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6 speed gearbox conversion finished (Long)

TLicense

By TLicense
in mkiv Technical

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TLicense Newbie

TLicense

Posted
Posted

Well I finally got the car back a little under a week ago, and as promised here is the write up....

 

When I bought the '93 J-Spec GZ auto, I was told by a friend of mine that I should have gought a manual. I had tried to get one but had spent a little over 3 months looking to no avail. I laughed it off at the time saying that manual or auto, 320 bhp will be enough to please whatever. However, after about 3-4 months of ownership, and finding Mohd's "how to" on MKIV.com, I soon starting to think that I wished I'd bought a manual and that maybe I should try a conversion as I wanted to keep the car I'd bought.

Anyway you're reading this to find out about the conversion not about the why's and wherefore's of doing it. So here goes.

 

Gearbox's.

Obviously the biggest single item is sourcing the getrag 6 speed gearbox. Finding one of these is rumoured to be a nightmare, but within about 4-5 phone calls I'd found two scrap yards, both offering gearbox's at the same price. In the end I went with Celica breakers, based in the west country. At the same time I ordered a drive shaft, clutch master cylinder and slave cylinder. In total, including delivery and VAT this came to about £850. (The gearbox was only £450 exc VAT I seem to remember)

 

Pedal box,

This is where the real searching comes in. Basically I called every breakers yard that I could find to see if there were any clutch pedal assemblies available. All of them said no. In the end I resorted to buying a complete brand new pedal assembly from Toyota. I bought this through Kevin at Envy. Whillst I was ordering toyota parts through Kevin, I also ordered the clutch lines, the gear shift surround and the centre tunnel which needs to be replaced in order for the 6 speed gearbox to fit. All in all these parts came to somewhere in the region of £800

 

Clutch and flywheel,

Whilst talking the project over with Kevin at envy I mentioned that I needed a clucth and flywheel, and that I would probably prefere to go with something above stock. Mainly because I knew I would be increasing the power output, and didn't want the hassle of replacing a clutch later on. For the output goals that I had, Kevin recommended the RPS Street cluctch. As far as flywheels, the RPS light-weight flywheel was recommended as being the best aftermarket fly-wheel for the supra, so I went with that. Total cost of flywheel and clutch was in the region of £900 including the release bearing.

 

This was the basic cost of parts for the task ahead, however I had neglected to get a number of parts which were later bought at the time of fitting, for example flywheel bolts, pilot bearings, all the clips and washers for the clutch/flywheel assy, dust covers for the gearbox (it came with none) and a clip for the clutch line to bolt to the gearbox. In total these came to around £350-400.

 

ECU

There is a difference between the auto ECU and the manual in that the auto ECU is known to pull timing at the shift points. Not ideal. So a replacement ECU would be needed.

One thing I was very sure about was that I wanted the car to be future proof. The car was reasonably stock beforehand (hks mid-pipe and exhaust) producing 321 bhp on Thors dynopack, I knew I would soon be wanting more power, but didn't want to have to pay out to replace items that I had bought whilst doing this conversion. This ruled out replacing the auto ecu with just a plain manual ecu on it's own.

I looked at all the options and finally chose the AEM. Mainly because anything is possible with this ECU, and I decided that I would be interested in completely mapping the car from start to finish by myself at some point. (Something you can do by simply saving your current map, and downloading a map of your choice)

Although there were several other possibilities available (AVC-R, E-manage etc) It was the toal functionality of the AEM that finally sold me.

I bought an AEM, 3.5 Bar MAP sensor, AEM wideband 02 sensor, AEM inlet air temp sensor, HKS DLI, Warlbro fuel pump and FSE from Paul Whiffin at whifbitz for around £2300. I chose the warlbro fuel pump and FSE to help compensate for the small JDM 440CC injectors and fuel pump, which would be struggling at 18 psi.

 

Boost control

I'd not decided which boost controller to use until quite late in the project. The AEM is perfectly capable of controlling boost, and with some inventive wiring, it's even possible I belief to have a switched boost limit. However, I felt I would rather go with a dedicated unit, with specifically designed solenoids. After some advice from people who would be deemed to be in the know on this forum, I chose the Blitz SBC ID III. Mainly because I was told that the Blitz solenoids are the best at controlling boost, and as a secondary reason, because coupled with the powermeter, they simply look fantastic. I bought both of these from Takakaira in Japan for a total cost including shipping and customs of £550.

 

Fitting

For a small amount of time I did consider fitting this myself. Then memories of my other mechanical adventures set in, and I quickly brushed that idea aside. I had spoken to a number of local garages to see if they were interested in doing the project. One or two said the would be interested but had never done anything like this before. I then got in contact with Leon at JPS motorsports near Milton Keynes. He had done a conversion before, and after looking at his car and with the knowledge that he is a Supra specialist, I decided to go with him.

