Upgrading 395 Gearbox with Shorter Ratios & Limited Slip Diff

[Mecky]

Hi guys,

as some of you may already know, I'm racing a Europa S2 with crossflow engine in Belgium and Germany. The engine is quite nice in torque and power and it seems that I have now sorted out the most important issues of the car, such as cooling, brakes and (hopefully) reliability as a whole. Now, I'm finally at the stage where I can try and upgrade the car, instead of just making it work.

As you can see in this YouTube-video https://www.youtube.com/watch?v=V-YlW0TTYUc, my lap time is limited by my own driving. But it's also limited by my gearbox. I use a Renault 395 5 speed gearbox, which I have overhauled in 2020. The gearbox works fine, but it has very long gear ratios and no limited slip diff.

I got in touch with the best-known Renault Alpine tuning company in Germany, but they can't help me, as their limitied slip diff is developed for Alpine A110, which has the gearbox in front of the engine. That would mean 5 reverse gears in my case.
Thus, my idea was to try and find out, if anyone here in this forum knows a source for a limited slip diff, which fits into the 395 gearbox. If that's unobtainable, I'd like to find out, if it's possible to get another set of crown and bevel gear, in order to make my gear ratios adjustable. My current final drive ratio is 9/34. That means a top speed of 236 kph in 5th gear at 7500 rpm. But for example at Circuit Zolder (refer to video), I only use gears 3 and 4. While this is quite relaxing for me as the driver, this is not really optimal for being fast. I guess, just a ratio, with well-useable 3rd, 4th and 5th gear would help me gain one or two seconds per lap, without even improving my own driving.

Attached, you can see some pictures of my gearbox. I have already worked on it myself, thus execution of this work shall be possible for me. But I don't know, if there is any gearbox which can be a possible donor for me. I know that an NG3 gearbox is not the right choice, as the shaft of the bevel gear is completely different, which makes it impossible to fit 1st, 2nd, 3rd and 4th from the 395 gearbox on it. But maybe there are other Renault 5 speed gearboxes (older than the NG3), which have the same form-locking connection between gears and shaft. In this case, there may also be a different final drive ratio available, which could allow me to have shorter ratios in all gears.
On the longest straight in my racing series (Kemmel straight at Spa-Francorchamps) I reached something around 6000 rpm in 5th gear at the braking point. That means there is room to shorten the ratios for all tracks. But even, if the new ratio would be too short for Spa, it would be great for Zolder. We are going to race there three times this year.

I'm looking forward to your replies. Thank you in advance!

[Pfreen]

Quaife make lsd for the 365 and 336 transaxles.  I don't know about a 395.

Check with them.

[Kendo]

We had a lister many years ago who autocrossed his Europa. He cursed his LSD and tried to find oils that would kill it. Now autocross is different from road racing. What leads you to think lsd would be an upgrade?

I am no racing expert, just genuinely want to know your thinking on this.

[jbcollier]

Quaife’s ATB diff for the 336 fits in the 395.  I have one in mine.  ATB (Torsen) is different from LSD.  ATB requires both wheels to have at least some contact with the road for it to work.  If one lifts completely, it will let that wheel spin.  In practice, I have not found this to be an issue with a Europa though I’m not racing.

The ratios in a 395 have short gaps between 1-2 and 2-3 followed by a large gap between 3-4 and either a medium or short gap between 4-5.  The difference is that early 395s (395-00, 395-10) have 0.93 5ths and later (395-11 and up) have 0.85 5ths.

It sounds like you have a later box.  You can easily swap 5ths with just removing the rear cover.

The ideal set of gears is from an early-ish 365, perfectly spaced with a 0.91 5th.  Hard and $$$ to find.

Diffs are another matter.  The Alpine people search out R17 365 gears (365-34) and cut and shut a different pinion gear on.  I do not have my books with me but a 4.11 diff might have been used in some version of the R15/17 that could be adapted.

I’m in the same position but want to go the other way to a slightly higher final drive 3.78 to 3.4x for the highway.  Cut and shutting a Lotius 336 pinion on might be enough for me though (3.56).

