I'm basing my question on completely disregarding the turbo. hopefully some of you performance guys can chime in.

for the sake of this arguement, lets say the up-pipes are 1.5" in diameter, and the flow of exhaust gas at idle is "X" cfm. If at a point in that pipe, the diameter is constricted by 25%, so now the diameter is 1-1/8", what is the effect of backpressure on the motor? is "X" cfm now "X + 25%" cfm? does the motor have enough strength to overcome it? will the idle jump up any, if any to make a difference?

??????????

You listed 'X' CFM as the volume of exhaust flow... constriction will increase VELOCITY but will, overall, DECREASE VOLUME. X will be 'X - Ycfm' where Y CFM represents the volume exhaust, at idle, that a 25% constriction will cause to decrease.

Will the motor overcome that? Of course, but barring any weird science you will have a decrease in peak performance

That gives me a 20 year flash back to high school mathematics class..


So basically what you are asking is what effect would a moderate restriction of 25% of the pipes diameter have on engine performance?

more or less... YellerMax made some sense out of it.

You pretty much described running the up pipes into a T4 flange (or smaller). Food for thought.

Up pipes are actually 1.9something ID when they go into the T4 flange they are less, trust me.

Then you add the venturi effect into the equation, this is easily researchable to everyone and anyone in physics knows what it is. If you are running the exhaust gas through the standard 2'' tube up pipes and it goes into a 4'' downpipe the gas will excelerate in the turbine as it escapes into the less restrictive downpipe, this exceleration helps to drive the turbine wheel.

Increasing the size of the up pipes will help nothing, any increase in area pre-turbine will only increase the amount of time for the turbine so excelerate, in that this larger area will have to be filled and compressed to the same amount of pressure.

OK, I'll bite what is your reason for asking /wanting to know?

now that's the stuff. would you say that increasing the velocity of the exhaust gasses through the up pipes, while losing some volume would spin the turbine faster?


"OK, I'll bite what is your reason for asking /wanting to know?" i'll get to that soon.

A more basic way to say what I was getting at above....you want the exhaust housing to be the restriction in the system (nothing before or after), this will cause the gas to expand/excelerate in the housing.

So this means you want a consistant size of feed ALL the way to the turbine, then after the turbine, the bigger the better to allow rapid gas expansion and cooling. The cooling will further excelerate the process.

No, your volume is constant, pressure is the variable. 90% of volume is decided by the engines displacement/speed the other 10% is amount of fuel.