UN 1-horsepower

[Bob Stoeger]

Hi,
I have a question to anyone who can answer it, could a UN-1 trans handle 600 HP and is there any bullit proofing that could be done to make it strong enough to handle that kind of power, any response or advise would be greatly appreciated
Thanks,
Bob

 

[Mark Charlton]

Mine handles 410 HP nicely and rolling along in third gear can break racing slicks away from the pavement (with two people in the car) when I step on it. 600HP??? I would expect that to eat a UN1 (and driveshafts) if you plan on really using it hard.

This may help: http://www.un1.co.uk/

I'm sure many others will chime in with more valuable input.

 

[Ian K]

Short answer - maybe.

There is a 6 spd conversion that might be good around 600 HP available
through Tornado:

Tornado Performance Parts

scroll down some. It's real plus is the improved torque load.

Also, there used to be a Derek Bell modification (the shaft is a much more
solid piece). Info can be found here:

UN1 Bell conversion

It has handled 500 HP and 420 lbs/ft. I believe the UN1 box Brian had with your
car originally had this modification.

Ian

 

[Paul Thompson 'Hooligan']

Hi Bob,

The DB (Derek Bell) conversion in Roy Smart's GTD has handled about 500 bhp and been driven fairly hard for a number of seasons. Weighed about 1100kg ish + slicks.

Another DB conv fitted to Dave Parker's GTD R42, had about 500bhp also, + 150 of NOS on a number of occasions. Weighed about 1380kg and definately driven hard - also on slicks.

He now has a GTO 6-speed dog conversion in his UN1, still has about 480-500 ish, + has used the +150 hit of NOS again.

A definate weak link on the UN1 (inc DB conv) is the oiling to 5th gear, which hangs right on the back of the box, not good and prone to failure, especially if driven fast for long periods. Dave's R42 and Roy's 40 have both 'lunched' 5th gear sets after high speed runs, 170+.

600+ is pushing it to the limit (and probably beyond) on any converted UN1 IMHO - although having 600 is one thing, putting ALL of it to the ground is another. If you have an ATB type diff fitted, you can also expect a large amount of heat to be generated with that sort of power, so you'll need to consider fitting an external scavenge pump and oil cooler solution too.

On another note, Rodger Burston's GTD runs a std UN1 with Quaife ATB diff on the back of his 408ci (351 stroker) with webers. Won the Dave Wilson Memorial trophy at the Brighton Speed Trials again this year with an 11.99s quarter - again. Theory is that a 7" twin plate clutch 'softens' the transfer of torque which would normally break the input quill shaft at the joint. His power? - who knows....i'd guess at 500+

Doh! even more decisions.....

ps - ever thought of fitting the Cima unit from the Ford GT? 6-speed, very slick, VERY strong!...

 

[Bob Stoeger]

Ha Guys,
Thanks for all the great response on my question I've got some serious homework to do now keep the info coming.
Thanks,
Bob

 

[BruceA]

The oiling to the 5th gear was increased on the UN1-13 boxes with a small 'oil dripper' cast into the rear gearchange housing, this directs oil straight into the input shaft - if this is what you are meaning Paul? But in 5th gear, the gear is locked on the shaft, so wont be turning on its own bearings, so I guess you're talking about the 'lets play strip the teeth' trick! The 5th gear is only 18mm wide and clearly the smallest in the UN1/369 style boxes. I will be increasing the size of my gear by 22% on my UN1-13 box. This will take the size of the 5th gearset to 22mm wide, and hopefully an increase in strength in this area.
Otherwise, Bob, its not so much the horsepower the box can take, its the torque and I think you'll have some serious problems if you are wanting to pop 600 ft/lbs through it, as you try and light up a set of slicks off the start line. You will most certainly have to replace the standard '2-spider' diff unit.

Just another note Paul, the 7" twin plate clutches are quite radical on their takeup. They have no centre sprung hub, or Marcel spring, so I cant see how they can 'soften' power take-up like a sprung centre plate has. I would say they would be more harsh on the driveline.

 

[Paul Thompson 'Hooligan']

Hi Bruce -

5th gear failure has mainly been tooth failure and we fitted an external scavenge pump / cooler which fed back directly over the upper 5th gear - seems to have helped.

The 'theory' behind the smaller clutch is that as the power/motion is transferred around a smaller diameter from the shaft centre, then the torque loading on the shaft is less. Only a theory, I have no scientific data to back it up, but RodgerB's GTD Mk1 seems to have survived his 408ci (b&s 351) on Webers. He runs slicks, has done loads of hard launches and his UN1 is standard (2-piece i/p shaft) but with a Quaife ATB diff and his clutch is an Alcon 7" twin plate unit.

He has previously destroyed a diff (2-spider Renault) but so have many others and it usually follows excessive wheelspin. The spider diffs are just not up to the speeds of wheelspin and the plain bearings on the planet gears heat up, sieze, break the pin and lock up. IF you're lucky you lose drive.... If you're unlucky, the broken pin exits the diff via the large access hole and passes between crown and pinion - BANG!! - OUCH-£££!

The twin plate does have a more fierce bite to it, but is the only reason we can see for Rodger's UN1 not breaking.... unless of course he actually drives it like a 'pussy'....

Anyone else have a theory on 'Large Dia' vs 'Small Dia' clutch units???

 

[Tony Hunt]

The 'theory' behind the smaller clutch is that as the power/motion is transferred around a smaller diameter from the shaft centre, then the torque loading on the shaft is less. Only a theory, I have no scientific data to back it up.................

