ZF 4HP22 step by step.
- Thread starter WarrenL
- Start date
The engine will hopefully receive an overhaul in the summer. It's just a question of options and comparing this to similar cars with the ZF, for example various BMWs, Peugeots etc. The overall gearing on the P6 is quite a bit higher.
For example the Jaguar 3.2 XJ40 auto which has more power but slightly less torque:
Rover (Jaguar) [with 3.54 diff]
1000rpm speed:
9.6(7.1) [8.3]
15.3 (12.4) [13.3]
23.9 (19.3) [20.8]
32.8 (26.4) [28.5]
So it seems to me that the 3.08 final drive is a function of the lack overdrive gearbox with the 3500, not so much the extra oomph of the engine over the 4 cylinder car. Even allowing a little extra for the torquier Rover V8 over the Jaguar. If you repeat this for other vehicles, then the pattern is clear, the V8 with the ZF is most probably overgeared. I reckon the 3.54 diff isn't far wrong, shame it isn't as strong. You could of course fit 195/60 tyres and get 8.7, 13.9, 21.6, 29.6 which I reckon is bang on. The 195/60s would also lower the car 1.2" and have less flexy sidewalls.
Point is, at lower speeds also the ZF equipped P6 should be a fair bit quicker. Unless you need 160mph gearing of course.
For example the Jaguar 3.2 XJ40 auto which has more power but slightly less torque:
Rover (Jaguar) [with 3.54 diff]
1000rpm speed:
9.6(7.1) [8.3]
15.3 (12.4) [13.3]
23.9 (19.3) [20.8]
32.8 (26.4) [28.5]
So it seems to me that the 3.08 final drive is a function of the lack overdrive gearbox with the 3500, not so much the extra oomph of the engine over the 4 cylinder car. Even allowing a little extra for the torquier Rover V8 over the Jaguar. If you repeat this for other vehicles, then the pattern is clear, the V8 with the ZF is most probably overgeared. I reckon the 3.54 diff isn't far wrong, shame it isn't as strong. You could of course fit 195/60 tyres and get 8.7, 13.9, 21.6, 29.6 which I reckon is bang on. The 195/60s would also lower the car 1.2" and have less flexy sidewalls.
Point is, at lower speeds also the ZF equipped P6 should be a fair bit quicker. Unless you need 160mph gearing of course.
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For reference here are the figures for the Range Rover 4.0 using effectively the same engine and gearbox. The 4.6 is identical BTW.
1000rpm speed:
(km/h/mph)
I: 13 / 8.1
II: 21.8 / 13.5
III: 32.2 / 20
IV: 44.3 / 27.5
I rest my case: The P6 with tthe ZF is overgeared due to the final drive being compromised for the 3 speed BW. And not by just a little bit...
1000rpm speed:
(km/h/mph)
I: 13 / 8.1
II: 21.8 / 13.5
III: 32.2 / 20
IV: 44.3 / 27.5
I rest my case: The P6 with tthe ZF is overgeared due to the final drive being compromised for the 3 speed BW. And not by just a little bit...
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Of course the wished overall gearing is a matter of personnal choice, but unless you find the engine labouring on motorway inclines, i wouldn't touch it as it is.
The comparison with the Range Rover isn't really valid, as the later is a much more heavier and taller vehicle, destined for a completely different use, hence the lower gearing.
At the end of day it really boils down to the use: Town, motorway, hillclimbs? For motorway use, the overall gearing isn't long enough as long as the engine can pull it without breaking a sweat.
The comparison with the Range Rover isn't really valid, as the later is a much more heavier and taller vehicle, destined for a completely different use, hence the lower gearing.
At the end of day it really boils down to the use: Town, motorway, hillclimbs? For motorway use, the overall gearing isn't long enough as long as the engine can pull it without breaking a sweat.
The Range Rover seems pretty similar to most road cars (in fact a little higher) and has a dual range transfer box so these are the higher, road gears.
The equation also considers top speed of course. This is where installations seem to vary. For example the Rover with the ZF is STILL higher than the 150mph Jaguar 4.0, which is around 31 mph/1000rpm. As a 125mph or so car this doesn't strike me as sensible.
The ability to hold gear while cruising is but one factor remember, another is in gear performance and flexibility around town. Also if too tall, especially with this installation, it could work against you as the lock-up is less inclined to engage. Ideally at standard motorway speeds, you want this locked always and some ability to hold this as conditions change.
