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BIG Bore x LONG Stroke XR100 input?

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Posted (edited)

The Cam of Doom finally completed it's journey from Japan...!

Gun drilled / Hollow design.... Lighter than stock cam... Lots of overlap...

IMG_20200527_074452.thumb.jpg.5d8471d04c21304c54daf8786f759dae.jpg

Edited by mixxer

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20 hours ago, Alexxxx said:

Any specs ?

This is all they give you ...

They had 3 models listed and from these numbers you can get that it has 250 degrees duration and also 40 degrees of overlap with the valves open a minimum of 1mm during that time...Screenshot_20200526-172431.jpg.d79ee7e5bbe9f77799dcb7463216420d.jpg

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   Looks pretty nice. Wonder why they didn't bath-tub the chamber. Seems like that would be better (higher comp. ratio with a flat top piston and a shorter burn distance) than a straight up hemi. I mean, heck, if I'm going to the trouble to make a whole new casting why not go whole hog, change the port angles , raise the floors,,,everything.  Oh well, still, it looks a lot better than the stock starting point. Real nice looking casting by the way.

 Looks like you're having fun Mix.  :cheers:

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5 hours ago, Doogee57 said:

   Looks pretty nice. Wonder why they didn't bath-tub the chamber. Seems like that would be better (higher comp. ratio with a flat top piston and a shorter burn distance) than a straight up hemi. I mean, heck, if I'm going to the trouble to make a whole new casting why not go whole hog, change the port angles , raise the floors,,,everything.  Oh well, still, it looks a lot better than the stock starting point. Real nice looking casting by the way.

 Looks like you're having fun Mix.  :cheers:

Awesome observations Doogee!!!

As soon as I put the heads side by side I was hmmmmmmm 🤔🤔...

Thinner stems with bigger valves....

Exhaust port volume is a LOT less...

Flat faced valves for better compression...

Then true hemi head to LOSE compression...?? WTF??!! How come nobody ever mentioned that in a thread in all the years this head has been available???  Stock head has tighter / bathtub chamber...

 

Lots to map out... Absolutely should be fun!!🤘

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Do people de-shroud the valves on the stock castings? Doesn't look like there'd be much room to with the oversized valves. Just curious if it's worth the effort as it was a thing I used to do on the 4 cylinder heads when I was racing Datsun 510's.

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30 minutes ago, defdes said:

Do people de-shroud the valves on the stock castings? Doesn't look like there'd be much room to with the oversized valves. Just curious if it's worth the effort as it was a thing I used to do on the 4 cylinder heads when I was racing Datsun 510's.

3mm is sufficient for effective unshrouding on these mini thumper engines... 

The bigger valved Spartan head in the pics already comes with a good amount of unshrouding....

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Do you break all those sharp edges shown on the factory unshrouding?

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Kitaco 145  based home brewed  on track. K1 XR75 frame.

I've another one out to 171cc with the Kitaco stroke and Takegawa 62 mm bore, 14.5:1 compression, 31 mm titanium intake valve, 32 FCR pumper.

That one has an 8 stud head to hold compression.

XR75 Betty.jpg

CSC XR MS CF.jpg

Edited by Momus
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On 5/15/2020 at 8:33 PM, Mrrcx said:

I am half the age of all of you.  Let me know if anyone needs help crossing the road.  I could really use that merit badge.

Ill speak in 'lord of combustion' language: 😛

I run a 12.5:1 CR 57mm bore with the ring gap opened up a tad.  I went 57mm because of piston weight since i wanted revs.  I did not touch the stroke because it would have changed the mean piston speed to unfavorable for what I was doing.  I am running large intake and ex ports.  28mm intake valve and 23mm ex valve with 4mm stem diameters.  I run a good amount of overlap on a DLC coated cam,  the piston pin is also DLC, VM26-671 carb (No, not the VM26-606)  and an FMF exhaust with some head pipe flange transition smoothing.  The exhaust has header wrap on it to keep the heat in and change the speed of sound.  The spark plus is a smaller diameter because the valve are large.    I am running a daytona coil and CDI for better combustion at the higher speeds.  The bike runs an oil cooler, kitaco oil pump, dirtdigger clutch setup.  I have the crank and piston under balanced, the flywheel has had material removed.  What has all of this BS gotten me?  around 13 hp, flat torque curve, linear power, crisp response, and 14krpm.  For a fixed length intake system the VE does pretty dang good for all those RPMs too.  Bike sees flat track, MX, TT, and general shenanigans.  As you know, singles suck for friction so anything you do to help that will be peachy.  Dont over valve spring it because you think you need to.

I built this one like 7 years ago now and its had a hard life.  No smoke, fires up easy, and is very predictable.  I still teach people how to ride on it. (This is all on my black XR100 if you know which one that is)

You are wise to use the TB jug and take advantage of the oil cooler, make sure you take a good look at the bottom of the casting before doing anything.  I Seem to remember the oil feed and return are merged there, but you can drill and press a little slug to separate the areas.  

 

What cylinder are you using with the 57mm piston?

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46 minutes ago, RBracing said:

What cylinder are you using with the 57mm piston?

Clipping point (knock off Kitaco)

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1 hour ago, Mrrcx said:

Clipping point (knock off Kitaco)

Clipping Point head as well?

I have that kit still sitting in a box.

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On 7/14/2020 at 3:54 AM, defdes said:

Do people de-shroud the valves on the stock castings? Doesn't look like there'd be much room to with the oversized valves. Just curious if it's worth the effort as it was a thing I used to do on the 4 cylinder heads when I was racing Datsun 510's.

They're semi hemi heads, not bath tubs.

No unshrouding is needed or desirable:  the valve moves away from the chamber.

 

Edited by Momus

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On 7/14/2020 at 4:27 AM, mixxer said:
5 hours ago, RBracing said:

What cylinder are you using with the 57mm piston?

 

 

 

Best  57 mm cylinder will be either a Kitaco or Takegawa Nikasil item.

The iron bore cheapies are ok, but usually pretty soft, but the plated ones last many, many times longer and give more power and better cooling.

Edited by Momus

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On 11/21/2020 at 6:17 PM, RBracing said:

Clipping Point head as well?

I have that kit still sitting in a box.

Yup!  Does well for what it is.  I have a VM26-671 on the front of it.  

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9 hours ago, Mrrcx said:

Yup!  Does well for what it is.  I have a VM26-671 on the front of it.  

Cool! I will be using the Clipping Point kit with a VM26 and a Yosh exhaust, not sure which cam yet.

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8 hours ago, RBracing said:

Cool! I will be using the Clipping Point kit with a VM26 and a Yosh exhaust, not sure which cam yet.

Hell yea!  You putting in a road racer?

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