1 7/8 or 1 3/4 for LS2

[grfperformance]

Anyone have an explanation for Datamaxx offering C6 headers in 1 7/8 and 05 GTO headers in 1 3/4?

I know Kooks has both and I emailed them the question, they recommended the 1 3/4.

Anyone have numbers for 1 3/4 vs. 1 7/8 on the LS2?

[batboy]

I don't really know specifically how they affect power in the LS2, but generally the larger diameter tubes help with top end HP, especially if you have the cam and heads that flow good. Smaller diameter is not neccessarily a bad thing since they tend to generally help boost mid-range torque (which is what I really like).

[GTO_Scott]

I don't think you need 1 7/8 unless you have a 427 stroker that puts out quite a lot of power.

[WillieD]

It has been proven that 1 7/8" primary headers make more power on a bolt on LS1 vs 1 3/4" primaries. You do not need H/C or more cubes to use them. A myth has floated around for a long time that you will loose power going that big on stock cubes, but it is BS. When I buld up my exhaust I will go with Kooks 1 7/8 headers with 3 inch x-piped duals (either stainless works or custom).

[GTO_Scott]

It has been proven that 1 7/8" primary headers make more power on a bolt on LS1 vs 1 3/4" primaries.

Would be interested in seeing a comparison side by side on the same car, same dyno, same day, same header maker, just different primaries.

[Josh-'04GTO]

Would be interested in seeing a comparison side by side on the same car, same dyno, same day, same header maker, just different primaries.

Already been done. I believe it was Car Craft Jan 05 issue. Stock GTO manifolds kept up with 1 3/4" longtubes. Only the 1 7/8" showed any appreciable gain.

I do think the 1 3/4" longtubes would have made a better showing versus the stock manifolds though if the motor had heads/cam...

[GTO_Scott]

Stock GTO manifolds kept up with 1 3/4" longtubes. Only the 1 7/8" showed any appreciable gain.

:gr_jest: - Guess my dyno results were false then with the addition of only 1 3/4 LTs with cats.

http://home.comcast.net/~gto_scott/328_41_dyno_com pare_small.jpg

[CSiJason]

Already been done. I believe it was Car Craft Jan 05 issue. Stock GTO manifolds kept up with 1 3/4" longtubes. Only the 1 7/8" showed any appreciable gain.

I do think the 1 3/4" longtubes would have made a better showing versus the stock manifolds though if the motor had heads/cam...

Got this issue handy? Mind scanning the article?

[Sam 04 GTO]

Something else to remember is that the Car Craft test used Corvette manifolds for their baseline.
;)

[mistermike]

I had a conversation a couple of months ago with a fellow who manufactures headers. He basically stated that 1 7/8 was too big for most peoples engines and will not achieve the same velocity as 1 3/4. That having been said, people still insist on ordering bigger headers than they need. Bigger is better, right? He also noted that Corvette owners seem particularly vulnerable to this mentality. Nonetheless, he's a businessman and if he doesn't build them, someone else will. I'm sure he chuckles a little as he counts his money.

[Josh-'04GTO]

:gr_jest: - Guess my dyno results were false then with the addition of only 1 3/4 LTs with cats.

http://home.comcast.net/~gto_scott/328_41_dyno_com pare_small.jpg

Was that a straight up swap or any tuning as well? Again, sorry to disappoint but I didn't write the article. If you have beef, take it up with CC. :slap:

[GTO_Scott]

Was that a straight up swap or any tuning as well? Again, sorry to disappoint but I didn't write the article. If you have beef, take it up with CC. :slap:

Straight swap, have not tuned the car yet - but that is in the works.

[Josh-'04GTO]

Straight swap, have not tuned the car yet - but that is in the works.

Then that's a nice gain! :thumbs: I was surprised by the article's findings as well, but on a bone stock motor with no tuning I think it's possible to see minimal gains as they did. As I mentioned, I think the 1 3/4" headers would really shine on a heads/cam motor.

[RA7 GTO]

Whether 1 and 7/8 are too large or not, I think I would trust the Kooks people. I put large headers on my '94 LT1 T/A and totally killed my bottom end torque. I had to add H/C to get it back.
That said, I've upgraded to the 1 and 7/8 for the 455ci (no dyno yet). That means I have a very lightly used pair of Stainless Works 1 and 3/4 headers (less than 1500mi) available. I will sell at half-price, whatever that is.

