Can you build either using the stock 2.5 block? Or do you need to get a 3.0 block from a 944 S2/968?

Do you need crank, rods, pistons for both, or just crank and/or pistons for the 2.8?

What are good pistons to use and why? What compression ratio and why?

 

Here is some good info from Chris Cervelli,

"Of course there is the right way and the wrong way to do a stroked 2.8. The right way:

Turbo block bored to 100.5mm
New Mahle pistons for 8:1 CR and 100.5mm bore. These pistons have the pin moved to accomodate the extra stroke. Otherwise the piston would stick out of the bore by about 4.5mm at TDC.
Carrillo rods. The stock rods won't clear the block with the longer stroke. Plus the Carrillos are the best rods you are likely to see.
944S2 or 968 Crankshaft.

The wrong way:

Stock pistons
4.5mm shorter rods to fix the piston problem.
944S2 or 968 crank.

This is really screwed up. The CR is way too high and the rod angle situation is much worse. This engine will never make any power and always want to detonate.

Here is what I expect to see from a stroker 2.8 compared to a normal 2.5 (all other things being equal):

A very large increase in low end torque and a very small increase in top end power. This borne out on the dyno as my 2.8 makes 320rwhp and 375 ft/lbs at only .95 bar. You would also expect to see the peak power and torque occur at a lower rpm.

For the all bore (106mm??) 2.8 I would expect to see a roughly 10% increase up to say 5000 rpm or so, where the percent of increase would dwindle unless the cylinder head's breathing ability was improved. I have not done a 2.8 this way, and don't intend to, because I feel if you can't use factory type pistons, you can't guarantee 100,000 mile durability. (I could be wrong here, I have heard a few sleeving success stories lately)

If we are talking about street cars only, it is obvious that the area in which the 951 needs the most help is low end torque. The stroke 2.8 is going to acheive this much more effectively than the bore 2.8. Plus, you can use all factory type parts are be assured of the durability.

For an all out race engine, the bore 2.8 has more potential. The larger bore allows more room for big valves and should improve breathing automatically. But if you are going this far, why not make a 106mm bore engine with the long stroke? That would be around 3.15 liters I guess.

I have built a ton of stroke 2.8 and found them to be really great for street cars and mild race cars. They have two problems that seem to recur over and over:

They are a lot easier to blow up than a 2.5. The extra displacement puts you that much closer to the fueling limitations with all the stock engine controls. Go lean with a 2.8 and they melt quick. To get a 2.5 to melt you have to work at it.

They are not necessarily better race engines. If you keep all your other stuff and just switch from a 2.5 to 2.8, it is unlikely that you'll go faster. The extra low end torque can be a liability in a race car, since traction should be in short supply. Also your peak power occurs earlier, which means you shift earlier etc.

Now if you put the right turbo on a 2.8 you have a nice race engine. It has some grunt even off boost, so if you get caught down there you are not dead in the water. With the right turbo you can easily make 400 hp at 6500 rpm, which should run very, very well. The torque band will always be wider, so you can be a little lazier with the shifting."

 

compression ratio is all about fuel and how you want the car to drive higher comp ratios will make more responsive engines with that generally come on boost quicker .but require higher octane fuels
Lower comp ratios generally can make more max power and are ok with low octane fuels .

i think for high octane engine a standard 968 engine with a turbo is fine the pistons are forged and the only piston failure we've seen on the board was more than 25 psi on a high compresson engine.(duke ) this engine made 500 hp for a while when Markus had it and it was not put together with any expert chris white magic either it had E85 modest size turbo 3582 and a good programmable computer ..
for lower octane lower compression .

and i still think its heaps more effective to turbo a 3.0 car then it is to cube up a 951

its pretty expensive to get the size from the 2.5 costs about 2k to big bore and sleeve and buy new pistons
and it costs 2k for big crank and fancy rods

so thats 4k ... so ya should have bought that 968 engine...

then you spend another 2k trying to get the head to flow like the 16v..
i guss youl spend 1 or 2 k getting the turbo to bolt on to he 16v..

e85 is great as it allows you to run high comp ratio but on a 3.0 the fuel sustem does get pretty extreme ..

 

The crank is about 900 to 1k. Last I checked, which has been a while, pistons were in the 1100 area. After that you need to address the block and head. You can turn a 2.5 into either, atleast Chris can with his sleeves. The head needs the water jackets modded. you'll need a turbo, perhaps, and the ability to manage it all.

 

Oh...and rods...about 900 to 1100 ish.

 

yeh every piece or the puzzle is about 1000..
pistons , rods, crank, sleeve job or big block .and they add up fast ..

 

Why not just get a known-good short-block and go...?

 

So at least $3000 in parts. My current Vitesse stage 2 turbo isn't enough? I can't use my current Vitesse V-flex and SMT6 to tune?

Shop labor will be 35 hours, at least. That makes this project cost starting at $7000...

 

Doc, if you want to chat thru PMs I can share my 3L build experience and cost.

 

Cause there are no good known short blocks. I'm unwilling to drop in a used short block and hope that it's in good shape. That means opening it up and doing new bearings and rings at least, then slapping it in there and hoping all is well.

Hard to find good, low mileage short blocks on cars that are 21-25 years old...

 

Doc,

Contact Chris White at 944 Enhancements. IMO, that is the only way.

 

'meh, rings and bearings aren't a big deal.

$100 bare block from a reputable guy:

Block

Sure shipping is a bitch, but there are blocks out there - just have to look.

Additionally, there is a 'lister selling his complete built 3.0 right now:

3.0 FS

 

That's a bare block. I have no idea if my pistons, etc are in good shape. That means tearing down my current block to see ($$), then if not, buying pistons and whatever else I need.

Plus the shipping, making sure everything is sound (Lart is a good guy, but I doubt he's measuring the bores for roundness, etc), assembling the short block, installation along with new gaskets, etc, etc, etc.

That will easily turn into a $3000+ project. The reality is as much as I'd like to do something like this myself, I simply don't have the time to. That means farming it out to a shop and if I'm paying this kind of money I can't see doing a 2.5 vs a larger motor or an LS1.

 

You can ask John, but no,I don't think the Stage II will do it, and you'll need chips to handle a bigger turbo, etc.

 

I would go with either a 2.7 (104mm bore & 2.5 crank) or a 3.0 (104mm & 3.0 crank).
The 2.7 would have to be a sleeved block but the 3.0 can be done with either a sleeved 2.5 block or a stock bore 3.0

Many choices!

I’ll shoot you an email directly….