Anyone running 1.7" (stage 3) valves in a 750 long stroke?

Anyone running 1.7" (stage 3) valves in a 750 long stroke?
If so - tell us about it and if there's any valve shrouding near the cylinder wall reducing flow.

Interesting question . Stan Shenston , I think his name was ,used to recess the top of the cylinder on tuned Triumph race motors for this very reason. There was an article about it in Motorcycle Mechanics ..even with a helpful diagram about where to grind. This was back in the day when Boyer where in Bromley and had established a reputation for tuning Triumphs..

Stan Shenton, famous Triumph tuner.

Ken

The Triumph tuners bible .


Tho I havnt seen the second book , so I guess my Triumph was only half tuned .



Still sounded good though .

Most consumers won’t pay for quality anymore. Be damned the country of manufacture. If it’s cheaper they don’t care whose job was eliminated, even their own.

Got an email today from Steve Maney who said the stage 3 valves will fit but the ex valves get reangled into the gasket which I dont understand because the stage 3 and 2 ex valves are both 3mm over. He only recommends the stage 1 or 2 for a 750 long stroke. But the stage 3 can fit with some finess. Maybe stage 3 is pointless but I want to research it for piston design options.

Maybe the issues the Valves getting tangled, as in days of yore .

Which is why Triumph ran Cam wheel GEARS , tho with in & ex on one cam , chances of it shifting are remote .
Note the Norton Cosworth ran Geared Cams after the belt to the head .

ANYWAY ,

Probably more the issue IS the valves clipping the piston ?

The re angled Norvil / Dunstall ( a copy of works 650 heads ? ? ? )
was to give room for the larger valves , & maybe stop seat / head cracking . in that vicinity anyway .

Presume youd use the std. .040 thou , through the range , of rotation . Valve to piston .

Be intresting if a few degrees variation in the valve timing dramaticly alters piston to valve relationship .


just to clarify it, are you asking about valves in the Std. production , or the re angled inlet heads. Or Both, actually ? .

1.7 inch Diameter . Thems fairly big valves , even . Any pitchers fitted .

Matt Spencer said:

....just to clarify it, are you asking about valves in the Std. production , or the re angled inlet heads. Or Both, actually ? .

1.7 inch Diameter . Thems fairly big valves , even . Any pitchers fitted .

Click to expand...

Definitely re-angled on both intake and exhaust. A Stage 3 Maney head has in valves 5mm larger than stock. Ex valves 3mm larger than stock. My personal opinion is that 3mm over is enough for a 73 to 74.5mm piston. I'm not sure there is any point in going to 5mm oversize IN valves with the small pistons because of cylinder wall shrouding. Presently I have 73 to 74.5mm pistons that will work for 5mm oversized intake valves but I'm thinking of bringing them down for 3mm oversized valves.

You may be interested in a head I've been working on using a 42mm valve. It's a BSA A65 Thunderbolt single carb head I'm experimenting with, setting it up for two carbs. I follow the oval XR750 port shape as much as I can. At the moment, on my gear, its flowing around 168cfm @ 28"W and .385" valve lift. Although the port isn't particularly big it does need a carb of around 34mm. Even for a 750 engine with a short 74mm stroke like the A65 it means fairly decent rpm. So a 43.18mm valve possibly isn't that necessary if you can get a similar port into the Norton head.

My experience with Steve's stage 3 head in a 79.5 mm bore with an N480 cam is that the exhaust valve gets very close to the edge of the piston in a high compression setup. I think that could be a real issue in a 73 mm bore. I'm pretty sure you'd at least have to notch the bore, as well as running a piston with lower top ring groove. I'll make some measurements on my head and cylinder to see how much bore clearance there is, and let you know.

Ken

jseng1 said:

Anyone running 1.7" (stage 3) valves in a 750 long stroke?
If so - tell us about it and if there's any valve shrouding near the cylinder wall reducing flow.

Click to expand...

Hello Jim,
I have done a lot of theoretical research on my drawing board. It's a DIN A 1 drawing with a 1:5 (or 1:10? I don't remember) scale.
As well as that I have done a lot of geometrical calculations. I have no idea how much performance or flow you will get from all those bigger valves. But I can show you what works and what doesn't (geometrically!). What I found is that 43/33mm (34mm max.) will work (gemetrically) with a 73mm bore. But you know yourself that portshape and try/error gives us the practical results that we are looking for. Just to put it short: I will send you the calculations, drawings etc. (Again) in a PN.
Best Regards and Good Night
Klaus

With a large 43mm intake valve right up against a 73mm cylinder wall I'm not sure the flow would be any better than with a 41mm valve. Maybe worse.