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Discussion Starter · #1 · (Edited)
I dynoed this fall, posted this before - could only boost 15psi (spark plug problems), BPU auto, sequential mode.

What I noticed, however, while studying other BPU dyno graphs, my torque curve is EXTREMELY low on the low end. The car was in temporary TTC when I got it, and I put it back on Sequential right away. Is something not functioning properly? Can anyone explain why my torque curve is so low relative to other BPU dyno graphs?

I noticed others with similiar numbers were seeing minimum 250ft/lbs at 3.5k rpms, and 300ft/lbs at 4k, whereas I'm nearly 50ft/lbs behind. My car seems to have extremely LOW numbers from 3k-4k, but it seems to be fine and it seems the second turbo is kicking in right at 4.2k, like it should, which would eliminate a boost leak.

I now have done the spring mod and have better plugs with a .028 gap, and I plan to dyno again in 2 weeks at 18-19psi with 100octane, but going over my old dyno graphs again baffled me. Can anyone explain why my car is so weak under 4k?

I've always maintained my car FELT slower than it should. Could this be the cause of it?

Thanks,
Marc

 

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do you have a tq conv?
do you lock it in gear when you dyno?
what gear was the car in when it was dynoed?
is there a CEL on?
is this graph corrected?

also go over your car with a scan tool:
check your STFT, LTFT then run the car and check for knock while driving

did you have a wideband hooked up? if so was it running really rich or lean?

there could be hundreds of things wrong, you just need to give a bit more detail to allow someone to diagnose
 

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Discussion Starter · #3 ·
The car does not have a torque converter. It was dyno'd in 3rd gear with O/D off. No CEL was on when the car was dyno'd, and the graph is SAE corrected.

No wideband was hooked up on the dyno, as I do not have an SAFC, but here are the A/F numbers:

 

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Well it does look pretty damn rich going off the top end. I bet you can pick up some more hp by richening up between 4.5k and 6k and leaning out after 6k. Btw, what transmission are you on? I'm not quite sure what tranny you have since you say you have no torque converter, but you say the o/d was off.
 

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Discussion Starter · #5 ·
cornpops said:
Well it does look pretty damn rich going off the top end. I bet you can pick up some more hp by richening up between 4.5k and 6k and leaning out after 6k. Btw, what transmission are you on? I'm not quite sure what tranny you have since you say you have no torque converter, but you say the o/d was off.
Sorry for the confusion - stock auto transmission.
 

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Something is definately killing the topend. When my car was BPU, my HP was pretty flat until about 6200 and then fell off gradually. Yours look normal until 5800 or so and then plummets. Maybe an ignition problem. New plugs might fix it. Also, your A/F curve looks a little lean (until 600 RPM) from others I have seen. Most go down to 11.0-10.0 just after 4500. Can't say what would cause that. Maybe a dirty MAF sensor or a leak into the intake just after the MAF? A weak wastegate spring might cause the boost to fall off on the top also.

good luck fixing it,
 

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Discussion Starter · #7 ·
97twinturbo said:
Something is definately killing the topend. When my car was BPU, my HP was pretty flat until about 6200 and then fell off gradually. Yours look normal until 5800 or so and then plummets. Maybe an ignition problem. New plugs might fix it. Also, your A/F curve looks a little lean (until 600 RPM) from others I have seen. Most go down to 11.0-10.0 just after 4500. Can't say what would cause that. Maybe a dirty MAF sensor or a leak into the intake just after the MAF? A weak wastegate spring might cause the boost to fall off on the top also.

good luck fixing it,
The problems on the top end have been addressed. I did the wastegate spring mod, and I am holding boost rock solid until redline. I definitely expect to make much better numbers, especially on 18psi.

The real problem is: Why are the numbers so low from 3k-4k? Will adding more fuel fix this? My torque curve in this range just seems LOW for the average BPU Supra, by about 50ft/lbs minimum.
 

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welll... here is the thing, your car is either dangerously lean on the bottom end...

or the person dynoing the car did not lock it in gear, which would mean he eased it up to bout 4k and hit it to prevent it from downshifting (which would give you a bad low end torque number)

retry using the MANU button to lock the car in 3rd gear and hit it hard from bout 2 k
 

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Discussion Starter · #9 ·
swearitsstock said:
welll... here is the thing, your car is either dangerously lean on the bottom end...

or the person dynoing the car did not lock it in gear, which would mean he eased it up to bout 4k and hit it to prevent it from downshifting (which would give you a bad low end torque number)

retry using the MANU button to lock the car in 3rd gear and hit it hard from bout 2 k
According to mkiv.com, the trac fuse is supposed to be pulled when dynoing an automatic car, with the O/D disabled. I have heard that with the trac fuse pulled, the "manual" mode does not operate correctly. I may be incorrect in this assumption, but I was under the impression most auto TT owners dyno'd NOT using manual mode.
 

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MarcSMT said:
According to mkiv.com, the trac fuse is supposed to be pulled when dynoing an automatic car, with the O/D disabled. I have heard that with the trac fuse pulled, the "manual" mode does not operate correctly. I may be incorrect in this assumption, but I was under the impression most auto TT owners dyno'd NOT using manual mode.
sorry.... i forgot im running AEM EMS and i can lock in gears at any time....

its not necessarily adding more fuel... seems the reason your a/f was soo lean is becuase the car still wasnt full throttle... ~15-16 af is cruising or low/mid throttle

IMHO the car was just dynoed wrong
 

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Discussion Starter · #11 ·
swearitsstock said:
sorry.... i forgot im running AEM EMS and i can lock in gears at any time....

its not necessarily adding more fuel... seems the reason your a/f was soo lean is becuase the car still wasnt full throttle... ~15-16 af is cruising or low/mid throttle

IMHO the car was just dynoed wrong
That makes a lot of sense. When I get it back on the dyno in two weeks, maybe I should try doing one pull in manual mode.

Thanks for your help.
 

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MarcSMT said:
According to mkiv.com, the trac fuse is supposed to be pulled when dynoing an automatic car, with the O/D disabled. I have heard that with the trac fuse pulled, the "manual" mode does not operate correctly. I may be incorrect in this assumption, but I was under the impression most auto TT owners dyno'd NOT using manual mode.
It should also force the converter to lock up... Not the greatest thing in the world for longevity... ;) Personally, Just easing up to the start point above 4k has worked for me. Lay into it after that, and it shouldn't kick down.

~Nick
 
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