XL600 head

[JOOLZ]

I have just obtained an XL600 cylinder head in excellent condition, complete with new valve springs and valve seals.
I have spent the last 3 or 4 years regularly looking on ebay for one at a reasonable price, they crop up fairly infrequently and getting one from America (where there seems like loads for sale) was very expensive and import duty on top put the price well out of my reach.
Last week I noticed there was this one for sale in Hungary for e160, so being an EU country no import duty, I grabbed it.
It will match the bore much better than my 500 head, I will give the ports a mild reshape and clean up, and hopefully get some big fins welded on to it

[guest564]

I don't recall there being a lot of difference in the combustion chamber, if anything the 500 head is better for squish. Which head did you get? the LM head is a bit more restrictive compared to the R head but can be opened out. What are you doing for carburation?

[JOOLZ]

My mistake its an XR650l head. You do get more squish and a higher compression ratio with the XBR head, but there are problems with valve masking using them on 100mm bores, and I would rather have it breath better and sacrifice a little compression. My compression ratio at the moment is 11.7:1, the new head will drop that to 11:1. I will be using my Amal 40mm carb

[guest564]

Valve masking by what? with the shallow combustion chamber and 100mm bore valve masking should be reduced. 11.7:1 sounds about right, I measure mine at 11.6:1 with a 100mm Wiseco piston and an XBR head. Are you using a filter? my 40mm Amal stuck open when it got dirt in it, a couple of other racers had the same problem.
What size valves are in the 650 head?

[JOOLZ]

valve sizes are 30 ex and 34 in. Valve masking is caused by the step in size between the combustion chamber and the wider bore, it causes a turbulent effect at the side of the valve nearest to the bore and reduces overall flow by a marked amount.
I have never had any problems with my Amal carburetor, It runs a special velocity stack (made for when it ran on a G50) I liked the looks of it and it flows well, I run a chrome plated brass slide and I have never had it stick open even when covered in ice from the methanol injection, I just never forget I have a kill switch in case something does happen.
I do have further long term plans for the bike lower compression again to 9:1 and use an amr 300 or 500 supercharger from a Japanese 660cc microcar breathing through twin 40's. Unfortunately thats some time off yet.
I am very pleased with the performance of the bike already, in a couple of drag races with a friend with a Suzuki 600 bandit I can out accelerate it up to 70, after that thing happen more slowly