fett wrote,...
I would love a set to upgrade the 8.25:1 pistons in my 1972 pre sd1 range rover engine if they are going in the bin otherwise
Hi Fett,
You may well find that even with 10.5 : 1 CR pistons fitted, your engine doesn't deliver the sort of power increase that you might be expecting. This is especially so if you have to run the initial timing at TDC so as to limit pinging as a result of the high compession. It is much better to have a lower compression engine and be able to use more ignition timing than have a higher compression engine and have to use less.
My original engine was a 10.5 : 1 version, and it always pinged although if I used an octane booster (at $20 per tank extra a bit on the expensive side!!) it did make a noticeable improvement. Still, I had to run it at TDC, very inefficient, much better in my humble opinion to limit your compression to 9.25: 1 if you really want an increase.
Low compression engines may deliver less maximum power and even slightly less maximum torque, but the real difference lies in how that power is delivered across the rev range rather than just the peak figures. Certainly it is the case with the 4.6 litre engines, the low compression editions put their power down more rapidly than the high comp versions. It could well be the same story with the 3.5 litre engines too. Given that your engine came from a Range Rover, in such a vehicle you would want power delivered rapidly in the low to mid range, such would make for a much more useable and driveable vehicle.
What initial ignition timing are you running with your engine? Have you ever had the distributor regraphed to suit your P6B?
Ron.
