Track day dump pipe

[JCMarshall_Law]

Track day dump pipe

Hey all,

I’m planning on making up a dump pipe for track days. Most of these type of dump pipes I’ve seen connect to the front pipe and exit out the side of the car before the rear wheel. I’m wondering if anyone sees any problem with just making a dump pipe that dumps straight off the front pipe to the ground underneath the car. Just makes it heaps easier to make.

See the pics.

I’d really appreciate anyone telling me about any experience they have had with this idea.

[someonestolecc]

lol - I don't think you really needed the diagram

Won't it just be smelly and a bit silly since carbon monoxide is going into your cabin?

If it's just for a track I don't see the problem in aiming out to exit next to the passenger door area, then welding another pipe so it makes it to the side of the car, then welding some sort of bracket (hell even if it's just coat hanger) that can then be threaded with one of those elastic ties then tied around your passenger seat or something (obviously the door would then close over it).

That way you're not getting carbon monoxide seeping into your cabin through the floor/shifter/driver window etc.

[Ronin 09]

and the nice warm BBQ under the car from the heat haha

[Roy]

It all helps, but say it frees up 10hp over your current street exhaust system, consider its a 1400kg car, think power to weight:(

Sure it will free up power, and liek others have said, id say plumb it out the pasenger side inder the B-pillar...but the agro of swapping it over, drivint their and back etc etc...perjhaps the money could be spent on maximising the performance of your day to day exhaust..i dont know, just thinking out loud:Confused:

[GTRgeoff]

did someone say bbq???

im wth roy

[foznice]

just while we're sort of on this topic... Isn't there a point where too little backpressure is bad as well?...I always think about trying to breathe through a drinking straw (lots of backpressure/stock exhaust)... but then if you stick a really massive pipe into your mouth its actually hard to breathe?.. maybe I'm talking crap but isn't there supposed to be a happy medium someplace, where there is enough backpressure to make it just right?

[MELV]

i found this pic

looks like its just bi-passed the rear muff

hope it helps

[Abo Bob]

You don't need back pressure in turbo cars.

I think it would cook your diff.

I want to make one to go out the side.

[4door_Sleeper]

You dont want backpressure on ANY car, but there are issues around noise that are fixed with mufflers (which add pressure).

A NA car needs the correct exhaust harmonics to function at its peek efficiency, so disconnecting the exhaust can reduce performance in some cases. (this is often mistaken for a need of backpressure)

[JCMarshall_Law]

Ok, people have come up with the same sort of probs as I thought of. I think I'll just build the side pipe - it's not really much extra work, just that a side pipe will have to be supported at the exit i.e. I'll have to bolt some bracket to the car. The dump pipe could have just bolted on and used the existing supports on the front pipe because its weight would be minimal.

I'mm post pictures when its done.

BTW: I know a couple of people who go to the effort of putting on the side pipe for track days and they still say its worth it. Its really only a 10 min job that can be done at the track with the car on ramps.

Anyway. if it does not drop my track times by 20 seconds - at least it will sound cool

[xRHETTx]

As long as its pumbled out the side i think its a good idea. You'll prob save 10-15kg of exhaust and make 10-15kW or so more, so it would make a difference. I suppose it depends if you run a std cat and how good your normal exhaust is?

[foznice]

hmm ok so whats the difference between back pressure and natural harmonics?.. I thought harmonics where always things to do with sound. I guess not. Also why don't turbos need backpressure or natural harmonics?..

[JCMarshall_Law]

Basically back pressure is a bad thing - higher back pressure = more work engine has to do to pump the exhaust gasses out of the engine. Ever wondered why drag cars don't have any exhaust? The problem is most of the time you do need an exhaust to put the exhaust gasses where they are not going to be a hazard. This is where exhaust tuning or "harmonics" comes into play - by properly tuning an exhaust you can avoid back pressure waves initiated by the rapidly expanding exhaust gasses bouncing of the walls and other exhaust pulses. This topic gets really theoretically heavy and I still have not found any easy to use sources of info for exhaust tuning, most exhaust experts just call it a black art.

hmm ok so whats the difference between back pressure and natural harmonics?.. I thought harmonics where always things to do with sound.  I guess not.  Also why don't turbos need backpressure or natural harmonics?..

[Abo Bob]

That's why a quality japanese exhaust can flow as much as a slapped together one but be much quieter.

[4door_Sleeper]

You will always get a harmonic when air moving in a pipe, exits the pipe. The length/diameter and other considerations effect the harmonic (just like a flute or other wind instrument) of the pipe. Turbo'd engines don’t need to worry about these harmonics because unlike a NA engine (which in effect has an open pipe from the valve to the exhaust tip) there is a spinning impeller in the way and this destroys any harmonic coming back up the exhaust.

The benefit of good harmonics in NA engines is that they can create a scavenging effect that helps extract the exhaust gasses from the cylinder (it actually produces a positive effect, like having a vacuum, and is better than having no exhaust at all).

It was this technology that gave Yamaha motorcycles their advantage in the 1950s. Yamaha used to make musical instruments (and still do) but a motorcycle company in Germany closed shop at the end of WWII and went over to Japan to work in partnership with Yamaha (I believe it had something to do with the government compulsory acquiring businesses to rebuild Germany at the end of the war, or limitations on the types of machinery that businesses could have to stop them making military equipment)

[foznice]

interesting, thanks for the imformative posts guys.