V2Rocket

Tuomo- What would +1000rpm get you, that adding 1-2 more psi at the current top end via your EBC wouldn't achieve without any added cost?

Swapping to a different intake like Greg's wouldnt hurt either.

ptuomov

Once you take it to the maximum safe peak cylinder pressure at 6700rpm, then the next possibilities are either lower compression, higher displacement, or higher rpm. Or all of the above. The cylinder tower strength and the knock considerations suggest to me that it's 100-100.5mm bore. Then there's the question of either increasing the stroke and increasing the combustion chamber size or increasing the redline rpm. The piston weight, ring width, and piston cooling issues are approximately the same whether you increase the stroke or the redline rpm.

The S4 intake is seriously underrated and can be made to work pretty damn well with turbos. If you are referring to the Greg Brown prototype intake, in my opinion, it's a good intake for a normally aspirated engine but precisely the wrong kind of intake for a pump-gas turbo car because it makes torque at rpms where the turbos have no problem hitting the knock limit. The best non-flappy single-mode passive intake for a turbo car would be something like the Helmholtz resonator intake of 928 S3. And S4 with the flappy operational can get the turbos to spool up 400rpm earlier.

My exhaust manifolds are more of an rpm limiting factor because of the packaging doesn't allow for pulse separation of cylinders 1&3 and 5&6. That would suggest a longer 95.25mm stroke and -35cc dish on the pistons, thinner rings -- and of course the oil squirters! ;-)

V2Rocket

What info do you have suggesting you've maxed the cylinder pressure?

you're around 750 hp right? From a 5.0.

there have been multiple 600+hp 944/968 turbo engines over the years in the 3.0L neighborhood. Highest output im aware of is around 700hp from Duke's 3.2L.

so i think there's more head room for you?

ptuomov

Yes, there's more headroom and plans to use that headroom, too. What's the peak torque that people here have produced _reliably_ with a 93-octane pump gas 2.5L turbo engine at 100mm bore and 78.9mm stroke? And, more generally, peak torque per liter of displacement using race gas?

V2Rocket

With good tuning and turbo, 350 torque at the wheels, even with a 2v head, has been doable reliably for 20+ years thru a stock 100/78.9 short block.

raceboy might be the best person here for you to talk to- hes got a turbocharged 944S 4-v about 9.3 compression, 1.6 bar ~420rwhp for 4-5 years now on euro pump gas. And he's the proprietor for VEMS ecu...

ptuomov

951and944S

What transmission is holding up to 750-850 lb/ft of torque...?

T

ptuomov

With proper cooling, the 928 S4 automatic transmission seems to have no problems with that level of torque.

The 928 S4 manual transmission has also lasted reasonably well for me, but I've only used it with street tires and on street, I don't think it would do as well on slicks on track. That transmission is pretty damn strong, but it must stay cool such that the gears don't weaken and that the case doesn't pull apart due to thermal expansion.

Back to squirters: Does anyone know what the nominal opening pressure of the 968 piston oil squirters is? I would need a high opening pressure because of the about 2.75" main journal diameter requires that the mains see high oil pressure at high rpms.

333pg333

We saw 550whp @ 13psi and about 620whp @ 16psi via the ECU pressure read. Pretty decent spread of tq with over 425ft/lb to the wheels from 4000-7500rpm.
I think Rod saw higher as they ran more boost. I think they ran maybe 25-28psi? Probably somewhere up 800-850bhp.
There's a few more that I know about too. The head (especially modified) is very good. The block...hit and miss. Luck of the draw with a 25+ year old Alu open deck design. You'd have to think the 928 might be a little stronger due to the extra meat in the block?

333pg333

Can give anecdotal info re oil squirters. On one 3.1lt 8v motor that was retrofitted with some squirters (I think 968) we couldn't get oil pressure at first. Wound up blocking the squirters off and hey presto...half decent o/pressure.

Thom

968 oil squirters open at 1.8 bar.

ptuomov

951and944S

That's pretty impressive, considering the FWD clutch pack is just alternating steel and frictions applied by a pressurized piston at about the same size as a 1 liter motorcycle clutch basket....
More modern cars have the ability in the ECM/TCM to discern component slippage by comparing input speed vs output speed and knowing what ratio to expect.
More than a couple hundred RPM slippage between two values and the transmission goes into failsafe mode to protect itself.
I don't see how you are not already at this threshold. If I knew the surface area of the frictions, the number of frictions, the diameter of the forward apply piston and the expected line pressure at WOT in D range, I could tell you what torque the forward clutch could withstand....all components being brand new.

In perspective, the Allison 1000 5 speed automatic found in 1 ton GMC 3500 dual wheel trucks with GM Duramax diesel engine has a torque rating of 650 lb/ft.
GM proper (hydramatic) has a unit rated higher but without torque management (software that limits torque during shift) the transmission would die catastrophically in short time.

Your next hurdle is going to be the expense of transmitting more power to the ground, either by some kind of ECU that nose dives power output at shift points or adaption of some kind of racing manual gearbox.

Not piston ring flutter or oil squirters.....

T

ptuomov

If I just put a 928 S4 automatic in it and cool it with big heat exchangers, the tranny is going to log on to RL and reply with ROFLMAO to that comment. You're projecting based on parts designed for the half motor.

At high rpms, engine oiling, blowby, and temperature management are the biggest problems for a street-driven 928 S4 with street tires, not the transmissions (if properly cooled).

951and944S

25 years in the automatic transmission business, servicing everything from government contract, police all the way to Fire Trucks, school buses, etc. to 8 second 1/4 drag race stuff and the normal public in between. Cooling can help keep viscosity on thrust components and keep plastic washers from melting () but does little holding force of clamped clutch discs that I can bend with 2 fingers laid over the edge of a table.LOL, the clutch material is probably held onto a steel based spline disc with adhesive like most other automatics.....

Carry on though, you got this....

T