Just curious if anyone north of 500 whp has any type of high flow cat on their car?. If so what is the performance loss . My car is 3.5 in to 3 in cat back two magnaflows. It sounds good a little loud but not to bad. Is it possible to make big power and have exhaust that does not stink up the whole house. Any one have any experience w this w dyno numbers to prove a loss or gain. Or loss of spool time.

Thanks

John

 

A high HP setup would burn a cat out pretty quick.

 

Quick as in 500 miles or 10000.??? I only drive my car on nice days and only short burst of boosting .lots of cops everywhere where I live.

 

I have a few customers with both the rx7 store and bonez high flow cats in the 400-420 wheel hp range. Beyond that they seem to become a restriction and blow out. A good tune with proper cruising afrs will make a big difference.

 

Thanks for the reply. My car on high boost is at 500 whp so that may be a bad option. Most of the time im on low boost 15 psi guesing its around 4_ 420 whp.

 

i think it would take some research and a lot of tuning time, but Chrysler sells a 700hp car with a cat, and GM sells a 640hp car with a cat, so big power with a cat is possible. i would imagine it would need a pair of cats. i'd also put an EGT probe in the cat to watch temps, and then tune accordingly.

 

+1

 

Just so we are comparing apples, those vehicles are running Cats on separate banks. So effectively it's really half the flow as one would have in a single pipe. Not saying it's impossible. There are emissions compliant exotics that push big power. No clue if what they are using are off the shelf parts or something unique and proprietary. I was considering the same thing so the fumes were not such an issue in the car.

 

This might work. Claims it supports 500-850hp and comes in 3, 3.5 and 4". Melting point of 2800 degrees F.
Vibrant Performance ::.

 

i would use a cut out to by pass it under boost...?

 

It's not so much a Horsepower thing that kills cats. It's a mixture issue.

Most people are running down around 10.5:1 or lower. this sends loads of unburned fuel, and CO to the cat. This drives the heat way up and either melts or breaks down the substrate.

Like Ihor said, If you tune it to run close to stoichiometric at cruise and not too rich at lower boost levels You may get by for a while. But if your on it hard all the time, don't expect it to last.

 

What miles may be involved per each scenario? I'm done with the odor issue also.

 

I would be concerned it could lean it out even more and want to be sure to check my tune between running it thru the cat and the cut out. Other than noise I don't see a huge issue running a cut out if it's a dual purpose car. Prob help prolong the life of the cat. An unmuffled rotary is too damn loud for most sane humans.

 

oh i meant just a cut out to bypass the cat and feed backin to the mufflers.. which would require two cut outs per cat to prevent back flow.

 

I dont have any cats on my car.
I recently let it run inside with the doors closed at idle while trying to find a bad hvac blend door motor( low heat output)...
i thought it had died as there was no smell.. no fumes burning the eyes.. checked thru a few things.. turns out my mixture finally found the sweet spot. i wish i could tell you exactly what AFR is it but i have an leak and i beleive the reading to be skewed at idle, i see 13s and 14s. on the guage. i had been fiddling with my idle mixture for weeks after breaking the idle stop screw off and having fabbed a new one up.

my point is your tune getting fixed will help alot more then you think! so much you may not even need cats.
i really couldn't tell my car had been running, for over 30 minutes, inside doors closed in a small 3 car garage...( i left and went inside)

 

Arghx has posted some info on emissions and cats before, and he's really one of the most knowledgeable people on the subject, but i'll put my $2 in. i DO live in CA, and i have had to smog every car i've every owned since the mid 90's... so i know my way around the emissions system.

anyways, its a multi faceted problem. we can break it down into parts.

the first issue is flow, we need to make sure the cat isn't a restriction. second we need to make sure there is enough cat. the stock FD main cat is relatively gigantic, if you just look at the core and compare the Mazda cat to the aftermarket, the Mazda is larger than basically anything you can get, closest used to be for a 7.4L Ford truck.

the next thing is that the rotary exhaust as it exits the port is supersonic, which is why cats tend to live short lives. its like hitting them with a hammer.

the next is the mixture, the cat works best when the mixture is hovering around 14.7:1, the cat actually wants to see a little mixture variation. this is relatively simple, most of us are cruising around there anyways, you'd just need to fine tune it a bit.

the next issue is heat, the cat only works from ~450c-650c. 450c isn't a problem, but 650c is. if you looked you'd find all the OEM's, run really rich up top to try and keep cat temps under control. if you put an EGT probe on a stock rotary Mazda you'd find the EGT doesn't go over 700c coming out of the engine.

i propose to run a pair of cats, as this should give you plenty of cat material, and flow enough. it was also Mazda's choice for the JC cosmo. the rest is tuning.

so there are hurdles, but its a solvable problem.

 

You may wanna try this. Here's the mid section from my NA 20b. Right side is the front with the valve in the back. With the valve closed in the back, the exhaust flow is redirected through the cat. The valve is in the back for two reasons. 1. It creates a pressure wave in front of the valve to redirect the exhaust flow to quiet the pulses. 2. It also keeps the direct heat off the valve so it doesn't get damaged. I'm running a 3" Race Ready valve. My 1st design was a failure and this is the design that works reliably. Behind the valve is a turbo vacuum control actuator from the fd. My engine re-uses the front vacuum chamber w/check valve from the fd and my Haltech to control the solenoid. With my NA setup, I'm running rpm activation at 3,500 rpms. This keeps my engine nice and quiet for around town driving. I also used my fog light switch to ground the solenoid to have instant open. NA rotary's with open exhaust are some of the loudest engines on the planet. Not mine! When built this way the aftermarket cat doesn't take the full abuse of a full load/high exhaust heat run because it's being bypassed in the upper rpms. I also like my exhaust exiting the rear muffler as dumping to ground underneath the vehicle is annoyingly LOUD, and dangerous since our engines shoot flames. You may not believe this but I also built just a pure large straight Hi flow cat section and my bypass set-up is quieter than the pure cat. The re-direction really makes a HUGE difference in noise. Mine is off my car for now since I have to rebuild it to make room for the T56 I'm putting in.

You could build something similar and use load/rpm threshold activation to open your valve if your using something other than a PFC. Example 2,000rpms activation threshold and 40% load opens the valve. If you track the car, you could do like I did and use a bypass switch to go full open. As far as tuning, I would tune the set-up with the valve full open. This way when it's closed in the lower rpms, your A/F naturally goes richer from the back pressure.

 

i like that!

 

That dual purpose exhaust looks like good idea. Is there a hesitation or a point where u can notice the valve switch ing over? As far as the tune my car has a microtech and with e85 it will idle between 11.8 _ 12.4. Pump gas 12.8. Any thing leaner and its not happy. 720cc primary injectors
I guess there is only one way to find out. Put one on and do some tuning and compare before and after. It may b a route I go in the future for a street car

 

^No hesitation but you do feel I difference in power. I like my exhaust nice and OEM like and can't stand drone.

 

needs more negitive split at idle. maybe

 

this is why Mazda used an air pump. they could then tune the engine so it ran the best (no lean misfires), and the cat sees a mixture its happy with.

 

ive been running a high flow 3" cat with 300whp at 10psi for a few years now with no problems.. post-turbo egts rarely get above 1250F, but definately near the upper temp limit j9fd3s posted during cruise

 

Not sure I can do neg split w microtech
The trailing map is 0~15 .

Would cat placement make a difference?
What if two 3.5 in cats after the y in the pipe beffore the muffler s . It would not be as hot as the post turbo factory location in downpipe.
I