jseng1 said:
There is no doubt that the Weslake is a great motor. And the 4 valves per cylinder is a big advantage over 2 valves. But there is another way to keep Norton in the front - technically - and that's to go with the Harley 750 XR D ports etc. 100 HP is available with the HD 750 and 110 or 120 HP should be available a 1000cc. 100+ HP should be available with a 1000 Nort if someone were to go to the trouble of researching the HD XR (I have and that info is available). This means welding up the combustion chamber and lowering it about 3/8" & ad a fin to raise the port in relation to the valve heads and copying the Harley D ports. It also means looking at the intake track length, ex pipes and cam etc. The Harley has a very good cylinder filling design for a pushrod twin. And they should be when you consider how far they have been developed. Its not likely that anyone would ever get to this because of how much trouble it would be. But thats where I would go if I were still racing. It would also require welding on more fining as Comstock has done in the past because that much power is going to overheat things (the Weslake motor would have the same problem if it managed that much HP). Looks like I'm getting off topic of my own post.
Look at the big difference in down draft height between the HD port (front) and the Norton below
More Harley port info here
http://www.accessnorton.com/norton-intake-ports-compared-harley-750-t16544.html?hilit=harley
Well, I'll try to do my fair share in keeping things off topic too.
If someone were attempting to modify a Norton head, ala oval port XR-750 as described above, there may be merit in pointing out a couple features of the port that may not be obvious from the pictures and description. The XR port is certainly a higher port with larger short-side radius than the Norton port, as shown by Jim's picture above. However, the picture might imply to some that both ports are oriented as shown in the picture, i.e., side by side and aiming straight at the bore, however, the XR port is not oriented like that. The XR ports are "swiveled" about the guide centerline to set them well off the fore/aft centerline of the engine, where the IN port is positioned to the right rear and the EX is positioned to the left front. But the more significant thing that occurs when the port is rotated is that the floor, i.e., the short side radius, is no longer on the "bottom" of the port (6 o'clock), but rather has been rotated up the side of the port to ~ 4 o'clock. By rotating the port in this fashion the short side radius is not discharging into a shrouded/masked position at the extreme edge of the combustion chamber as it would be in the 6 o'clock orientation, but rather is discharging from a significantly more favorable position. How the port location/orientation affects tumble, swirl, etc is well beyond my comprehension, but the performance suggests it's all working well together. And of course the large XR IN valve (44mm?) also doesn't hurt a thing.
Thought it worthwhile to bring this stuff up in the event some ambitious practitioner takes on such a project, and in the end wonders why he can't get it to flow like the rotated XR port. I think we need the late Ken Augustine to undertake something like this, since he is the one that developed the XR oval port for HD in the 1st place. Come to think of it, I seem to have some vague recollection of a forum post somewhere that he had done some major reconfiguring of a Norton head to get it all working as Jim S described above. Someone here know anything about that?
Hopefully the pictures below will allow the imagery to come clear in your mind's eye.
Valve guides are oriented fore/aft on engine centerline, degree of port swivel/rotation is obvious.
Port floor is rotated well up the side of combustion chamber. Note large anti-reversion shelf on EX port.
The port floor can be seen here rotated well off the edge of the combustion chamber to the upper right.
As along as we're off topic let's continue on. There are so many Norton performance related threads going on simultaneously on this forum I can't keep them all straight. Earlier in this thread hobot said
"Now picture how to make an over square 360' twin from scratch with all we now know."
His thought has overlap with other current threads so I'll post my thoughts on the subject here.
I think it's already been done via the Kawasaki Ninja 650 or whatever else they use this 650 vertical twin in. It's a sturdy little engine having 3 main bearings, 180 deg forged crank (yeah I know it's not a 360, but 270, 180, what's a few degrees between friends), balancer, B x S of 83 mm x 60 mm, 4-valve DOHC design, liquid cooled, fuel injected (38 mm throttle bodies), etc that when poked and stroked to 750cc, makes ~ 100 HP. So IMHO this is the best thing presently going in small vertical twins.
Last fall in flat track these Kawas were spankin the XR-750s pretty handily (XRs were 32 mm restrictor plate engines at ~ 85 HP). In light of these results the AMA did what it always does when Harley gets beat, they gave it back an advantage by removing the restrictors from the XR. Stay tuned for how this season goes. If both bikes are at 100 HP the Harley should be handily spanking back with its superior ability to put the power to the ground. But in the end, I believe the Kawa is tough and very economical to campaign vs an XR which takes 10s of thousands of dollars to campaign.
My $0.02.
