kayvan_pour

I have some questions about exhaust flow, mine in particular. For now while I'm still N/A and am runing the T1r 63mm (2.5 in) exhaust. I'm planning on getting some headers thats outlet will be 63mm also. But the thing is my test pipe right now is only a 2.36inch inlet which is smaller than my 63mm exhaust. So I think this may be effecting exhaust flow and my performance. So wouldn't it be wise to get a test pipe thats 63mm also? But some times I wonder if I have little changes in the diameter if that will help flow? Like I know with aem v2 intake they have different sized diameters to get better flow, will this idea work with the exhaust also? So is a pure 63mm exhaust the best set up for now, or is it cool to have different diameters in the piping? Your thoughts would be great, I know exhaust design is extremely important for the s2k so any insight is welcome ...


Wanted to also know if the t1r test pipe is a 63mm piece and which test pipes are a 63mm piece...

04RioS2k

This one is 63mm 2.5 inch and really popular with alot of people.....

https://www.s2ki.com/forums/index.php?showtopic=321104

04RioS2k

also I believe same diameter would help with an exhaust as you have a little bottleneck effect going on with the testpipe which probably hinders the exhaust flow a little bit....

kayvan_pour

Thats what I thought... Thanks for the info


And body else have any thoughts?

S2kracka

First off, the AEM V2 does not have a drastic change in diameter, look inside the pipe and you'll see its a slow taper.

You'll want the same diameter testpipe as your catback so the 63mm T1R would be a good choice.

DrunkNmunky

I would agree that you would probably find yourself with a "bottleneck". Although the change in diameter is very slight, I think it would still effect flow.

SlidinS2k

You want the testpipe to be the same diameter as exhaust for the smoothest flow...I'm running the Berk Tech. testpipe, great piece and still no cel after 3000 miles.

mr. clockwork

The only cases where an increase of piping diameter can give an increase in power is when you need to increase airflow. The increase in diameter, like what is found in the V2 intake or the J's intake causes a vacuum as the air expands when it enters the piping, causing an increase in suction at the mouth of the pipe. the same thing is found in dirtbike pipes where exhaust velocity is important to help the motor breathe more.

In our exhausts, we don't rely on vacuum clear exhaust gases. Increasing exhaust velocity through consistent piping will increase the vacuum effect further down the chain...i.e. on the intake side where it is the most important. Now, if you could make an exhaust header which was something like what is found on a dirtbike pipe, that could potentially yield some power gains. Since that isn't really feasable, changing the piping diameter further down the pipe wouldn't be effective. This is why headers are made with longer primaries to increase power as they increase exhaust velocity the most. That is the most that we can do.

Race Miata

I would sell the 2.36" test pipe and get a 63mm to match the rest of the system. Narrower diameter is one thing, the actual transition going into the smaller test pipe could be a bigger problem.

Race Miata

Dirtbike is a different scenario. They run a 2-stroke engine which doesn't have exhaust valves to control timing precisely. Instead, the exhaust ports are open much longer duration while the pistons move down to expose the ports. Expansion chamber in the 2-stroke exhaust system is REQUIRED to scavenge exhaust gas or else intake/exhaust gas can easily flow in the non-designated direction.

For intake system, relatively narrow piping increases velocity and thus torque but the CHANGE of velocity also increases on varying throttle opening which means that throttle response can be adversely affected. The solution is to run the narrow pipe further upstream for torque and a big air chamber further downstream to supply enough air for quick throttle change.

The OP is not talking about expanding exhaust diameter further downstream of header. He's talking about a test pipe narrower than the header and catback.