ZF 4HP22 step by step.

PeterZRH

Well-Known Member
Hi Mike, That'll be very interesting. Keep me posted. I'm just surprised any discussion of this hasn't come up before. The compromise and the impact actually quite obvious. I know it's a novelty to have a 4th gear, but I driven many 4 speed autos over the years and his installation as a direct ZF swap simply doesn't work in the same way as any factory setup.

Even with the BW box you'll obviously still be higher geared top than the 2200 as you have bigger tyres.

Interesting that the 3500 EFi VDP has an even more massive 2.85:1 final drive!
 

WarrenL

Active Member
I haven't noticed a problem. The car is so much more responsive with the ZF all told. At 100kph, the NZ open road speed limit, I find the engine, at 2100rpm or so, has plenty of torque available to keep things ticking over nicely - more power, if required, is just a quick kickdown away. It might be that on paper the ZF overgears the V8; in practise I find it doesn't at all. At least for my style of driving, and then bear in mind my car hasn't yet done 100,000kms. The engine is still youthful and strong.

Brown Rover sits on Series 1 SD1 14" alloys with 215/70s.
 

ghce

Well-Known Member
View attachment 10507

(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!
Having a bit mre spread in the gears would be heaven in the P6, as you say the 4 speed doesnt offer a lot in that regard as the first 3 are much the same as the BW unit and the overdrive top is a smidgen too high for performance driving but probably ok at steady state cruising.
My thoughts have always been a 6 speed box. The Toyota AB60 6 speed box seems ideal if as you say were to change the diff to a better ratio.
With 2 overdive gears and the right final drive you could position this box for cruise and performance.

Gear Ratios AB60
1st 2nd 3rd 4th 5th 6th Reverse
3.333 1.960 1.353 1.000 0.728 0.588 3.061
 
It appears that the 3.08 gearsets have one ring machined in the side on the outside where as the 3.54 sets have two. Still isn't off the stands.... I did put the number plate plinth and boot handle on though! I think I have a solution to the black parts fading and wearing off. I had mine done in gloss black vinyl at a signwriters! I was careful though not to actually turn the csk screws, just tightened up the nuts so as not to damage it.
 
Generally the six speed boxes have a lower ratio (<2) torque converter which tends to offset the extra gears and they would be a nightmare to program. Mind you most of my six speed experience is with GM box and it is well known as not terribly nice.
 

PeterZRH

Well-Known Member
Hi Mike, Any updates on your lower final drive? The more I think about it, the more it makes sense. 3rd gear with the BW looks pretty tall on paper but I'm led to believe converter slippage can be up to 5-7% or so. Which puts the locked ZF 4th with the lower final drive more than 20% taller in practice than the already tall top ratio of the BW with the standard final drive.


It appears that the 3.08 gearsets have one ring machined in the side on the outside where as the 3.54 sets have two. Still isn't off the stands.... I did put the number plate plinth and boot handle on though! I think I have a solution to the black parts fading and wearing off. I had mine done in gloss black vinyl at a signwriters! I was careful though not to actually turn the csk screws, just tightened up the nuts so as not to damage it.
 
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Got the car off the stands last weekend and have fitted a choke cable so I can start it. Should be running this weekend but I have to get some temporary rego so I can drive it legally. Top speed will be down somewhat but then I've only had the car over 100mph on a few occasions anyway. I'm expecting better pickup in all gears (still with BW box).
 
Gave car first tentative drive today, really just a three point turn to turn it around. It feels noticeably lighter and doesn't have the buildup time when taking off. the drive is uphill at about 30 degrees
 

PeterZRH

Well-Known Member
Anyway, last weekend I really got my first real major opportunity to use the car since it got the ZF. I spent all day cruising around the Swiss and German countryside with the car effortlessly changing between 3rd, 4th and 4th lock-up. Absolutely fantastic. It really has given this car legs it otherwise didn't have. I did a fuel economy test between Zürich and Basel which is fairly flat at as near to 100kph (60mph-ish) as I could keep it. I reckon in these unrealistic conditions the car did a tiny bit over 34mpg. Consider that as an absolute theoretical maximum in the way VW advertises their latest Golf diesel will do 74mpg but you won't. It's difficult to be sure as topping the tank consistently isn't so easy. Certainly at the UK limit of 70mph, the magic 30mpg looks a distinct possibility with care. With regards to my earlier comments about gearing it would be interesting to learn how this would affect economy. It could go either way. 4th and lockup are going to come into play more frequently at realistic speeds but of course the engine runs faster. But still 20% or so less than standard AND with no converter slip.

