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Exhaust Length
Posted: May 18th, 2009, 2:25 pm
by G.B.
Gentlemen,
Are the rules regarding ideal exhaust length?
Thanks
Re: Exhaust Length
Posted: May 18th, 2009, 3:13 pm
by Caracal99
Exhaust must terminate 1"-3" beyond the bodywork.
Paul F.
Re: Exhaust Length
Posted: May 18th, 2009, 6:37 pm
by G.B.
Thanks, but I was after the total length of each pipe.
Re: Exhaust Length
Posted: May 18th, 2009, 8:38 pm
by Caracal99
The rules do not address the length of the primaries, only the end of the exhaust system
Paul F.
Re: Exhaust Length
Posted: May 19th, 2009, 7:29 am
by nick_fv71
Caracal99 wrote:Exhaust must terminate 1"-3" beyond the bodywork.
Correct me if I'm wrong (which is highly possible), but I believe this rule has been removed from the most current version of the GCR. In any case, I belive the original poster was not looking for a "rule" but more the ideal length of the primaries
Nick
Re: Exhaust Length
Posted: May 19th, 2009, 8:14 am
by FV80
nick_fv71 wrote:Caracal99 wrote:Exhaust must terminate 1"-3" beyond the bodywork.
Correct me if I'm wrong ...
Nick
From 2009 GCR...
D. Allowed Modifications
1. Replacement of standard exhaust system with any exhaust system terminating one (1) to three (3) inches behind the rearmost
part of the body.
Steve
Re: Exhaust Length
Posted: May 19th, 2009, 8:23 am
by jmattox
My latest GCR is still in its "plain brown wrapper." but, the online version offers in paragraph 9.1.1
D. Allowed Modifications
1. Replacement of standard exhaust system with any exhaust
system terminating one (1) to three (3) inches behind the rearmost
part of the body.
My question is, however, besides possibly hurting horsepower, what keeps me from bending tubing and welding on VW connectors to "create" my own exhaust system?
John (inquiring minds want to know) fv42
Re: Exhaust Length
Posted: May 19th, 2009, 10:11 am
by fv31
this has a simple answer. the answer is 9 feet.
simple....but not correct. lol when you get into exhaust building, it's complicated to get the best tuned exhaust to get the most performance out of the engine. it's easier, much less work, and less of a headache to farm this out to a qualified exhaust builder. these guys do all sorts of testing on lengths, tube sizes, collectors, and lots of other stuff to make the best performing system they can. i personally have a set of roxanne stainless steels on the car and am quite happy with the performance. i'm sure there are other qualified builders out there that can build something that you are sure will work, without all of the headache and expense of experimentation.
i think at some point you have to look at your intent. are you doing this because you love to tinker with the car and it's components, or are you here to race? there is no wrong answer to that question....but your answer dictates whether this is something worth your time or not.
bill
fv31
Re: Exhaust Length
Posted: May 19th, 2009, 12:34 pm
by brian
John, the desired length of primaries is from 38 to 41 inches. The shorter length is favored for high speed tracks, the 41 for short courses. You can also use extensions on the end of primaries to adapt shorter systems to short tracks.
Re: Exhaust Length
Posted: May 19th, 2009, 2:17 pm
by hardingfv32-1
Brian's length estimates are correct, but there could be some interaction between the style of collector you are using, 4-1 or 4-2-1, and the correct primary length. When testing exhaust systems on the dyno, most changes are subtle when close to the optimum exhaust setup. I will venture to say that changing the primaries from 38 to 41-42 (with 4-1 collector) will move the peak hp point down about 400 rpm.
Brian