does anyone have a cut out for there exhaust iv seen it on muscle cars alot been wantin to do one for my cobalt but was wondering if anyone else has it or maybe has some audio of a cut out on a cobalt also i was looking at this kit and wanted to know if it would work for my exhaust . hope this isnt the wrong place to post this i wasnt sure where it went

http://racereadyperformance.com/stor...ba70ca0ace7b45

 

In my opinion, it would do more negative than positive...

 

i wasnt gona use it for performance i just wanted to have some killer sound with it open but be able to close it for around town so i dont get hassled by cops. or do the cobalts just sound like crap runnin like straight header

 

I dont know, when i drove open header for a week, it seemed to get up and go a lot faster. maby it was just me but it seemed a hell of a lot faster.

 

yeah those arent as effective as open headers

 

You need to have some amount of backpressure, I think it would do more HARM than GOOD. Just my opinion.

 

I've seen it on a Cobalt.. I watched a video on YouTube, or maybe it was Streetfire where I guy was showing it off.

 

we just put one on my friends Jetta, and I drove it before and after and I can notice a differnce and soo can he, but then agian, thats aJetta, were talknig about a cobalt,

Im not sure, It like makes the whoel car vibrate too its funny. lol

 

itd be bad for low end torque, but mainly for higher end power.

with my custom exhaust, I lost some low end power, but got alot more higher end which is the way I like it....since you figure, when your jammin through gears, your always at mid/high end power ranges anyway.

 

You don't need nor do you want backpressure.

Backpressure is a negative effect. What coincidentally happends is that the smaller your exhaust system, the higher exhaust velocity you have...and also the higher backpressure is being created. The larger the exhaust system, the slower the velocity build up but you'll have less backpressure.

It's all about a balance between the 2.

Having open headers and having a exhaust cut out by your b-pipe is creating almost the same effect when it is open. You're creating a huge exhaust leak which will decrease backpressure, yes but what will also slow down your exhaust velocity. Slowing down of exhaust velocity will coincidentally shift your powerband upwards in RPMs.

Another point to make is with your supercharged setup, even if you're pushing 20 PSI of air pressure into your cylinders (which you're more than likely not seeing all 20 PSI of pressure from your manifold going into your engine), the lift/duration of your camshafts and the size of your exhaust ports determine the appropriate size exhaust system and balance of the 2. Just because you have a forced inducted vehicle doesn't mean the largest exhaust system is the best thing for you or that exhaust cut outs or ideal. Think of your car as a naturally aspirated vehicle and the same velocity theories apply. If you were turbocharged, it would be a totally different story.

So overall, it's getting rid of back pressure that's benefiting you but the decrease (and slowing down) of exhaust velocity that hurts you.

 

what he said ^^^

 

I disagree. the theory is ok, but not quite right. back pressure is very necessary to make torque. however if all you want is big HP numbers then less back pressure is needed. but some is still needed. the reason for this is called scavenging. basically its keeping burnt fuel from going out the exhaust, it helps make the engine more efficient in terms of burning all the fuel it receives. the speed of the air isn't that important, whats important is that fuel (AKA. energy) isn't being wasted. being able to breathe is important as well, and like adam said a balance is needed. but that balance must be between flow and back pressure.

I had one of those on my T-type, it worked pretty well. the one i had would let you open it to any point, it wasn't just open or closed, it would be barely cracked, 1/2 open, 2/3 open, anywhere you wanted it. That is a turbo car which is different as far as whats needed on the exhaust. the turbo gives you all the back pressure you could possibly want and then some (thats the reason for the insane torque numbers compared to the hp numbers. I was making in the neighborhood of 400hp. but had about 650 ft/lb torque.) everything after the turbo needs to be as free flowing as possible to keep the turbo free to spin with no restrictions from the hot side.

i don't know how an ecotec will sound with a dump, i'm guessing very loud and ricerish.

 

I understand what you're trying to say but something doesn't make sense...

If what you're saying as far as fuel being wasted through the exhaust, at the end of the power stroke, the excess fuel being pushed out during the exhaust stroke, wouldn't air pressure trying to go back into the cylinder port cause an interruption with the exhaust airflow exiting the engine? I mean, isn't the whole point to get the exhaust out as fast as possible?

Also, the amount of excess fuel depends on how much fuel is being sprayed in the first place. If you're running in the 13s of a/r, then how much fuel you think you're going to be able to scavenge back into the combustion chamber? Also, even if fuel is going back into combustion chamber to be "re-used", the fuel injectors are still going to spray the same amount of fuel as was sprayed in the first place and if in the previous cycle, that amount of fuel was being wasted, I would think (theoretically) it be the same amount of fuel being wasted all over again and a repeated cycle of unburned fuel trying to be used again.

Maybe I'm missing something.

 

of course it doesn't make sence. I'm on my 3rd drink of the night and i couldn't explain anything other than why beer tastes good.

I'm not drunk, but to be absolutely honest with you i don't fully understand the concept myself. i've heard it many many times from people that do know what they are talking about, and the way they explain it makes a lot of sense. google it, if you find anything post it, if not i'll look for something tomorrow and post it.

 

I'll post something up soon...

Here you go: http://www.proficientperformance.com...k_pressure.php

http://www.nsxprime.com/FAQ/Miscella...austtheory.htm

and I can go on.

 

Those articles are directly stating the backpresure is a bad thing. Hands down. Exhaust velocity is important, and by the first article I gathered that is often confused with backpresure.

In any case, it doesn't directly state what size exhaust we should be going with, but being that our engines are 122ci a 2.5in exhausts is probably the biggest we should go.

 

He even says it, the SCAVENGING is the important thing. Low end torque is helped by getting a smooth exhaust flow, in which each pulse helps pull out the next one, simplisticly speaking. At higher rpms, you need a different length of header to get that effect. Now the fun discussion is backpressure vs. power on a 2 stroke Why is my jetski more powerful with a tuned pipe?? I don't think we should discuss that here though. Many people might get even more confused.

 

wow, I am glad i decided to post something here rather than write my econ paper last night. I didn't think that through all that much. basically we are arguing the exact same point.

http://www.turbobuick.com/forums/gen...ght=scavenging thats one of the better explinations i've read. most of the guys there REALLY know their stuff, so most everything you read there is reliable information.

http://www.turbobuick.com/forums/tim...ght=scavenging
they talk a little more about it here, look at the headers on this car to see more of what they are talking about.

 

okie...it may finally be time for me to teach adam
adam was right, all back pressure is bad...exhaust velocity is what s needed. Exhaust velocity has a direct impact on scavenging ability and back pressure does not help scavenging at all...so basically, you want to keep the exhaust gasses moving fast....wide pipes=less restriction for high RPMs but slow acceleration of exhaust gasses at the low RPMs

now, if i remember correctly, exhaust scavenging was this: the exhaust leaving the combustion chamber helps to produce a vaccuum to draw in fresh air when the intake valve is open into the cylinder....this scavenging takes place very close to TDC and is maximized when there is some overlap in the valves in which both exhaust valves and intake valves are open. This helps fill the cylinder with an A/F mixture before the cylinder begins its descent to BDC, which is what drives the engine normally

basically, it boosts the vacuum level of the engine a bit, creating a vacuum sooner than would normally take place without scavenging.

(im finally starting to feel more knowledgeable than the average guy on these forums now

 

What you're saying is correct.

What I was referencing to was him saying that he was told that backpressure is needed to bring back fuel to help the a/f mixture. That part didn't make any sense to me.

You basically said what I said Codey...I mean Casey LOL

lol yeah we are kind of arguing the same point but I think you were confussing backpressure with scavenging.