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GS673 VS Tuned CB750 Thoughts please?

  • Thread starter Thread starter ashdricky
  • Start date Start date
A

ashdricky

Guest
Recently I have noticed more and more guys converting old CB750's into cafe/race styled bikes. I must say that some of these creations are pretty neat. Last summer an acquaintance of mine boasted no other vintage bike in the area could out perform a tuned CB750. This got me thinking and for the past few months I have been doing research and collecting parts to build a GS to test his logic. Here is my theory please tell me what you think.

- base the build on a 550 as it is relatively small and will require less weight reduction than any other 4cyl GS.
- Swap the cylinders and head form a 650 onto the 550 block resulting in 673cc's mated to a 6 speed transmission. This will start me at ~78hp (very close to a stock CB) prior to tuning
- construct an aluminum 1-4 air box sporting a K&N flter
- Replace the heavier 4-2 exhaust with a new 4-1 system &correctly re-jet carbs
- replace the nippon denso points with a Dyna 2000 kit & replace stock coils with 3 Ohm green dyna coils and wires to match.
- replace lead acid with a dry-cell battery weighing 1.8lbs
- fabricate a rear cowl to house all electronics
- Upgrade to wire wheels with twin disc front
- replace fork springs with progressive ones
- Use front brakes from an 07 gsxr 1000, with matching master cylinder and steel braided lines.
- run Avon Roadrider tires as I've found these to work quite well

There is definitely alot more that I cant think of right now but that is the outline. I feel that I need to prove that our zookies deserve recognition too, as I have such a respect and love for the brand.
 
Did you sneak a peek into my garage?
You describe my new project very accurately.
 
Tell your buddy to put the crack pipe down first of all.

After '73 when Kawi rolled the Z1 out, the CB750 was toast. Period. Antequated technology. Slow, heavy, and not nearly as powerful as the 900cc Kaw monster (for the time, 900cc was huge)
Fast forward four years..The Suzuki GS750 is unleashed on the world.
While not as straight-line fast as the Z1, it wasn't off by much, and better still, it didn't have a hinge built into the middle of the frame. This bike could flat handle. And the Honda felt like it was built out of swizzle sticks. Believe me..I owned em.

From then on, Kawasaki and Suzuki duked it out in the cycle mags. Honda came in last in nearly every comparo. The only one I recall them winning was the 80 GS1100E vs the CBX. The CBX won, based on looks. Hard to blame em. Six pipes sure are sexy. And heavy. The CBX was dusted in every meaningful category.

So sure. You're giving up a few CCs. But you'll be lighter, stiffer chassis, and better suspension.
Just don't make it a drag race. Throw some corners in there. You'll smoke em if you can ride at all.

Those Honda cafes are pretty, but they're all show and no go. ;)
 
If I remember correctly the Honda CB750 was geared pretty high.
But, it was a great bike as far as reliability and looks I thought,
just a nice overall bike, no screamer though.
 
Ha, I've tried working with this man before and we have TOTALLY different ideas of how things should be done. So we came to a mutual agreement that we would be fierce competitors. I feel it would be quite demoralizing to lose to a smaller bike, especially after making sure everyone in ear-shot Knows that Terrance Toolbag is the fastest and coolest guy on two wheels. I don't know what the layout of the track in Toronto is but if we run at Watkins glen I think i will do well. Even though his attitude says a lot about his engineering skills, I still want to go about this as if his "team" is a capable and formidable opponent. If all goes well I will accurately illustrate how far lip-service will take a man.
 
ashdricky said:
Send me a PM, Ill show you mine if you show me yours?
Click to expand...

Mine is not much to look at yet...
Picture a 550 frame here, a 650 engine over there in boxes, a couple 550 engines on the floor, most of a disassembled 550 in a few bins and tubs...
Maybe this winter I'll get going on it.
 
