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The mkiv Supra Owners Club

1.4 bar boost (1.2 bar restrictor)


Matt H

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So we're saying then that 1.25 bar is ~80% duty cycle on the 440's. If it can be scaled up in this sort of fasion then, that means the 440's can handle 1.56 bar at 100% duty cycle.

 

OK?

 

I'm just wondering now because I have a Jap spec car coming. My UK car just needed de-cat, exhaust, and a bleed valve. Now I have to start pissing around with restrictor rings and worrying about injectors and stuff.

 

Can't I just replace the wastegate with one from a UK motor?

 

Well, i'm just going by what the EMU is logging the injector duty cycle at, i don't have any reason to doubt it, but you never know,

and the couple of logs i have taken since have showed the same,

I have no idea if the UK and J spec actuators are the same or even the same psi rating, i know the std J spec are 17. something.

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So we're saying then that 1.25 bar is ~80% duty cycle on the 440's. If it can be scaled up in this sort of fasion then, that means the 440's can handle 1.56 bar at 100% duty cycle.

 

OK?

Even if that were true (which it isn't) you really don't want to be running your injectors at anywhere near 100% duty cycle if you can help it. Besides which, there's no point running stock Supra turbos at 1.5bar as they're way past their peak efficiency at that kind of pressure - they're just making lots of heat and not giving you any more power than they would at 1.2 - 1.25 bar, probably less.

 

I'm just wondering now because I have a Jap spec car coming. My UK car just needed de-cat, exhaust, and a bleed valve. Now I have to start pissing around with restrictor rings and worrying about injectors and stuff.

 

Can't I just replace the wastegate with one from a UK motor?

Not unless you also want the lagtastic UK turbos too. Just BPU your j-car to 1.2 bar and forget it, enjoy the extra torque and faster spool, and be happy. You won't regret it.
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Even if that were true (which it isn't) you really don't want to be running your injectors at anywhere near 100% duty cycle if you can help it. Besides which, there's no point running stock Supra turbos at 1.5bar as they're way past their peak efficiency at that kind of pressure - they're just making lots of heat and not giving you any more power than they would at 1.2 - 1.25 bar, probably less.

 

Not unless you also want the lagtastic UK turbos too. Just BPU your j-car to 1.2 bar and forget it, enjoy the extra torque and faster spool, and be happy. You won't regret it.

 

OK. Thanks for that Jake. I had no intention of running 1.5 bar but I just wanted to be sure that they're 100% safe with the 18psi that I was running on the UK car. I suppose it's obvious that they will be, within reason (injectors anyway.. turbo lifespan is another story).

 

I'm really looking forward to the spool/torque. UK car was pretty poor off the line.

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Just an interesting side note, i have std injectors and i hit 1.2 -1.25 bar and my EMU log was showing injector duty cycle of no more than 79% with AFRs of 10.2 and occasionally into the 9s and thats with no adjustments, now i run water injection which will lower the AFRs but it is not going to affect injector duty cycle, the 79% is both input and output, somewhat puzzling!

 

Can you post the datalog up so I can have a poke around in it :)

 

-Ian

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the restrictor is hardly a pain and if your car is otherwise standard (i.e. not had the turbos fiddled with) you should find it quite easy to hit exactly 1.2bar every time (mine does) allowing for .05 bar tolerance either way due to weather variations...

 

and j-spec turbos rock! the low down grunt and lagless performance means a bpu car is quite a mental street weapon :D even if it can't compete in a straight line with the big single cars.

 

never driven another turbo car quite like it, you might be mistaken for thinking you have something instant like nos or a supercharger lol

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You just need a pair of my de cat pipes and one of my restrictor rings, job sorted. You'll love the spool and power of the proper Jap spec engine ;)

 

oooh I'm getting quite excited :D

 

I'll be putting the Greddy exhaust (that I got from you Chris) on there. Does this alter the situation with regard to ring size?

 

super excited :D

 

MOT is due October so might wait 'til just after to do the decats.

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