Header Tube Size

[Rick]

Lets hear it guys. What are your thoughts for an out and out competition 289.

[Dwight]

I think 1 7/8"
check this link out

Autolounge.net | Calculators | Exhaust Primary Sizing



Dwight

[Bob Stoeger]

Ha Rick,
There are a lot of questions that really need to be answered before you can say what size tubes you need, like for instance Edlebrock told me that on my 347 strocker with vector Jr heads and the cam and compression I have 1 3/4" was the proper size to use. Take a good look at what you have or what you want and then base your final call on that not just what others say. Just my 2 cents on it.
Bob

[Ron Earp]

I imagine you'll find smaller to be better. I'm having a brand new header made for my race Z and it has itty bitty primaries to keep the velocity high. Look under any up-to-date race cars and you'll find much smaller primary pipe than you did ten years ago, with more attention to how the collectors merge and the various steps inbetween.

Burns Stainless - Home

Is a great resource. Fill our their engine sheet and they'll do a design program on it and give you the details. They are not cheap, but they are highly regarded in race circles.

Ron

[Ricardo Montalvo]

Originally Posted by Dwight

I think 1 7/8"
check this link out

Autolounge.net | Calculators | Exhaust Primary Sizing



Dwight

That calculator is way off. It trends way to large imo. It doesn't ask enough questions.

Originally Posted by Ron Earp

I imagine you'll find smaller to be better. I'm having a brand new header made for my race Z and it has itty bitty primaries to keep the velocity high. Look under any up-to-date race cars and you'll find much smaller primary pipe than you did ten years ago, with more attention to how the collectors merge and the various steps inbetween.

Burns Stainless - Home

Is a great resource. Fill our their engine sheet and they'll do a design program on it and give you the details. They are not cheap, but they are highly regarded in race circles.

Ron

I agree. Excellent info.

[Will Campbell]

Not that I'm an expert or anything, but I agree with Ron. Larger tubes kill response, especially at the low end.

I think the sentiment that the smallest tube that flows the CFM the engine needs is right on the money.

[Ron Earp]

By the way, Burns will do the design for you at no cost - as long as you are serious about possibly using their components. Burns is in CA, but Jeff Y pointed out to me that their design guy is located in the SE US as the design info comes back directly from him.

I'll make a guess based on what I've learned from Burns and what I've seen at the track - I'd suspect 1.5" ID primary pipes, probably around 25-30 inch primaries that might have a step up in pipe size, 4 into 1 merge collectors (these are quite long, usually about a foot in length with gently opening primaries into the collector) with probably a 2.25" outlet and then as quickly as possible transition into a 2 into 1 with a single 3" or 3.5" exhaust. I'm sure a whole lot smaller than common lore would suggest. You can improve your midrange and suffer no hit on the top end but you need to invest the time to research it and design it correctly.

Yep, the single exhaust doesn't look as cool but it seems to have the power advantage based on what we see and test.

[Kelly]

I'm in the middle of a build and have been (re)educating myself on the subject. I agree the recommendations will be smaller and think Ron will be pretty close. I had Vince at Burns provide a recommendation for me on a 427 sbf 180 header build. ~6.5krpm peak power. It was a 1 3/4" stepping twice to 2". 2 3/8" merge collector with expansion cone to 3". The merge diameter will be smaller for a 180 than ordinary 4-1 configuration.

Which raises the question, will these be for a GT40 I presume? If so, I dont think you stand much of a chance of making a 25" or perhaps even 30" primary in equal length 180 configuration. 35"-36" was about the best I figured I could which turned out to be pretty good for my peak rpm. Higher Rs would likely draw shorter primary recommendation.

Beside primary diamter and length, power can be very sensitive not only to collector diameter but also collector length. Vizard has some good commentary on exhaust design in his making horsepower book and is definitely of the mind of smallest diameter that can shoulder needed flow. High exit velocity means highest potential for max scavenging and this can be a surprising big factor in tune and associated power.

Best,
Kelly

[Ian Anderson]

My memory will get me in trouble one day!

I remembers Adam posting on this thread (Yes in 2003!)
Primary pipe length formula

And again this thread
MKII Headers: My 2006 Summer Project

Worth a read as he's pretty clued up on his information
He also did al load of wonderful stuff on webber trumpets

Ian