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"SR 650"
- Thread starter JP50515
- Start date
Royboy
many roads, little time
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That is cool! More info please, I want to do this!
roy
roy
If I remember correctly, it's someone here on the forums! But it's an SR500 frame with an XS650 motor fitted in it. Besides that is appears to be almost all stock SR with the exception of the clubman bars and rear shocks. But the major difference is that the SR is about 320lbs with a tank of gas and the XS 450lbs dry. XS engine is about 150, SR is about 95. So in conclusion we have the SR frame with the XS engine weighing in at around 375 lbs....which is a SIGNIFICANT amount of dropped weight from the stock XS...especially when you take into consideration that the SR produces around 30HP stock and is notorious for being a wheelie nut! The XS is closer to 50HP stock...now bump to a 750 big bore kit and we're talking 65-70ish HP on 375 lbs of bike.....that's almost sport bike ratios. The SR and XS share the exact same front end from the factory, and many rear end dimensions which is why lots of guys take XS frame loops and weld em onto their SR. For example the Radian swingarm mod for the XS can be done the same to the SR. They are brothers if you ask me...and this picture proves it!
....I want to do this...if whoever owns/owned this bike is on the forum please speak up!
....I want to do this...if whoever owns/owned this bike is on the forum please speak up!
On the track, the only party that machine would be deadly to would be its rider. Nobody with a serious interest in handling and weight reduction is going to use those heavy OE cast wheels, and from the little I can see, the front brake rotor appears to be a solid OE unit--again, a lot of weight. 10 or 15 lbs. might have been saved on the frame. It's a pretty job of cosmetics, that's about all.
So you think a 100 cc. displacement bump will get you a 30 to 40 percent power boost? Sorry, but it ain't so. If you want to find out what it takes to get serious results, click the link at 650 Central and buy yourself a download of Craig Weeks' performance modifications manual.
As to power-to-weight ratio in modern bikes, my 03 SV650 Suzuki is rated at 72 hp with around the same weight as a stock late XS650--a tad under 450 lbs. wet. It's a very docile machine compared to serious performance rides in the 600 cc.class like the Yamaha R1, Suzuki GSXR, and Honda CBR.
So you think a 100 cc. displacement bump will get you a 30 to 40 percent power boost? Sorry, but it ain't so. If you want to find out what it takes to get serious results, click the link at 650 Central and buy yourself a download of Craig Weeks' performance modifications manual.
As to power-to-weight ratio in modern bikes, my 03 SV650 Suzuki is rated at 72 hp with around the same weight as a stock late XS650--a tad under 450 lbs. wet. It's a very docile machine compared to serious performance rides in the 600 cc.class like the Yamaha R1, Suzuki GSXR, and Honda CBR.
To make something unique, I'd say yes, but I would build a big bore/stroker TT500 motor and really roost on the SR. I love big singles.
Where did I claim a 30-40 percent power boost from 100cc? I said up to 750 from the stock sr500 would be significant. I wasn't arguing that "that exact" bike would be a killer racer. I'm meant that combination of frame and engine has the potential to be potent.
Obviously there's always more that can be done to eliminate weight, especially on what appears to be a mock stock build. When I said 65-70 hp on a 375lb bike, was I incorrect about that being close to sport bike ratios? A Gixxer weighs in just under 350 lbs with just over 100HP...375 to 70 is much closer than 450 to 50 or 320 to 30.
My point here is, in terms of vintage machines not only is this a cool concept, but one that I think would make for a pretty fun bike to try and race. Just my opinion.
Obviously there's always more that can be done to eliminate weight, especially on what appears to be a mock stock build. When I said 65-70 hp on a 375lb bike, was I incorrect about that being close to sport bike ratios? A Gixxer weighs in just under 350 lbs with just over 100HP...375 to 70 is much closer than 450 to 50 or 320 to 30.
My point here is, in terms of vintage machines not only is this a cool concept, but one that I think would make for a pretty fun bike to try and race. Just my opinion.
Royboy
many roads, little time
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This may be a pretty old photo in as much as those appear to be the original tires!
roy
roy
Tomterrific
XS650 Junkie
Well, it is a cool machine but there are problems. The big problem is the SR rear wheel can't take a small enough rear sprocket for the XS 650 engine. Also, the SR frame isn't all that great. I'd certainly be all over the bike if I came across it but I can't say I can suggest starting to build one. An SR is so much fun and simple to soup up that it is better with the big single.
