Introduction & Head machining question

[maineSS]

Frank-

After looking at your head, I'd want to CC it and measure the volume before doing any more cutting- looks like it's been down that road already. The maximum stock compression ratio was 8:1 with the late model head and cam (specs changed in the mid-late 50's).

If you could take some close-up shots of one of your head chambers and post it as a reply to my "late model 230 head" thread, that would be great!

David Vizard installed 3 SU carbs on a Toyota Land Cruiser about 1978 for one of his friends for extreme off-road use in the West. It pulled like a freight train down low, and had better mid to top end than the stock carb. He had to do a lot of intake manifold development work, but it all paid off well in the end. What kind of Bike carbs have you used, and have some worked better than others?

[fha772]

What should the CC be on a standard unmachined head?

I'll get some close ups in the morning for you.

To be honest i had thought of using SU's, then let a couple of friends talk me out of it. I personally think they'd be the ideal carbs to use. I was thinking of using triple 1 1/4" SU's (1 per port). Then if i go for forced induction i can simply swap them for SU's off of MG Turbo Mini Metros which are built for the job. Plus i've got 6 Mini's and 2 MGB's, so i know SU's quite well.

Also i've been told to watch out for having trouble with vapour lock on these engines.
Is this a common problem?
I was thinking of removing the mechanical petrol pump and fitting a modern electronic petrol pump instead, to try an cure the effects of heat soak causing a vapour lock.
What do you think?

[maineSS]

I've never experienced vapor lock, but there is a heat shield between the exhaust manifold and the pump, so I suppose it could be a problem. If you fit an electric pump, you should have a "bump switch" to turn it off in the event of a crash to avoid fire.

SU's are a very good carb when tuned right, and if you know them and can get the parts, use them.

I've never CC'd the stock head, so I can't say. Compression started at 6.7:1, then went to 7:1, and finally to 8:1 over the years on the stock engines, one tractor puller ran 9.5:1 on 93 octane with the late-model head.

[maineSS]

I looked up Vizard's SU Land Cruiser installation- he used (3) 2" SU's. The motor idled at 450 RPM, and low end "was like a steam engine from idle on up". It added 35 Hp to the top end, and was virtually unstallable.

The 6 cyl was likely the 3.8L (236 cu in) F or the 4.2L (258 cu in) 2F engine with a 3.5/3.7" Bore and 4 1/64" Stroke (102 mm). The F's developed 105 or 125 hp @ 32-3600 rpm, and 189 or 209 lb/ft Torque depending on compression ratio. The 2F developed 135 hp @ 3600, and 210 lb/ft @ 1800 rpm. Both had a single 2BBL Asin downdraft carb, and redlined @ 4000.

The 230 bore/stroke (3 1/4 X 4 5/8) and 3.7L displacement is very similar. I keep hearing that the vacuum characteristics of flatheads are different than OHV"s, but the SU has been around a long time, and was probably used on them. I think your friends might be in for a surprise.