I was reading through an older thread where someone was discussing performance mods on a V12.
In the discussion on using Pre-HE heads there were several mentions of a "broadspeed style piston top" or "broadspeed piston"

Does anyone here know what this is? Any photos available?
Thanks

 

Broadspeed raced XJ12C cars for a couple of seasons in the 70's. They were very fast, but fragile. About the time they got the cars sorted, British Leyland ended the program. A Google search will turn up lots of info on the cars, but I didn't find much on the engines.

 

Since the road car piston is dished and the head is flat, clearly the Broad-speed Piston had a smaller dish for higher compression.

I've always been facinated the Broad-speed cars and the problem was the weight. The Broadspeed cars suffered from the weight spiral. For example. the car was heave so they needed us use an onboard water system to cool the brakes, that system in turn adds weight and helped on and acerbated another problem at the same time. Then you need to up the power to compensate for the weight, that leads to digger diffs, more cooling systems, complexity, failure points and the spiral goes on. After a while you run out of the ability to over power all the issues. It's amazing they got as far as they did and I applaud them for their valiant efforts none-the-less.

Conversely the Lotus motto 'add lightness' really works and was successful for that a reason. Same goes for the Porsche 911. With no cooling system or power steering system to add weight or fail they are were very successful on racetrack even with poor weight distribution and low horse power relative to their on track peers.

 

If you have a pre-HE XJ-S, the pistons are dished and the heads are flat.
U.S.-spec cars came with low compression pistons (engine number ends in LA or LB) that have larger dishes.
U.K.-spec cars came with standard compression pistons (engine number ends in SA or SB) that have smaller dishes.
So one simple way to get more power is to use SA/SB pistons and achieve a higher compression.
The MAP sensor and a few other D-Jetronic components are also different.