Long Runner Exhaust Manifold Question
 

If a short runner turbo exhaust manifold was not an option and you had to make a long runner manifold would you collect the individual runners close to the block and ensure equal length or would you collect right at the turbo? More importantly, why?

It seems to be common practice to collect at the turbo, why is that?

I'm looking for theory and or technical information so I can research more and make an educated decision.

Don't do either of the above. Run them separate all the way to the turbo and run a divided turbine housing.

~Mike............

what if you cant get a divided turbine housing for your turbo?

If that is the case i believe you want to keep them separated as long as possible. IE joining at turbine inlet flange again if possible.

^^ What he said. Make the transition as shallow of an angle as resonable and as smooth as possible from two round tubes to one square/rectangle. Your going to want to place your wastegate taps as close to the turbine housing as possible and in the direction of flow. Worst case perpendicular. No need for two WG taps or dual gates. 1 would be sufficient if placed neae the turbine inlet and a gate with a big enough valve is used.

~Mike...................

Why is it that most people suggest that the gate must be as close to the turbine as possible??
I have seen great results with the gate mounted at the exhaust port end of the pipe,this is with a small(1.5'') header pipe though.to bring on better air speed and producing more turbo response. Still get good top end flow through the small pipe as alot of the gas is dumped before hand.

It is common to collect at the turbo because:
1) Individual runners help maintain exhaust gas velocity. If the exhaust expands into a large single runner, its velocity will slow down, reducing its energy and therefore its ability to turn the turbine.
2) Individual runners keep the exhaust pulses from interfering with each other, reducing turbulence, allowing for the exhaust gasses to better maintain their velocity.
You should really try to use a divided turbine housing if possible.

Equal-length runners are mostly for keeping a consistent pulse timing so there is no turbine surging (not to be confused with compressor surging).

Mounting the wastegate close to the turbine allows for less plumbing because you are basically fabricating only 1 1/2 sets of runners or less vs. 2 sets of runners. Also, it ensures the wastegate is mounted far enough away from the exhaust ports to allow for less turbulent airflow and less heat. I guess you could mount the wastegate close to the exhaust ports on a drag car that only operates a max levels for a few seconds, but the intense heat would most likely lead to premature diaphragm failure on a road car.

^^^what do you mean to say that the egt has drop so much in the short distance of a few inches from the beginning to the end of the runner??
Your dreaming if you think so:lol:
Like most people,I think you may look way to far into it.
Think about it.

Your also kidding yourself if you think a rotary engine will out last a diaphram from INTENCE heat:lol: I've never seen a failed diaphram,just lots of apex seals:lol:

^^well maybe you should not build rotaries if you cant keep the seals in side the keg! :rolleyes: j/k

thanks everyone.

also have some questions about the materials. I was thinking 304L stainless sch 10 with 3/8" stainless flanges. the turbo will be supported so little to any load will be on the manifold and the car will be occasionally street driven. do you think sch 10 will suffice? Its going to be a bit of an experiment so I didnt want to make the investment to sch 40 stainless.

what do you guys think?
anyone with experience with sch 10 stainless manifolds?

sch 10 is all good, no need for 40.