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

[pk2]

Given a well tuned induction system (air/fuel/intake temp, etc), what is semi-reasonable limit as to how much HP (at the crank) caan be milked out a stock build 2.5L boxster motor without it going kaboom. I know anything above stock HP is going to tire the motor sooner, talking here though about catastrophe.

Thinking about bottom end or wherever else it might fail. I know there can be problems with the cylinders (sleeves?). I’ve also heard that one will let go, if it’s going to, regardless of what you do with it.

Thanx PK

[Gary in BR]

I have 226 at the wheels so maybe 270ish at the crank
based on 201hp Porsche numbers and the 164 base dyno I ran prior to any mods.

But I am running a turbo setup on my 2.5.

Dynos:
http://www.pcars.us/albums/11310_porsche_cars.jpg

[Brucelee]

Originally Posted by pk2

Given a well tuned induction system (air/fuel/intake temp, etc), what is semi-reasonable limit as to how much HP (at the crank) caan be milked out a stock build 2.5L boxster motor without it going kaboom. I know anything above stock HP is going to tire the motor sooner, talking here though about catastrophe.

Thinking about bottom end or wherever else it might fail. I know there can be problems with the cylinders (sleeves?). I’ve also heard that one will let go, if it’s going to, regardless of what you do with it.

Thanx PK

If it were me, I would not invest any real dough in a 2.5 engine. I don't think the motor set any records for durability.

There is no replacement for displacement.

[Gary in BR]

I second Bruce...An engine swap is a good option, you get about the same power as you do with a turbo or supercharger.

Sc and Turbo will run around 7k
An engine swap runs around 15k last time I looked into it a year ago.

[porsche986spyder]

If you go to a 3.2 or 3.4 ltr engine swap, do you also have to change out the trans or gear box for a 6 speed if you only have the base 5 speed? Sounds like even more money is needed.

[Gary in BR]

From my research the 5speed tranny can handle the 3.4 upgrade without any modifications.

[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.

[pk2]

Gary, Brucelee, Speedster guy, thanks for the input.

Truth is it’s already supercharged and depending who you talk too, it’s between 250-280hp (at the crank, I’ve yet to put it on a dyno though). But with a %10 or so change in the pulley and h2o/meth injection, I could pick up another 1-2 psi, or about 15-25 hp.

I’m not crazy about stressing the _ell out of the little 2.5 motor. And if I wasn’t already where I’m at I’d consider a 3.2, 3.4 or 3.6. I am surprised though at the relatively modest power gain with such significant displacement increases (and hassle), not much bang for the buck.

My SC mod pondering works out to be about $25 per hp. A bargain if I can get the psi I need without going over the SC’s 14k rpm max mark, (gotta do the math) and the engine doesn’t explode.

With H2O/Alcohol injection and competent tuning, I’m not too too concerned with the usual top end failures. It’s the rest of the gear I’m concerned about, whats going to crack under the strain and at what point.

Regards, PK

Gary, Doesn’t the maker of your setup claim 290 HP? How is it and the motor holding up?

[Gary in BR]

Originally Posted by pk2

Gary, Brucelee, Speedster guy, thanks for the input.

Truth is it’s already supercharged and depending who you talk too, it’s between 250-280hp (at the crank, I’ve yet to put it on a dyno though). But with a %10 or so change in the pulley and h2o/meth injection, I could pick up another 1-2 psi, or about 15-25 hp.

There is also the intercooler option, I think I forgot to get those measurments for you, if you still need them I will take them this weekend.



Gary, Doesn’t the maker of your setup claim 290 HP? How is it and the motor holding up?

I dont remember what the claims are but I do know my at the wheel numbers are within a few percentage points of his at the wheel numbers.

My motor is holding up very well, I am checking the oil more frequently and still changing the oil every 10k miles. The water temp is at oem levels. I still drive the car the same. I run it up the rev range daily. I never rev past 4k until the water temp is at 180ish

My car is dynoing at 230ish at the wheels I have a dyno chart posted on the board somewhere. I can repost it later tonight. I am basing my crank on rough math.


I have looked into water/meth injection but I do not have any experince with it so I decided to leave it to those that know what they are doing.


its exciting to see someone squeeze more horsepower from these engines. keep us posted.

[efahl]

Originally Posted by pk2

And if I wasn’t already where I’m at I’d consider a 3.2, 3.4 or 3.6. I am surprised though at the relatively modest power gain with such significant displacement increases (and hassle), not much bang for the buck.

PK,

It's not so much that the peak HP, but the fat torque curve that the 3.4 gets you. Any gear, any time, just mash the pedal and it goes. Stomp it in first and the traction control kicks in (if the pavement is wet, same thing in second, no clutching needed, just floor it). Just for comparison, my engine is putting down 259 rwhp on the dyno, about 9 more than the motor produced in the C2 from which it was pulled (headers, exhaust, intake, tuning et cetera).

I'm running a stock G86/00 (code CWA) five speed transmission on my car, with a light flywheel and sport clutch, and it hasn't broken yet, even with a fair amount of abuse.

Regarding your original question, I have yet to see a German motor that could not take at least 75 HP per cylinder; older iron-block Audis are good for about 100 per hole with stock internals. I would expect the stock bottom end in a 2.5 to be good for 400-450 HP without problems (going forced induction would prompt me to put in different pistons though, I'd lower the static CR and increase the height of the top ring land).

