4.6 engine information

we warmed up a p6 3.5 for a client with mildly reworked 4.6 heads ph1 newman cam, standard hifs6 with just the poppet valves removed and freeflow air filters in the standard p6 air box ( its going back to the USA so has to look standard) that produced a little over 200lbft and 173bhp.

the same engine now has had an upgrade, i swapped out the 3.5 bottom end for a 4.6 same cam, carbs, airbox etc, power only rose to 188 bhp, but torque is now an immense 288lbft @2600 rpm, im now worried about the rest of the drive train!

looking at the way the torque curve for the 4.6 falls away it is desperate for air, even with free flow cone air filters in the air box the air box on its own so strangling air flow so much that if you run it without the air box the AFR at light load changes for 12.5 to 17.1! obviously you could correct that but as the car cant be used without the airbox there was no point in going down that route. graph below for you enjoyment, 3.5 in red 4.6 in black
 

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@Penguin - I assume this is at the flywheel, not on the road?

That's fairly tragic. TBH what are we trying to achieve here? I've done some mild tuning (similar to the 3.5 set up in the previous post) and it feels about as fast is as the chassis wants to be without the commitment to some major chassis mods, which I'm not going to do. Mine has the roll bar upgrade and HD rear springs and I don't want to change the fundamental character. I might consider better brakes and that's about it.

I'm planning a chipped Hotwire EFi and a better manifold exhaust which is likely to give 190BHP but more critically it should drive a lot better and have none of the flabby response of SU carbs. That should get it to 60 in under 8 seconds with the auto and maybe under 7 with a manual.

I'm just not sure exactly what people are expecting with a 60 year old car. I suspect something unstable when really pushed and prone to breaking things.

Even 190-200BHP is a LOT in a car weighing 1275kg even today. This would have been Porsche and entry level Ferrari territory in the late 1970s. Getting towards serious performance car territory really requires an properly engineered solution to be satisfactory - sticking a big motor in isn't that to me.
 
Penguin, Did you get to drive the 4.6 installed?

I'll confirm the gain in torque is insane. With the mildly worked 4.6 fitted, a guest driver commented, "There's no need for the gearbox!".
For driving on public roads, the gain in torque is what is noticed and needed :rolleyes: most. Overtaking is so effortless, in 5th gear a quick squirt on the throttle makes it so easy. Acceleration from 50mph to 70+ makes motorways fun to drive.
I've not had a power curve measured, but it doesn't feel like I get the drop-off in torque shown by your graph. (That was painful, I like graphs they don;t lie);
My engine sould very I put the plate between the two sides of the airbox and doubled the size of the inlet cone.

Having said that my standard carb, inlet and exhaust is restricting the power. I built the engine with a very high CR, to aid volumetric efficiency at higher revs. Resulting in full throttle at low revs causing detonation, but is not a problem at higher revs. This would suggest that the volumetric efficiency is much better at low revs than higher up the rev range. With is seen in the dropoff in torque.

Getting towards serious performance car territory really requires an properly engineered solution to be satisfactory
I totally agree, upgrade the suspension and brakes first, it has to be predictable in a power induced slide. You'll have them :cool:
G.
 
Penguin, Did you get to drive the 4.6 installed?

Having said that my standard carb, inlet and exhaust is restricting the power. I built the engine with a very high CR, to aid volumetric efficiency at higher revs. Resulting in full throttle at low revs causing detonation, but is not a problem at higher revs. This would suggest that the volumetric efficiency is much better at low revs than higher up the rev range. With is seen in the dropoff in torque.


I totally agree, upgrade the suspension and brakes first, it has to be predictable in a power induced slide. You'll have them :cool:
G.

the car does have uprated standard height springs, uprated roll bar and gaz shocks those make it much nicer to drive


but no not driven it with the 4.6 , in fact i havnt taken it off the dyno yet. i could of probably picked up some more power if i had raised the compression, its still standard 4.6 9.37, one things for sure it wanted a hell of a lot less ignition advance than the 3.5 did (same distributor) and unlike the 3.5 its running without vac advance, it wants to det like hell if you connect that, but disconnected its not to fussy on timing
 
@Penguin - I assume this is at the flywheel, not on the road?



Even 190-200BHP is a LOT in a car weighing 1275kg even today. This would have been Porsche and entry level Ferrari territory in the late 1970s. Getting towards serious performance car territory really requires an properly engineered solution to be satisfactory - sticking a big motor in isn't that to me.

yes flywheel, its been dyno'd on a superflow engine dyno not a rolling road.

with the mild 3.5 the car was nice, the upgrades had made for a nice revy engine, but it did still leave you wanting for more grunt, it still didnt have the poke to make the p6 get up and go without working the gearbox. in truth i suspect it will never see full throttle ever again
 
...in truth i suspect it will never see full throttle ever again

which brings me to my questioning what the goal/point of this is. You are paying for bhp/torques you won't be using (and would likely break the drivetrain if you did use it on a regular basis) and you still have the slow dynamics of running carbs. Having a livelier and more responsive engine which you can use at road speeds seems more worthwhile and fun to me. If the gearbox is redundant then there is little advantage from the driver's perspective of the 3500S manual. The 4.6 is what it is unless seriously reworked like TVR did i.e. ideal for a 2 and 1/4 ton truck.
 
the same engine now has had an upgrade, i swapped out the 3.5 bottom end for a 4.6 same cam, carbs, airbox etc, power only rose to 188 bhp, but torque is now an immense 288lbft @2600 rpm, im now worried about the rest of the drive train!

