UN1 Query

[Stew Stau]

Guys, I'm just checking the points on UN1s that I've gleaned from the net and other posts.

The 21 on (013) boxes are recommended as being the stronger ones.

The turbo boxes have better gear ratios for road use.

The Alpine boxes need to be inverted for use which would allow a lower engine fit, reducing the need to cant the engine forward or accept a high engine fit/odd driveshaft angles.

My questions are these:

1. What is the standard torque limit of these boxes for street use?

2. What improvement in torque limit does the one piece shaft upgrade give?

3. What does the the modified 2nd/3rd gears and drilled out oil ways achieve? (Tornado does this)

4. What modifications would be required to invert an Alpine box?

5. What torque limit does the 6-spd kit have.

I'm curious about this gearbox as I enjoy the challenge of modifying mechanical things. I know that there are better boxes out there, but as a pet project, the UN1 seems like an interesting place to start.

I figured I'd modify an Alpine Turbo box to run inverted and handle a decent amount of torque as a project. If I decide to run a higher power later on, I could replace it but if my budget is restricted, I'll just wait until it blows or take it easy on power mods until I can afford a ZFQ or similar.

Stew

 

[Stephane Goria]

Hello,

I have few comments and answers to your post.

The UN1-13 is not the stronger of all the UN1, it only offers the closest gear ratios in respect to the original ZFgearbox. It also offers a mechanical sensor for tachymeter wich is the easiest way to connect the gauge to it.

Through the years many improvments were made. For example, talking about a UN1-13, a 1988 UN1-13 has a different rear locking plate then a 1989 (the 1989 rear locking plate was extended to include a support (hole) for the 5th gear fork). Also, during 1989, the 5th gear fork has changed material...etc...But all are minor improvments.

Through all Renault UN1 (including Alpine), the internal material is the same : The pinions combination change but the building material is the same. Only the differential is different for Alpine with a 4 satelittes build instead of the normal 2 for the common UN1.

For torque, it is what i am trying to investigate. According to models specifications, it seems that a torque of 35 mkg is the upper bound, but this morning I discovered that Venturi's cars were also fitted with raw UN1 and the Venturi 260 Atlantique handled 41.3 mkg of torque. There was also the 400 GT model with 53 MKG, still with the UN1 but ehanced by SADEV.

I don't know about the 2nd/3rd gear drills, if you can learn more please report here.

The UN1 weakness comes from the primary shaft on its both side.

Front : Floating input shaft stresses the hub, generates vibrations and can flex + hte floating input shaft can drives to a mislalignment with the engine if you change bellhousing or goes through an adaptor plate.

Rear : The lack of support for the rear side can drives the shaft to flex too or to break.

The ehanced shaft is certainly the simplest answer to these troubles. The cost is high but it is a real great product.

I am now designing "budget" solutions for these 2 troubles. They should offer an answer for the common driver who wants a gearbox that can handle power from time to time without racing hard all days. My personal target is to have these improvments not to cost you an arm and to be fitted with no modifications of the gearbox.

Cheers

Stephane

 

[Stew Stau]

Stephane,

Thanks for the info. Just to ensure I've not got it wrong:

Normal UN1 used for applications up to 35 kg.m (343 N.m or 254 ft.lbs) torque
Venturi 260 used UN1 for application up to 41.3 kg.m (405 N.m or 300 ft.lbs) torque
400 GT used modified UN1 for application up to 53 kg.m (519 N.m or 384 ft.lbs) torque

Having researched the Lotus Esprit application I've found that Lotus used the UN1 but with an improved quality material in the crownwheel and pinion. They conducted a full torture test on the box and rated them as follows:

016 - 4 cyl box - 300 N.m or 222 ft.lbs
026 - High Torque Turbo box - 400 N.m or 296 ft.lbs
027 - V8 - 026 with tall 5th - 400 N.m or 296 ft.lbs

I've made several separate enquiries into the improvement made with the 1-piece input shaft and the general advice is that they're good for 450 ft.lbs (608 N.m). It was pointed out to me that nobody had yet broken a UN1 modified with a Derek Bell single piece input shaft and several were running 400+ hp in competition.

