timd38

If you have a stock engine and all you are doing is adding1 7/8 headers, you may not be happy with the results. You may actually have less power.

dennis50nj

yes he did have more then that, its my car LS2 with bolt/ons cartek H&C, i was just stating that usually you lose hp with gears and big stall converters, how much i don't know, most sticks go from 342- 410s and lose 7-10 hp i have read, so how much does the automatic lose, 315 to 373=58 same as 342-410=58 273 to 373=98 so does the optional 315 gear dyno less off the assembly line? over the standard 4l65 273 and the standard 342 m6 also the standard 256 a6

Mike Farris

I think you're thinking of area under the curve. Assuming correct gearing/similar weight the biggest area under the hp/tq curve will win the race.

If you are serious about FI and big power I wouldnt be afraid of the 1 7/8. Even if its a little down on tq just pulley up and boom its back. When you make bigger power(I dont know how much) the bigger primaries will be your friend.

peter pan

My experience with 1 3/4 and 1 7/8 on my deceased blower car. I made 7 more hp and 9 tq with the larger headers, lost a tad in the lower range but did not notice with the boost either a gain or loss, but I liked the sound better with AR headers.

N/A 1 3/4 are best for hp and tq where you use it mostly.

C7/Z06 Man

I like curves, whether I'm over or under them.

You are right, it's referred to as under the curve and the only way that makes sense to me is that there is "nothing" above the curve.

mabryusmc

AWESOME GENTS! this is exactly what I was looking for. While the price tag did look pretty good at first.... after reading everything I think I might just pony up the $$$$ and get the 1 3/4. Its a weekend warrior car and I dont push her hard enough to really use the TOP end and even if I did FI id would be a ways down the road.

Thanks again gents!

mowe

Smart move....

FloydSummerOf68

I'd save the money and get the cheaper headers.

Pfadt Racing

For a cammed/heads/intake Ls motor...the 1 3/4 is ideal. There are two things making power and torque, one is flow and the other is the scavenging. So there is an optimal size, not just bigger is better. We could have offered the 1 7/8 first if the engineers found it produced more power. For big blower setups, I understand the need of 1 7/8, 2", ect. But we are talking 900+HP. We are about to offer the 1 7/8 in our Tri-Y design....I pretty much see my days convincing my customers to get the 1 3/4

gonzala

Interesting thread. I just had my shoppe install the Kooks catted 1 7/8 long pipe with x pipe, Callaway CAI on my 2008 C6 A6 at 35k miles with a new tune since we had been discussing a blower in the future. I got the dyno to 411rwhp with a 408 torque reading. From other posts these numbers seem decent. I love the way the car sounds and runs with much better accelaration and torque compared to pre mods for sure.

It seems you can't go wrong with either set up compared to staying stock. Good Luck with your choice.

There are a lot of good headers out there. As important is the shoppe you work with if your having the install work done. Just my .02

OBSSSD

Not true with the LS3

1-7/8" make more power everywhere with a 4 into 1 header

FloydSummerOf68

I said torque and you said power.

A 1 7/8 is not a good idea for a max-effort setup unless you're making crazy power. Like PFADT said, 900+

ITS STOCK

On my virtually stock ls2 (CAI, tune, DR) I went 12.2 at 115mph. With just the addition of 1 7/8 LG Longtubes and a retune the car went 11.6 at 118mph in worse air. Yes the 1 3/4 may make a little more torque under the curve, but you wont lose power or torque anywhere compared to stock manifolds. The car was still very snappy and fun to drive around with more power everywhere in the powerband. If I were to do it again I would still go with the 1 7/8.

OBSSSD

1-7/8" make more torque and hp all the way from idle to redline on the LS3 with a 4 into 1 header setup. I have tuned about 30 cars that made the swap and none of them lost anything to the 1-3/4" headers anywhere.

True with a tri-y design the 1-3/4" diameter header is sufficient for the LS3. I ran a set of 1-3/4" tri-y's on my LS3 powered GXP and they made comprable (but not more) power as 1-7/8" headers that I replaced them with.

By purchasing 1-3/4" headers in a 4 into 1 design you gain nothing and lose room to upgrade down the road. IMO not a smart decision

C7/Z06 Man

Usually when your making more torque "under the curve" you are usually making more hp too.

CHECK THE DYNO SHEET GRAPH. PAGE 1

OBSSSD

The graph is of an LS2 C6 I am not disputing 1-3/4 is better for that application. LS1 and LS2 cars should use 1-3/4" headers unless going heads/cam or FI.

The LS3 is different than the LS1/2 in that it does not lose bottom end power for an extra punch up top. It simply makes more power everywhere (hp and tq).

LS1/2 = 1-3/4"
LS3/7 = 1-7/8"

Hope this clears things up

C7/Z06 Man

Just a general statement.

TripleAstyle123

I'm going to do with Pfadt's actual research over 30 cars tuned. Thanks though.

OBSSSD

Tri-y design doesn't require the same size primary as a 4-1 design to make good power - you're missing the point

LS2 = 1-3/4"
LS3 = 1-7/8"

** with a 4-1 header which is what most manufacturers make

I don't care if you believe me or not get the smaller headers if you have an LS3 and go slower

dprescott878

Great read. I went with 1-7/8" due to me being Heads/Cam/FI (750rwhp). It seems like the general consensus is 1-3/4" for N/A bolt-on cars, and 1-7/8" for high power builds (700+). Bigger is not always better, just depends on your end goals.