I dropped the car off the first week in December, and picked the car up a little over 8 weeks later. This should have been a lot sooner save a few problems. First of all I hadn't ordered all the parts as I mentioned above. Secondly, the clutch msater cylinder I ordered was useless. A big chunk was missing from the side wall. The initial diagnosis was that it just needed the seals replcing. The overhaul kit took a week to arrive. The kit sent was the wrong kit, and so needed to be re-orderd. This took another half a week. Then the broken cylinder was spotted, and a complete master cylinder ordered which took another couple of days. These problems as well as the Christmas and new year holidays cause the initial 3 week timescale to soon more than double.

All that was left after fitting all this was mapping the AEM, which thanks to Wez, wasn't too much of a problem as he came up trumps in the form of a useable, and very similarly to what I needed, set-up basemap for the ECU. Once this was downloaded it was just a matter of hours to get a well working map for my car.

The total cost for fitting everything and including the parts I'd not orderd mentioned above was £2,900. So about £2,500 for fitting and mapping of everything.

 

Troubleshooting

As some of you have been aware, I've had a few niggling problems since picking the car up, however I would hasten to add, none of these seem to be down to the actual conversion, but more associated with the additional things I had done to the car.

Current problems that need to be fixed are:

CAT overheat light staying on - An AEM problem that is due to the fact the AEM was designed for US spec cars.

Slight flat spot in engine map @ 1000 rpm. I managed to fix this by adjusting the rpm vs throttle% idle adjustment on the AEM.

Rattling flywheel. A result of the lightened flywheel. Nothing can really do.

Flashing trac control light. I fixed this by removing the trac ECU which is not used by the AEM (It has it''s own trac control). However it seems removal of this also disables the cruise control, so at some point I may re-instal this and just remove the trac bulb.

Clutch bite point at very end of travel. I fixed this by adjusting a screw behind the clutch pedal.

Powermeter back light going dark. Not sure what is causing this but will let you know when it's fixed.

 

In total the complete conversion including the £50 increase in my insurance has cost me £8516.84. The car originally cost me £8,500. I could have probably sold it for somewhere in the region of £7000. I know I could have bought a manual for the money I've spent to be honest, by replacing the items that I have uprated with stock items the total cost would have been more like £5,000, which puts the total spent in the region of what a low mileage, good condition 6 speed supra tends to cost. Plus I have the satisfaction of knowing that I managed to go against the grain (something I enjoy doing).

 

If pestered enough I'll look into posting the part numbers from Toyota needed to do all of this as stock, but as it is I'll leave it like that unless there are any unexpected developments, until I start stage 2 (Secret for now :) )

 

I'd like to thank all the people that have given me advice over the past few months, and in particular Kevin at Envy, who without I would have never got all the parts for this, and to Leon and his team at JPS, who did what can only be described as an absolutely outstanding job. Thanks to you all.

 

Thanks for reading.

 

Tony License

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  • 3 months later...
Alex Newbie

Alex

Posted
Posted
Originally posted by Soop Dogg

Hmmm....got me thinking now!

 

Just one thing that I thought was necessary when doing this, but I was never sure about, does the auto Diff need changing for the manual box? I might have missed it in your write up, I read it a bit quickly.

 

I believe you'll be short geared with the auto diff, so a change to a UK one or TRD one would be best.

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TLicense Newbie

TLicense

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  • Author
Posted
Originally posted by Alex Holdroyd

I believe you'll be short geared with the auto diff, so a change to a UK one or TRD one would be best.

 

Apparently the TRD one doesn't change the gearset, so you'll still need to change the diff.

The speedo with the auto box will read about 20% fast. Not sure what it'll do to top end, as haven't reached it yet, but itll go off the clock (less the 20% error)

 

It's a job that anyone can do in all honesty. There's nothing trick to do. If you can change a gearbox then you can do this conversion.

 

If you have any questions then I'll be happy to help.

 

Regards

 

Tony

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dude Newbie

dude

Posted
Posted

I think the easiest / cheapest way to do this conversion (for someone like me ) would be to import a manual car and swap all the bits between the 2 cars , the only part you would HAVE to buy would be the gearbox cover , this would save around £2-3K in parts and if you could sell the newly auto'd import at a profit it would be even cheaper !!!! and youd have the diff /half shafts etc

 

Dude:flame Dev

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dude Newbie

dude

Posted
Posted
Originally posted by dangerous brain

Why will I have to buy a new gearbox cover? Can I not use the one from the donor car?

 

Its welded/stuck to the floor and is only a tin plate and very cheap !!!!

 

Dude:flame Dev

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  • 2 years later...
supra steveo Newbie

supra steveo

Posted
Posted
Hmmm....got me thinking now!

 

Just one thing that I thought was necessary when doing this, but I was never sure about, does the auto Diff need changing for the manual box? I might have missed it in your write up, I read it a bit quickly.

 

yeah you got me thinking now aswell....................

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

about how to rob abank and get away with it, well whats the use of having a decent car when your inside.

and i thought i was the only mad man to bring threads back to life

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