Even on my 1.5L civic motor?? got any links to these dynos?

 

Backpressure is no myth, it just doesnt happen now on modern motors - this is worth pointing out.

 

He meant backpressure being a good thing was a myth

 

Technically, the density of the gas is not a constant either. Its going from super hot temperatures at exhaust ports and is relatively "cool" by the time it exits the muffler.

 

Designing around tuned length pipes so your standing waves provide scavenging is the most important part of header design.

I've seen crappy looking press bent headers of the right lengths outperform expensive work of art but wrong length headers.

 

^ Thanks for clearing that up for me

 

Look for a dyno compairison of any Honda or N/A motor for that matter. You'll be surpriced that a 3" makes power EVERYWHERE in the powerband not just in the top end like everyone would think. This should tell you that exhaust velocity is complete BS; after the collector.

EDIT here's a link for the lazy
http://bbmoto.net/wiki/index.php?ExhaustTheory

 

Instead of linking to some website no one has ever heard of take a look at an exhaust built by some of the smartest people in the world (F1 engineers). You will notice that even on this 1000bhp motor they have an exhaust under 3"... Someone should tell them they could make more power



Funny thing about running a dyno is you can show a gain/loss for whatever you want...

 

It's a little more complex. There are several pulses inside the exhaust - at least between the Exhaust valves and the first reflector (it can be discussed what that would be).

Here's a picture of a measured exhaust pressure curve inside the header. Measuring was done 100mm after the exhaust valve and begin when the exhaust valves opens (Aö). The first peak (A2) is measured just before the piston reaches BDC (UT). There is a low pressure peak (A4) where the exhaust valves are wide open and a third low pressure peak when both valves (intake and exhaust) are open. This is an optimum for just this engine speed (3000 rpm in this case).


This example brings up the question how much water is spilled out of the hose during the same time when comparing to a full open hose?

 

The website belongs to Blake(98vtec) on various Honda forums. He's a very good tuner and has a degree in Engineering.

I didn't want this thread to turn into a debate but here you guys go.

You said that F1 Engineers run a smaller than 3" on their motors. I don't know what pictures you've been looking at but as far as I know all F1 motors run basically just headers. The exhaust system you are refurring to is part of the header itself; collector. The tuner from the link I gave you has even talked to an F1 Engineer and guess what? He said the same thing I'm saying.

You can throw theory's onto the table all you want. At the end of the day a theory is just a theory and nothing more. Their has been ZERO proof to argue that bigger isn't better.

You are right about being able to asque dyno numbers. But half of the dyno's I've seen have been from respected tuners. Not someone trying to sell a product.