arrio76

I am leaning toward installing a 400 SB with headers and a fair amount of performnce upgrades in my 76. I was wondering about the primary tube diameters. The general consensus I have seen thus far indicates that 1 5/8" for the 350 is desirable. Most manufacturers list them with 1 5/8" also. What has me thinking is that the header mfg's list primaries for 396-454 as 1 7/8" to 2+". Would the SB400 benefit more from an 1 3/4" or 1 7/8" primary? Or would the 1 5/8" be the better choice?


[Modified by arrio76, 10:05 PM 10/22/2003]

Smokehouse69

From everything I've seen or read, 1-5/8" is the desired size for 350-383 engines. With a SBC 400, I don't know. I know the tech articles on the Chevy Highperformance website, have done some tests on different sized header tubes, you might try reading through some of them and see if they have any dyno runs for a SBC 400 and different sized header tubes.

MotorHead

I am building a 427ci SBC this winter and am going with the Hedman Hulser headers 1 7/8 in primaries and 3 1/2 in collectors, they aint cheap though :D

You need at least 1 3/4 in.


[Modified by MotorHead, 10:14 PM 10/22/2003]

Les

I agree w/ Motorhead. I wouldn't waste time w/ a 1 5/8" header for your application. You'll have plenty of torque as is- I've got Hedman 1 3/4" headers on a 355 in my Camaro that's putting out a solid 425 HP & even w/ alot less cubes I've got plenty of torque. Depending on how much you're willing to spend I'd say go w/ 1 3/4" or 1 7/8".

Pete79L82

For a street car an 1 5/8 by around 34 to 36" lomg primary is your best all around choice. On the race track we find that even bigger inch motors like a smaller headers. And that is on 406 inch motors turning 7500RPM. Unless you are making over 650HP and turning consistantly over 7000RPM you do not need a header bigger than 1 5/8".

1 3/4" will fit a standard bolt pattern but I do not believe that 1 7/8" will fit without going to a stahl pattern adaptor or a spreadport head.

Headers are like carberators. Bigger is not always better.

arrio76

Thank guys, I just went to the Chevy Highperformance website and read a few of the article suggested, and came away with prety much what you have said. Based on what I read and your comments here, I believe I will be going with 1 3/4 or 1 7/8 header when I install my 400. Thanks again for the help.

Hmm, I was just typing this when Pete79L82 posted, Thanks Pete.



[Modified by arrio76, 6:40 AM 10/23/2003]