edcmat-l1

iTrader: (10)

OK. Had a chance here recently to do some "testing". Now, let me preface by saying this is done with 2 different cars. Now, I know some will poo poo this because of that, and I'm just letting everyone know up front.

Anyways, the 2 cars are both 08s (Vettes). Both autos. Both bone stock down to the airbox. Both 3 inch catted x pipes. Both with NPPs. Both run with them open. THIS IS AS CLOSE AS I COULD COME TO A BACK TO BACK SWAP ON ONE CAR.

OK then. On to the results. The first graph is the best before out of each car. The red line is the car we did today. The blue is a car we did about 3 months ago. Both pretty low mileage. We believe the before difference may just be the ambient temps. Notice how close the A/F is.
Both cars were run, each run, at 196 degrees at the start of each pull.
There were no dyno tricks, no nothing. I tried to make this as even a comparison as I could using 2 different cars.



The second graph is both cars after a header install, catted x-pipe, and tuned. I didn't try to "max" either cars tunes. Only got the knock retard out, and got the A/F to high 12 something to 1. Actually, to start off with, on the car we did today, I just plugged the other cars tune in and started from there. Can you tell which one is the 1 3/4 and which is the 1 7/8?



The third graph is the car we did today, before and after.



The forth, the car we did 3 months ago, before and after.



Let the debating begin.
I'll throw in my .02 after some input.

STAR

iTrader: (1)

The 1 7/8 header did not loose any torque down low and made a few more ponies up top. Where the bigger header will really shine is on a FI set up or a big cube NA motor. Might as well buy the bigger headers that way if you upgrade in the future you don't have to spend money twice!

Am I right?

speed_demon24

iTrader: (6)

Were both headers/x-pipes/cats the same brand with the pipe size being the only difference?

slowandrichws6

iTrader: (2)

i agree 100%, im tryin to get rid of my 1 3/4's right now!! definately wish i would have bought the bigger ones so i didnt have to spend the money twice

edcmat-l1

iTrader: (10)

Both were the same name brand. Both catted x pipes were the same size. I tried to keep everything as equal as possible, with the exception of the header primary tube size.
Cars were the same, engine size, trans type, mufflers. Everything but the header primaries.

1989GTA

I have no idea which is which. I will say that the exhaust gas velocity is key. It will help in the scavenging and during over lap help with the intake side of things to exceed 100%VE. I will also say bigger is not necessarily better.

1989GTA

I would like to see a dyno test between 5/16" pushrods and 3/8" pushrods. I noticed on the LS7 GM went to the 3/8" pushrod.

nitr0racing21

iTrader: (5)

So my question how uch will you gain from a Intake manifold with 1 /8th and 1 3/4th???? all guesses of course

(**** everyone off lol)

edcmat-l1

iTrader: (10)

Well, chances are you won't gain much with a 1/8th header LOL.

speed_demon24

iTrader: (6)

Since that is the case the last dyno graph had the biggest gains across the curve, so there is no disputing that header design/size is the best one for that application.

squarehead

iTrader: (16)

do you guys record intake air temps...not necessarily ambient air temps

since there is a greater difference in the before readings, perhaps it would be beneficial to know the intake temps for all runs

jmilz28

iTrader: (13)

I predict ChocoTalker will come in, talk ****, and say nothing within 12 hours. But I won't know what he says as all I see is:
"Sorry, this user is on your Ignore list"

This is a pretty good test, not 100%, but VERY good - closest I have seen and thanks for taking the time to run this. It is HIGHLY indicative that these cars REALLY like to breathe, in and out, and they are very forginving by giving gains on both ends.

I would LOVE to see the big tube Kooks or ARHs, ported FAST combo on a stock longblock. Then I would like to see you add a 405hp LS6 cam and AFR205 heads. Anyway, back on topic---

This is a great test, not 100%, but close and awesome nonetheless! Looking like a preponderance of the evidence points one way...breathing is good! Thanks again for taking the time.

edcmat-l1

iTrader: (10)

These are LS3s. Why would you want to add a LS6 cam? And AFR heads?
Regardless, not relative to a header test.

edcmat-l1

iTrader: (10)

Ambient temps were not significantly different.
We do plan on testing both on the same day though, in the very near future.

DeltaT

iTrader: (5)

I think the car you did 3 months ago got the 1 3/4" headers.

I agree with jmilz28 "It is HIGHLY indicative that these cars REALLY like to breathe, in and out, and they are very forginving by giving gains on both ends."

I'm betting that the bigger headers will respond better to future mods if you keep them sane.

I like your test methodology. Refreshingly different than the usual 5+ differences between the cars, on different dynos, with a bunch of emotion thrown in for good measure.

Jim

VIPERBLUELX

iTrader: (2)

with the larger cubes of the LS3 I'd say the 1 7/8 made more power, I'd LOVE to see this same test on two LS6 Z06's.

squarehead

iTrader: (16)

I am attempting to understand why the before (baseline) dyno runs of each setup varied….were the before setups of each car nearly identical?

Without closely inspecting the graphs I assume there would be no significant difference in gains between the 2 cars, if each setup had the same before dyno numbers

thanks for the tests and look forward to your future tests

edcmat-l1

iTrader: (10)

The before base lines were absolutely identical, with the exception of ambient temp, which itself wasn't significantly different.

JS

iTrader: (4)

Well I tested 1 3/4 vs a 1 7/8 on a 402 we built and we lost some torque with the 1 7/8 headers.

I was very suprized since the car was making 505RWHP.

Just goes to show u the 1 3/4 can make good power.

Now on a FI engine I would opt for the larger tubes but if it were me I would just stick to a quality 1 3/4 for anything under 427 cubes

the_merv

iTrader: (88)

^^That's interesting. I was wondering how they would do on my 402 with L92 Heads, I guess the 1 3/4 I have will suffice..