2500 rpm at 70mph
Discussion
Its a 4.3BV precat and in 5th at 70 mph, the engine is doing 2500 rpm. I am sure that in my 400 pre-cat it was more like 2200 rpm and that the 500's are similar. The gearbox and diff are standard as far as I know. What rpm is 70mph on other 4.3 precats?
On the factory 4.3BV that I used to have before FFG, it was 3000 rpm at 70 but that did have a later diff and was low ratio. I am just wondering whether the 4.3s or 4.3BVs have a slightly different ratio diff.
I don't do a lot of cruising on the motorway so I quite like a lower ratio feel to the car, I think it suits it. I will check the speedo with a GPS later to make sure that I am doing 70!
On the factory 4.3BV that I used to have before FFG, it was 3000 rpm at 70 but that did have a later diff and was low ratio. I am just wondering whether the 4.3s or 4.3BVs have a slightly different ratio diff.
I don't do a lot of cruising on the motorway so I quite like a lower ratio feel to the car, I think it suits it. I will check the speedo with a GPS later to make sure that I am doing 70!
FactBV said:
Its a 4.3BV precat and in 5th at 70 mph, the engine is doing 2500 rpm. I am sure that in my 400 pre-cat it was more like 2200 rpm and that the 500's are similar. The gearbox and diff are standard as far as I know. What rpm is 70mph on other 4.3 precats?
On the factory 4.3BV that I used to have before FFG, it was 3000 rpm at 70 but that did have a later diff and was low ratio. I am just wondering whether the 4.3s or 4.3BVs have a slightly different ratio diff.
I don't do a lot of cruising on the motorway so I quite like a lower ratio feel to the car, I think it suits it. I will check the speedo with a GPS later to make sure that I am doing 70!
Do you know the ratio on J631 as there are no tags on the diff. I wish it wasn't 3000 at 70 as it can be quite tiring. On the factory 4.3BV that I used to have before FFG, it was 3000 rpm at 70 but that did have a later diff and was low ratio. I am just wondering whether the 4.3s or 4.3BVs have a slightly different ratio diff.
I don't do a lot of cruising on the motorway so I quite like a lower ratio feel to the car, I think it suits it. I will check the speedo with a GPS later to make sure that I am doing 70!
FFG
You can work out the diff ratio by jacking the rear of the car up onto axle stands. Mark a spot on one tyre and the prop. Turn the wheel 10 complete turns while counting how many times the prop turns then divide this number by 10.
For exams prop turns 39 time for 10 turns of the wheel. 39 divided by 10 = 3.9 diff ratio
For exams prop turns 39 time for 10 turns of the wheel. 39 divided by 10 = 3.9 diff ratio
FlipFlopGriff said:
FactBV said:
Its a 4.3BV precat and in 5th at 70 mph, the engine is doing 2500 rpm. I am sure that in my 400 pre-cat it was more like 2200 rpm and that the 500's are similar. The gearbox and diff are standard as far as I know. What rpm is 70mph on other 4.3 precats?
On the factory 4.3BV that I used to have before FFG, it was 3000 rpm at 70 but that did have a later diff and was low ratio. I am just wondering whether the 4.3s or 4.3BVs have a slightly different ratio diff.
I don't do a lot of cruising on the motorway so I quite like a lower ratio feel to the car, I think it suits it. I will check the speedo with a GPS later to make sure that I am doing 70!
Do you know the ratio on J631 as there are no tags on the diff. I wish it wasn't 3000 at 70 as it can be quite tiring. On the factory 4.3BV that I used to have before FFG, it was 3000 rpm at 70 but that did have a later diff and was low ratio. I am just wondering whether the 4.3s or 4.3BVs have a slightly different ratio diff.
I don't do a lot of cruising on the motorway so I quite like a lower ratio feel to the car, I think it suits it. I will check the speedo with a GPS later to make sure that I am doing 70!
FFG
Having driven yours at 3000 and my current one at 2500 prm, I think 2750 would be spot on for me. Obviously not for cruising but I like the 'pick up' in any gear. When J631 went on the Austec dyno, they couldn't initially understand why it picked up as quickly as it did.
Ironically, on the drag strip with J631 I think I needed an extra gear change to get over the line, so not sure if it helped with the times, although I saw that you were getting somewhere around 13.5, which is very good.
Russell Mc said:
You can work out the diff ratio by jacking the rear of the car up onto axle stands. Mark a spot on one tyre and the prop. Turn the wheel 10 complete turns while counting how many times the prop turns then divide this number by 10.
For exams prop turns 39 time for 10 turns of the wheel. 39 divided by 10 = 3.9 diff ratio
Thanks Russell, I hadn't though of that and will check it that way if the diff doesn't have any markings, which I will also check later on. Having only really noticed the rpm / speed last night I though that I would just ask the question first, it could be that all 4.3s / BVs have a slightly lower ratio. Its strange that the factory should also have changed the ratio on their BV, even though it was the later diff.For exams prop turns 39 time for 10 turns of the wheel. 39 divided by 10 = 3.9 diff ratio
By the way, any nibbles on the car, it must be handling well with those Nitrons on?
FactBV said:
Paul - it is the later BTR diff in your car as you know and I am sure that I was told it was the diff that was a lower ratio but unfortunately, that is as much as I know. I had wondered whether it was a lower ratio gearbox as that would have the same effect, but I never got to the bottom of it.
Having driven yours at 3000 and my current one at 2500 prm, I think 2750 would be spot on for me. Obviously not for cruising but I like the 'pick up' in any gear. When J631 went on the Austec dyno, they couldn't initially understand why it picked up as quickly as it did.
Ironically, on the drag strip with J631 I think I needed an extra gear change to get over the line, so not sure if it helped with the times, although I saw that you were getting somewhere around 13.5, which is very good.
Yes, 13.5 with those old Dunlops. Got some R1R's but not fitted yet so should improve. Does need to be in 5th at the end of the 1/4 mile which don't help. Best terminal was 111.Having driven yours at 3000 and my current one at 2500 prm, I think 2750 would be spot on for me. Obviously not for cruising but I like the 'pick up' in any gear. When J631 went on the Austec dyno, they couldn't initially understand why it picked up as quickly as it did.
Ironically, on the drag strip with J631 I think I needed an extra gear change to get over the line, so not sure if it helped with the times, although I saw that you were getting somewhere around 13.5, which is very good.
FFG
I may be talking b
ks here but if you are using the car speedo as your measure of speed the diff ratio is unimportant because the speedo sensor is on the gearbox or or on the propshaft before the diff. The speedo is measuring the speed that the prop is turning, this will be the same regardless of the diff ratio
The speedo is set up to convert the propshaft rpm into a speed indication. In theory if you change the diff ratio you should get the speedo re calibrated.
ks here but if you are using the car speedo as your measure of speed the diff ratio is unimportant because the speedo sensor is on the gearbox or or on the propshaft before the diff. The speedo is measuring the speed that the prop is turning, this will be the same regardless of the diff ratioThe speedo is set up to convert the propshaft rpm into a speed indication. In theory if you change the diff ratio you should get the speedo re calibrated.
LongBaz383BHP said:
FlipFlopGriff said:
Yes, 13.5 with those old Dunlops. Got some R1R's but not fitted yet so should improve. Does need to be in 5th at the end of the 1/4 mile which don't help. Best terminal was 111.
FFG
Blimey, I am just snatching 4th before the 1/4 mile @116 terminal . 3.45diff and 245x45x16.FFG
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