Some topics have been raised and discussed on the topic of headers and I have a few questions of my own.

If tube length is a function of cam overlap/duration then does this mean more overlap/duration the longer the header tubes?

Is there a general length, that is, are the lengths so insignificant that a one size fits all header is built?

On desktop dyno the more cam, the more headers improve performance. On my 65 with the 30-30 cam the dyno claims almost 75 HP gain from open tube headers. Does this sound right, or is my set-up with the software incorrect?

With cam overlap, you get an induction and exhaust pulse that moves as a function of RPM. So at low RPM (idle) is this pulse in the intake? (Hence poor idle quality)? And as RPM increased the pulse travels to the exhaust? (I am not sure so correct me if I am wrong). Is the idea to keep this pulse inside the header tube? Or have it exit the tube? Or is the open headers just a function of less restriction and free flow?

Say you had a set of headers, and unchambered, straight side pipes would the benefits be the same as open headers. Did the L-88 have the "stovepipe" type side pipes that were essentially straight pipes?

Help me straighten this out.
Mark

 

Cam's with lots of overlap result in lower cylinder pressures due to both valves being open at the same time for a longer period. When the pressure in the exhaust is greater than the pressure of the intake charge that is trying to enter the cylinder, there will be reversion and exhaust gasses will push back into the cylinder. Besides diluting the intake charge, and making it less potent than it would be otherwise, some more power is also lost due to the engine having to pump against the reverse flow of the exhaust gasses that were invited by more overlap. As I've said many times before, the reason a big cammed engine lopes at idle isn't because it's making gobs of power, it's because it's running really crappy at that rpm.

In most cases, headers will make more power than stock manifolds and not only at high rpms. Typically, longer and narrower tubes make for more low and mid rpm torque, and also more high rpm power than stock maniflolds. Shorter and larger tubes benefit high rpm power but sacrifice low rpm power. This is because the smaller and longer tubes increase exhaust gas velocity ( more noticible at at lower rpms), helping to overcome the effect of long overlap periods. High rpm power is increased by better cylinder scavenging as well as lower exhaust pressures that result in less pumping loss.

In any case, as with most all mods, it's all a matter of compromse. Nothing is free and you're gonna have to give up one thing in order to get another.

 

Agree with Vetterodder (was going to say more, but had a brain fade night!).

Plasticman


[Modified by Plasticman, 1:48 AM 12/28/2002]

 

http://www.ecklers.com/product.asp?p...N0SM2EPK2U7JT5

So what about these?

Could this be installed on a non-sidepipe car with out mods?

I am just brainstorming.

Mark

 

"The Scientific Design of Intake and Exhaust Systems" by Phillip Smith would probably be worth procuring if you want to understand the basics of wave dynamics in an internal combustion engine. It's an old book, but the basics haven't changed and a layman without a background in computational fluid mechanics can understand it. I expect it might still be available from classic motorbooks, or you might even be able to find it through your local library system.

For a street engine, a "tri-wye" header will improve the torque curve over the broadest range, but they aren't commercially available for a Corvette as far as I know. Four-into-one systems provide the greatest benefit at high revs, with little benefit at low revs. A commercially available set with about 1.5" ID tubing and 36" primary tube length would probably work best, if you can find any that are truely equal length - most aren't.

Headers are a PIA as you loose the and spark plug RFI andradiant heat shields, so you end up frying wires, and have to resort to "bubbaeering" to keep them from melting. Headers also radiate a lot of heat into the engine compartment because they have a lot of total surface area. A light colored ceramic coating will really help with this in addition to keeping them from rusting.

The benefit of headers will be reduced by overall exhaust system backpressure, but the C2 2.5 inch system is about as good as it gets.

Try selecting "pocket ported" heads from the DD2000 menu, and see what this does. I'd rather see you work the heads than install headers since I take it your car is relatively unmolested.

Duke

 

I added a "H" pipe (crossover) which has significantly increased my low & mid range torque, while keeping (and propably enhancing) the high range power with the headers (when running with "turbo" stlye mufflers/exhaust system) . It also reduced the exhaust noise somewhat, so that a conversation can be held while cruising at 70+. Since my header system uses short (about 8" long) connectors between the header collectors and the exhaust system with flanges on both ends, it was relatively easy to run the H pipe between these 2 connectors. If I need to remove it for any reason (trans removal, etc.), the (2 header / exhaust connectors and H pipe) assembly is just unbolted at these flanges. Did have to make the H pipe in 3 sections, so that it drops below the trans far enough (no need to heat the trans with the exhaust).

Plasticman

 

Sounds good to me. I use Hooker sidemounts. Look cool. Provide LOTS of HP for racing....without muffler inserts. And they are streetable with muffler inserts. Quieter that stock sidemounts. They are chrome, so they don't rust, however, they do occasionally spit out their gaskets, and do require some "maintenance" to keep the gaskets located. Just depends what you want.

 

Thanks for the referance guys. I am not planning a header instalation on my car, for the reasons mentioned. This was just a topic and area of the hobby I was just interested in reserching. Although I do have a buddy with a 58 that is not so concerned with numbers and originality and we are going to do an engine re-build and he is set on trying to use some type of header system. I am just trying to understand the mechanics of the idea.

Although, I would love to here my vette with the open side mount hooker system, all the time, money, and trouble is not on the menu.

Mark