ive been told, its fine, as long as you keep the boost down....start turning it up, and running high octane, youll wish you hadnt. There are also ways to close the deck. Maybe someone else here has done it, kept 108mm, and could shed some more light on that. Sleeving is one option, but the only person i woould trust a sleeved motor from, can only go 106mm with sleeves.

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[firefish]

As the saying goes - thick walls make more power.

For our engines, how much does the cylinder pressure differ between a built N/A-engine, let's assume 12,5:1 and a peak hp at about 280-300, compared to a rather mildly specced turbo charged piece with about 350 hp?

And how much gain could be anticipated for the above mentioned engines if increasing the displacement from 3.0 to 3.2, assuming everything else is the same?

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[ds968]

I was also wondering about the anticipated gain in hp and torque and if both would be proportional with the displacement percentage change.. or what the variances may be otherwise. My mechanic said there are way too many variables that would come into play and while logically you will have more power and more torque to estimate the gain in either one would be entirely speculative..
I would have considered doing this when I had the head rebuilt, IF any pistons and/or other part of the cylinders would have also been damaged from the timing belt incident.. but they weren't so I did not pursue the option.
I do recall we sourced ( just to satisfy curiosity ) the cost of custom pistons to fit the new 3.2 and, IIRC, they were about $ 2,000 for the four.

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[flash]

all things being equal, a 3.2 will give you about 10ft/lbs and about 15hp over whatever you have with a 3.0 - this is pretty much across the board though, and not just peak, so it makes a bit more sense

cooling is the issue with larger displacement, so you have to figure that out

the rev limit also comes down a bit

balance is all different too, as the mass is changed, so the balance shafts would very likely need to be altered or deleted to avoid harmonic disruption, as well as a complete balance job done on the crank, rods, and flywheel setup

it can work, and i will quite possibly be doing this at some point, but it won't be cheap or easy to get it right - between sleeves, pistons and balancing, i'm guessing an additional $8k over a standard rebuild

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