SEiGHT Rev Counter

[DMS]

On the rare occasion that I've dared look at the dashboard whilst flooring the go faster pedal I'd noted that the engine would run out of steam and blip at about 5000 rpm - I'd thought it should be quite a bit higher than this.

I've just been on a nice straight bit of road with nothing around so could stare at the dials.  It seems that the counter is happy to increase fairly uniformly up to 4500 rpm after which it just sort of waggles left and right meaning that I have no idea as to the level of revs beyond that point.

Is this normal or is something going horribly wrong?!?!

[mattstead]

dependant on the exact age and spec of the engine, and the acuracy of your rev counter then apparently running out of steam at "5000" Rpm is quite normal. Rover V8's tend to have hydrualic tappets and above a certain amount of revs, (quite often 5500 rpm) you get hydraulic "lockout" where by the lack of a solid connection with the tappet is unable to keep pace with the engines revs. It wouldn't take much inaccuracy in a rev counter to show this around 5000 rpm.

Where was your engine from? an Sd1, a TVR or a Range Rover? I've personally noticed it more on range rover units...but then again I've allways had to rev range rovers to get any action...I get scared well before 5000 in the seight  

[neilwillis]

I know you guys with V8s get a little forgetful, but there's a box of cogs behind the engine with a stick poking out of the top.

Try stirring the stick round a bit when the engine gets loud.

We poor unfortunates with ornary engines don't have the luxury of oodles of torque    

[Liam]

My rev counter jumps about 300 revs at the top end - Pinto. Any clues

[VeeEight]

To get a more accurate picture of your higher rev range

it is useful to have a shift light. These can be set to a reading

such as 5000 or 5500 so you know when to shift at a safe limit with the added advantage of knowing exactly what your revs are.

It sounds as if you have a problem with your rev counter as it should have a good reading up to its limit.

Top revs for a standard V8 should be about 5500.

Phil

[DMS]

Thanks, guys.  It's a standard 4000 V8 in a factory built car - December last year.  I'm guessing Range Rover.  I'm having someone check a couple of things for me soon so I'll get him to look at the rev counter whilst he's at it!

[SEiGHT]

Not sure if the engine revs are actually dropping too, or just the indication of revs, but the rev limiter is set low on factory ECUs and running out of revs in low gears seems to be a fairly standard occurance on factory built cars. At least it was on the "old" 3.9 EFI's (hotwire) that the factor used to build, although it sounds like you have one of the newer 4.0 GEMs systems.

The problem used to happen in 2nd/3rd gear coming off roundabouts. You'd floor it and reach down for gear pedal, stick your foot on the clutch ready to change gear, but just as you were about to press the clutch the rev limiter would be hit and you'd end up jerking forward and losing your revs. It would normally happen around 4800/500 revs in those gears.

I fixed it by replacing the ECU chip with one from Mark Adams and this has increased the rev limiter a few clicks and now I can go round to 5500 or so (not that I push it to the limit)

The problem now is that it can be difficult to change from 2nd to 3rd at 5k+ revs. When running at Santa Pod I have to short shift the 2nd/3rd gear change or else I lose a whole lot more revs. Perhaps this was the reason for such a low rev limit in the factroy map.

However, if your rev indicator is just playing up and you're not actually feeling the revs drop, then thats normal too   I can be sat still in traffic and the rev indicator will jump up to 2000 or so without the engine revving at all. Sometimes the speed shoots up to 30MPH while stationary too I put it all down to crappy VDO equipment plus a bit of electrical interference.