Documentation of CB450 head on CB

MBellRacing · Post by **MBellRacing** » Sun Sep 05, 2010 7:00 pm

I know this has floated around, but every time I search, it comes up with REALLY random things...

I found this on another forum. Couple guys (who seem to stay quite quiet-- I guess pictures really are worth 1000 words...) are replicating the road going CR72 prototype based on a Japanese magazine they found. Pretty interesting pictures of a [only slightly] modified CB77 frame to fit the 450 head. Apparently the engine case is an original CR72 part but most of the other parts (like the frame and head) have gone missing. Looks like an incredible project!

Not the same bike, but still seeeexy...

It's cool seeing in-progress shots of someone doing the swap. I know it's often taboo in these groups, but I'd LOVE to just see what this little motor could do with some modern tech. Maybe use electronic ignition and fuel injection with the twin cam head... one ponders...

ricksd · Post by **ricksd** » Sun Sep 05, 2010 9:32 pm

I really like this sort of project too- the CB77 engine looks so great that it's hard to see how someone could get the 450 head to look right- it's huge. I happen to have a 450 head laying around, and have held gaskets up, trying to visualize how hard it would be, and concluded it wouldn't be easy. The center/center spread of the rods looks to be a match, but the cylinder studs would require lots of welding and careful study of oil flow, etc.
The CB450 head is an incredible bit of casting/engineering- a tempting project, but the head is so big sitting on the CB77 cylinders- looks awful. If anyone is interested I can take some pictures of the 450 gasket or head sitting on the 305 crankcase, but it may be discouraging. Plus, I don't like the 450 cams running in the aluminum cam blocks without a replaceable bushing or bearing- I know it's supposed to be turning on an oil film with no metal to metal contact, but it just looks wrong.
In it's favor, the 450 head conversion looks to be easier than the picture that was recently posted of the 5 speed transmission conversion- gave me a headache looking at the picture.
It wouldn't take much to get me interested in doing this- may take a new cylinder- like the big fin BSA Gold Star, to make it look right.
Rick

teazer · Post by **teazer** » Sun Sep 05, 2010 10:15 pm

5 speed is basically a drop in. 6 speeds are a touch more involved though.

That CB/CR hybrid is interesting as is the 450 top end on a CR lower end.

Pete Rhodes did a 450 top end conversion a few years ago and I seem to recall that was a lot of work.

MBellRacing · Post by **MBellRacing** » Sun Sep 05, 2010 10:53 pm

I've seen a couple images floating around. Seemed to involve a lot of welding and machining, but nothing impossible. Quite simply the sort of thing a pocket full'o cash and a good machine shop could take care of. You're never going to get the CR's gear driven cams, but you'll have something rarely seen. My friend owns 034 Motorsports, the maker of stand-alone ECU company specializing in low-tech EFI conversions for previously carbureted engines. That, mixed with maybe a hot cam, some custom pistons, and means to rev the bejeezus out of a little motor like this would be one hell of a rocket!

Would it be possible to just mount the block and the head to the 305's case, or am I missing something? That would seem to be the way to go since then you could just machine the case and send the studs up in the CB450 fashion. There also seems to be much more of a market for true 450 racing pistons and it would be much easier to retrofit.

Also, now that I really take a look at it, is there THAT much of a performance advantage to the 450 head? It's still 2 valves per cylinder, isn't it? The 305 head also has ball bearings for the single cam which probably results in significantly less restriction, not to mentioned less need for precise oiling of those lubricated bearings in the 450. Obviously there was a good reason to prototype the style of head since Honda spent so much time building it.

teazer · Post by **teazer** » Mon Sep 06, 2010 9:01 am

450 conversion takes a fair amount of welding and machining to move the studs, but nothing complex.

The advantage is an extra 100cc if you swap in a different crank, and the head flows better than most of us can manage with a CB77.

But it's hardly the only way to get 500cc. Ask Jerry Kooistra! he has an incredibly fast 500cc CB77 and has built several of them.

The real reason is because you can. It's the challenge.

MBellRacing · Post by **MBellRacing** » Mon Sep 06, 2010 1:46 pm

I see. But would I achieve much more power than, say, do extensive porting on the original head, used electronic engine controls, built it up to 400-500cc naturally, and swapped in a 5-speed? Just dreaming of course, but could you imagine?!?

teazer · Post by **teazer** » Mon Sep 06, 2010 8:19 pm

5 speeds are a simple swap - more or less, so the question is which would be easier and cheaper - 500cc CB72 or CB450/72 hybrid. But a race kit/NOVA 5 speed still uses a chain drive which is fine for say 45 - 50 HP, but for 60 I'd prefer a gear drive and 6 speeds.

The stock head doesn't flow enough to support 500cc, so that means removing the skulls and welding and machining for different ports, seats and valves. Both require a different crank, so there's not much difference there.

The CB77 barrels would have to be opened up and new liners installed and so on, so a 450 may actually be easier, believe it or not.

Bottom line. Neither way is simple and both paths require skill and dedication.