jrtoffroad

Not sure the best place to put this, but was hoping you guys could help me re-design my exhaust system.

I have a 6.2L LSA based engine with an F1R procharger hitting a little more than 20psi and revs to 7500 with max hp @~6800. Nothing to crazy, LS9 heads, LS3 intake, etc. The car is an Ultra4 race car that runs 38" tires and put down 682hp to the wheels.

Currently I'm running an 8 into 1 header that has 1 7/8" primaries and a single 3.5" collector outlet. Prior to the outlet the collector has a venturi area that reduces to 3". After the header I have a single 3.5" pipe that's ~32" long and runs through a borla race muffler.

I'm under the impression that the collector is WAY too small. During dyno testing the collector was attached with springs and it shot off the engine at ~6500rpm breaking the springs. It's now bolted on.

So, a few questions:
-Is an 8 into 1 design an advantage at all, or am I leaving power on the table?
-Is a 1.875 primary tube large enough for a 6.2L engine spinning to 7k+ with >20psi of boost?
-What collector & exhaust pipe size would you recommend? Is the venturi or transitional exit worth it?

I'm tempted to leave the primary tubes alone and rework the collector to a 4 or 4.5 outlet and maybe a 3.5 or 4" transition.

Thanks!
Jordan

Bob@BruteSpeed

iTrader: (16)

I'm not a header expert by any means but for the power you are making I'd go with 2.0" header tubes with four into one collectors. You should run your questions by Kooks, Stainless Works and American Racing to see what info they recommend. Bob

Blown06

iTrader: (32)

Yeah, I'd say you are leaving power on the table. Have any pics of this 8-1 header with only one collector?

mOtOrHeAd MiKe

iTrader: (8)

Go here: https://speedtalk.com/forum and get solid advice. You will probably be told to buy some software like Pipemax.

JakeFusion

iTrader: (7)

I'd run a 2" primary into 4-1 or Tri-Y design with 3.5" collectors per bank. LSA heads need a bit of help on the exhaust side anyway and you need a very high flowing exhaust with a Procharged motor.

682 is incredibly low for an LSA with 20psi on a F1R. I'd expect to see north of 1000rwhp with that combo in an F-body with 26-28" tires (assuming it's over 65k RPM on the F1R - if not then you're seeing a lot of backpressure to push the boost up to 20psi if you aren't spinning it that hard). The 38" tires aren't helping. Probably losing 100-120rwhp with them vs an F-Body. Even still right at 800 or so is still low for an F1R assuming it's being spun that hard.

jrtoffroad

Here's a video that shows the car and exhaust:

jrtoffroad

The engine actually has ported LS9's, but I agree the exhaust flow is probably still lacking. At my 7500 rev limit I'm spinning the procharger slightly past its rated 68k speed.

I'm sure I'm leaving power on the table, but the losses of the drivetrains we run in Ultra4 are crazy. It's not just the big tires, it's the high output power steering pumps, high output alternators, heavy thick wall driveshafts, heavy transfer case components, heavy diffs and axles, etc.

From everything I've read, a 2" primary and 3.5" 4-into-1 collector sounds about right. I guess I'm still wondering if there's any gain to be had with a 8 into 1 system. If nothing else I really like the sound. One thing I've read is you don't need a crazy big collector with the 8-into-1. Since the pulses come at a constant 90 deg interval you don't need a collector much larger than a 4-into-1 collector on a standard header (where collectors are typically oversized due to the 90 deg separation of 2 cylinders).

Thanks for all the input!

JakeFusion

iTrader: (7)

That's pretty awesome.

Tig

****, I was watching this video the other night. Bad *** man, that thing is sick.

conan

iTrader: (5)

That thing is bad *** man. I agree the 3.5 collector is too small, it looks in the video like the elbow to the muffler is blued from the heat. Thats alot of exhaust merging together with 20 psi of boost, guess im not shocked to hear the pipe popped off. Also how restrictive is the Borla muffler ? Wounder how it would with a straight pipe out the side. Never the less thats a cool machine you have there.

jrtoffroad

Thanks guys!

The Borla muffler is one of their race units. It's straight through with no baffling.

The min collector size right now is actually only 3", it then flares out to 3.5.

I'm pretty set on new headers now, just not sure if I want to stick with the 8 into 1 style. Need to measure the primary tube lengths, if I can't get them short enough that might be my answer.

jrtoffroad

Here's the DYNO run on the car:

chuntington101

What a car! Off topic but have you got any details on the drivetrain used?

On the headers have you messured backlressure in the headers and after the collector? Would be nice to see if it's higher than what other are seeing. I must admit I to love the sound of the 8 to 1s. Don't they also give you more torque in the mid range than2 4 to 1s?

Are you sure the issue is in the headers? From the video the intercooler looks pretty small. Do IATs stay low for pass after pass?

jrtoffroad

Sure. The trans is a NAG1 5 speed auto out of a SRT8 Grand Cherokee. The T-case is a 1.5:1 Atlas Race Case. The rear axle is a flipped reverse rotation 60 with 10" 488 gears, detroit locker and 40 spline axles. The front is a flipped 9" with 9.5" 488 gears arb comp locker and Nitro Gear billet aluminum 3rd.... The car is always run in low range, hence the tall axle gears.

jrtoffroad

I haven't measured back pressure, but it would be a great test. Although sadly, I'm pulling the engine right now so can't test before I redo the exhaust. I've heard lots of mixed opinions about the 8 into 1 system, wish I could find some DYNO numbers.

IAT's actually have looked really good, although I haven't checked boost before and after the intercooler. The intercooler is the 1500hp unit from Frozen boost. Not exactly a top dollar piece, but I've actually heard very good reviews.

jrtoffroad

Huge derail to the thread, but am also curious about everyone's thoughts on the ls3 intake for my application. Am I asking too much of it spinning the engine as high as I am? In a boosted application, would the loss of low end be noticeable if I were to run something like the holley hi-ram? Think I'd gain very much up at say 7k?

Thanks again!

Husker98

iTrader: (11)

I think the 8-1 sounds awesome and is great for an n/a motor but that F1r is trying to shove a lot of air through that motor and if you're going for performance I don't think primary length will matter but I wouldn't go any smaller than 2" primarys and 4" collectors. The holley hi ram really shines in the upper rpm's. The tests I've seen the hi ram gains 30-40 hp over the factory intake over 5000 rpm