newguy here, I have a 1976 XJ12 and am going to build this car up to get decent gasmileage. Some of the things I hope to do is use 2 taurus ignition coil packs, a megasquirt ECU, a 700r4 transmission, and maybe some kent cams, (where do I get valve springs and retainers btw?), polished ports and intake manifold, a homemade 2.5" exhaust, and K&N air filters. Can anyone tell me the likelyhood of what kind of projected mpg would be (assuming I drive like a grandma.) I'm just trying to get 20mpg at best and want to rock my V12 all day long.

 

My suggestion, find a scrap late model V12 XJS and take out the engine management with the engine and gearbox. Fuel system too. Install this lot into your car.

I recently did this with my father for a customer, and he's reporting good news. Your side of the pond has extra gas emission I bet.

It's a large job, but going this route enables mapping for fuel economy, and no teething from all sorts of spurious parts to try and work like a $50 million developed engine....

I might even upload a video of the engine running in the car, it's a series I XJ 1972 Daimler flavour.

 

Hi Locke

I don't think you will get 20 mpg, (and the US gallon is smaller than the UK !!). Best bet is to try to find the later V12 HE heads and pistons plus injection gear of 1983. This will give a large improvement.

 

I was thinking the flexability of the megasquirt ecu would help alot in a addition with a decent camshaft and the 4 speed transmission.

i suppose in truth, while these things would make the car faster, it wouldn't really increase gasmileage (maybe around 12mpg instead of the present 8mpg)