8.0/8.5 CR for 930 ???

[David]

Even with methanol injection, my guess is that 9.5 at 1.2 is too much. Maybe 9.5 at 1.0 or 8.5 at 1.2. Where's Juan?

Of course drag racing you could go higher.

[Raceboy]

I'll throw my few pennies worth of experience here regarding air cooled 911 engines.

Combo:
*stock (116 000 kmon the clock) 993 Carrera 2, 1994 (twin-plugg, 11.3 CR).
*TPC supercharger kit @ 0.5bar
*custom made intercooler by me
*630cc Siemens Deka injectors
*ign. dizzy delete, Bosch Motorsport coilpacks instead.
*VEMS 993 PnP Motronic ECU with WBo2, EGT, LCD etc

Max safe advance at WOT is 17 degrees BTDC, WOT fuel is lambda 0.8-0.82.

It made 389 rwhp and I tuned it more than a year ago. Since then the car has seen around 10 track days, few top speed challenges, some dragraces (12.2 @ 187 kph) and it hasn't knocked once after finding the detonation treshold on very hot conditions on the dyno.

Here's the scoop: it runs 98 octane (same as 93 in US) pump gas.

And engine is running fine.

What do you think?

[kenikh]

˄˄˄ This nets an at rest DCR of 12.7:1, well within the established OK range for a boosted motor with full ECU ignition and knock control. Another great data point. Thanks!

[Raceboy]

Kenik, did you factor in the error on CR with 993 engine as it's 11.3 by Porsche but in reality ends up more towards 10.7-10.8 range?

And just as an observation, Eaton M62 that TPC uses on its 964/993 kit is too small for these engines (As rpm rises and engine needs more and more air, boost drops to 0.35bar (135 kPa) as blower can't keep up with the engine needs). M112 is more appropriate supercharger for 3.6 engine.

[kenikh]

Originally Posted by Raceboy

Kenik, did you factor in the error on CR with 993 engine as it's 11.3 by Porsche but in reality ends up more towards 10.7-10.8 range?

And just as an observation, Eaton M62 that TPC uses on its 964/993 kit is too small for these engines (As rpm rises and engine needs more and more air, boost drops to 0.35bar (135 kPa) as blower can't keep up with the engine needs). M112 is more appropriate supercharger for 3.6 engine.

That static CR adjustment makes 12.2:1@ .5 BAR and if the boost tapers to .35 BAR you end up at 11.2:1 (this ignores VE charge loading). At idle, with no boost (assuming very low VE), a 993 makes 8.25:1 CR, which is still .75 - 1 pts higher than the early cars at idle.

[strokher racing]

I would REALLY like to swap to E98 on my Porsche

[911st]

Originally Posted by 125shifter

How would one go about getting over 8:1 compression? Custom pistons? Weld up the head and re-machine?

My engine's already built with 7.7:1 compression using 98mm JE pistons. So I'm not looking to change, just curious.

Get J&E to make the pistons to get you there.

Or, add a 964 crank with longer stroke.


I suspect a well built 8/1 CR motor running .7 bar could be very drivable and make a lot of HP.

Concentrate on breating efficiency, heat management, and proper AFR & timing.

Just because one is running 1 bar boost dose not mean the cylinder is seeing it or it will make a relitive amount of more power.

While a C2 cam might lower the dynamic compression ratio. It might let more of charge into the cylinder under boost for even a higher peak cylinder pressure at peak TQ than a stock 930 cam with higher DCR.