dunl

Well, I have finally gotten back to my neglected $500 Porsche 951 upgrade, and while I couldn't remove the cat, last night I did manage to cut a hole in the front of it (a big 2" square), and the response proved that the cat was clogged as I finally suspected (and as others have repeatedly told me ).

Now, I have heard that deleting the cat robs the car of power. Is there a nice replacement that I should be looking for? (don't need a racer, but I don't really want anything plugging up again in the future if possible...)

Thanks.

CDH-CTT

There are a couple Companys that make "high flow cats" Magna Flow comes to mind...
I personally only run a cat when emissions are due(every 2 years here)....
It might rob some high Rpm power just due to flow, but I cant really tell a diff on my car with the cat is on or off, only the exhaust note changes.....
Some else might have a better test that they might have done......

67King

What you heard was wrong.

dunl

Thanks for the reply. My understanding was that these cars are tuned for the back pressure provided by the exhaust...and that while running without one seems to provide more power, it's actually robbing a little.

If someone could clarify, I would be just as happy to have it cut out......

gruhsy

I took out the cat on my 86 and it ran better. Less restriction in the exhaust the better.

If you really want to keep a CAT in it I have one from my 87 in Calgary that is never going back in my car and it's good.
I would recommend just leaving one out. There is no Cat requirement in Alberta.

Whoever told you about robbing power is absolutely incorrect

Let me know if you want the CAT portion of my exhaust.

Jason

Paulyy

NO Turbo is tuned for back pressure. any back pressure in the exhaust robs power.

Just cut the cat out an be done with it. you'll gain upto 10 or so hp depending up clogged up it is.

drift a 944

As previously mentioned, this is untrue and removing the car would actually be beneficial by reducing exhaust restriction. If your 944 was a non-turbo model, however, you would need to have some back pressure in order to not lose all your low-rpm power. So I reckon somebody probably told you that information based on a non-turbo 944.

odb812

N/A cars need the backpressure to maintain low-end torque.

Any modern cat really shouldn't hurt power too much. Rather than buying the high-flow cat with my fabspeed exhaust, I got them to send me an extra bypass pipe and welded in a $65 cat from summit. I used to just put the cat on for state inspections and take it right back off. Now that I'm in CA I have the cat on all the time in fear of the hippies lynching me. I don't notice it at all. In fact, I dynoed the car this past weekend with the cat in place and put down more power than I had expected.

dunl

Thanks all, I must have misunderstood and read that re: a N/A instead of the turbo. Sounds like the cheaper option of complete removal is a better option all around.

JohnKoaWood

How about a free one?



Sorry, couldn't resist...

odurandina

these myths.

back pressure is the most misunderstood part of the exhaust context. backpressure is an unintentional by-product of a healthy exhaust. but by no-means helpful. what engine exhausts need is scavenging. that is to say the process where each of the exhaust pulses enters into an environment that allows it to accelerate to the highest possible velocity, then flow through and exit with highest velocity near the engine's peak power/rpm range.... when this is accomplished, each pulse leaves a zone of low pressure in it's wake.... and thus sucks in the next pulse of expanding gas... this is best accomplished with long, narrow-ish (but not too narrow) straight pipes with as few bends and obstructions as possible. the good length of the pipe and it's narrowish width permits the velocity of gas to be maintained at it's highest, but the by-product is back pressure (and some confusion)... recall that you can't siphon gasoline out of a tank without a decent length of hose... well, the same principle applies when seeking to get the same free ride flowing hot exhaust gas...

in a perfect world, you would want a narrow pipe in the mid-rpm range to render maximum flow near the engine's peak torque, thus making good low end power.... but a wider pipe when nearing the engine's maximum power/rpm range... the wider pipe wins, because this results in maximum power where you can still use it..... but, it reduces torque slightly in the mid-rpm ranges. but of course, the overall benefit remains... turbo engines benefit from the exact same principle, but with significantly wider pipe to proportionately flow more exhaust gasses.


.

Ronin-951

Back pressure moves the Torque curve down, but that's not the thing to worry about, ... do as you wish, ... but it is a Federal Crime to remove, or not have, the Cat for any reason,[Except Track use] no time limit. Take responsibility for your actions, lobby for a Law change, but don't whine if your caught.
P.S. The fed's now have online the biggest Ear on this side of the Galaxy, hope you didn't cross a keyword.

dunl

Slayer - that's a great explanation, thanks.

Ronin - Last time I checked, we weren't the 51st state. The cat's coming off as soon as I have the spare cash to get into it.

Ronin-951

Praise the Lord and pass the citizenship papers!

dunl

LMAO.