[darkpuppet]

boost til'bust,Aug 31 2004, 11:1 Wrote:

Jays2000ZX3,Aug 31 2004, 01:20 PM Wrote:ONly thing I have to say here is:

-Look at Honda's.. (Yes, they are real cars) all the SC guys, be it JRSC or vortec run a Race header. Most guys use the Kamikaze header because of the big tubes. A Race header is worth it FOR SURE.

exactly...every other fast car uses a race header, but for some reason people with focus' seem to think that the engine in a focus is different than all other motors.

guess thats why their are no fast focus' out there :rolleyes:

good grief.

You folks are missing the point. I have not said anything about backpressure building ultimate power... I mentioned that the existence of backpressure can be beneficial for building low end power (due to tuned pipe properties)... something meford may wish to consider with the relatively anemic torque curve of the JRSC system.

Unfortunately, that statement can be a bit confusing... backpressure is bad, but the tuned pipe properties existent in a system is good. I should have probably stated it in terms of exhaust velocity. Maybe a quote from Sport Compact Car's Suck Squish Bang Blow article would make it a bit clearer what I mean?

Quote:Some self-proclaimed engine gurus claim too large of an exhaust tube on a car can cause problems; engines need a certain amount of backpressure to run correctly. Although the statement about not running too large of a tube is correct, the assumption about engines needing backpressure is not. A vehicle needs the lowest backpressure possible to produce the maximum power by keeping pumping losses low. Too big of an exhaust pipe causes power loss, especially in low-end torque, because a big pipe has less exhaust stream velocity than a smaller pipe. Velocity is essential to get the best scavenging effect from tuned headers. (We will discuss this in more detail later.) In simple terms, if the exhaust gas flow is kept high with good velocity, a vacuum can develop behind the closed exhaust valve allowing even better scavenging when the exhaust valve opens on the next exhaust cycle. Good scavenging is even more critical on valve overlap, the part of the four-stroke cycle where both the intake and exhaust valves are open.

I agree that on a turbo'd car, bigger is ALWAYS better, but that's because a turbo's efficiency is reliant on the pressure differential between the exhaust inlet and outlet sides.

Meford's car could definitely use a different exhaust cam, but once that's done, if he's looking for driveable power, he may not gain much with a race header other than a few extra HP in the upper reaches of the RPM range... but he could be sacrificing the torque that gets him going at a green light.