Everyone agrees that the Mustang exhaust is restrictive, whether it's the exhaust manifold, catted h-pipe, or the catback exhaust. If you eliminate some of that restriction by replacing stock parts with performance parts, you can add horsepower. What happens, however, if you replace all three components? I installed Hooker LT headers, o/r x-pipe, and Magnaflow catbacks, hoping to increase my horsepower. I gained 23 rwhp with the headers and x-pipe. But, when I traded out the stock catbacks for Magnaflows, I actually lost low-end power. Using a G-Tech, my 0-60 mph time went from 5.1 seconds to 5.6 seconds. At higher rpms, I appear to have gained power. I found a thread on stangnet that explains the physics behind this loss in power: http://forums.stangnet.com/showthread.php?t=458814&highlight=catalytic+converter.
Too much exhaust flow = loss of power
- Thread starter 01mgvert
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Defleshed
Satanic Mechanic
yalp... loss of backpressure = more high end, less low end. Just wait'll you put some aggressive cams in, that'll throw you for a loop!
Premium Speed
New Member
G-tec's aren't very accurate unless the conditions are perfect...take it to the track
yes, you lost some backpressure and low end responce, but you made up for it on the high end(where it matters when drag racing).
yes, you lost some backpressure and low end responce, but you made up for it on the high end(where it matters when drag racing).
FallenPhoenix
New Member
you never want back pressure what causes a loss of low end torque is the exhaust gases slowing down. You ideally want as much flow as possible while maintaining a constant exhaust speed through the system, one reason chambered mufflers show lower power than straight through. When the exhaust gasses get to the open chambers they expand and slow down.
jrc_03_gt said:
I already have 4.10s.
Don't get me wrong, I like the high-end power. But, I like the low-end power for neck-snapping take offs. The reason for my thread was to warn others about removing all restrictions from their exhaust, thus eliminating back pressure. This is beneficial only for forced air induction. For those of us who are n/a, we need some back pressure for low-end power.
i know this is on a camaro but here is what my car did when i open my exhaust dumps. i had two 2 1/2 dumps right after the long tube headers
http://home.earthlink.net/~blkchevyz/306hpnumbers.htm
as you can see i lost some low end and gained alot on the top end... it also moved my torque up.
http://home.earthlink.net/~blkchevyz/306hpnumbers.htm
as you can see i lost some low end and gained alot on the top end... it also moved my torque up.
Canuck Stang
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- Apr 8, 2002
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FallenPhoenix said:
Where are you getting this info from?
I think you've been sadly misled.
You're all bass ackwards...
FallenPhoenix
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Canuck Stang
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From physics.....physics taught you about air flow though internal combustion engines?
Well, I think the only thing physics will tell you is that air flows faster w/ no restrictions. ie: laminar flow.
Problem is, you are talking about an *engine* here, that is a little more complicated.
Engines require exhaust gasses to be scavenged from the cylinders properly.
At low rpm, this requires a certain backpressure to be accomplished.
With a straight through exhaust, this doesn't happen until high in the rpm range.
Don't get me wrong though, the best possible HP comes from a straight through exhaust. Although, this moves your torque curve higher along in the rpm, and in the process, you lose a fair amount of low end. And, you engine may not rev high enough to take advantage of this.
Well, I think the only thing physics will tell you is that air flows faster w/ no restrictions. ie: laminar flow.
Problem is, you are talking about an *engine* here, that is a little more complicated.
Engines require exhaust gasses to be scavenged from the cylinders properly.
At low rpm, this requires a certain backpressure to be accomplished.
With a straight through exhaust, this doesn't happen until high in the rpm range.
Don't get me wrong though, the best possible HP comes from a straight through exhaust. Although, this moves your torque curve higher along in the rpm, and in the process, you lose a fair amount of low end. And, you engine may not rev high enough to take advantage of this.
kah9911
New Member
I plan on have the full SLP exhaust- from LT to o/r X to Loudmouth. The way I am going to get the power curve pushed back down is with the cam. It may hurt my 1/4 but the 60' will be good. Also it will be more streetable. After all where do you spend more time?
Backpressure increases torque. 
.
However, adding, or removing pipelenght,
will have an affect on scavenging.
I suspect that people will sometimes compare:
a more or less stock arrangement, with a muff and
several feet of pipe ... to ... a cutout.
.
You're changing two things with the cutout.
.
However, adding, or removing pipelenght,
will have an affect on scavenging.
I suspect that people will sometimes compare:
a more or less stock arrangement, with a muff and
several feet of pipe ... to ... a cutout.
.
You're changing two things with the cutout.
You would think it is common knowledge:
Less backpressure = Less low end very little more top end
Normal back pressure = Good low/high end
More backpressure doesn't = More torque
No backpressure doesn't = More high end
It's all about balance.
Dual 2.25 pipes is more than enough for a N/A 4.6 under 400hp.
Less backpressure = Less low end very little more top end
Normal back pressure = Good low/high end
More backpressure doesn't = More torque
No backpressure doesn't = More high end
It's all about balance.
Dual 2.25 pipes is more than enough for a N/A 4.6 under 400hp.
WRXracer said:
0-60 mph times are everything if you are racing street light to street light. Also, if you lose too much on the low end, you will never make it up on the top end. In the quarter-mile, you are probably running 90-100 mph. 0-60 mph is an important part of the equation. Fortunately for me, most of my recent street races have been roll-ons, 50-100 mph. The high rpm power is great for this.
True to life example.
Took the mufflers off the other day and lined up against a guy I know. With just my dynomax mufflers we were dead even. Now that I don't have the mufflers he not only beat me off the line but I couldn't even keep up. The sound is great but the loss of power sucks. The gain is only when I get above 70 and that only helps with drag racing but not really that much.
I also noticed that the top of my 2nd gear is now 65 instead of 60. I'm know that has something to do with the straight pipes but I can't figure it out. Argue that it won't increase speed but I saw what I saw and I don't care what you think
Took the mufflers off the other day and lined up against a guy I know. With just my dynomax mufflers we were dead even. Now that I don't have the mufflers he not only beat me off the line but I couldn't even keep up. The sound is great but the loss of power sucks. The gain is only when I get above 70 and that only helps with drag racing but not really that much.
I also noticed that the top of my 2nd gear is now 65 instead of 60. I'm know that has something to do with the straight pipes but I can't figure it out. Argue that it won't increase speed but I saw what I saw and I don't care what you think
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