Can Exhaust Exit Under the Car?

[JimW337]

I'm ready to install the headers on the ITB Rabbit and I'm really tired of the exhaust banging on the rear beam. The rule book says the exhuast must exit belind the driver and away from the car. Can I just leave the pipe in the center of the car and turn it down toward the ground? Or does the pipe have to clear the body of the car, like in front of the rear tire?

Anyone have an opinion?

Thanks,
JimW
74 ITB Wraycer Wrabbit

[Greg Amy]

Can I just leave the pipe in the center of the car and turn it down toward the ground?[/b]

Yes.

[jhooten]

I have had no problems with tech for the last three years with a turn down.
Helps with sound too.

[Jeremy Billiel]

Yes this is legal, the only downside that I have on my high reving honda is the vibration, which can be obnoxious from the exhaust bouncing off the ground and back up to the car floor. Besides that no problems at all.

[JamesB]

Just make sure the turndown is PAST the driver and your legal.

[JimW337]

I was thinking this would be legal, but wanted to check if anyone had been through tech sucessfully.

Now, how much weight will I save getting rid of the cast iron exhaust manifold and all that extra pipe?

JimW
#74 ITB Wraycer Wrabbit

[JamesB]

say 7ish for the extra tubing, going from the cast iron to a 4-1 header will save a lot, at least mine is very light weight compared to the cast header. But the question that will remain, will it make the same or more power with the header to make the savings worth it.

[charrbq]

My understanding is that the length of the exhaust should be double the distance from the collector to the exhaust port for maximum top end. I don't know if that's true, but that's what I've been told by someone who's engine building talents are well known to be successful.

I've also run across the problem at some tracks with the unibody of the car acting as a loud speaker for the exhaust if it exits under the car...actually magnifying the sound through vibration. One way, I've found to help with sound issues isn't the turn down, but rather by cutting the exit at an angle (30 degree) to the surface. It allows the exhaust to follow the path or least resistance without restricting it with a turn down.

2cents

[TimM ITB]

Hey Charrbq;

can you expound any more on the statement: "My understanding is that the length of the exhaust should be double the distance from the collector to the exhaust port for maximum top end." ???

Do you mean from the collector "up" to the exhaust port manifold?? Exactly where are the measurements taken?? Any more info??

thanks,

Tim M

[charrbq]

From the exhaust port in the head to the collector...provided you're using headers with equal length tubes. You double the distance from the collector to the end of the exhaust. Not from the end of the collector, but from where the tubes meet into the collector.

Due to design restrictions, I've never been able to achieve this. The guy who told me that builds pretty strong production car engines. They can do things with exhausts that we have trouble with.