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Out of curiousity why does everyone use 2.5" on the crossover pipe

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Out of curiousity why does everyone use 2.5" on the crossover pipe

 
Old 01-30-2013, 09:29 PM
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Originally Posted by o2camaross View Post
Haha funny you say that about Corky Bell, Phil. I just bought his Maximum Boost book. Are the formulas in there?
Yuuuuup
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Old 01-30-2013, 09:30 PM
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Originally Posted by green94z View Post
After this thread and thinking about it a while I'm thinking about redoing my kit into 427/truck manis/2/2.25inch crossover to 2.5/2.75 into my 1.32 lf88
Turbo sounds small for a 427. What kind of cam is in that thing?
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Old 01-30-2013, 11:17 PM
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Originally Posted by Taubr Unit View Post
I'll just use my huge 2.5" hotside for spots when grudge racing, lol.
^ Lmao! Good thinking!

Originally Posted by Phil99vette
I dont really remember seeing too big of a downpipe on a turbo car.
^ Very true.
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Old 01-30-2013, 11:59 PM
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Originally Posted by Phil99vette View Post
Turbo sounds small for a 427. What kind of cam is in that thing?
Was going to be a grudge car, changed after I ordered the motor to a 275 car
I gave you the specks on yb
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Old 01-31-2013, 02:37 AM
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Originally Posted by Phil99vette View Post
We're not talking about downpipe. We're talking about pipes before the turbo. The downpipe is usually sized at 120-125% of the exducer size. I dont really remember seeing too big of a downpipe on a turbo car.
I understand that but was looking for actual numbers with dual 2.5 inch pipes on a 5.7 with a tc 7875 turbo.

2.5 will tuck nicely in the tunnel 3 inch duals however will not. My car has dual tail pipe exits and wanted to use them so if 2.5 pipes will work and not restrict then o want to use them. Just am not sure on that yet.
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Old 01-31-2013, 07:53 AM
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Originally Posted by green94z View Post
Was going to be a grudge car, changed after I ordered the motor to a 275 car
I gave you the specks on yb
You definitely need a new cam.
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Old 01-31-2013, 08:17 AM
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I guess the reason I used 2.5 was becaust the vette manifolds I used had 2.5" outlet and the t6 turbo was just about perfect for a 2.5" pipe to either side of the flange. I honestly saw no reason to neck it down to 2.25" coming out of the manifold only to increase it again going into the turbo. I figured keeping it the same throughout would work better. Is this incorrect thinking?
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Old 01-31-2013, 09:29 AM
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Originally Posted by Sarg View Post
I guess the reason I used 2.5 was becaust the vette manifolds I used had 2.5" outlet and the t6 turbo was just about perfect for a 2.5" pipe to either side of the flange. I honestly saw no reason to neck it down to 2.25" coming out of the manifold only to increase it again going into the turbo. I figured keeping it the same throughout would work better. Is this incorrect thinking?
I thought that the 2.5" had to be trimmed to fit on either side of a divided T6 Flange. someone mentioned that the 2.25" actually fits perfect.
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Old 01-31-2013, 09:33 AM
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If the T6 flange is a divided flange, two 2.25" pipes fit snug after a little hammering.
Looking at the area needed to feed a T6 flange, two 2.5" pipes equates to the open area.
That little divider will make a difference if a 2.25" or 2.5" crossover should be used (if you are basing your piping on matching the cross-sectional areas).
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Old 01-31-2013, 09:52 AM
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Donno, maybe my divider was a little on the slim size, but after hammering the pipe to a rectangular shape that pretty much matched the flange it was almost perfect. I tested with a 2.25" and it was pretty loose. So I decided to step up to 2.5" since that was what fit the c6 manifolds I was using. The flange matched the gasket and the turbo well though. Ideally something in between 2.25 and 2.5 would have been perfect.

