exhaust manifold diameter

[syka24et]

Does anyone know of a formula for calculating the the best pipe diameter of an exhaust manifold? I want to keep the velocity as high as possible without choking the engine. I plan on using a t3/t4 60trim with a 82a/r on the tuirbine side. Since the ar is a little big I want to make sure my manifold flows the best it possibly can. Thanks in advance for any help.

[hannibal]

I came across an article about manifold piping size a few weeks ago. I'll see if I can find it this evening. Its pretty complex stuff, seeing how companies spend big bucks in designing their mainfolds.

[silviaNE]

My tubular manifold is 1 3/8. Has pretty good flow. Due to the lengths of the runners full boost doesnt hit till 3700rpm though.

[hannibal]

Everything Ive read about headers so far seems to put more emphasis on the length of the primaries than their diamter. I believe those same ideas hold for a tubular manifold.Even built domestic V8s run 1 3/4'' primaries. If fact, I dont think Ive ever seen anything larger than that. (on a street car, at least)So basically, there's a pretty small range of practical tubing sizes...My guess: 1 1/4" - 1 3/4".If you go too small, I guess it just adds backpressure and therefore decreases gas speed. But I dont know where the point occurs.

Jay

[C-Kwik]

As long as you don't use tubing that is smaller than the ports, than I doubt it will be overly critical. I would be incliced to keep the size about the size of the port to promote smooth flow. Then focus on keeping the flow smooth at the collector.

[syka24et]

Thanks guys. What is your honest opininon, on a say 400 hp engine, how much horsepower do you think a decent log manifold will choke compared to a nice equal length. I am trying to see if the added cost is worth it.

[C-Kwik]

Choking will be more of a factor of having tubing that is too small. Log-Style are slightly less efficient than a good runner-style manifold as each port will have it's own path to the collector. The log-style collects more air as it gets closer to the turbo flange. As this air is added to as you pass each port, it becomes more turbulent. But it is not extrememly detrimental. An Equal length mani would be nice to have but the true advantages of it are shown not from flow as much as it is though even exhaust pulses and if you design it to work with a split-turbine entry, then it can help spool up a little in 4 cylinder applications.

[MarkEmark]

Iwannas15--could you send me the link to that article that you found a couple of weeks ago? I'm doing a project on the design/build of a forced induction setup and would love to read the article. Thanks[email protected]