[CSiJason]

Oh snap! With cats? Lemme fish through my wallet for spare change real fast... LOL!

[dozlert]

Lingenfelter book says 1 5/8 is ideal for LS1 w/LS1 heads if I remember correctly.

[FlyinGTP]

Yeah and lingenfelters gto goes like 12.7 with a million dollars in mods on it. I'm sure i would listen to him. Hell thats the primary diameter i ran on my little v6 and it still wasn't enough, boost is good for that though. The guy knows c4 vette thats for sure but i will leave it at that. Heads and cam ls1 weather they are stock cubes or not respond very well to 1&7/8 headers. Go take a look at ls1tech sometime. I'm not saying 1&3/4 is bad but that depending on the setup and tune you can make a ton of power with both.

[dozlert]

Folks that have the 1 3/4 and 1 7/8 haven't posted any issues in this forum, so they must be ok. Dyno result for any of the LTs seem pretty good. The book I was reading is a little outdated, though.

[CSiJason]

I ran headers with huge short primaries and a huge long collector on my supercharged Honda. It made horrable power below the power band without the supercharger but not as bad with it. It was clearly more torquey with smaller primaries but less top end.

[grfperformance]

I just read an article in popular hot rodding about the Cartek C6 corvette build up. They used Kooks 1 3/4 headers and got 375 RWHP with a few other minor mods. Latest post they have made 475 RWHP. Not sure if they switched headers for the second set of updates.

[grfperformance]

I checked with Cartek and they used the 1 3/4 on their Vette. Not sure if they would make more power with 1 7/8. Maybe Julio will chime in here......

[gtopulse]

grfperformance could you please answer a question. when you installed your kooks headers did you need two 12" o2 extensions or just one? thanks in advance for your answer!

[Dmitry]

I talked to a gentlman at kooks, the guy said you will have absolutley no power loss with the 1 7/8 headers on a stock bloc/head

however he said that if you are planning on doing h/c work and or spraying 1 7/8 is the way to go.

i think the exact quote was " she'll run like a raped ape" :drink:

[grfperformance]

grfperformance could you please answer a question. when you installed your kooks headers did you need two 12" o2 extensions or just one? thanks in advance for your answer!

I used two front O2 extensions. I also needed two rear extensions. The fronts are the square kind and the rear are flat.

[tekhombre]

I checked with Cartek and they used the 1 3/4 on their Vette. Not sure if they would make more power with 1 7/8. Maybe Julio will chime in here......



With stock CID, the 1-3/4 work best up to ~500 rwhp.



Julio

[spd98]

I had a conversation a couple of months ago with a fellow who manufactures headers. He basically stated that 1 7/8 was too big for most peoples engines and will not achieve the same velocity as 1 3/4. That having been said, people still insist on ordering bigger headers than they need. Bigger is better, right? He also noted that Corvette owners seem particularly vulnerable to this mentality. Nonetheless, he's a businessman and if he doesn't build them, someone else will. I'm sure he chuckles a little as he counts his money.

Velocity isn't everything either. The more flow volume you have with less restriction the less velocity you will have. So long as you have enough for scavaging your fine. Alot of this has to do with the confuguration of the collector as well. you can design headers with a larger volume in the primaries and a funky collector that would maintain the same velocity as a header with smaller primaries. ( I do ALOT of flow analysis at work) :p

Basically you have to look at TOTAL design not just the primary size.

[grfperformance]

With stock CID, the 1-3/4 work best up to ~500 rwhp.



Julio

Thank you, Nick at Kooks had the same advice. It's all about power under the curve, not just peak numbers.

[Dmitry]

so if someone is planning to swaping heads or cam in the future, 1 7/8 is the way to go. even if you loose some power in the curve for the time being.

[CSiJason]

Swapping heads? If you are making over 500whp with just heads alone, I want to know where you are getting them so I can order a set!

