How much hp would I loose for getting the 3" metal core cat compared to no cat?

 

How much HP do you have now? Unless it is a whole lot, probably nothing noticeable.

 

It depends. Probably a 3-7% loss in peak HP, less of a loss at lower powers as there's less flow so less total resistance.

 

Pat's on the right track, here's a good read from the EvolutionM forums: Test Pipe VS 130 cell MS high-flow cat - evolutionm.net

 

^ the chart in that link (good one) is an eye opener.

And the number of cells dictates flow and emissions effectiveness. It's a give and take.

 

however, he didn't build boost any sooner. Hmmmm...this changes plans for me significantly. Now I'm back to "jocking" the sheet-metal intake idea.

 

Probably about 5 - 10 hp. Those were the differences when we measured it on an MSM, but it was also a 2.75" CAT.
Stephanie

 

I wonder what the flow rating on the CAT in that graph was. As you can clearly see that CAT has no impact at all on power, untill you go beyond a certian exhaust flow and it starts to create meaningfull backpressure. If that exact CAT were used on a miata, most of us would never see a difference between it and a test pipe, because most of us are below 300whp. If you go beyond that the CAT is undersized and starts to impact performance, like it did in that test.

 

That is very interesting and great info to learn from. Cat's not a problem when tuned until it basically hits the wall in it's ability to flow. Would be interesting to see what happens with the 100 cell or going to a larger cat (4"?) in that evo's system.

I love that they call it a "stock" evo. Look at the mod list! It ain't stock. I'm not so impressed by the 360 hp with this list of mods.

WORKS throttle body
WORKS 76mm DP
WORKS 3in TB exhaust
Cosworth 272 IX cams
HKS exhaust adjustable cam gear
SAMCO IC hoses
Nisei LICP
Denso 720cc Injectors
GM solenoid
Perrin FMIC
Hyperforce System
RRE rally cat
GST SuperDuperDefcon5 open air filter
Titek tubular 02 housing
Ported stock exhaust manifold
Ported and coated hotside
ARP head studs
FP actuator
Stock evo 9 turbo (ported)

 

Bigger turbine's operate at lower delta P's, so any back pressure causes a larger change in work output to drive the compressor vs. a smaller turbine.

IE- a GT2554 might operate the high side of the exhaust at 30 PSI to run 15 PSI of boost to the intake manifold. Assume that's with an open down pipe. In this case if the cat causes 2 PSI of back pressure then the wastegate has to close a bit more, brining pre-turbine pressure up ~2 PSI higher to to ~32 PSI to keep the same delta P across the turbine. That's only about a 7% increase in back pressure pre-turbine though.

But say you're running a GT2876 or whatever you use and you're running 11 PSI of boost and making the same power/ same mass flow rate through the exhaust. Say your running 11 PSI of boost and 23 PSI pressure pre-turbine. If you add in a cat that has a 2 PSI pressure drop, it will add ~2 PSI to the pre-turbine pressure to maintain the original 23 PSI delta, which is ~ 9% increase in back pressure. If I had to guess, the the GT2554 setup will see less HP drop adding a cat then a larger turbo setup.

 

Well, I Went with the Reasonator Test Pipe.

I just got the the reasonator test pipe in today from enthuza! I can't wait to get home.

I bet it is going to sound sweet!

 

And I wonder how much difference a 200 cell version makes (even more restriction?) when the core is loose in the housing - such as in my case. I now fitted a test pipe and will re-dyno soon.

 

I pulled my "bullet" cat a year ago and went .3-leaner in open-loop. I don't know how big of a change that is in output, but it probably wasn't worth the money to make the pipe. It also got louder, but considering it's a track car I'm less likely to cook the cat with fuel.

 

I'm not leaner but fatter at idle at least. Prolly due to replacing the tired oem fp with a Walbo 255lph HP at the same time.