Ferocity02

iTrader: (60)

I have always thought that with the more displacement you have, the larger headers you should get. For my 427, I was planning on getting 1-7/8" stepped to 2" with a 3.5" collector. However, there is a question of the exhaust velocity relative to the primary diameter. Obviously the larger diameter primary will have less exhuat velocity than a smaller header primary. My question is, how do you know when more velocity is better than more volume? I assume this may have something to do with the cam duration/lift/ramp rate as well as head exhaust port flow/velocity/volume. Thanks!

Beast96Z

iTrader: (21)

Old SStroker

Primary pipe diameter should relate more to power output than engine size. If you are well north of 600 fwhp on your 427, 1-7/8 > 2 is probably close. If you are more like 500 fwhp, it's probably too big.

Another thing primary pipe diameter influences is torque peak rpm.

Have you heard of software called "PIPEMAX" ? It will help you a lot.

racer7088

Yes I agree with the Old one here as the power you are making will also give you an idea of the flow rate through that header and for the most part the more power you make the larger the headers will need to be.

66deuce

iTrader: (1)

does anyone make a 1-5/8" header for an LS1?considering the HP of a stock motor or even a mild H/C motor,it would seem that the 1-3/4" would be a little big.

racer7088

Even the 1 7/8 Kooks seem to pick up on the 346 inchers whereas the small header cars always seem to be weaker and slower. Maybe the smaller headers are also not as nice in design and construction but invariably they seem to be weaker most of the time?

J-Rod

Exhaust Valve Opens - EVO

Header pipe length (in inches) = ((850*(360-EVO))/RPM – 3
Header diameter (in inches) = ((cylinder. disp. * 16.38 / ((hdr len + 3) * 25))) * 2.1

These formulas are from A. Graham Bell’s Performance Tuning in Theory and Practice. For a street engine, the RPM used should be the peak torque RPM. For a race engine, the peak hp RPM should be used. For me, I've found that using the peak torque makes the headers way too long. So, I tend to stick with the peak HP number.

Rick@Synergy

iTrader: (5)

I always asked the same thing. The one header I did try was headmens, its a 1 1/2 stepped to 1 5/8 header. Worked good.

Rick

Ferocity02

iTrader: (60)

The only 1-5/8" header that I know of are only shorties.

ToplessTexan

The TTS long tube for the C5 is 1-5/8".

52172

iTrader: (2)

I would go with a set of LG 1 3/4 new f bod headers. They made 630 whp with their 1 3/4 header on an ls7 427. The torque curve was great and they stated that they would lose low end torque with a larger header and also only pick up maybe 5-10 whp.

UMD_Jesse

iTrader: (6)

LG makes a f-body header???? the only ones for f-body's I see on their website are hookers