The two that I'm looking into are the Quaife upgrade from GTO Racing (Derek Bell developed?) and the Holloway Performance upgrade. They give the following ratios:

Quaife - 1st - 2.66
2nd - 1.75
3rd - 1.38
4th - 0.96
5th - 0.89/0.82/0.76
FD - 5.8/4.11/3.89/3.44/2.88

H.P. - 1st - 3.00
2nd - 1.94
3rd - 1.38
4th - 0.96
5th - 0.76 (assuming turbo Renault/Lotus or V8 Lotus base)
FD - 3.44/3.89 (depending on base box)

It would seem that the Quaife would be very good as a close ratio box for track/hillclimb work with the diff to suit. However, with a tall diff ratio, the 1st gear could be a clutch burner in town.

The Holloway ratios would initially seem to be more street friendly and with a 3.44/3.89 diff give reasonable compromise between clutch burning, acceleration and cruising legs.

Has anyone got any comments or corrections to any of my findings? It would seem that for a small-block application, the modified UN1 with a decent LSD should work and last quite well in all but the sticky tyre drag racing where you sidestep the clutch at 3500rpm every launch.

Stew

 

[Ian K]

Hi Stew,

It all depends. How much track/hillclimb use will you see vs. cruising
around town, vs. highway travel.

Also, what will your desired shift point be?

That said, since both options offer the 3.44/3.89, start from there.
Street cruising should nominally be 10:1 in first gear, the 2.66 gives
a final drive of 9.1504 w/3.44 and 10.3474 w/ 3.89, while the 3.00 gives
10.32 w/3.44 and 11.67 w/3.89.

Ian

 

[Stew Stau]

Ian,

Drag racing - none! I wouldn't do that to a car designed for a much more civilised form of competition.

Sprints/Hillclimbs - unlikely and if so, only rarely for a bit of fun.

Circuit work - 4-6 track days per year with the option to do some racing if opportunity allows.

Road work - Open road, in town only when forced at gunpoint or when forced in to refuel.

I like the look of the Holloway Performance ratios with the 3.44 diff. However, with a 400ish hp 302/331, the 3.89 might be a better choice, particularly for track work. I suppose it depends on how it pulls on idle.

I'll likely be sticking with a Mass-Flo FI system on a roller cam engine so it'll be more civilised at that HP level than a carbed engine on solid lifters so I'll probably get away with the 3.44 diff.

Any thoughts?

Stew

 

[Ian K]

Well, if you go with the 3.89 diff, I would say the Holloway is a little
low in first gear for street cruising, and if you go with a 3.44 final,
the Quaife is a little high.

Richmond has a pretty cool gear ratio calculator:

RICHMOND Optimum Transmission Calculator

It gives the following:

With a 3.00 1st gear, desired ratios are 2.00 for 2nd, 1.5 for 3rd and 1.2 for 4th, and
from the 6 spd chart, 0.83 for OD (sub in 5th - though really, 0.76 would be fine).

With a 2.66 1st, you get 1.88 for 2nd, 1.45 for 3rd, and 1.18 for 4th, 0.85 OD (again,
0.76 would be fine too).

The 2 - 4 spread for both the Holloway and Quaife are nice and close, good for
track/hillclimb, but the 1st/2nd change is larger with the Holloway. I'd say the
Holloway is best with the 3.44 for cruising, and the Quaife is best with the 3.89,
but the Quaife isn't too bad with the 3.44, whereas the Holloway seems awfully
short with the 3.89. Based upon the Richmond calculator, the Holloway is closer in
the 1st/2nd change, but the Quaife has a slight edge in the 2nd/3rd and 3rd/4th
changes.

So, I would let the final drive dictate which way you go - 3.89 go for the Quaife,
3.44 go for the Holloway. So, now you just need to decide which final diff you
want

Ian

 

[BruceA]

Its all been said above. I dont think there is going to be much of a difference in strength from any of the gearbox types - having had most of the versions open, the physical sizes of shafts and gears are all the same.
But I have found that the 369 model gearbox (this is the first model made from 76 - 79 or so, found in the Renault 30 roadcar) has proved to be quite strong. I have personally witnessed some severe thrashing in a GT40 with a SBC of 450/450 and after years of this, no problems. The -13 box has a 2-spider diff that really needs to be changed for a 4 or a quaife unit. Yes the 1-peice shaft upgrade will work wonders. First because the shaft diameter is slightly larger overall and being 1 peice there is 3 bearings supporting the shaft, so the spigot bearing end will assist in not having the shaft flex between the case bearings when you are thrashing it in 2nd gear or 3rd. The overhanging 5th is a real problem and the 1peice shaft addresses this. I do think though the width of the 5th gear at only 18mm is a bit small and there are many reported cases of stripped gear teeth in these boxes. It is possible to remanufacture the gear up to a size of 22mm and I will be doing that shortly with one of my boxes to strengthen up this weak link. I believe and oil cooler will also help.

