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exhaust.... horsepower?

Old 02-13-03, 08:35 PM
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exhaust.... horsepower?

(83 gsl, stock ports, stock carb, stock manifold)

the new SRX7 rules say exhaust is "free" after the manifold, meaning you can do whatever you want. now the question....

do you think it would make more HP with just a straight pipe, or would it make more with a muffler at the end because of the little bit of backpressure? a friend of my dads has done a large amount of dyno time and came up with the conclusion that the manifold is the biggest restrictor and after that it doesnt really matter much. so would a straight pipe be better due to the extensive amount of backpressure the engine is already receiving from the manifold?
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Old 02-14-03, 07:05 AM
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Can you survive the SPL meter with no muffer? Just a thought.

Last edited by Cwaters; 02-14-03 at 07:08 AM.
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Old 02-14-03, 07:43 AM
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Rules creep huh Eric? Oh well. Yes the manny is the most restrictive part, but w/o a muffler I dont think youll get below 103db. Id keep the pipe dia constant to keep velocity up till the back of the car. Then a supertrapp without caps. I say super crap muffler cause its like a megaphone too, which might help some.
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Old 02-14-03, 01:38 PM
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my dad tested the car on a practice day with a hollowed out cat (so basically a straight pipe) and it still made sound
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Old 02-14-03, 05:10 PM
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I use a straight pipe on my PRO7 that terminates right before the rear axle. In dyno tests it produced more horsepower than any other configuration. Most recent race the db was 96 consistently. We also run stock exhaust manifold, but we are allowed to jet the stock Nikki. It would probably work for a Spec7 too.
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Old 02-16-03, 02:12 PM
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as long as you get on a dyno and tune it for a striaght pipe, it will give you more HP!

If not, you'll be the first one in the history of automobiles to have made more HP with a muffler then with out one, yes it will be loud but who cares
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Old 02-16-03, 05:02 PM
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Originally posted by skunks
yes it will be loud but who cares
i do, if it goes over the decibal limit. but i dont think it will. so its all good.
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Old 02-16-03, 09:21 PM
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i though u said the "new SRX7 rules say exhaust is "free" after the manifold, meaning you can do whatever you want." i actually dont know what the SRX7 rules are or what they apply to.
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Old 02-16-03, 10:51 PM
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thats alright... its actually not and SRX7 thing, its a Summit Point thing. the neighbors to the track complain i guess so there forced to do sound readings and other rules like 'no starting of engines before 8am'.
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Old 02-19-03, 12:49 PM
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Did your dad test with only a hollowed out cat and nothing else on the car?

The exhaust has the manifold, pre-silencer, cat, and muffler.

With just a straight pipe from the manifold, I think it would be too loud.
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Old 02-20-03, 03:34 PM
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it never had a pre cat or muffler, just a cat.... and he didnt dyno it with the hollowed out cat. he drove it like that for a practice session. i was just saying that it WOULD pass sound with a straightpipe, so you can forget about the noise factor when giving me opinions.
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