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Eyeballing 78 550 cams

  • Thread starter Thread starter mlinder
  • Start date Start date
M

mlinder

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So, I started to tear down the 78 550 motor last night to start fitting my 650 top end on it.

I got to the cams, and by my eyeball, the gs550 cams do not appear to have 1mm less lift, which is what I had found the difference to be stated here on these forums. They also have far more duration.

See pic, 550 cam in head, 650 cam in hand:

550650cams.jpg

550650cam.jpg


Since I'm building for top end power, I think I'll stick with the 550 cams.

I will measure once they are out, but I'm pretty sure I'd be able to discern over a mm in lobe height difference by eye.
 
You you have equipment to measure them?
Do you have the factory specs for both bikes?
 
tkent02 said:
You you have equipment to measure them?
Do you have the factory specs for both bikes?
Click to expand...

Sort of. I can measure lift. I spose I can spend time figuring out duration, but it's clear which one has more.

These are the specs I found, here on this site. (I think this is where I found em, anyway.. been a little while..)

GS650: 8.12mm lift on the intake and 7.53mm lift on the exhaust
Intake Opens 20 degrees BTDC
Intake Closes 52 degrees ABDC
Exhaust Opens 49 degrees BBDC
Exhaust Closes 23 degrees ATDC
Duration 252 degrees
Overlap 43 degrees

GS550: 7.08mm lift on both camshafts
Intake Opens 26 drgrees BTDC
Intake Closes 54 degrees ABDC
Exhaust Opens 54 degrees BBDC
Exhaust Closes 26 degrees ATDC
Duration 260 degrees
Overlap 52 degrees
 
The specs are in the factory service manual. Basscliff has them for download if you don't already have them.

More duration is good for high rpm. More lift is good for torque, and power in general.

I'd figure out the cam centerlines (I'm too lazy at the moment to do it). The CL is another characteristic that related to high rpm power or low.

Seems to me you can't go wrong either way.
 
Like I said, so far I don't see higher lift from the 650 cams, though I haven't measured them yet.
 
For more power, use the 650 cams.
For more torque, use the 550 cams.

Daniel
 
7981GS said:
For more power, use the 650 cams.
For more torque, use the 550 cams.

Daniel
Click to expand...

Think ya got that backwards, Daniel. More overlap = more highend. The 550 cams have quite a bit more overlap. Less overlap with more lift = low end. The 650 cams have less overlap.

Initially I was going to go with 650 intake for better low end response, and 550 exhaust for a tad more overlap for top end response. But like I said, so far I can't see the increase in lift on the 650 cams.
 
mlinder said:
Think ya got that backwards, Daniel. More overlap = more highend. The 550 cams have quite a bit more overlap. Less overlap with more lift = low end. The 650 cams have less overlap.

Initially I was going to go with 650 intake for better low end response, and 550 exhaust for a tad more overlap for top end response. But like I said, so far I can't see the increase in lift on the 650 cams.
Click to expand...

That's how they run, 550s are much pipier, 650 has a broad powerband.

I would be tempted to test them both in the engine to see how it runs.

Are there any performance cams available?
 
tkent02 said:
That's how they run, 550s are much pipier, 650 has a broad powerband.

I would be tempted to test them both in the engine to see how it runs.

Are there any performance cams available?
Click to expand...


Many. But that's another, later build.

I don't think I'd like to do this particular engine build more than once, so I guess measuring them is going to have to happen to make the correct choice.
 
I will spend the hour or so it takes to swap cams to try each set out.
I'd rather know I have the right one than think I guessed right.
 
Math is math, and I know I'm going for top end, which means as much overlap as possible. That said, after I measue, if the lift on the 650 intake cam isn't at least .5mm higher than the 550 intake, then I'll be using the 550 cam. Otherwise, I'll be giving my engine guy a call to see what he thinks I should go with.
 
mlinder said:
Think ya got that backwards, Daniel. More overlap = more highend. The 550 cams have quite a bit more overlap. Less overlap with more lift = low end. The 650 cams have less overlap..
Click to expand...

