Explanation on long-mid-short tube headers

[wrd1972]

I am considering some headers for my 95 LT1. Im leaning toward the RK sport which seem to be a very good buy. Some say they are the same as the AS&M which i have heard good things.

http://www.rksport.com/product/p_01096556/view_detail

Can someone also explain the differences in the 3 types of headers. Im looking for somthing that goes in without removing the engine and bolts up as apposed to fabbing pipes. What are the gains in the variuos types.

Does anyone have a better suggestion for a header which is the best bang for buck.
Thanks

[Injuneer]

In theory, the tube length affects the RPM at which you see your largest gains. Longer tubes produce torque at lower RPM. Shorter tubes move the peak gains upward in the RPM range. Longer tubes may limit peak HP, because of the increased pressure loss. Shorter tubes may make more peak HP. Traditionally, long-tube headers are the best for street cars, mid- and shorter lengths for track cars, that never operate below 4,000 or 5,000RPM.

About 6 months ago, one of the magazines tested the theory on a 383 SBC, and it was really hard to see the theory produce the predicted results. In some cases the long-tubes produced both low end gains and higher peak HP. It's really specific to the engine firing order, how the package fits in the cars (sharp bends or large numbers of bends hurt pressure drop), the match to the camshaft, and a bunch of other things.

Many people have found significant gains with the long-tube headers in the LT1's. But I've seen frist-hand a dyno test that showed the AS&M's made almost 50HP more than a set of Hooker LT's. But that was a blown 383, making about 850HP, and tuned to operate primarily in the 5,000-7,000RPM range over the course of a 1/4-mile. But, they changed the cam, pushed the engine to over 900HP and the Hookers showed the best HP. I immediately gave the guy $175 for the AS&M's and they are still on my car. To be accurate though, they were not running through the AS&M supplied Y-pipe, but through a custom 3" setup.

Long tubes may also create ground clearance problems, particularly with lowered cars. There just isn't much room on the drivers side for the collector to come straight back, and include a cat (if you plan on using a cat). Typically the Y-pipe will have to come from a separate source. I think the FLP long tubes include the Y-pipe, fully coated and twin bullet high flow cats, but the price is $1,295.

I've heard the RK Sport headers are identical in configuration to the AS&M's. But I also remember that one of the people who used to post here, at least 5 years ago was able to compare the RK's to the AS&M's side by side and found some subtle differences.

The other issue with "long tube" headers is emissions legality. Since they move the catalytic convertor(s), they can not be emissions legal, so in any state/area with rigid visual enforcement, you may fail inspection.

[Kevin - Blown 95 TA]

Header rules change with forced induction. With NA cars, the tuning of primary diameter, primary length, and collector length is all very important because you are trying to scavenge the cylinder of exhaust and pull in the intake charge in some kind of efficient way at some rpm where the cam is working & everything is in sync and that's where the most torque is made. With positive displacement where you have the blower pushing the intake charge into the cylinder and, to a lesser extent, helping force the remainder of the exhaust out of the cylinder, you are interested primarily in no restrictions in the exhaust path. You can have a larger diameter unequal length primary, more exhaust duration, and polished exhaust ports to help out there - everything is less picky regarding head design & cam size (unless it's an all out race car where EVERYTHING matters). But with NA cars, tuning of the exhaust system is vital to good performance, and on a NA street car, headers that make a lot of low end torque are more fun, cause that's where your car lives the majority of it's life, not at 4000 rpm and above. If you can get a flat torque curve from down low, then you make more average power in between shifting gears and the car will be faster overall. Harder to do with an automatic, than a manual cause you can't stay in the rpm sweet spot as long (a converter helps here). Header design is more science than most people give it credit for, but with a street car, there are design compromises due to routing, ground clearance & emissions. Sometimes, the ones that fit the best and require the least maintenance are the best choice for a street car...

[Joe 1320]

It looks like the subject has been covered. However, I am a real fan of SLP shorties combined with a random tech Y pipe for street cars. The scavenging benefits of headers, fantastic ground clearance and 50 state smog legal. The Y pipe is a critical addition as the factory one stinks at best.

[wrd1972]

Thanks all,
One last question.
What is the realistic no BS gains I can expect from the RK sport headers in terms of 1/4 and 0-60. See my sig for engine specs.

[BomberZ]

I have the AS&M headers. They have a great power gain on my 355. Plus no clearance issues. What more could you ask for.

[Need4Speed]

This was a great read, helped me understand a little more about headers/cams... and how it all works.

[wrd1972]

any other comments