Rover powered 289's

289, FIA & Daytona topics
catsx11
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Post by catsx11 »

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Last edited by catsx11 on Wed Aug 23, 2017 6:26 pm, edited 1 time in total.
CobStang
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Re: Rover powered 289's

Post by CobStang »

I think I have around 30 mph per thousand rpm in 5th so 90 mph = 3000 rpm, but using the above calculator with the following inputs.......
205 / 70 /15,
0.79 5th gear
3.07 axle
I get 32.26 per thousand, equates to 96.78 mph at 3000rpm

So a little discrep somewhere.
Early B.R.A. Warmed 3.9 Rover, 5 sp, 3.07 rear, Fully adjustable front suspension with AVO coilovers, 4 link rear suspension AVO coilovers and Panhard bar, Big 2 pot front calipers, rear discs, servo'd, adjustable front / rear bias, scruffy paint job !
Paul Blore
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Re: Rover powered 289's

Post by Paul Blore »

David,
Your quoted speed/engine revs figures would suggest that your 5th gear is a 1:1 ratio rather than an overdrive, which surprises me. I have a 2.88 diff and 3,000rpm is around 80-85mph.

French BRA 289,
That sounds like very short gearing to me and would make touring a real headache I would have thought.

Paul
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Roger King
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Re: Rover powered 289's

Post by Roger King »

PaulB wrote:David,
Your quoted speed/engine revs figures would suggest that your 5th gear is a 1:1 ratio rather than an overdrive, which surprises me. I have a 2.88 diff and 3,000rpm is around 80-85mph.

French BRA 289,
That sounds like very short gearing to me and would make touring a real headache I would have thought.

Paul
I don't know anything about Rover gearboxes but a direct drive 5th is actually pretty common. All my 5-speed BMWs (E30, E36, E46 and E36/8 MC) were direct drive 5th, which makes for a much nicer drive than the current 6-speed economy boxes. My Jensen-Healey had a direct drive 5th gear also. My Cobra is setup as direct top (4th - T10) with a longer than stock 3.07 CRP ratio. Hopefully this will give similar cruising to you, Paul, although rolling radius will be down a bit. That's if I ever get the damn thing on the road. Currently stripped out again for major surgery on the driver's glassfibre footbox before the exhaust can be made.

edit - an internet search reveals 5th in an LT77 should be either 0.793 or 0.833:1, so Paul is right to be surprised.
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David Large
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Re: Rover powered 289's

Post by David Large »

Maybe my rev counter reads incorrectly having been modified to read in 8s as opposed to 6s as Jaguar intended.

I am not sure why Paul is surprised. He gets say 27.66 mph/1000rpm on a 2.88:1 diff and I get say 25 mph/1000 on a 3.07:1 diff, with no allowance in the calculation for any rolling tyre diameter differences?

David
David Large
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Paul Blore
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Re: Rover powered 289's

Post by Paul Blore »

It's not your engine or road speeds that surprise me David, it's that your 5th gear is a direct drive rather than an overdrive.

Paul
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David Large
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Re: Rover powered 289's

Post by David Large »

Well it seems from the internet search Roger did and I looked also this afternoon that my LT77 is not the direct drive I thought it was in 5th gear.
regards

David
David Large
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CobStang
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Re: Rover powered 289's

Post by CobStang »

So putting in 0.83 as a 5th ratio means I get 30mph at 1000rpm in the calculator which is what I have on the road.

Cheers Roger for finding the second ratio, I could only find one.
Early B.R.A. Warmed 3.9 Rover, 5 sp, 3.07 rear, Fully adjustable front suspension with AVO coilovers, 4 link rear suspension AVO coilovers and Panhard bar, Big 2 pot front calipers, rear discs, servo'd, adjustable front / rear bias, scruffy paint job !
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David Large
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Re: Rover powered 289's

Post by David Large »

Investigating all of this is proving interesting.

When I changed the diff in my car some years ago (certainly in excess of 15) I remember doing some calcs and coming up with 30mph/1000rpm in 5th gear - hence earlier in this thread I said that 3,000rpm was 90mph.
Next time I was in the car the gauges showed that 3,000 rpm was just over 75mph.

Putting the data into the calculator earlier in this thread I find that like Cobstang I should have 30mph/1000rpm, the data being:

Back tyre width -205mm
Back Tyre ratio - 70
Rim dia - 15"
5th gear ratio - 0.833 (assumed option, if I take the other option there is a bigger gap)
Diff ratio - 3.07:1

Result 30.59 mph per 1000 rpm.

My speedo has a very close relationship with the satnav speed so I am concluding that my rev counter has some inaccuracy, I cannot believe that it was so far out when we changed the diff as I would have noticed it when I did the original calcs. The only other thing I can think of is that I changed to a Pertronix electronic ignition module since the diff change. Does anybody have a view on that?

None of this is vital but it is a bit interesting.


David

David
David Large
Bald surfer with a BRA 289, Porsche 968 Coupe and a Radical PR6!
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Migge
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Re: Rover powered 289's

Post by Migge »

The LT77 has the same ratios like the later R380 in 5th gear = 0.77

http://www.v8engines.com/transmission-3.htm#sd1
Special customized BRA289
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