4.2 Big Valve Head Swap

[politeperson]

Well that was hard work. However it is all back together and seems OK.

Diff back together, fitted to the cage, brakes on , drive shafts etc, etc etc.

She complied with my demands until about 5pm when the radius arm bolt just refused to thread.

Then one of the shock spring collets fell on the floor and I was left trying to figure out how to compress the spring without at compressor. I did it though with zip ties and a press.

Eventually it did, the brakes bled easily, the exhaust almost fell back on, so I am ok for the rolling road tomorrow. No oil on the brakes and no fuel smell.

I am very tired now.

[politeperson]

Well the results of all this shenanigans are in.

I brimmed the tank and I arrived at Emerald in Norfolk at 9am, who strapped the car down, ran it on the rollers remapped the new configuration and these are the results.

Then I brimmed it again when I got home.

"Before" is with a standard 1967 4.2 head and "after" is with a mid eighties Jaguar XJ6 Injection "big valve" head and cams. Nothing else has been changed apart from the ignition map for the new head of course.

Before, Max bhp 198.5 bhp 146 kw @ 4,775 rpm, 220 ft lb 300 nm @1,000 rpm, 250ftlb 340 nm @3,425 rpm

After, Max bhp 229.2 bhp 171 kw @ 4,800 rpm, 225 ft lb 305 nm @1,000 rpm, 275ftlb 372 nm @3,775 rpm

192 miles used 36.1l (7.9 gallons) 24.5 mpg including full power runs.

85 mph is achieved at 3,276 rpm. So 70 would be 2,697 rpm. that is 25.9 mph/1,000 rpm with the 2.88:1 axle.

So BHP is up 15.5% at 30.7 hp 22.8 kw and torque is up 10% through the range an increase of 24.5ftlb, 33 nm.

The car certainly feels nice, smooth and quicker

The engine has 8:1 pistons and 3,600 miles on it, running 175 psi an all cylinders..