Headers 1 and 3/4 vs. 1 and 7/8???

[Mick3]

I am planning a few basic modifications to a stock G8GT with stock exhaust. My goal is to mildly increase power (25-50 RWHP gain), increase low end torque, and significantly increase sound. I plan to do a CAI, headers, and tune (only)! I plan to use a Vararam CAI. I am considering Kooks long tubes and X pipe with high flow cats. It seams like most members with high HP goals use the 1 and 7/8" headers. But, I am considering the 1 and 3/4" LTs since I do not plan to race the car or do additional engine modifications. It comes down to the differences in performance with the different size headers with ONLY CAI and tune (as apposed to cam, ported heads, etc). Will the 1 and 3/4 be a better fit for my application (better low end torque). I think I am focused on the low end performance (light to light) instead of peak RWHP. Any thoughts? I have also considered shorty headers since they can bolt up to the stock mids and save some money on the X pipe. But, I am favoring long tubes for sound and performance. Any input would be greatly appreciated. 1 and 3/4 vs. 1 and 7/8???

[Daniel Linnett]

Yes 1 3/4!!

Funny thing is I am still running then at 750rwhp lol


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[Virus]

You will lose no low end hp or tq with the 1 7/8 and you will gain hp/tq up top. There's no reason to go with the smaller headers especially since they only cost around $25-30 more. That's cheap hp/tq.

If you already had the smaller headers, it makes no sense to upgrade given the modest increase.

[polo]

Get the 1 7/8" unless you find a killer deal on the 1 3/4". Right now you say you have no future plans to mod the car, but I believe we've all said that at one point.....

[XplicitPerformance]

Yes 1 3/4!!

Funny thing is I am still running then at 750rwhp lol


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good to know. I was regretting the 1 3/4 we put on the car considering now we plan on a magnacharger after the new year.

[TomPierce]

I have always believed that you will lose low more end torque with the larger diameter headers as compared to the smaller diameter headers due to the loss of exhaust velocity. (But I have never seen a head-to-head comparison between to two.) Given that your level of mods that won't be able to really take advantage of the higher flow rate of the large diameter headers, I would go with the smaller diameter headers to minimize the torque loss.

[TomPierce]

http://www.carcraft.com/techarticles/horsepower_vs_torque/index.html

(abridged)

One of the biggest mistakes made in exhaust-header application is the selection of primary tubes that are too large. Big primary tubes are only necessary to carry the gas volume generated at high engine speeds. It is usually better to err on the small side for a street engine so that torque remains strong. Pipes that are too large generally hurt the bottom end more than small pipes hurt the top end.

[johnbell2]

There are tables/charts/equations out there which address this question... executive summary, our cars fall in a gray area where 1-3/4 vs 1-7/8 primary makes little difference unless you're looking at extreme edge cases. Cams and power adders benefit from the slightly larger primary but not dramatically so - either one will do a good job of scavenging the heads.

Primary and collector -tube length- actually plays a larger role than diameter in our case.

[Virus]

I have always believed that you will lose low more end torque with the larger diameter headers as compared to the smaller diameter headers due to the loss of exhaust velocity. (But I have never seen a head-to-head comparison between to two.) Given that your level of mods that won't be able to really take advantage of the higher flow rate of the large diameter headers, I would go with the smaller diameter headers to minimize the torque loss.

Livernois posted some comparisons between the two on this board showing the 1 7/8 losing no power down low and gaining up top. Polo also makes a very good point. How many of us have said, "this is all I'm going to do?" Even when this is stated with the best of intentions and complete honestly, it rarely ever comes true. It's an addiction :D

[98aggie]

1 7/8 on the 6.0 and 6.2L engine make mre power and tq across the whole powerband. The 2" headers lose none down low and pick up even more up top. This is one of the reason you aere seeing 2" headers being produced by more companies now after testing them.

1 3/4" have allways been to small for these engines - even the stock Ls1 5.7L

[Mier]

I'm with Kurt on this. I have 1 7/8" and they deliver instant results. If I had known I would have found some 2" to try.

[I12XLR8]

Get the 1 7/8" unless you find a killer deal on the 1 3/4". Right now you say you have no future plans to mod the car, but I believe we've all said that at one point.....

Amen, Brother!

[STL_G8GT]

Amen, Brother!

X3

[Mick3]

Interesting notion about the 2" primaries. A friend and I have a similar dilemma. We are doing a LS7 swap in a different car. The LS7 (rebuilt by TEC, in Riviera Beach, FL) has forged internals, flat top pistons, Katech LS7 torquer cam (220/242, .615/.648, 110), TSP ported LS7 heads, stock LS7 intake, and Nick Williams 92mm TB. We plan to keep the car NA and would like to maintain low end torque since it will used as primarily a street car. So, the header choices are 1 and 7/8" vs. 2" vs. stepped 1 and 7/8 to 2" headers. We planned to get the standard (LS1/2/3/6) non-stepped 1 and 7/8 headers without the LS7 "D" shaped flange. Again, I would be concerned about loosing low end torque with the 2" primaries. Any thought on these choices on a 427 with a torquey cam? Any thoughts on using standard flange headers vs the D shaped LS7 flanges?

