Hi-Flo cat vs. no cat?
04-09-2007, 11:19 AM
#2
Rennlist Member
...the hi-flow will still not flow as much as no cat at all...
Was that what you were looking for? You'll need the cat for emissions; when I do my exhaust I plan on eliminating the cat w/ a straight pipe and then bolting the cat back in for emissions.
Was that what you were looking for? You'll need the cat for emissions; when I do my exhaust I plan on eliminating the cat w/ a straight pipe and then bolting the cat back in for emissions.
04-09-2007, 11:21 AM
#3
Captain Obvious
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my car is exempt from emissions due to age where I live... 
any hp gains without a cat? or just nicer sound?
for an S I'm asking...
any hp gains without a cat? or just nicer sound?
for an S I'm asking...
04-09-2007, 11:26 AM
#4
Rennlist Member
Well hell, if you're exempt from emissions, go w/ the straight pipe. The cat will certainly do you no good.
As for gains, you might feel something; maybe not. Coupled w/ a high-flow exhaust/muffler you'll feel a bit more (as well as hear a bit more).
Also, the cat doesn't really change the sound of the exhaust; it might make it a bit quieter.
As for gains, you might feel something; maybe not. Coupled w/ a high-flow exhaust/muffler you'll feel a bit more (as well as hear a bit more).
Also, the cat doesn't really change the sound of the exhaust; it might make it a bit quieter.
04-09-2007, 11:32 AM
#5
Originally Posted by ausgeflippt951
Well hell, if you're exempt from emissions, go w/ the straight pipe. The cat will certainly do you no good.
As for gains, you might feel something; maybe not. Coupled w/ a high-flow exhaust/muffler you'll feel a bit more (as well as hear a bit more).
Also, the cat doesn't really change the sound of the exhaust; it might make it a bit quieter.
As for gains, you might feel something; maybe not. Coupled w/ a high-flow exhaust/muffler you'll feel a bit more (as well as hear a bit more).
Also, the cat doesn't really change the sound of the exhaust; it might make it a bit quieter.
IPSC
04-09-2007, 11:45 AM
#6
Rennlist Member
I have an SFR weld-in racing cat for sale with only 500 miles on it if you are interested. $150+shipping. I got it off of a parts car, so unfortunately I can't give you any feedback as the to the performance gains per your original request.
04-09-2007, 12:19 PM
#7
Race Director
The 8v NA cars seem to gain about 10 hp when remove the stock original cat and replace with a test pipe. Not sure how much of that is an old cat vs simply not running one. These numbers seem consistant based on dyno results.
I have no data for 16valve cars.
I have no data for 16valve cars.
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04-09-2007, 12:22 PM
#8
Captain Obvious
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Thanks Joe...that was my thought @ 10 hp....I would think the 16 valve should have similar gains to that of an 8V.
Dyno results would be nice to have from anyone who has run without a cat on a 16V.
Dyno results would be nice to have from anyone who has run without a cat on a 16V.
04-09-2007, 02:12 PM
#10
Rennlist Member
You will notice a LOT more sound with no cat. I have a Bosal Brospeed muffler on my car and it was pretty quiet with the cat, but once I put in the test pipe it got a lot louder. Sounds great though.
04-09-2007, 03:31 PM
#11
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Magnaflow makes the Carsound brand high-flow cats, which can be had for as little as $55 new... they are emissions legal and low restriction. It's worth considering, especially since it can be hard to find an exhaust shop who will remove a cat entirely.
04-09-2007, 05:14 PM
#12
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Originally Posted by harrisonrick
Thanks Joe...that was my thought @ 10 hp....I would think the 16 valve should have similar gains to that of an 8V.
Dyno results would be nice to have from anyone who has run without a cat on a 16V.
Dyno results would be nice to have from anyone who has run without a cat on a 16V.
You'll probably lose some low-end snap off the line by going with a straight-pipe, but it will be made up in the upper rpms.
For a daily driver though, you're better off going with a hi-flow catalytic converter. You'll retain your better off idle performance, and still get the upper rpm benefit.
04-09-2007, 05:23 PM
#13
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DON'T DELETE THE CAT ON AN S!!!! You will lose power. Your exhaust's flow velocity will DECREASE. Thisis coming from true dyno tests with AND without a cat.
Buy Skip Wolfe's SFR high flow cat... It is the best High Flow Cat on the market IMHO. It put's just enough restriction in your exhaust to make low end power. I made 15WHP, 11WTQ ACROSS THE BOARD with my exhaust that included an SFR high flow cat.
Buy Skip Wolfe's SFR high flow cat... It is the best High Flow Cat on the market IMHO. It put's just enough restriction in your exhaust to make low end power. I made 15WHP, 11WTQ ACROSS THE BOARD with my exhaust that included an SFR high flow cat.
04-09-2007, 05:29 PM
#14
Race Director
Originally Posted by 82-T/A
You'll probably lose some low-end snap off the line by going with a straight-pipe, but it will be made up in the upper rpms.
For a daily driver though, you're better off going with a hi-flow catalytic converter. You'll retain your better off idle performance, and still get the upper rpm benefit.
For a daily driver though, you're better off going with a hi-flow catalytic converter. You'll retain your better off idle performance, and still get the upper rpm benefit.
I cannot comment on any performance impact of a test pipe below 3000 RPM. I just never run my track only 944 in that rev band. Heck even cool down laps are 3000 to 4500 rpm range.
While I have not see the the back to back dynos first hand just about every 944 spec car picked up hp by deleting the cat and my car was not exception when I removed mine many years ago although I do not have the dyno chart to prove it. ( I have two charts at 131 hp and 134 hp with a test pipe). Most stock street 944's pump out 123 is whp. Spec race cars are in the 130-135 whp range and the biggest mod is removing the cat. Off the shelf Chips and headers don't yeild much gains most of that HP is from the deleted CAT.
Again this applys to 8 valve cars. I have no experience on the 16 valve cars.
04-09-2007, 05:56 PM
#15
Rennlist Member
Actually, you both have points: deleting the cat WILL get you a gain in hp. However, it WILL give you a decrease in torque.
Think of a hi-flow cat like a smaller-diameter pipe. In order to push as much air thru the smaller surface area, the air must travel faster. The effect felt by this is torque. Thus, eliminating the cat will enlarge the effective surface area, thus decreasing air velocity, and consequently making more horsepower.
For our 600cc formula car we deported the head to see better torque gains. HP decrease was on a couple lost at 13.5k.
Think of a hi-flow cat like a smaller-diameter pipe. In order to push as much air thru the smaller surface area, the air must travel faster. The effect felt by this is torque. Thus, eliminating the cat will enlarge the effective surface area, thus decreasing air velocity, and consequently making more horsepower.
For our 600cc formula car we deported the head to see better torque gains. HP decrease was on a couple lost at 13.5k.