if only takegawa made a head for the 73-76' xr 75s..... - Page 3

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if only takegawa made a head for the 73-76' xr 75s.....

This is a discussion on if only takegawa made a head for the 73-76' xr 75s..... within the Vintage Honda XR75 and JDM Vertical Motors forums, part of the General Talk category; Originally Posted by sgtbilco Hey Storminnorman Love your work i to have the bug here's a pick of my 73 with a take r head ...

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Thread: if only takegawa made a head for the 73-76' xr 75s.....

  1. #31
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    Quote Originally Posted by sgtbilco View Post
    Hey Storminnorman
    Love your work i to have the bug here's a pick of my 73 with a take r head fitted
    i went about it by re-aligning the stud holes seems to fit up ok have had it running
    and will race it this season in a mini series over here in OZ
    it was my original race bike i had in the 70s


    Attachment 203889
    I like it! I intially thought about doing something like that but figured the purist would burn me on a cross. Interestingly enough in the mist of deciding how to build mine I found that if one machined a custom cam tower you could take the Takegawa roller cam and rockers and mate it with the 73-76' head. What bore and stroke did you go with yours?

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    Would the reason to use the Takegawa roller cam be because its easier to machine the tower than to get a cam made for the 73-76?

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    Quote Originally Posted by FlyinBrian View Post
    Would the reason to use the Takegawa roller cam be because its easier to machine the tower than to get a cam made for the 73-76?
    Haha heck no. I can get a cam reground way faster and cheaper than retro fitting a take cam on there.

    I may selling the difficulty short on this. It's not as simple as make a cam block and your good. There will be clearance issues every where...guides....over lap...etc..

    The reason why it's tempting are for the following reasons.
    1.) It's a bearing cam vs the non bearing xr cam. Granted with the 73-76' xr 75s that's not a huge gain cause you can do this

    2.) The big reason is cam profiles. A roller cam lends itself to being able to have more aggressive profiles. Then you factor that the stock xr cam tower parameters really limits how big you can get with the cam profiles makes the Takegawa cam even more pleasing. I could on with why it would be better but it's much easier just showing results. we are looking at the red and green lines on this pull. Both engines are same everything except for heads. The red line is a takegawa +R the green line is a takegawa stage 3. Between the stage 3 and R head they are basically the same casting other than the R head has roller rockers and roller cam where as the stage 3 is like the stock xr 100 head. The roller cam setup yielded over 2 hp more which is pretty substantial for a mini engine.

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  5. #34
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    Quote Originally Posted by storminnorman07 View Post
    2.) The big reason is cam profiles. A roller cam lends itself to being able to have more aggressive profiles. Then you factor that the stock xr cam tower parameters really limits how big you can get with the cam profiles makes the Takegawa cam even more pleasing. I could on with why it would be better but it's much easier just showing results. we are looking at the red and green lines on this pull. Both engines are same everything except for heads. The red line is a takegawa +R the green line is a takegawa stage 3. Between the stage 3 and R head they are basically the same casting other than the R head has roller rockers and roller cam where as the stage 3 is like the stock xr 100 head. The roller cam setup yielded over 2 hp more which is pretty substantial for a mini engine.

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    Blue line looks good!! Must be a lot of resistance caused by the rockers / bearings, or else the geometry on the roller rockers is advantageous, to open the valves more given the same cam profile.
    How much loss is created by valve spring selection? I suppose you want the lowest spring constant spring that doesn't float, or approach the resonant frequency.

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    Quote Originally Posted by FlyinBrian View Post
    Blue line looks good!! Must be a lot of resistance caused by the rockers / bearings, or else the geometry on the roller rockers is advantageous, to open the valves more given the same cam profile.
    How much loss is created by valve spring selection? I suppose you want the lowest spring constant spring that doesn't float, or approach the resonant frequency.
    Blue line was first dyno run with the mutant. There is more parasitic losses but most of gains are due to geometry.