[98aggie]

stepped headers were designed for running open headers not full exhaust.

[Mick3]

The 1 and 7/8" seam to be the best size headers for the L76 since loss of low end torque is minimal. I am still considering the 2" primaries for the LS7. But, I have not seen data comparing the 1 and 7/8 vs the 2" headers on the LS7. I definitely don't want to loose torque with the Katech torquer cam!!!

[Livernois Motorsports]

Livernois posted some comparisons between the two on this board showing the 1 7/8 losing no power down low and gaining up top. Polo also makes a very good point. How many of us have said, "this is all I'm going to do?" Even when this is stated with the best of intentions and complete honestly, it rarely ever comes true. It's an addiction :D

That's correct, we did a 1 3/4 vs 1 7/8 comparison on a G8 and found exactly that. With that said, we use 1 7/8 on any engine 6.0L or larger. We did the same test with a 5.7 and the results were different; it did lose some power/tq down low with the larger headers.



Interesting notion about the 2" primaries. A friend and I have a similar dilemma. We are doing a LS7 swap in a different car. The LS7 (rebuilt by TEC, in Riviera Beach, FL) has forged internals, flat top pistons, Katech LS7 torquer cam (220/242, .615/.648, 110), TSP ported LS7 heads, stock LS7 intake, and Nick Williams 92mm TB. We plan to keep the car NA and would like to maintain low end torque since it will used as primarily a street car. So, the header choices are 1 and 7/8" vs. 2" vs. stepped 1 and 7/8 to 2" headers. We planned to get the standard (LS1/2/3/6) non-stepped 1 and 7/8 headers without the LS7 "D" shaped flange. Again, I would be concerned about loosing low end torque with the 2" primaries. Any thought on these choices on a 427 with a torquey cam? Any thoughts on using standard flange headers vs the D shaped LS7 flanges?

With those mods, you should be able to do a full 2" header and not lose anything. See the graph below from a recent Z06 we did.

It was a stock shortblock with:

Livernois Motorsports Stage 3 LS7 Cylinder Heads
Livernois Motorsports Stage 3 LS7 Camshaft
Livernois Motorsports Dual Valve Spring Kit
Livernois Motorsports Ported Throttle Body
FAST 102mm Intake Manifold
Halltech Cold Air Intake System
Kooks Longtube Headers
Kook’s X-Pipe
Corsa Exhaust
RPS Billet Carbon to Carbon Clutch
Tuned by Livernois Motorsports

http://i540.photobucket.com/albums/gg324/LivernoisMotorsports/stg3z06.jpg

-Rick

[donkeyGT]

I just recently asked your same question and most everyone said go with the 1 7/8"..Andy @ Livernois also said definitly go with the 1 7/8"..they will be doing my cam/dod package and tune so my question has been resolved.

[hivoltagedriver]

There are some interesting results here regarding header size. Maryland Speed did a dyno comparison for the GTO headers on an LS2. Everyone always told me to stick with the 1 3/4" for my LS2, but the only reason I did was because I got them super cheap. My 6 liter was making right at 500rwhp with them, but I truely think it would have picked up some top-end with the larger 1 7/8" or the stepped-tube headers. I will be buying 1 7/8" Kooks for the G8.

http://www.ls1gto.com/forums/showthread.php?t=196642

[Tooler]

I vote fore the Kooks long tubes and X pipe.. 1 3/4"

Hopefully I will have the ones I just ordered from marylandspeed.com a week from today. :rocking:

I also chose to get the coat for the heat. It sounds like you want to do the same mods as i do, more power but not a whole lot.

[MY SRM GXP]

Buy ARH they have better ground clearance and fit better then kooks. Just in case u lower the car later on. U can ask Steve GT about the difference between the two brands.

[Rawyzf]

Lots of good info here


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[Crazy8]

I just recently asked your same question and most everyone said go with the 1 7/8"..Andy @ Livernois also said definitly go with the 1 7/8"..they will be doing my cam/dod package and tune so my question has been resolved.

That's weird b/c they recommended I go with 1 3/4".

[donkeyGT]

That's weird b/c they recommended I go with 1 3/4".Hmmmm that is weird:uhm:

[rjones916]

I got Kooks LT's and am lowered on H&Rs, isn't bad at all. Don't think i've ever scrapped my exhaust honestly, I do scrape my front hide away plate all the time though.