[Dmitry]

Well a decent h/c combo is going to get you at about 500 crank HP. You are talking about whp? Even then i seriously doubt you are going to make better/more power with smaller headers. Nitrous is also something to think about. If h/c isn’t quite enough a 75 shot will put you over the "magical 500hp mark" we have now set :rolleyes:

[GTO_Scott]

Daily driver head and cam combo will give you between 380 to 440rwhp. I think 1 3/4 would be fine with almost all 5.7L head/cam street combo unless you also put a high psi supercharger on it and really had a flow restriction causing problems.

EDIT: Thats just my personal opinion, but not from experience.

[Dmitry]

Daily driver head and cam combo will give you between 380 to 440rwhp. I think 1 3/4 would be fine with almost all 5.7L head/cam street combo unless you also put a high psi supercharger on it and really had a flow restriction causing problems.

EDIT: Thats just my personal opinion, but not from experience.

what about a reverse cam that relies more on exhaust removal than intake flow to produce power?

[GTO_Scott]

what about a reverse cam that relies more on exhaust removal than intake flow to produce power?

Have no idea, like I said just an opinion from reading and from racing back in the 80s and 90s. From what Kooks has said, you want to go with the 1 3/4 until you go big cubes or real high output.

[Dmitry]

thats weird, thats completley opposite from what i was told when i called them. i dont know... i guess i will find out when i get my 1 7/8 and toss them on my stock block/heads

[GTO_Scott]

thats weird, thats completley opposite from what i was told when i called them. i dont know... i guess i will find out when i get my 1 7/8 and toss them on my stock block/heads

Guess it is who you talk to :confused: - several others have posted Kooks told them they'd have better results with 1 3/4 over 1 7/8.

[Dmitry]

i know thats whats throwing me off.

[Hawkeye]

My 411ci gained almost 50 ft/lbs of torque on an engine dyno switching from 2" headers to 1 3/4" primaries (530hp/515 tq). This is an engine that makes peak power at 6600 rpm.

Don't even waste your money on 1 7/8" unless you have 427ci or greater or are planning on a big shot of nitrous, big boost, or extremely high rpm (race only).

Lingenfelter is dead, btw. But I'm pretty sure he understood header function and design. I'd use a 1 5/8" header if it was available for the LS2.

[paco loco]

here's some info I pulled off of their site:
I want to know if KOOKS makes a stepped header for the 2004 GTO. What cat back system will work best if one is available with the header?

Thanks

The headers that we currently produce for the GTO are 304 stainless long tube's that were designed with the maximum horsepower and torque gains ,,WE have two headers a 1-3/4 X 3 AND ALSO A 1-7/8 X 3 FOR 475 HP PLUS..jr
Take it as you will. I emailed them as well, hopefully I will get a response soon before the GP in the other forum is over with (they probably get a ton of emails :rolleyes: )

[paco loco]

Alright, just got an email back from them (talk about good response time)!

...Regardless of engine size, if you're going to introduce a supercharger into the mix, go 1-7/8. The 2005 GTO, with its power advantage over the 2004 model, doesn't need all that much to benefit from the larger primaries. It's why we made them.
We learned from our ZO6 Vette customers, who opted to go with larger primaries on their bone stock engines because of their future plans for major upgrades, that the 1-7/8 headers responded almost as well as the 1-3/4. Bottom line, if heads and cam are in your future, go with the larger primaries. You won't regret it.
Nick is the person that responded to me from Kook's.

[Dmitry]

so let me get this straight... either 04 or 05 gto if you are going to go with heads/cam in the future he is saying that you should get the larger headers?

[paco loco]

so let me get this straight... either 04 or 05 gto if you are going to go with heads/cam in the future he is saying that you should get the larger headers?
That's what he is saying. Also, if you check out the GP on the Kook's Lt's by Tbyrne they say:

1 3/4" primaries are designed for stock or modified GTOs with air intake systems. 1 7/8" primaries are designed for cars with aftermarket camshaft and heads
so I must say that I would go with the larger primaries.

[Dmitry]

word... thats the plan... and if i cant wait to put the h/c on and notice a lack of power i am just going to spray the universe at it and see what happens

[GTslOw]

I'm planning to go w/a H/C setup one day, but I won't mind running the 1 7/8's for a while, it's not like it's gonna be slower than stock

[Dmitry]

thats what i am planning as wel. i ordered the 7/8 then changed the order then changed it back :)

[GTslOw]

thats what i am planning as wel. i ordered the 7/8 then changed the order then changed it back :)


who cares if it doesn't quite make the same max HP as a 1 3/4, it will still make a lot more power than stock! I'm planning for the future and I want a nice little H/C setup for the street....so I'm going 1 7/8's :thumbs:

I'll get a dyno for you guys, my headers are at the shop I ordered them from
should be on soon, and prolly get a dyno there while I'm at it

[Dmitry]

04 or 05 goat. what other mods?

