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The mkiv Supra Owners Club

De-catting the jap-spec TT


adi2009

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Ok, i m a little confused about this. I read that a restrictor plate is needed when a de-cat is performed on a jap spec TT to keep boost from exceeding 1.2 bar. But isnt it the wastegates job to dump excessive boost?

 

so when de-catting the jap car would i need a boost controller to bump up boost?

 

THanks

 

adi

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The jap turbos have very small wastegates as they use the cats to keep the boost below 1 bar. If you remove the cats the wastegates cannot cope and you can hit between 1.2 and 1.5 bar. That's where the restrictor ring comes in to bring it back down again.

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That I couldn't tell you, someone like Chris Wilson would be the best person to ask. Also worth remembering that the boost level will change with the weather, so setting it to 1.2 now will result in slightly less in the summer - but it's safer that way round then having 1.2 in summer and blowing your engine in winter! :)

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It's also worth noting that you'll need a FCD and colder plugs if you want to raise the boost. And I think there's something else, but I can't remember now. I've got an aftermarket ECU so I didn't have to bother with any of that when I took one of my cats out, I got 1.2/1.3 straight away. :)

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Fuel pump?
Yeah it is recommended, not that I've changed mine though and the dyno showed plenty of fuel getting through. Depends on the car really and the condition of the pump.

 

Oh yeah, obvious addition is a boost guage to make sure it doesn't raise too high.

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thanks a lot for all the response.

 

basically just wanted to give you'll some idea of what i m doing.

 

I am doing a NA to TT engine swap but running the W-58 5spd transmission from the NA as the TT engine is and auto tranny. (but i ve got a set of manual ecu and wiring loom separately)

 

the following mods i will be performing are:

 

255lph walbro pump

manual boost controller

de-catted exhaust (well got to think carefully about that now)

Greddy BCC

HKS SSQ blow off valve

NGK iridium spark plugs (not sure yet as i dont know if the one i already got would fit the TT)

A/F gauge

Boost gauge (manual not electronic gauge)

 

thanks

 

adi

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I am doing a NA to TT engine swap but running the W-58 5spd transmission from the NA

Wow. That's going to be a lot of work!

Will the NA transmission be able to handle the TT torque? What about the gearing, are you planning on using the NA diff?

 

Is the car an Aerotop or hardtop?

 

Anyway, good luck with it. Please keep us posted as it progresses

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Ya mate, its gonna be some bit of work. well i really dont know if that 5spd is going to handle that torque (although i have read in places that it is reliable up to 500bhp crank and the jap spec TT only would put about 400 max with stock twins) and running the NA diffs also, well atlest until i find a 6spd tranny and diffs. my car is a hardtop. will get some pics of it up when i do the swap.

 

cheers!!!

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Fuel Cut Defencer stops the car from hitting fuel cut when the boost is raised. Fuel cut is a preventitive measure which cuts off fuel to the injectors if the ECU senses the boost is too high and could possibly run lean. From my limited experience of TT Supes, i think the factory set fuel cut is around 1 bar

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1.3 bar is a little too much

 

i'd consider an uprated walbro fuel pump and possibly a fuel pressure regulator to make sure you dont run lean at the top end, im not sure whether an old standard fuel pump can deliver enough fuel for that much boost

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whoa whoa whoa,

 

Your just looking at getting a warlbro and an FSE???? Looking at your sig, aren't you running hybrids and a 100 shot of nos? You're going to need a bigger boat...

 

The J-spec fuelling is going to struggle with standard tubbies at 1.2 bar. You're putting a significantly larger amount of air through that the stock fuel system is trying to cope with.

 

Try to remember that no matter how much air goes into the engine, it still needs to stick to about 14.7:1 ratio air-fuel. There's no way the jap injectors will be supplying that with your hybrids and then a 100 shot of nos. I would suggest a complete overhaul of your fuelling system, ie larger injectors, a fuelling computer to control those injectors and the pump and regulator that you mentioned. (Although if I was you I would go for the aeromotive over the FSE and just get the right sized injectors/pump and have it mapped more linearly - Just my humble opinion!)

 

Best of luck,

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