So how much power can you put through it? If you revise your driving technique, you may well get away with even 500+ftlb. But like anything - you abuse it, you can break it.

 

[Howard Jones]

I have the following:

UN1-13
3.44 final
Quaife TBD
One piece main shaft from Chris Cole with:
1st - 2.66
2nd - 1.75
3rd - 1.38 (standard Renault)
4th - .92 (standard Renault)
5th - .82 (standard Renault

I use this car for mostly street driving 60% @< 50mph and 40% @ 70-85 mph highway.

I also have been doing about 600 miles per year on track 4-5 days.

The first two gears are almost never used on track. These cars have mid corner speeds on good tires that is usually faster than 60mph. This will equate to middle/top of 2nd or leave it in 3rd. The added lost time shifting twice to use 2nd is almost always slower than leaving it in 3rd and being nice and smooth.

5th gear is over 140mph @6200 rpms. Very few tracks will see these kinds of speed. At the three tracks I run at I am right on the rev limmiter in 4th at the end of the main straight. Thats good because 5th is the weak link in the gearbox anyway.

1st (2.66) isn't a problem for ME in traffic. The light weight of these cars along with huge torque/vehicle weight ratio doesn't require a short 1st gear. The 3.0 1st's are useless. With a short 3.0 1st you will be using 2nd to start moving especially with a 3.89 final.

The 3.44 final and .82 5th will net 2850ish at 80mph. (26 in tire) I just about find this combination perfect for a "both steet and track" car.

LSD. Don't bother with any of this if you don't put a limmited slip in the car. If you do nothing else an LSD is the thing to do. I really like my Quaife. So much so I had one put into my Porsche G50 thats going into my RCR-SLC.

Lastly, expect good service up to about 450-475HP on very good street tires or DOT slicks with LSD installed and a one piece shaft. I would hold a stock box to 350HP. Run a quality sin oil and keep it full. I have some data on trans oil temps. Expect about 160F to about 180F on a hot day. (mid 90F) and track runs of less than 30min. I don't believe that a cooler is necessary BUT pumping oil onto the ring gear is a good idea so a pump should be consideded for track work. If you intend to run the car under full power in 5th then you should pump oil onto the 5th gear along with the ring gear.

I have had no problems with my Chris Cole R21. 12K miles and about 3000 track miles. I change the oil every year for Chrismas with Redline

 

[Ian K]

Thanks for the real world input Howard. Nice to be able to backup my
theory with someone who actually drives one.

Some day ...

Ian

 

[Howard Jones]

I may have misled you a little. You will need to rev to 6200 @ about 140MPH before you need to shift into 5th from 4th. Top speed in 5th would therefor be about 170 with a 3.44 diff and .82 5th. Think real hard before you try that.

 

[Stew Stau]

Guys,

I just thought I'd post some ratio, rpm and shift comparison info related to my initial enquiry.

As you can see, the 2.66/1.75 upgrade gives the closest ratios to the ZF 5 DS-25-2 transaxle. 1st is still lower than the ZF but the ratios look like they're better all round for street/track use.

I guess the 3.00/1.94 Holloway Performance upgrade would work too, but the lower first and second is aimed at the Lotus crowd where a lot will go into 4-cyl cars with a lot less bottom end torque.

All comparisons with a 3.44 FD.

Stew

 

[Stephane Goria]

Hello,

I don't have the same numbers for the original ZF, neverthless I arrive to the same conclusion for the Quaife choice.

Neverthless, I think it fits better with a UN1-13 than with an Alpine one for ratios.

Here si my sheet. Green = in the average; Red = over the average.

Cheers

Stephane

 

[Stew Stau]

Stephane,

Sorry, got my numbers a bit mixed.

I've updated my spreadsheet to include the stock ZF box, optional FD and then a few Gulf racing setups.

Cheers,

Stew