10 bolt head upgrade
- Thread starter Penguin
- Start date
Very interesting. I was of the understanding the big leap was from P6 haeds to the Sd1 type, the obvious gain being valve size. Looks like I was misinformed, the final castings look notably better. It's noticeable that the gains this time are power and torque - there's no small torque drop off low down for more power at the upper end - so this does work too for the auto.
Colin had my auto on a dyno and for a 10.5:1 3.5 with these heads, a slightly hotter cam and Austin montego filters in the standard housing his tuner was measuring 118 at the wheels where you'd expect to see 95-100 as standard. He says there was a bit more there but it would change up. So it looks like 25bhp is easily there for the taking with some basic tuning which is a big jump percentage-wise at the wheels.
I'm looking to go EFi more for better driving characteristics than performance and hope to get a bit more over the standard SUs. That'll take the basic P6 engine up to the 180 ish at the flywheel and I'm guessing there's not much more without dealing with the manifolds and small bore exhaust.
Keep up the great work Mr. Penguin!
Colin had my auto on a dyno and for a 10.5:1 3.5 with these heads, a slightly hotter cam and Austin montego filters in the standard housing his tuner was measuring 118 at the wheels where you'd expect to see 95-100 as standard. He says there was a bit more there but it would change up. So it looks like 25bhp is easily there for the taking with some basic tuning which is a big jump percentage-wise at the wheels.
I'm looking to go EFi more for better driving characteristics than performance and hope to get a bit more over the standard SUs. That'll take the basic P6 engine up to the 180 ish at the flywheel and I'm guessing there's not much more without dealing with the manifolds and small bore exhaust.
Keep up the great work Mr. Penguin!
Penguin
Active Member
so far i have only dyno tested one totally standard P6 engine, from the power that made i dont think SD1 heads are a big leap, certainly not on a standard engine.
Standard p6 exhaust manifolds look awful but for mildly tuned road cars i dont think they are that bad, as proof i would say look at the SD1 engine even with better heads as well as airbox and improved heads it doesnt make much more power than a p6 engine.
a ford pinto will easily make over 120 bhp on a its standard cast 4/1 exhaust manifold, so given a rover has two of them 240bhp from a rover v8 should be possible without too much difficulty.
from what ive seen the best thing for low speed torque is a standard cam and or making the engine bigger
clive P62
Active Member
Even though I have a Hurricane camshaft I am still undecided if I will fit it to my 4.6 which will be going in my P6 auto soon,
It's only going to have S.Us but will have S manifolds + bespoke auto downpipes made to S size.
Penguin
Active Member
my only concern would be if the gearbox can cope with the torque. Even on SU's you it will/should generate around 300lbft
Penguin
Active Member
i think how well the diff holds up will largely be down to driving style.
my only experience of using a 4.6 is a P6 is that a perfectly good standard 3.5 clutch couldnt cope with the torque and would slip even with fairly gentle throttle applications
clive P62
Active Member
I will build a spare box just in case
I rebuilt the diff a couple of years ago with new diff shafts and planet gears / shafts.
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As state before. The thing that made the most difference was switching to slightly smaller tyres - which consider the car as a system multiplies the effective torque at the wheels - which is what any gear is. The problem is the stretched gearing for the 1:1 top of the standard car for the V8 also pulls up 1 and 2 (and 3 in the manual) higher than they need to be which blunts the acceleration at "real world" road speeds. You can add more power of course but this will give you most performance in the higher gears at speeds that are greater than most roads. (I'm talking sub 50mph b road driving)
To me the way to create a "performance P6" would be to fit the 3.54 diff (if it were strong enough - Colin mentioned it might be possible to build one up using the 4 planet gears) with the tall 5th gear to still give you near 30mph/1000rpm cruising and then do the basic cost effective tweaks to bring the power up a little. A car of this weight- with 170-175ish bhp should be in the range of 0-60 in 7.5 seconds which is quick enough without serious chassis upgrades. And it's partly psychological as well - such a car would feel faster, especially out of slower corners, regardless of what the measured times were as you'd more often have a gear to match and you can genuinely use 4000rpm in more circumstances.
To me the way to create a "performance P6" would be to fit the 3.54 diff (if it were strong enough - Colin mentioned it might be possible to build one up using the 4 planet gears) with the tall 5th gear to still give you near 30mph/1000rpm cruising and then do the basic cost effective tweaks to bring the power up a little. A car of this weight- with 170-175ish bhp should be in the range of 0-60 in 7.5 seconds which is quick enough without serious chassis upgrades. And it's partly psychological as well - such a car would feel faster, especially out of slower corners, regardless of what the measured times were as you'd more often have a gear to match and you can genuinely use 4000rpm in more circumstances.
Penguin
Active Member
4.6 is ideal for that, as i said ive only ever driven a 4.6 p6 as a manual, but having driven the same car as a 173bhp 3.5 then as a 4.6 using same heads cam etc, the 4.6 was just so much nicer, you could just squeeze the accelerator when doing 25 ish mph and it would just pick up and go as if you had dropped it down to 2nd gear. As a side not the owner reports that the 4.6 uses LESS fuel than the 3.5 used to, probably because less throttle revs and down changes are required.
I agree to a point, but no final drive change can have anything like the effect of the torque increase the 4.6 gives
I'm running a 4.0L which was producing 266bhp and 284lb/ft of torque. I rebuilt the LT77 and fitted a standard SD1 clutch, both of which seem to handle the power very well, with no slippage or creaking of any sort. Even before the engine rebuild to get the power improvement the diff was complaining.
