Best Header Primary Size for 305?

[Benm109]

I've been doing a lot of searching on headers for my car. I've pretty much narrowed it down to 2 sets, Edelbrock T.E.S. or the Hooker 2055s (< leaning towards these). The interesting thing is that there are plenty more header options out there with various header primary sizes. I've seen 1 5/8", 1 3/4", and 1 1/2". From what I've found, 1 5/8" is the best for a 305, but I'm not totally sure. If 1 5/8" are the best, what would you need 1 3/4" or 1 1/2" primaries for?

[N20LT4Bird]

Header primary sizes vary for different engines making different amounts of power. If the primary is too small it will restrict the flow of exhaust. But, many people make th emistake of going too big and this negates the scavenging effect the headers are designed to produce. As each exhaust pulse flows through the header primary, it leaves a vacuum behind it which sucks the next pulse through. If you go too big, you wont create a significant vacuum in the primary, and flow will actually decrease. I think 1 5/8" is definately big enough if not too big for a stock 305.

[Benm109]

Cool, that makes sense. So, what size would you recommend for a stock 305, or better yet, a mild 305 (heads, cam, full exhaust, etc.)?

[N20LT4Bird]

You could run 1 5/8" headers if you have some head and cam work done.

[Benm109]

Thanks for the help. Now all I need to do is learn how to tune .

[DeWynter]

I have a program called engine analyzer pro that I can run a test to see if its better to have the 1.5 or 1 5/8. All I need is all specs from your engine. Head type, size, chamber size, valve size
Block stroke, bore, deck hieght
Cam specs
Header specs
exauhst specs (CFM)
Intake type (I have made the TPI intake already)
Injector size
thermostat temp
Head gasket thickness

If any of these specs cant be found I will use standard values. Or if you tell me brands I have a very big list of specs for all engines, and components. Takes about 2-4 hours to input all specs and run program. I can e-mail the sheats to anyone interested. The more accurate the values the better the estimates.
My 383 was only 7% off from the finished product.

I have completed making the stock LB9, L98, LT1 for f-body so I can calculate those
If anyone knows the specs on the stock manifolds for any of these I need them.
I can run test changes for anyone if they like, I just need all info stated above.
I can get any spec for the running engine and Dyno HP/TQ. If anyone has any questions about the program they can ask me or hit the website. It is extremly accurate as long as I get the specs as they are.

[DeWynter]

By my calculations I would say the 1 1/2 will give better TQ in the 3000-3500 RPM Range but the 1 5/8 will give just slightly better HP in the 4000 RPM Range. on a stock LB9. I dont have all the specs for the TBI intake and trottle body to get a good calc.

[Benm109]

Thanks for the info, DeWynter. Could you possibly e-mail me the sheets to me? I know the info won't be exact since it's an LB9 instead of an LO3, but I'm just curious. Is there anyway you could get me all 3 primary sizes for comparison? Thank you, regardless.

[DeWynter]

I can e-mail them all to you It will take a bit though. If anyone Has msn Im firebirdta@hotmail.com Plus Benm109 I need a e-mail address your profile says you dont accept e-mail. I cant send them by PM.

[Benm109]

My e-mail is Jones3451@charter.net . I don't know why it says you can't e-mail me, I'll look into it.