Nice sunny day down here,
Time to take the '79 coupe out for its monthly run.
This has a Turbo Supra 5 speed box.
Driving in the suburbs not able to let it rip, but did try a few times to let it over run ( no fuel ) then slip the clutch. RPM dropped to around 600 usually, couple of time it dropped momentarily to perhaps 300 but quickly picked up to 600. Never stalled, although on a cold day with engine still cold that may happen.
This is a 5.3 HE engine with an aftermarket EFI system. I will have to hook my laptop up to it again to check all the settings. I think the over run limit is set around 1200 - 1500 RPM. There are other settings that might influence how it starts up the fuelling again, so it is a lot more sophisticated than the OEM ECU.
I still have the OEM over run valves in the intake manifolds.
The Turbo Supra box does not give a quick change 1st to 2nd, quite disappointing really. I totally stripped the box and found a website with a very good overhaul guide.
The synchros looked good and everything else cleaned up well. Fairly sure I rebuilt it according to the guide and everything else is fine. Anybody have a Turbo Supra box with a similar issue ? I once drove an XJ-S with a standard Supra box and that was very slick changing in any gear. Pity they are a bit marginal for strength behind a 5.3.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
22
What does it do? Does it grind if you try to get there too fast? Does it balk so hard you physically can’t shift it any faster?
1st to 2nd it does not grind, it tends to balk or at least be significantly harder to change compared with all the other changes which are quick and easy.
I do not think there is an unusually large ratio change from 1 to 2.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
24
What lubricant is in the tranny? You might want to switch to RedLine MTL. Users report you can feel the difference in the shifting.
I recall looking up a number of sites discussing the best lubricant for this box.
This was in relation to getting the quickest shifts out of this box.
Whatever was the most popular choice, that is the one used.
Redline rings a bell, I would have to search the garage for the old can.
I checked the program of the Motec EFI unit in the coupe.
The RPM limits for fuel cut out are 1200 and 1800.
No particular reason for those values, and easily changed.
There is a setting for increasing the first injector pulse after fuelling is reinstated.
I have this set to zero but could easily increase it. Next time the laptop is connected I will see what happens if I set the increase to 100%. That will give a double width pulse.
Looking at the fuel map the pulse width under 2500RPM with closed throttle is typically 15% of what you would have at WOT. I guess that means if you are on over run and slip the clutch the engine drops down thru 1200RPM before the injectors start up again. The fuel map cell at that operating point gives a narrow pulse and it might take a few pulses after the fuelling kicks in before enough fuel is in the cylinders to get it firing. If you try turning over a V12 you know how much torque is needed to overcome the friction. At 1200RPM there is very little time before that friction stops you dead unless the cylinders fire up again. That could cause a stall.
That supposedly is why the Motec EFI lets you set a much wider first pulse.