I now have a 2.88 LSD jag diff, still with the standard SD1 clutch and it all seems to work well. Time will tell though
I now have a 2.88 LSD jag diff, still with the standard SD1 clutch and it all seems to work well. Time will tell though
cobraboy
Well-Known Member
I looked after the diff after my 4.6 install and never had any problems with it. By looking after it I mean I used the car properly, and drove it properly hard, but I did not try to launch with both wheels smoking, but I had good fun with it.
IIRC, and the figures were accurate I had 270 bhp and 286 torques, it made for a very rapid P6, but could have been even faster with lower rear gears.
Stock SD1 clutch for me as well.
I think the unibody is well up to those figures, but I never really cracked the suspension to my satisfaction. The one area that I felt was ess than optimal was the steering and it's various rods and boxes. This needed seriously beefing up, or a conversion to a rack with stronger links.
The flex in the bellcrank forgings was also a weakness despite them being triangulated.
IIRC, and the figures were accurate I had 270 bhp and 286 torques, it made for a very rapid P6, but could have been even faster with lower rear gears.
Stock SD1 clutch for me as well.
I think the unibody is well up to those figures, but I never really cracked the suspension to my satisfaction. The one area that I felt was ess than optimal was the steering and it's various rods and boxes. This needed seriously beefing up, or a conversion to a rack with stronger links.
The flex in the bellcrank forgings was also a weakness despite them being triangulated.
Absolutely, its all about torque in the right place. If you are turning big gears, you need that big engine. In the standard manual car 3rd and 4th are 17.77 and 24.71 mph/1000 RPM. That 4th gear is pretty close to what most sub 2 litre cars had as 5th in the 80s and 90s. Which means on a 60 mph B-road, you only get to 3380rpm or 2400rpm respectively - you are never going to see all that lovely power you see on your dyno in anything other than 2nd gear! The 3.54 will get you nearer 4000rpm in 3rd and 4th is well into where it wants to be for maximum torque. My conjecture is it'll be a much more satisfying car even if not particularly much quicker on "real roads". Because no P6 is really going to be a fast car by modern standards.
I tend to use Sparky for a longer distance cruiser, and don't really like that many revs at motorway speed. At 3.54 and a standard grearbox 70mph would need around 3,500 revs, and over a long distance, that would drive me nuts. Mine, with its 2.88 and LT77 gives me around 2,250 at 70mph.
It's all down to what you use your P6 for I suppose.
Penguin
Active Member
I'm running a 4.0L which was producing 266bhp and 284lb/ft of torque. I rebuilt the LT77 and fitted a standard SD1 clutch, both of which seem to handle the power very well, with no slippage or creaking of any sort. Even before the engine rebuild to get the power improvement the diff was complaining.
I now have a 2.88 LSD jag diff, still with the standard SD1 clutch and it all seems to work well. Time will tell though
i can only say what i found, but on my engine dyno i had a little over 290lbft and the clutch SD1 couldnt cope
The LT77 with 3.54 would be a touch under 2500 at 70mph in 5th, not 3500. With slightly bigger tyres 195 or Vitesse wheels, I reckon the gearing is about perfect - around 30mph/1000 in 5th.
2.88:1 gives 34.44mph/1000 gives just under 2000rpm at 70mph. I'm not sure what the utility of this is. I drive my car through France at 130kph or 82mph and a really don't wish for more gearing (ZF with 3.08 and 185/70 tyres giving 31.9 mph/1000rpm). But I DO wish for response in mountain roads...
While researching fitting the ZF box I looked a lot at vehicles of the late 80s and 90s which used these boxes. The reason "sporty" brands like BMW and Jaguar are sporty is clear. They geared their cars to around 27-28 mph / 1000 rpm in top regardless of manual or auto transmission. "Cruising" brands like Peugeot and indeed Rover would hit 30ish per 1000rpm. No normal road car (in Europe anyway) used the type of gearing you have until 7,8 or 9 speed came along and these were available as "holding" gears for the motorway. The crucial issue being these transmissions still have the cogs to do the "real world" driving. That's not a luxury you have with 3 or 4 speeds.
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All of the P6Bs I have ever driven with the 'standard' (4 speed or auto) gearbox have run at 3,000 rpm at 70mph in top, the needles on both Tacho and Speedo move together and point directly upwards at 70. If you change the diff to 3.54 you get 3,000x3.54/3.08 which equals 3,448 rpm.
My LT77 is a G19A which I believe has around 0.8:1 5th Gear giving me 3,000*0.8, or 2,400rpm at 70mph, and 2,244 with the 2.88 diff.
I am running 205/65 R15 tyres which surprisingly enough are nearly 1% smaller that the 185R14 standard tyres, leaving me with a cruising rev at 70 of 2,260, which is about right looking the tacho on the motorway.
If you're looking for a fast response P6, why not lever a jag diff in there, then you can change ratios just by dropping any ratio from 2.88 to 4.55. in there.
Correct. 24.7 allowing a 2-3% overread on the speedo gives about 3000rpm at 70mph as shown in my table. And give/take whether 185s are really 80 or 82% profile.
The Lt77 is 0.792:1 which is taller than most. All the more reason not to push the final drive too high.
Incidentally the ZF is massively massive at 0.728:1 - and of course it locks in that gear meaning its directly comparable to the manual.
The Lt77 is 0.792:1 which is taller than most. All the more reason not to push the final drive too high.
Incidentally the ZF is massively massive at 0.728:1 - and of course it locks in that gear meaning its directly comparable to the manual.