Decat Dyno Results - With Or Without Cat? Power Gains?

[GTR Grey Ghost]

Hi guys and gals, having a discussion with the lads and we have varying ideas relating to anti-polution OBI 1 - 2 etc some think that a decat can net some huge gains of up to 25kw atw on a health RB26 - N1 spec turbos, 1 bar, others disagree, there really is nothing much on the net relating to a RB25 or 26 decat and with cat dyno results, only other makes and models of cars, experience here guys and gals, what were your results on the dyno? cheers

[skylinekid]

because its highly illegal on the street im not sure you'll get much of a response but guess it cant hurt to try.

[GTR Grey Ghost]

because its highly illegal on the street im not sure you'll get much of a response but guess it cant hurt to try.

Hi there, the question was purely to answer a debate with the mates and specifically tests on a dyno, no intentions of driving a decat on the streets, discussions also related to the Lean Burn on the old CL Chryslers and different cam combinations that Chrysler and Ford implimented in 1976, huge decreases in power but they had no catalytic convertors back then....................pretty sure no one here would be interested in discussing the old Chryslers and Fords any further, we all agreed how the polution gear robbed the power output as it is clearly written, nothing much on the effect of cats though which happened years later, cheers and thanks for coming back to me.

[skylinekid]

riteeeeeeee

[GTR Grey Ghost]

riteeeeeeee

Cheers mate, not sure what riteeeeee actually means, maybe us old guys that dabble in mopar muscle but have an appreciation for gtr's should chat elsewhere, dont seem to be going anywhere here, lol

[R31Nismoid]

Yes there are gains, a factory cat is of course restrictive.

[NSNPWR]

because its highly illegal on the street

And you'll probably find 50% + of the users on here run a decat or a gutted cat or similar....

I cant say exactly what gains I made on my last car (ADM S15 with basic boltons, PFC, FMIC, Zorst, Disco Potato etc) but once I took the cat out and fitted my highly illegal decat pipe, the car made more boost (infact I had boost control issues) was noticably more responsive and revved easier. Seat of the pants dyno tells alot and I know it wasnt just a Placebo effect...

The 32 GTR I bought recently has some wanky $350 cat on it so im reluctant to pull that out but if it was a stock cat...gtfo of there!

[TiTAN]

you can try it on a dyno if you want to, the power difference between a decent highflow cat (fully functional) and some pipe where the cat would be is going to be very similar you will more than likely find a difference of less than 10kw.

sure there would be a much larger gain if you only had a stock/compliance cat with an engine/turbo setup for 300kw @ the wheels. but if you are going to spend money to get that far how is spending the small amount for a highflow cat that hard to justify?

[skylinekid]

And you'll probably find 50% + of the users on here run a decat or a gutted cat or similar....

I cant say exactly what gains I made on my last car (ADM S15 with basic boltons, PFC, FMIC, Zorst, Disco Potato etc) but once I took the cat out and fitted my highly illegal decat pipe, the car made more boost (infact I had boost control issues) was noticably more responsive and revved easier. Seat of the pants dyno tells alot and I know it wasnt just a Placebo effect...

The 32 GTR I bought recently has some wanky $350 cat on it so im reluctant to pull that out but if it was a stock cat...gtfo of there!

guess im in the 50% then :-P

either way i like flames :-D

[lachlanw]

i had a good book about doing everything to a mr2 from stock to v6 conversion . super charged , turbo charged , then twin charged to 22 psi (with all supporting mods ) at 540 whp putting the cat back in knocked it back to 500 whp

[Duncan]

you guys running no cat on the street are mad, hectic flames or not. the epa fine is somewhere over $20k.

anyway, I have no cat and a big diameter exhaust (3.5"). Not making a lot of power (lets face it, 400 is the new 250) and I have never back to back tested a similar size exhaust with a high-flow cat. however....mine seems to make a couple of kw more than I have seen from other similar spec cars.

not at all scientific, and my guess is a good high flow cat (eg 4") would flow just as well as no cat

[scotty nm35]

Ive had this debate with a lot of "good cat is a dead cat" people, My two cents...

