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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 01-29-2013, 08:19 PM
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Originally Posted by green94z View Post
Phil what about same turbo on a bigger 408/427
Basically if your looking at making the same power through less boost, the pipe size would be the same inorder to maintain the same velocity at peak airflow movement. A bigger motor would allow you to have a larger margin of error in the pipe size and still have the bottom end performance.

At the end of the day, no matter what pipe size you use, its going to make the same boost out the back door of the track. The smaller pipes aid velocity and drive pressure down low enabling boost faster off the line and at lower RPMs.

On a smaller 346-370, pipe size is going to be critical in generating drive pressure down low early and fast.
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Old 01-29-2013, 08:27 PM
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I swear you had this same thread some years ago... interesting info...
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Old 01-29-2013, 08:42 PM
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Phil...ur setup is weak...just saying over a 1000hp at 10 or so psi?...should ran bigger pipes! it woulda made 100-200hp more at the same boost! Lmao....so 2-1/8" on a 370 with a 1.0 g-trim at 20psi?
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Old 01-29-2013, 08:44 PM
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I think everyone does it just because the "true duals" thing and they see guys like you doing it
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Old 01-29-2013, 08:48 PM
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After the wastegate my crossover is 2 inches.
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Old 01-29-2013, 08:49 PM
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This is what makes racing. People doing what they want regardless of "right" or "wrong". I did 2.5" because a 2.5" vband is the perfect size diameter for a truck manifold and I didn't want it necked down. To each their own IMO. No matter how much people preach the bible, people will not believe and believe another.
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Old 01-29-2013, 08:59 PM
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Originally Posted by Taubr Unit View Post
This is what makes racing. People doing what they want regardless of "right" or "wrong". I did 2.5" because a 2.5" vband is the perfect size diameter for a truck manifold and I didn't want it necked down. To each their own IMO. No matter how much people preach the bible, people will not believe and believe another.
amen brotha!
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Old 01-29-2013, 09:03 PM
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Originally Posted by MUSTANGBRKR02 View Post
What about the ever popular 370, manifolds and up to a 80-88mm turbo?

That seems to be what most people here run in a street/strip car.
Bump for an answer to this.

In the case of using 2.5" v-bands on the truck manifolds, would a conical reducer such as this, http://www.acestainless.com/tube-fit.../sf-31w-25x20m, or a transition cone such as this, http://www.mandrel-bends.com/catalog...-cone-680.html, be a better fit, or would it not matter as long as the transition is smooth and gradual? Take note I could only find that conical reducer in the 2.5" x 2" size with a few different Google searches.
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Old 01-29-2013, 10:43 PM
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2.25 here.
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Old 01-29-2013, 10:59 PM
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Originally Posted by turbocamaro125 View Post
Phil...ur setup is weak...just saying over a 1000hp at 10 or so psi?...should ran bigger pipes! it woulda made 100-200hp more at the same boost! Lmao....so 2-1/8" on a 370 with a 1.0 g-trim at 20psi?

We will see how weak it is when it goes 175-180mph to the 1/8 mile.....

I think you might be able to go up on the turbine A/R.

Big pipes require more time and engine to develop the same drive pressure, once its up to pressure its going to take the same drive pressure to maintain boost and where the wastegate comes into play.

My motor makes about 1300hp through a single 2.5" OD pipe. Remember, pre turbo its about velocity.
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Old 01-29-2013, 11:06 PM
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Originally Posted by Taubr Unit View Post
This is what makes racing. People doing what they want regardless of "right" or "wrong". I did 2.5" because a 2.5" vband is the perfect size diameter for a truck manifold and I didn't want it necked down. To each their own IMO. No matter how much people preach the bible, people will not believe and believe another.
My days with imports taught me a thing or 2 about turbocharging along with reading and more reading.

I bet you would **** your pants if you put a velocity sized crossover on with the next size AR and it spooled faster with less backpressure down track.

Tracy did the same thing, went from 2.5" pipes to stepped pipes down to 2" and put bigger A/R housings on the turbo, spool picked up and lost backpressure.
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Old 01-29-2013, 11:34 PM
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I'm not saying your wrong by ANY means Phil. Hell, it be easier making a hot side out of 2.25. I know velocity is key with a turbo and why I'm wrapping mine with heat wrap and a very short 5" DP to keep the heat velocity up. I'll just use my huge 2.5" hotside for spots when grudge racing, lol.

Off topic.. Kinda strange/wow/crazy how "smaller" stuff goes soo fast. Small 5.3's, small hotside a etc. Yet on the other side of the quarter people are going 8's with a 5.3 and 90+mm turbos. Guess anything works on a ls engine?? Did god really bless these motors?! Lol
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Old 01-30-2013, 01:05 AM
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Phil... is this the tech version of the Turbocharging 101-102 threads???

Btw.. 2 inch pipes going on a 4.8 with an S480R...

I still agree with you... lol
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Old 01-30-2013, 01:20 AM
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Per your thread a couple years ago, I did 2.25 for the crossover into the merge. Thanks for the advice. It works great and I haven't had any issues. Packaging is better and easier to route as well. so far on 16 psi 767whp through a unlocked 80e with a gt4276 1.15 AR
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Old 01-30-2013, 02:00 AM
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Good info. Subscribing
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Old 01-30-2013, 02:04 AM
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Okay so with all this talk in here about piping size maybe someone can answer this for me.

As I have seen already and read ppl have made 900whp with a 3inch dp that being said would running a 3inch dp and y'ing into dual 2.5 inch pipes all the way to the rear bumper hurt flow at all?

Only looking to make 800-900whp by the way.
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Old 01-30-2013, 10:32 AM
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Originally Posted by LilJohn View Post
Phil... is this the tech version of the Turbocharging 101-102 threads???

Btw.. 2 inch pipes going on a 4.8 with an S480R...

I still agree with you... lol
No, I was just goofing off over here and just see some strange ****. If I ever get enough money to build an X275 motor, I'd love to try some new stuff. I am still looking for a 1.7 AR turbine housing for my T6.
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Old 01-30-2013, 10:42 AM
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Originally Posted by 95bowtie View Post
Okay so with all this talk in here about piping size maybe someone can answer this for me.

As I have seen already and read ppl have made 900whp with a 3inch dp that being said would running a 3inch dp and y'ing into dual 2.5 inch pipes all the way to the rear bumper hurt flow at all?

Only looking to make 800-900whp by the way.

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.
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Old 01-30-2013, 10:48 AM
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I just use what I have laying around . 2.5 inch pipe is the most common around here. I just don't think anything bigger would be any better unless you got some big cubes.

Last edited by Twin turbo c5; 01-30-2013 at 11:03 AM.
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Old 01-30-2013, 11:00 AM
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Would the smaller crossover help us cheapskates with undersized turbines in our budget turbos?

I already have the tubing and everythign for the 2.5 hotside since 2.5 v-bands but weld perfectly to the truck manifolds.
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