Assumed output for Rover v8.

Oldskoolrob

Oldskoolrob

Active Member
Hi Groovers,
If I build my 3.5 with standard bore, 'stage 1' cam, 4.6 heads and 9.75 compression ratio, Electronic ignition, Holley 390 on an Edelbrock manifold, P38 extractors and single 2.5" exhaust, what would you expect a reasonable/average assumed output figure (range) to be? Just curious, so I can consider torque converters/diff ratios.
Cheers :)
 
With any 3.5, it's hard work to get more than 180-190, the exhaust manifolds being compromised due to packaging. I think as much as the real, measurable performance, what you gain is responsiveness and the willingness to get up and play compared to the standard motor, which let's face it, prefers not to.

What choice of diff ratios - unless you are doing a Jag diff? You've got 3.08:1, you can tweak it with tyre size. That's a tall ratio, you're unlikely to outgrow, certainly in real-world road conditions. The limitation is lack of cogs in the transmission, hence the popularity of transmission swaps.
 
PeterZRH said:
What choice of diff ratios - unless you are doing a Jag diff? You've got 3.08:1, you can tweak it with tyre size. That's a tall ratio, you're unlikely to outgrow, certainly in real-world road conditions. The limitation is lack of cogs in the transmission, hence the popularity of transmission swaps.
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Engine's actually going in a Mk2 Cortina with a BW65 or 66 (haven't decided which one to rebuild yet) with a Hilux diff in an RN20 casing. :)
Popular ratios are 4.3:1, 3.7:1 and 3.58:1 for these centres. Any guess on HP? Just looking for a figure to use to see if the standard converter will be too stiff in such a light car. How does 160 sound?
 
I think you have no option but to use the 3.58:1. Even then, the thing is going to be spinning fast at highway speeds assuming the rims are not crazy. I think you'll get more than 160 when things are setup correctly with that spec. At well under a tonne, that's going to move...
 
Hi Rob,

It is the torque delivered that is the real mover. As Peter indicated though, with the V8 in a car with a mass under a tonne, it is going to move regardless!!

In terms of achievable power, I know it is not comparable but the Rover 3.5 litre engines that were fitted into the TWR Bastos Rovers that campaigned in the european touring car championships delivered circa 300HP. TWR (not to be mistaken with TRW) did all their own mods so those engines really had some poke.

Ron.
 
It's going to accelerate like a scalded cat, but you may need some aircraft quality ear defenders to drive it :cool:
 
lol the mechanics in my family are pushing the 3.7 or the 4.3 lol. I forgot to mention I have to go to 15" wheels to cover the brake upgrades so that'll help a little...
 
IIRC, which I may not, the Auto P6B would be revving at 3,000rpm at 70mph, on a standard 3.08 diff, or thereabouts. If you have the same size wheels (Or 15" with tyres to get the same diameter) at 70mph your car would be revving at 3,600rpm with the 3.7, or nearly 4,200 with the 4.3.

I used to think that a standard set up was too noisy at 3,000rpm, my P6B revs at 2,350 rpm at 70 (in 5th) and is smooth and fairly quiet.
 
I got 270bhp from a 4.6 using 3500s exhaust manifolds. Everyone pans the cast manifolds, they can't be that bad.
 
Its a little hard to pick the diff without knowing the wheel size. P6 use 14" wheels with 80 aspect ratio tyres. Engine in My P6 using a mild cam (stage two) bespoke headers and 2.5" exhaust almost standard manifold and twin SUs plus grp A heads but standard valves gives over 200hp on the dyno with something over 230 ft lb of torque. It does run a 11:1 compression ratio though
 
I have 15" vitesse wheels with 205/65 tyres, as they're pretty much the same rolling diameter as the original 185/14s
 
mikecoombs said:
Its a little hard to pick the diff without knowing the wheel size. P6 use 14" wheels with 80 aspect ratio tyres. Engine in My P6 using a mild cam (stage two) bespoke headers and 2.5" exhaust almost standard manifold and twin SUs plus grp A heads but standard valves gives over 200hp on the dyno with something over 230 ft lb of torque. It does run a 11:1 compression ratio though
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Like I said it takes a lot of effort to get over 180-190bhp.
 
those numbers are similar to the standard P6 gearing, Note that I might have 230 ft lb of torque but their isn't much till you get to 2500 rpm, hence I lowered my diff to 3.54 using 2200 gearset which really puts a spring in its step and no lag. There is a P76 BW35 on ebay at the moment. They have a longer tail cone and the same hardened gears as the 65.
 
mikecoombs said:
those numbers are similar to the standard P6 gearing, Note that I might have 230 ft lb of torque but their isn't much till you get to 2500 rpm, hence I lowered my diff to 3.54 using 2200 gearset which really puts a spring in its step and no lag. There is a P76 BW35 on ebay at the moment. They have a longer tail cone and the same hardened gears as the 65.
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Interesting you say that Mike. This has long been my contention with the P6 V8 - the gearing is too TALL due to the need provide a cruising gear with no overdrive.