The equation also considers top speed of course. This is where installations seem to vary. For example the Rover with the ZF is STILL higher than the 150mph Jaguar 4.0, which is around 31 mph/1000rpm. As a 125mph or so car this doesn't strike me as sensible.
The ability to hold gear while cruising is but one factor remember, another is in gear performance and flexibility around town. Also if too tall, especially with this installation, it could work against you as the lock-up is less inclined to engage. Ideally at standard motorway speeds, you want this locked always and some ability to hold this as conditions change.
The corollary of all this of course is that this explains what I've always felt about the V8; it's slower than it should be. It stretches 3 gears further than they really should go. I always felt it about a second or so off the 0-60 you'd expect from a relative light car with a big engine. Be interesting to know if anyone ever benchmarked a V8 with a 3.54:1 final drive.
My next thought is 195/60 R14 tyres which drop the gearing 9.7% and deliver a triple whammy of other useful improvements; less sidewall flex, a 1" lowering and are much cheaper and easily available.
However I wonder if these will look daft as they are too small?
My next thought is 195/60 R14 tyres which drop the gearing 9.7% and deliver a triple whammy of other useful improvements; less sidewall flex, a 1" lowering and are much cheaper and easily available.
However I wonder if these will look daft as they are too small?
Well, there ain't much I can do with the ratios in the box but the 3.54:1 gives good numbers compared modern cars with this box. This only underlined the fact the 3.08:1 ratio is really not ideal. 100mph at only 3000rpm is clearly silly.
The ZF with the standard V8 axle is well into the territory of 6 speed manuals or modern 8/9 speed automatics with far more gears to play with.
Does anyone know if the 2200 crownwheel and pinion slot straight into the V8 diff keeping the rest of the uprated components in place?
The ZF with the standard V8 axle is well into the territory of 6 speed manuals or modern 8/9 speed automatics with far more gears to play with.
Does anyone know if the 2200 crownwheel and pinion slot straight into the V8 diff keeping the rest of the uprated components in place?
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It doesn't, just from memory you need a spacer between the crownwheel and the carrier, (ISTR 3mm being said) and the bolts holding the crownwheel to the carrier are smaller so need sleeves made up to take up the slack.
Personally I'd just sling a 2200 diff in there to make sure it all works on the gearing front before getting that involved, and then wait till the 2200 unit breaks before doing it.
Years back I worked at a place that did recon diffs, and they sold one to a proper nut-job with a V8 that drove like a lunatic and kept breaking them, so after they'd given him about 4 free replacements under warranty, they slung a 2200 unit in as they had hundreds of those lying around, and he never managed to break that one. Well, not within the warranty anyway.
Personally I'd just sling a 2200 diff in there to make sure it all works on the gearing front before getting that involved, and then wait till the 2200 unit breaks before doing it.
Years back I worked at a place that did recon diffs, and they sold one to a proper nut-job with a V8 that drove like a lunatic and kept breaking them, so after they'd given him about 4 free replacements under warranty, they slung a 2200 unit in as they had hundreds of those lying around, and he never managed to break that one. Well, not within the warranty anyway.
(white cells are manual, grey auto)
Anyway looking at this table the ZF P6 3.08 installation is at least 10% higher than any Rover V8 installation auto or manual. Even with the 3.54 drive, it's still very similar to the much more powerful Jaguar 4.0. The 4.0 has the beefier ZF 4 HP24 BTW.
And here's why your P6 auto is so slow 0-60, look at gears 1 and 2 compared to a standard ZF 4 speed in either a Jag or Land Rover - 20% higher. And this is borne-out in practice; it feels a bit sluggish in initial getaway but picks up as you hit 30-40mph.
So I'd conclude fitting the 3.54 is likely almost as much of an upgrade as fitting the ZF itself!
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If you compare the Manual and automatic tested times it is obvious the auto is high geared. It also shows up in the car comparison tests. I have just installed a 2200 gear set in my F series diff and it is a straight swap. The ring is about a centimetre thicker though. hopefully I'll have it off the stands tomorrow and can see if there is much difference. Of course you need a 2000/2200 speedo to match if you haven't gone electronic. I still have my BW box installed so top speed will drop somewhat.