Topic: Planning custom camshaft grind..looking for lift & duration ideas:XR200

[grcamna2]

I've got a little XR200 and rebuilding it.I have the stock cam specs which are:intake .288 lift and 222 degrees @ .040,   exhaust .270 lift and 221 degrees duration.
This engine has a little midrange w/ peak torque @ 7500 rpm and max HP @ 9000 rpm.
I'd like to give it a bit more mid-top end power.
Do you have any ideas or recommendations for me ?

[grcamna2]

I'm just asking generally,when it comes to changes in camshaft grind; what will an increase in lift yield compared to an increase in duration?
Any thoughts ?

[flatlander]

take this with a grain of salt as i'm not a cam expert but as nobody has chimed in yet, here's my sketchy understanding of things:

if you want more torque you'd basically want to increase compression. closing the valves sooner rather than later generally gives higher compression - but i don't think you can reduce it to only lift vs. duration as the profile of the lobes is important.

other ways to get more torque are increasing bore and/or higher compression pistons. a hotter cam often requires these measures otherwise your power shifts very much to the top of the rpm range a.k.a. overcamming.

probably you're best off getting some pistons if you're looking to increase torque for mid-range. you will also gain some top out of them and might be ok with what they provide overall. then if you need more top end hp you can still go for a hotter cam.

[grcamna2]

take this with a grain of salt as i'm not a cam expert but as nobody has chimed in yet, here's my sketchy understanding of things:

if you want more torque you'd basically want to increase compression. closing the valves sooner rather than later generally gives higher compression - but i don't think you can reduce it to only lift vs. duration as the profile of the lobes is important.

other ways to get more torque are increasing bore and/or higher compression pistons. a hotter cam often requires these measures otherwise your power shifts very much to the top of the rpm range a.k.a. overcamming.

probably you're best off getting some pistons if you're looking to increase torque for mid-range. you will also gain some top out of them and might be ok with what they provide overall. then if you need more top end hp you can still go for a hotter cam.

Thanks for the reply flatlander.The engine started out w/ 9.2:1 CR as an XL200R single and I've gone up to 10:1 XR200 piston. I'll be running this dirt bike engine in a street bike frame for road riding.
Edit: I've decided to go with the 10:1 XR200 piston and now trying to decide on a decent camshaft,also I like your thoughts flatlander on when you mentioned in your previous post about: "but I don't think you can reduce it to only lift vs. duration as the profile of the lobes is important"  Good point and well taken 

[flatlander]

just a thought: does the XR use a different cam or the same as the XL? if they are different and can be swapped you could try both and compare the numbers vs. effect. that would give you a starting point for further experimentation.

[flatlander]

i'm sure those who master the black art do have some rule of thumb
but i feel far from being knowledgable enough to determine my own grind. all i know are some general principles that i took into account when selecting a commercially available grind for my 550 which was hard enough but much easier than coming up with your own design from scratch. this seems something where learning through experience and experimentation could be quite rewarding if you have the time and funds. i almost envy you for this project!

[FunJimmy]

Thee are some good cam manufacturers that post cam specs and performance expectations that you should consider. Andrews Cams has several profiles for Harley Sportsters. Also look for Red Shift cams through Zippers. What you'll find is shorter duration gives higher torque numbers and moves the power band down the RPM range. Longer duration biases higher RPM power at the expense of midrange. Obviously lift plays into it too, as would port flow efficiency.

[grcamna2]

Thanks flatlander and FunJimmy 
I've got the cam catalog from Megacycle from back in 1996 which gives me a few different choices of cam.Their mildest grind cam #143-00 has .365 lift and 240 degrees duration on both intake and exhaust on 104.5 degree lobe centers;they say it increases mid-range power and torque and is recommended to be used w/ stock piston and valve springs.I was considering sending one of my cams to the place in WA. that will hardface it and grind it to my specs when I'm done researching this.
Thanks for any ideas and feedback 

[flatlander]

check the websites for megacycle and webcams, you can download their latest catalogue there. also if you search specific forums for these bikes you may find out about other manufacturers.
designing your own grind would be the hard way to do it, picking an existing one will make life a lot easier. but it would be a fun learning experience if you don't mind the risk of getting it wrong.

