Which Camshaft Should I Use on GS550

[Guest]

I have the choice of two camshafts for my 550/650 conversion and I need your expert opinions. Especially after reading Jim's (POSPLYR) article on camshaft lift.

The 550 cam has 260 degrees duration and 7.08mm lift on both camshafts (intake and exhaust).

The 650 only has 252 degrees duration and has 7.53mm lift on the exhaust and 8.12mm lift on the intake.

From a performance point of view which camshaft would be best suited to my conversion.

Thanks for any advice given.

[Nessism]

You might want to look at the opening and closing points of the valves, that has a lot of effect on how the cams will work. Based on the duration and lift alone, the 650 cams will provide more torque, with a slightly lower rpm peak. The 550 cams will be slightly more gentle on the mechanical parts although I doubt you would have a wear problem with the 650 cams.

[Suzuki_Don]

You might want to look at the opening and closing points of the valves, that has a lot of effect on how the cams will work. Based on the duration and lift alone, the 650 cams will provide more torque, with a slightly lower rpm peak. The 550 cams will be slightly more gentle on the mechanical parts although I doubt you would have a wear problem with the 650 cams.

Ed; How do you determine which cam is more gentle on the mechanical parts.

Here are the figures I obtained from the Suzuki Workshop manual, any advice would be great as I don't really understand how early or late opening valves affect performance.

GS650:
Intake Opens 20 dergrees BTDC
Intake Closes 52 degrees ABDC
Exhaust Opens 49 degrees BBDC
Exhaust Closes 23 degrees ATDC
Duration 252 degrees
Overlap 43 degrees

GS550:
Intake Opens 26 dergrees BTDC
Intake Closes 54 degrees ABDC
Exhaust Opens 54 degrees BBDC
Exhaust Closes 26 degrees ATDC
Duration 260 degrees
Overlap 52 degrees

The question is which cam will give the more torque, pulling harder from lower revs and which cam is best for better performance. Is there much difference between them both in practice, on the road.

Thanx

[tkent02]

550 = more duration and more overlap, better suited for high RPM engine, small lift works OK on a smaller displacement engine.

650 = less overlap and duration, designed for power at lower RPM but more lift to let a larger volume of air through anyway.

Disclaimer, I know nothing about this stuff but that's my guess, from having ridden both bikes and from thinking about it for a while.

I have experimented with moving cam timing away from the factory settiings, less overlap equals lower power band, with less top end kick, as does advanced cam timing.

You need to talk to Ray or someone who really knows how high performance engines work.

[Suzuki_Don]

550 = more duration and more overlap, better suited for high RPM engine, small lift works OK on a smaller displacement engine.

650 = less overlap and duration, designed for power at lower RPM but more lift to let a larger volume of air through anyway.

You need to talk to Ray or someone who really knows how high performance engines work.

Thanks. Yes I am waiting for the race experts to chime in.

[Nessism]

You don't need a race expert Don, both of those cams are so similar you could flip a coin. The 650 cam is the one I'd use because of the greater lift. Only proviso is if you are using a 650 cylinder and a 550 head; because the head has a smaller combustion chamber your compression may be sky high so the greater overlap on the 550 cam will bleed off some compression which is a good thing in a situation like that.

[tkent02]

Here's a better idea, try them both and tell us what you find out.
I will be following in your footsteps if I ever find another 550.

[Suzuki_Don]

You don't need a race expert Don, both of those cams are so similar you could flip a coin. The 650 cam is the one I'd use because of the greater lift. Only proviso is if you are using a 650 cylinder and a 550 head; because the head has a smaller combustion chamber your compression may be sky high so the greater overlap on the 550 cam will bleed off some compression which is a good thing in a situation like that.

Ed does the greater lift give more torque. If not what is the advantage of more lift.

I am using both the 650 cylinders and 650 head so no problems using the 650 camshafts.

