Zorst and decat Q

[Guest paperboy]

Dear all,

 

I have a 93 j-spec with 2nd decat removed now the question is if I fit the likes of a nur spec r of rsr will i have to make any other mods (ie cooler plugs, new intercooler, walbro, FCD etc etc)??

[Jake]

That would depend on how much boost pressure the car is making once the new exhaust is on.

[Suprasteve]

depends on how well your car copes. answer is yes probably will need a restrictor ring to keep the boost level below 1 bar and prevent full cut and if your car misfires then you'll need colder plugs and for safety reasons you should get a new pump cos the one you'll have on the car could be past its sell by date.

 

i've decatted the mid pipe and all i've done is colder plugs but didn't know if i needed them as did them first when service was due.

 

I do occationally hit fuel cut but could be the MBC set too high - not had a chance to play with the settings since fitting the decat.

[Jake]

Steve,

I think he's talking about still having the front cat in place

[Suprasteve]

oh right.

 

so you won't over boost if you just replace the cat furthest from the engine?

 

just litually done mine but not really tested it yet, although i did hit fuel cut in 4th once but as i said could be cos i've not adjusted my MBC yet ?

[Guest paperboy]

Steve,

I think he's talking about still having the front cat in place

 

yeah thats right I still have the first cat in

[Guest paperboy]

oh right.

 

so you won't over boost if you just replace the cat furthest from the engine?

 

just litually done mine but not really tested it yet, although i did hit fuel cut in 4th once but as i said could be cos i've not adjusted my MBC yet ?

 

so can you use a mbc without fully decatting?

 

cheers for all the advice btw

[Jake]

so you won't over boost if you just replace the cat furthest from the engine?

Not usually. The front cat is pretty restrictive. My RZ never made more than 0.9bar while the front cat was still in place.

 

just litually done mine but not really tested it yet, although i did hit fuel cut in 4th once but as i said could be cos i've not adjusted my MBC yet ?

Yeah, that'll be more to do with your bleed valve than the decat.

Forcing it to run high boost via a boost controller with the front cat still in place is A Bad Idea.

[Jake]

so can you use a mbc without fully decatting?

You can, but keep the boost down to

 

....unless you like buying new engines.

[Nic]

Remove the other cat at the same time, it will absolutely bring the car alive. If you do do this though first check the condition of your intercooler, if it is the original one it is probably well past it's best. The parts you would also need to fit are:

 

1. Restrictor ring (speak to Chris Wilson, member on here who supplies cat replacement pipes and restrictor rings.)

2. Fuel Cut Defender (see Thor in traders section)

3. Cooler grade spark plugs

4. Boost gauge (you want to be around 1-1.1bar max)

5. Would also be advisable to fit a new Walbro 255L/hr fuel pump, these are quiet reasonable in price.

[Suprasteve]

i run mine at 1 bar with both cats in for 6 months + ,

 

only just got the (bigger, more restrictive) cat furthest from the engine removed.

 

nothing gone bang.....yet

[Nic]

The front cat is the most restrictive of the 2, removing this (and ideally the second as well) will really bring the car alive and make it so much more responsive.

[Suprasteve]

The front cat is the most restrictive of the 2, removing this (and ideally the second as well) will really bring the car alive and make it so much more responsive.

 

i personnally don't know....just going by what CW told me

 

"The second cat is the biggest cat. The one nearest the engine (1st cat)

is the smaller one."

 

If i'm wrong - sorry !

[Jake]

i run mine at 1 bar with both cats in for 6 months +

You've been lucky then. Long on-boost high speed runs would see your EGTs soaring to nasty levels.

only just got the (bigger, more restrictive) cat furthest from the engine removed.

"bigger, less restrictive" I think you mean.

nothing gone bang.....yet

Good luck.

[Jake]

With just the front cat in place my car made 0.9 bar max.

With just the second cat in place my car hits fuel cut and peaks at about 1.1 bar.

 

That says to me that the front cat is the more restrictive.

[Guest paperboy]

So just to sumarise i will not need to do anything else as long as i sit at 1 bar or below?

[Nic]

As Jake says, it you up the boost with both cats still fitted then you run the risk of dangerously high exhaust temp. Removing both cats will help teh exhaust flow and should keep temps down to safe levels.

[Nic]

So just to sumarise i will not need to do anything else as long as i sit at 1 bar or below?

 

Fuel cut off is around 1bar so below this you should be okay, I would still check your intercooler and replace you fuel pump though as both of these are 12 years old now (if they are the original parts) and so may well be past their best.

[Suprasteve]

fair enough make sense to me.

 

I'm still fairly new to this modifying lark and still learning and taking advice from so many people i suppose i will get conflicting views right.

 

If you're sure its bad to constantly run at 1 bar with the front more restrictive cat still in, then best i reduce the boost.

 

What would you say is a safe level ?

[Nic]

fair enough make sense to me.

 

I'm still fairly new to this modifying lark and still learning and taking advice from so many people i suppose i will get conflicting views right.

 

If you're sure its bad to constantly run at 1 bar with the front more restrictive cat still in, then best i reduce the boost.

 

What would you say is a safe level ?

 

You may be okay, but without an Exhaust Gas Temperature (EGT) gauge you don't know, so there could be a risk of high exhaust temps on extended runs in hot weather. I believe Chris would tell you exactly the same thing, he normally advises to remove both cats.

[Suprasteve]

You may be okay, but without an Exhaust Gas Temperature (EGT) gauge you don't know, so there could be a risk of high exhaust temps on extended runs in hot weather. I believe Chris would tell you exactly the same thing, he normally advises to remove both cats.

 

cheers Jake & Nic

 

you learn something new every day right

[Nic]

Anytime this is the best place to learn, as most of us have asked the same questions and gone through the same thing in the past.

[jase_93tt]

Ive recently had both cats removed via an apexi front pipe, blitz middle pipe. Which hooked up to the already fitted Apexi N1 rear muffler. The difference in performance (and a little extra noise) is very noticeable. The cars eager to accelerate in any gear and boost comes on strong. Ive had a TRL VFCC fitted and it hasnt fuel cut yet (I believe the VFCC is set to 1.2-1.25 bar overboost protection).

 

Straight away, after fitting the fully decatted system, I did a test run with a temporarily fitted mechanical boost meter. When putting the car in manual A/T mode, 2nd gear did see some major boost creep, up to 16psi or so, but only when flooring the gas. Under moderate, 'busy street' style driving, there was no boost creep.

 

Other mods fitted are Greddy I/C, PE air filter kit, HKS SQV, Greddy plugs (stock grade)

 

Im going to fit a permanent boost guage, boost controller and walbro pump in the morning and hopefully get the car on the dyno for her first set of power figures. I may change the plugs to some NGK grade 7's too.