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The mkiv Supra Owners Club

What boost


Chris and Alana
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Im going to get a cat back exhausts (hopefully a Miami GT) after christmas and a second decat (keeping the first cat). I would like to know what the boost level will increase to with these mods. there must be lots of you guys nd girls out there with the first cat still in. Iv searched for an answer but give up and thought I would ask instead.

 

The only thing I found was 'You might as well take the first out aswell'. (not to helpfull) I found that someone said his boost went upto 1.1bar and another comment that said it wont increase the boost much. Its a bit varied.

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I would like to know what the boost level will increase to with these mods. there must be lots of you guys nd girls out there with the first cat still in.

 

If you're just taking one out, remove the first as it's far more restrictive. About 1.0 bar is your limit, above that the remaining cat will start to melt and you'll hit fuel cut. You can use an EBC or manual boost controller to reach this. Some cars suffer from boost spike with one cat still in though.

 

If you remove both you'll need a FCD to get over 1.0 bar along with a restrictor ring. :)

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Sorry for the hijack, but if you take out both cats at the same time, when its time for an MOT can you put them both in, still attached together? Also does anyone know if the HKS Front Down pipe is any good and can it mate to the original exhaust? or is it 3 inches needing a reducer?

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If you're just taking one out, remove the first as it's far more restrictive. About 1.0 bar is your limit, above that the remaining cat will start to melt and you'll hit fuel cut. You can use an EBC or manual boost controller to reach this. Some cars suffer from boost spike with one cat still in though.

 

If you remove both you'll need a FCD to get over 1.0 bar along with a restrictor ring. :)

 

So even with the first cat in turbos can still overboost. I was under the impression that leaving the first cat in would allow the tubbies to produce 1.0 bar but I dont know if that is true. I also thought thought the first cat would leave enough back pressure to stop over boosting.

If they over boost anyway with thje first cat left in I might as well do a full decat and use a restictor ring but I was only wanting to produce about 1.0 bar boost? :help:

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So even with the first cat in turbos can still overboost?

 

Not generally. A very few cars every now and then can spike, but I know of at least one person on here that had boost spikes when all they'd changed was the cat back section (still had both cats in!).

 

Chris Wilson can make restrictor rings to suit different boost levels. I've had one sitting in my garage for six months that's supposed to hold the car at 0.9-1.0 bar.

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I may be tempted to go full BPU :D Iv already got a HKS SSQV and apexi power intake. I checked out my SMIC and all the fins are still there :D so my intercooler should be up for it. I take it I should get a walbro fuel pump first then buy an exhaust and decat. What do you think. Am I missing anything? I wont need a EBC on a J-spec to reach BPU with the correct restrictor ring will I. (I know I will need to change the plugs, I will do after exhaust)

 

Thanks guys for all the info.

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I still have both cats in but have an Hks ti 4" cat back system and on a cold day i have seen nearly 1Bar boost on the guage.As others have said best to get rid of both cats rather than one at atime as the cats can melt.

Try to find a friendly mot station as they can pass it with both cats out,mine just said "well its not life threatening haveing ni cats in is it"lol:d :D

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As others have said best to get rid of both cats rather than one at atime as the cats can melt.

 

The cats shouldn't be damaged as long as you don't go over 1.0 bar. There's nothing stopping you sticking a restrictor ring in even though a cat is still there if there's a problem with boost spiking. :)

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