Optimal Header Size

[Z71Silverado98]

after wading through countless header manufacturer web-sites all theyre bs has me confused, everyone claims theirs is the best blah blah blah. Several give contradictory information about optimal primary tube dia. and so on. knowing that no one here is just out to sell a product and that several have experience in the matter, i turn to the members of FSC to help not only understand the concepts in header sizing (longtube/shorttube primary lenght/dia. collector) but to help determine the configuration best for my truck. its basically a daily driver/ weekend 4x / 24-7 rice killer. i dont want to lose any of my low-end grunt seeing as i dont know what i may need her to tow in the future, and i dont really care about tremendous power above 80-90mph because for one i dont plan on removing the gov, and two i dont need to be tearing up my tires. just want to add some more good ol'e domestic muscle to my truck through the entire range.

im pretty well read up on the coatings, as well as the brands,

[URBAN COWBOY]

From what I've read 1 5/8 primaries is the way to go for good low end torque. That Vortec 350 you have will respond well with a set of long tube Doug Thorley Tri-Y's in the bay. Low end torque is what Thorley's are all about. I recently ordered a set for my '99 Rado. If you don't want to spend the money for the Thorley's ( around $500), a set of short headers (JBA, Gibson) will give the 350 some punch too. The Stock manifolds on the '98 are pretty restictive so she will respond well to any set of good free flowing short headers. One thing to think about here is that if you get a set of ceramic coated JBA's or stainless Gibsons, they can cost you as much as a set of nickle plated Thorley's. I paid right at $600 for my ceramic coated JBA's three years ago.:cussing:


URBAN COWBOY

[Don454SS]

My comments are similar to Urban Cowboy's. Go with 1 5/8s on a street/mild performance SBC. Long tubes provide low end TQ, but can be generally more problematic to install or meet state inspections in some areas. Another brand to consider is Edelbrock. Their shorties are 1 5/8s, 409ss, CARB certified and easy to install. I don't know how well they perform on a SBC.

[James B.]

Look closely at these headers for a 5.7L Vortec with a.i.r. These are The Other Guys headers. They use three different size primary tubes to help equalize flow from the cylinders. I think this is smart, I know of nobody else doing this.

http://james.jaguar.net/pics/tog1.jpg

[Hit Man X]

http://www.dfwstangs.net/forums/showthread.php?s=&threadid=94552

I asked the same thing over on another site...enjoy!

[Old88]

I'm from the Old School.
Depending on your heads and application the Optimal size primary tube ID should be the same size as the exhaust valve diameter if you are looking for torque.

It's very hard to find 1.5" headers for a truck but Flow Tech makes long tubes for the 73-87 FSC. These work well with GM's 1.94"/1.50" heads on a truck and helps keep exhaust velocity high at low/mid rpm for good results on a truck. Add an "H" or "X" pipe for a better sound or even a "Y" with a large single muffler. I run these with an "H" pipe on my 82 FSC.

With GM's 2.02"/1.60" heads the optimal primary size for a truck should be 1 5/8" (1.625")

With long tube headers the primary tube length should be between 30" and 34" but most manufacturers don't make equal length longtubes anymore.

Thorley/Jardine makes the Tri-Y deal that works well. For best low end TQ a "7 Y" works well (2 tri y headers with a "Y" to join both sides). There are others that make a Tri-Y design also.

A 2.5" collector does a better job of scavenging at low RPM than a 3". Nascar and others have gone to "merge" style collectors that are smaller than traditional collectors.

In a light car that screams to 9000 rpm it's a different story......

[Old88]

Here's what a "merge" collector looks like. There a many variations but the idea is the same:
http://www.burnsstainless.com/MergeCollectors/mergecollectors.html