    As far as losses via spring pressures it varies. But as your thinking it's kinda like octane not enough the engine detonates to much and you lose power. Very similar with valves springs not enough spring pressure and you get valve float and valve bounce. To much and it's hard on valves, seats, rockers, rocker pins and bosses, cam journals or bearings and cam chain as well as a degree of loss of power

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    Quote Originally Posted by storminnorman07 View Post
    Blue line was first dyno run with the mutant. There is more parasitic losses but most of gains are due to geometry.
    Was the mutant the subject bike? If so, I suppose it was it the stock cam version? Are the "parasitic losses" characterized by the choppy curve?

  8. #37
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    [QUOTE=storminnorman07;2172665]I like it! I intially thought about doing something like that but figured the purist would burn me on a cross. Interestingly enough in the mist of deciding how to build mine I found that if one machined a custom cam tower you could take the Takegawa roller cam and rockers and mate it with the 73-76' head. What bore and stroke did you go with yours?


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    Here is a couple of pics of the engine and some flow specs std XR head in the red versus take R head
    the piston i used was a 54mm take R piston out of a Z50 it had the right pin height and pin size and worked well with the valve reliefs
    the cam is a SR35 had a bit of trouble with spark plug clearance so modified the piston a bit and made up a spacer so the plug didn't screw in as much
    a bit slack with the stroker side i cheated a bit as you can see in the picture of the rod, had this crank that was done years ago for a engine by dad put together
    think it brought the CC up to 120cc so i used it, im not as set up as you to do alot of stroker work on cranks haven't had enough practice i also thought of the roller set up on the std head or after market big valve head

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    Quote Originally Posted by FlyinBrian View Post
    Was the mutant the subject bike? If so, I suppose it was it the stock cam version? Are the "parasitic losses" characterized by the choppy curve?
    Just a test to see where I stood against what most would consider the best kits for the xr 100. In case you have never read my mutant guild thread that mutant did have the stock yx cam in it but that's not why the curve is a little rough. I was getting some wheel hop on dyno for some reason that day.

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    [QUOTE=sgtbilco;2172969]
    Quote Originally Posted by storminnorman07 View Post
    I like it! I intially thought about doing something like that but figured the purist would burn me on a cross. Interestingly enough in the mist of deciding how to build mine I found that if one machined a custom cam tower you could take the Takegawa roller cam and rockers and mate it with the 73-76' head. What bore and stroke did you go with yours?


    Click image for larger version. 

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Name:	KO XR bottom end.jpg 
Views:	23 
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ID:	204017
    Here is a couple of pics of the engine and some flow specs std XR head in the red versus take R head
    the piston i used was a 54mm take R piston out of a Z50 it had the right pin height and pin size and worked well with the valve reliefs
    the cam is a SR35 had a bit of trouble with spark plug clearance so modified the piston a bit and made up a spacer so the plug didn't screw in as much
    a bit slack with the stroker side i cheated a bit as you can see in the picture of the rod, had this crank that was done years ago for a engine by dad put together
    think it brought the CC up to 120cc so i used it, im not as set up as you to do alot of stroker work on cranks haven't had enough practice i also thought of the roller set up on the std head or after market big valve head
    Impressive work. It's barely noticeable where you relocated the holes. Am I seeing it correct you got away with just having to relocate 2? Also nice flow numbers. Every do any dyno work with it?

    Looks like you got yourself a powroll stroker. Bit it's pretty revvy with that inner rotor

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  11. #40
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    [QUOTE=storminnorman07;2172985][QUOTE=sgtbilco;2172969]
    Impressive work. It's barely noticeable where you relocated the holes. Am I seeing it correct you got away with just having to relocate 2? Also nice flow numbers. Every do any dyno work with it?

    Looks like you got yourself a powroll stroker. Bit it's pretty revvy with that inner rotor

    Yes your right got away with only 2 holes used a Wurth brand metal filler to refill the holes before i re-jigged for the dowels
    came up better than i thought
    I think your right about the powroll crank dad got it years ago thats when power roll was a heavy hitter in the go fast mini scene of the 70s
    the inner rotor set up is a PVL unit yes it is pretty responsive
    got a YZ80 ive restored with alot of modified engine bits and the man that did all the extra porting for me has a bike dyno and he wants me to bring the YZ down once ive base tunned it will ask him if he will put the XR up as well would be good to see all the figures

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