Optimum Muffler for Backpressure
05-11-2006, 08:59 PM
#48
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If an ITS (or PCA stock class) 944 can't turn lower lap times with a properly-sized open exhaust and a non-stock header (and I'm not talking about Bursch or Martin Schneider's <sp?>), then that 944 hasn't been prepped properly. This isn't a street application. While the stock system is almost perfect for street use, it is not what is going to give the lowest lap times. I'd strongly advise spending $100 and buying Jon Milledge's ITS organizer. I know what he did in determining what works best in an ITS exhaust, and $100 is cheap for that real, and extensive, knowledge.
05-11-2006, 10:48 PM
#49
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Originally Posted by Travis - sflraver
How about this Campeck? I will take my car down to the dyno and take all the plates off of the super trap so its open all the way to the headers. Then I will do a run with my plates on. If the low end stays the same or increases, open vs. restricted, then you will have your numbers. If backpressure increases low end torque then I will send you the bill for the dyno runs and a few hours of my time.
Fair enough?
aka put your money where your mouth is.
My stance on this is that backpressure tuning moves the HP/Tq curve in the RPM range. A slight increase may be seen with open exhaust but the high range it will fall in will be all but unusable.
Fair enough?
aka put your money where your mouth is. My stance on this is that backpressure tuning moves the HP/Tq curve in the RPM range. A slight increase may be seen with open exhaust but the high range it will fall in will be all but unusable.
05-11-2006, 11:23 PM
#50
Race Director
Originally Posted by baldheadracing
I'd strongly advise spending $100 and buying Jon Milledge's ITS organizer. I know what he did in determining what works best in an ITS exhaust, and $100 is cheap for that real, and extensive, knowledge.
05-12-2006, 12:05 AM
#51
Campeck Rulez
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Originally Posted by Travis - sflraver
How about this Campeck? I will take my car down to the dyno and take all the plates off of the super trap so its open all the way to the headers. Then I will do a run with my plates on. If the low end stays the same or increases, open vs. restricted, then you will have your numbers. If backpressure increases low end torque then I will send you the bill for the dyno runs and a few hours of my time.
Fair enough? aka put your money where your mouth is.
My stance on this is that backpressure tuning moves the HP/Tq curve in the RPM range. A slight increase may be seen with open exhaust but the high range it will fall in will be all but unusable.
Fair enough?
aka put your money where your mouth is. My stance on this is that backpressure tuning moves the HP/Tq curve in the RPM range. A slight increase may be seen with open exhaust but the high range it will fall in will be all but unusable.
05-12-2006, 12:11 AM
#52
Administrator - "Tyson"
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Originally Posted by Campeck
um...dindt hacker just say that he alrady did it with his 928 and lost 4 hp and tq...why do you have to do it?
Eventhough 5hp is not that big of a deal - everyone at the dyno was pretty suprised it was that much. It always felt slower with the muffer in the closed (quite) position. Then again, if you could hear what this thing sounds like, the noise alone makes you feel faster.
05-12-2006, 12:29 AM
#54
Campeck Rulez
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this source just sounds like hes marketing..no real info.
http://www.enjoythedrive.com/content/?id=8179
heres another.
http://www.uucmotorwerks.com/html_pr...torquemyth.htm
and here...I like what he says
"The standard for exhaust diameter is to not run too large of exhaust, for the engine needs a certain amount of backpressure. This is correct in the sense of one should not run too large of diameter exhaust tubing, but the statement of the engine needing backpressure is not. You need to have the least amount of backpressure possible to produce maximum power."
http://www.proficientperformance.com...k_pressure.php
wow..look at this. not sure if the guy is too credible. or he said it wrong. he said that gas momentum pulls vacuum on the exhaust valve but its more the reversion pulses that flow positive and negative waves up and down the headers.
http://www.warnertechnology.com/Cars/backpressure.shtml
http://www.enjoythedrive.com/content/?id=8179
heres another.
