Is there such a thing as not having enough backpressure on an engine? Everyone talks about reducing backpressure through aftermarket exhaust systems, but can you open up your exhaust too much? i.e. running open headers/ headers straight into mufflers with turndowns?

 

Actually what happens is you usually lose a lot of bottom end when you open up your exhaust. A while back when I added my cat backs to my stock exhaust, I noticed a huge loss in low end. I didn't like it at first but at WOT its better.

 

Small displacement engines need backpressure. Our engines don't.

 

my v6 needed backpressure, this one dont :P

but some chamber wouldnt hurt it...

 

Here is a little on the subject of backpressure:

"No, you absolutely cannot have too little backpressure. That is one of the biggest and dumbest fallacies that exist in relation to 4 stroke IC engines. Why? I'll tell you.

Pumping Losses --- The concept of backpressure means that there will be a high pressure area at the exhaust port. When the valve opens, the escaping exhaust gases have to push against that high pressure area. How can a parasitic loss be good for your engine? The only engines that NEED backpressure are various small engine designs, mostly 2 stroke. The problem with them is they have the tendency to be too effective at driving the exhaust out, loosing compression. I assure you that on a big 4 stroke engine such as an SBC you want the exhaust to have the free-est path possible. In fact, it would be ideal to have a low pressure zone at teh exhaust port. A low pressure area would help to pull the exhaust gases out. Freeing up more power that your engine would have wasted pushing the gases out...which brings up the next topic beautifully.

Scavenging --- We've heard this before, but what does it mean in relation to our discussion of exhaust. Easier for me to use an example. So your engine fires and now it's on the way up on the exhaust stroke. Exhaust doesn't come out at a consistent rate, it comes out in pulses. Each pulse is a high pressure area, and as it moves, it leaves alow pressure area behind it. Aha, there's our scavenging. You want that low pressure area to be at it's peak when the exhaust port opens on the next exhaust stroke. Thats another reason why headers make better power than manifolds. besides just flowing better, instead of all the pulses being dumped in a log fighting with each other, the tubular runners allow the exhaust pulses to stay seperate and create a nice low pressure area behind it. This is also where tuned and equal length headers come into play. Tuned headers are sized such that the length of the tube corresponds the speed of the exhaust pulses so that the low pressure area is maximized at certain rpms. No surprise that short headers are better for high rpms than longtubes.
Problems can surface if you use too large of a primary diameter, loss of torque. The morons are quick to spout 'you lost backpressure and thus torque.' Next time you hear that you will smile and know that that person failed physics in high school. The problem with using too large of a primary is this. The exhaust pulse only has so much gas and energy in it. If the tube is too large, the pulse expands to much, losing energy and thus velocity. When it loses velocity, it can potentially stall and stop moving in the tube, or at least slow down. aha! Too large of a header actually CAUSES backpressure, and thus lost power. We feel this power loss as a loss of torque because usually this effect is much more pronounced at low rpms as much less gas is moving.

The same principles apply to the entire exhaust system, from primaries to collectors to pipes to mufflers. I am too tired to explain it all, books have been written on these topics. I have just scratched the surface, but hopefully you all understand a little better why their is no such thing as good backpressure. I know some of this has been a little oversimplified, but it think it gets the message across.
thank you please drive through~~"

 

Got-LT1... in theory, you're right

but I'm sure you realize the difference between theory and practice.

If you're building a high RPM / dyno Queen, sure, backpressure is bad, but S.J.S.'s description is pretty close.

if backpressure is so bad, why don't you just take your headers off and run open HEADS?
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exactly.

 

First: I didn't write the article, a someone else did.

Second: the essay tells why you need to run headers (the part about exhaust pulses). Besides you'd burn the valves with no headers.

Exactly

 

I was gonna type something else just before you and cancelled. He is right, but in laymans terms...........

 

got lt1 that was explained good A+ on that report