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GS550 / 673cc transmission settings (chain kit)

  • Thread starter Thread starter boris.h
  • Start date Start date
B

boris.h

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Hi all;
I did not found any clear answer on the forum, so I created this post.

This post concerns the GS 550 / 673cc swap, increasing the power from 50hp to 72hp, at least, with the 6 speeds gs 550 gearbox.

My question is about the last transmission ratio, with the chain kit. On the gs 550, this is a 15 x 50 ratio, on the gs 650 this is a 15 x 45 ratio. I want to try the 15 x 45 gs 650 chain kit, for this swap because I'm affraid that it would be very "short" for the gs 550 transmission full setting, with that power....Any advice here?

thanks!
Boris
 
What do you plan on using the bike for? I'm going with the standard 550 sprockets at least at first, because I never ride on interstate highway anyway. I'm mostly blasting up and down the local canyons and little mountain roads. Occasional zip across town or down to the store. Have no need for lugging the engine all day at highway speeds. All of these GS engines need to wind out anyway. After I get used to how the new engine runs I might make changes.

15 x 50, 15 x 45, are the internal ratios the same? Transmission ratios? Primary drive ratios? I dunno, going to just see how it works.
 
This bike will be used for week ends, and also going to work sometimes, not driving on the french highways. I often drive the bike on roads which are speed limited at 110Km/h (70 mph), and, at this speed with the gs 550 gearbox and final transmission, this speed means around 3500 / 3800rpm, I find that a little too much.... I calculated that, at the same speed, I would be around 3200 rpm instead of 3800 rpm....
 
Isn't the Redline at 9000 rpm? Not sure why 3800rpm seems too much to you.

I found that my 550 likes to run around these rpms, doesn't re-charge the battery too well below that.
 
At this speed I use to cruise, not push it up to the redline. I also think that the true redline is around 10000 rpm, not 9000...IMO
 
You can't hurt a 550 by winding it out, as a 550 you can't really even ride it below about 5,000 RPM, it doesn't have enough torque to get out of it's own way.
Mine always spent most of it's time in the 6,000 - 11,000 range, and they have lasted forever anyway. That will all change with the 650 top end, but I don't know how much.
That's why I don't want to buy any chains and sprockets until I get to ride it, really have no clue what it will be like.
I'm lucky, my old chain is worn but still usable, do you still have your old stuff?

If I were to do it only from guessing and not from riding, I'd go for the same ratio in sixth as the GS650G had in fifth. It was geared pretty good for it's engine. You would still get a little better power since the 550 is smaller and lighter, but it would be very similar. Still be better in the lower gears due to the six speed transmission. Slightly higher RPM at highway speeds would make a slightly more interesting bike to ride, quicker.
I certainly WOULD NOT go for a lower RPM on the highway than the 650 had. Chugging these engines is not good for engine life, or fuel mileage or anything else.

If you ant to ride at 3,200RPM, get a Harley.
 
boris.h said:
This bike will be used for week ends, and also going to work sometimes, not driving on the french highways. I often drive the bike on roads which are speed limited at 110Km/h (70 mph), and, at this speed with the gs 550 gearbox and final transmission, this speed means around 3500 / 3800rpm, I find that a little too much.... I calculated that, at the same speed, I would be around 3200 rpm instead of 3800 rpm....
Click to expand...

Better go back and do some more calculations because your rpm numbers are incorrect. No way the engine will be turning in the 3800 rpm range at 70 mph, more like 5800 rpm.

The 550 top ratio, including the overdrive 6th gear is 3.18.
The 650 top ratio, including the 1:1 ratio 5th gear is 3.00.

Basically, both are similar.

Add in the taller 650 final drive reduction and the 650 will spin slower than the 550, but not by tons.
 
ok, thanks!
I have an opportunity for a gs 650 chain kit for few € (brand new)... I'll test it
 
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