Question about UN1 strength vs engine

[benjamincalleja]

Hi guys, I found this info below. Presuming it's correct which I believe it is, how could the initial UN1 have been used on the SE when it made ~350nm torque? The turbo had no electronic control, I imagine boost was maximum in every gear (ie it hit 300nm at 4250 from 1st to fifth) but did the SE have some way of limiting boost in the early gears or something? It just seems odd, given the below it would seem the engine torque on the SE would outstrip the original UN1?

I thought that "The One Stop Shop" compiling all information under one roof would be nice to have.

Would you please post technical data, tips, specifications, dimensions, reworks, etc.

I"ll start with some specs for different versions of UN1 specimen:

UN1/xxx

> The initial Lotus unit - UN1-016 had a Torque Limit set at 315 Nm (232 lb.ft).

This Version used different Crown Wheel & Pinion Material compared to most other Renault Applications (except Alpine, which had a different direction of rotation). Differential also had 4 Pinions like the Alpine & some of the Agriculture Units

(UN1-023 and UN1-024).The Lotus Version also had extra Dowels in the bell housing joint to further control bending.

>The UN1-026 (known as the High Torque Box) had new Casings which were stronger to reduce Bending under the increased Torque. The Main Fixing Bolt Size & Torque was also increased. There were some revised bearings and retaining plates introduced at that time. The Torque Limit was increased to 400 Nm (295 lb.ft)

> When the V8 came along (UN1-027), it carried over all the 026 features. Plus, there were also updates to the shaft machining & gear assembly procedures as well as well as the revised 5th gear ratio, synchro was added on reverse.

> For the GT3 (UN1-028) we changed 3rd gear the Final Drive Ratio to suit the Engine Performance. This revised Final Drive Ratio came with a lower Renault torque limit of 300 Nm (220 lb.ft).

The Gearboxes had to use a specific lubricant to eliminate Severe Crown Wheel & Pinion wear (Mobil SHC-630M... no longer produced, or Castrol TAF-X... also recently discontinued by Castrol).This was introduced during the initial development testing. The standard Renault lubricant (Elf Trans elf TRX) did not give enough protection due to the Load and Heat produced by the rapid Esprit Turbo Engine Torque rise.

> At all times the gear ratios used in the Lotus application were standard Renault, but the Lotus Crown Wheel and Pinion used upgraded materials. The Renault CWP parts will fit, but they're not as strong.

The main problem was in the stiffness of the Transmission Casing and the loading on the Crown Wheel & Pinion. The Lotus versions of the Renault UN1 Transaxles are the strongest variants available. The only thing that comes close is the later Renault Alpine GTA UN1-019, but it has a different direction of rotation and different final drive Ratio.

> The UN1-013 from the Renault 21 Turbo would provide some of the gears (not 3rd, 5th or final drive) and synchros suitable for the GT3.

An original Esprit Renault UN1-016 is standard in the non-SE and the SE.

The high-torque box started in 1993... 1993.5 SE and the S4 in Oct 93.

Just by looking, the shift translator is on the left side, and there should be an ID tag, or stamping, on the gearbox.

Esprit Original .... UN1-016 ... Started with first Renault equipped Esprits

... 1988 DOM / ROW intro

... 1989 Federal intro, non-ChargeCooled, and SE.

... With 0.8205 5th gear ratio (0.8205 x 3.89 final = 3.1917:1 overall). Left side shift translator, 315 Nm (232 lb.ft) torque rating

Esprit Hi-Tork ... UN1-026 ... 1993 intro (1993.5 SE and the S4 in Oct 93)

... Stronger case with new castings

... RIGHT side shift translator

... 400 Nm (295 lb.ft) torque rating

Esprit V8 ....... UN1-027 ... 1996 intro, for the most part carried over 026 features

... V8 bell housing - does not share 4-cyl bolt pattern

... Higher 5th ratio (0.76)(0.76 x 3.89 = 2.9564:1 overall)

... Synchro-ed reverse

... LEFT side shift translator

... 1998, modified cross shaft for DIRECT CABLE shifter, no translator.

... Minor durability improvements w/ Sport 350 intro.

... 400 Nm (295 lb.ft) torque rating

Esprit GT3 ......... UN1-028 ... 1998, for the most part like 027

... With lower third & final drive ratios (1.41 & 4.11 ??)

... With higher 5th gear ratio (.076)(0.76 x 4.11 = 3.1236:1 overall)

... 4.11 CWP ratio not suitable for torque of 910 or V8

... CWP is Renault parts, not as strong as Lotus 3.89 CWP

... 300 Nm (220 lb.ft) torque rating due to a weaker CWP

[troutrou]

Hell that was plenty interesting and informative, detailed, thanks for sharing all this !

 

I obviously new about the revise gearshift selection mechanism, but the V8 having a synchro'd reverse, never heard of that, that's quite something so I wonder how I managed to miss this over the past 15 years !

