Lotus Elan

Engine speed Vs road speed

PostPost by: kwhittle » Mon Oct 22, 2018 1:32 pm

stugilmour wrote: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


I have a 1700cc BDA fitted that has a dyno sheet showing 166 at 7000rpm. It's in a mild state of tune with twin 40dcoes
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PostPost by: kwhittle » Mon Oct 22, 2018 1:35 pm

In the past with my three +2S130/5, I never exceeded 115mph.
My latest +2 has a BDA fitted.
So am interested to know what the 166bhp at 7000rpm BDA will propel the car at?
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PostPost by: stugilmour » Mon Oct 22, 2018 3:28 pm

kwhittle wrote:In the past with my three +2S130/5, I never exceeded 115mph.
My latest +2 has a BDA fitted.
So am interested to know what the 166bhp at 7000rpm BDA will propel the car at?


Nice sounding engine Kevin.

So what transmission, diff ratio, and tire size do you presently have?

At a guess you will be able to eventually pull redline in 1:1 (fourth or fifth depending on your gearbox). This would be an approximate speed of 125 to 135 mph depending on the other details. Again at a guess, shifting in to fifth would lower the revs from 7000 rpm to about 5600 rpm, but I doubt there would be usable acceleration left at this portion of the power curve.

As Devid mentioned above, all the spreadsheet generated estimates are best compared to GPS speed readings. The speedo error at elevated speeds can be significant. I actually used the results from David’s spreadsheet to specify the required speedometer head turns per mile I needed to match my Garmin and had it rebuilt as required. Also indicated the tach was well past it’s best, so I had it rebuilt and converted it to work with electronic ignition at the same time. All works very well now.

HTH

Stu
Last edited by stugilmour on Mon Oct 22, 2018 3:37 pm, edited 1 time in total.
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PostPost by: kwhittle » Mon Oct 22, 2018 3:37 pm

It's a std 4 speed with we think a 3.55 diff. Tyres TBA
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PostPost by: stugilmour » Mon Oct 22, 2018 4:07 pm

So pretty close to the 19.03 mph per 1000 rpm listed above for the four speed. Simply multiplying by rpm provides speed estimate. The tire size impact will be modest at about 3% or 5% or so (don’t have David’s sheet in front of me). Typically Plus 2’s are using 175/70R13 tires if switched from the stock 165/80R13’s. An online tire calculator will provide the numbers if you don’t want to venture in to the spreadsheet.

Cheers!

Stu
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PostPost by: Donels » Mon Oct 22, 2018 4:51 pm

With 166 bhp you would get 130 mph max. At this speed with ratio's you describe the engine rpm will be approx 6600 rpm, ie 400 rpm below the peak power at 7000 rpm. So you won't actually get 166 bhp or 130 mph. It depends on what your dyno figures are at less than peak revs and then you would need to iterate.

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PostPost by: msd1107 » Mon Oct 22, 2018 5:03 pm

RE: 130 mph max.

It depends on your car.

I had a FHC Stromberg. At the 36,000 mile service, I complained the rev limiter was cutting out at 6,200 rpm. Afterward, I was able to run up to 7,000 rpm. This was with 3.55 and 165-13 tires. That is >130 mph. A DHC will be substantially slower. I think I had a pretty strong car.

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PostPost by: Donels » Mon Oct 22, 2018 5:42 pm

With a 3.77 diff you would be perfectly geared to get 7000 rpm and 130 mph.

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