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# ZF 4HP22 step by step.

- Thread starter WarrenL
- Start date May 25, 2013

H

#### harveyp6

##### Well-Known Member

Apr 4, 2017
#101
Apr 4, 2017
#101
PeterZRH said:
Anyone finding the overall gearing a little too tall with the 0.73:1 overdrive gear? Top gear locked gives you 32.8mph/1000rpm which is more than my diesel with 50% more torque...
I'm thinking 195/70 tyres which will drop about 4%... Or more? Opinions please.
Click to expand...
You could fit a 2200 (3.54:1) diff.

#### Cafcpete

##### Active Member

Apr 4, 2017
#102
Apr 4, 2017
#102
Is it the gearing (my zf is being fitted at the moment), or is it a teeny bit of wear on your cam, dropping engine performance?
Be good to know when your engine was last over hauled so I know if I need to start worrying !
P

#### PeterZRH

##### Well-Known Member

Apr 4, 2017
#103
Apr 4, 2017
#103
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.
Last edited: Apr 4, 2017
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#### PeterZRH

##### Well-Known Member

Apr 4, 2017
#104
Apr 4, 2017
#104
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...
Last edited: Apr 4, 2017

#### corazon

##### Well-Known Member

Apr 4, 2017
#105
Apr 4, 2017
#105
Or fit a Jag 3.54 like I am
Jim

#### Demetris

##### Well-Known Member

Apr 4, 2017
#106
Apr 4, 2017
#106
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.
P

#### PeterZRH

##### Well-Known Member

Apr 4, 2017
#107
Apr 4, 2017
#107
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.

#### ghce

##### Well-Known Member

Apr 4, 2017
#108
Apr 4, 2017
#108
Demetris said:
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.
Click to expand...
Yes and you must remember that the P6B is only 1300KG which is very light by modern standards for a car with this engine size.
P

#### PeterZRH

##### Well-Known Member

Apr 4, 2017
#109
Apr 4, 2017
#109
corazon said:
Or fit a Jag 3.54 like I am
Jim
Click to expand...
I reckon that'll play very nicely with the ZF.
P

#### PeterZRH

##### Well-Known Member

Apr 4, 2017
#110
Apr 4, 2017
#110
ghce said:
Yes and you must remember that the P6B is only 1300KG which is very light by modern standards for a car with this engine size.
Click to expand...
But that's more than negated at speed by lack of areodynamics....
P

#### PeterZRH

##### Well-Known Member

Apr 6, 2017
#111
Apr 6, 2017
#111
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?

#### Demetris

##### Well-Known Member

Apr 6, 2017
#112
Apr 6, 2017
#112
The tyres in the 2200 below are 185/60/14 and in my opinion look too small.
P

#### PeterZRH

##### Well-Known Member

Apr 6, 2017
#113
Apr 6, 2017
#113
I'm inclined to agree. and 195 isn't going to help much. The V8 really needs 15" 6J rims and something like a 195/65 R15

#### ghce

##### Well-Known Member

Apr 6, 2017
#114
Apr 6, 2017
#114
I agree also, the p6B needs to fill the wheel arches to get that more agressive and better balanced look. Rather than compensating with wheel diameter either diff ratio or box ratios should be considered first.
P

#### PeterZRH

##### Well-Known Member

Apr 6, 2017
#115
Apr 6, 2017
#115
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?
Last edited: Apr 6, 2017

#### Demetris

##### Well-Known Member

Apr 6, 2017
#116
Apr 6, 2017
#116
PeterZRH said:
Does anyone know if the 2200 crownwheel and pinion slot straight into the V8 diff keeping the rest of the uprated components in place?
Click to expand...
I think that someone on here has already done it.
Mikecoombs perhaps?
H

#### harveyp6

##### Well-Known Member

Apr 6, 2017
#117
Apr 6, 2017
#117
PeterZRH said:
Does anyone know if the 2200 crownwheel and pinion slot straight into the V8 diff keeping the rest of the uprated components in place?
Click to expand...
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.
P

#### PeterZRH

##### Well-Known Member

Apr 6, 2017
#118
Apr 6, 2017
#118
I'll probably overhaul the engine with the standard setup first and see how I get on. I'm actually quite excited as this is a double bonus of the ZF. I get better performance AND still have an overdrive gear.
I just get the feeling 4th gear is mostly wasted as standard.
P

#### PeterZRH

##### Well-Known Member

Apr 6, 2017
#119
Apr 6, 2017
#119
(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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Last edited: Apr 6, 2017
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#### mikecoombs

##### Active Member

Apr 7, 2017
#120
Apr 7, 2017
#120
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.
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