Topic: Performance upgrade for Honda 450 3 valve motor

[Stephengmarth]

Would anyone know of any performance parts that I could add to my 1983 450..I'm not sure if they make parts for them or not. I was thinking maybe a new cam, re-jet the carbs and open exhaust. But I cant find any cams

[jweeks]

     Yes, you can improve your 450 twin. If you remove the air filter, you will have challenges in getting the carbs right. I like EX-500 CV carbs with a little rework to fit the Honda head.  Web Cam used to do reqrind cams for those motors. Keep the duration fairly short with more than stock lift. There isn't much you can do with the cylinder head. Get rid of the flashing in the ports and do a good valve job. The head won't flow a lot of air, nor can it be improved much. The pistons can be replaced with other brand factory pistons that use the same pin size. More compression than stock helps up to around 10.5:1 for the street and pump premium. You can sleeve and bore the block up to 84mm. That's the biggest change that will affect the bike. The flywheel on the end of the crank can be turned to lighten it. There's a couple of pounds off of the rotating mass that improves throttle response.  MSD makes a box for a single that works very well for the lost spark twins. You can set up your own timing advance curve with it.
     I've known of Suzuki/Kawasaki stock pistons with heat barrier coatings finding their way into a few Honda twins. If you want more performance than that listed above, I'll be happy to spend your money on more radical stuff. A friend has a Cb450A at 84 mm bore, stock stroke, 34mm CV carbs, and a few tweaks that has gone 13.499@96 mph in the quarter mile. For the street, bigger strokes, and better breathing cylinder heads would be ideal. Unfortunately, neither one is affordable. I've gotten around the cylinder head limitations, but it wasn't cheap! Hope that this helps!

                                                                 Jon Weeks

[Stephengmarth]

Wow Alot of info I really appreciate it. How far can I bore out the existing cylinder? .Ill be staying in touch with you. Ive built alot of Race/high performance motors but never for motorcycles.

[Pinhead]

What is causing a 3-valve head to have "breathing problems?" it seems that performance has been found on older 2-valve heads without running out of breath...

[jweeks]

Pinhead,
     My memory of Honda twins had the performance heads of the '70's having 4 valves. The '80's heads had 3 valves. The 80's heads had the two intake valves right at the edge of the combustion chamber. You can't put in bigger valves/valve seats with this design. I got opinions from Lazer Porting and Mike Rieck on modifying the head. With an 84mm bore possible, you can get to just under 550cc. You can't increase the air flow significantly without enlarging the stock valves. Moving the valve guides to allow larger valve seats is very, very  expensive. It's a limited flowing, can't be economically modified cylinder head.

Stephengmarth,
     I haven't been into the garage lately to check out the stock sleeve od. I'd limit the overbore to allow a minimum of a .150" thick sleeve wall. Any thinner and the sleeve distorts too much with heat. You can't keep a ring seal with an oval bore.  You want to start with a 450 motor. The 400cc motors of the '80's didn't have the extra top end oiling circuit. That circuit helps with the life of the camshaft. It's significantly improved in performance applications.

If anyone wants to see how I fixed my 80's twin cylinder head limitations, here's the url  http://forums.dragbike.com/forum_posts.asp?TID=8794

                                                               Jon Weeks

[Pinhead]

Pinhead,
     My memory of Honda twins had the performance heads of the '70's having 4 valves. The '80's heads had 3 valves. The 80's heads had the two intake valves right at the edge of the combustion chamber. You can't put in bigger valves/valve seats with this design. I got opinions from Lazer Porting and Mike Rieck on modifying the head. With an 84mm bore possible, you can get to just under 550cc. You can't increase the air flow significantly without enlarging the stock valves. Moving the valve guides to allow larger valve seats is very, very  expensive. It's a limited flowing, can't be economically modified cylinder head.

                                                               Jon Weeks

Very interesting. Could you hazard a guess as to how well the head flows when compared to a 2-valve Honda twin, relatively at least? I wonder if port bias could be used in these heads to introduce some swirl to the chamber (as 3 and 4 valve heads produce good tumble but very little swirl).

With the limited improvability in the airflow department, the other end of the equation is combustion efficiency.

Even though it seems to be very difficult to cram more air into the chamber, it's relatively easy to get the air/fuel mixed better on it's way.

Going with bigger pistons should allow at least a little squish around the circumference of the piston. This, IMHO, should be maximized to allow for higher compression without detonation especially if you're willing to run mid-grade or premium pump gas.

A good, strong spark is the next step. I like the idea of the single-cylinder MSD ignition being used to get a good jump-start on combustion. If you want a cheap upgrade to your stock ignition, replace the stock coil with a Wells C849 coil from a Chevy Cavalier.

If everything is done correctly, running 10.5:1 should be pretty easy even on 87 octane pump gas (my '79 CB650-ST is running 11:1 on 87 octane without issues).

[jweeks]

Doug,
     I've never modified any Honda two valve twins. Don't know how good/bad the potential is for that head.  I do know the 400/450 3 valve early 80's Honda twins. Due to the lack of modifications that I could do to the 450 cylinder head, I went to the Suzuki two valve head. That head can be modified for more air flow and better air flow than I could get out of the stock Honda heads. Before I went to the Suzuki head, I looked into the 70's Honda 4 valve twin heads to see if they could be adapted. They couldn't be adapted without major expenses. I'd suspect that any older Honda twin 2 valve heads also wouldn't be adaptable to the motor in question here. I'm only trying to answer Stephengmarth's particular questions.
     Yes, the flow of any intake port can be improved. One of the areas of interest is keeping the atomized fuel from slowing and puddling in different areas of the port, valve, and combustion chamber. That area of performance is measured using wet flow modeling. There are several major head porting companies doing a lot of research on this. I know that Air Flow Research does a lot of work for Nascar in this area. Their area of knowledge is far beyond swirl marks in ports and on valves. They make one "perfect" port and cnc copy it for the rest of the heads they make. I'm not a porting expert. I don't know everything about wet flow testing. I just read about it like anyone else can. I've worked with AFR on a different air cooled cylinder head that I had to bow out since I couldn't afford their costs of development.
     I've found 3 ohm dyna green coils on Ebay/Dragbike.com  for around the same $35 cost. A little smaller than the Chevy alternative.

                                                                       Jon Weeks

[Pinhead]

     I've found 3 ohm dyna green coils on Ebay/Dragbike.com  for around the same $35 cost. A little smaller than the Chevy alternative.

                                                                       Jon Weeks

I may be mistaken... Isn't the '83 CB450 ignition CDI, driving a 0.7 ohm coil? If not, the C849 won't work. My '79 CM400 is CDI and the C849 is a solid upgrade. If it's not CDI, disregard my suggestion.