HP, how much can a LIL 2.5L take? How do they Blow?

[Topless]

PK2,

Yes, In a word I think the Honda, Nissan, Mitsu. motors are much stronger as a Hot rodding platform. They are also low compression so they adapt well to variable boost turbocharging. Complete sets of racing pistons, rods, cams, etc. are cheap and available everywhere. They are easy to keep cool and there is usually room under the hood for lots of HP add ons. It is not uncommon to get 200hp/liter on a built VTEC motor and have it hold together pretty well.

The 986 2.5L is a very highly developed, high compression N A motor. At 11/1 compression it doesn't adapt very well to forced induction (detonation is a problem). Essentially zero internal parts are available and there is no aftermarket for internal racing parts. The radiators are far away from the motor so it is harder to get rid of excess heat. And no room under the hood. From what I have seen I think that 100hp/liter is the ragged edge of a reliable performance envelope on this motor and you are already there.

Pushed to the breaking point, cause of death could be: blown head gasket, broken pistons, thrown rod, IMS failure, broken crank, failed main bearings, slipped cyl. sleeve, seizure due to overheat etc. The blown head gasket is the only one that is repairable. Quite a different story than a Chevy small block or Honda VTEC.

You are a pioneer. You are blazing a path over the dead bodies of others who have pushed the performance of the 986 and lost. I hope you succeed. This country was built by those who didn't accept conventional wisdom. It's your car. If you want it I say go for it. What would Chuck Yeager or John Glen say?

[pk2]

Originally Posted by Topless

PK2,

Yes, In a word I think the Honda, Nissan, Mitsu. motors are much stronger ... Essentially zero internal parts are available and there is no aftermarket for internal racing parts.... You are a pioneer. You are blazing a path over the dead bodies of others who have pushed the ...It's your car....

That’s incredible, 200hp/liter. How can a “highly developed” Porsche motor be put to shame like that? It’s to bad there’s no internal aftermarket stuff for these things. Guess there’s just not the market volume out there. (Maybe if more people like Gary and me start blowing up motors, a market will develop )

11:1 comp. ratio and the potential for detonation has been on my mind from day one. Currently I spike my pump fuel with racing fuel to mitigate that possibility.

From what I’ve read & heard from reasonably credible sources, H2O/methanol injection is quite good at mitigating detonation issues and, it doesn’t depend on any airflow or any optimal positioning to function effectively. So if that’s the primary issue, I may have it licked (in principle).

Of the litany of catastrophes you mentioned, have you personally seen them in conjunction with a well tuned, forced induction Boxster under real world conditions? (I’m really & truly curious). I’ve had just about every failure you’ve mentioned on cars while doing nothing at all heroic (my old stock 928 threw a rod while idling in the driveway).

If your professional opinion is that I’m already on the bleeding edge…hmmm…I dunno…and what about Gary’s car…

Thanks allot for your input,

PK

P.S. Chuck Yeager, pleeeze. More like PeeWee Herman at a soapbox derby...

[Topless]

PK,

I am interested in what you and Gary are doing, otherwise we would not be chatting. Maybe you will find that missing piece of the puzzle. I don't think a 986 2.5L would survive for long at 200hp/liter but I could be wrong. I have been wrong before.

If you still want more, methanol is a good place to start. It has a lot more energy/gal than gasoline and has a chilling effect on the A/F mixture so it works similar to intercooling. We used to run two motors on 50% methanol and at the end of the race the carb was completely iced over. I have no experience with it in a fuel injected motor so I don't know what other issues are involved.

If you want to continue to develop this motor why not tune it like the pros. Take it out to Willow Springs, bolt on some instrumentation and push it around a bit. After a few runs download the data to a laptop and take a look. A picture should emerge of the strengths, weaknesses and opportunities for further development. You can do basic tuning on a dyno but there is nothing like tires on pavement to tell you what you really want to know.

[pk2]

Originally Posted by Topless

PK,

If you want to continue to develop this motor why not tune it like the pros. Take it out to Willow Springs, bolt on some instrumentation and push it around a bit. After a few runs download the data to a laptop and take a look.

I certainly do appreciate your input and am flattered by your interest (or is it a fascination with impending train wrecks?). I may sound like a contrarian twit, but I really just have a need to know, the nuts & molecules of an issue when I want to do something clever and cool. Generalities or conventional wisdom (which may or may not be well founded in the first place), doesn’t do it for me. Little at face value ever does.


As far as taking it out to Willow, I intend to do just that (or the like). I’m not sure what a “pro” would hang on the car. My somewhat foggy intent was:

A Laptop:

Wideband A/F with a PC interface & software.

OBD II/ laptop software setup (parses OBDII signals into a ton of output with data logging).

My AIC hooked up to the PC if for no other reason than to make “on the fly” tweaks. (Don’t know what feedback it might offer in its software)


What would you add or subtract from my proposed morass? (don't say "the car" please)


Thanx, PK

i think the motor can handle that amount of power, Garry seems like hes doing fine.

[pk2]

Originally Posted by blkboxster

i think the motor can handle that amount of power, Garry seems like hes doing fine.

Ya, he seems to be defying conventional wisdom. Wonder how many others are out there.

PK

[Topless]

PK,

As far as instrumentation goes you may want to add a GPS logger or G-timer to get some real world acceleration curves coming out of turns and down the straights. They can match up to the other telemetry data from the car. You may want to talk to Richard at Clewett Engineering in LA. He specializes in engine mgmt. systems for Porsche racing teams. He has more experience with tuning FI Porsche motors than anyone I know. He is far more comfortable at the ragged edge of performance and reliability than I am.

Gary's car is posting some good numbers. 11k miles with a 270hp+/- turbo may be a new record for a 2.5 motor. It's an accomplishment to be proud of. Still a long long way to go to see 200hp/liter though. Now that would really defy conventional wisdom. One step at a time.