Revs vs MPH

[peter m]

The S manual states that in 5th gear, the ratio is 23.39mph/1000 rpm. But my rev counter reads 2100 rpm at 70mph !!!!

Is the manual wrong, or has someone fitted an 8cyl rev counter to my car ??? 2000 rpm gives about 65mph on my meters. Is this correct ?

[HarryW]

Either your speedo or rev couter is out. My money would be on the speedo, as 2K rpm should be a bit above 50mph for a V8 box and a bit below for V6 one, both in 5th gear obviously.
When you are cruising on the motorway and you're doing an indicated 70mph what is the relative speed of the other traffic like, as this should tell you either way IMHO.

Harry

[WuPPerTaL]

70mph on my S2 in 5th is almost bang on 3000 revs ;-)

Just had all the dials reconditioned/recalibrated so I'd guess they are about as accurate as they're going to be.

[Rozza!!!]

[quote=WuPPerTaL]70mph on my S2 in 5th is almost bang on 3000 revs ;-)quote]

Mine too..... I think!

Roy.

[peter m]

I will have to look into this. The speedo reads about right compared to other traffic, so it must be the rev counter. Another job for a rainy day

[spivvy]

peter m said:

The S manual states that in 5th gear, the ratio is 23.39mph/1000 rpm. But my rev counter reads 2100 rpm at 70mph !!!! Is the manual wrong, or has someone fitted an 8cyl rev counter to my car ??? 2000 rpm gives about 65mph on my meters. Is this correct ?

not sure if this affects the rev counter but have you got a lower profile tyre on as this will affect you speedo and give you a false reading

[HarryW]

spivvy said:

peter m said: The S manual states that in 5th gear, the ratio is 23.39mph/1000 rpm. But my rev counter reads 2100 rpm at 70mph !!!! Is the manual wrong, or has someone fitted an 8cyl rev counter to my car ??? 2000 rpm gives about 65mph on my meters. Is this correct ? not sure if this affects the rev counter but have you got a lower profile tyre on as this will affect you speedo and give you a false reading

Agreed but not by 1000rpm though .
Agree with the orignal post that maybe the wrong rev counter or some such. Not sure how they work but I would have thought counting the LT pulses is part of it, as those naughty kit car Ultimas 'may' do the opposite to this to make 'people' think they are doing more rpm than they actually are for reasons I cannot fathom .

Harry

[peter m]

If a V8 part is fitted, it would read 75% of true reading as there are 2 less cylinders. Luckily I have another electronic counter I will clip onto the coil lead to measure the actual engine speed and compare this against the rev counter reading. I'll let you know what readings I get