[jbcollier]

ATB diffs are not “lockers” like some LSD diffs.  They work great on the track as long as one wheel doesn’t lift right off.

[Mecky]

Dear JB,

thank you very much for your reply. I'll check on the Quaife differential. Would be great to purchase one.

In the attached picture, you can see my current ratios. A shorter 5th would be great, but also a shorter final drive. My actual one is 3.778. A 4.11 would be great.

[GavinT]

Stefan,
Have you considered a gearbox from the original mid-engined Renault 5 turbo? Pretty sure they had a close-ratio version available. I think they were a 369 gearbox but I don't know the ratios or other details re suitability. I reckon France is the place to look.

Another option might be a Hewland out of a Formula Ford which should be reasonably available and with the benefit of alternate ratios but, perhaps not exactly cheap even for a 4 speeder.
Of course, you'd need a bell-housing for either of these options.

[jbcollier]

I would think that the R5 Turbo box might bolt on as they are the same engine family but with the block in cast iron.

[jbcollier]

A 395-00 or -10 would also give a 3.4x first rather than your 3.8x one.

[Mecky]

We had a lister many years ago who autocrossed his Europa. He cursed his LSD and tried to find oils that would kill it. Now autocross is different from road racing. What leads you to think lsd would be an upgrade?

I am no racing expert, just genuinely want to know your thinking on this.

Hi kendo, in the video from the first post you can hear the engine revs go up faster that the car accelerates out of the two last corners of lap 1. The inside wheel is unloaded and loses traction. That costs lap time. Thats why I want to get a LSD, which keeps traction to both tires under cornering.

I have found two suppliers in Germany, who seem to have the Quaife Differential in stock. It's not exactly cheep, but affordable.

Next thing will be a used Renault gearbox. A 4.11 diff is my target, but a shorter 5th gear could also help. First is not really useful to change for me.

So, the gearbox types, I need to search for are 365 and/or 395 gearboxes from R15 and R17. Is there any addition to this list? What about Fuego, R8 etc.?

I need this information to find a used one on the internet. I want to set search alerts in order to get one. Does anyone have a list, which shows all Renault gearboxes, which fit in the Europa with the respective ratios?

Thanks guys!

[SwiftDB4]

The following has all NG series ratios:
http://www.lotus-europa.com/manuals/misc/ng.pdf
 I have an NG1-037 gearbox with 4.1 diff. Unfortunately it's a North American only Renault box so you probably won't find one in Europe.

[Kendo]

Gavin mentioned the 369 gearbox, too.

[jbcollier]

There’s an Excel spreadsheet with all the various ratios so you can compare ratios, spacing and final drive.  I have it at home but not with me.  Can someone else who has it sent it to Mechy?

[jbcollier]

The Fuego Turbo’s NG3-65 has a nice spread of ratios but still with the 3.7x final drive.  The NG series is a much stronger unit.  There are longer final drive options, might be shorter too.

[GavinT]

Check me on this but the original Renault 5 turbo used the Sierra cast iron block which harks back to the R8 days.
The Renault 12 also used the Sierra engine and was mated to a 352 gearbox. We know the R12 bell housing doesn't fit an 807 engine, so that's not an option.

The 369 morphed into the UN1 with apparently only minor differences and was fitted to many Renault models. The 369 /UN1 is also a much larger unit with more torque capacity. It was used in later Esprits and is also popular with the GT40 replica crowd along with Porsche G50 - and no one wants to rent a kidney for a ZF transaxle.

So, after all that, I made the mistake of assuming the 369 might be suitable based on the 'number' of the gearbox being part of the 3xx family of transaxles - it ain't. A 3xx bell housing bolt pattern is very different to a 369. (see pic below)

A UN1 would need some careful consideration.
It's both longer and wider, meaning the existing Europa drive shafts won't work.
It'd still need a bell housing and some thinking around adapting to the input shaft.

But everything is doable with enough perseverance. And on the up-side, apparently the crown wheel can be flipped, plus Albins Gears in Australia made special gear sets for them at some point.

Below is a 369 /UN1 application list I picked up somewhere along the way.
I can't remember the origin, so don't take it as gospel.