well a couple friends of mine with ss s/c and redlines tell me they have 3" downpipes and i was wondering if i would gain anything from upgrading whatever size this pacesetter DP is (2.25 or 2.5") to a 3" since one of my friends is giving his away to me cause hes getting a new exhaust soon or if it would be pointless. thanks.
i dont see why i would lose any though, the LSJ's are doing it and seeing a gain but i just wanted to see for sure on j-body.
the lsj's are also running a lot more boost
LE61T PTE6262 Powered 
you need to look at their before and after dyno sheets and see exactly where their gains are.. they may gain 6 whp but lose 3 or 4 down low (for instance)
LE61T PTE6262 Powered
QBE (The Boosted One) wrote:the lsj's are also running a lot more boost
? isnt the lsj's and the l61 SC the same?
even still with all boost aplications backpressure is the devil. your forcing air in and out passing a volumetric efficenciy number of well over 100 percent, which means there is no reason for the scavangeing effect of back pressure, if anything a bigger exhaust will help.
and one last thing A down pipe is usually refered to the part that comes off the turbo. But I guess thats the name for the part that goes into the cat.
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Kick azz is my boost hero!!! 
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Quote:
same s/c different displacement. 2.0 w/ m62 will make more psi than the 2.2 w/ m62.
put the crack pipe down. the 2.2 has more displacement and compression... how do u figure it will make more? it will be able to handle more power due to stronger internals.
http://www.myspace.com/15102113
I'm saying that since the 2.0 has less displacement, the charger makes more psi with the same pulley. is that not the case? Cause I thought the cobalt ss/ion redline used the same pulley as what comes with the gmpp eco kit, but the ion/cobalt see more psi because of the smaller engine.
or AM i smoking crack?
'00 Grand Am 2.4L LD9
http://www.cardomain.com/ride/816505
both run 11psi. u can get an aftermarket pully get or gm staged upgrades on the cobalt to go to like 16psi.
2.0 has a stronger bottom end so it will take alot more power. also is suppose to have a better flowing head. but the 2.2 eco has higher compression and more displacement.
http://www.myspace.com/15102113
you will not see as much boost being produced but you will see more power being made anytime you let a supercharged engine breath better
but you have to think of where that power is being made..
peak numbers look great on paper. but the curve is where its at
yes on a turbo application the bigger the better, you will see the same amount of backpressure no matter what because it's comming of the turbo
on a supercharged application surely you will pick up a few top end ponies, but if your making it take longer to get there what is the point?
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EXESIVE FIRE (Andy Brooks) wrote:but you have to think of where that power is being made..
peak numbers look great on paper. but the curve is where its at
yes on a turbo application the bigger the better, you will see the same amount of backpressure no matter what because it's comming of the turbo
on a supercharged application surely you will pick up a few top end ponies, but if your making it take longer to get there what is the point?
hmmmmm, im adding a high flow cat in place of my gutted cat so i guess ill decide on what ill do after that cause i know i lost noticeable low end after the cat was gutted.
top end power is more fun
low end torque means excessive wheel spin most of the time especially in the cavi. Sure if you want to race to 50 you want tons of bottom end but if you have ever had a small turbo and raced on a roll you know how much it blows when it falls out of its powerband. When you have a turbo that pulls gradually across your rpm curve making smooth power its great. On a roll the higher you get in rpm the more power you make at the wheels well depending on turbo specs. But ive had both and prefer top end power. As for a 3 inch dp on a supercharger well i think less back pressue in a situation of making the most power for your dollar its a good idea. Are you gonna team this 3 inch dp with a 3 inch cat and a 3 inch exhuast cause that would probably be quite excessive for the charger. If your doing a high flow dp to a 2.5'' cat and a 2.5'' cat back i would say yes you'll see minor gains but how much? know one knows unless they have a dynosheet. If its free why not try it if you dont like it switch back. But when you get it go to the dyno and let others know so we dont all have to guess. Whatever your choice is good luck to you hope you get what your looking for.
*2012 mazdaspeed3*
Jcavi wrote:even still with all boost aplications backpressure is the devil. your forcing air in and out passing a volumetric efficenciy number of well over 100 percent, which means there is no reason for the scavangeing effect of back pressure, if anything a bigger exhaust will help.
Actually the scavenging effect isn't an effect of back pressure. It helps maintain velocity thru the exhaust to minimize back pressure and reduce the work the engine has to do to push out the exhaust by creating a low pressure pulse back thru the exhaust system. If you go to big with your exhaust your going to hurt your low end power because as the exhaust cools it moves slower and the slower exhaust resists the hotter exhaust and will actually causes back pressure. This effect lessens as the RPM's increaase because more gasses are leaving the block due to the increase in RPM's so in the top end your 3" exhaust will be better, but overall it is a much less efficient design
2.5" will allow you to maintain that thermal velocity even in the lower range of the RPM band and the effect will be minimal on the top end. There is more to exhaust than bigger is better to lower the "backpressure", back pressure is the enemy of any engine.
Turbos can usually get away with a larger exhaust because of the increase in thermal velocity they create when spooled, even still there is a point where the exhaust will be to large to be efficient and will sacrifice power at other RPM's to increase power at the top and last time I checked, none of us here were building dyno queens.
-Chris
Dyno queen = the poo. So what if your so-called daily driver made a peak of 350HP at 7K RPM on a dyno. If you're not seeing those numbers between 3K and 5K, you've pretty much wasted your time.
