Comparative gear ratios in UN1-013 & UN1-07

I'm still busy researching alternative gearboxes for my GTD (engine is a 302). I have narrowed the choice down to two, both based on the 3.44 final drive.
The UN1-013 was originally specified for the 21 Turbo. The other box, UN1-07 was specified for the Alpine Turbo. The boxes are very similar - ratios on 1st, 2nd and 3rd are identical, but the UN1-07 has slightly higher ratios for 4th and 5th.

My question is - has anyone else looked at the comparative merits of these two 'boxes, most particularly with their gearing on the road once tyre sizes are taken into consideration?

Any user experiences would be much appreciated,


Peter Delaney

GT40s Supporter
Hi Peter,
The attached spreadsheet might be helpful. I set it up to compare the Porsche G50-50 & G50-00 gearboxes, but if you know all the ratios for your UN1 boxes, you could just substitute these new numbers. Enter the tyre diameter & the final drive ratio, & you will get graphs of rpm vs speed in each of the gears in mph & kmph.

Hope this is useful - Kind Regards, Peter D.


Thanks for the French lesson, Paul!

Peter, your Porsche data was interesting, and actually very close to the data I have for the UN1-07. The big difference is the much wider spacing between 4th and 5th on the Porsche set. Just for interest, I'm attaching a .pdf output from the data I have on the UN1-07, calculated for 265/50x15 wheels. Please excuse the output, it ran into empty pages. The key point here is that 4th on the UN1 box fills the gap between 3rd and 5th quite well.

What is missing of course is a chart of engine bhp/torque, the better to match these gear ratios. However, it is interesting to note that the same 'box was used on the Renault Alpine (bhp 200, weight 1180 kg, bhp/ton= 177). My GTD has a bhp/ton of just over 200, which would suggest that the tall 5th gear on the UN1-07 'box is well within spec for my car. The Renault rear wheel/tyres are sufficiently similar to mine to be overlooked.

Thanks for your input,


Paul Hendrickx

On my 310 v6 pack gt version i had as per original 285/40/15 yoko with 1.96 mt. development
and i had a 3.0lt 24v zpj engine (ex 605 Peugeot) withe small upgrade to 225 bhp

Peter Delaney

GT40s Supporter
Hi Peter,

With regard to the big spacing between 4th & 5th - this is from the worksheet tab "G50-xx & Mods". The standard G50 ratios are shown in the worksheet tab "Stock G50-xx".

At the time, the cost of a higher final drive setup was out of reach, so I opted to just go with a higher 5th. That sorted out the ridiculous revs at highway speeds, but left the big 4-5 gap - annoying !

If I had my time over again, I would have left the individual stock ratios alone & gone for the higher final drive (and $ and hassles). The stock ratios are nicely spaced, but the whole setup is just too low-geared for a GT40. 1st gear is good for pulling stumps out of the ground or frying tyres - not much else !

For what is worth, I reckon that the UN1-07 is the go - still has nice even separation between the gears, & will be less annoying at highway speeds (unless, of course, you are building a track car! !

Good luck !

Peter D.
Thanks for your comments, Peter. I must have gone down the same route as you, as my car originally had a 4.11 final drive. As you say, ridiculously low, running out of revs far too early. Hence my faffing about looking for something else. I solved it now, 3.44 final in the UN1-013 box.
During my research, I came across this extremely helpful site which enabled me to calculate exactly what speeds in what gears and at what revs etc. Admittedly it is on a site devoted to VW cars, but the data is universal. It really is useful:


You probably know but I thought I`d mention the Alpine GTA? is rear engined like a 911 so the diff has to be turned around or the gearbox inverted like mine was done many years ago. The bellhousing is shaped so the diff can be swapped around with no clearance issues.