engine speed/road speed

[miller1899]

Has anyone got a table for engine and road speed? Just fifth gear would be interesting. Does 120 mph at 5000 sound right? Makes me wonder where the other 35 or 40 mph is supposed to come from.

[dnb]

Does this help? Gear down the LHS and RPM steps along the top. Based on what I have written down for Griff 500 ratios (which may be a bit wrong in a couple of places).

	1000	2000	3000	4000	4500	4750	5000	5500	6000	6500
1	7.69362699752873	15.3872539950575	23.0808809925862	30.7745079901149	34.6213214888793	36.5447282382614	38.4681349876436	42.314948486408	46.1617619851723	50.0085754839367
2	11.6990719807782	23.3981439615564	35.0972159423346	46.7962879231129	52.645823913502	55.5705919086965	58.4953599038911	64.3448958942802	70.1944318846693	76.0439678750584
3	16.9374624199326	33.8749248398653	50.8123872597979	67.7498496797306	76.2185808896969	80.45294649468	84.6873120996632	93.1560433096295	101.624774519596	110.093505729562
4	22.6961996427097	45.3923992854195	68.0885989281292	90.784798570839	102.132898392194	107.806948302871	113.480998213549	124.829098034904	136.177197856258	147.525297677613
5	31.0906844420681	62.1813688841363	93.2720533262044	124.362737768273	139.908079989307	147.680751099824	155.453422210341	170.998764431375	186.544106652409	202.089448873443

[davep]

I'm (was) looking at doing a correlation in Excel between road speed signal and the detailed results from RoverGuage's data logger. Unfortunately, for the moment, an engine vibration problem has taken precedence.

[Doc Toad]

...must get my speedo fixed!

[miller1899]

Thanks very much. Presumably this table is theoretical and doesn't take account of wind resistance etc etc.

[dnb]

Yes, it's theoretical based on my belief of the gear ratios. It is however not affected by wind resistance etc!! You just can't get to the RPM to get to the speed...

On the subject of measuring speed, I am working on an accurate speedo at the moment - I have learned much about it since implementing the speed sensitive EPAS. I have written some software to count the speedo pulses and assess accuracy against a GPS feed and found the sensor is actually pretty good (on my car at least) and stands up well to the GPS comparison.

It is the speedo itself that is lousy and has defied all efforts on my part to calibrate. It's just counting pulses - how hard can it be? I will publish my results when I complete the experiments.

[chris52]

Not to sure how accurate my speedo is and I guess a lot depends on what your diff ratio and tyre size is but here is a picture taken on a private road, Speedo showing 147mph and RPM 5k in 5th gear.
My car 1997 Griff 500 standard wheels and GKN (I think) diff
Edit to say roof down of course

Edited by chris52 on Monday 25th June 12:31

[miller1899]

Thanks - this is what I meant. This road and engine speed combination makes sense but 120mph at 5000 rpm doesn't sound right to me, even allowing for different gear ratios and inaccurate speedos.

[FlipFlopGriff]

miller1899 said:

Thanks - this is what I meant. This road and engine speed combination makes sense but 120mph at 5000 rpm doesn't sound right to me, even allowing for different gear ratios and inaccurate speedos.

Looks like 145 to me not 120.
FFG

[miller1899]

I agree and that is the problem. In my car it was 120 at 5000.

[dnb]

Sure you weren't in 4th?

[miller1899]

okay, now assuming I wasn't in 4th, or reverse, does anyone have any comments about why it read 5k at 120? At 80 it's about 3k. The 120 was on a recent trip to Germany, before anyone asks.

[dnb]

A 3.9 ratio diff would give you 130 mph at 5000RPM in 5th. I know that my tacho over reads slightly at high RPM. Not sure if such a diff were ever fitted to a Griff.

[FlipFlopGriff]

miller1899 said:

okay, now assuming I wasn't in 4th, or reverse, does anyone have any comments about why it read 5k at 120? At 80 it's about 3k. The 120 was on a recent trip to Germany, before anyone asks.

Mines at 3k at 70.
FFG

[grngriff]

Mine at 3k is 78 (4.3)

Pete

[Quietlybonkers]

Miller, for what its worth, my 99 Chimaera 4.0 (ducks swiftly) with a T5 gearbox registers 80 at 3k rpm

[JamesK]

For reference my 4.5 with LT77 is 2.5k at 70 and about 3k at 80mmph. I always felt that was higher rpm than my old 500 but that was 10 years ago and it may just be that this one is so much bloody louder!

(or that I'm older )