Six speeds Speed Six?

[rthierry]

When I was cruising on some continental motorways over Christmas I noticed that my rev. counter indicates 4000 rpm when moving at 100mph. I check the speedo by timing the time required to cover 1km (convenient sign on all French m'ways - at least you pay for something!), so speedo is fine, and I guess rev counter is okay as it is clear that the engine is fairly high in the revs. All TVR engines have torque aplenty, so why not a 6th speed to cruise along at 3000 rpm rather than 4000? It would keep the noise down - more confortable for long journeys - and use less petrol.
Any thoughts?....

PS: Sorry for the tacky title, just couldn't resist !



PS2: I've finally taken the time to put a picture of my car in my profile... for those who care

[Don]

Actually you haven't! Your photo is missing from the fotango site...just thought you might like to know...

[EdT]

Reckon our 500 could use a 7th too!
Ed

[Roadrunner]

Does it sound as high as 4000, as the indicator could be well out. Autocar tested the new tuscan's real speed against indicated speed and it was totally out. A real 170mph showed over 195mph for example. Not exactly precision instruments used there.

[rthierry]

Paul,

I've heard about these unreliable speedo on recent cars. However, mine really seems fine. I have plenty of time to verify this in hundreds of miles on the motorways. I would appreciate if yellow Chimaera owners could tell me what their rev counter reads in 5th gear. I have read about a short ration gear box option and I am wondering whether my car has such a gear box.

Thanks!

[plotloss]

Roms,

In my 450, 3000rpm is about bang on 80mph.

Do you have a particular speed in mind? I could check it later if you want.

Matt.

[rthierry]

Matt,

Stop me if I am wrong but in a given gear, rev and speed move in proprotion. Therefore, 3000 rpm for 80mph means 3750 rpm @ 100mph. I seem to be 250rpm higher


Anyone with a close ratio gear box here?

[plotloss]

Dont think its proportional as peak power is at 5200rpm, so in theory, though I could be wrong, the increase in speed will be greater from 5000 to 5200rpm than it would from say 3000 - 3200rpm

Although, that may be late night physics!

Matt.

[foggy]

Our survey said.... X plotloss

Engine speed proportional to road speed so long as you keep in the same gear. Double engine speed, double road speed.

More power at higher RPM will mean you get through rev range quicker so will accelerate quicker, but ratio between engine speed and road speed stays the same.

[rthierry]

C'mon guys. Are you never looking at your rev counter ?

[plotloss]

Well there you go, thanks Foggy!

Roms, I am out for a bit of motorway action this evening. I will let you know about 4000rpm (when I go on that deserted stretch of private runway between my house and my destination!!).

HTH

Matt.

[jj_work]

I've got a GPS Hand Held Receiver.. Apparently accurate to within about 5 feet. When the trev speedo reads 80mph, the GPS reads about 72mph... In my other car (Audi) when the speedo reads 80mph, the GPS is 77mph... Tested in a variety of other cars as well, all proving the same thing. The Trev speedo is inaccurate.

Don't trust the speedo on your Trev...
jj

[Roadrunner]

You could try calibrating it with help of a friend. Keep in contact with friend on mobile, you driving the tiv and your friend in a 911. Reach and maintain desired speed, read off your indicated speed, then check actual speed from the 911 over the mobile. Simple. Now mark on new actual speeds and rev counts with a marker pen. Mind not to slip and mark your interior. And careful not to crash. Hope that was helpful.

[tone]

The simple answer is to do what plod does and use the measured miles on the straight bits. You'll recognise them by the red and white quartered circles, one quarter filled per quarter mile, perched on the barrier in the middle of some dual carriageways.

As long as you maintain a constant indicated speed and get a mate to time the mile you can easily work out the true speed.

[plotloss]

Roms,

Quick note to say, got on my private runway last night and 4000rpm is way over 100mph.

HTH

Matt.

[tvradict]

to check your speedo, you can also use the White Boxes on the roads! can't remember the exact distance but plod use them to time you if they think your speeding! these are on most A roads!!!

[rthierry]

Matt,

Thanks you for checking. I guess my car must have a short ratio gear box. Probably explains why it accelerates so bl33din' quick

Roadrunner thanks for you tip (lol, but as I said I have already checked my speedo and it is - fairly - reliable, i.e. at least as reliable as a Porker's.

Cheers
TGI Friday !

[Roadrunner]

Ok then!