need some advice for making my own exhust, problems? ect

[Cliff@BrownBags]

o.k. guys i have a 67 that i did a tranny raise on and i am running into the typical issues with a header system. i see a lot of guys use the old type of muffler but i want to still be able to use my header/stinger. my question is this (sorry for any bad explinations, i will post a pic if needed). i had to cut off the top 2 pipes that come out of the head right behind the spot they ty into the piece that comes down from the intake tube. so now i need to make them turn down about a 90* turn to avoid hitting the body and also the new engine bay seal. so anyway while i was cutting i noticed that once i cut the the top tubes and shorten them down and turn them at a 90* they almost line up with the one going to the other side. so here is the question...
how bad will it realy be if the tubes are not 'equal' length? if instead of trying to make one tube go to the other side and curve back into the main flange and vise versa, but rather turned them down to meet the what used to go to the other side? this would shorten the top 2 by around 50% or so. i dont know what differance this would really make. please fill me in. thanks

[drscope]

Equal length headers are built so that every pipe has the same length. This is why they call them "equal length".

What they are after is trying to make the work requirment for each cylinder the same to evacuate the exhaust. On the exhaust stroke, the piston must push the burnt fuel/air mixture past the exhaust valve and into the exhaust pipe.

Many systems are designed so that as one exhaust pulse leaves the pipe and enters the collector, it is helping to pull the next pulse from the pipe of the next cylinder to fire.

When you shorten or alter the length of these pipes, you affect the timing of each pulse that enters the collector.

So, you may loose the performance advantage of having the previous pulse helping to pull the next pulse out of the following cylinder. Or, worse yet, you may have one pressure pulse wave trying to enter the following cylinders pipe which in turn will be sending that pulse back toward the cylinder in place of pulling it out.

You may find that at a certain RPM range, you really have no power, but at other's it is ok.

These things are carefully engineered to give the best possible compromise. Even the stock muffler which appears to just be a can with unequal pipes going in is engineered to take into account the timing of each exhaust pulse. Inside that can, you will find perforated tubes from the rear two cylinders that make up that length.
_________________
Mother Nature is a Mean Evil Bitch!

[Cliff@BrownBags]

damn, i didnt know all that. i am going to have to alter the pipes no matter what but one way i will have to make them a decent amount shorter. do you think i should make it work and see if i feel a differance. its a stock motor and if i loose a hair on the performance side then thats fine.

[Cliff@BrownBags]

also since its a stinger not a muffler type like a stock muffler do you think it will be o.k. since its not realy 'collecting' anywhere but just a straight exit?

[drscope]

The collector is the area where the 4 pipes come together to go into one. As one pulse goes out the single pipe, it creates a vacume behind it that helps to pull the next pulse out of it's tube.

If you have the talent and abilities to do this once, you can always do it again latter if this attempt dosn't work out. So I would do what you are doing now and see how it works. If it is really a slug, then you can try something else latter. You may get luckey and not notice any loss in power.

Here's something to think about with an open type exhaust...When you are tooling along, the exhaust valves are glowing white hot. They are so hot they have gone past glowing orange and are actually glowing white. If you have an open type system that will allow cool air to enter the pipes when you shut the engine off, this can cause problems for the valves.

That cool air hitting those white hot valves can cause the valve to warp. When this happens, the valve will no longer be able to close tightly on the valve seat. The result is that the burning gasses are allowed to be pushed past that valve. When this happens, the temperature goes way up. This will melt the valve and/or the valve seat and is known as a "burnt" valve.

This is why you are better off on the street running some sort of muffler that will help to hold in some heat when you shut the engine off.

In addition to having your headers running into the body work, you will probably also find you have far less room between the pavement and the rear apron to run your collector.

You may want to stop and think about your options. There is plenty of room up high in the wheel wells and over the axle tubes to run a nice system. If you have to do a little fabrication, you may want to do a little more and come up with something totally trick.

On my autocross beetle, we came off the collector and went forward with a muffler over the right side axle and then dumped out ahead of the right rear tire where the jack port used to be. This allowed us to have a nice long exhaust system and a free flowing quiet muffler and still not having things hanging out from under the body.
_________________
Mother Nature is a Mean Evil Bitch!

[Cliff@BrownBags]

awesome man, thanks a lot. you seem to have a decent amount of info. between you and glenn it seems you guys know about everything lol. i think ill do like you said and just build it and see whats up. if i have problems then back to the drawing board lol. i have heard of stingers burning up valves before too but didnt know why. honestly i dont see me getting rid of it just because ive had once on all my bugs for the last 14 years.