Sports Cat or Decat Celica GT4 + boost creep question

Hi

Been struggling to get a clear cut answer and thought someone on here might be able to advise me better.

I have a GT4 and want to increase the boost pressure, yet would if at all possible prefer to not have to swap a decat out for the mot every year so have been looking at high flow cats instead. from what i can gather you need a minimum of a 200 cell sports cat to pass an mot. will a sports cat have any drawbacks compared to a decat as reliability is key as i use it daily (only looking to raise it to 1 bar) the current exhaust (3") on it needs a fair bit of work as it rubs on the front sub-frame and the rear bumper, so could theoretically get a 2.5" sports cat put in, possibly on the down pipe in place of the stock cat? and also the 2.5" cat would help to stop boost creep? or is that wrong

I fear i have overly complicated this whole process so any advice would be great

thanks in advance

Max

Do you need to change the exhaust on a GT4 to increae the boost? I just had a boost controller on mine with standard down pipe and CAT.

I was told i needed a decat as the stock dosent flow enough? Iv already got a boost controller so if just that would work would be great, also need to block of the vs valve that limits the boost in 1st and 2nd dont you?

Bumping this just in case anyone can offer any more insight

I build gt4s all day.

If your going to raise the boost pressure i would fit a nice freeflowing exhaust system and decat. Just find a friendly mot guy as the cats in the mid pipe dont really work.

Raise the boost with a boost controller, disconnevt the tvsv valve on the bottom of the intake manifold, this will allow full boost in 1st and 2nd gear.

If you do plan on keeping the cat dont go above 0.9bar on a st185 or 1 bar on st205

What version gt4 do you have as this will dictate the fuel cut level

Tim

TBDevelopments

I build gt4s all day.

 

If your going to raise the boost pressure i would fit a nice freeflowing exhaust system and decat. Just find a friendly mot guy as the cats in the mid pipe dont really work.

 

Raise the boost with a boost controller, disconnevt the tvsv valve on the bottom of the intake manifold, this will allow full boost in 1st and 2nd gear.

 

If you do plan on keeping the cat dont go above 0.9bar on a st185 or 1 bar on st205

 

What version gt4 do you have as this will dictate the fuel cut level

 

Tim

TBDevelopments

Thanks Tim, don't know why i didn't think to PM you about this as i remember reading about you specialising with them now.

I have the ST205 model and 1 bar in all gears would be fantastic till i can afford a Decat pipe, i assume i just need to set up the boost controller and block of the piping now. is there a trick to the tvsv or will i get it when looking at it?

kind regards

Max

yeah when you get a decat fitted you can go to 1.1/1.15 bar safely, Its best to fit an electronic boost controller to do this.

The biggest gains will be in the 1st and 2nd gears as your hitting 6psi then boost creep upwards as the revs climb. With the controller and tvsv disconnected you'll be getting full boost by 3k instead.

the tvsv i find the easiest way is to just reach under the intake manifold and unplug the solenoid. It'll have a blue plug. You can also cut and disconnect the pipes if you wish but unplugging allows it to be put back to standard prietty easily if you ever need to.

The boost controller will only connect to the left port on the actuator. the right port goes down to the tvsv which will then become redundant, and with the solenoid unplugged basically blocked off.

Hope that helps

Tim

TB Developments