 

I guess you live and learn !

 

 

So in short, for a 4 pot that's a bit on the edge, like the S4s (no info on the S300 ?), might be a good idea to use a V8 box, and mix it with the S4s specific parts (bell housing, relevant gear ratios...) ?........

[Bibs]

That information started here...

 

http://www.lotusespritworld.com/EGuides/ETechnical/Gearbox_Testing.html

 

and has chinese whispered around the internet to the above.

[Escape]

Hi guys, I found this info below. Presuming it's correct which I believe it is, how could the initial UN1 have been used on the SE when it made ~350nm torque? The turbo had no electronic control, I imagine boost was maximum in every gear (ie it hit 300nm at 4250 from 1st to fifth) but did the SE have some way of limiting boost in the early gears or something? It just seems odd, given the below it would seem the engine torque on the SE would outstrip the original UN1?

 

The SE does have an electronic boost control. The wastegate is mechanically set to 0.64bar. The ECU controls a solenoid that allows it to bleed off pressure from the wastegate, allowing boost to rise higher, depending on gears and other parameters like engine temperature.

[glynherron]

I don't know much about the tech spec but the V8 didn't have synchro. It has a brake to slow things to a halt to allow selection.

[CHANGES]

I think you will find that the '' syncro'' referenced to on reverse was actually a pre

engagement of reverse selector gear on the main shaft. It does not have bulk rings

and synco as such just a straight cut gear that locates. On the early box's it had to

locate with both shafts , later box's it slides along the main shaft gear and only has

to locate with the secondary shaft.  This does help with selection but will not prevent

grating with clutch drag.. The down side is the reverse gear is in constant motion being

permanently engaged with the main shaft which will create some drag. This is why the

race spec box's go for the early type reverse set up within the later 027 box.

 

You can see the difference in the gear's marked in the red box's

 

 

I think it is also safe to say that it is very rare for any four pot engine to break the box.

There are the usual problems such as second gear syncro  failing, but in most case's 

this is caused by forcing the change to quick.. It would take a lot of abuse from a 4

pot to actually break one.. so don't be over concerned..

When fitted to the V8 its a different matter and quite common when driven hard in high

gears to break the main shaft at the rear bearing next to fifth.. This is cause by the higher

torque loading available from the V8 in high gears which the 4 pot does not have..

hope this helps 

[benjamincalleja]

The SE does have an electronic boost control. The wastegate is mechanically set to 0.64bar. The ECU controls a solenoid that allows it to bleed off pressure from the wastegate, allowing boost to rise higher, depending on gears and other parameters like engine temperature.

Ah ok yep got it, but nevertheless how could the Se ever use its full 350 NM torque if the limit is 315nm?

I think you will find that the '' syncro'' referenced to on reverse was actually a pre

engagement of reverse selector gear on the main shaft. It does not have bulk rings

and synco as such just a straight cut gear that locates. On the early box's it had to

locate with both shafts , later box's it slides along the main shaft gear and only has

to locate with the secondary shaft.  This does help with selection but will not prevent

grating with clutch drag.. The down side is the reverse gear is in constant motion being

permanently engaged with the main shaft which will create some drag. This is why the

race spec box's go for the early type reverse set up within the later 027 box.

 

You can see the difference in the gear's marked in the red box's

 

GTO Racing Gear kit 003.JPG

 

I think it is also safe to say that it is very rare for any four pot engine to break the box.

There are the usual problems such as second gear syncro  failing, but in most case's 

this is caused by forcing the change to quick.. It would take a lot of abuse from a 4

pot to actually break one.. so don't be over concerned..

When fitted to the V8 its a different matter and quite common when driven hard in high

gears to break the main shaft at the rear bearing next to fifth.. This is cause by the higher

torque loading available from the V8 in high gears which the 4 pot does not have..

hope this helps

Thats really interesting, but wow, look at your break, thats full on!

[DanR]

My understanding, correct me if I'm wrong, is the v8's bust their 5th more due to back loading than the torque they create.

 

With their taller 5th ratio, coming off throttle after a powerful run, the weight of the car and torque mutiplication back through the gearbox with engine braking is just too much for the mainshaft to handle.

 

Be interesting to know if the .86 5th of the four pots would survive better. Doubt though that any v8's have had the lower 5th swapped in.

 

In the same vein I'd be interested to see the GTO Maxi box in an Esprit. Having those 5, instead of 4 c/r + overdrive, gears with a 5th of 1:1 (or near enough) could be a delightful combination. It would need a taller final drive though to keep the rpm/kph in top similar. I think GTO have some c/w and pinion ratios around 3:1.

[sailorbob]

The Delco ecu'd cars do not have have any boost control based upon gear.

