calgarybandit

I am going to be purchasing headers today and I am stuck on what size to get. I have read allot of debates about 1 -3/4 and 1 -7/8 long tube headers. I have decided to purchase Kooks as the brand just stuck on what size. In the future there is a slim chance I would maybe go FI with a 5 PSI pulley.

My mods are

91 octane Bama & Jon Lund race tunes
C&L CAI
Magnaflow street series exhaust
DSS Carbon fiber drive shaft
Circle D 3000 - 3200 convertor
4.10 gears

Glenn

less than 500hp I would say go for the 1 3/4 inch headers.

QuadCammer5.0

I really don't think you will tell the difference. I got 1 7/8 and don't regret it cause they are sick as hell either way

calgarybandit

Ya I could care less about cost just what is most optimal for our motors. I think AHR, Stainless and Kooks are top because they use 304 compared to lots of vendors who use 409 stainless steel.

Trailhawg

Bigger is better! Think long term.

BlackMamba03

ARH 1 7/8" and O/R X-pipe

2k7gtcs

I went 1 3/4" and now wish I had gone 1 7/8".

AlsCobra

If you are not going forced induction, 1 3/4 is fine especially long tubes. N/A and big primary long tubes will redirect some of your low end power unless you're going FI.

calgarybandit

Yes I have read that but I also read about engines that rev above 7000 the 1 - 7/8 also help higher RPM. Even with a supercharger 5PSI pulley you won't be over 600+ so 1 3/4 should work great. I sure have not found any articles or dyno results that show different unless the cub is bigger or cams etc. And I change my car like my underwear so supercharger is a slight change.

Glenn

I say give the kooks people a call and see what they have to say.

http://ls1tech.com/forums/generation...xperience.html
I know its not your engine so its not apples to apples

AlsCobra

Yep. If on a n/a car, the torque curve will shift over to the high end rpm range and suffer a little on low end. Just depends on what type of running you will be doing. 1 3/4 will be sufficient for most street cars. I will NOT run any american V8 car past 7000 though. Just asking for trouble.

bob

That'd be my vote as well. An 1-3/4 LT is a good compromise all the way around. It always seems to be the best header with the least amount of low end loss with the biggest gain across the mid-range and top.

And yeah that link the LS1 Tech forum pretty much coincides with all the data I've seen on engines under 400 cid unless they were intended for use really high up in the power band (5000-9000 rpm)

Hell, ARH reccomends an 1-3/4 header for my car unless its a race application.

Bmeline916

I have 1 7/8" pri and they are great if going forced induction go big it will make positive difference!

Glenn

but won't to big make a negative difference?

Trailhawg

1 7/8" is not too big for the 5.0. Headers alone will not make a huge difference no matter the size but they respond better with other mods

bob

Show me tha' science! Seriously, if you can dig up the numbers I'll believe it.

Even spotting the 5.0 around a 110% volumetric efficiency didn't require more than an 1-3/4 long tube with a 28" primary and 3" collector.

I did finally get to an 1-7/8 with a ridiculous 150% VE

BTW here is a pretty good link for estimating header size.

http://www.wallaceracing.com/header_length.php

calgarybandit

I spoke to Kooks and the guy said the 5.0l runs efficient smaller valves he said easily could run 1 5/8 he mentioned the only reason they build 1 7/8 is people always think they need bigger. He recommended 1 3/4 would be more than enough for 8psi IF i ever went with forced induction. I called American Muscle and AHR and they said 1 3/4 also was the best fit.

Scuba-Matt

If you plan out turning the boost up get the 1 7/8 tubes. So you won't have to do it twice.

Glenn

rule of thumb is certain hp ratings get certain size headers. I would trust the people at KOOKs I bet they know what they are talking about.