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

[pk2]

Originally Posted by Topless

Unlike Honda, Nissan, Ford, and Chevy a 2.5L 986 doesn't make a very good platform for hot rodding. At 80hp per liter there is not much left in there without driving reliability over a cliff. Most of the guys who supercharged them promptly removed the SC, quickly sold the car, or quickly blew them up. Heat and cylinder pressure are the enemy.

I will drive mine until the motor gives out and then quietly drop in a 3.8L X51. As it is I can still get into plenty of trouble with 201hp.

Your thoughts are intuitive and make sense. Mine aren’t & don’t, I guess. But, are you saying Nissan and Hondas, etc. have much lower hp per liter and with lots of tweaking would max out at 80 hp per liter too? Or (god forbid), are you saying they’re stronger motors?

What do you see as the negative effect of more cylinder pressure, rods, rod bearings, the crank? What’s going to break as opposed to wear out faster?

I’ve heard lot’s of anecdotal stuff about them blowing up to, never met someone who had that experience though. Whereas I’ve also heard and met many who drove/drive them uneventfully for years, probably much harder & more often than I do.

Rationally I agree & understand most of what you say but dam it’s fun. can’t see someone going back even if thy knew better.

Regards, PK

[Gary in BR]

Originally Posted by pk2

Rationally I agree & understand most of what you say but dam it’s fun. can’t see someone going back even if thy knew better.

I AGREE 100%

[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 Gary in BR

I AGREE 100%

Thanks Gary for the encouraging words. Glad yours is holding up well. I’m actually holding it up as a benchmark.

I kinda studied the crap out of cooling (IC; air to air, air to water, etc) and the water/alcohol seems to make the most sense for an SC in this car. In the past I've pooh pooh’d it as a kludgey solution but the more I’ve read…it’s legit, not really tricky and not really a big hassle.

The concept and implementation was actually developed for super charged fighters and bombers in WWII. Got them up in the air... fast.

Aside from heat, the super charger itself has limitations. It needs to be the pretty small form factor it is to fit the car physically. How much more it can be milked at the low end without actually being a drain at the top end or, spining the sc to fast, isn’t clear yet, pretty much a matter of doing some math though.

So, if your getting 270hp comfortably, thats what I'll aim for. According to the manufacturer, I’m already there and then some, but I’m not buying…yet.

Regards, PK

BTW, how many miles have you chalked up on your turbo?

[Gary in BR]

Thanks I'll be that benchmark...In the new year I have a few tweeks for the turbo and do some exhaust work.

After each mod I will be back on the dyno to see what sort of results I get.

Everyone here will be updated along the way.


Jaay looked into the air/meth for his supercharged 2.5. Perhaps he can chime in with his research.

pk, from your research do you feel as if the ecu would need a different map than the standard sc map?

[pk2]

Originally Posted by Gary in BR

Thanks I'll be that benchmark...In the new year I have a few tweeks for the turbo and do some exhaust work.

After each mod I will be back on the dyno to see what sort of results I get.

Everyone here will be updated along the way.


Jaay looked into the air/meth for his supercharged 2.5. Perhaps he can chime in with his research.

pk, from your research do you feel as if the ecu would need a different map than the standard sc map?

Hey Gary
Please do keep us apprised of results from your mods!

ECU remap; actually maybe, but the kit consolidator said “DON’T”. There such… dicks I never asked why. I rely completely on an AIC and at this point I don’t have any complaints (But I also don’t know how well I’m optimized either). With an AIC, for simplicity, I’d steer clear of messing with the ECU. I’d think trying to juggle the 2 while tunning would be a pain.


I’m not altogether sure how much remapping can be done to the ECU. I know they can be flashed from “a” to “b” and “chipped”. But what can be tweaked in-between, I really don’t know. If I could do it, (have an interface and software) and ditch the AIC, It sure seems like it would be a lot cleaner.

I do intend on getting a more advanced AIC. Unfortunately, the ones I like don’t have any baseline maps for this car, means starting from scratch. I’m not crazy about pinging the _ell out of the motor just to get to something close. I suppose I could hack into mine and use some sort of data logging software/hardware to extrapolate a map…dunno.

Anyway, good luck with the mods, look forward to the results.

PK

P.S. Do you have an AIC and if so, who makes it?

[Gary in BR]

BTW, how many miles have you chalked up on your turbo?


Forgot to answer this in a previous post:
I have done around 11,000 miles in the last 6 months on the turbo.