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The mkiv Supra Owners Club

Performance Drop over 6krpm


Alex
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Whenever I really nail the car hard to the red line I get a noticable drop in willingness above 6000rpm could this be due to the air flow metre? badly mapped ecu? or just having the cats in place?

 

I've heard alot about the MAP and MAF sensors could could airflow sensor cause a lack of power top end?

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Hi there,

 

Take a look at the power curves for the Supra and I think you'll find that you are passing the maximum torque output when you get up to 6000rpm. The power curve drops off quite quickly in that region of the rev range (torque output is what gives you your acceleration).

 

I'm trying to remember but I think the max torque is in the 5000-5500rev region but as I say thats just from my not always to accurate memory.

 

AJI

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You might be thinking of peak power?  That's around 5,600rpm on a stock MkIV.  Once you get beyond that, power drops off remarkably.

 

However, Alex, it sounds like the car *used* to feel better at 6k+ than it does now, is that what you mean?

 

-Ian

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Not a new problem just more noticable since I've started racing people :)

 

In my mind the car SHOULD pull strongly right through to the red line not give up 1000 rpm short.... is it just running out of breath?

 

Has anyone got a copy of the standard power curve?

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Quote: from Alex Holdroyd on 12:52 pm on Oct. 1, 2001[br]Not a new problem just more noticable since I've started racing people :)

 

In my mind the car SHOULD pull strongly right through to the red line not give up 1000 rpm short.... is it just running out of breath?

 

Has anyone got a copy of the standard power curve?

 

I've been thinking about this since your first post. There doesn't seem to be a standard behaviour profile for a Supra does there. It must be different ECU versions, different diffs, etc.

 

Since I got rid of my 120MPH problem, my car now hits the red line like a wall in every gear except 3rd to 4th above 120MPH. I find myself looking down at the Tacho, worried that it's going to hit 8,000 RPM, then at the last pixel, it changes up.

 

Above 135 MPH, it doesn't accelerate like I'd like. It's a bit sluggish.

 

I'm betting, my diff version, early ECU software, etc. is what gives mine it's own personality; same for you.

 

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My MkIII never, ever saw the redline, simply due to the fact that at 6000rpm, it utterly ran out of puff.  You could really, really feel the power drop off, and redline was at 6500.  You would have to be a murderour b'stard to persuade it up to there.  Peak power was at 5400.  So I can understand a MkIV getting a bit wheezy at those levels as well.

 

The thing is, the redline isn't anything to do with power.  It's just the point at which the engine can rev at before it suffers undue wear and tear, or catastrophic failure.

 

Cars which have their peak power near the redline (Ford Mondeo ST200 - 6500rpm redline, 6300rpm peak power!) are nasty to drive anyway.  Be happy with your spread of torque :)  You don't need to rev the arse off a Supra to accelerate quickly - just change up at 5500 to 6000 and you'll drop right back into the 2nd turbo power band - lovely.

 

-Ian

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I agree that you don't need to be anywhere near the redline on the road.

But on a *UK-spec* the 2nd-turbo doesn't come in til a lot higher up than a Jap-spec.   about 4800rpm is when it goes.

 

At TRAX on the track session, I deliberately went no higher than about 6000rpm or so, which made it go plenty quick, BUT i distinctly noticed that when i changed up to the next gear it dropped way off the big power band, and there was a small delay until the revs got up to about 4800 or 5000rpm anbd the 2nd turbo blew hard.

 

So definitely on a UK-spec when you really do want to go flat-out then i think that you need to be really quite near the redline (is it 6800rpm ?? not sure...) in order that you engage the next gear at a high enough revs that you don't suffer a delay before the 2nd turbo comes in again.    

 

Like Ian said, it's not so much to do with peak power, but it *is* to do with what revs you get when you change up to the next gear.

Jap-specs are probably less affected as the 2nd-turbo comes in about 4000rpm or so.

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Hmm maybe I do have normal turbo's then (gunna send the boys round to the bloke who sold it to me!)

 

My second T is on-line and pushing from 4000rpm...

 

Ian C you have Hybrids at what point can you notice that T2 is online an you're hitting nigh on full boost.

