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!
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,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
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.
I would be concerned about the diff as well.
I will build a spare box just in casemy only concern would be if the gearbox can cope with the torque. Even on SU's you it will/should generate around 300lbft
I am not after a road rocket but something that when it's in top gear I can accelerate easily without kicking down.
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
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
To me the way to create a "performance P6" would be to fit the 3.54 diff (if it were strong enough -.
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
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
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.
The LT77 with 3.54 would be a touch under 2500 at 70mph in 5th, not 3500.