MBR44

Yes, the 591 with arh 1 7/8" run was july and the 608 with kooks 2" run was in october of the same year. I am sure the temp in october was not accurate at 102.5. It was toasty warm in MI that weekend in october though. I am sure the tune was a bit different than the previous too. Dan Millen was awesome to deal with, I drove down to detroit and he dropped me off at the airport then picked me up sunday to delivered the car before he took off to Texas to win another big race.

Vito.A

I doubt you will see any substantial gains in horsepower switching from 1 7/8" primary headers to 2" primaries in a normally aspirated LS7 427CI engine, especially through the mufflers.

If you have over 450CI and large aftermarket heads/valves, you may benefit from the Kooks/ARH 1 7/8" to 2" step primary headers. But even then, the gains will be small.

heavyhitter

Its not an ls7 but will be pertinent. Had a 370cu lq4 with 225cc trick flows with all the bells and whistles - 2" kooks picked up an average of 12 hp and 8 ft of torque across the board vs 1 3/4 kooks. Thats with 370 cu

Stars_Fan

no dyno yet?

FamousRR

Sorry car is still in shop. Ended up doing a cage and race seats which delayed everything a lot. Had a hard time figuring out what seats. The headers are on. Car should be complete in the next week or two. Then I'll have it dynod and I'll post up.

Josh B.

I found this info to be very useful. Thanks to the MBR44 for posting up dyno charts, we all know that can be time-consuming and costly, but it helps everyone to know what works and what doesn't.

SteveDoten

Great question!!

I noticed a big push towards the 2" while working at ARH over the past few years.

I was surprised myself to see the bigger tubes used on 580whp NA builds.

Never did any testing personally.

RGT

I remember this thread. Yes it does contain some good info.

Georgies

Any results? Im getting my first set of headers along with everything for a cam upgrade including the MS4 cam. Some guys are saying the 2" ARH longtubes are overkill and will hurt low end...

Any info on this?

MTPZ06

Wrong...at least on an LS7. Gains across the board by going with 2" ARH LT's over 1 7/8".

redbird555

it's been proven on a bone stock ls3 2" make more power everywhere.

People who say bigger headers lose low end have no experience with them

Georgies

Ok thanks alot! Do you think the same would apply to a ls6 with just a bigger cam and aftermarket intake?

Cordes Performance Racing

here is a graph i posted awhile back showing the lack of zero low end loss doing a 2''. These two cars are absolutely identical,

Same heads, same cpr cam (alpha), same msd intake, same cold air, same state, same dyno, both done by us, etc, etc. The only difference is the lower powered one had ARH 1 7/8 and the higher powered one had ARH 2''. That's it!

nuke61

While this may not be a direct apples-apples comparison, HotRod tested a big block Chevy 427 and found that the 2-1/8" headers actually had better low end torque/hp than the smaller tube headers, and slightly *less* peak horsepower. More or less contrary to all conventional "wisdom" posted on the forums.

http://www.hotrod.com/articles/headers-dyno-test/

Georgies

Anyone else wants to voice their opinion on the 2" on a ls6??

Racingswh

I have a question Joe. What's the difference then between the AMERICAN RACING 2" X 2-1/8" X 3-1/2" HEADERS & 3-1/2" H-PIPE and the 2" ARH C6 Z06 CORVETTE 2006-2013 LONG SYSTEM.








The proof is that 2" headers make more power than 1 7/8" but the 1st picture above has a cross connecting tube whereas the 2nd looks like it has two elbows that join together. The first is more expensive than the second. I just want to make sure I get what makes the most power. NA 600-650 rwhp for road course is the application.

Unreal

The 2 1/8" are stepped headers with 3.5" collector and pipe. Would need custom exhaust from their back, and is for bat **** crazy full race stuff.

Unless you are planning a 1500+hp blower build, I would do the 2" as they bolt on and work. More than enough for 600-650rwhp.

Racingswh

Exactly the answer I was looking for. I appreciate it!!

Maybe someday I will have a road race twin turbo engine built that makes power like you are used to but until then I am excited for this build to be completed and get the car on the track.

SPDKLZ1

I was on the fence until the very last second a month ago. I'm glad I went with the 2" American Racing header setup even though my builder thought it was overkill.

Ghost Knight

I've heard this many times, however people have failed to supply the test data. Please share the controlled before and after comparison you have.

That's a great start, however it is comparing two different cars so not 100% controlled. It is encouraging, however.