high ratio primary gear set? any thoughts?

urbandork

I was wondering if anyone actually has or has any thoughts about the high ratio primary gear set found here.
www.xs650.org.au/Racers.htm

I currently have a stock 5th gear and a 17/32 sprocket set up. I love the low end torque but at high freeway speeds (75 to 100) my motor sounds like it hates me. (I very rarely do 90 because of this)

After reading tons of sprocket threads here I thought about going to a 17/30 and might try that soon, but not sure how much of a difference it will make (i used that xls file that pamco. made to compare numbers). I also thought about a 18/30 set up but Im not sure if ill hate the low end. (although i am also only 145 lbs)

but after hearing about the high ratio primary gear set i was curious as to what the thoughts and opinons of it are.

... I also was thinking that maybe sticking with the 17/32 would keep me from going 90 all the time... kinda like a speed cut off lol.... since i guess i shouldnt even be going that fast anyway.

Big thanks in advance

btw
i think my dream set up would a mikes 750 kit, high per. valve, matching carbs, longer 5th, and the high ratio primary set along with a 17/30 sprocket set up.... but thats a lot of cash to put down lol.

yamaman

Well Mikes 5th gear is definately a cheaper option!

If I was doing a rebuild & had the cash, then yep I'd go the primary set, I don't think I'll ever have that cash to splash, so wont happen for me!

But, yeah if money was no object, for certain I'd run Ivans gears. You then have a much bigger sprocket range to work with!

xsjohn

18/29 and be done with it..........xsjohn

urbandork

xsjohn wrote:

18/29 and be done with it..........xsjohn

ive seen ur post stayin that i was wondering how much u weigh and what you think about the torque and the get up and go out of the hole???

xsjohn

Gearig it up won't make it a motocrosser...........I weigh 140.......and was never really happy till I lowered the compression......this gets rid of most if not all the racheting and vibes and some more heat and it now runs like my toyota........really depends on what you are looking for......riding enjoyment is first on my list along with longivity...........and the lower gears like 3nd and third make more since now instead of just pasing over them............and even a 18/29 high gear could be higher..........

18/30 with mikes 5th gear would be about perfect.........and timing needs to be retarded for the taller gears to work right..............if not it won't pull right down low and will break things..............

Reducing the heat is the same as adding power........as the cylinders get real hot the power goes down..........if you learn to play these a lot of good things will happen........

xsjohn

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

I haven't done this but have talked to a couple of people who have. With the high ratio primaries you need to run 17/36 for the road. The gearing is about the same ratio as xsjohns 18/30 but the advantage is lower revs for the same speed than xsjohns and better fuel economy.
The high ratio primaries make the gearbox run faster making for smother gear changes and transfers the extra speed through to the rear wheel, meaning same engine revs, faster front sprocket, faster rear wheel revolutions less fuel. I was told the special tank will give an extra 80km per tank with the HRP gears but i would have to see that for myself.
I have a set i will install with mikes 750 kit and i think it would probably be to much for the 650, the extra torque of the 750 will make for easier starts and using xsjohns take on heat then if the engine doesn't have to run as fast for the required speed at cruising then the engine should not run as hot.

xsjohn

Good anology for all this I need power thing.....which you will never really have with a XS anyway.....at least not for long.........

Is catching a monkey.........using a jar and banana or same.......small mouth on the jar and he sticks his hand in and grabs...........refuses to turn loose..........even if it kills him........

xsjohn

650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

As for cooling the engine, having some sort of flaring directing more air onto the motor, (as per the post by xsjohn and pamco), especially with the extra fins on mikes barrels, will bring the operating temp down.

As for monkeys hands in jars, meaning every one here is stupid unless they do exactly as you have done john Shocked

xsjohn

No.......just most are not willing to give up anything to get ahead...then again too maybe I'm right........ complain about 5th turning to many revs and then worry about first gear ......and the whole thing hotter than a frying pan........calm down ladies......... Laughing

I happen to know for a fact if mine ran any hotter it would not run as good..........and most are 40 degrees above me.......ah but winter is comming up...but not down under....... just rub some lanolin on it..... Laughing

xsjohn

pippend650 · Full Member Joined: Aug 27, 2009 Posts: 10

Mine was 18/30 when I got it and I did not like the lack of getting out of the way fast enough when sitting still. I changed the front and am at 17/30 and it is way better for me. I spend a lot more time taking off from a dead stop (and wanting to take off without having to slip the clutch or kill the engine) than I do cruising along at 70 or 90MPH. For me it is not safe being unable to get moving when you really need to or going 90MPH either. 18/30 gives me 65 at 3800 RPMs and no significant vibrations. I would recommend it to others over going taller unless you spend all day riding down the interstate. Just one man's preference having tried it both ways. To my knowledge no changes to timing or compression have been done to the engine. It is just a stock 78 650SE and happy at 17/30.

xsjohn

Maybe mike will make a lower 1st gear someday.......I would buy one...and 2nd too......I live rural and seldom do traffic........and my weight is as close to nothing that is possible and still be alive.........and there is things to do to make a high first better .......but few explore it.....

xsjohn

nj1639

Give some to get some.
Happy with 18/30 gearing and 8-1 compression. Cam and timing mods help. Haven't stalled from a start since the changes.
A lower 1st and 2nd gear, Mikes' 5th, hmm, what would be left to do then?
I believe that would be the topper.

xsjohn

Maybe mikes 750 at 8-1.....and all that stuff you said....and 18/29 at that point too.. Cool

.....maybe 3300 at 70mph..............

and after all that they would lower the speed limit to 55........... Laughing

www.aircooledtech.com/...lating_cr/

xsjohn

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