Engine speed Vs road speed

[kwhittle]

Hi

I have in the past owned three Elan +2S 130/5. And have just bought my 4th +2, but this time an early +2 fitted with the 3.55 Diff

Can anyone tell me the engine speed at say 70mph for a 5 speed, a 4 speed 3.77, and a 4 speed 3.55 ??

Or road speed at 1000rpm in top ?

Kevin

[stugilmour]

Hi Kevin.

David (forum username msd1107) has posted an excellent Excel spreadsheet that makes more detailed calculations of various transmissions quite easy.

From his spreadsheet here are a few numbers for you. I have assumed use of stock Plus 2 tires (165/80/13). I have also assumed the Lotus five speed has a fifth gear overdrive of 0.80 (taken from one of David?s earlier posts).

Four speed 3.55: 19.03 mph / 1000 RPM = 3,678 RPM at 70 mph
Four speed 3.77: 17.92 mph / 1000 RPM = 3,906 RPM at 70 mph
Five speed 3.55: 23.79 mph / 1000 RPM = 2,942 RPM at 70 mph
Five speed 3.77: 22.40 mph / 1000 RPM = 3125 RPM at 70 mph

Using the spreadsheet allows you to easily see the impact of tire and final drive changes in the other gears.

My modified Plus 2 uses a Ford MT75 five speed with a 0.82 overdrive and a 3.54 final drive. On stock tire size it is pretty much 3,500 rpm at 80 mph, which I find great.

HTH

Stu

[69S4]

My S4 manual gives:

3.77 4 speed with 145 tyres - 17.41mph /1000rpm
3.77 4 speed with 155 tyres - 17.62mph / 1000rpm
3.55 4 speed with 155 tyres - 18.50mph/1000rpm

No 5 speed stuff in the book but I'm sure others will know

[nmauduit]

My S4 manual gives:

3.77 4 speed with 145 tyres - 17.41mph /1000rpm
3.77 4 speed with 155 tyres - 17.62mph / 1000rpm
3.55 4 speed with 155 tyres - 18.50mph/1000rpm

No 5 speed stuff in the book but I'm sure others will know

the Lotus 5th speed is 0.8 compared to 4th which is straight through, so that would give under the same circumstances

3.77 5th speed with 145 tyres - 17.41/0.8 = 21.7625 mph /1000rpm
3.77 5th speed with 155 tyres - 17.62/0.8 = 22.025 mph / 1000rpm
3.55 5th speed with 155 tyres - 18.50/0.8 = 23.125 mph/1000rpm

[Elanintheforest]

Kevin, if Stu's numbers are right (19.03 mph per 1000 rpm with the 3.55) you have a top speed of 152 mph @ 8000 rpm!!

In his write-up on your car Eric Lyons managed 140 mph @8000 rpm for a short burst, and I'm now wondering if the car has a 3.77 fitted rather than the 3.55 I thought it had.

Sounds like Chris needs to have a quick wheel rotation session!

Mark

[Donels]

I did some work recently to establish diff and gearbox ratios for my +2. See attached chart in xlsx with gear ratios for a std 4 speed, Lotus 5 speed and Type 9 with a 3.77 diff ratio and a Lotus 5 speed with a 3.55.

I also calculated a power vs speed chart for a +2 to see what the ratios looked like to achieve max speed vs rpm vs peak power. See charts 3 and 4.

Hmmm. Apparently you cannot load xlsx file, so had to load them as pdf's.

Dave

Elan +2 Gearing & Power charts 1.pdf

(16.52 KiB) Downloaded 352 times

Elan +2 Gearing & Power charts 2.pdf

(27.08 KiB) Downloaded 354 times

Elan +2 Gearing & Power charts 3.pdf

(14.95 KiB) Downloaded 380 times

Elan +2 Gearing & Power charts 4.pdf

(22.78 KiB) Downloaded 353 times

[kwhittle]

Well, interesting information, thanks.

I wonder what the stability of a +2 is at these elevated speeds.
It looks a very clean shape, but what sort of experiences owners have had at 120+ mph ?

