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The mkiv Supra Owners Club

Downpipe/decat differences...?


Glanza_Mike

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Hi guys,

 

Just a quick question about the 1st decat really.

 

I know facelift and pre are different but what exactly was changed on the facelift model to require a different downpipe shape?

 

The reason for the question is I've bought an American turbo kit. And then turbo kit is obviously made for the US spec Supra, so I need to use a UK spec decat, but I have a facelift Supra.

 

And I'd just like to know before I splash out on a new one, if, in theory, in will fit.

 

Thank you.

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I'm not sure about vs a U.K. decat, but I know that the flange angle on the VVTi decat vs pre-VVTi is different by a few degrees, meaning you would foul the gearbox casing if using the wrong one.

 

Is it an aftermarket turbo kit and manifold you're going for? If so, you'd have to change your downpipe regardless? :)

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As James said, the difference is between VVTi and non VVTi, NOT facelift and pre facelift. Facelift non vvti cars have the same first decat as pre facelift cars. But as you will be binning the first cat anyway (the turbo downpipe replaces it completely normally), it should just bolt up to any car regardless, as all second cat/decats are the same (IIRC).

 

Also, don't be concerned if the downpipe needs a little fettling, it is quite normal, especially when using a turbo kit designed for LHD on a RHD car.

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Ahh, play I didn't realise it was the vvti that made the difference not the pre/post facelift. Thanks chaps.

 

So basically I've bought the PHR turbo kit, and it come with a short downpipe that bolts up to a UK/US spec first decat (because of the different flange). So I just wanted to make sure that if u buy a UK spec decat to swap for my current facelift decat, I wouldn't have any clearance issues if you know what I mean.

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I've never heard of anyone fitting a UK spec cat pipe to a vvti, but I can't see why it would be an issue?

 

Personally I'd bin that downpipe and get another that removes the first cat entirely, otherwise you have an extra, unnecessary join in the system. I would also recommend getting a flexi section welded in your second decat pipe, to take some strain/shock off the manifold :)

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I'm guessing you have bought the PHR street kit with cast manifold? Which uses the shorter downpipe that is designed for that set-up.

 

I don't see why you'll have any issue as the only reason for the difference flange angles on the decats is to do with the downpipe of the stock manifold between UK/Non-VVTI and VVTI. As your changing all that anyway you have no issue.

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I'm guessing you have bought the PHR street kit with cast manifold? Which uses the shorter downpipe that is designed for that set-up.

 

I don't see why you'll have any issue as the only reason for the difference flange angles on the decats is to do with the downpipe of the stock manifold between UK/Non-VVTI and VVTI. As your changing all that anyway you have no issue.

You are correct mate, got the cast manifold setup with the shorter downpipe.

 

I was under the impression that all the turbos and manifold etc were the same for vvti and non but eh downpipe was different to clear the gearbox or something like that? So wouldn't that still be the case when changing turbo?

Has anyone run this kit on a RHD car? My first concern would be getting stuff past the steering column.

Yes Chris, Berg has it fitted on his car, he has a non-vvti though and used a UK spec downpipe and it fit perfectly.

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OK, let's assume you had a UK / USA spec engine and a VVTi J-Spec engine. The 1st cat differences are the flange size and the angle of the flange, both determined by the adaptor after the exhaust control valve casting. There are only effectively three different TT 1st cats. UK /USA, none VVTi J-Spec and VVTi J-spec. Does that help? I think, if I am following this right, you need a UK spec downpipe as any VVTi specific stuff above that is now gone?

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What do you mean mate? I will be doing this essentially.

 

The PHR turbo kit come with a short downpipe, that bolts straight up to a UK spec downpipe/1st decat. And then it's all just standard from there.

 

I just want to make sure the UK spec decat will align properly in my vvti car.

 

Ignore me, I know nothing. I shouldn't be posting past my bedtime :D

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:D

 

Well it's too late now lol And i'm not sure either way to be honest. You and Rob W both seem to think a standard UK spec would be best so that will do for me.

 

It will be fine mate, the different flange angles are nothing to do with running past the gearbox or subframe parts. Purely down to the design of the stock manifold downpipe.

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