The result is the V8 is slower off the line than a car of its power and weight should be and a lack of intermediate gears which you really notice coming out of corners and can't easily find the right ratio to accelerate out again. The car just feels dead at times.

I have the ZF transmission which give a truly massive top (4th lock up) gear (~34mph/1000rpm with standard tyres). I lowered the gearing slightly using 185/70 tyres and the improvement was obvious right away even with only a 6% change, the car just felt "lighter" for want of a better word - 185/65 would be better but the car starts to look silly.

I suspect the best spec for a "fast road" P6 is a 2200 diff as you have it plus slightly BIGGER than standard tyres. Overdrive should be in the 30-31mph range and 3rd somewhere in the 21-22mph arena.
 
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PeterZRH said:
I suspect the best spec for a "fast road" P6 is a 2200 diff as you have it plus slightly BIGGER than standard tyres. Overdrive should be in the 30-31mph range and 3rd somewhere in the 21-22mph arena.
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I thought the same, which is why I bought the strong cased 2200 diff. Sadly I never got to try it, but it is available to buy for £250.00 ;)
 
Of all the changes I've made to my P6 The lower diff and thicker sway bar were the two most noticeable. The lower ratio makes driving far more relaxing. The car responds immediately to changes in pedal height...The F series diffs should all be four pinion AND they are far better sealed than the earlier ones. lots of extra O rings to seal up the front flange so no oil around the front mount. Plan has always been to put a 4HP22-24 in to give me back the top speed and lazy cruising. I have three sitting in the new shed...

When i was doing my research I noticed fairly early on that the Auto boxes run the top three ratios of the Manual box and use the torque converter to obtain first. When the Bw35 and its predecessor, DG. , box were designed most American cars only ran three speed transmissions so the Automatics didn't drop a gear. Base model cars were still being sold with three speeders up till the early eighties.
M
 
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3 speeders lasted into the 1990s and not just in basic cars. I had a very late model Audi 100 C3, high tech aerodynamic car, lovely 5 cyl injected engine and utterly crap 3 speed slush box from Noah's ark. Possibly the weirdest mix of new an old tech I've ever encountered. Basically a good car ruined by the transmission. After that I had a BWM e34 (530i - V8), this was my first experience of the ZF4HP - in this case with a switchable "sports" mode - a massive improvement from the 3 speeders I knew before. After that a BMW E39 528i - 6. This had the ZF 5HP and was the first automatic I owned which I felt wasn't significantly compromised compared to the manual. That's 20 years ago now...

I'm generally happy with my marginally downgeared ZF V8. The torque converter as a get-away gear only works to a point. The very first thing I noticed with the smaller tyres is pulling away from a standing start - sharper. I feel the 3.54:1 with 195/80 14s are about perfect (or similar on Vitesse rims). this gives 8.90, 14.92, 22.08 and 30.32 mph/1000rpm. Frankly, it feels a little strange to drive at first. I drive it quite frequently on the French autoroutes. Here the limit is 130kph (83mph). This is just about where the car hits it's peak torque and without the torque converter losses the car really wants to pull and go faster - a totally different experience to driving a P6 with a BW35/65 which gets increasingly reluctant to go faster. Before you know it you are rapidly heading towards 100mph without breaking a sweat (my car is tuned a bit - 20-30bhp more than standard).

This is why I say for a fast road car the 3.08 as standard with the ZF isn't useful. It won't really hold lock-up/4th at the national non-motorway limit of 80kph (50mph) very well - down gearing this a fraction means it can hold this in general driving and the car is massively better on these roads as a result. My other car is a modern Mercedes with 9 speeds. When we have so many ratios it's fine to give over 1 or 2 ratios as holding gears for high speed cruising. 4 speeds is not enough to sacrifice any for this purpose, it needs to be a viable "driving" gear and it isn't with a simple ZF swap - sure it's nice as an overdrive but can be used to make the car so much better - a complete win-win as you get better driving gears at all speeds AND a tall enough overdrive... I'm happy to hear Mike that you appreciate how important gearing is, it really needs to match not just the engine but the roads and the speeds we drive at - the original fitment is a kludge to make the old transmission work in the motorway age and it shows. I think so many neglect this and say "job done" when the transmission is swapped. Despite the legend, the V8s torque isn't that great, nor does it reach low down by modern standards. The 1.6 turbo petrol in my Merc peaks at 1500rpm...
 
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