F***! Dual Exhaust
10-15-2004, 02:14 PM
#41
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the stock y is fine, until youget up into a high hp machine or a really big engine our stock one will work jsut fine. I did true duals becasue I love the sound they make. I was hoping for performance but I lost some low end, I think I can ake that up with different mufflers on my regular cab. my vho I am doing right and since they already have true duals I going to keepp the stock style setup but replace it with a (2) 2.5inch in and one 3 inch out dumped.
10-15-2004, 03:16 PM
#43
Originally Posted by Yelo
guys.....an exhaust is the LAST thing to be developed for a vehicle, and they are mostly designed around the space they have to work with and the tone that will please 99% of the buyers of that vehicle, Has anyone cut open the garbage can that GM uses for a muffler on thse trucks ??....it ain't a pretty sight and it certainly isn't "tuned" to do anything but keep the exhaust QUIET !!
When I had my stock y pipe set up and no cats, I put 1 3" tubing through a 3" quickflow and out the back with a 2 1/2" cut out right in front the muffler. Went to the track and it proved that I was faster with the cut out open. So, I went put 2- 2 1/2" cut outs on the y pipe right where the cats were and went back to the track. This proved that 2 cut outs were faster than 1. So with that being said, my engine prefers less back pressure. I put dual 3" from the headers back b/c I wanted to do without the cut out b/s and it doesn't seem to hurt me a bit, you think???? A while back a friend of mine put a set of ASM's on his truck and went to the track that night open headers and ran his best e.t. ever. These engines DO NOT like back pressure. No offense to anyone but, maybe some of you guys should do less researching and more experimenting.
10-15-2004, 05:02 PM
#45
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I read the article posted. And while it does a great job of talking about burning valves it fails to convince me that no backpressure is good.
Other than stating that the modern engine CPU can compensate for the lack of backpressure by adjusting the fuel tables.
Thats all good and well, but it does not explain away the severe low end losses suffered by trucks who remove most or all backpressure. Obviously the computer can't compensate enough, and remember it can only compensate as much as the injectors will allow it, they do have limits.
I don't have time to do the research into the physics and chmestry of the system. I'm going to build my exaust. If it does not work, I'll re-build it. And i'll keep rebuilding it until I get the results I want.
As for Chevy with all of their engineers. Thats all good and well, but lets think. No one will argue that you can gain power with an aftermarket intake, or aftermarket programming, and in most caes you can keep gas mileage. The Chevy engineers don't push it to the limit, they leave room for improvement. There are several reasons for this and I don't claim to know them all.
I will say that true dual exaust would cost more in labor and parts to install and since cost drives alot of General Motors (and all automotive manufacturers) engineers. I would imagine that is a big reason that dual exuast is not used or researched.
If they can get by cheeper, it does not make sense for them to spend the money.
Other than stating that the modern engine CPU can compensate for the lack of backpressure by adjusting the fuel tables.
Thats all good and well, but it does not explain away the severe low end losses suffered by trucks who remove most or all backpressure. Obviously the computer can't compensate enough, and remember it can only compensate as much as the injectors will allow it, they do have limits.
I don't have time to do the research into the physics and chmestry of the system. I'm going to build my exaust. If it does not work, I'll re-build it. And i'll keep rebuilding it until I get the results I want.
As for Chevy with all of their engineers. Thats all good and well, but lets think. No one will argue that you can gain power with an aftermarket intake, or aftermarket programming, and in most caes you can keep gas mileage. The Chevy engineers don't push it to the limit, they leave room for improvement. There are several reasons for this and I don't claim to know them all.
I will say that true dual exaust would cost more in labor and parts to install and since cost drives alot of General Motors (and all automotive manufacturers) engineers. I would imagine that is a big reason that dual exuast is not used or researched.
If they can get by cheeper, it does not make sense for them to spend the money.
10-15-2004, 06:28 PM
#46
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Now I'm just more confused!!!!!!!!! I thought I knew what setup I was going to go with but now I dont freakin know!!! Backpressure / no backpressure / a little backpressure. AAAAAAAAAAAAAAHHHHHHHHHHHHHHHHHHHHH!!!!!!!!!!!!!!
How about open headers, yeah thats it, open headers!!!!!!
How about open headers, yeah thats it, open headers!!!!!!