Tom, both an SR and XS
Tom, both an SR and XS
Royboy
many roads, little time
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Agreed Tom, I would never cheese up a decent original SR. Been in love with the bike since 78'. But... if one was to come across a frame and a few odd bits, 
D), it still looks like a neat project to me. Hell of a conversation piece.
roy
D), it still looks like a neat project to me. Hell of a conversation piece.roy
Check your math, JP; 15/50=0.30=30%. You might be aware of this, but for those who haven't done performance work on the XS650 mill it might be worth pointing out that you won't get to the 65-70 hp range on the old twins without boosting compression to the point that race fuel is required, and you won't have a motor that will behave very well on the street. For the track? The frame, fork, and swingarm will need to be braced six ways from Sunday, and you'll need to add an oil cooler regardless, so your weight estimate is going to need some revision. And where are you going to race it? No matter what you do you won't compete with modern iron, and you won't be legal for AHRMA.
Agreed, Roy, that bike is very cute, and if a guy has time on his hands, an SR donor that's past rescue, realistic expectations, and the skill to do frame and suspension mods safely, well, have at it. And right, Tom, cutting up a viable SR would be plain vandalism; you could sell the SR and buy a Trackmaster, Shell, or other race frame.
Agreed, Roy, that bike is very cute, and if a guy has time on his hands, an SR donor that's past rescue, realistic expectations, and the skill to do frame and suspension mods safely, well, have at it. And right, Tom, cutting up a viable SR would be plain vandalism; you could sell the SR and buy a Trackmaster, Shell, or other race frame.
CDNTX650
XS650 Guru
Meh...i bet its barely any lighter. Stock mags...heavy. better off using some modern forking and shocks with a braced swinger in your stock frame. The 650 mill is where most of that weight is from. Or as suggested...race frame
Alright guys we're taking this too seriously. Again i'm not talking about racing the bike pictured, I guess my original comment was misleading, That's my fault... But my only point here is that I think it's a cool combination of two of my favorite yamaha's and am willing to bet that it'd be a blast to ride.
Grizld1 you win man. I'm not talking anything technical here, simply concepts/ideas with basic math from specs I found on google lol. I know nothing about the AHRMA rules and regs but i'll take your word for it. When I said race it, I meant race it around a field with some buddies/scramble with it...idk.
On the subject of the SR...I would never chop a good SR for this swap. It took me three years to find this XT lol....literally three years of searching and I still had to settle for a basket case XT...not SR....with a seized motor and no title (now it has one ) if I wanted one for under $1500....This one cost me $300, plus another $100 for a motor that wasn't blown up everywhere. Pic is from the day I bought it.
Agreed, If I had the frame and motor lying around maybe i'd give it a go...but i'm not likely going to invest in creating it.
They are beautiful bikes...just thought some might get a kick out of this SR650 pic.
Grizld1 you win man. I'm not talking anything technical here, simply concepts/ideas with basic math from specs I found on google lol. I know nothing about the AHRMA rules and regs but i'll take your word for it. When I said race it, I meant race it around a field with some buddies/scramble with it...idk.
On the subject of the SR...I would never chop a good SR for this swap. It took me three years to find this XT lol....literally three years of searching and I still had to settle for a basket case XT...not SR....with a seized motor and no title (now it has one
) if I wanted one for under $1500....This one cost me $300, plus another $100 for a motor that wasn't blown up everywhere. Pic is from the day I bought it.Agreed, If I had the frame and motor lying around maybe i'd give it a go...but i'm not likely going to invest in creating it.
They are beautiful bikes...just thought some might get a kick out of this SR650 pic.
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jayel
#9 Guru 74 TX650A
the smallest rear sprocket you can put on a stock SR rear hub is a 40T, with a 18T front on the XS motor that gives a 2.22 final rear wheel ratio , higher than the stock XS 17/34 2.0 final ratio, most guys feel the xs is overgeared at stock, so while is good looking and probably fun I'd rather have a real SR
jayel
#9 Guru 74 TX650A
that 48 chainsaw motors bike ought to do it RING_DING_DING
Bigfeet
to many projects
That pretty much hits the nail on the head for me.
Royboy
many roads, little time
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Sitting here playing with the measurements it seems to me that the hub, sprocket and rim assembly on my 77'D would slip under the SR with only minor mods. That would satisfy the sprocket issue. Of course it might look different without the gin 
.
roy
.roy
racerdave
^ Gone not forgotten ^
I doubt you drop 75 #'s from a XS650, just putting the XS motor in the SR frame.
A set of "High ratio primary gears" would get you down to a lower gear ratio than the Standard 17/34.
Money ain't the problem
Money ain't the problem
Look at the first photo. With CV carbs on there, there's no room for filters of any kind.
