Jump to content
SAU Community

Recommended Posts

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

  • Replies 40
  • Created
  • Last Reply

Top Posters In This Topic

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.

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

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!

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?

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

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

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

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.

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.

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!!!

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:

tr43cacat.JPG

CA18det using retired version of TR43 without cat:

tr432ndrunkw.JPG

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

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

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

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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • Well, after the full circus this week (new gearbag, 14 psi actuator on, injectors and AFM upgraded, and.....turbo repair) the diagnosis on the wastegate is in. It was broken. It was broken in a really strange way. The weld that holds the lever arm onto the wastegate flapper shaft broke. Broke completely, but broke in such a way that it could go back together in the "correct" position, or it could rearrange itself somewhere else along the fracture plane and sit with the flapper not parallel to the lever. So, who knows how and when exactly what happened? No-one will ever know. Was it broken like this the first time it spat the circlip and wedged itself deep into the dump? Or was it only broken when I tried to pry it back into place? (I didn't try that hard, but who knows?). Or did it break first? Or did it break between the first and second event of wierdness? Meh. It doesn't matter now. It is welded back together. And it is now held closed by a 14 psi actuator, so...the car has been tuned with the supporting mods (and the order of operations there is that the supporting mods and dyno needed to be able to be done first before adding boost, because it was pinging on <<14 psi with the new turbo with only a 6 psi actuator). And then tuned up a bit, and with the boost controller turned off throughout that process. So it was only running WG pressure and so only hit about 15-16 psi. The turbo is still ever so slightly lazier than might be preferred - like it is still a bit on the big side for the engine. I haven't tested it on the road properly in any way - just driven it around in traffic for a half hour or so. But it is like chalk and cheese compared to what it was. Between dyno numbers and driving feedback: It makes 100 kW at 3k rpm, which is OK, could be better. That's stock 2JZ territory, or RB20 with G series 550. It actually starts building boost from 2k, which is certainly better than it did recently (with all the WG flapper bullshit). Although it's hard to remember what it was like prior to all that - it certainly seems much, much better. And that makes sense, given the WG was probably starting to blow open at anything above about 3 psi anyway (with the 6 psi actuator). It doesn't really get to "full boost" (say 16 psi) until >>4k rpm. I am hopeful that this is a feature of the lack of boost controller keeping boost pressure off the actuator, because it was turned off for the dyno and off for the drives afterward. There's more to be found here, I'm sure. It made 230 rwkW at not a lot more than 6k and held it to over 7k, so there seems to be plenty of potential to get it up to 250-260rwkW with 18 psi or so, which would be a decent effort, considering the stock sized turbo inlet pipework and AFM, and the return flow cooler. According to Tao, those things should definitely put a bit of a limit on it by that sort of number. I must stress that I have not opened the throttle 100% on the road yet - well, at least not 100% and allowed it to wind all the way up. It'll have to wait until some reasonable opportunity. I'm quite looking forward to that - it feels massively better than it has in a loooong time. It's back to its old self, plus about 20% extra powers over the best it ever did before. I'm going to get the boost controller set up to maximise spool and settle at no more than ~17 psi (for now) and then go back on the dyno to see what we can squeeze out of it. There is other interesting news too. I put together a replacement tube to fit the R35 AFM in the stock location. This is the first time the tuner has worked with one, because anyone else he has tuned for has gone from Z32 territory to aftermarket ECU. No-one has ever wanted to stay Nistuned and do what I've done. Anyway, his feedback is that the R35 AFM is super super super responsive. Tiny little changes in throttle position or load turn up immediately as a cell change on the maps. Way, way more responsive than any of the old skool AFMs. Makes it quite diffifult to tune as you have to stay right on top of that so you don't wander off the cell you wanted to tune. But it certainly seems to help with real world throttle response. That's hard to separate from all the other things that changed, but the "pedal feel" is certainly crisp.
    • I'm a bit confused by this post, so I'll address the bit I understand lol.  Use an air compressor and blow away the guide coat sanding residue. All the better if you have a moisture trap for your compressor. You'd want to do this a few times as you sand the area, you wouldn't for example sand the entire area till you think its perfect and then 'confirm' that is it by blowing away the guide coat residue.  Sand the area, blow away the guide coat residue, inspect the panel, back to sanding... rinse and repeat. 
    • The detail level is about right for the money they charge for the full kit... AU$21.00 each issue, 110 issues for a total of $2,300 (I mentioned $2.2K in the first post when the exchange rate was better). $20/week is doable... 😐
    • If planning on joining us for the day(s) please indicate by filling in this form. https://forms.gle/Ma8Nn4DzYVA8uDHg7
    • You put the driver's seat on the wrong side! Incredible detail on all of this. It looks like you could learn a lot about the car just from assembling the kit.
×
×
  • Create New...