Realistically, it'll play all day on open roads at around 28mpg so. Which you can quite easily do in actually quite a modest petrol car even today. I was certainly shocked as how bad a Mercedes c-class hire car could be if you put your foot down and that's only a 1.6 with several turbochargers in the modern idiom.

Anyway my question is to you all because I'm not used to the ZF and I wonder if this is normal. 3rd and 4th are as near to silent in operation as makes any difference but 1 and 2 aren't as you might expect in an auto. Oddly 2nd is noisier than first, which is the opposite of the BW. Is this normal? It's not intrusive and it's lower overall than the BW anyway, but noticeable given the overall improvement in refinement.

Get those ZF projects done. You'll be glad you did. I'd not want to go back to a standard car after this experience. It's difficult to describe the effect without mechanically stating the obvious but the whole effect is simply to make the car "in tune" with modern road conditions with affecting the character of car.

Better still I have some suspension work to eliminate some unwanted movement and a new cam to restore a limit more power. So things are only going to get better! The lack of power I currently have I'm hoping will explain a slight reluctance to kick down which so far is my only criticism. The up changes seem very well judged, so I'm thinking the control cable is adjusted well.

Do I sound pleased? Couldn't be happier with the results. Could be happier with the labour costs though. If you can't DIY, this is going to be an issue. Even supplying the ready made cross-member, gearbox and speedo drive, bespoke engineering takes time..... A bracket here, a heat-shield there.... Mine shall we say cost the price of a fairly decent P6, certainly all of what my car is worth over again but then my car has a mission to drive from Switzerland to the UK and to Spain.
 

ghce

Well-Known Member
I just wish I could afford the time and the dollars to do mine. The 30 plus mpg is a very nice carrot as is the very much quieter cabin.
 

WarrenL

Active Member
I've made a few trips between Christchurch and Ashburton recently, a flat run of 90 or so kilometres each way, and Brown Rover has been averaging a shade over 30mpg, cruising at a steady 60-70mph. And so quiet! Couldn't be happier...
 

ghce

Well-Known Member
Those are the comments I like to hear, with MPG like that it makes even more attractive as a daily driver.
Want to sort mine but too many life things happening at the moment but it usually is on my mind at least once a week, that and fitting a baby seat in the back.
 

PeterZRH

Well-Known Member
I'm averaging 26-28 which includes a little commuting. About 4mpg better than before overall which in context is a hell of a lot, in fact suspiciously so. In fact I'm wondering what contributes most to the improvement, 4th gear, lock up or perhaps a different driving style which is encouraged by this transmission. I wouldn't be expecting 20% improvements in isolation except perhaps specifically touring/motorways. It might be some quirk of keeping just below the torque peak which it does in general driving on fairly level roads. This goes back to my earlier contention the gearing is too high to work properly. I guess you need to define "properly" as in simply making the car a lot slower than it need be.

Considering how absurdly high top is, it can hold it remarkably well - under 1000rpm in 50kph zones. What's important is having the control cable calibrated properly. The car is utterly dead on its feet if it doesn't kick down whenever you need even very moderate acceleration. Even then, it's not ideal. When you start playing around with this, then you still end up yearning for more gears. As I've said before, I had a late 90s BMW 5 series and this was the first car I didn't miss having a manual shift, it would always seem to find an appropriate ratio. That had a 5 speed auto (probably a 5HP) and electronic control.

BMW did a 5 series automatic in the 1980s tuned for economy, the 525e and overall it feels a bit like this. This was geared at 31.4mph/1000 according to my calculations and had a different camshaft profile for lower torque. Most automatic BMWs ran about 26/27mph in top.

Still, the main benefit for me is the car suddenly has a very useful range.

Another interesting thing is comparing this to the LT77 conversion. These figures are as far as I can see are every bit as good if not somewhat better than that transmission. I'm guessing the higher ratio in lock-up plus gentle driving encouraging higher gears earlier than you would with a manual (and less temptation to "play").
 