Yes Mark Daniel does have it back to front. I have the 650 cams in my 550, they need to be degreed in though using the centreline method. You will see what I mean when it comes to timing the camshafts with either the 19 or 20 links between sprockets. The 650 cam give immediate pulling power from way down low all the way up to 8 grand. The 550 cams would be peakier.

I have not tested the 550 cams in my enlarged motor, but before I took it out to the larger size and operating the bike with the 550 cams there seemed to be about three different points where the engine would lift away and increase power as the revs climbed. Below 3000 the motor didn't have a lot of oomph, but was happy enough as long as there were no large throttle requirements. At 3000 it would start to pull harder, at 5000 it would really start to pull harder again and at about 7000 it really took off.

It performed well for its size. But comparing that motor with the 650 conversion is really like chalk and cheese. There is a 49% increase in hp using the 650 cams, so there would be even more on tap with the big overlap 550 cams. The big thing I have noticed with my bike with the 650 cams is that there is no real power band. Just solid performance and torque whenever you turn that throttle. I like the smooth, flat power curve of the 650 motor. But don't read "FLAT" power curve as not having performance. This bike has been over 120mph with me in the saddle.
 
Hiya Don :)

Since I'm a tad partial to peaky motors, I think the 550 cams are what I will go with (after measuring, of course.. I'm not convinced what I have are stock 550 cams... top end has been apart before by a previous owner, it seems..)

The 8k rpm 'rush' of the 550 was always my favorite part of this bikes engine, so I'm wondering what the 8k rush with another 125cc's and a vastly improved head design will be like.. :)
 
mlinder said:
Hiya Don :)

Since I'm a tad partial to peaky motors, I think the 550 cams are what I will go with (after measuring, of course.. I'm not convinced what I have are stock 550 cams... top end has been apart before by a previous owner, it seems..)

The 8k rpm 'rush' of the 550 was always my favorite part of this bikes engine, so I'm wondering what the 8k rush with another 125cc's and a vastly improved head design will be like.. :)
Click to expand...

More than 75hp I would think, should be a buzz.
 
Checking the cam specs shows the 550 uses a 104 cam centerline for both cams. The 650 uses 106 Intake and 103 exhaust. The lift is a positive thing so I'd use the 650 cams and then degree them both to 106, or higher even, if you want high rpm power. I think this will make a bigger difference than the small amount of extra overlap afforded by the 550 cams.
 
Moving 550 cams to the same lobe centers as the 650 will keep dynamic compression up, while still giving me quite a bit more overlap. I know, everyone wants more low end throttle rsponse from their tiny metric inline 4's, but I like to accentuate their natural tendencies. :)
 
mlinder said:
Moving 550 cams to the same lobe centers as the 650 will keep dynamic compression up, while still giving me quite a bit more overlap. I know, everyone wants more low end throttle rsponse from their tiny metric inline 4's, but I like to accentuate their natural tendencies. :)
Click to expand...

It's only 8 degrees more duration with the 550 cams, I doubt this will make up for the lower lift when all is considered.
 
Nessism said:
It's only 8 degrees more duration with the 550 cams, I doubt this will make up for the lower lift when all is considered.
Click to expand...

Only 8 degrees, but the profile is important too, and the 550 cam has what appears to have a much less abrupt profile, with the valve open considerably more for the amount of time it's open. This is very important for an engine that will see 9 grand frequently.
 
mlinder said:
Only 8 degrees, but the profile is important too, and the 550 cam has what appears to have a much less abrupt profile, with the valve open considerably more for the amount of time it's open. This is very important for an engine that will see 9 grand frequently.
Click to expand...

The 550 cams are lower lift and higher duration, so the ramps are shallower. This does nothing for you other than it's more gentle on the valve springs compared to the 650 cams. The important thing is the lift amount, cam centerline, and duration. More duration means less cranking pressure and less torque, you won't make this up with only 8 degrees more duration.
 
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