i was gonna point out your thread, but I think this kinda a cool test. IMO Shhh.LOL

 

True, it would seem the more modded an engine is the less likely big pipes would hurt power anywhere in the band.
This makes sense, with a higher stall you shouldn't be operating in the lower bands where you could potentially see some loss anyway.

I think it just goes to show how everything has to work together just right to see maximum performance.

 

The noise vs motion of the vehicle wasn't my point, I was stating that I have seen timeslips with a better 60' and slower ET with full exhaust and then running cutouts with a slower 60' and better ET. I'll see if there are any on here I can post up or if I can find some.

Also I wasn't saying anything about peak HP #s and such, just the affects on the 1/4mi times. But I'm glad I got these replies it brings more experience on the topics than I probably have

In any case wheather it works or not I'll be trying it out here in the near future. Should be interesting to see.

 

i have seen exctly the same thing on at least 5 diferent vehicles. most of them nearly stock and NA. .1+ ET reduction and 1+mph gain at the track just with a simple cut out. sometimes after the cats and sometimes in place of the cats. in the fbody world .1 and 1mph is the expected gain with a cut out(so i am told).

most of my experience is with a power adder so i dont have much data to throw at this subject. here is the a dyno chart i found from awhile back. this is a stock 6.0 with full exhaust and then a dump after the cats. the chart only goes down to 2500rpm but there is allready a slight gain at that point. i think we can assume from that chart that as low as 2000rpm the hp/tq will be even. under that it is hard to say if there will be a loss or just no gain.



i would love to see some more back to back dyno charts to help hammer out this one since it comes up a couple of times a year. some that go as low as 1500rpm would be nice too.

 

I think this theory is probably correct. It's backed up by data AND it just makes sense.
Thanks to those of you who pointed out the facts about back pressure (being a bad thing). It drives me nuts when someone tells me "an engine needs a certain amount of back pressure."
Velocity is the key.

 

Good find Jim... thanks for the data.

 

So according to your statement why do we even need exhaust manifolds?

If you have proof of what you say then put it up, if not your post is worthless.

 

I think losses occur right off idle and through the lower cruising rpms. That's where I noticed some sluggishness on my current system. But every situation is different and I would agree not all vehicles will lose power. Also using a cut-out and having too large of an exhaust system is not the same thing. Maybe it's possible to eliminate any loss using a cut-out if there's enough pipe of a suitable diameter in front of it. I'd like to see some low rpm tests on that.Well we don't really except to keep cool air away from the extremely hot exhaust valves which could be damaged by being cooled off too quickly coming into contact with outside air. If you notice top fuel dragsters use just small lengths of pipe.

There's no question that exhaust velocity and the accompanying scavenging effect create hp because that's the concept that headers are based on.

 

i dont feel like the one graph i have is enough to conclude much of anything but together with the track times i have seen from more than one car it is enough for me to wonder if there is anything to the "to little back presure and lose low end" theory. what is low end anyways?

 

Lemme get this straight; I agree with YOUR theory and my post is worthless. Did I get that right?
If you're referring to back pressure, I already answered that. "Velocity".
However, even if we didn't care about performance, we'd still need exhaust manifolds. Without manifolds, the exhaust valves would bend on a very regular basis.
Headers help keep the gas hot (which makes the gas flow better) while providing a better path for the gas to flow through than manifolds. Stainless steel allows better flow than mild steel or cast iron. Coated SS headers flow best because they are SS and (because they are coated) they keep in the most heat. All this promotes VELOCITY. <~~KEY Imaginge that. If the tube is too large, the velocity will not be optimum. If the tube is too small, it creates back pressure which, by definition, is a restriction (bad), slowing the exit of the gas, forcing the engine to work more (that's a loss of power).
But hey, I don't know anything about this stuff. I've never built headers and I'm not building a custom turbo set-up any time soon, either. WAIT! That's not right.
No matter how you look at it, your theory is probably correct. Like it or not!