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racerdave
^ Gone not forgotten ^
You are in big trouble
blackbetty
XS650 Junkie
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hahahaha Classic
Go to 650 Central. Click the link there to order a copy of Craig Weeks' "XS 650/750 Engine Modification Guide." There's no magic; performance costs money. Do not, repeat do not, rely on the old Joe Minton articles on "Building a Better 650." It's full of the kind of omissions that will make you wish you'd left your motor stock before you've put many hours on it.
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Who ever told you that,doesn't know the Xs650 quite well. To reach those #s,one would need to invest most of his efforts in enhancing the heads ability to pull lots of air,along with the aid of a decent cam(shell #1 or megacycle cam with .420 lift),both offering good street manners. Carbs,flat slides all the way, 700CC or 750cc big bore,etc.etc. If you have the money,the head is the real "Key" to start with, then slowing progress with the other mods. There's many ways to open the head up,just stay away from big valves for street use. The Xs head responds quite well to port volume reduction,with minimal flow loses in the upper flow curve which wouldn't be a concern to you while using the #1 or the megacycle .420 cams. Hoos Racing has a excellent reputation since they race the XS. Also with the poor breathability of the Xs head, going long rod will aid the head in pulling harder in the upper RPM's where you'll encounter the 65HP and Good luck! So many options.
And don't be afraid to ask Griz for a few XS mod recipes of his own,he's quite familiar the XS in what it takes.
Since Jack has put me on the spot, here's my recipe for performance, Chop: SUSPENSION FIRST. If you can't put it to the pavement you'll be the slowest guy on the ride, no matter what you have in the motor.
Read what Craig Weeks has written; it'll give you an idea of what's involved in a performance motor. 65 at the wheel in a streetable motor is a pretty difficult target.
Jack, are you going to ride with us in September? The Society has a new director, John Chaves. He has a lot of road race experience and plenty of motor savvy, a guy you'd probably enjoy meeting. The rally is being held in the same place--Tally-Ho Inn, Townsend, TN.
Read what Craig Weeks has written; it'll give you an idea of what's involved in a performance motor. 65 at the wheel in a streetable motor is a pretty difficult target.
Jack, are you going to ride with us in September? The Society has a new director, John Chaves. He has a lot of road race experience and plenty of motor savvy, a guy you'd probably enjoy meeting. The rally is being held in the same place--Tally-Ho Inn, Townsend, TN.
FLEA
XS650 Guru
jack, why do you say keep away from big valves for street use??? my project motor has o/sized valves. what problems can they cause???
jd750ace
Front Toward Enemy
By comparison, my 02 SV650 is water cooled, 4 valve heads, 10:1 compression and revs to 10,500 RPM. 64 RWHP out of the box. A VERY lofty target for an XS motor in my opinion. I'm content with the 30 something it has now. I want that kind of steam, I swap bikes. 60 pounds lighter and radial tires too, plus an L twin is SMOOTH when it's right.
Plus about a million on suspension too. The first time you decide to do suspension RIGHT, you'll kick your own ass for all the farting around you've done with carbs and pipes and airboxes seeking performance. Suspension rewards with performance at ANY speed.
Plus about a million on suspension too. The first time you decide to do suspension RIGHT, you'll kick your own ass for all the farting around you've done with carbs and pipes and airboxes seeking performance. Suspension rewards with performance at ANY speed.
Griz,didn't mean to put you on the spot but you and jd have spoken wisely.
Won't be attending the rally for obvious reason,sorry.
I'm an old fart who still believes oversize valves reduce port velocities to a certain extent until piston speed momentum comes into play to overcome this loss and should be used accordingly for displacement and application. One of the biggest faults with the Xs head is it's ability to flow enormous amounts of air from .050 to .200 lift in the right hands and during the early stages of overlap,this sort of draw opens the door for exhaust reversion. Through my research,talking to several knowledgeable porters in my region and by my own experiments of getting the XS head flowed after severe port mods, that you can reduce this reversion by a flow reduction at those lifts and biasing the flow charge to come in like a freight train around .175 to .200 ,thus broadening the torque band and HP but it takes practice and patience in modifying the ports. You'll find the best guru porters and brightest engine builders on the planet at Speed Talk.com who aren't on some ego trip but who are willing to share their knowledge.
I'm no XS head expert by I do have a few ideas flowing around
racerdave
^ Gone not forgotten ^
Jack, what is a ballpark cost for the headwork you would recommend for a HiPo reliable streetable XS650 motor
Hey Jack, I was just pulling your leg, not grousing at you!
Joe, to save Jack the aggravation of stating the obvious, there are two things going on with flow: volume and velocity. Ports have to be big enough to move a given volume of gas and small enough to move it quickly.
Joe, to save Jack the aggravation of stating the obvious, there are two things going on with flow: volume and velocity. Ports have to be big enough to move a given volume of gas and small enough to move it quickly.
FLEA
XS650 Guru
does this mean o/s valves arnt suitable on street bike as normally operating in to low a rev range to be effective???? (also had a look at speed talk,looks very intresting,will be spending a bit of time there)
650performance
XS650 Addict
The properly built 750cc race engines do typically use oversize valves, but to get 69 - 70 RWHP they only need to be slightly bigger ... only about a mm or a bit more.
So if you decide to use Kibblewhite or other oversize valves don't be put off that they aren't much larger than stock.
In the real world, the port size vs. velocity "balance" Griz and Jack are talking about is best obtained with these size valves. A 650-based performance engine would never need oversize valves. (perhaps you'd change the back cut and seat angles, but would not need to make them larger)
Any attempt to maximize the valve size has never been demonstrated to actually add power (except, of course, on the bench racing dyno).
So if you decide to use Kibblewhite or other oversize valves don't be put off that they aren't much larger than stock.
In the real world, the port size vs. velocity "balance" Griz and Jack are talking about is best obtained with these size valves. A 650-based performance engine would never need oversize valves. (perhaps you'd change the back cut and seat angles, but would not need to make them larger)
Any attempt to maximize the valve size has never been demonstrated to actually add power (except, of course, on the bench racing dyno).
Speak of the devil! How have you been, Craig? Still making those XR's wish they'd never left Wisconsin?
Folks, if you're thinking about hopping up your motor and fail to buy this man's book, you're making a serious mistake.
Folks, if you're thinking about hopping up your motor and fail to buy this man's book, you're making a serious mistake.