[GTslOw]

04 w/just spintech catback, gonna have an ASP pulley and maf pipe soon to go along w/the headers

[Dmitry]

nice, cant wait for the results.

[GTslOw]

I'm skeptical of everyone who puts down the 7/8 for stock CID...I still have yet to see dyno graphs showing a loss of power. If someone shows me, that'd be great, because then I'd have them take back the 7/8 for some 3/4

I read on a z06 forum that nick at kooks spoke to a reputable race car guy and he put some 1 7/8's and got a gain all accross the board (20hp 20tq)

[newdamage1]

Augh, you guys are killing me. Just when I think I have decided on one....

On a "medium" street H/C setup how much HP/TQ would I be losing by going with the 3/4's? (I was thinking my goal would be around 450RWHP daily driver)
10? 20hp?

Kelly

[Hawkeye]

Might be a good idea to read up on what a header actually does. Then you'll have an idea why too big is much worse than too small. A too big header will slow exhaust scavenging, thus slowing the incoming intake charge. I've seen it kill torque on an engine dyno of my 411ci.

A properly sized header will scavenge the exhaust so efficiently that the rapidly exiting exhaust stream will actually pull in the incoming intake charge. Too big a header and you'll never see this scavenging. There is a formula to help determine header size.

Kelly, your car will be quicker with the 1 3/4" primary header. Forget peak numbers, your average power will sigificantly better with the 1 3/4".

[GTslOw]

Velocity isn't everything either. The more flow volume you have with less restriction the less velocity you will have. So long as you have enough for scavaging your fine. Alot of this has to do with the confuguration of the collector as well. you can design headers with a larger volume in the primaries and a funky collector that would maintain the same velocity as a header with smaller primaries. ( I do ALOT of flow analysis at work) :p

Basically you have to look at TOTAL design not just the primary size.
:thumbs:

[05GoatBoy]

Larger primaries tend to increase reversion, which pushes gas back into the manifold runners. This usually happens when the intake valve is opening and the piston is still moving upward. There are many factors that can cause reversion and using larger exhaust primaries is one of them. Low engine speed is another cause of increased reversion which explains why larger headers robs the low end of torque and HP. This must be balanced with the rest of the engine, too small and flow is restriced, too much you get reversion. This balance is much better taken care of with a pair of step headers. They must be matched to your particular components as well.

EDIT: I'd stay with 1 3/4" unless you are making tons of power, and if so someone involved with your purchase/build would recommend the proper primary dia.

[Hawkeye]

Huh. A "funky collector" will make up for the incorrect primary size. Not sure what that is. But in any event, all the available headers for this car all use the same type of collector, so you can't crutch the wrong choice by using the old "funky collector". :rolleyes:

I think there is an unconscious desire among some that bigger has to be better. Bigger cam, bigger carb, bigger cubes, bigger plug wires, bigger headers.... If that's what will make some happy, then get the biggest primary size header that will fit. But you'll get your ass handed to you by someone who makes the more intelligent choice everytime. Ask the 455-474ci boys about my 411ci. They always have an excuse. :cry:

[GTslOw]

no dyno charts no care, theory is nice, but I'm not sure about all this unless I see some dyno charts...on both sides of the fence, I just hear talk, I wanna see some charts

so someone out there has to have a stock 346 dynoed before and after w/ 1 7/8 headers...soemone dig one up, I dont mind being wrong, I just want some quantitative evidence as far as power goes

[05GoatBoy]

Here's a snip from a good article: http://www.carcraft.com/techarticles/868/

"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. Most headers with 1-1/2-inch primary tubes will carry an engine well into the 300hp range, while 1-5/8-inch headers can support up to 400 horsepower, and a little beyond in some cases. This depends a great deal on displacement and engine speed. We have seen 1-3/4 headers support up to 550 horsepower without affecting power on a single four-barrel 350 Chevy running at 7500 rpm. Meanwhile, a 480hp, twin carburetor 302 Ford running at 8000 rpm gained 13 horsepower by switching to 1-7/8-inch primaries. 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."