10-15-2004, 11:05 PM
#48
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Its simple, want your low end back...put your cats back on. Its just like things that have been proven time and again. Hot Rod mag did a comparison with headers a while back on a identical "mild" chevy 350 sb. They tested a 1 5/8 primary header with a 3" collector against a 1 3/4 primary header with a 3 1/2" collector. That was all they changed in there tests....the 1 3/4 header gained about 15 hp over the 1 5/8's at 6K rpm but it also lost over 25 ft. lbs at 2500 rpm. The average gain of hp was 7 hp i believe while they had an average loss of torque of 5 ft. lbs. The peak torque shifted 800 rpm's in the band with just the header change. Its been a while since i read it so i maybe a little off in some of the exacts....but i remember them loosing alot of torque and they said that for a street/strip vehicle the change to larger primaries and collectors wasn't worth the loss in tq over the hp gained.
I think this pretty much proved to me that a less restrictive exhaust system is going to breath and produce more hp better in the higher rpms in a race condition. While the smaller primary, more restrictive exhaust produces a flatter lower rpm oriented power curve with more low end torque. If all your going to do is drag race and use something like a 3600 converter and not really care about low end...use the bigger pipes and less restrictive muffs without cats and try to cut some lbs to make up for low end loss. If its a heavy *** truck and you just do redlight to redlight with the stock converter or slight stall, then keep the cats and the smaller pipes and save your lowend. Plus, unless you have forced induction or shooting lots of juice...cutting off the cats is probably going to hurt you more than help you just for the fact's listed above. Our stock cats flow pretty damn good for n/a smaller cube motors. Im running the stock y with TOG headers with 3" pipe from the y back to a single inlet/outlet one chamber flow dumped before the axel, and it probably would flow MORE than enough for my 5.3 or a healthy 6.0.
I think this pretty much proved to me that a less restrictive exhaust system is going to breath and produce more hp better in the higher rpms in a race condition. While the smaller primary, more restrictive exhaust produces a flatter lower rpm oriented power curve with more low end torque. If all your going to do is drag race and use something like a 3600 converter and not really care about low end...use the bigger pipes and less restrictive muffs without cats and try to cut some lbs to make up for low end loss. If its a heavy *** truck and you just do redlight to redlight with the stock converter or slight stall, then keep the cats and the smaller pipes and save your lowend. Plus, unless you have forced induction or shooting lots of juice...cutting off the cats is probably going to hurt you more than help you just for the fact's listed above. Our stock cats flow pretty damn good for n/a smaller cube motors. Im running the stock y with TOG headers with 3" pipe from the y back to a single inlet/outlet one chamber flow dumped before the axel, and it probably would flow MORE than enough for my 5.3 or a healthy 6.0.
10-16-2004, 12:39 AM
#49
Oh man, there is a lot of stuff that goes into this. Its not ALL about the exhaust, its about EVERYTHING together as a system. Everything means the intake, heads, cam, air box, manifolds / headers, desired rpms, stall speed, etc.... A less restrictive exhaust is beneficial to a point. Lets throw out the term backpressure. Lets talk about the engine efficiency. A properly sized exhaust would net the best power. That would allow the exhaust to flow out as it needed, yet be small enough to keep the exhaust velocity high. The real key here is to let the exhaust velocity create a vacuum in the chamber just as the intake valve opens which pulls in the beginning of the intake charge. This boost in intake allows a better cylinder fill and more power. But too much exhaust can do the opposite - fast moving gasses exit early, create the vacuum in the chamber before the intake valve opens. Then that vacuum slows down the exhaust and starts to suck it back in the chamber. What I'm referring to is the openng and closing of valves, which is dictated by the camshaft.
So, you have a stock camshshaft which has a large split duration favoring the exhaust. The stock cam and restrictive factory exhaust were meant to be a team. Now you add a dual exhaust system which really opens up the flow. Your motor no longer needs the extra exhaust duration ground into the camshaft to perform. The stock cam and dual exhaust work against each other creating more than enough flow.
By changing cams to one with more intake and less exhaust duration, you'll get back in balance.
So, you have a stock camshshaft which has a large split duration favoring the exhaust. The stock cam and restrictive factory exhaust were meant to be a team. Now you add a dual exhaust system which really opens up the flow. Your motor no longer needs the extra exhaust duration ground into the camshaft to perform. The stock cam and dual exhaust work against each other creating more than enough flow.
By changing cams to one with more intake and less exhaust duration, you'll get back in balance.