But does necking down from the collector to a smaller size have any advantages?
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Old 01-31-2013, 10:13 AM
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Originally Posted by Sarg View Post
Donno, maybe my divider was a little on the slim size, but after hammering the pipe to a rectangular shape that pretty much matched the flange it was almost perfect. I tested with a 2.25" and it was pretty loose. So I decided to step up to 2.5" since that was what fit the c6 manifolds I was using. The flange matched the gasket and the turbo well though. Ideally something in between 2.25 and 2.5 would have been perfect.

But does necking down from the collector to a smaller size have any advantages?
Here is an analogy... You got a 1 mile race....
You run your ***** off for the first 200'(intake valve)
then you slow down to speed walk for alittle(header)
you transisition into a slowwww jog(crossover)2.5"
then you run at a good pace(merge)3"
then for the last 200' you run your ***** off again(turbine housing)

Or

run your ***** off for the first 200'(intake)
then you slow down to speed walk for alittle(header)
then run with a very good pace (crossover)2.0
transiition into a short sprint(merge)2.5
and run your ***** off at the end(turbine housing)
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Old 01-31-2013, 10:52 AM
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But slow and steady wins the race right? J/k.

So assuming you are not merging the two together (in my case divided housing), it seems like it would be a flow restriction going from a 2.5" collector to a 2.25" pipe only to widen back out to 2.5" again at the turbo. Am I missing something? I am sure I could rework my hot side piping later if need be, I just would like to know your thoughts on necking down then back up like that.
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Old 01-31-2013, 11:10 AM
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Doe double post.

Last edited by Sarg; 01-31-2013 at 11:55 AM.
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Old 01-31-2013, 12:56 PM
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Originally Posted by Sarg View Post
But slow and steady wins the race right? J/k.

So assuming you are not merging the two together (in my case divided housing), it seems like it would be a flow restriction going from a 2.5" collector to a 2.25" pipe only to widen back out to 2.5" again at the turbo. Am I missing something? I am sure I could rework my hot side piping later if need be, I just would like to know your thoughts on necking down then back up like that.
Its all about VELOCITY. The turbine is going to be the restriction not a 2.25 pipe.
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Old 01-31-2013, 01:11 PM
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Originally Posted by Sarg View Post
But slow and steady wins the race right? J/k.

So assuming you are not merging the two together (in my case divided housing), it seems like it would be a flow restriction going from a 2.5" collector to a 2.25" pipe only to widen back out to 2.5" again at the turbo. Am I missing something? I am sure I could rework my hot side piping later if need be, I just would like to know your thoughts on necking down then back up like that.
When you get time to look at a turbo like yours, measure the cross section at the throat where it starts to turn. On a standard un-divided turbo, your not widening it at the 2.5" section, its combining pulses from both sides and velocity increases again.

header tube sees 1/8 of the total airflow
Crossover tube sees 1/2 of the total airflow
merge at the turbo sees the entire engine airflow.
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Old 01-31-2013, 03:27 PM
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And on a divided turbo?
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Old 01-31-2013, 06:44 PM
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Does velocity remain constant with every fuel available to us? For example, 91, e85, e98, 100, c16?
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Old 01-31-2013, 07:46 PM
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I would say no, as E85 will produce increased exhaust volume to the best of my knowledge.
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Old 02-01-2013, 01:05 PM
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Originally Posted by Sarg View Post
And on a divided turbo?
A divided turbo still necks down, Just because the inlet is = to an "x" size pipe doesn't mean thats the best size for your motor.
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Old 02-01-2013, 01:09 PM
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Originally Posted by 94 slow View Post
Does velocity remain constant with every fuel available to us? For example, 91, e85, e98, 100, c16?
These calculations are based on gasoline combos that have worked well, methanol or an ethanol based fuel would be slightly different. I am using the same sized pipes from C16 and have changed over to methanol, you can tell there is more exhaust velocity/mass based on the additional fuel in the exhaust. The air is still the same just have more of a fuel mass.
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