Since we talk about the value of headers here from time-to-time here, I thought you guys may find this interesting.

Stock ZL-1 427 Camaro* engine @ 6750RPM:
Replacing manifolds with headers (factory exh system in place)--- add 43 HP
Then removing factory exhaust system (open headers)------- add 80 HP more

*Understand, we're talking Camaro manifolds/chambered exh system

Source: http://www.camaros.org/copo.shtml check it out, interesting reading

 

Well...yeah...just try to find a "stock" ZL-1 Camaro anywhere - it never happened!

Sorry, but I'm failing to find the relevance in finding out that a racing engine does not like little pea shooter exhaust.

Now the really interesting exhaust news is how some racers have turned the newer decibel/muffler rules into making faster passes.

Thomas

 

The ZL-1 isn't a SHP engine. It's a purpose built racing engine. The valve overlap characteristics are specifically designed for headers and open exhaust, and manifolds and mufflers will easily take away 150-200 HP.

With manifolds and mufflers the engine would probably make more power with the L-72 cam, because very large overlap actually reduces output if there is any significant exhaust back pressure. The L-88 and ZL-1 engines were offered as options in order to homologate them with the FIA, SCCA, and NHRA, and it was assumed that they would be equipped with a racing exhaust systems.

SHP engines will respond to headers and open exhaust, but the improvement is no where near as dramatic as L-88/ZL-1 because SHP cams are designed to provide good output over a broad rev range with the OE exhaust system. Also, the effect of headers is reduced in the presense of exhaust back pressure.

Duke





[Modified by SWCDuke, 8:54 PM 4/1/2004]

 

Sorry, I agree, the term SHP was a bad choice, I should have said a BB with a hot cam/high RPM intake :) Just Kidding, you're right.

The point is, a number of guys here add more cam and intake to a 425 and wonder if they really need headers &/or super low restriction exh sys. BTW, the L-88 cam is considered moderate now days.... with those running Hot street/track BB's (i just went with a 256/266@50 soild flat tappet, and some say I'll be under cammed).

 

No doubt that camshaft profiles are one of the most misunderstood of performance components - and how the exhaust ties into the equation. Call the L88/ZL-1 cams mild only because camshaft technology has progressed so far in the last 35 years - but I can guarantee that those old cam profiles will make for a lumpy uneven idling engine.

You are correct that many people do not understand the need for downstream flow capacity after improving the cylinder filling side of their engine's performance. Here's an amazing part of that same idea that applies to modern efi performance engines that really brings this to light: more than a few people have figured out how to build with balanced flow improvements on the intake and exhaust sides of their engines - then with no computer programming just add an equally balanced larger fuel injectors, and wa-la it runs great. Most people will still need efi computer reprogramming because it really is hard to know when everything is well matched in flow capacity.

Its really not suprising that some people wonder if they should replace the factory manifolds with headers - is it not true that most car enthusiasts prefer the image of speed and power over actual speed and power? And as much as they might understand the image of enhanced power via headers, they are more concerned about the nightmare stories they have heard about difficult header installations - not to mention spark plug access trouble with headers. Besides, only a small percentage of owners who modify their engines will ever actually make passes down the dragstrip.

Thomas