My only problem is the speedo drive on the exhaust cam on the 650 shaft is stuffed. Know anyone that has a spare for cheap with a good gear on it. I've looked up a few on EBAY but they are all in the States and freight on one shaft only is around $45 and they want up to $30 for a set of shafts. They can keep the intake and I only pay freight on the single exhaust one minus the sprocket. Anything to save on weight when shipping to Australia.

I might try the 550 shafts first and wait to see if I can pick up a 650 shaft off EBAY here in Australia. That might be some wait though. No big deal to swap the shafts at a later date.

I have had both sets of shafts mounted in the head and it is surprising the difference in shim sizes between one shaft and the other. The base circles must be different compared with the bearing journal surface.

[rapidray]

Those cams, while SEEMING close in numbers, are VERY different cams! The 550 cams are both installed at 104 lobe centers where the 650 cams are installed "backwards" of the way I would install them. What I mean by this is that you normally set the exhaust cam lobe center 2-4 degrees bigger # than the intake for better scavenging. In the case of the above 650 cams [unless the above is labeled backwards] those #s show the intake at 106 & the exhaust lobe center at 103. If it were MY motor, I would use the 650 cams, slot the cam sprockets, & degree them to 106 & 108, intake & exhaust. For a little more torque, maybe 104 & 106. Just remember that, when it comes to cam degreeing, smaller numbers are more torque, lower peak hp. Bigger #s are higher peak hp & more HP. I hope this helps. Ray.

[waterman]

I would think you would have best results with the 650 cams, the 650 heads are a different design, much shallower than the more hemispherical 550 heads. This coupled with the 650 flatter pistons makes it a different animal than the 550s.

I did a little research, wondering if the 650E chain version might be a better choice for cams and found that the cams are same on all 650 models (E, G, GL, and M) models. What is different is the sprockets from E to G. Piqued my interest since valve timing is different from E to G models in service manual. Might be good if we could get input from a 650E owner on how many teeth are on sprockets and if they could check their valve timing.

I own both 550 and 650. I can't honestly compare them since my 550 doesn't run nearly as well as my 650. What little I have driven the 550, it doesn't develop nearly the same low end grunt as the shaft, but does have a little more kick at high rpms. My 550 seams to struggle to get over 70, need to drop down to 4th gear to get there. Most likely I will need to look into carbs, previous owner had upped the main jets and I think it may be too rich.

The 650 is very linear in power output with little extra punch on top. It will simply smoothly accelerate, although leisurely, in high gear from 20 mph. Likewise, it will bury the 85 mph speedometer with no problems. It doesn't need to be revved out to accelerate smartly, but will run happily at higher revs.

I have an extra head or two, but don't think I have any extra 650 cams. I seem to remember someone here on GSR from Oz that had a 650 Kat that they were fixing for their wife, with a picture of their garage that had a huge stack of engines and parts. I will see if I can search them out. Someone on your island has to be able to help you set up your cams.

[Suzuki_Don]

Those cams, while SEEMING close in numbers, are VERY different cams! The 550 cams are both installed at 104 lobe centers where the 650 cams are installed "backwards" of the way I would install them. What I mean by this is that you normally set the exhaust cam lobe center 2-4 degrees bigger # than the intake for better scavenging. In the case of the above 650 cams [unless the above is labeled backwards] those #s show the intake at 106 & the exhaust lobe center at 103. If it were MY motor, I would use the 650 cams, slot the cam sprockets, & degree them to 106 & 108, intake & exhaust. For a little more torque, maybe 104 & 106. Just remember that, when it comes to cam degreeing, smaller numbers are more torque, lower peak hp. Bigger #s are higher peak hp & more HP. I hope this helps. Ray.

Thanks heaps Ray. I didn't quite understand the "backwards" bit, but the other information is very useful. Good to get some actual numbers on these motors.

[Suzuki_Don]

Thanks WATERMAN (Ed). Good to have someone with bikes with both the 550 and 650 motors to get a seat of the pants comparison.

Thanks again. Good information in your post.