5th gear conversion for 4cyl?

[LotusS4S 0]

Anyone make the conversion yet? PUK sells these, and was thinking about it for my S4s. How much of a difference will changing our stock .82 : 1 to PUK's 0.75 : 1 ? I like to do lots of long distance travels, and when at speed, my RPM's settle around 3K for much of the trip... not sure if that is good for the engine. Was hoping to drop that down, but not sure if there would be side effects to the conversion.. Any thoughts?

Ed-

[pitstoppete 6]

its all std gears from the other UN1 gearbox cars.

got half of the bits to do just this to my SE quite soon. the 0.76 fifth seems a good idea, and will keep the revs down when high speed cruising. seems a better idea on a 4 cyl car than going to the 3.44 diff ratio.

and if u have enough grunt it might get closer to 190mph, they say instead of the 170.

[Jonathan 13]

The only thing I can think of is the gear reaction when lifting off and then coming back on.

5th is damaged sometimes like this as the gear shaft is only supported at 1 end (unlike 1st-4th) - it'snot unknown for the UN1 under high power when decelerating and then coming back onto wide open throttle to damage and break 5th - I just wonder whether the ratio will be kinder or more harsh to this occurance.

IMO 5th should always be fed in slightly esp on higher powered Esprits (S300 / S4s / V8) - other than that I can't see any harm.

[bosbon_be 4]

Hello,

This driver has done it. (http://www.espritse.nl/) Look in the file upgrades/ gearbox. You can read that he changes gear from 4th to 5th at 230km/h. Look at the speedo upgrade and you can see his car running at 270km/h.

I'll think he can give you feedback on how to do it, and what to expect.

Best regards,

Peter

[Loose Cannon 582]

As I do a lot of motorway work I considered the PUK cog but was unsure how it would react in a GT3. I emailed Geoff at the factory and he gave this reply:

"Brian, Could I ask a question about the gearbox? One modification that always intrigued me was the tall (0.75:1) 5th gear ratio as offered by aftermarket companies like P.U.K. for the 4-cylinder models.

After researching this I see that the V8 'box has the type 027 UN1 box (31 teeth on the driven 5th giving I think 0.76:1) compared to the GT3's type 026 UN1 box (32 teeth on the driven 5th), so the V8 box already has something very near that ratio. One of the guys who was at the Heythrop meeting said you mentioned the boxes had different torque capabilities. Is it possible, or desireable, to fit the V8 cog to the GT3 box??? I know the P.U.K. conversion seems very expensive at around 700 Euros which seems a lot for a single cog"

"Mark, Hopefully the information below will explain the reason for the differing gear ratios on the various gearboxes.

When the Renault gearbox (UN1 - 016) was introduced on the 2.2 Esprit it had a final drive ratio of 3.89:1(9/35) and 5th gear of 0.82:1 (32/39)

The gear ratios were picked to give the desired vehicle performance (acceleration, top speed and drivability)

The High Torque UN1 - 026 had the same Ratios but improved strength.

When the V8 was introduced with the UN1 - 027 it was decided to change the ratio of 5th gear to 0.76:1. (V8 engine had more torque and was able to pull 'V' max with this ratio - the 2.2 was not able to do this - confirmed during testing at Nardo))

When the GT3 was introduced with the UN1 - 028 it was decided to further revise the gear ratios. An alternative Final Drive Ratio of 4.11:1 (9/37) was available (due to the reduced torque of the 2.0 litre engine). It retained the 5th ratio of the UN1 - 026 and had a revised 3rd gear ratio of 1.48:1. This gave the car the acceleration figures Lotus desired and made it a completely different car to the V8.

A few of the early GT3s (Prior to June '98) were built with the UN1 - 026 ratios.

Changing the 5th gear to that of the V8 would give more comfortable cruising. What it would do to the 'V' max is unknown.

The Torque Capacity of the UN1 variants is as follows :-

UN1 - 016 315Nm

UN1 - 026 400Nm

UN1 - 027 400Nm

UN1 - 028 300Nm

Hopr this helps

Cheers

Brian "

So it sounds like the GT3 doesn't have the puff....

[pitstoppete 6]

good stuff there from the factory.

when u work it out it is 0.76-1

not sure high 5th in mine will break any records, but i still wanna try it just coz of the wild revs at high speed. i know it wont pull hard in 5th, but its best not to strain that anyway.

im sure at the oxford meet, the guys said the uni16 was 400NM too.

[LotusS4S 0]

Thanks for the information guys. My next step is to actually talk to PUK about my S4s situation, and to see if it is worth it.