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In this post, we rejoin Geoff Winder as he contemplates a gearbox for his Lotus Esprit VQ project.
Read Part 1 here.
By Geoff Winder
The post-‘87 Esprits use a Renault UN1 gearbox. Considering, in race tune, the VQ engine will be capable of over 500N-m, I was concerned about the fragility and rarity of the Renault box. I was going to have to adapt whatever box I used to the Nissan engine and I thought it would be a good time to look at alternatives.
The Ford GT40 replica guys have, for a long time, pondered the problem of a suitable cost effective transaxle and it looks like the Audi 01E box will be my best option.
Here is my Audi box sitting next to the standard Lotus/Renault Box (with Lotus bell housing removed and a Renault installed (another idea)). This box came from a 2.5TDI Audi A8. The ratios are not what you would call close, ratio 5th and 6th are for country cruising..
Gearbox aligned to have the drive shafts centred.
The problem is that when I installed the gearbox in the correct place for the drive shafts to be aligned, the engine is placed a long way back (it can come 150mm further forward without hitting the firewall). Not optimal for weight distribution and hard to use the standard engine mounts.
As you can see in this picture the engine mount positions are 130mm apart. Whilst it would be possible to mount the engine here it would be much neater to have the weight pushed as far forward as possible.
A rather radical gearbox adapter was the solution. Start with the Nissan auto bell housing, cut it and machine on my rather underweight milling machine.
This was how I achieved a rough alignment. The 20mm shaft passes through the plate and into the spigot bearing in the crank shaft.
Plate pinned and ready for welding.
Mig welded, ready for cutout
I had the plate side of the adaptor surface ground to ensure it is perfectly parallel with the standard Nissan mount side.
Wow it looks like a drive train. Still no flywheel or clutch..
Engine mounts almost line up now, the rear hole on the chassis now lined up with the Nissan mount.
Here you can see the Air-conditioning compressor at a safe distance (just) from the front of the engine cradle in the chassis.
Remember that little milling machine? Well it is earning it keep. Solid billet of aluminium to get the correct angle for the engine mounts.
As I am using an Audi transaxle I decided to use Audi engine and gearbox mounts as they would be matched
Seems to work. Whilst the some of the mount adaptor is cantilevered, the centre of the mount is placed directly above the rear engine mount bolt hole in the Esprit chassis. This an extremely strong point.
Probably better if I use Aluminium rather than wood.
Gearbox mounts in progress.
This is a input shaft extension I had made.
Checking that everything is parallel.
I was really worried about getting this right, but in the end it was quite easy. Bolt up the auto bell housing tight and the Audi box just snug to the adaptor. Then, with the aid of a little camera, watch a dial gauge attached to the crank turn around the gearbox input shaft. A little tap on each side of the gearbox to fix any runout, job done.
Then drill and install dowels in the adaptor plate to ensure it goes back where it is supposed to when taken apart.
Stay tuned as we continue this unusual and fascinating project.