Anyone else have a theory on 'Large Dia' vs 'Small Dia' clutch units???

The moment of a couple is constant at all points in its plane. Something we used to snigger about in Applied Maths at school!
Clutch diameter per se should therefore not be relevant.

Tony Hunt

 

[Paul Thompson 'Hooligan']

The moment of a couple is constant at all points in its plane. Something we used to snigger about in Applied Maths at school!
Clutch diameter per se should therefore not be relevant.

Tony Hunt

Oh well - looks like Rodger is a 'pussy' then! :lol::lol::lol: (or possibly very very very lucky!)

Thanks Tony -

Anyone else....?

 

[Julian West]

I'm no scientist, but here's my theory on the small clutch...

The WEIGHT (mass?) of the clutch/flywheel assembly is more relevant than the diameter?

Correct me if I'm wrong, but a fast rotating 'heavy' flywheel/clutch assembly carries alot of stored energy (inertia?), whereas a lightweight assembly stores far less.

When the clutch is snapped out, that stored energy is 'suddenly' transmitted thru the input shaft, perhaps the stock flywheel setup can store enough inertia to snap the input shaft??

FWIW I replaced the stock flywheel clutch witha 7.25 inch paddle clutch & a spuerlight flywheel. the complete assembly is 17 KILOS lighter than standard.

Anyone got any comments, I'm sure one of the engineers here could word the theory better than me....

 

[Wayne M.]

Julian
I agree with your thoughts but here is something else to think about. Assume two different engines, one with a 200lb flywheel and the other with a 2lb flywheel. The heavier one would have enought stored energy to twist off the stoutest input shaft while the lighter one would most likely bog the engine. But.... Once the clutches were engaged and the throttles opened abruptly the light flywheel engine would instantly transfer all of its torque to the shaft while the heavier flywheel would absorb the torque and spare the shaft. I doubt an engine would run with a 2lb flywheel but makes for a good story..

 

[Julian West]

Wayne,

Interesting, I understand what you are saying, that the weight of he flywheel acts as a type of damper.

I can't really explain but I've got the idea that the input shaft is less likely to break if it hasn't got a weighty flywheel on the end of it!.. However as you say, the flywheel has no effect on the output of the engine, just he way the power is delivered.

I'm sure there are many other factors in the lifespan of the input shaft, probably all been discussed many ties before......

 

[John Fitzpatrick]

There's an article in a recent Lotus magazine which goes into depth describing the specific weaknesses of the UN1 box and their remedies. If there's any interest, I'll see if I can find a link or PDF the article.

 

[Julian West]

John,

I'd be interested, pls post a link!

Thanks in advance,

 

[John Fitzpatrick]

The article by Craig Stephens is in the May/June 2007 issue of the Lotus Remarque newsletter. Unfortunately, their site is down, so I've uploaded a scanned PDF of the article. I'll leave it up until the Remarque site is functional.

http://www.rainbrush.com/lotus/images/UN1.pdf

 

[hydra]

Interesting thread..
So what would you say is the primary failure mode on a UN1 with an upgraded input shaft and an ATB diff in place of the stock one?

I'm considering using a heavily-modded UN1 in a twin-turbo V8 application pushing 550-600lbft of torque, in 4-speed form with a set of custom gears...

 

[Howard Jones]

It's a funny thing. It is commonly understood that the 5th gear design being in single shear so to speak it is the weak link in these gearboxes along with the stub input shaft design. By upgrading the input shaft you have fixed the input shaft and to some extent the portion of the 1st motion shaft related to 5th gear failures. But in the R21 type UN-1 with the 3.44 final you will find that's its unusual to use 5th gear on most tracks anyway. After all with a 26 inch tire it will go over 140MPH in 4th even with a fairly low redline (6000ish).

So if you have done all the upgrades, input shaft, 1st and 2nd gear, Quaife TBD, oil pump and cooler with return lines to the diff and 5th, and you limit the use of 5th gear, then the last thing in line will more than likely be the R&P. That is if the CV joints, clutch, and half shafts don't break first. Over all these upgraded UN-1's are a fairly stout gearbox. I just think running more than 600HP though them isn't a reasonable thing to do and expect them to live a long life.

To answer your question. My guess is at about 450Hp and 400Ft/lb the upgraded boxes ought to hold up pretty good. As you go beyond 550/500 you are on you own. People have told me that turbos make a lot of torque but it kinda comes on smoother than a high compression big cubic inch motor does. If this is true then it might help you. If you were to build a 400 inch 400hp motor and then gain another 200 from the boost, that ought to take about 8-10PSI from the turbo, then maybe that might work depending on how it comes on .

At those kind of numbers your driving style and grip will have as much to do with reliability as anything else. In the end nobody can really give you a solid number. Just like everything else in life I suppose.

 

[BruceA]

After looking at details of other transaxles, hearing what problems have been had etc with the UN1, I have come to the conclusion that shaft flex is probably one of the main issues with overall (ultimate) strength. I havent read or heard (yet) of anyone doing a crownwheel, apart from when the diff unit spits the broken parts into the teeth. (assuming you have a 4-spider or ATB in the diff area). There are lots of similarities between all transaxles in one way or another. One thing I marvel at is the 930 box where it has huge shaft diameters, and short distances between the bearings (190mm vs 230mm of the UN1).
Also, I'll agree with Howard, driving style and technique is right up there too. Speed shifts and clutch popping isnt going to help!