PeterZRH

Well-Known Member
Anyone got any tips for adjusting the control cable? I currently don't seem to be able to get more than 3500rpm with the foot to the floor. It also seems somewhat over-enthusiastic changing up and very reluctant to kick down at all on part-throttle. Is it fairly safe just to tighten it a little progressively until it holds say 4500rpm-ish, or are there more consequences of playing around with this?
 

Cafcpete

Active Member
Anyone got any tips for adjusting the control cable? I currently don't seem to be able to get more than 3500rpm with the foot to the floor. It also seems somewhat over-enthusiastic changing up and very reluctant to kick down at all on part-throttle. Is it fairly safe just to tighten it a little progressively until it holds say 4500rpm-ish, or are there more consequences of playing around with this?
I am having issues with this. Here is what has been recommended to happen (not been done yet!).... I will hopefully be able to tell you what happens in a few days when the garage are able to do this. But don't hold your breath!

This was included with this picture
kickdown.jpg



"
discount kick down cable from throttle, then pull cable until you feel resistance (kick down point). I would pull past this point once just to prove you have found the sweet spot, hopefully this should only move a little bit more!

Once you’ve reached the resistance point (but not the kick down one), adjust so that the collet is 39.0mm.
I am guessing this is the internal gearbox cam travel.

Once the 39mm is set correctly, reconnect to the throttle so that at WOT the cable has activated the kckdown point (passed the resistance point).
Hopefully (!) once the throttle is back at rest the gap on the collet should be between 1.5 and 3mm. If not then get it as close to this and then test-drive.
We may need to adjust how much movement we get on the throttle cam, but lets see what happens
"

Good luck!
 

Cafcpete

Active Member
Anyone got any tips for adjusting the control cable? I currently don't seem to be able to get more than 3500rpm with the foot to the floor. It also seems somewhat over-enthusiastic changing up and very reluctant to kick down at all on part-throttle. Is it fairly safe just to tighten it a little progressively until it holds say 4500rpm-ish, or are there more consequences of playing around with this?
Well I haven't got to drive it my self, but with the above adjustment I am advised that kickdown now works and the box respond as you would expect. So happy days :)
 

Cafcpete

Active Member
Quick update, the garage hadn't adjust kickdown and I was having similar performance issues as peterZRH. However I have had a quick fiddle this morning and set the crimp to 39mm and adjusted the cable so that it just sits on the stop when at rest.... In my case almost the full adjustment....
I haven't tryed with revving hard/high as the car only has 300 miles on a rebuilt engine, BUT performance is MUCH improved.
So have a quick look peterZRH, you might find a simple solution :)
 

PeterZRH

Well-Known Member
Just a quick update I'd like to share. I've had this box now for a couple years and have enjoyed it but have never been completely happy with the way it responds to spirited driving. Well recently, I made some relatively minor changes fitting KP needles and large, Montego air filters. All I can say is the result is the single most transformative change I've ever made that didn't involve moving large amount of new metal into a vehicle. The car flies and plays nicely with the gearbox, responding exactly as you'd want. In fact its the best I've driven without electronics to assist the cog swapping. I remember @chrisyork saying the downside of the ZF was that you couldn't control it on the throttle like the BW and I quite agreed with him at the time. Well, not now.

This got me thinking as to why this might be and this may be speculation but I don't think the control block is quite a perfect match to the wheezy P6 V8. Remember the Discovery has large valve heads and EFi giving a wider, sustained upper power band. This compounded by less power and very tall gearing in the P6. It might also explain why this installation in the Triumph Stag is such a spectacular success (really beg someone with this for a drive) with the sportier engine. This of course the opposite of conventional wisdom on slush boxes which is all about low down torque. Of course no Rover V8 is every going to be anything other than a low down lugger, but you really can even the score up higher in the rev range somewhat and I think this conversion really needs this.

I'm now very curious as to what dropping the overall gearing just a touch would achieve (see earlier posts).

Opinions please.... This is something those thinking or have done this might want to factor in. Those standard air filters are a joke for an engine this size!

@WarrenL All I can say is get those Disco heads in and do some tuning. You'll be glad you did!
 

cobraboy

Well-Known Member
I fitted big air filters a couple of weeks ago and have had to custom grind needles to suit. I have gained a ton of 'seat of the pants horsepower', I cant believe the difference.
Beware fitting big filters will make the motor run very lean !
I need to get a dyno test to report on gains, but am very pleased.
 
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