Eric

[JAAY]

Hey, Sorry to get into this one so late. I did have gary's supercharger, I was going to put a 7lb pulley on it. If you do the water injection on it there will be no issues with heat at all. It is very reliable and safe to run more boost. As a matter of fact the damn thing runs too rich anyway. They detuned the crap out of it to make it more reliable. I have since sold the charger and am now doing the 3.4 swap. As far as I can see it is going to cost me just around 8k to do it.

[Gary in BR]

Jaay,

Glad to see you in this one.
I thought the map was too rich myself. I have a dyno that at the end of the pull the car kicked out a little black smoke.
http://www.youtube.com/watch?v=5X5IUNKJMgQ

PK,
You asked if I am running an AIC....I must be on my backup brain today becasue I dont know what AIC stands for.

Dont worry you guys will be kept up to date on the mods.

[JAAY]

Yea, when I talked to the guys over at turbowerx they even said that too. Well I am in the market still for a 3.4 if anyone knows of one. That project has been put on hold though for a few months. I warped the heads on my saab so that is getting a new motor in the next couple of weeks. When it rains it pours.

[pk2]

Originally Posted by Gary in BR

Jaay,

PK,
You asked if I am running an AIC....I must be on my backup brain today becasue I dont know what AIC stands for.

Dont worry you guys will be kept up to date on the mods.

AIC is a crappy acronym, in that means a hundred different things. In this context it’s “Auxiliary Injector Controller”. It Times and squirts an extra injector, and usually tweaks the timing to. Saves messing with the ECU for Fuel and timing tweaks. So if you have a seventh injector you probably have one of these things…an AIC.

Regards, PK

(PS I “hunted” JAAY down last night in order to invite/drag him into the fold…)

[pk2]

Originally Posted by JAAY

...If you do the water injection on it there will be no issues with heat at all. It is very reliable and safe to run more boost. As a matter of fact the damn thing runs too rich anyway. ....

----------------------------------------------------------------------------------
JAAY,

Glad I found you & Have fun with the 3.4. Hate to pester you, but you’re the first person I’ve heard of that has messed with this sort thing in the same way I’ve been planning to.

I’d come to the conclusion on my own that H20/methanol would do the trick nicely and then some, but I’d not heard of anyone doing it. Only lot’s of horror stories of catastrophic blow-ups, (likely due to detonation).

I was planning to “pulley” just up to 6 PSI, a little nervous though with all the urban lore. Thus this thread. Did you have it on good advice that a 7lb boost wouldn’t hurt you with the h2o/meth injection (or was it an educated/extrapolated conclusion)? What sort of WI system did you opt for; a simple progressive stage 2 type? or a Stage 2 with MAF input (or similar feedback)?

And finally, were you concerned at all with stress on any of the internals? I know it will have a wear out faster, but as long as it doesn’t go boom I’m alright with it.

Thanx a ton, PK

BTW, Are you doing anything to your 3.4 or are you leaving it more or less stock.

[JAAY]

I never did the kit on the boxster. On my eclipse I have a boost activated kit on it with a 50/50 mix of water and alcohol. The 3.4is only getting headers and exhaust of what I already have and a sport clutch. I am hoping to get a motor in January. I may put a 6 speed in it too

[pk2]

Originally Posted by efahl

PK,

It's not so much that the peak HP, but the fat torque curve that the 3.4 gets you. ... I would expect the stock bottom end in a 2.5 to be good for 400-450 HP without problems (going forced induction would prompt me to put in different pistons though, I'd lower the static CR and increase the height of the top ring land).

Eric

Eric,

Thanks for your input.

250whp is certainly nothing to sneeze at, and that’s all stock? Tempting. I thought I’d seen “crank” numbers which didn’t seem terribly impressive.

I have forced induction. With a modest boost (a 10% pulley change) (and retuning) I figure I can hit or exceed 300 hp, (an arbitrary goal I set). I’d really like to do it though without blowing it up, to much fun to drive.

At 300hp would you still bother with new pistons? Would that be to lower the compression? Who sells pistons and other internals for these things?

Thanks, PK

[efahl]

Originally Posted by pk2

250whp is certainly nothing to sneeze at, and that’s all stock? Tempting. I thought I’d seen “crank” numbers which didn’t seem terribly impressive.

I have forced induction. With a modest boost (a 10% pulley change) (and retuning) I figure I can hit or exceed 300 hp, (an arbitrary goal I set). I’d really like to do it though without blowing it up, to much fun to drive.

At 300hp would you still bother with new pistons? Would that be to lower the compression? Who sells pistons and other internals for these things?

Hi Peter,

My 3.4 has a dry cone filter in front of a bigger MAF body and custom plumbing to the throttle body, TTP headers and cats, and re-mapped ECU (the dyno numbers came from the mapping session).

I really don't know what's inside any Porsche motors, haven't torn one apart yet, so I don't have any reason to say the stock 2.5 pistons won't be good for 300 HP other than that they are pretty high compression for a boosted motor.

I would go to Wiseco, Arias or Ross for custom pistons. You can usually get them for about $100 each, at least that's the ballpark for Audi parts. Rods can be had from Pauter or Carillo for about the same, if the Porsche parts turn out to be weak (the 2.5 is the odd man out with 72 mm stroke, I'm guessing that all the 78 mm stroke motors - 2.7, 3.2 and 3.4 - share their bottom end components for stocking and manufacturing efficiency).

Eric

[efahl]

Ok, guys, time to start accumulating motor part info...

http://www.not2fast.com/porsche/engine_dimensions.shtml

Who has an engine taken apart, or has access to parts and can measure them? I'm very interested as to whether my speculation about the 78 mm stroke engines sharing crank and rods is correct.

Eric