Do high performance cat converters really rob any power?
- Thread starter 5.0LOfFun
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I would not think that high powered cats would rob you of any additional hp gains. In fact, most any vehicle requires at least some backpressure for the engine to run at optimum. High powered cats are on the cusp of "lot's of free flow with just enough back pressure......................"
I wouldn't be surprised if you found a catted car ran better than one equiped with un-catted pipes.
I wouldn't be surprised if you found a catted car ran better than one equiped with un-catted pipes.
crazypete
All my crevices are greased.
How much of a restriction are the stock 4-cats anyway? Does it make any sense to upgrade other parts of the exhuast and leave the 4-cats in place?
Here's what I understand. The Mustang came with 4 cats. If an emissions cop knows this and looks under the car and sees only 2, they fail you on the visual even though 95% of the time you'd actually pass the smog test on just 2.
He said he had long-tubes. Well with long tubes the cats don't get hot enough for them to work properly so you may fail with just 2 cats, however, would pass (I'd think) with the stock 4.
Now if he's got long tubes, and a high degree cam in the car, he needs to be running no more than 2 cats as a stock 4 could harm his engine as the exhaust is not able to leave the engine fast enough for the amount that is being generated in the combustion chamber.
So, in the first case he'd probably fail emissions as his HC's are too high as too much raw fuel is not getting burned properly and in the second case I believe his HC's would be fine BUT his NO's would be too high.
If his state has no emissions testing, I'd say go with the long tubes and 2 high flow cats.
He said he had long-tubes. Well with long tubes the cats don't get hot enough for them to work properly so you may fail with just 2 cats, however, would pass (I'd think) with the stock 4.
Now if he's got long tubes, and a high degree cam in the car, he needs to be running no more than 2 cats as a stock 4 could harm his engine as the exhaust is not able to leave the engine fast enough for the amount that is being generated in the combustion chamber.
So, in the first case he'd probably fail emissions as his HC's are too high as too much raw fuel is not getting burned properly and in the second case I believe his HC's would be fine BUT his NO's would be too high.
If his state has no emissions testing, I'd say go with the long tubes and 2 high flow cats.
crazypete
All my crevices are greased.
Hmm, lets say the car came with 4 cats. Would having 4 different cats make it legal....like chopping up your factory pipe and rearranging it and sticking a pair into the muffler inlet pipes lets say or does it have to be bone stock pipes and location?
From what I've been told it's more based on the year. So not all cars had 4 Cats but they all had cats 2,4 doesn't matter as long as they are there and working. Not to mention I did much better on my test with the high flow then with the 4 ....I found that strange and the mechanic said the newer ones are far more advanced then they older ones, emissions and performance wise!...I thought they were all the same?
My understanding is that having hi-flow cats works to GIVE power by reducing restrictive backpressure. Although yes, you do need some, from all I have read, a straight thru setup with free-flowing mufflers has enough to let it run well but reduces it enough to free up power.
The stock 4 cat setup is HEAVY, ultra restrictive, and probably rusted if you haven't kept the car in the garage since it was new. Replacing them with X/H pipes with hi-flow cats (generally only two in these setups) you will free up power (and potential power when future mods added), not to mention get a killer sound.
There are still others who say no-cats..."off road" x/h pipes are the way to go.
I'm sure there are dyno results out there, but short of comparing them all, I would say it is personal preference.
The stock 4 cat setup is HEAVY, ultra restrictive, and probably rusted if you haven't kept the car in the garage since it was new. Replacing them with X/H pipes with hi-flow cats (generally only two in these setups) you will free up power (and potential power when future mods added), not to mention get a killer sound.
There are still others who say no-cats..."off road" x/h pipes are the way to go.
I'm sure there are dyno results out there, but short of comparing them all, I would say it is personal preference.
my car...
Stock 5.0, 76MAM, 1-5/8" LT's and 2chmbr flows.
brand new out of the box hi-flow cats on an H pipe robbed exactly 8hp and -i forget- tq at peak over off road H pipe.
average power was down too, but I don't have dyno sheets in front of me.
Stock 5.0, 76MAM, 1-5/8" LT's and 2chmbr flows.
brand new out of the box hi-flow cats on an H pipe robbed exactly 8hp and -i forget- tq at peak over off road H pipe.
average power was down too, but I don't have dyno sheets in front of me.
I would generally think that with cats on the car, it would rob some power. There is still enough back pressure without any cats, adding more only robs power. However, i dont think its a huge amount of power and if it gives you piece of mind knowing they are there, go for it. I'm going to find some heat shields and just weld those in place this spring since i only have to pass the visual.
ill advised
Member
I don't have any dyno numbers to clarify but the seat-o meter didn't register a big loss. 
Still wails at WOT too. My exhaust is similar to yours, only I have 3" 3-chambers. 8hp is alot though IMO.
With that said, I have heard of only rare occassions of Stang guys being cited by police. I know how you feel though. Plus, depending or where you live, you will need them at some point anyway.
Still wails at WOT too. My exhaust is similar to yours, only I have 3" 3-chambers. 8hp is alot though IMO.With that said, I have heard of only rare occassions of Stang guys being cited by police. I know how you feel though. Plus, depending or where you live, you will need them at some point anyway.
ill advised said:I don't have any dyno numbers to clarify but the seat-o meter didn't register a big loss.
With that said, I have heard of only rare occassions of Stang guys being cited by police. I know how you feel though. Plus, depending or where you live, you will need them at some point anyway.
To simply put it, an aftermarket H-pipe with high flow cats (or x-pipe for that matter) will not hurt power.. when compared to a stock h-pipe.
You will give up about 2 HP.. (on a relatively stock stang) when compared to an offroad h-pipe with no cats.
It wont hurt the car,.. it will hurt your wallet a tad,. but not the car.
crazypete
All my crevices are greased.
Like interceptor said: get a rusted 4 cat pipe from a junkyard and get the heatshields off it. Then weld those to your open pipe. Bingo. Fake cats. Advantages of both. Cop proof and good power
remat457
Founding Member
According to fordmuscle.com:
"In this article we'll show you just how clean a late-model Mustang runs, in terms of emissions, when using three-way catalytic converters. Then in an upcoming article we'll test the catalytic converter H pipe at the track against an "off road" H pipe, and show that the performance loss through converters is negligible..."
"In this article we'll show you just how clean a late-model Mustang runs, in terms of emissions, when using three-way catalytic converters. Then in an upcoming article we'll test the catalytic converter H pipe at the track against an "off road" H pipe, and show that the performance loss through converters is negligible..."
For what it is worth.....
Last year my GT failed emmissions in Chicago, Illinois. I found that the cats were "plugged" or at least not operating properly. I used this as an excuse to make some more changes. I added MAC shorty 1 5/8" unequal length headers and Dynomax hi-flo cats with crossover. Going from 4 cats to 2 worried me, but the new ones are larger than the old ones, so I assumed they did the same job. When I hit the street, what a kick in the pants. I had Flowmaster 2-chambers on it already (bought it with them on it), so the sound and grunt was beautiful. A bonus was that it passed emmissions last year and this year with flying colors.
Last year my GT failed emmissions in Chicago, Illinois. I found that the cats were "plugged" or at least not operating properly. I used this as an excuse to make some more changes. I added MAC shorty 1 5/8" unequal length headers and Dynomax hi-flo cats with crossover. Going from 4 cats to 2 worried me, but the new ones are larger than the old ones, so I assumed they did the same job. When I hit the street, what a kick in the pants. I had Flowmaster 2-chambers on it already (bought it with them on it), so the sound and grunt was beautiful. A bonus was that it passed emmissions last year and this year with flying colors.
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