Ok I was about to buy some KOOks 1 3/4 headers with 3"Xpipe and cats to 2 1/2" stock size exhaust for my 06 LS2 ,But i was thinking i MIGHT want to s/c my car next year (My goal is about 500 rwp)and im thinking if i should instead get the 1 7/8 headers as the 1 3/4 headers might restrict my power with the s/c ,But im also wondering are the bigger headers going to hurt me when im JUST N/A

well give me your input .

 

You have to make up your mind as to what you want. If you go the S/C route, then I would get the 7/8. If you are going to stay mostly bolt ons, then the 3/4 will do just fine. Supposedly, the 7/8 don't lose much torque over the 3/4.

LS2 or LS3? The LS3 will handle the bigger headers more easily.

Rick

 

ls2

 

I was in the same boat, I decided to go with 1 7/8 and I am glad I did now since I have a SC on order.

 

This is one of those persistent myths on the forum that will simply not go away: the idea that if you supercharge your car, or if you are making over "X" horsepower, you need the larger primary headers to flow all the exhaust gas out otherwise you will lose power.
Unfortunately, and against my bad judgement, I bought into the myth but instead of then posting back that "it feels so much faster" I actually did a scientific back to back analysis. I say "unfortunately" because I spent about $2000 dollars to gain what amounted to about 5 horsepower.
Since you didn't search, here it is:
1 3/4" Vs 1 7/8" Header Swap Results.

To summerize: The difference between the two, IN A 600REAR WHEEL HORSEPOWER SUPERCHARGED CAR, was less than 1%. The accuracy of a Dynojet is less than 1% too. What we can learn from this is that at those power levels the headers are not what is restricting the system. My best guess is that when you look at the size of the exhaust port opening when the valve is at full lift, vs the duration of the exhaust valve opening event, the amount of gas that can flow out is less than what even the smaller primary size headers can handle. I.E. The exhaust is not the restriction, but rather the camshaft commanded exhaust valve opening event duration. Throw in a bigger cam, and probably some ported heads on the equation and you might begin to see some gains.

Otherwise pick whichever size and brand you like best; it does not matter. Both the Kooks I had before and the American Racing Headers I have on right now are real works of art and fit and perform as well as they look. My only advice is whichever headers you pick, try and get them ceramic coated; it is worth it.

 

When I worked at a hot rod shop I rebuilt my own B&M 144ci blower. I bought and read the B&M manual on their blowers. They had test showing virtually no difference between stock truck cast iron manifolds and headers. The reason is proper blower cam overlap and the forcing of the exhaust out of the cylinder with the incoming charge. They said the biggest help was porting the exhaust side of the heads to help the gas escape.

 

I forgot about PowerLabs header experiment. I agree if you want 500 to 600 HP, 1 3/4 should be enough. I have seen many SC LS2's with 1 3/4, I never heard any complaints from the owners. I have the LS3 and might not be able to stop at 600HP, so I think in my case 1 7/8 header may be needed at a later date.

 

There are many of us that have 1-3/4".

 

The primary's as Powerlabs said didn't show a big difference.
He changed primary size, but left the same 3 inch x-pipe.
I think there is a bigger difference going to 1 3/4 with 2 1/2 x-pipe
to 1 7/8 with 3 inch x-pipe. Which I did but I also picked 1 psi in boost
from changing to hard pipe!

 

You realize that the only way your boost could have increased, is if you INCREASED exhaust restriction, correct?
The supercharger forces air, not pressure, into the engine. Pressure results when gases can not escape... If you picked up boost, like you think you did, then you must have made it harder for exhaust to escape the engine...
Case in point; a camshaft usually causes your boost to drop 2-3PSI, and causes power to go UP by 50HP+. Another case in point: An LS3 engine will make the same power as an LS2 with 2 less pounds of boost: less restrictive heads, more agressive cam, and bigger engine = same airflow at lower boost level.

Trust me, if high boost was the key to making big power I would just stick a potato in 3 out of my tail pipes and my boost would skyrocket as backpressure built up

 

My opinion based on countless swaps is you could almost never have too much primary with a supercharger. Heed my wisdom, go 1-7/8". Dyno's don't always tell the whole story.

Nick

 

 

This is what makes me wonder about going 1 7/8" on my LS3

http://forums.corvetteforum.com/c6-t...s-and-vid.html

 

With forced induction your exhaust system is of much less importance than with NA. Just as long as the burned exhaust has a way out and the system is big enough to handle the amount of exhaust being pushed through it, that's about it. Where the differences come into play is in a NA situation. One of the benefits of headers is their scavenging affect. An X-pipe or H-pipe is to used as an aid to this scavenging affect by equalizing out the exhaust pulses.

