how to calculate optimal header primary size?

i am upgrading my headers, but i was wonder what would work best for my application. keep in mind i don't care if i lose a bit of low end with a larger primary, afterall i launch the car at 5k on the bottle and even higher on motor.

tia1
taner

According to "Scientific Design of Exhaust and Intake Systems", the primary
diameter should be 1/8" larger than the exhaust port of the head (unshrouded).

The extra 1/8" is to account for fluid drag on the surface of the pipe.

The book puts emphasis on primary header length, collector design and exhaust system tuning for best average power in a certain RPM band.

taner, you must be looking at the new kooks headers huh?

this might fit yours well...not sure about your cubes or compression. these are just estimates. look like the kooks may be better for you though.

Primary Pipe Inside Diameter 1.8 in.

Primary Pipe Length 28.7 in.

Collector Inside Diameter 3.05 in.

Collector Length 12.9 in.

Engine Displacement 397.4 cu. in.

i am upgrading my headers, but i was wonder what would work best for my application. keep in mind i don't care if i lose a bit of low end with a larger primary, afterall i launch the car at 5k on the bottle and even higher on motor.

tia1
taner

"Optimal" diameter depends on a lot of things including rpm range where you run the engine, amount of N2O, valve timing among others.

If you really want the optimal header it probably needs to be fabricated for your combination. If you plan to use an off-the-shelf header, perhaps the valve timing should be specified to take advantage of the header length and diameter.

If our car is strip only with lots of bottle, it's probably easier to spec the header size than if you run hard on and off-bottle. Of course your exhaust port flow and valve timing should be optimized for that too.

FWIW, if you are in the 600+ fwhp range, 1-7/8 primaries are probably pretty close.

i am close to 600 fwhp on motor. then toss over 250 of spray at it?

so 1 7/8 is a good starting point? is a 1 7/8 to 2" overkill? i don't care if it loses a bit on motor.

tia!
taner

i am close to 600 fwhp on motor. then toss over 250 of spray at it?

so 1 7/8 is a good starting point? is a 1 7/8 to 2" overkill? i don't care if it loses a bit on motor.

tia!
taner

IMO, if you are nearly 600 fw on motor and going for 850, you definitely need headers fabbed for lyour combination. You are pushing more exhaust than a Nextel Cup car. 2 inch might be close. It all depends on the combination.

I'm not a huge fan of stepped headers unless they are designed and tested for your engine. At your hp level, ask your engine designer for his recommendations. If you don't have one, consider hiring one.

My $.02.

i agree with the above 100%.

for some strange reason (and i dont accuse you of this) but people seem to think headers need to do nothing but "flow exhuast"

Exhausts need to be tuned just like a camshaft, cylinder head, intake manifold, carb- you name it.

Primary length is very important but what we found most important would suprise you. It WASNT equal length, but radius of bends, and having equal radius through all bends of all the primaries.

Normally and unfortunately, packaging restrictions define the exhuast shape.

i agree with the above 100%.

for some strange reason (and i dont accuse you of this) but people seem to think headers need to do nothing but "flow exhuast"

Exhausts need to be tuned just like a camshaft, cylinder head, intake manifold, carb- you name it.

Primary length is very important but what we found most important would suprise you. It WASNT equal length, but radius of bends, and having equal radius through all bends of all the primaries.

Normally and unfortunately, packaging restrictions define the exhuast shape.

Good thoughts.

I think of headers as having two distinct jobs:

Job 1 is FLOW, getting the exhaust out with the least restriction. Here is where minimum number of bends and the largest bend radius possible helps flow. You hinted at bend radius maybe being a tuning thing. IMO, it's a flow thing. The more pipe the gas has to travel thru the more restriction it feels. The more bends it sees, the more restriction it feels.

Job 2 is TUNING to get the pressure pulses to scavenge the cylinders. Here's where length gets important.

Sometimes the length, number of bends and configuration needed for packaging to achieve Job 2 hurts Job 1.

Car Craft, in the Jan 05 issue ran engine dyno tests on their crate LS1 to evaluate just headers vs. stock Corvette cast iron exhaust manifolds and Camaro manifolds and 1-5/8, 1-3/4 and 1-7/8 long tube headers. The engine wasn't yet modified, so it was around 400 fwhp. The results may surprise you.