I noted the Ashmore race +2 had a chin spoiler.
Kevin

[Donels]

I just noticed I picked up the wring chart for power vs speed. Please ignore chart 4 and see attached correct version.

Elan +2 Gearing & Power chart 4.pdf

(31.8 KiB) Downloaded 337 times

[stugilmour]

Kevin, in my experience you will probably not get near red line in overdrive top on the road. Depends on how customized your engine is I suppose, so just my experience here. My car has had a Federal engine on SU?s, so certainly not the max performance you can get from a Lotus TC.

At any rate, in my car the acceleration available in fifth is so marginal it is not needed on the track. For example, I kept the car in fourth down the Ullman straight at Sebring, which is a fast entry 0.6 mile long straight terminated by a high speed right turn.

In terms of stability of the chassis, spreeds over 100 mph have not been an issue. I prefer using the stock tire size. Suspension on my car is essentially stock configuration with new components sourced from Spyder. Stock configuration brakes and steering are completely adequate for elevated speed.

Don?t know about others, but I get a hell of a lot of body lean in slower speed corners. Installed new shock cartridges and rubber springs for next year, so will se how that all works.

For next year I have installed a very cool engine upgrade which should give me a lot more power. Will be interesting to see the improved top end.

What the five speed and taller diff offers is more relaxed cruising. This is really great over here as we travel such long distances to various events. e.g. my home track is three hours away and I have taken several multi-day trips in the Plus 2.

What combination of Gearbox, diff, and tires do you have now?

Cheers!
Stu

[Mazzini]

Well, interesting information, thanks.

I wonder what the stability of a +2 is at these elevated speeds.
It looks a very clean shape, but what sort of experiences owners have had at 120+ mph ?

I noted the Ashmore race +2 had a chin spoiler.
Kevin

Thirty years ago I held a +2s 130/5 at around 100mph with bursts up to 120mph (indicated) for two, perhaps two and a half hours. The car was utterly stable and relatively quiet. My ex-wife sat next to me reading a book, had she realised how fast we were traveling I would have been ordered to slow down. It was early on a Sunday morning when the roads were quiet...nah doesn't happen anymore.

I think +2's are much more stable than Elan's because of the lower flatter nose, In the mid 60's manufacturers started using wind tunnels. The 1965 Rover BRM gas turbine car and the Plus 2 must have shared wind tunnel development time. Yet the Europa, which was developed slightly later had a front end that rose up, though that could have been to meet head light height regulations.

[msd1107]

stugilmore mentioned spreadsheets. Here is a selection that have been published. You might be able to determine what you want.

lotus-suspension-f42/updated-spreadsheets-t18445.html

lotus-gearbox-f37/speed-candidate-conversion-chart-t16331.html

David
1968 36/7988

[Lotus 50]

Was there a lower gear then 3.77? Either my tach is wrong or my gearing is short

[msd1107]

Several more or less common R&P combinations. 4.11 and 4.56 are two, but there are others.

To determine road speed relatively accurately, install a GPS speedometer on your smart phone.

David
1968 36/7988

[prezoom]

From a strictly mathematical point, the following speeds in my Plus 2 with 165-13 Vredestine tires with an OD of 73.6 and a close ratio 4 speed in 4th gear:

3.77 3,54
3000rpm 55.5mph 3000rpm 59.1
3500 64.7 3500 69.0
4000 74.00 4000 78.8
4500 83.8 4500 88.6
5000 92.5 5000 98.4
5500 101.7 5500 108.3
6000 110.9 6000 118.1
6500 120.2 6500 128.0
7000 129.4 7000 137.8

I have found a distinct reduction in acceleration with the change from the 3.77 final drive to the 3.54, added to which, the change from the middle close to the close ratio 4 speed also reduced the acceleration rate. But, I would not change back, as the 2L Zetec provides ample torque to keep me happy.

Disclaimer, tach is not entirely accurate, and neither is the speedometer. Anybody got a couple of spare black speedometer drive gears?

[gus]

The lots 5 speed 3.55 diff numbers are wrong, listed 1-4 as semi close