VM26 SS on GS 650 head and GS 550 bottom question

[Guest]

Hello From France!
I am currently buying some parts to update my GS 550 this winter, to swap the gs 550 head by a gs 650 head and cams, gs 650 pistons and cylinders.
According to my little calculus, A 26mm hole for carbs could not restrict the new configuration. So, I'm trying to buy VM26SS carbs from a 750 GS. Why not CV or CR carbs? I just want to still have the original look of the '79 GS 550 (VM22SS)....

Any feedback about putting the VM26SS on a 550 or 650 head? I know maybe I'll haveto drill the head ports to center the new carbs, but that's not a problem because I'll make some drilling stuffs on the head...

thanks!
Boris

[Steve]

Will the 550 head fit on the 650 cylinder block? I have no idea if that is possible, but would be the easiest solution.

If you change cams, check the sprockets. I don't know how many teeth are on the 550 and 650 cam sprockets, but I do know that they are different on the 650E and 650G. Looking at the cross-reference chart, the sprockets on the '79 550 were only used on the '77-'79 550, not sure how they are different than the 650 sprockets.

One more thought, ... VM26 carbs were used on the 750, 850 and 1000. They might be just a bit too much for your 650. Not sure if the VM22s that you have now would choke it down that much, but you are apparently going to have to compromise somewhere. Either use your 22s or switch to BS carbs. You will also have to find a way to transition smoothly from your 26mm (or 22mm) carbs to the 32mm intake ports to minimize turbulence. You may find that all that turbulence will offset any gains found by using your stock-looking carbs.

.

[tkent02]

The problem is the 650 pistons and 550 head are shaped differently, 650 pistons don't fit into the 550 head all that well, and most of the power increase is from the better combustion chamber shape of the 675 head and pistons.

Figuring out how to put the VM carbs on the 650 head shouldn't be that hard, but it won't make as much power and won't be as efficient as it would be with the bigger CV carburetor.

[boris.h]

Hi, thanks for all!
I want to clarify smg, I think you understood wrong: I just bought a gs650 head! I will put on my gs 550 (so gs 550 bottom to keep the 6 speeds transmission) a gs 650 bottom end (cylinder block with pistons), and gs 650 head! I have with the gs 650 head the cams, so I'll be able to choose which cams I want to use.... I can easily understand that gs 550 cams have a bigger duraction time thant the 650 cams. I want to get more power, but I want all of all more torque. Because, this is more usefull to have lot of torque because we drive more below 5000 / 6000 rpm than > 6000 rpm.
So the block configuration that I want to get is:
- bottom gs 550 with 6 speeds transmission (chain)
- bottom end with pistons of gs 650
- top end head of gs 650 withs gs 650 cams

I made some calculus, reading my favorite preparation book. The results are a carb diameter of 32.8mm, so a 26mm diameter of the venturi (diameter where there are the slides). Moreover, I want to keep VM carbs, for two reasons: I want to keep the original look of the bike, I have personal experience about VM carbs so it would be easier for me to set them.

About sprockets, even if I have gs 650 cams I could keep the 550 sprockets. And, about timing the cams, I have all the material to make a precise timing (already made lots af timing on grA, grB rally cars). If necessary, I will machine the sprockets to be able toadjet them precisely (<1° rotation).
And, about the top end, I will receive a gs 650 top end with a broken spark plug inside, so a lot of operations to do before use it again... surfacing the gasket face to get a biggr compression ratio, polishing exhaust ports, machining the valves ports... If interested I will send some pictures of my job in a specific subject.

[Nessism]

Sounds like a fun project Boris. Get yourself a Photobucket account (or similar) and load up the photos there, then post the IMG link here and the photos will show up in high resolution. We love photo threads so take LOTS and post them up so we can share with your project.

If you look at the cam specs between the various bikes you will see that the difference between them is minor. The 650 cams have a little more of a torque profile so you may want to go that way but it won't matter much either way.

There are several good threads on how to build an engine such as you are interested in so don't forget to search them out.

Oh, and regarding the carbs, I'm sure you can figure out how to get those VM's mounted up. The KZ650 came with VM24's for a few years so those may be a better choice if you can find them. You should be able to mod up some Kawasaki intake manifolds too (slot the holes). As a bonus the Kawasaki manifolds are quite a bit cheaper than Suzuki manifolds.

Good luck

[boris.h]

Very good, thanks nessim!
SO you advise me to keep the 550 cams and sprockets?
About the carbs, I didn't watch about other carbs. I will study the VM24 case

[DimitriT]

This might interest you:

http://www.thegsresources.com/_forum/showthread.php?89845-It-runs!-Gs550-650-Top-end-swap-w-pics

[boris.h]

thanks!

I'm considering in KZ 650 parts..... I saw that this motor has the same compression ratio than the suzuki gs 650 motor... Maybe someone has ever tried to adapt KZ parts as cylinder block and pistons...?

[boris.h]

Moreover and as a potential uptdate, kawasaki sold a 700 cc kit.... so why not use the kz cylinder bloc and pistons?

[boris.h]

just received the top end head today... happy, because my gsxr header will be just "plug and play" on it...

[Bikelife2]

Bringing this back fromthe dead. I have access to vm26ss carbs off a gs1000, and am planning the 650 top/550 bottom build. Anybody try the vm26 on the 650? May be too big, but would like to work with what i have available. Opinions?

[Steve]

Opinions?

Read posts 2, 3 and 5.

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[Bikelife2]

Opinion may have been the wrong word. Shouldve used "experience ". Whats your opinion Steve?