[Kevin D]

Some coaching offered in this link, I was searching for pow roll... I got a motocross cam from powroll back in the 70's for my sl100. I think they went out of business, but still I got a hit and found a phone number in the second link. Have you been to thumper talk?

http://www.oldrice.com/Powroll200.htm

http://www.powroll.com

http://www.thumpertalk.com

[grcamna2]

Some coaching offered in this link, I was searching for pow roll... I got a motocross cam from powroll back in the 70's for my sl100. I think they went out of business, but still I got a hit and found a phone number in the second link. Have you been to thumper talk?

http://www.oldrice.com/Powroll200.htm

http://www.powroll.com

http://www.thumpertalk.com

Hi Kevin D,
I had an SL125 engine back in the day which I ordered a big bore piston for and a stroker crank kit w/ a mild cam from Powroll and sure enjoyed the performance improvement over stock.I had it in a CB100 street bike and did a good amount of miles w/ it until I sold it to my brother in-law who rode it and gave it to my youngest brother who rode it into the ground 
I liked Powroll but  they seem only just barely in business..
This XL/XR200 engine is the largest bore/stroke comb. Honda used for basically the same size cases as the CB/CL/SL/XL100/125's series from back then;it's a very light engine so whatever mods I do to it should yield a decent perf. improvement over stock 

I imagine it is best to check out a few camshaft companies before I decide on using an already manufactured and proven cam that'll fit my wants.
Hey coach,thanks for those links 

[Kevin D]

I was kinda surprised, in the old rice link to powroll advertisement they talked about exhaust, carb, airbox mods but not cam. Also the remark about weak clutch.

SL125 engine back in the day, rode it into the ground 

+1
I thrashed my 100/125/150, then gave it to my nephews for some more thrashing. I was just a skinny 17 year old, but that bike hauled me through the Michigan woods without fail. The "motocross" cam came with the second rebuild and improved the bottom end pull.   

[cbornotcb]

http://www.tighecams.com.au/bikes.htm
The 399 grind will do what you want, I built a land speed race 175 using an XR200 closed chamber head, strong mid & happy @ 9,000 rpm, pulled 84 mph on the salt (Swiss designed exhaust)
Tiny

[grcamna2]

http://www.tighecams.com.au/bikes.htm
The 399 grind will do what you want, I built a land speed race 175 using an XR200 closed chamber head, strong mid & happy @ 9,000 rpm, pulled 84 mph on the salt (Swiss designed exhaust)
Tiny

I appreciate that info Tiny;whats a "closed chamber head"? stock ?

[cbornotcb]

The bike ran on Methanol, mainly to keep combustion chamber temps down (wot for 3 miles takes it's toll on little Honda singles)

[cbornotcb]

The welded chamber

[cbornotcb]

Tighe profiles

[grcamna2]

Got it  You welded up the chamber in the head to increase CR. I like the look of the Tighe camshaft compared to the stock one next to it,lot's more lift. 

[grcamna2]

http://www.tighecams.com.au/bikes.htm
The 399 grind will do what you want, I built a land speed race 175 using an XR200 closed chamber head, strong mid & happy @ 9,000 rpm, pulled 84 mph on the salt (Swiss designed exhaust)
Tiny

Again,thanks for the link

[grcamna2]

I know it's been years since I posted to this thread,I put it away and am just now 'resurrecting this little project. 

What does "Duration at .040" and "Lobe centers 104.5" do to the equation? I'm asking so I can compare camshaft specs as they advertise them in their catalogs online.
I read somewhere how these two measurements somehow changes the advertised specs...

[grcamna2]

just a thought: does the XR use a different cam or the same as the XL? if they are different and can be swapped you could try both and compare the numbers vs. effect. that would give you a starting point for further experimentation.

The XR200 is the hotter cam,it'll give me more power on the top end,riding this little bike on the street, I would like more 5500rpm plus performance.

[MRieck]

I know it's been years since I posted to this thread,I put it away and am just now 'resurrecting this little project. 

What does "Duration at .040" and "Lobe centers 104.5" do to the equation? I'm asking so I can compare camshaft specs as they advertise them in their catalogs online.
I read somewhere how these two measurements somehow changes the advertised specs...

In general, duration is measured @ .040, .050. Doesn't make a difference though the farther up the cam lobe you travel (.050), your advertised duration will be less than measured @ .040.
 You should concentrate on what lobe center you want ground into a single cam engine. I'd recommend something around 110 lobe center for real LSR work.

[grcamna2]

Thanks Mike, I appreciate it.