[cammmy]

Does this mean people who are looking at any serious torque increase on a GT3 need a new CWP? Would swapping to a (Quaife?) LSD from SJS alleviate this?

[Escape]

The Delco ecu'd cars do not have have any boost control based upon gear.

 

The S4 workshop manual states: "This information (from vehicle speed sensor) is used by the ECM to control the boost control solenoid valve." I remember seeing a diagram of boost vs gear somewhere, I think it was for a Delco. Which seems to correspond to the information in the manual. Happy to be corrected and learn something!

 

Filip

[sailorbob]

Vehicle speed is not the same as using a gear  The only time vehicle speed is used is to limit overboost duration.

[Escape]

Off course, but the only way for the ECM to know the gear being used is by comparing vehicle speed and rpm. Hence my assumption.

What influence does the speed have on the overboost duration?

[benjamincalleja]

Either way the torque limit of the 4 cylinder gearbox is 315nm (fine for the turbo) but the SE produces 354nm so i still dont get how it can use that gearbox without breaking it!!!

[sailorbob]

If a set speed (110 mph on the SE) is exceeded then overboost is cancelled.

[Escape]

Didn't know that, thanks. What could be the reasoning behind it? Something to do with the gearbox strength in 5th or is it just that a short overboost wouldn't be of much use at higher speeds?

[DanR]

These boxes have been used in many high powered and racing cars. They are popular in kit GT40's which can have serious v8's powering them. The basic upgrade from GTO which includes the stronger mainshaft generally overcomes any issues v8's have breaking them.

 

The guys on the various GT40 site are skeptical about the information there are strong and weak versions. If they can start with any UN1 or 369 and insert the GTO kit they are happy.

 

The c/w and pinions are not known for breaking.

 

My theory about 5th breaking off with the v8's relates to the back-driven loads on weaker (skinnier) mainshafts. The fours aren't known to do that especially with their .86 overdriven fifth.

[troutrou]

I think you will find that the '' syncro'' referenced to on reverse was actually a pre

engagement of reverse selector gear on the main shaft. It does not have bulk rings

and synco as such just a straight cut gear that locates. On the early box's it had to

locate with both shafts , later box's it slides along the main shaft gear and only has

to locate with the secondary shaft.  This does help with selection but will not prevent

grating with clutch drag.. The down side is the reverse gear is in constant motion being

permanently engaged with the main shaft which will create some drag. This is why the

race spec box's go for the early type reverse set up within the later 027 box.

 

 

Thanks for that info.

[cammmy]

Does anyone know if the torque limit on the GT3 box is just down to the diff and whether putting in a Quaife unit would alleviate this? I'm assuming so based on what I read above.

 

The GT3 already has 216lb ft from factory, so they are saying there's basically no scope for increasing power?

[Bibs]

It's down to the CWP I believe. 

[cammmy]

Sorry for my ignorance, but would that be considered part of the diff in the UN1? i.e. If I bought a Quaife ATB diff, would it incorporate a new CWP or is this separate?

[CHANGES]

No you get just the ATB diff... you will need to swap over the CW. The pinion is part of the secondary shaft.

Just a note, fitting an ATB or slip diff will increase the loads within the box, because you will have doubled the

traction grip from the wheels..

As i said before it is rare for a 4 pot to destroy a box, unless blatantly abused.. I put 370 ft lbs through mine with

quite a bit of abuse for 6k miles, it was only when i went up to 409 ft lbs that 5th let go.. The rest of the box seems

to be able to take a lot ..

And the CWP can shatter if you do snap changes while spinning the wheels, or aggressive burn outs.

The weakest point on the GTO competition  box is the CWP , but it take some doing to brake it on a road car..  

[cammmy]

Cheers for that. I'm hoping to get to 340, maybe 350BHP (not sure what the peak torque would be for that) in the future. Just a bit concerned that the rating for the GT3 was dropped down to just a bit more than the car produces standard.

 

I drive enthusiastically when appropriate but I don't abuse my cars.

Edited March 11, 2015 by cammmy

[Kez]

Guys, 

 

who's the gearbox expert ?  if the gt3 box is capable of taking more torque than it says on the specs, can it be put into other models with higher torque without causing damage ??

[benjamincalleja]

The gt3 un28 box was different, different ratios to suit the engine but the axle ratio meant it cant really take more than the 300nm torque the gt3 has (un28 is not suited to 2.2L engines due to the earlier torque development in the 2.2 engines, compare the gt3 vs 2.2L torque curves). At the end of the day the un16 was the only gearbox up until 1993, meaning it was fitted to the turbo and the SE and the SE had 280hp and 354nm torque.  In theory, you could increase your gt3 up to that limit with no worries if you were using the un16 box but with the un28 gt3 box it literally may break beyond 300nm.  If you can increase the power and keep the torque the same the un28 you have would probably be fine within reasonable limits.