[Hawkeye]

no dyno charts no care, theory is nice, but I'm not sure about all this unless I see some dyno charts...on both sides of the fence, I just hear talk, I wanna see some charts

No care enough to post dyno charts. Not that interested. Not a theory. Buy what you want. See ya at the track.

[Dmitry]

:rolleyes:

when i get my 1 7/8 on i will get it dynoed... it would be nice to see someone elses dyno chart on the same type dyno with 1 3/4 headers...

[gtore62]

:rolleyes:

when i get my 1 7/8 on i will get it dynoed... it would be nice to see someone elses dyno chart on the same type dyno with 1 3/4 headers...
there is mix talk about which headers to use. just get the carcraft jan. 05 issue about 8bucks mailed. "project light speed" covers 3 different size headers and stock corvette and camaro manifolds gues what the 1-7/8 out performed the all of them, all on a stock gto ls1. end of story is this engine responds well to many mods. i got the kooks 1-7/8 and will install and dyno maybe by the end of the week.

[Dmitry]

you would think people would fold and believe you but no, people will argue and argue and argue with you untill they are blue in the face.

[Hawkeye]

http://carcraft.com/techarticles/116_0312_test/ind ex1.html

Here's the pertinent text regarding a comparison between a 1 7/8" primary header and a 1 5/8" on a 406ci/Dart head/roller cammed small block.

"The Big Tube Test

This is a great example of how larger headers affect the power curve. The larger 1 7/8-inch headers lost a tremendous 47 lb-ft of torque at the bottom of the curve. By 3,400 rpm, the big headers were actually making a little more than the smaller 1 5/8-inch headers. This may be a hiccup with the smaller header power curve that could be addressed with jetting or timing had we spent more time on tuning. By 4,400 rpm, the smaller headers were making as much as 33 lb-ft more torque than the larger headers. Then by 5,600 up through 6,600, the larger headers took over and made as much as 26 more horsepower at 6,600 rpm.

If you look at the average power curve numbers, you can see that the larger headers actually made slightly less average power. That's because the horsepower gain at the top did not completely make up for the torque loss at the bottom of the curve. So what's the bottom line here? If this engine is going into a light car with a manual trans and a deep rear gear, or at least an automatic with a stall speed of no less than 3,600 rpm, the larger headers might be a slight advantage. The important point here is that a 1 3/4-inch header is probably the answer, since it would improve the low-speed power while not sacrificing nearly as much horsepower at the top end.

Another point worth mentioning is that what we're seeing here with these two primary-pipe-diameter power curves is not really as much about power loss or gains as it is about moving the curve around where the engine makes its best power. Had we tested a set of 1 ¾-inch headers, we're confident we would have witnessed an average power increase over the other two primary pipe diameters. This merely reinforces the idea that engines operate best when outfitted with the right set of parts that complement the rest of the engine package.

Test 7: A 406ci small-block Chevy outfitted with a set of Dart Pro 1 heads, a healthy mechanical-roller camshaft, a set of Hedman 1 5/8-inch-diameter primary-pipe four-into-one headers, and a 2 ½-inch exhaust using a pair of Borla XR-1 mufflers.
Test 8: The same engine outfitted with a set of Hedman 1 7/8-inch-diameter primary-pipe four-into-one headers with the same Borla exhaust system. "

Ultimate peak numbers were higher with the 1 7/8", but average power was down, and low end torque was destroyed with the larger tube headers (down 47 ft/lbs at 2800 rpm and didn't catch up until 5600 rpm). And this is on a race prepped 406ci. The article mentions that a 1 3/4" would've outperformed both the 1 5/8" and the 1 7/8".

[gtore62]

http://carcraft.com/techarticles/116_0312_test/ind ex1.html

Here's the pertinent text regarding a comparison between a 1 7/8" primary header and a 1 5/8" on a 406ci/Dart head/roller cammed small block.

