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1/4 mile sprinting on an xs650

Discussion in 'The Garage' started by jay760, Oct 23, 2018.

  1. jay760

    jay760 XS650 Guru

    27th April at Smeatharpe tge nsa have organised a few through Straitliners this year so a few more on the calender unfortunately ill miss the next one on May bank holiday weekend at Westonzoyland as im away.
    gggGary, MaxPete and TwoManyXS1Bs like this.
  2. jay760

    jay760 XS650 Guru

    Top picture 2 xs's going head to head, was only 12 ft behind the very quick Rob Broom at the end after he missed a gear, funny how you make mistakes when you are racing someone you know in the same class or similar performance as it's suddenly not about the best time it's who gets to the line first. Normally around 0.5-0.7 seconds slower than Rob.
  3. MaxPete

    MaxPete Lucille, Betty, Demi & Gretel: I ask, THEY decide. XS650.com Supporter Top Contributor

    gggGary likes this.
  4. jay760

    jay760 XS650 Guru

    FB_IMG_1570382849045.jpg FB_IMG_1570382837196.jpg 20191004_161428.png Last race of the season last weekend, unfortunately it was wet so very slippery on the start line, I took my fairing off for the last meeting to see if it was the engine or the fairing increasing the top speed as I've had a terminal speed of about 2mph faster than other years though still putting in the same times of high 11s/ low 12s but as it was a different venue I think the timing was slightly out to Westonzoyland so I'm none the wiser, what it could be is slower start times due to the extra weight of the fairing but higher top speed at the top end.
    gggGary, TwoManyXS1Bs and MaxPete like this.
  5. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

    wow ...that was f*****g amazing ! :bike:

    That bike can certainly shift Jay
    gggGary and MaxPete like this.
  6. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

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  7. jay760

    jay760 XS650 Guru

    I'm anorexic now, every time I look in a mirror I see a fat person looking back at me.
    Yes need to loose weight but very difficult as I work away a lot so lots of weeks with cooked breakfast, meals with chips and cider, not a good combination to loose weight.
  8. Jack

    Jack XS650 Junkie Top Contributor

    Jay,,,,,If I recall you're using a megacycle cam and looking at your ports, if you rework the guide boss area it'll bias more flow up the curve in
    correlation to cam lift boosting top end pull. You're not concerned with low lift flow cuz you're at WOT racing. Shorting the intake guide and working the boss will aid hi flow. Don't have a good visual of the exhaust.
    gggGary and TwoManyXS1Bs like this.
  9. jay760

    jay760 XS650 Guru

    Exhausts are 1 3/4 from Hoos with megaphones on, I'll have a go at tidying up around the guide boss over the winter.
    gggGary and TwoManyXS1Bs like this.
  10. jay760

    jay760 XS650 Guru

    Almost misread what you said then for a moment I thought you were talking manifolds, what is your view on manifold length?
    Bewarethemoon and gggGary like this.
  11. Jack

    Jack XS650 Junkie Top Contributor

    I"m a big fan of longer manifolds,they produce a better ram effect while increasing torque but longer manifolds also lower peak power at higher RPMs,there's a trade off where you want the power to come in at. What RPM does your power start dropping at, with that cam you have power should start to drop around 8 to 8500 rpms. You could try experimenting with reducing the length of the manifolds by half,if that doesn't produce better ETs,mig weld them back to stock, retard the cam 3 to 4 degrees for better top end pull,it's a torque cam with good surge but maybe lacking up top for the 1/4 track.Also the inside of the manifold needs a good barrier finish texture 36 grit, it helps creating turbulence( does not effect flow) to keep the fuel droplets suspending off the walls,etc for better fuel atomization.
    Last edited: Oct 10, 2019
    JAX71224 and jay760 like this.

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