http://www.uucmotorwerks.com/html_pr...torquemyth.htm
and here...I like what he says
"The standard for exhaust diameter is to not run too large of exhaust, for the engine needs a certain amount of backpressure. This is correct in the sense of one should not run too large of diameter exhaust tubing, but the statement of the engine needing backpressure is not. You need to have the least amount of backpressure possible to produce maximum power."
http://www.proficientperformance.com...k_pressure.php
wow..look at this. not sure if the guy is too credible. or he said it wrong. he said that gas momentum pulls vacuum on the exhaust valve but its more the reversion pulses that flow positive and negative waves up and down the headers.
http://www.warnertechnology.com/Cars/backpressure.shtml
05-12-2006, 12:29 AM
#55
Yeah, gee guess you're right Campeck, except that doesn't explain Exhaust C fitted with Muffler 3, which had very little back pressure yet had the second largest power loss. Or even Exhaust C fitted with Muffler 1 which had 0 backpressure but still had a 1.3 percent loss. Hmm, guess you shouldn't be so dogmatic with your comments. I think there is more too this than you are comprehending in your reading.
05-12-2006, 12:34 AM
#56
Campeck Rulez
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youll notice they are not "open TUNED tailpipes" which means they were just shoved right out the back of the car without maybe stepups in diameter or other considerations. it looks pretty clear to me that when looking at backpressure, all the ones with zero did better than ones with... Who cares if one with a little backpressure did bad...that really only goes on to prove my point even more. which is backpressure is BAD.
I still dont see how yall can still argue. hacker has results, the book has results, and not to mention its logic that if theres pressure holding ALREADY BURNT mixture in with a NEW MIXTURE it will hurt power.
I've said enough. hopefully ya'll will see the light
.
I still dont see how yall can still argue. hacker has results, the book has results, and not to mention its logic that if theres pressure holding ALREADY BURNT mixture in with a NEW MIXTURE it will hurt power.
I've said enough. hopefully ya'll will see the light
.
05-12-2006, 12:39 AM
#57
Administrator - "Tyson"
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My 79 has CIS injection - reacts very well with no tuning to "bolt on mods". With the "newer" L-Jet system on 80-84 928's you must do something to add fuel if you expect a serious gain from exhaust. I'm not a 944 (or even a 928) expert, but I have a feeling 944's will react similar to 80-84 928's since their injection systems are very similar.
Take away stock back pressure with zero fuel changes - sure you might see a hp loss. Search around the 928 forum - find how many people bolted on all new exhaust who didn't see a serious HP gain until they installed a RRFPR.
Take away stock back pressure with zero fuel changes - sure you might see a hp loss. Search around the 928 forum - find how many people bolted on all new exhaust who didn't see a serious HP gain until they installed a RRFPR.
05-12-2006, 12:49 AM
#58
Originally Posted by Campeck
youll notice they are not "open TUNED tailpipes" which means they were just shoved right out the back of the car without maybe stepups in diameter or other considerations. it looks pretty clear to me that when looking at backpressure, all the ones with zero did better than ones with... Who cares if one with a little backpressure did bad...that really only goes on to prove my point even more. which is backpressure is BAD.
Originally Posted by Campeck
I still dont see how yall can still argue. hacker has results, the book has results, and not to mention its logic that if theres pressure holding ALREADY BURNT mixture in with a NEW MIXTURE it will hurt power.
Originally Posted by Campeck
I've said enough. hopefully ya'll will see the light .
.
05-12-2006, 12:53 AM
#59
Campeck Rulez
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manning you are right. but with a 944 its hard to overscavenge with no overlap. 
my arguement is backpressure is bad. thats it. and its true is it not?
ok...im for real going to sleep now..
my arguement is backpressure is bad. thats it. and its true is it not?
ok...im for real going to sleep now..
05-12-2006, 12:57 AM
#60
And my statement is you CANNOT make a blanket statement like that. The goal is to have as little as possible, but as Erik points out, without modifying anything else on the engine, you cannot eliminate backpressure without possibly harming performance
And were are you coming up with the 944 having ZERO overlap? There has to be some amount of overlap to help draw enough mix into the cylinder, no?
And were are you coming up with the 944 having ZERO overlap? There has to be some amount of overlap to help draw enough mix into the cylinder, no?