Do Magnaflow high flow cats do much for performance? Rumors i have heard from friends are that the high flow cats don't really do all that much, but I'd like to go with someone who has some first hand experience with them on a Bonneville.

first hand... yes they do a lot... and they make it a LOT louder

my 95 ssei with no pulley and just high flow cat and muffler, ran along side with a stock 99 GSE

If you get a high flow cat, get a high flow muffler. I got a flowmaster muffler, and just purchased a magnaflow cat, you should see at least a 5hp increase over OEM.

I got from 14.9 @ 94mph to 14.6 @ 96mph with my high flow cat.

Note that i im supercharged, you will see less difference with the NA bonneville.
But still make a diference

...and if you remove it altogether you will see an even greater improvement.
But we would never do that.

Ditto. Went from a 15.06 to a 14.81 by removing a 1 week old high flow cat and installing regular pipe in its place. But this should never be done. I am talking about a car that is strictly a race car of course.

Shawn

Okay, Iam in the middle of this debate myself, This seems to be a hot button issue, All things being equal it is bad for the environment, to remove a cat altogether.

Put all the environmental issues aside for a moment, I am talkin about performance, I have read some posts that say removing the cat actually hurts horsepower, and I have read it doesn't . I'm not boosted so where would that put me??

Is no cat a power robber or no??

And the Magnaflow...it would actually add around 5 hp??

No cat, how much gain are we talkin about??


Thanks,

Bonnevillemac

Based on SC engine only.
Performance Cat will gain you about 5 hp
No Cat will gain you about 10-15!
Sound high? Some would argue that.
Think about what a Cat does. It scrubs your exhaust gases and converts it to harmless water vapour. It needs residence time and develops a lot of backpressure to do this. Not unlike another muffler. That'* why your exhaust will sound a lot louder (sweeter )with it removed.

If you're not supercharged, a high flow cat is better than no cat. And better than a stock cat. And they're cheaper than stock cats. No brainer.

Thanks guys, You know Paul I had never thought of it like that. I t makes sense that it would be louder. It would give it more of a performance sound huh.... , and also the power gain because of less backpresure.


However Bill makes a good argument also. I have checked on various mods on Intense'* site, and the give power gains for some mods. And It seems us NA guys wind up with roughly half of what you SC'd guys get.

So am I correct in deducing that if SC'd with no cat gains 10-15 hp, NA'd would gain 5-7??

Now with the point Bill makes, Being NA as I am will a hi flow gain me more than ~5 - 7 hp. Anywho thanks for the help in my quest for better performance.

Thanks again,

Bonnevillemac.