2.5

 

Either will work fine

 

The 2.5" fits nice to the T6 flange. Just square the tube and two of them slide right in.

 

Thanks I'll stick with 2.5

 

2.5 and give you a little room to grow.

Keep the banks separated and use two smaller wastegates on each tube, spool will be alot faster.

 

I see zero reason for 2.5" on a street 408.

May want to read this and decide for yourself.

He basically says 2.5" crossover will support 2300hp+ so why use it on lowish HP builds?

http://ls1tech.com/forums/forced-in...-induction/1619207-out-curiousity-why-does-everyone-use-2-5-crossover-pipe.html

Or this longer YB thread saying the same thing. Paying attention to 95mmRenegade who is the same as Phil99vette.

http://www.yellowbullet.com/forum/showthread.php?t=308464&page=21

 

Yea , smaller .
Just put on 1 5/8 crossover, it should spool at idle and build enough heat to last 2 weeks before metal fatigue sets in.
Matter of fact 1.25 primary tubes in the headers.

 

Not every one out there makes 2500 hp... It's been proven time and again on the mild builds that smaller piping works well. I switched form 2.5" to 2" on a mild 370 LS setup. Lost no power up top and the turbo lights of MUCH faster. Would also allow me to run a larger turbo housing/wheel which would net less back pressure. Packaging is also easier/cheaper/lighter.

Factory cast manifolds and 2" hotside... Running 8.8X 1/4's @ 169 on 17lbs of boost. Which I know is nothing to write home about around here, but it works well for a street car IMO.

Here it is in all it's glory...

 

8.8X @ 159... that was a typo... Also for the record stock48 is trapping 170+ with 2.25 on a 3400lb nova.

 

I would do 2.25"

 

You need velocity.

 

What kind of power and RPM are you planning on? I’d look into their “gangsta” T4 S476 if you want quick spool times. Guys are making 1200 whp with it around your cubes. Seems like plenty for the street. Would spool faster than a T6 S480 anyway.

 

I'd like to see around 800rwhp and run 8s. Cam is lil John with around 6500 shift point he said. I think I have a decent foundation for that power but I know I'm limited on the block. I am trying to keep back pressure in check also. Opinions and advice is greatly appreciated.

 

Our Duramax diesel truck puller uses 2" sch. 10 stainless pipe for the crossover. That has an ID of 2.15. That feeds a T6 G trim HX82 just fine. Around 1600hp.

 

I order 2.5 yesterday from mandrel bends. I try to call Dr turbo today to get the turbo but got know answer. I will try him again tomorrow. I hope it spools fast. I am going separate all the way to the flange. If not I can go 2.25 at a later time. I'll let you guys know how it hits on the street. Gotta figure out my exhaust now and where to mount the turbo.

 

Called Jose today and ordered the S480. Got my piping from mandrel bends and EV standard hat with no divider so can start the crossover this weekend and hopefully the hat it will fit under my hood. Gonna go with dual JGS 40mm gates.