HP gain from Headers

[charger1970]

Does anyone know what kind of HP gain I could get from a set of short or long headers for my 383?

[Doug Wilson]

Headers are the single most cost-effective way to inprove the output of any engines. The amount of improvement depends very much on the state of tune of the engine. Equal length long tube headers produe more gain than shorties, although virtually any header system is better than almost any factory manifolds. They also save a bunch of front end weight.

On a stock 383 Magnum, you may see 10 to 15 horsepower gained - shorties would be about 15 to 20 percent less. If you build a stout 383 - 10:1, medium cam, good heads, etc - the gain could be on the order of 25 horses. Again, The short ones would be less. There is also afactor to consider of the RPM at which you want the engine to "tune".

More later - gotta go.

[Doug Wilson]

OK - I'm back.

There are some formulae available to use in determining header tube length and tube diameter, which are based on the volume of exhaust gas to be moved and the RPM at which you want peak torque and horsepower to occur. I don't have them to give you, but they might be available from hotrodmagazine.com or in the edelbrock.com technical section.

Generally, the bigger the displacement of the engine, the larger the diameter of the tube needed. Also, the higher the RPM you want to tune at, the shorter the primary tube length you want. If you have a small block that is going to rev to 7500 and you want to shift at 7200, you might want your torque peak at 5800 and your horsepower peak at 6800. You might select a header with 1 7/8 primary tubes 26 inches long. On the other hand, if you have a 440 used in a towing application, horsepower peak at 4800 and torque peak at 3500, a tube diameter of 1 3/4 (or even 1 1/2) with a primary tube length of 40 inches might be the right combo. Other points are that fenderwell headers are more effective than under-the-chassis headers, full length headers are better than shorties, and headers that are metal/ceramic coated are better than uncoated - the best are coated on the inside of the pipe as well as the outside.

The formulae that are available are mostly only usable if you are having your headers custom built. The truth is, the differences between a precise custom header output and that of off-the-shelf pipes would be very small. Maybe 4 or 5 horses on a true race engine. Probably unnoticable on a street car. However... some headers are better than no headers on nearly any engine.

The bottom line is to design your entire engine and drive train for what you want to do with it. Ask the people on this forum for suggestion and you'll get all the help we can give you.

I bet that this is way more information than you wanted.

Sorry - someetimes I can't help myself. If you want more boring stuff, you can email me at ThunderboltRanch@msn.com

[rumblefish360]

I would bet that the gain would be more than that. The ol'school rule of thumb was 15% I think it was. I'm gettin old. Brain isnt remembering as well as it used to. Anyway...
On a 340 HP engine, no other mods but the exhaust from header to tail pipe, you can go from 275 HP to 300+. Easy.

[Doug Wilson]

I agree with you when talking about the entire exhaust system. Pipes and mufflers can add quite a bit as well. I was just trying to address headers only, not for a specific application, just in general, for all cars ever made. There are some cars whose factory exhaust manifolds aren't improved with headers.

[rumblefish360]

Very true Doug. Very true. Funny how the factory can step up huh?

[Doug Wilson]

Yup!

[PapaBato]

what about a good pair of headers on a relatively stock 440?

[Doug Wilson]

How "relatively? Cam? Intake? Heads? What vehicle? What you want to do with it, and how much can you spend?

If it is really mild, and you can only spend maybe $150, just about any of the brands carried by the mail order places can take care of you.

Let us know the details, and we will try to help.