 

By the way I have a MINES ECU, not a normal J-spec, uprated injectors, K&N induction SuperDrager exhaust IF that makes any difference

 

(Edited by Alex Holdroyd at 2:56 pm on Oct. 1, 2001)

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Quote: from Paul Booth on 1:46 pm on Oct. 1, 2001[br]
Quote: from Ian C on 1:30 pm on Oct. 1, 2001[br]just change up at 5500 to 6000 and you'll drop right back into the 2nd turbo power band - lovely.

 

-Ian

 

Maybe you should have a talk to my ECTS ECU.

 

 

OI!  ECTS!  CHANGE UP!  NOW!

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I didn't realise that the UK spec 2nd turbo takes so long to get going.  The hybrids on mine get going at 3500 to 4000 rpm.  On fast upchanges, you can get the power back on with minimal boost being dumped, and the turbo will be back on song almost immediately.  An upchange at 5500-6000rpm takes you back to 4500-5000, if that helps.

 

-Ian

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Guest Martin F

Ian, I think Stu is refferring to a non-modified UK spec car.

 

As soon as you remove cat's, change exhaust etc the lag on the UK spec seems to be decreased. This is one of the biggest differences i noticed when i test drove my car at JIC in comparison with a standard UK car.

 

 

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well yes the lag is decreased on a modded UK car BUT it's still there (obviosly you can't get rid of it as it's a turbo....).

I still notice a very definite delay when going for it.   I think it's more to do with the fact that there is now a really noticeable power-step at about 4800rpm (SAME rpm level as an unmodded car, but the power-step is bigger so it's much more noticeable).    When i was at TRAX, on every upchange it dropped off the 2nd-turbo and there was a delay before the revs and boost picked up again.  

I think actually (having experienced Martins car) that this *may* be partially due to me having a bleed-valve.   The characteristics of the bleed-valve (compared to a DSBC for example) result in a more noticeable power-step.    I remember from the run in Martin's car that although the power was roughly the same, it had a smoother transition from 1st turbo to 2nd turbo.        might have been my imagination but would be interested to do a bit of back-to-back comparison.       DSBC is probably a better way of controlling boost than a bleed-valve but i don't really want to spend that sort of money to buy one and install one.

 

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Quote: from Ian C on 12:55 pm on Oct. 2, 2001[br]I didn't realise that the UK spec 2nd turbo takes so long to get going.  The hybrids on mine get going at 3500 to 4000 rpm.

 

Sweet that means I could still have Hybrid's!!  :biggrin: :biggrin: :biggrin: :biggrin: :biggrin: :biggrin: :biggrin: :biggrin: :biggrin: :biggrin: :biggrin: :biggrin:

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I might be wrong but I think a de-catted J-spec cars No 2 turbo would be up to speed at about 4000-4200 rpm (quicker spool time with the j-spec ceramic internals over the UK spec steel internals).

 

From what I have understand from my own research and conversation with Hybrid Turbo's owners suggests an increase in lag over the stock system (regardless of UK or J-spec origins). Not to mention that hybrid Toyota turbo's can be specced to your requirements e.g. mild through wild and varing stages in between.  

 

Alex, did you not get a receipt/documentation from the previous owner?

 

regards............

 

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Gav,

 

All the work was done in Japan so no records... on face value the deal looked shady BUT every thing else on the spec list is there so I hope they are hybrid the only way to find out is to take them apart. That aside the money I paid for the car mean't it was worth it whether they were hybrids or not.... The second T is online by 3800 and can be spooling from 3600rpm full boost by 4000rpm. I still have both cats.

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Sorry, I should have looked at the specs of your car.

 

The spec of this car included all the things you have plus the items you are looking to do, cams, decat, intercooler etc .

 

Given the fact that someone has gone to the trouble of fitting a special ECU and fueling upgrades you may well be running Hybrids.

 

What boost are you running by the way?

 

 

 

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The intercooler is a nice idea at the moment...I haven't got the cash....and JF is selling me his de-cat pipes for a very reasonable price. I shall test them out and if I think I'm boosting too high then I 'll put the second cat in until I can afford a small intercooler.

 

I don't know if the MINES ECU is actually managing to lower boost or not as it seems to be impossible to find anyone who can help! Both the companies I've been pointed at recently have been a bit elusive!

 

It's all a bit theoretical right now.... but thanks for the suggestions...

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