Cross Over Pipe Science

[TYTILIDIE]

Whats the deal with xover pipe sizing? I see RPM sells their headers with a 2.25". I ordered my parts from SPD last week and he talked me in to 2". He made the point that divided flange I am using wont accommodate more than 2" anyway and it would be pointless to have bigger pipe with the bottle neck of the flange.

I did the math, and the overall area of the 1.5" primaries is larger than the 2" and 2.25" xover area. Is this the wrong line of thought?

 

[mattw]

Re: Cross Over Pipe Science

I thought about the EXACT same thing when I was building mine. I ended up going with 2.25" and I wonder sometimes if thats really big enough for a V8 application..

 

[qbnkiller]

Re: Cross Over Pipe Science

The thing to keep in mind for most applications is velocity versus volume. There is such a thing as too large a crossover. This will show slow spooling.

I had a 3" crossover on my V8 build - even knowing it would be a bit laggy. When I redid the crossover this year I dropped it to 2.5". Noticeable difference. I would venture to say I could get away with a 2.25" no sweat.

A turbine wheel needs heat, volume, and velocity to spin it efficiently. Have one of those variables out of kilter and performance will suffer.

 

[Ty1642]

Re: Cross Over Pipe Science

There's a long thread on yellowbullet about turbo design, starting with crossover sizing. I didn't have time to absorb it all, but as I understood it, the piping sizing should gradually decrease from the exhaust port to the turbo. This increases the speed of the exhaust gas entering the turbo and helps spool up time. The reductions in sizing should be done as gradually as possible, and the tubing should never increase in size. Again, this is my limited understanding.

Here's the thread:

http://www.yellowbullet.com/forum/showthread.php?t=308464

 

[TYTILIDIE]

Re: Cross Over Pipe Science

So does anyone know the mathematical equations to figure this out? Maybe I should start reading my Corky Bell book for the answers. Just need to find it.

 

[eviltwin]

Re: Cross Over Pipe Science

2" will be fine. Its not gonna be any more restrictive than the turbine on the turbo. My Sy has a 2.25" crossover on 370ci without a hint of issues. My GTO has a 2" crossover on 364ci without issues as well.

 

[Don W.]

Re: Cross Over Pipe Science

Want some formulas? Check this. I suddenly have a headache.

http://www.turbobygarrett.com/turbobygarrett/choosing_turbo

And a little more in English.

http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html

And one last that just looked interesting.

http://www.cobbtuning.com/Technical-Articles-s/70676.htm

Have fun, don't stay up to late.:rotf:

 

[nallj92]

Re: Cross Over Pipe Science

i have a 2.25 crossover on a 6.0 ls. 2.25 is good up to 1000-1200 hp at least, you could prob get away with 2 inch. Like alex said, its all about not choking the motor but keeping the velocity up to the turbine as well. I would say 2.5 is still too big for a 4.3 imo.

 

[MikeRenz]

Re: Cross Over Pipe Science

or just take the crossover out of the equation and go twin turbo. That's probably your best option