Please take a look at this link and let me know what you think. It kinda goes against everything most people preach on here about exhaust back pressure.

Getting your exhaust system right
by Adian Yein Khalid
http://www.teammatrix.com.my/CarMods/exhaust_1.html

 

Yeah, he's pretty much right. The reason you don't want wide-open exhausts is to maintain flow velocities at low RPM's, he talks about that in the scavenging paragraph on the second page.

Basically, the piston is pushing the exhaust gasses out on the fourth stroke, and backpressure means that it requires more effort to push it out, creating power losses at the crank. If you have a wide-open pipe this is great at this point. But when it stops pushing, the gasses continue moving due to momentum. This creates a vacuum effect as the gasses continue to move down the pipe. This effect increases with velocity, which increases with decreasing pipe size.

The key is to find a happy medium that gives you the power curve you want. A torque curve that looks like an apartment building isn't going to do you much good--all your power in a narrow band is pretty useless unless you always drive in that band. A broader torque curve with a lower peak is more useful for acceleration. A wide-open exhaust will give you the former, a somewhat tigher one will help with the latter. Either way, it's not actually backpressure that's helping you wink

 

Yeah sure let's just turn our backs on all the mechanics and their knowledge of cars and trust this guy. He can't spell "minimise" and spells "back pressure" and sometimes "Backpressure"

Tommorow, I'm gonna remove all the exhaust after the header. Perhaps then my car will work better?

I get it that stock systems are there to reduce noise, but come on, who's gonna "shockwave" tune their car? WTF whould you use to do it, anyways? I'm sure you'd have better power gains by just adding a higher-flowing filter...

 

I'm quite willing to. I design systems that are an industrial equivalent to automotive exhaust systems, and I'll tell you now that 95% of the people who claim to be experts are wrong half the time. Trained monkeys have as good a chance at designing a good system as these folks.

There are plenty of intelligent, experienced people who have quite thoroughly debunked the backpressure myth. For some reading, a 20-second web search turned this up:
http://www.uucmotorwerks.com/html_product/...etorquemyth.htm
http://www.hondalife.com/articles/backpressure.htm

Perhaps if you bothered to educate yourself you'd avoid foolish statements like this. wink I've got a stack of books I could lend you.

He goes on to state that shockwave tuning is only useful on straight-through exhausts, racing applications only. I don't like the spring comment that was linked to in the other forum though. My basic metallurgy knowledge shies me away from that one.

EDIT>P.S. minimise is Canadian/British, minimize is American etymology.

 

The thing you should consider is POWER vs GAS MILEAGE.

Yes, headers are required. If they were not...why even have headers at all on race engines? Why not just let the exhaust ports vent into the open air? Why? The "scavenge" effect. Air has mass. When you give mass velocity, you get momentum. The momentum of the gas leaving the exhaust port is a good thing, as it can pull ALL the exhuast gases out, and also create a slight vaccum to pull the intake air/fuel mixture in.

However...the other thing to consider is fuel economy and low RPM torque. Higher backpressure exhausts will create the scavenge effect at a lower RPM which will help your daily driver MPG. Lower backpressure will create the "scavenge" effect at higher RPM, but at the expense of low RPM torque and Daily driven fuel economy.

You just have to decide which you want to go for. Peak power at the expense of Fuel economy and low rpm torque, or go for low down torque, and daily driven fuel economy...at the expense of some top end power.

 

Please do. I've been meaning to go to the library and borrow a whole load of books and "ejoocate" myself further. I haven't the time though... always too busy working on the Pony!

 

Aight man, that pretty much covers everything, except compensating for EGV drop because of thermal loss to the atmosphere. External conditions effect the performance of the exhaust system also, so in order to list such statements as true, the thermal depletion of the gases and the pressure drop which comes along with it must follow a linear, constant curve in all conditions. This is where thermal coating comes in, to kill temperature loss as far as possible, preserving EGV, which would sustain the momentum of the exiting exhaust pulse and in the end increase or aid the scavenging effect, helping to more effectively scavange(suck)the effective swept volume of the given cylinder.

To hell with it all man, TeamSR and the other companies are gonna do it for us anyway!!!!