Standard cat for an XR6t flows over 300kw and can be picked up cheap, not enough? Run two in parallel and you will have no restriction at all. Why damage the enviroment, get a huge potential fine and pretty yellow sticker for the sake of a couple of kw? Its the first thing a cop will check and some have infra-red thermometers. Leave the dead cats for race cars.

Much easier ways to gain more power like a simple water sprayer on your cooler, water/meth injection or 80mm suction pipes.

[rob82]

Ive had this debate with a lot of "good cat is a dead cat" people, My two cents...

Standard cat for an XR6t flows over 300kw and can be picked up cheap, not enough? Run two in parallel and you will have no restriction at all. Why damage the enviroment, get a huge potential fine and pretty yellow sticker for the sake of a couple of kw? Its the first thing a cop will check and some have infra-red thermometers. Leave the dead cats for race cars.

Much easier ways to gain more power like a simple water sprayer on your cooler, water/meth injection or 80mm suction pipes.

Such a good point - its the BF onwards triangular shaped cats that will flow 300rwkw the BA's are a bit crap. We have trouble getting 4" 200 cells to flow over 500rwhp the 100cell will go another 50-75 before running out - thats on the XR's anyways.

[XRATED]

To answer your enquiry... I doubt you would see a 25rwkw gain by just removing a stock GTR cat on a simple set up. GTR cat's arn't that bad. There are gains to be had though, especially if it's the restriction in a higher flowing exhaust.

I'm planning on running 2 high performance cats for my new set up. Aiming for 500 rwkw.

PS I'm a (not so) younger fella who dabbles with GTR's and has a healthy appreciation for mopar muscle.... They're everywhere here in florida!!!

[hypergear]

Just give you some idea of how much cat can affect performance. This was done back in Jan 2007. The cat used during the time was a magna flow 3inch high flowed cat. I don't think Honey corn cats were available back then.

CA18det using very old and retired version of TR43 with cat:

CA18det using retired version of TR43 without cat:

[GTR Grey Ghost]

Hey there, 208 to 230kw, as I thought and this was with a smaller engine but running considerable boost, thanks for the reply, is good that we got some communication going here, was starting to think that I am too much of an old fart, also "XRATED" really good to chat to someone from the states, nice to see that the GTR's are making a statement there too, ofcourse I still have the love for the Mopar Muscle and occasionally enjoy a cruise in my cousins 68 Dodge Charger, 400 stroked to 500 cubes, has a bit of curry :-) (visiting Plymouth Cuda Project here currently) and for those others out there who seem confused about this post, this post was not intented to suggest the removal of CATS on the road NOT even an option........it was clearly in reference to the results on a dyno in a controlled environment to satisfy a debate between mates, cheers

[XRATED]

That's pretty crazy results... especially if they were using a "high flow" cat...

Hey Tony, I'm an Aussie working on a super yacht thats docked in Ft Lauderdale Florida... There is actually a mopar club event at Moroso motorsport park this weekend... A buddy of mine here with a big hp 33GTR is going. Show some of the old drag racers how versitile a GTR can be.

Cheers

Justin

[R31Nismoid]

I can feel the difference when my 4" hi-flow cat is in, and when it's not (3.5" straight pipe)

So there is certainly something to be said for it all IMO.

[l_uk3y]

Although I haven't tried this since well before my Power FC went in (so the typical exhaust, cooler and boost).

For laughs I swapped my 3" metal cat to a gutted factory cat. Couldn't feel any difference in the seat of the pants in terms of revvability or speed. Just a bit more crackle (No idea if it popped any flames or not as I was in the drivers seat) With a video camera from behind whilst the car was stationary revving it didn't do squat though.

Needless to say. The metal cat is in place full time. With plans for an unrestricted bolt on side pipe behind front wheel for track work to save weight and hopefully pop flames on the track.

Luke

[Birds]

I used to run de-cat pipe and there was a noticeable different in power for the vehicle, though I never got the difference dynoed. Along with the power increase came a raspy sound it would make in the high rpm range. But whenever I was near a cop car it scared the shit out of me the thought of getting hit with a couple of grand worth of fine. Ditched it for high flow cat when I got my exhaust system replaced and I'm much less paranoid driving around now. Really, if that extra 10-20kw means alot to you go for a bigger turbo / high flow. There are other ways to get it that don't cost you alot of money if you get caught using de-cat.