Why doesn't dual cat exhaust flow better?
 

I have a single turbo tuned with a hi-flow cat that put out 325rwhp. With the cat removed I got about 360rwhp. I want to keep some cats in to keep me sort-of enviro friendly. So I made this- http://home.earthlink.net/~taspargo Problem is it seems to flow worse than a single hi-flow cat.

I know the splitting suddenly into 2 3" pipes from 1 3" pipe isn't the best. I figured even if it flows 1.5x a single cat at the same backpressure I'll be set. Also it seems like the area where the two pipes join back together is more important and I thought I did an ok job there.

Any ideas on why it don't work?

You don't need to tell me the welding looks ugly; this is the first welding project I've done! ;)

air flow likes to take the most direct freeflowing route possible....u have a pretty sharp bend in there...plus air now has to flow thru 2 cats

no cats is better than on3 :D

double post

Two cats in PARALLEL. That should be better than one. Should be....

Low velocity from two huge pipes?

I have always been curious about making a twin midpipe with smaller diameter pipes (2.25" or something like that) and have one opened/closed by an electric cut-out valve operated by an RPM switch. I am curious about this for two reasons. One, you could arrange a muffler (2 in, one out OR a single muffler on the always-open pipe) to make the car quieter at idle and low RPM cruising. And two, that you might get some additional torque from the higher velocity at low flow levels. I am not really sure if the torque thing would pan out or not, but I'd like to try. I figure you could dyno with the second pipe closed and then do a run with it open, and set the RPM switch the open the secondary pipe at the point that the two curves cross (if that is indeed what happens).

I figure if I mention that enough someone might try it.

-Max

Yeah, instead of splitting into 2 3" pipes using 2 1/2" or 2 1/4" pipes might have been better. Thing is, once you get into the cats the cross section gets even bigger and slows it down more, so I figured the big increase in cross section is going to happen anyways....

Your idea sounds pretty cool, but I'll let someone who knows what they're doing take up the challenge.

Even with the 3" pipes though, it seems like it should still be somewhat better than a single cat.

Does anyone know what effect a dual path exhaust has on a turbo rotary? I'm thinking one that splits to two pipes somewhere close to where the downpipe attachs to the turbine and exits through two mufflers.

I've wondered about a dual exhaust on the FD ever since seeing the Japanesse downpipes that split into two pipes but those DP's are like $700 and $800.

On normally aspirated longer primaries increase top end but I've never heard anything about dual path on a turbo rotary. I recall old Cartech turbo systems for the first gens having a dual exhaust with two seperate muflers but I never saw where it split from one to two pipes.

My butt dyno sure did notice an increase in top end pull when changing from Racing Beat single exhaust system to dual path on my old street ported, NA 12A. This joined the two primaries just before the muffler entrance.

Jack

Jack,

I don't think the dual pipe would have the same effect for the stock turbos (that join the exhaust paths both in the manifold before the turbos and after) as it would on an NA. The same is true for singles since they join the exhaust paths for the turbo and usually for the wastgate piping. You could have two completely separate aftermarket twins, each with their own wastegate and turbo to keep them separate, but I am not sure that would have the same effect as it does on an NA, either.

-Max