Vette manifolds were 9 avg hp and 9 avg lb-ft better than the Camaro manifolds. Not very surprising. The BEST headers (1-7/8) were 3.4 avg hp and 2.1 avg lb-ft better than the Vette manifolds. Peaks were 5 hp and 6 lb-ft higher for the headers. The other headers weren't quite as good.

Sure this was an unmodified engine, but just looking at the headers vs the Vette manifolds gives you the idea why lots of extra pipe and smooth bends may not due Job 1. FWIW, the 1-7/8 LTs peaked hp and torque at lower rpm than the Vette manifolds. A couple of the numbers posted look inconsistent, but, hey, it's a magazine article!

Not saying the LTs are bad, and for the correctly modded LS1 they will probably help quite a bit, but just bolting headers on a Vette without other significant changes probably isn't very cost-effective.

thanks for the great input guys! i don't know if i can afford to hire someone to spec out headers for my motor. wallet isn't big enuff to do that, lol!!! at least not at this time. I will talk to my engine builder and see what he recommends based on all of the bits and pieces that make up the motor.

i do plan on running the car hard on and off the bottle, motor is ultimately built for spray. Even though the cam is middle of the road. Not a full blown nitrous cam, and not an all out motor cam. I have no problem sacrificing a bit of et on motor, to get the most on spray, hell the car isn't even geared for all motor application.

again thanks for the feedback, it is definitely edumacational ;)

taner

Good thoughts.

I think of headers as having two distinct jobs:

Job 1 is FLOW, getting the exhaust out with the least restriction. Here is where minimum number of bends and the largest bend radius possible helps flow. You hinted at bend radius maybe being a tuning thing. IMO, it's a flow thing. The more pipe the gas has to travel thru the more restriction it feels. The more bends it sees, the more restriction it feels.

Job 2 is TUNING to get the pressure pulses to scavenge the cylinders. Here's where length gets important.

Sometimes the length, number of bends and configuration needed for packaging to achieve Job 2 hurts Job 1.

Car Craft, in the Jan 05 issue ran engine dyno tests on their crate LS1 to evaluate just headers vs. stock Corvette cast iron exhaust manifolds and Camaro manifolds and 1-5/8, 1-3/4 and 1-7/8 long tube headers. The engine wasn't yet modified, so it was around 400 fwhp. The results may surprise you.

Vette manifolds were 9 avg hp and 9 avg lb-ft better than the Camaro manifolds. Not very surprising. The BEST headers (1-7/8) were 3.4 avg hp and 2.1 avg lb-ft better than the Vette manifolds. Peaks were 5 hp and 6 lb-ft higher for the headers. The other headers weren't quite as good.

Sure this was an unmodified engine, but just looking at the headers vs the Vette manifolds gives you the idea why lots of extra pipe and smooth bends may not due Job 1. FWIW, the 1-7/8 LTs peaked hp and torque at lower rpm than the Vette manifolds. A couple of the numbers posted look inconsistent, but, hey, it's a magazine article!

Not saying the LTs are bad, and for the correctly modded LS1 they will probably help quite a bit, but just bolting headers on a Vette without other significant changes probably isn't very cost-effective.


I have difficulty trusting any word I read in a magazine, whether or not they agree with me.

Someone, somewhere did a ceramic coating vs header wrap article which IMHO was totally skewed and bias- and dare I say even intentionally erronious.

Their results were completely contrary to those of our inhouse race program/engineering team's findings. I was reading about it somewhere else too.

but what do I know other than the ceramic headers are in the trash.

"Primary length is very important but what we found most important would suprise you. It WASNT equal length, but radius of bends, and having equal radius through all bends of all the primaries."

Try telling that to those who hammer their headers to clear their plug wire
boots.

I'm in the midst of searching for a complete exhaust from headers to muffler,
so I'll be re-reading my book and following these posts with a close eye.

Hi All,

I am in the same boat. Not enough money for custom but worried that Kook's 1 7/8 or Dynatech's 1 3/4 don't really cut it.

http://www.headersbyed.com/index.htm

looks like they may have possibilities. I've just about decided to go with the Dynatech's for the next couple of years though.

