Mike does more of a high-performance sort of port job in these heads.
I aim more toward touring-commuting use of the engines.
In the 500/550 and the 1972-74 CB750 heads there is quite a bit that can be done.
Thanks for the reply Hondaman. It was after reading your tips in the SOHC4 Library that I decided to find the 650 cam, and have the head ported.
"Bruce" is definitely not a race bike. And while I have done some moto-camping with it (see photo), it's mostly my "have fun on the weekend" bike.
It currently tops out at 83... downhill, with the wind. I'm really just hoping to get that speed up.
I never feel 100% comfortable on the freeway here in SoCal where the everyone is doing 75-80 minimum.
If I could gain 10-15mph extra, I'd be happy.
I think that would give me that extra power to pull away from other cars on the freeway, and some extra zip in the twisties on the weekends.
I'm happy to send it to you or Mike. As you have a good read on your differences, I'd trust your opinion.
The cam will certainly improve the top end. I've ridden a 550 with the 650 cam in it before, and it made the 550 feel like the 650, but with some torque - which the 650 seemed to lack when pushing Vetter gear like my brother used on his. He had the 500 first, with the Vetter, then got the 650 with everything Vetter made added on: the 650 had more top end, but the 500 got to the ton sooner. I think the tradeoff became one of hanging in the 3-4 gears longer in the 650 to 'get it up there', rather than just the top end numbers.
Mostly the 550's breathing issues seemed to come from a conflict between the engineers who designed the 2 components: the carbs that would not suffer the airbox issues of the 750 was one camp and the 550 head (i.e., high manufacturing costs) the other. In the end I think the carbs won that battle as they are more efficient in the 500/550, and the head designer(s) seemed to settle on simply making the intake port cross-section the same diameter as the carb throat. The result of that was the very 'linear' feeling on the throttle, regardless of the current speed, which the 750 never has enjoyed. This led to such stunts as cruising the town square at 20 MPH in 4th-5th gear with the 500/550, when the 750 would pitch you clean off the saddle for even trying it!
To improve the mid-throttle response in the mid-Four, the intake ports need to be reshaped a bit and a slight pocket opened above the intake valve: too much of this will make it fall flat in the 1/4 throttle range and make city riding kind of tentative. I did this last with one of the members here who had me build his 590cc version of the 500, and the top end jumped past the ton right away. IIRC he/we also installed the Megacycle 126-00 cam with it (or he might have done this later?) and it got better still, but did lose the 4th-gear 20 MPH capability in the tradeoff.
What I found most interesting in this port stuff was: the 650 factory intake ports look a lot like what we used to do with the 500 intake ports back in the 1970s.