As the exhaust flows down the exhaust pipe it will create a slight vacuum in the header tubes of the cylinders with closed exhaust valves. This vacuum gives the exhaust an initial "pull" as it leaves the cylinder helping to quickly withdraw the burned exhaust. In the case of a cam with a good bit of overlap, it will even help draw in the next cylinder full of air/fuel while the intake and exhaust valves are open at the same time.

With a too large primary tube backed up by a too large exhaust pipe, this scavenging affect will be reduced because of the significant decrease in the velocity of the exhaust flow. This causes a loss of torque in lower rpms, which is where most people spend most of their time. This can make a car "feel" slower.

 

Dead wrong here! Put the 3 elbows in like I DID them talk!

Boost was measured on the dyno along with HP/TQ! Then I changed to less restrictive exhaust! Can't argue that! I added hard piping to the intake. In otherwords remove all rubber hoses. Less couplers.
Measured again Hp went up with the SAME TUNE and showed 9.03
psi. Instead of the 8.04 psi. SAME pulleys! Dyno sheets prove it!
You should try it ! But in tell, you do, your ALL wet! On this one!

 

To the OP,

I would take these words with the utmost of seriousness. After all, it's coming from the horse's mouth.
If primary size didn't matter, the top fuel cars wouldn't have 2 1/2" primaries.

 

Seriously, you are not arguing with me, you are arguing with basic science. Boost is the resultant pressure you can not push through your engine, it is NOT an indication of power . If you do something to the exhaust and boost goes up, you have increased exhaust restriction. You CAN argue with that, but you will be just proving that you don't understand how forced induction works by doing so

Edit: And because you LOVE to argue, even when you are completely wrong, I am going to offer you someone else to argue with.
Meet A. Graham Bell. He wrote the book "Forced Induction Performance Tuning", arguably the best book on forced induction out there right now.
Chapter 14, page 217:
"Many enthusiasts, and even some tuners, have got the idea that the basis for improved performance from a forced induction engine is more boost pressure. However, this is false reasoning. Consider for a moment the CART champ cars in the USA. The purpose built 8-cylinder race engines are restricted to a capacity of 2.65 litres and a single turbo pushing a maximum of about 3 1/2 psi boost [...] Obviously, it is not as a result of massive boost pressures, but rather because the inlet and exhaust systems and cylinder heads flow efficiently, consequently encouraging good flow into and out of the cylinders...
Don't ever think that you can beat flow restrictions simply by upping the boost, and likewise don't ever think that increased boost pressures are the key to improved performance. Just take a look at your garden hose for proof of what I am saying. With the tap opened right up and the nozzle on the garden hose closed down, pressure in the hose is high, but water flow from the nozzle is dismal, or even non existent. Opening the nozzle will drop pressure in the hose right down, but flow from the nozzle improves. Getting rid of flow restrictions will have a similar effect on any engine"

Corky Bell, author of "Maximum Boost" and "Supercharged!" agrees. As does Earl Davis, from "Supercharging, Turbocharging & Nitrous Oxide".
From Davis' book intro, page 15:
"Improving the efficiency of the engine will cause the residual pressure (boost) to decrease. Remember, the output of a blower is somewhat fixed. The blower still pumps the same volume of air, even though the amount of residual pressure (boost) went down. It is worth remembering: Boost is residual pressure, not an indication of results"


Google their names so you can e-mail them and request changes to any upcoming editions of their books if you STILL think I am wrong. I am not arguing over this any more, it is getting ridiculous. Do I need to quote more books? Would you like me to dyno my car with a plug on 3exhaust tips and show you a before and after where the plugged up tips show more boost and less power? How about a dyno of a supercharged car before and after headers being installed, showing a drop in boost and an increase in pressure? The ONLY time an increase in boost translates into extra horsepower, is if your boost is going up because you are driving the supercharger harder. Since you never replaced pulleys, that is not the case.
Or how about you just realize that we are talking about some REALLY SIMPLE, REALLY BASIC concept here that can be argued with as sucessfully as you could argue against newton's first and second laws of motion?

 

If top fuel cars ran 93 octane gasoline they wouldnt have 2 1/2" primaries.

 

Boost is backpressure, and exhaust on a blown car is EXTREMELY important. Its easy to cram it in, and needs to get out.
On a NA car its about efficiency without losing torque.

 

Riiight... So if 2 1/2" primaries are the correct primary size for an 8THOUSAND horsepower top fuel drag car with an 8.5L engine pushing 50PSI on Nitromethane, it logically follows that it too must be the correct primary size for the OP's 500WHP V8?

I guess my side by side dyno comparison really wasn't needed when we can take some relevant real world examples like that and extrapolate to our cars... Wish someone would have told me that before I spent money doing a scientific comparison