Backpressure in exhaust (how to add and remove)
Discussion
Ive seen dyno charts testing factory exhaust vs free flowing or chambered aftermarket exhaust. The difference is usually 3000 rpm and down the backpressure adds HP but after 4000 the free flowing just takes off and backpressure stays steady in gaining HP.
has anyone ever made an aftermarket muffler that changes flow given a certain rpm or vacuum ? quiet when you just drive but free flowing when you are wot or above a certain load
Yea I've seen some car manufacturers have something like that and I've had Motorcycles with the flap in the exhaust that opens at like 6-8k and adds a lot to the bottom end. I took it off when I did a muffler on my 600 and could tell a difference
But was thinking more like a flowmaster
But was thinking more like a flowmaster
^^ yes with intakes the same theory applys.
That the free flowing intake doesn't have the velocity down low but up top it can move much more air. Factory intake versus a FAST 102, HP down low will drop but up top will gain an unreal amount.
So how can you get the best of both worlds? Besides getting an intake not to big or not to small... There's still meat on the bones up top and down low that way
That the free flowing intake doesn't have the velocity down low but up top it can move much more air. Factory intake versus a FAST 102, HP down low will drop but up top will gain an unreal amount.
So how can you get the best of both worlds? Besides getting an intake not to big or not to small... There's still meat on the bones up top and down low that way
Jhonno said:
You never want back pressure on a 4 stroke.. It is a complete misconception. Try dynoing or driving an car with a partially blocked exhaust..
What it is is gas speed.. A smaller diameter exhaust will have a higher gas speed at lower rpm, boosting the low end by increasing scavenging at that point. However, at the top end it might then be restrictive due to the fact it can't flow enough volume. This is where back pressure comes from. You don't want it, but it is a side effect of a smaller flowing exhaust which helps the bottom end.
The perfect exhaust would have high gas speeds, and no back pressure, however with many things engine flow related it is a compromise..
How can you mathmatically find the perfect balance?What it is is gas speed.. A smaller diameter exhaust will have a higher gas speed at lower rpm, boosting the low end by increasing scavenging at that point. However, at the top end it might then be restrictive due to the fact it can't flow enough volume. This is where back pressure comes from. You don't want it, but it is a side effect of a smaller flowing exhaust which helps the bottom end.
The perfect exhaust would have high gas speeds, and no back pressure, however with many things engine flow related it is a compromise..
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff