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efahl · 01-19-2008, 02:48 AM

pk2 wrote:
Somewhere I think it was you who said the bottom end of a 2.fL could handle 350 hp or more. It’s my understanding (anecdotally) that most people who overboost these things that blow their motors do so as a result of insufficient cooling at the top end…detonation.

Hi Peter,

My ~350 number is only a guess, based on experience with Audi and VW bottom ends (80-100 HP per hole, before rods bend), but none with Porsche's. I'm assuming that Porsche builds solid cranks and rods like their friends across town.

I would concur, most broken forced induction motors happen due to detonation, which might cascade into pre-ignition or maybe just break stuff directly.

I’ve been doing tons of homework and figure with WI, progressive or better, 270cc/min nozzle, 100/150 psi pump, 20-30% meth., injected right by the opening of “spider” manifold would do it for the cooling (no?)

Yes, water/methanol injection will do a good job of cooling, with or without an additional intercooler. This alone can net some significant HP (go play with my turbo calculator for any generic engine and just add a bit of water injection to see how density increases -> HP increases).
http://www.not2fast.com/turbo/glossary/turbo_calc.shtml

(Also read the caveats on the math I use to model the water injection so you don't get too optimistic:
http://www.not2fast.com/thermo/water_injection/opt_mass.shtml)

Pulleying down from 2.6 dia. to 2.5 would put me at about 288 hp (from 260 approx). with the super operating in it safe rpm, zone (14k rpm’s). A 2.4 pulley would put me at about 300hp. But my super would be at 15.3k rpm’s (in a 14k-16k- iffy zone).

Only issue I can see is diminishing returns, the super taking more hp than it can contribute at high revs.

You need to worry about loss of efficiency with higher revs, too. Here's a graph of the older, much less efficent M62 (the Eaton guys were going to send me newer maps, but I never followed through with them, oops) showing temperature change as a function of charger speed, and you can see it is not linear, but increasing faster than the speed does. At some point, the compressor efficiency is such that spinning it faster merely makes the charge hotter and nothing else, so at that point you are way beyond diminishing returns.

P.S. I picked up a EGT (exhaust gas temp) guage an sensord and a wideband

More data is always good, do you have a way to datalog the EGT and lambda along with some other engine parameters (RPM, throttle position and that sort of thing)? Analyzing logs is so much easier than trying to look at gauges while you're driving (but then, if you make a video of all the gauges, you can do a fair amount of "log analysis" that way).

Eric

01-19-2008, 02:48 AM	#34
efahl Registered User Join Date: Jun 2007 Location: San Clemente, CA, USA Posts: 55	pk2 wrote: Somewhere I think it was you who said the bottom end of a 2.fL could handle 350 hp or more. It’s my understanding (anecdotally) that most people who overboost these things that blow their motors do so as a result of insufficient cooling at the top end…detonation. Hi Peter, My ~350 number is only a guess, based on experience with Audi and VW bottom ends (80-100 HP per hole, before rods bend), but none with Porsche's. I'm assuming that Porsche builds solid cranks and rods like their friends across town. I would concur, most broken forced induction motors happen due to detonation, which might cascade into pre-ignition or maybe just break stuff directly. I’ve been doing tons of homework and figure with WI, progressive or better, 270cc/min nozzle, 100/150 psi pump, 20-30% meth., injected right by the opening of “spider” manifold would do it for the cooling (no?) Yes, water/methanol injection will do a good job of cooling, with or without an additional intercooler. This alone can net some significant HP (go play with my turbo calculator for any generic engine and just add a bit of water injection to see how density increases -> HP increases). http://www.not2fast.com/turbo/glossary/turbo_calc.shtml (Also read the caveats on the math I use to model the water injection so you don't get too optimistic: http://www.not2fast.com/thermo/water_injection/opt_mass.shtml) Pulleying down from 2.6 dia. to 2.5 would put me at about 288 hp (from 260 approx). with the super operating in it safe rpm, zone (14k rpm’s). A 2.4 pulley would put me at about 300hp. But my super would be at 15.3k rpm’s (in a 14k-16k- iffy zone). Only issue I can see is diminishing returns, the super taking more hp than it can contribute at high revs. You need to worry about loss of efficiency with higher revs, too. Here's a graph of the older, much less efficent M62 (the Eaton guys were going to send me newer maps, but I never followed through with them, oops) showing temperature change as a function of charger speed, and you can see it is not linear, but increasing faster than the speed does. At some point, the compressor efficiency is such that spinning it faster merely makes the charge hotter and nothing else, so at that point you are way beyond diminishing returns. P.S. I picked up a EGT (exhaust gas temp) guage an sensord and a wideband More data is always good, do you have a way to datalog the EGT and lambda along with some other engine parameters (RPM, throttle position and that sort of thing)? Analyzing logs is so much easier than trying to look at gauges while you're driving (but then, if you make a video of all the gauges, you can do a fair amount of "log analysis" that way). Eric __________________ http://www.not2fast.com/porsche/raymond/rly1_sm.jpg Last edited by efahl; 01-19-2008 at 02:57 AM.