Rick

I have difficulty trusting any word I read in a magazine, whether or not they agree with me.



I know what you mean. I know some folks in the car mag business, and some of them I trust. Interestingly in this article, the header supplier's product got basically trashed because they didn't do much better than the Vette manifolds. Hmmm. Maybe they don't advertise enough. :)

FWIW, a little creative dimpling of a primary tube rarely has very much effect on power in my experience.

I always wonder about all the underhood heat long, convoluted equal-length headers radiate into the engine compartment. Look at Impala SS LT1 long tubes sometimes. I could cook my 20# turkey just driving 100 miles with LTs on my "Killer Whale". :)

so don't waste the money on ceramic, spend it on wrap?

so don't waste the money on ceramic, spend it on wrap?
PROBLEM IS, heat wrap = rust. use only on stainless:) or maybe coated headers.

this is just my expeirence, but ceramic coating did squat for us.

I always figured header primaries at 110% of the diameter of the exhaust valve. I run a 1.60" valve, so my 1.75" primaries are just right.

As for ceramic coating, I think there were a couple threads on that in here before. Might be something for the Jet Hot guys to chime in on (if they're still on here). I had the hot side parts for the IROC ceramic coated by Swain Tech and it cut down temps under the hood a lot. They look "ok", but the price was a tad high. I'm having CE Coatings do a thermal coating on my downpipes, manifolds, wastegates and exhaust housings for the TA. We'll see how it turns out. :)

I always figured header primaries at 110% of the diameter of the exhaust valve. I run a 1.60" valve, so my 1.75" primaries are just right.

As for ceramic coating, I think there were a couple threads on that in here before. Might be something for the Jet Hot guys to chime in on (if they're still on here). I had the hot side parts for the IROC ceramic coated by Swain Tech and it cut down temps under the hood a lot. They look "ok", but the price was a tad high. I'm having CE Coatings do a thermal coating on my downpipes, manifolds, wastegates and exhaust housings for the TA. We'll see how it turns out. :)
turbo motor ehh?
the car that i was talking about was/is a TT V8

thnaksa boost it! i always coat them anyways, helps for rust! but i will keep that in mind for the future!

Tanner..you can't be changin stuff...I'm having a hard enough time catching you as it is. :D

Tanner..you can't be changin stuff...I'm having a hard enough time catching you as it is. :D

lmao!!! just small changes, like you i am trying to optimize what i have. only difference is i am leaning towards getting the most out of it on the bottle.

are you done your next phase? hope to see you shatter my best. now get your a$$ back out at the track, you know i can't even race up here if i wanted to :D

turbo motor ehh?
the car that i was talking about was/is a TT V8

You said you have your own inhouse R&D...did you find no power gains from ceramic coating or what? I'm curious because I also have a hard time believing magazine articles, especially when an ad for the product being tested is a couple pages over. :D

lmao!!! just small changes, like you i am trying to optimize what i have. only difference is i am leaning towards getting the most out of it on the bottle.

are you done your next phase? hope to see you shatter my best. now get your a$$ back out at the track, you know i can't even race up here if i wanted to :D

yea..I know you can't race..at least I hope to hold the record for a little while..heheheh. Almost done with it. Waiting on a weatherpack hookup then it to the dyno and tune it. May be at the track this weekend..we will see. I'm also gonna try some 28S tires...I think mine are dead.

yea..I know you can't race..at least I hope to hold the record for a little while..heheheh. Almost done with it. Waiting on a weatherpack hookup then it to the dyno and tune it. May be at the track this weekend..we will see. I'm also gonna try some 28S tires...I think mine are dead.


Tim,

g'luck! and let me know how those tires work for you :)

You said you have your own inhouse R&D...did you find no power gains from ceramic coating or what? I'm curious because I also have a hard time believing magazine articles, especially when an ad for the product being tested is a couple pages over. :D



we did see gains, just nowhere NEAR those of header wraps.

and by gains i mean wires not melted, MUCH MUCH MUCH cooler engine bay temps (which is critical for us) and since its a turbo motor, power gains. our turbos are small, we make boost beofre 2000rpm so it didn't help that much... but in a different situation with a bigger turbo i'm sure it could and would