Despite all the history and rose tinted glasses the SOHC 750 was really a bit of a slug - not much faster in the real world than its little sister the CB550. A GS750 will leave one for dead and what you're knocking together will as well.
 
They are the matching coils (grey ones) but the 3ohm (green) ones will work too.
 
Yes Salty Monk is right, I called Dynatek and they recommended 3ohm for my setup
 
If he ever makes it to Indy, tell him to bring his bike. I have a vintage 750 that I would put against him. Not a GS, but he said "any" vintage bike.
I will even handicap myself further by putting a different rider on my bike, a friend of mine who goes by the handle bwringer. ;););)
 
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I have a friend who has been playing with and tuning cb750's for years now. I once heard him say - " I used to ride old Hondas because I couldn't afford anything newer, now I ride old Hondas because I can't afford anything older."
According to him, he can coax around 80 rwhp out of one; but it'll be totally unstreetable.
 
Or you could save yourself all the trouble and go and borrow Allie's box stock 750 and blow him into the weeds with that, and Allie's bike sure is a damn site prettier than any CB I have ever seen.
 
ashdricky said:
Swap the cylinders and head form a 650 onto the 550 block resulting in 673cc's mated to a 6 speed transmission. This will start me at ~78hp (very close to a stock CB) prior to tuning
Click to expand...

At that hp figure you are already way up on what the CB750 produces in stock form. The original CB put out 67hp, which is already 11hp down on what you have planned and you are on a much lighter bike which redlines at 9,500rpm as compared to the CB750s 8,000rpm. Then there is the better handling with you having a half decent frame.

IT IS A NO CONTEST -- take it from me.
 
Suzuki_Don said:
At that hp figure you are already way up on what the CB750 produces in stock form. The original CB put out 67hp, which is already 11hp down on what you have planned and you are on a much lighter bike which redlines at 9,500rpm as compared to the CB750s 8,000rpm. Then there is the better handling with you having a half decent frame.

IT IS A NO CONTEST -- take it from me.
Click to expand...

Don I am certain you are right, as my competition has cut many corners as far as design goes. It seems that this rivalry is more of a clash of personalities than a competition of machines. on an unrelated not is there any advantage to using 11K as a shift point? or dose this just over stress the motor?

second, now that I have the head off and valves out, is it possible to use valve springs from an 1100?

Third frankie fish(the competition) apearently has an xs1100, which he is doing up in a 'cafe' style. I am curious to know what kind of performance these bike carry? Is it out of the realm of reality to think i could build a 5/650 to beat it?
 
ashdricky said:
Don I am certain you are right, as my competition has cut many corners as far as design goes. It seems that this rivalry is more of a clash of personalities than a competition of machines. on an unrelated not is there any advantage to using 11K as a shift point? or dose this just over stress the motor?

second, now that I have the head off and valves out, is it possible to use valve springs from an 1100?

Third frankie fish(the competition) apearently has an xs1100, which he is doing up in a 'cafe' style. I am curious to know what kind of performance these bike carry? Is it out of the realm of reality to think i could build a 5/650 to beat it?
Click to expand...
Those XSive 1100s are power monsters. But they shift like crap, they're heavier than a Sherman tank, and they don't handle all that well.
In a straight line, not a chance you'll beat it, unless he really sucks. But on a road course, you have the handling advantage clearly. With a big bike you have to sort of square the corners off. Point and squirt. It's harder to be smooth and clean and consistent. It's easier to overpower out of the corner as well. So if you can remain smooth and keep the throttle clean you should have him easily in the corners, and just have to hustle to fend him off in thenstraight.
 
As TCK stated, there is no way you could take it in the straights. However, there is a quirk with them which will allow you to blow it away in the twisties. It "comes on the cam" somewhere around 5-6k and takes off dramatically. (I ran one with my then new 78 750E.) So, if he stays low in the rpm range he won't have much power, if he stays on the cam he will have too much power, and if he passes through that band while leaned over it will go sideways on him.
 
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