Any examples of with and without power runs? Just wondering. At some point I'm going to flange the back side of my cat so I can swap it out and get an actual number, along with checking a muffler vs. a straight pipe.

 

hmm at a 15 psi car with decent size turbo probably 30 whp given you adjust the fuel and timming. given 8 psi maybe 15 whp. Seems like a fun thing to try though.

 

It all depends, has it been de-clawed?

 

hey rob, I plan to pull my cat at some point so i can flange (v-band) a new one in. I can probably whip up a test pipe and see what difference it makes if you want.

want = buy me another pair of v-band flanges so I dont have to shell out for them.

 

nice....:gay:

but good question, i have no clue, magna's numbers sound a bit too high for me, it would be awesome if someone made an actual comparo...i think a lot of people would benefit from that knowledge...i myself am going cat less without even knowing what my power gains will be

 

the next time i dyno will be with no cat.

the next time after that will most liekly be with a cat. if you can wait 6 months ill let you know.

 

Not terribly direct, but my test pipe power run made 255 whp. My with cat power run made 233 whp. BUT I also changed intercoolers AND only made 11 psi to redline. With the test pipe it held 13 psi to redline. And the two runs were months apart. They were on the same dyno, but with different operators.

There is also a small loss of spool/response at positive pressure transition with the cat. I liked the test pipe response, but also like how the cat makes the exhaust not stink.

 

still a big gain over small changes, but IMO the response is just as important

 

This isn't a direct data point for Miatas but it is interesting. When I gutted the cat on my Talon I went from being able to make 0psi at the line to 10psi at the line.

 

I don't have any power charts to compare, but I will say that when I had the cat on, I'd only be hitting 57 mph at the top of second gear. In the same run with my test pipe on, I now hit 63 mph.

 

Uh RTN top o 2nd is gear limited not hp per the same rpm you will always hit the same speed. unless the tire goes flat etc. now if you are talking about over a certian distance then that is relavent to the hp in question

 

So the cat came with a new rear diff ratio too?

 

didnt yours?

 

I know mine did, torsen too. (picked it up yesterday)

 

IDK... That was what I noticed before I installed the test pipe. I purposefully did a test run before and after I swapped everything out. I made sure I shifted at the same point, and that's what I came out with. I'm not trying to argue with what y'all are saying, but that's what I got. However, I didn't even think about it from a gear mindset and seeing how it wouldn't make sense. If I had, I would have tried things over again to see if I did something different. I'm not too savvy yet on gearing, so it doesn't click in my mind real fast.

 

all you had to do was say you hit a higher mph before you had to hit the brakes to avoid driving off the edge of the cliff Of course better brakes would've achieved the same.

I just brought it up because if the difference is big, then it could be an "apples to apples" issue when comparing dyno runs across turbo setups. I'm set on testing it and the muff because I really want to see just how much of a choke these things put on the turbo.

Way back I swapped to what I thought would be a more restrictive cheapie turbo style muffler and got datalogs that showed a 200rpm+ quicker spool across the board over the "flowmaster" that was on the car. Looking at a cutaway of both muffs you wouldn't think the turbo muff would flow better, but me thinks those flat panels do bad thinks to exhaust flow on a turbo setup (as someone mentioned in that thread.)

 

well you gotta remember, if you reach a choked condition before the cat, removing the cat and all that **** wont increase flow or power. I dont think thats the case so do it.

 

I'm sure there's some choking due to my crap OE internal gate dumping through the 2.5" internal gate exit. After that it's 3" all the way. The external gate will come after the next dyno round. I think the more setups we get, the more interesting it will be to see how things differ.

 

acutally i forgot. ive done this before.

ive dynoed twice at the same boost level before.

first time ever, making 173rwp. second time with the begi manifold and dp and no cat making 171rwhp. the plots are almost identical with a bit less torque with the begi setup as i was too rich.

i suspect i need an exhaust that actually flows good and then try again. oh, interesting i just ordered a 3" exhaust and test pipe :gay:

 

well its adding resistance to the flow. It would be choked if flowrate couldnt increase, and I dont think we hit that condition ever