Rev counter measurement & accuracy

[mightyyid]

Chaps

I have a Dax with Rover V8 and standard 5-speed gearbox. The gauges in the car are Jaguar but interestingly, the rev counter says 6 cylinder on it (6 cyl) at the bottom of it. Assuming that this has probably been taken from a different Jag and dropped in, and assuming the feed for the rev counter just comes from the coil (if indeed I am right here), and given I have a V8, what difference is there likely to be on the reading?

I take up her to an indicated 5,000 rpm, but have no idea if this is reality or not - certainly it sounds as if the engine has more, but anyone any thoughts on how to assess what it should read versus what is does?

Your in confusion...

Andy

[Sidecarbod]

Its going to be over reading by some amount (maybe 8/6?) in other words it's "seing" too many HT pulses. You are probably only revving your RV8 to about 4k! (It should be good for a real figure of 5.5 to 6 assuming that its a 3.5 lump).

[mightyyid]

You are correct that it is 3.5 lump. Sweet though - that was my initial thoughts but did not want to cloud the judgement. Think I need a rev counter. And speedo - and dash...

[Clive]

Caerbont www.caigauge.com will change your tacho from 6 cyl to 8 cyl for you. They will even alter the "6 cyl" lettering to "8 cyl"! From an article in Kit Car Magazine (Oct 2002) the cost is around £55.

[mightyyid]

Thans Clive - would be worth it although will probably, when funds allow, change everything. main aim is to redo the entire inside of the car with carpets, new dash, gauges, seats and all the cockpit trim which is in grey - and I am not a grey man. It looks OK but black would be so much nicer. Will cost a few grand I know but if the funds come, so will the new interior...

Andy

[wilf]

It may have been converted to 8 cyl already. Do you know your differential ratio? Also rear tyre size - if you post those I can tell you (within reason) how mnay revs you should be using at various speeds in 4th gear (4th because it is 1:1 ratio).

[Sidecarbod]

Can you get timming strobes with rev counters? If so that would also help you work things out.

Or if someone who lives nearby has a ETB rev counter or something similar you could connect that to your battery and coil very easily then compare the two gauges.

[craggle]

My Multimeter has a setting for Revs.
I think you connect it between the coil negative and earth then set the number of cylinders.

Unfortunately I have lost the instructions so if anyone else has a Gunsons Digimeter 320, let me know.

Craig.

[Clive]

Speak nicely to your MOT garage and they might put it on their tester to compare.

[mightyyid]

Good thought here chaps - Will check as I think my Gunson has a setting for revs and it would be worth it.

I'm pretty sure it has not been altered - the guy who built it took 10 years and still hadn't finished it so I doubt he did something like that. May try it tonight but apparently it 'wakes the kids' which is not so nice, or so Mrs Yid says.

Much appreciated fellas

Andy