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Re: Flat response through power curve. (archive)
[ Follow Ups ] [ M5 (E28) Message Board ] [ Msg. Board FAQ ]
Posted by matt evans on October 19, 2001 at 19:55:25:

In Reply to: Re: Flat response through power curve. posted by Neil Deshpande on October 19, 2001 at 19:40:03:

My torque curve flattens @ ~4500 rpm, stays flat until ~5500rpm, then steadily goes downward.

HP is similar.

My problem - excessive exhaust backpressure. Originally 13lbs under load and full throttle.

The car _creeps_ to redline in 4th gear on a dyno.. instead of screaming all the way there.

If the car has any non-factory exhaust component, that _could_ cause the problem you're seeing... lack of cross sectional area (and thus flow restriction) really hurts this cars performance.


I am seeing a 30+ hp loss with 1 square inch lower than stock cross sectional area on my exhaust components..



Todd:

Note that the compression test is with closed throttles. I spoke with Phil in connection with this car and felt that the closed TBs would lower compression due to the engine having to suck vacuum. Also, the uniform readings are strange as any deterioration would be non-uniform most likley. Wet compression, should the reading increase, will indicate worn rings.

What do you think of the post-4000 RPM flatness in the curve? I have no explanation for that.

Neil Deshpande
http://www.neilwerke.com

***


That is crap compression at sealevel, where it should be around 190. Don't know how that converts at 8000 feet, what is atmospheric pressure there? It's probably sluggish just because of this low compression, question is whether it is simply altitude realted or something else. Did you try a wet test (tablespoon of oil in cylinder)? Another caveat. There seems to be an unwritten rule that the S38 is good for 200k miles max w/o a rebuild.
While test driving an 88 M5 I noticed that the power was down and there was no increase in the power curve around 4k and above. The experience was pretty flat. The owner admitted that the car hasn't been tuned in a long time and the car is in need of TLC.

I am considering buying this car and would like feedback on what other M5 owners have experienced regarding the above.

Here's the specs:
- 158k
- compression 120 near even on all 6 (throttles closed).
- Altitude 8k feet aprox

Thanks, Phil.





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