evo462

iTrader: (27)

Lately I have seen 2" piping recommended here by various people instead of 2.5", citing increased velocity as the benefit for "lower" HP builds. Maybe I just hadn't paid much attention before, but it seemed like 2.5" is most commonly used.

Id be interested in hearing from people who have fabbed or installed both their experiences between the sizing. I think the 2" hot side piping would be easier to finangle around the engine bay, but at what point is it a restriction? I can't say I've seen any hard data either way, more or less opinions/recommendations.

pwrtrip75

iTrader: (8)

Curious to know also... and at what HP level should one go from 2" to 2.5"?

slow67

iTrader: (2)

The real question is at what velocity in the 2" pipe begins to hurt flow. I know that near .5 mach in the intake runner is when it starts to take a hit on power, but exhaust is different as it more viscous.

yelo04goat

iTrader: (11)

in for info as well i know phil99vette will chime in here bein that he had some good info before in another thread...

if you still have doubt then go with the 2.5 in had shown to work many times...

or go with 2.25 best of both worlds right... ...

rotary1307cc

iTrader: (5)

my up-pipes are 2.25"

505OUTLAWZWS6

iTrader: (13)

I used 2.5 on both kits i have built. 2.5" also fits perfect inside the truck manifold flanges. So if a stock exhaust system is using 2.5" pipe why go smaller on a turbo build?

TracyRR

iTrader: (8)

i'd go with 2.25 unless you're shooting for 2000 hp. I'm still learning but i can tell you that i went with 2.25 and it improved spool by approx 500 rpm on my twin rear mount.... phil99vette recommended it and i'm glad i took his advice.

Phil99vette

iTrader: (11)

We've made over 2000hp with a 2.5" crossover.

Phil99vette

iTrader: (11)

After looking at countless logs and spool data tied to engine combos the exhaust tubes do play a part in spooling. Just some food for thought....

On a 438" motor @ 40# of boost @ 92% VE and 8200rpm the motor can make 2400hp.

Header tube options:
1.750 = 444cfm
1.875 = 387cfm
2.000 = 340cfm

We noticed when we switched from 1.75" to 2" the spool suffered and the boost rise rate seemed more mechanically limited.

Crossover:
2.50 = 870cfm
2.75 = 719cfm
3.00 = 604cfm

Merge:
4.00" = 679cfm
3.50" = 887cfm
3.25 = 1029cfm

Turbo: T6 housing 1.32
3.25" inlet tapers to a 3" before the turbine
3.25" = 1029cfm
3.00" = 1208cfm

Now seeing other combos that have spool problems show lower air velocities.

On a 370" & 20# of boost & 7200 should make 1100hp....
Most factory 205/215 castings have a exhaust port that measures 1.400 x 1.600
Headers:
1.50" = 276cfm
1.62" = 235cfm
1.75" = 203cfm

Crossover:
2.00 = 622cfm
2.25 = 491cfm
2.50 = 398cfm

Merge
2.50" = 796cfm
2.75" = 658cfm
3.00" = 553cfm

Now I just need some turbo measurements for a T4, The T4 looks to have an inlet with about 5.6-5.7" sq/in of area

Turbo inlet @ 5.65" = 700cfm

Going with a larger tube between the header and turbo will increase the area which will require more time to fill and generate the drive pressure for the turbine. You can go too small....

onfire

iTrader: (17)

Do you mean fps instead of cfm?

Phil99vette

iTrader: (11)

Yeah, I was multi-tasking.

Chicago TDP

iTrader: (3)

So, if I am reading this correctly, I need to build my log manifolds with:

TRUE 1.5" ID primary
TRUE 2.00" ID "log"
TRUE 2.00" cross-over
2.75" merge into the T4 housing

3.5" DP????

I ask because I am about to order all the stainless sched 10 to build a set-up for my ls1 with a MP T70 Q trim.....

Phil99vette

iTrader: (11)

If your building it with weld els, why can't you do a simple 4 into 1 instead of a log? I really dislike the log style setups. Be careful on the head, most ports are 1.600" wide, you'll need to do some massaging there. You can use a 1/2" flange and taper the flange, Madman sells 1/2" flanges in SS and MS. The velocities in the 370" package are well below the numbers we use on the race car so it should work bad *** if you get the transitions right.

slow67

iTrader: (2)

Hey PM me your email...I have a spreadsheet I want you to look at

Phil99vette

iTrader: (11)

phillip _ eclipse at hotmail dot com

yelo04goat

iTrader: (11)

i know that the 4 into one is best and im goin to try to get that done but if i do go with the log and run the crossover into the back of the log shouldnt the log be bigger then the 2-2.25 crossover?

thanks for all the info phil making me rethink how im goin to do things.. glad its all before i start!

Phil99vette

iTrader: (11)

The log creates turbulence where each of the primaries join. If you can make a log, a 4 into one is easier to build because you dont have to join 6 tubes to a main body. I would make them like my 1 3/4" headers, drop down and swoop forward.

Phil99vette

iTrader: (11)

Chicago TDP

iTrader: (3)

just to play the devil's advocate here, aren't truck manifolds similar to the log manifold in a sense? or even the new camaro manifolds???

Adam

Phil99vette

iTrader: (11)

Post a pic... the truck manifolds I've seen are no way close to a log.