"The Big Tube Test

This is a great example of how larger headers affect the power curve. The larger 1 7/8-inch headers lost a tremendous 47 lb-ft of torque at the bottom of the curve. By 3,400 rpm, the big headers were actually making a little more than the smaller 1 5/8-inch headers. This may be a hiccup with the smaller header power curve that could be addressed with jetting or timing had we spent more time on tuning. By 4,400 rpm, the smaller headers were making as much as 33 lb-ft more torque than the larger headers. Then by 5,600 up through 6,600, the larger headers took over and made as much as 26 more horsepower at 6,600 rpm.

If you look at the average power curve numbers, you can see that the larger headers actually made slightly less average power. That's because the horsepower gain at the top did not completely make up for the torque loss at the bottom of the curve. So what's the bottom line here? If this engine is going into a light car with a manual trans and a deep rear gear, or at least an automatic with a stall speed of no less than 3,600 rpm, the larger headers might be a slight advantage. The important point here is that a 1 3/4-inch header is probably the answer, since it would improve the low-speed power while not sacrificing nearly as much horsepower at the top end.

Another point worth mentioning is that what we're seeing here with these two primary-pipe-diameter power curves is not really as much about power loss or gains as it is about moving the curve around where the engine makes its best power. Had we tested a set of 1 ¾-inch headers, we're confident we would have witnessed an average power increase over the other two primary pipe diameters. This merely reinforces the idea that engines operate best when outfitted with the right set of parts that complement the rest of the engine package.

Test 7: A 406ci small-block Chevy outfitted with a set of Dart Pro 1 heads, a healthy mechanical-roller camshaft, a set of Hedman 1 5/8-inch-diameter primary-pipe four-into-one headers, and a 2 ½-inch exhaust using a pair of Borla XR-1 mufflers.
Test 8: The same engine outfitted with a set of Hedman 1 7/8-inch-diameter primary-pipe four-into-one headers with the same Borla exhaust system. "

Ultimate peak numbers were higher with the 1 7/8", but average power was down, and low end torque was destroyed with the larger tube headers (down 47 ft/lbs at 2800 rpm and didn't catch up until 5600 rpm). And this is on a race prepped 406ci. The article mentions that a 1 3/4" would've outperformed both the 1 5/8" and the 1 7/8".remember the ls1 is a different animal, other engines different story,

[Hawkeye]

I keep hearing that, but it's just not the case. Engines are engines, all pump air. The LS1 is not magically different than all other engines. But, again, buy what makes you feel good. I'm just trying to prevent newbies from making a mistake in header selection. Header selection is not theory.

[Hawkeye]

Here's how to mathematically determine proper header size:

We'll do it to a stock LS2. Published factory torque peak is at 4400 rpm.

Volume of a cylinder is 45.5 ci (364ci).

Cross-section area = (rpm) x (volume of one cylinder) / 88,200

Cross-section area = (4400) x (45.5) / 88200
Cross-section area = 2.27"

Pipe radius = square root of (cross-section area / 3.1416)
Pipe radius = sq/rt (2.27 / 3.1416)
Pipe radius = .85

Pipe i.d. = 2 (.85)
Pipe i.d. = 1.70"

Add .080 for o.d. = 1.78" ~ 1 3/4" primary size.

For an LS1 (346 ci), a 1 7/8" header choice requires matching components for a torque peak at 5200 rpm. Cylinder heads, camshaft, valve train, intake and gearing will need to be selected with that torque peak in mind.

[gtore62]

Here's how to mathematically determine proper header size:

We'll do it to a stock LS2. Published factory torque peak is at 4400 rpm.

Volume of a cylinder is 45.5 ci (364ci).

Cross-section area = (rpm) x (volume of one cylinder) / 88,200

Cross-section area = (4400) x (45.5) / 88200
Cross-section area = 2.27"

Pipe radius = square root of (cross-section area / 3.1416)
Pipe radius = sq/rt (2.27 / 3.1416)
Pipe radius = .85

Pipe i.d. = 2 (.85)
Pipe i.d. = 1.70"

Add .080 for o.d. = 1.78" ~ 1 3/4" primary size.

For an LS1 (346 ci), a 1 7/8" header choice requires matching components for a torque peak at 5200 rpm. Cylinder heads, camshaft, valve train, intake and gearing will need to be selected with that torque peak in mind.
you make a lot of sense, but 427 stroker is always in view for anyone of us who own this car.