Hitchcocks Forum

Here's one for Paul again!

I am about to tweak the cylinder head of my 350. I was going to take it out to 30mm But I am thinking of going max with it and fitting a Del-Orto pumper..

My mates an engineer and will be doing the porting and milling 2mm off of the mating face.

What the largest you've gone with the inlet tract?

Obviously I want to leave some meat there for a bit of strength but was thinking of going to say 32mm (31.8mm = 1 1/4") or 34mm (33.4mm = 1 5/16") or 34.2mm = 1 11/32"

Tom

Hi Tom, we actually have a 1 7/32" Amal TT carb, which I opened out to about 32mm on the 350. The inlet manifold face on the head is opened out to this amount, but tapers off quite suddenly to about 30mm, which continues almost to the valve guide, but gets wider and shallower here to keep up the flow while going around the guide and also to avoid 'breakthrough' at the rear portion of the valve spring seating area, a real pain if that happens! I have since built up the critical area with alloy weld and raised the spring seats by shimming, to give more space below the springs and more preload on them, as well. Regards, Paul.

I tuned a humble 350 BSA B40 head to 32mm, and it worked very nicely with a VM32 Mikuni jetted for a 350 BSA Gold Star. The fact that the 350 Bullet/350 Goldie's bore and stroke dimension are quite close compared to my short stroke (79x70mm) B40 suggests that this might work well for you too. No reason you can't use the Dell'Orto of course, though sorting out a mounting flange for the 2" stud centres will need a bit more work. 2" centre Mikuni flanges are more easily obtainable.

Regards,

A.

Thanks for the replies guys! :0)

All things considered I think I will stick with 30mm inlet and I am considering a jrc30 flange mounted carb, which is basically an adapted Keihin with a velocity stack.