Stock horsepower ??

jfboy · Posted: October 27, 2005, 2:05 am Post subject: Stock horsepower ??

How much Horsepower does a 1981 XS650 make ?

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

Horsepower is on the sluggesh side of around 42 hp and a additional 18 hp is easily obtainable through head work,carbs,camshaft and complete exhaust system changes and while ya at it,you might as well lighten the beast by a 100 lbs for a greater power to weight ratio.............Jack

jfboy · Posted: November 1, 2005, 2:10 am Post subject: Re: Stock horsepower ??

thanks !

Phred · Posted: November 1, 2005, 3:04 am Post subject: Re: Stock horsepower ??

What type of head work are we talking about-simple clean-up and polish or serious porting?
Also, what are the hot carbs?

Thanks

odw650 · Full Member Joined: Aug 05, 2005 Posts: 28

I thought it was 48hp. On another xs650 forum they keep saying it makes 50hp, so I'm guessing theyre rounding up.

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

A stock 650 should dyno right at 42 rear hp +or- due to frictional drag loss through the drive train.

As for porting,I achieved a 15% gain on the intake and A 23% on the exhaust port.The exhaust port is in my opinion is where the most performance will be gained on a XS 650. The Xs head isn't gonna set the earth on fire but it does have potential and will support 100 plus Hp projects. There is a link here that'll direct ya to a porting thread I did over on pro boards,that goes into great depth of porting the XS head..........Jack

xs650mike · Posted: November 6, 2005, 2:33 pm Post subject: Re: Stock horsepower ??

Well you can get a rough estimate from the top speed of the bike, it takes about 15 hp to reach 70 mph. I've seen road tests of the XS650 where they say top speed is 100-105 which means 48 to 50 hp. My own SJ pulled 7,000 rpm in top gear...over 100 mph...let's call that 50 hp.

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Yamaha xs650