de-cat and fuel cut

Hi, I plan to do a double de-cat very soon (probably using the Chris Wilson pipe as I hear it's good). I have a J-Spec car and want to keep the boost to 1.2bar, so I'll fit a restritor ring to control boost.

I've heard mixed reports of some people saying they can run higher boost and still don't hit the fuel cut limit.

My question is, will I definitely be hitting fuel cut at that pressure and so should fit an fcd (Thor VFCD looks the best) before the fitting the pipe, or is there a good chance I won't and therefore I should just try it out first?

I think the majority do hit it at 1.2 bar, there may have been a couple that didn't, got lucky or had one fitted and didn't know!!

I'd get the TRL VFCC and have it fitted (or do it yourself). Not worth the worry when you're gunning it and waiting for the big warning triangle to flash!!

thanks for that, I'll be ordering the Thor vfcd then, I don't mind fitting it myself. I'm asuming I don't already have one fitted. The car currently makes 1 bar with both cats in (Jap moddified ecu) and at 1bar I don't think it would have needed one, would it? Never seen the warning triangle anyway. Think I'll just order the Thor device, that way I'll know where I am, even if it had one from japan probably I wouldn't know what it was and its probably not as good.

thanks for the help

Modified ECU???

Hmmm, if it has been remapped or altered, you might find that the fuel cut has been moved up...

I would get the de-cat on, and try it, see if you really need it...

Gav

When I was stock, I was making 1 bar and sometimes hitting fuel cut. (Both cats in, no Boost controller)

In Japan, some ECU's have been fiddled with - yours might be one of those.

Get a Thor fcd as it's reliable and adjustable

Thanks everyone, yes it makes a reliable 1 bar and holds to the rev limit, it goes very well considering how stock it mostly is.

What’s the general opinion on upping it to 1.2 bar on j-spec turbos, are they going to blow on me alarmingly quickly? Ideally I'd like to keep it at 1 bar and use an ebc to variably raise it to 1.2 bar as and when needed. However once it's de-catted it seems that you struggle to keep the boost down to 1.2bar! (damn those pesky wastegates!).

Somehow it just seems wrong to use an ebc to get the boost variable up to 1.2 and retain the cats just to keep the boost back down again!

1.2 bar is the very max I'd run. It's proven safe, but don't go over it. I would remove both cats, it gets a lot of heat away from the bay and reduces back pressure hugely. You'll almost certainly need a restrictor ring if you have a free flowing cat pipes back system.

Think I'm right saying that decatting will highlight any problems with your turbo seals if they're slightly iffy too.

Hi Chris, well I was intending to get the de-cat pipe from you anyway with the restrictor, so thats good to know.

Yes my cat-back is very free flowing as far as I can tell.

Is there such a thing as a 1.1bar restrictor? lol. That way I can fit an ebc and have a (small) amount of control until such a date as I am ready to replace the turbo's with something altogether more capable

Double check with Chris, as mines was somehow doing 1 bar anyway, When I de-catted the 'normal' size restrictor ring wasn't sufficient to hold the boost down to 1.2. Just had a smaller restrictor ring fitted at that's working better.

thanks supro, think I'm going to be in the same boat and I don't want blown turbo's until I'm ready with their replacements lol

A restrictor ring with a smaller hole will keep the boost down to 1bar ie. more restriction less boost.

Fuel cut on stock ECU is around 1bar, what ECU do you have fitted? You say it is modified?

I would be very careful going to high with stock fueling/ecu, I'd say 1.1bar max to be on the safe side. I would check the condition of your intercooler also, if it is the original it is getting on for nearly 10 years old now, so could well be past it's best and no longer cooling charge temps sufficiently (Chris does an uprates SMIC.) Same applies to your fuel pump, I would fit a new higher flowing pump, either UK spec Supra pump or Walbro 255l/hr. Also worth fitting new fuel filter whilst you are at it.

You will also need a boost gauge and ideally an exhaust gas temperature gauge, so you can monitor things.

and don't forgot to change the plugs to a colder grade!

and don't forgot to change the plugs to a colder grade!

forgot that

...and bigger brakes so you can stop

Ok, I have iridium plugs already and a boost guage. Car is completely happy at 1 bar, guess thats why I hoped going to 1.1 or 1.2 wouldn't be too much of a struggle!

Good point about the fuel pump and filter, might change that firstly then. Not sure what the ecu has had done to it, I need to take the lid off and have a look.

I realise that a smaller restrictor = less boost, but where can I get a 1 or 1.1 bar restrictor, or should I just make one perhaps.

lol about the brakes, too many things to do...

Fitting an aftermarket wastegate to stop this whole boost creep thing, is that an impossible task on the stock set up? That would appear to be the best way to regain control and yet not many people seem to go for it on the stock system, so I assume its hard to fit.

I think Chris will be able to supply restictor to your requirements.

I have HKS Actuators fitted on mine for better control of stock turbos, see details HERE

Thanks Nic, that links all in Japanese though,

who could fit these to my set up I wonder? I like the idea of having a free flowing exhaust but control over boost still, this might be the answer perhaps (depending on cost).

Thanks Nic, that links all in Japanese though,

 

who could fit these to my set up I wonder? I like the idea of having a free flowing exhaust but control over boost still, this might be the answer perhaps (depending on cost).

I'll find out cost of them here.

Translated HERE

I can supply a 1 or 1.1 bar restrictor if you buy the pipes off me. I can't accurately enough gauge the restrictor size for other pipes.

Thanks Chris, expect an order from me sometime in the near future then!

Nic, so those are uprated actuators not wastegates. Does the actuator help with the j-spec stock 20mm wastegate sizing problem then, perhaps by offering better control of the valve?

Shame there appears to be no easy way to just fit a better external wastegate on the stock setup, guess its new manifold time, and by the time you go that route it's probably new turbo time too, to justify all that labour