How does it feel and how much did it take off your et(for those who ran with and without the exhaust)??

Thanks!

 

A 3" exhaust gains are going to depend on how much boost pressure you are running. The less boost pressure, the more the wastegate is bleeding the exhaust gas/energy from the system. When this occurs there is less exhaust gas placed onto the turbine blade, and exited through the turbine housing. The less exhaust gas, the less backpressure built up inside of the exhaust system. Backpressure in a turbine housing is attributed to the exhaust gas going from very turbulent situation exiting the blades, and meeting a small diameter piping. The small piping limits how quickly the exhaust gas is allowed to turn to laminar, or smoother flowing. Back pressure builds up due to the smaller diameter of the piping, and causes a bottle neck after the turbine blade. This is the restriction that will make you loose horsepower since you cannot dispense the gases quick enough. The more boost pressure you run, the more you need a larger diameter exhaust. So to answer your question correctly, the amount of horsepower you'll gain is directly attributed to the boost pressure you are running. Gains from 5whp (lower boost levels) to 40-50whp (high boost levels) can be found depending on which size diameter piping you are upgrading from. The et's will drop corresponding to the horsepower increase.

 

What might the advantages of an exhaust that goes from 3" at the turbine and DP to 2.5" mid section to 2.25 rear miffler section? This would be for a turbo honda of course, maybe under 300 hp or so.

Turbo XS uses a similar tapering design i think it goes 4"-3"-2.5" That system gives a stock WRX 26 more WHP.

Does anyone know the theory behind this type of design? maybe reducing the back pressure immediatly at the turbine would have a better effect than tapering the exhaust the other way for example. It seems like you could make a pretty quite system that might have better gains than a system that stays the same smaller diameter all the way through (2.25" in my first example)

any ideas?

boosted hybrid - your idea about lower boost settings bleeding off and freeing the exhaust must be only with vent to atmosphere WGs, right? Any other type either internal or external closed loop, would just add gases back to the exhaust, or am I missing the point?

 

How about this one. I was thinking, just get the best of both worlds.

For me, I can only fit a 2 1/2 dp, so what about this setup:
2 1/2 dp
2 1/2 high flow cat
2 1/2 cat back leading to a 3" turbo muffler

I figure you may get the best of both worlds. Maintained tq and the gain of a little more hp. This is the type of thing that the Evo does with 2 1/4 up to a 2 1/2 muffler

Bad Idea ? Good Idea ??

Experts

 

The larger the exhaust system, the more power you'll make regardless. There really isnt any theory behind exhaust systems for FI applications. You just want to have the least amount of restriction. Any piping diameter is going to have a restriction associated with it. The largest diameter exhaust will make the most power. The reasoning behind the transistion on the exhaust systems may be packaging constraints, fitment issues, etc.

 

75hp difference on the dyno after unbolting the 3" exhaust right after the downpipe!
Of course this was on a fully built GSR with a PT70 T4 at 23psi.

The less back psi the better... end of conversation!

 

I don't have any numbers either, but going to a 3" exhaust will help out immensely. Almost zero power loss, but a lot of gain, no matter what your boost pressure is set at.

 

get it bout increase in hp with less resistance, but I thought, flame away if I'm wrong, that you want some resistance to keep your tq numbers up too?