Penguin, I am very curious, how did you fit the 4.6 crankshaft into the 3.5 block given the different journal size and the clearance issue with the counterweights hitting the inside of the block?

Ron.
 
Penguin, I am very curious, how did you fit the 4.6 crankshaft into the 3.5 block given the different journal size and the clearance issue with the counterweights hitting the inside of the block?

Ron.

I was thinking that but assumed he changed the block to a 4.6 with associated crankshaft.
 
which brings me to my questioning what the goal/point of this is. You are paying for bhp/torques you won't be using (and would likely break the drivetrain if you did use it on a regular basis) and you still have the slow dynamics of running carbs. Having a livelier and more responsive engine which you can use at road speeds seems more worthwhile and fun to me. If the gearbox is redundant then there is little advantage from the driver's perspective of the 3500S manual. The 4.6 is what it is unless seriously reworked like TVR did i.e. ideal for a 2 and 1/4 ton truck.

cost would of been same if we had used a 3.9 or 4.0 bottom end, i had a suitable 4.6 available so that was used, no harm in having a reserve of torque that you rarely use, its rare for any car to ever be used to its fullest power potential, what your saying no different to saying we should all be driving 4 cylinder p6's as we never use to max speed a V8 will go
 
It has cross bolts now, won't that be noticed by anyone who knows about Rover V8s?
its also got ARP head studs, but if anyone looks at it they are going to look at a picture in an old book or catalog as reference material see that it looks like it should and move on
 
You can, and I do use all of the power, it all depends on how you apply it. If you are going to be brutal yes it will break things. I would have thought with skinny stock tyres it will bleed away power through loss of traction anyway
270 bhp / 281 ft lb is not a hardship to enjoy ! My point / goal is to have fun.
 
You can, and I do use all of the power, it all depends on how you apply it. If you are going to be brutal yes it will break things. I would have thought with skinny stock tyres it will bleed away power through loss of traction anyway
270 bhp / 281 ft lb is not a hardship to enjoy ! My point / goal is to have fun.

you might use all the power but my client wont!

just out of interest ive just run it up again, when i recorded those numbers yesterday it was blisteringly hot, the dyno logged 49/50 degrees C intake air temp, its still hot this evening but with a more sensible air temp of 34/35 we pulled out 290lbft and 192bhp.
 
the other thing this does is make me want to build a v8 race car, but then again i do race against rover v8 powered tr7s, morgans etc, with 285bhp my bmw matches or beats most of them on horsepower, but my little old 2.8 doesnt come close to big v8 torque, and most of the time the huge low down torque they have doesnt do them any favours, especially if its not bone dry, so perhaps i will stick to racing straight six's
 
I was just pointing out that having the power to use is a nice choice, it is up to the driver as to how far down they push the right pedal.
My car drives like any other shopping trolley below 3500 rpm, prod it more and it wakes up.
Plenty of folks would say why have a car over 1000cc ? To that I say .... I want more, because I can !
 
the owner has the car back now, but i did get to drive it before it went back. wow its really nice and not a handful either. driven normally or briskly you dont really notice the torque curve as such, its somewhat like a modern turbo diesel now it accelerates well whatever gear/revs, whether you start out at 2000, 3000 or 4K the accel rate is very similar, as such it doesn't feel modified. if you gave it to someone that had never driven a V8 p6 but knew they were considered fast back in the day they probably wouldn't realise it had been modified. the exhaust now has a deeper more purposeful note. i could quite happily live with it as it is.
 
If you gave it to someone that had never driven a V8 p6 but knew they were considered fast back in the day they probably wouldn't realise it had been modified.

That's a compliment if I ever heard one, well done.
But I hope your client does recognise the additions, improvements.
They should get more MPG too, a mild worked engine should be more efficient, therefore pollute less. Or as the .GOV says under MOT exemption criteria:
Acceptable changes - It does not count as a ‘substantial change’ if: axles and running gear have been changed to improve efficiency, safety or environmental performance
:thumb::thumb:
 
That's a compliment if I ever heard one, well done.
But I hope your client does recognise the additions, improvements.
They should get more MPG too, a mild worked engine should be more efficient, therefore pollute less. Or as the .GOV says under MOT exemption criteria:
Acceptable changes - It does not count as a ‘substantial change’ if: axles and running gear have been changed to improve efficiency, safety or environmental performance
:thumb::thumb:

the client sent me a brief message

"Made it home with no issues - seems very healthy and plenty strong. "
 
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