Tubular manifold

[Cavalier9696]

Naw it's all good. K back to topic. Does the tubular have better air flow so to speak then the cast iron?

[david-b]

That's ideally the purpose. Smooth insides, wide runners... should all ideally help with flow. A perfect tubular has perfectly equal runners. Most "regular" ones do not though. A very poorly built one would typically have uneven runners and actually end up costing power over making it.

[ned032002]

Do the runners have to be the same so the flow stays even as each cylinder fires? Otherwise exhaust gas will cause turbulence when it runs into each other at the end of the runners?

[SilvrEclipse]

It depends on what cast manifold your talking about. The stock turbo manifold is cast but has a runner design compared to the log type that you will be using. Yea the tubular have a much better flow design, tubular manifolds actually allow the gas to flow into the turbo, where as the log manifold rely on pressure to flow the gas into the turbo. Now I have read before that there is not much difference in performace between the log manifolds and the tubulars untill you pushing some power.

Spool characteristics also play a huge part into the design of manifolds but Im not going to get into all of that.

[david-b]

Originally Posted by ned032002

Do the runners have to be the same so the flow stays even as each cylinder fires? Otherwise exhaust gas will cause turbulence when it runs into each other at the end of the runners?

Something like that. Uneven runners can actually cause better hp due to exhaust gas escaping quicker. There's lots of R&D about it.

Some good reading:

http://rusubaru.com/equal-length-vs-...ength-headers/
http://www.tfproject.org/tfp/tilted-...yth-truth.html
http://forums.pelicanparts.com/911-9...headers-5.html

[SilvrEclipse]

Actually manifolds are made equal length so that you can utilized the exhaust gas pulses to help spool the turbo. Each cylinder fires 180* (of the crank) apart so if you have a true equal length manifold then these pulses will each hit the turbo at separete times which will help spool up the turbo, if they all if the turbo at once then they start to cancel out and you will lose the benefit of these pulses. Now if you really want to go all out on a manifold you can time these pulses and build an unequal length manifold that still utilizes the pulses and have them reaching the turbo 180* apart. With this setup you can have a smaller manifold but still reap benefits of an equal length. Of course this will require lots of work and calculations to figure out, which equals lots of money that most of us do not want to spend on a manifold. Im not sure on how much these pulses will help spool but it may be 100-200 rpms or so. Not worth it for the majority of us tuners. There are also a lot of other things that come into play when building a manifold, the diameter of the pipe will have an effect on exhaust gas velocity which will change how your manifold performs.

[cantgo2fast]

This is all true. but there is one key thing missing.

Im designing the manifold for my schools race car
http://www.facebook.com/home.php?#!/pages/Colorado-State-Formula-SAE/184988848847?ref=ts

This is a pretty basic explanation cuz Im no expert and becasue there are lots of variables, and harmonics is always a really complicated subject not to mention getting your intake and exhaust manifold to work together. The reason tubular manifolds work is really all about harmonics. I wont go into the details but basically as an exhaust port opens it emits a sound wave that as it travels down the tube pulls exhaust gas out of the chamber (scaveging). Once it hits a wall (change in diameter otherwise known as collector/turbo) it comes back and pushing, helping to keep air in the chamber, so long as the tube is the right length to match the harmonics of the wave. Now the trick is to figure out what length of tube matches your exhaust pulse wave. If they aren't close you will cancel the wave and you wont gain any benefits. The longer the tubes the more power usually, hence the reason drag racers run their turbos way down in the bumper. They are probably tuned for the first harmonic of that wave. for a turbo application the scaveging helps spool the turbo becasue you are pulling more exhaust out of the cylinders faster.

The reason to use equal length headers is mainly to simplify the problem. You know firing happens every180* like stated earlier so you KNOW they will be hitting the turbo at different times and that they will be working for the individual port. Making uneven length headers does take a lot of calculations to get it right.

Anyone with more expertise feel free to jump in and learn me.

So buying one off ebay is up to you, it could or could not be equal length and its probably not the best put together or the smoothest, but it will probably work, especially if your not trying to make gobs of power.

[Cavalier9696]

Good topic. Cause before reading this I thought the turbo manafold was basicly made to just bolt the turbo to and do the same job the stock did. These manafolds have alot to do with HP as well. Cool.

[SilvrEclipse]

I take it you are studying mech engineering building a formula SAE car. We have been trying to find funding from our school to start back the formula SAE competition. Those cad drawing look pretty good.