Over-revving

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daneinter
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Over-revving

Post by daneinter » Sun Jul 02, 2006 6:15 pm

can anyone tell me what revs a 19tgd Hatch should be doing at 70 MPH. I feel my car is revving to much at about 3400 and it feels like there should be another gear (Clutch is ok). Are there alternative gearboxes that would give this effect. Thanks

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Post by AndersDK » Sun Jul 02, 2006 6:39 pm

Thats about the best you get it - if you dont want your n/a diesel to be slow as a 2CV.
A BX 17turbodiesel would be just below 3000 at 70mph.
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Post by jeremy » Sun Jul 02, 2006 7:46 pm

I'm a bit surprised as our ZX 1.9D is geared at 23 or so per 1000 revs in 5th and so is revving at about 3000 at 70 in 5th.

I expect you have 165.70 X 14 tyres. These have a circumfrence of 72.6 inches which means that they revolve 872 times per mile.

Your 5th gear should be 0.757:1 and your final drive 3.94:1. Multiply these together gives 2.9825 - the number of revs the engine does for 1 of the wheels.

So in 1 minute your car covers 70/60 miles - and we know that the wheels revolve 872 times per mile - so the wheels revolve 70/60 x 872 times - 1017 times and the engine will have turned 2.9825 times 1017 times - 3033 times!

So at 70 MPH your car should be revving at 3033 RPM

It is possible your car has been fitted with the wrong gearbox. The Estate one has a final drive of 4.0625 - which on the same tyres would rev at 3127 which is not the figure you are quoting.

The faster your engine revs the better the acceleration!

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Post by daneinter » Sun Jul 02, 2006 7:57 pm

The wheels sound right I think, its sleepys old car fitted with alloys, dont know what size though. My old estate seemed to rev obout the 3000 mark at 70. Would this increase MPG?

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Post by jeremy » Sun Jul 02, 2006 9:00 pm

Fuel consumption on cars - especially diesels is largely related to the work done - so slightly higher revs will just mean a little more internal friction in the engine.

As a matter of interest the officilal figures for the 1.9D are

Urban 43.5, 55 MPH 61.4 and 75 MPH 46.3
and for the estate
43.5, 58.9 and 42.8

This wonn't really be due to the increase in revs but more to the inferior aerodynamics of the estate which is also weighs about 40 kg more.

The TD figures are
40.9, 62.8 and 44.8 and the estate ones are
40.9, 58.9 and 41.5.
The reason I quote these is that the transmission is the same for saloon and estate TD's so you can see that the aerodynamics and weight are more important than the gearing.

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daneinter
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Post by daneinter » Sun Jul 02, 2006 9:16 pm

It's strange really. My recently deceased estate was perhaps the best car I ever owned in terms of consumption. Never really checked it to the mile but its performance on a long journey was close to 60mpg I believe. This one on the same journey was good but less and yet its a hatch. My first thought was that it was running at a different ratio and i must admit that I hate that "reaching for another gear" syndrome. What are the codes for the different boxes and is there an easy way to tell?

tim leech

Post by tim leech » Sun Jul 02, 2006 9:21 pm

Thought the same thing on my 19TZD but its about right, 95mph is 4100 and then it sounds like your killing it!

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Post by Barnsley BXer » Sun Jul 02, 2006 9:24 pm

tim leech wrote:Thought the same thing on my 19TZD but its about right, 95mph is 4100 and then it sounds like your killing it!
90 + gives a lovely growl on mine :shock: :D
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Post by Ian_Fearn » Sun Jul 02, 2006 9:25 pm

Put your foot down at 90 in the TZD Turbo and it'll pull strong right up to a highly illegal speed :D
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Post by DLM » Sun Jul 02, 2006 9:29 pm

My old TGD hatch did 3000 at 70 - this was the only point at which it was capable of overtaking anything!

The only time it exceeded 3000 at that speed was when the original clutch was old, and starting to slip. The increase in revs came in a surge as the clutch let go.
Relying on two wheels and musclepower since the last BX (or any car) had to go.

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Post by DLM » Sun Jul 02, 2006 9:33 pm

PS - to the best of my knowledge there was only one kind of box on a TGD - but the older 19RDs etc. did have the BE1 box. Normally the BE1s had a different kind of reversing switch in them (with a shorter switch pin, as far as I remember).
Relying on two wheels and musclepower since the last BX (or any car) had to go.

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Post by sleepy0905 » Sun Jul 02, 2006 10:13 pm

Hi the box that is in my old car is a BE3 these numbers are cast in the box at the top of the bellhousing near the HP Pump so as far as i know it is the correct box but there is a sticker on it saying it is a remanufactured box now they could of fitted different parts but it is unlikely and as billy says he could get his estate (the donor) to the 100 Mark, The clutch is not that old after it failed and had to be replaced but the service history will give you the mileage and date when done.
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Post by jeremy » Mon Jul 03, 2006 8:18 am

The figures i have quoted are for BE1 gearboxes - codes BN43 for hatch and BN44 for the estate. my information comes from Glass's technical service data - 1989 edition - (copyright is 1989).

I think the BE1 gearbox has reverse by 1st, protected by a sleeve on the gearlever which has to be raised to engage the gear. Reverse on the BE3 is by 4th and is unprotected (but the sleeve is still there but immobilised!)

Where the markings (if any) are I don't know.