Getting HP from an exhaust?
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Originally Posted by Sol
My downpipe/cat/ubend combo probably yielded me 10 to 15 HP.
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Well I just picked up my front ported manifold. Hopefully gonna bolt it on tommorow. Only cost me $40, its my first step. Next will be headers. After a cam that is
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#14
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Originally Posted by BonneMeMN
Backpressure is the amount of restriction in an exhaust. Backpressure doesn't make more torque. Backpressure can only make the gasses exiting the combustion chamber stay there more then not.
Scavenging, or the Scavenging effect, is how a good exhaust system or header design gives the engine more power. Performance exhaust is all about getting the exhaust gasses out from the combustion chamber as quick as possible. The exhaust pipe has VERY little effect on this. All engines benefit from this, highly tuned ones get A LOT.
Header design is the most important part of power in an exaust system. The key to the most power is getting it to exit fast. That usually means keeping it as fast as possible while giving ample room for al the gasses (diamter). The biggest constraint is the collector design, and length of the collector. As long as possible, while having very narow angles between primaries, and flow benched joints.
The exhaust diameter is the same, as long as you can get the air out as quick as possible, it doesn't matter what size it is, but if you make the diameter 3x the size of your collector, what'* the point?
Scavenging, or the Scavenging effect, is how a good exhaust system or header design gives the engine more power. Performance exhaust is all about getting the exhaust gasses out from the combustion chamber as quick as possible. The exhaust pipe has VERY little effect on this. All engines benefit from this, highly tuned ones get A LOT.
Header design is the most important part of power in an exaust system. The key to the most power is getting it to exit fast. That usually means keeping it as fast as possible while giving ample room for al the gasses (diamter). The biggest constraint is the collector design, and length of the collector. As long as possible, while having very narow angles between primaries, and flow benched joints.
The exhaust diameter is the same, as long as you can get the air out as quick as possible, it doesn't matter what size it is, but if you make the diameter 3x the size of your collector, what'* the point?
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If anyone wants to know what a good exhaust is, click the link in Rogue'* signature for his Mod List. He'* the second fastest Bonneville here, and hasn't made major changes. Please note that he'* also running a catalytic converter
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Originally Posted by BonneMeMN
Too add confusion to this place, here'* my opinions.
Go to the local strip. Are they out there bolting pipes up or taking them off?
Go to the local strip. Are they out there bolting pipes up or taking them off?
If your only concern is the quickest WOT run you can do...then go for open headers. If you have any interest in part throttle response you're going to want exhaust pipes.
Originally Posted by BonneMeMN
Backpressure is the amount of restriction in an exhaust. Backpressure doesn't make more torque. Backpressure can only make the gasses exiting the combustion chamber stay there more then not.
Scavenging, or the Scavenging effect, is how a good exhaust system or header design gives the engine more power. Performance exhaust is all about getting the exhaust gasses out from the combustion chamber as quick as possible. The exhaust pipe has VERY little effect on this. All engines benefit from this, highly tuned ones get A LOT.
Scavenging, or the Scavenging effect, is how a good exhaust system or header design gives the engine more power. Performance exhaust is all about getting the exhaust gasses out from the combustion chamber as quick as possible. The exhaust pipe has VERY little effect on this. All engines benefit from this, highly tuned ones get A LOT.
If you have backpressure as the result of a restiction (GP U-bend for example) it'* not going to help you at all...it will hurt you.
By maintaining the highest possible velocity, and therefore having slight backpressure (1 to 1.5 psi), then we would have an exhaust pulse with a median velocity at its centre, a higher velocity on the leading edge and a slower velocity at the trailing edge. The lower velocity at the trailing edge will help draw the next exhaust pulse down the pipe...or scavenge.
Originally Posted by BonneMeMN
Header design is the most important part of power in an exaust system. The key to the most power is getting it to exit fast. That usually means keeping it as fast as possible while giving ample room for al the gasses (diamter). The biggest constraint is the collector design, and length of the collector. As long as possible, while having very narow angles between primaries, and flow benched joints.
The longer your collector, in general and assuming a reasonably sized piep, the more your power band will be skewed towards low rpm power and conversly the shorter the collector the higher in the rpm range will be the peak exhaust efficiency.
Originally Posted by BonneMeMN
The exhaust diameter is the same, as long as you can get the air out as quick as possible, it doesn't matter what size it is, but if you make the diameter 3x the size of your collector, what'* the point?
While at the track with open headers, you'll loose a bit in the lower rpms versus a closed exhaust (assuming it'* reasonably well sized) but you'll more than make that up in the higher rpm range.
For those that have driven their cars to the exhaust shop with open headers will surely know how unresponsive the car is on the street in that configuration.
My $0.02...
Cheers,
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Good points Foghorn, you are correct, the tricky parts of exhaust theory are heat and expansion issues.
Rogue has headers, they're pretty, and very complex.
and a high flow cat. Both are for high flow, meaning his mufflers are the highest restriction, however he wants a quiet sleeper.
Rogue has headers, they're pretty, and very complex.
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All of the exhaust theories are true, but we do have to remember that we need more power in order to benefit from running open headers. Cutouts are an effective way of running open headers on the track.
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