Cylinder Heads, Standard or Modified.

[SydneyRoverP6B]

Over in the "Gearboxes and Drivetrain" thread, Jim was indicating some of the intended mods that he was intending for his cylinder heads. Rather than continuing the discussion there, I have started a new post here, where I'll also answer a question that Jim asked me,..are my 4.6 heads factory issue or modified?

Jim, they're standard factory issue, 10 bolt with 28cc combustion chambers. With the 4.6 litre engine, honestly, you don't need anything but standard. :wink:

It would be ideal Jim if you could have your Rover run on a dyno both before and after all the intended mods are done. Either with your existing transmission in both cases, or the ZF in both cases. Being able to compare pre and post results is the only real way to know just how successful or not the mods have been. Without such testing, you'll really never know for sure, so being able to conduct an experiment in a scientific way such as this is how useful knowledge is obtained.

Ron.

 

[rockdemon]

I've never ran sleipnir with p6 heads (apart from on a poorly engine when i very first owned it) so i dont know how different the power delivery feels. I've just followed 'conventional wisdom' in fitting the vitesse then sd1 heads. The sd1 heads are a bit smokey so i've now got some late discovery 14 bolt heads which are better in waiting for when i next feel bored

I'd be interested to hear other peoples take on how they behave...

Rich

 

[chrisyork]

Does anyone have an SD1 parts book that will tell us whether the SD1 cam is the same as the P6 one? As Ron says, best know whether we are comparing apples with oranges!

As I pointed out in the other thread, my rule of thumb is to make the breathing and combustion chamber as good as you can get it, and then choose your max torque point with the cam. So for my money SD1 (and later) heads are a no brainer.

Chris

 

[quattro]

When I rebuilt Thunderdog's engine, I did some research on heads, and found that stage one P6 heads flowed 9% more gas but standard SD1 heads flowed 12% more. Both than a standard P6 head that is.

Sparky runs stage one SD1 heads but has many other mods, I am not sure how much difference a stage one head would have on its own.

Richard

 

[LeeEFi]

I've never ran sleipnir with p6 heads (apart from on a poorly engine when i very first owned it) so i dont know how different the power delivery feels. I've just followed 'conventional wisdom' in fitting the vitesse then sd1 heads. The sd1 heads are a bit smokey so i've now got some late discovery 14 bolt heads which are better in waiting for when i next feel bored

Funnily enough, my cylinder heads are a bit smokey as well Rich. They're the original SD1 Vitesse/EFI cyl' heads from my original 3.5-L, and, I believe they have worn valve guides. The 3.9-L cyl' heads I removed to see how my replacement 3.9-L engine performed with the Vitesse/EFI items. As both sets are post-P6 it's perhaps of no interest anyway, but perhaps worth inclusion to this topic.

I'd be interested to hear other peoples take on how they behave...

To be honest I can only speculate really. As Ron says, without a printout of some sort, it is just assumption to say that one set of cyl' heads is better or worse than another. One thing I can say is that the Vitesse cyl' heads give the engine/exhaust a more interesting and exotic noise - presumably down to the gas-flowed exhaust valves in addition to the inlet valves and valve throat areas on those. The 3.9-L cyl' heads seemed to give a smoother idle and mid-range, and they have gas-flowed inlet valves but standard exhaust valves - apart from the slight lip behind the ex' valve head to reduce exhaust gas reversion - so that could be the secret?