Exhaust Question

[Simon]

Hey,

Ok, in the rules is states about how you have to have the exhaust come out behind the driver, does this mean actually come out behind the driver or pointing away from the driver? I am getting a custom exhaust made and need to know how long I need piping to be and all that. Thanks!

Simon

[Geo]

Simon, that just means that the exit of the exhaust must be farther back in the chassis than where the driver sits.

[Jake]

It's much safer to let the exhaust exit away from the body. With a wide open exhaust expect fire to occationally shoot out - so think about where it points!

[jc836]

Simon:
The exhaust must exit behind the driver on either side of the car. It is preferred to have it come out the side of the car when possible. Otherwise, have a downtube made for the end of the pipe so that it faces the track surface. Most muffler shops will take a piece of pipe-bend and cut on an angle for this. Final thought-make sure the exhaust does not go lower than the inner edge of your wheel, per the rules.

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Grandpa's toys-modded suspensions and a few other tweaks
'89 CRX Si-SCCA ITA #99
'99 Prelude=a sweet song
'03 Dodge Dakota Club Cab V8-Patriot Blue gonna tow

[SilverHorseRacing]

Hate to disagree, but the rule does not state that. It says any part of the car, except for the exhaust. Although, if I were building it, I would agree you wouldn't want it that low, unless you want it left somewhere on track when you hit a curb or bump.

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-Marcello Canitano
www.SilverHorseRacing.com

[tom91ita]

GCR 11.2.1G exhaust shall be directed away from the body and terminate at or behind a point equidistant from the front and rear hubs.

for my crx, this means behind the driver. i'm not sure what car could be behind the driver but not past the midpoint of the hubs. some sedans perhaps?

[Geo]

Originally posted by tom91ita:
GCR 11.2.1G exhaust shall be directed away from the body and terminate at or behind a point equidistant from the front and rear hubs.

for my crx, this means behind the driver. i'm not sure what car could be behind the driver but not past the midpoint of the hubs. some sedans perhaps?

Actually, the GCR is trumped by the ITCS.

ITCS17.1.4.D.g says:

Any exhust header and exhaust system may be used. Exhaust shall exit behind the driver, and shall be directed away from the car body. ....



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George Roffe
Houston, TX
84 944 ITS car under construction
92 ITS Sentra SE-R occasionally borrowed
http://www.nissport.com

[Greg Gauper]

And pointed 'down' IS away from the car body....

My car had a short straight pipe with a small glasspack that exited approximately 1 foot past my seated position and had a short turn down. My pipe length was tuned to my header and I used the next longest tuning length segment that was long enough to exit behind me.

Perfectly legal, very simple, very light.

[powerslide91]

Hey Greg,

How did you go about figuring the correct length of pipe to tune the exhaust? I have heard about this and that it works, but is there a formula to apply or does it need to be modeled using something like Desktop Dyno?

Thanks,
Jeff
'72 240Z

[Greg Gauper]

Naw, it's more scientific that that.....
It's called call up the guy who sold the header and ask what the proper tuning length for this particular header is

I don't know exactly how it's determined on a 4-1 header but I think it has to do with the individual runner length (from flange to collector) and adding the length of the exhaust port in the head. I think (going from memory) that in my case the magic number was 23 inches i.e. 23, 46, 69, etc. 46 inches was too short (didn't extend past my seat, so I chose 69 inches. My turn-down is factored into this length.

Can't tell you how a 4-2-1 header pipe length is calculated.

[This message has been edited by Greg Gauper (edited October 27, 2003).]

[JIgou]

Back when I used to hang around with some enduro guys (this would be $500 beaters on a dirt track for two hours - definitely NOT road racing), this is how they'd tune the exhaust:

1. Put a new pipe on the exhaust system after the manifold (we don't need no stinkin' headers....or they aren't allowed. Whatever.)

2. Run the car (obviously not on the track - the dirt kinda screws with the next step)

3. Cut the new pipe off where it changed color from the heat of the exhaust.

That's about as scientific as they got. I'm sure there are more accurate ways, but this should start the process.

I suppose a bullet muffler right at that spot "might" allow a bit of expansion, "quieting" the exhaust, but more importantly helping to scavenge the exhaust better? (HEY - I'm just shooting in the dark here. Someone with some knowledge chime in here!!!)

Making sound was DEFINITELY not a concern of theirs....

Jarrod

[theenico]

Jarrod,
Be careful of your wording. Some SM guy might protest your expansion chamber er... I mean muffler
Also can anyone truly define an expansion chamber and how it is different than a muffler (particularly a flowmaster) because I know the CB either can't or won't.

[JIgou]

Originally posted by theenico:
Jarrod,
Be careful of your wording. Some SM guy might protest your expansion chamber er... I mean muffler
Also can anyone truly define an expansion chamber and how it is different than a muffler (particularly a flowmaster) because I know the CB either can't or won't.

Why do you think I'm posting this stuff here, Nico? I'd never admit this stuff in the Spec Miata world. Or, as your other discussion points out: just how do you tell an expansion chamber and a muffler apart?

Wait.....uhmmm....I mean "Who the heck was using my computer and posting these false statements when I wasn't looking????"

Dropped the car off at Kraft's this morning for a new exhaust system....uhhmmm.....'cause the old one rusted out? Yeah, that's it!!! The rain at Heartland last time.....and.....and.....

Jarrod

[The Sleeper]

think of an expansion chamber as this, the exhaust exits the motor once it goes into the expansin chamber it is allowed to expand,each time a cyl fires and the exh opens the gases exit in a pulse these pulses entering the chamber expand strike the opposite end of the chamber and reflect back towards the engine before striking the other end of the chamber and redirecting back out the exhaust, most times this is tuned by means of a dyno for each perticular engine, most chambers utilize small flanges inside to stop reversion (the exhaust actually reenterng and traveling back to the engine)a chamber increases back pressure a very slight amount but more importantly helps in the exhaust scavaging of the combustion chamber. This is not as important on a heavily modded eng. with long cam overlap but more so on a slightly modded eng running stock cams.