What's the truth on the FULL CIRCLE STROKER CRANK?

To reduce friction giving you faster revs. The issue of loss in compression is arguable. Not sure if it has been proven. I've tried running one and two rings when I was running the bbk, felt no difference.

well i should be getting my big bore instal kit from adrenaline any day now. then i'll just take a brand new big bore bike apart for the head and piston and we'll see exactly what the big bore does on my bike with the stroker crank. if it keeps the same RPM's as the stock head (11,00 - 11,450) and gives mer more low end then i'll just re gear.

CLUNK CLUNK, that'sme beating head against wall..

Ok, have a look at this link:

http://www.nclra.org/Programs/PortTiming.html

32mm for stroke,
60.2mm for rod
10mm Port height
(Your's will vary)
press calc duration
what ya get? 151.26 degrees?

ok, now change the stroke to 35, what ya get? 145.92 degrees

So you lose 5.34 degrees duration, so what? well,

* you've made the engine bigger by stroking it 9% bigger (3.77cc @ 43.98cc)
* the port size remains the the same
* the time the port is open is LESS at the same rpm lets say 3.5% -
(5.34 degrees less)

Think of it this way, imagine you are a monkey (for trojan that would be easy) now you go about your daily tasks of eating and crapping, and you grew at an extra ordinary rate but your crapping has not changed, the result is you have become FULL OF CRAP.

ok, sorry about that, got side tracked.

Macdizzy's should help using angle areas:
http://www.macdizzy.com/cyl_primer.htm do it in 6 steps it wont kill you.

Using angle areas of step 5:

Now that you have read and followed that link you'd know the area of your exhaust port. My exhaust port *was* 23.4 wide and the radius top and bottom were 2.5mm, it's area was 228.63mm^2 or 2.28cm^2

And that's then divided by the cylinder swept volume (40.21) not the chinese volume 545cu" and then multiplied by the duration.
so: (2.28/40.21) * 151.26 =
= 8.57 we will come back to that

Now do it for
2.28mm^2 exhaust port is the same
43.98cc engine is bigger
145.92 degrees, duration is now less
(2.28/43.98)* 145.92 =
= 7.56

ok now we have two angle area numbers for the exhaust port, 8.57 for the 32 crank and 7.56 for the stroker crank. now we look at macdizzy's chart and look at what revs these ports work best at:
http://www.macdizzy.com/images/angle_area.gif

8.57 deg-cm^2/cm^3 is ~7500-11500 rpm for the stock stroked engine, does that look familiar?
where as the stroker is 7.56 deg-cm^2/cm^3 ~6500-10100rpm

Does that explain anything? anyone lost? anyone follow???

ok if you have read the macdizzy post, have your port timings and areas then you should know what to do, right? like i said, there's a few things stopping the stroker reving, one is port timing, do you agree now????

exactly, there is no point in running two rings when 1 will do the job. The extra ring is only realy good at the lower revs that we don't or can't use. The main advantages to just running the top ring are:
* less wear on the cheap nikel coated bore
* less friction, heat and drag = a small increase in power but it's not that important
* less weight, it may only weigh a few grams now but at 4000ft/s it can be like having a lump of lead tied to your left nut while your on a tramampoline
* reduces the chances of removing oil film from bores, it does, i didn't make that up

yeah, take both rings off without breaking them, they snap like chinese bolts, put them one at a time in the bore, push it up square with the piston and measure the end gap at the same point in the bore with feeler gauges to find the best one, they seem to have a large end gap, something like .23mm if i recall? air cooled engines run pretty sloppy i guess?

ps. while you have your piston out, fine file all the sharp edges on the bottom ends of the piston. It's less likely to scrape oil off the bore if it has nice smooth rounded edges or chamfers. The oil film is the only thing stopping this bit of aluminium touching the bore so don't lose it, do the same for the ports, it wont change the timing if you have at least a 0.5mm chamfer all the way around your ports.


Have a look at this pic, what do you think?




I

I think you spent to much time in school man... Not hating but **** you got me all twisted and im lost now. Hahaha... thats why I leave all that hard work in the hands of folks like mm64, mike93eh, PSWS, ADA, and NWminimoto.

Seasons over and rain is here. Time to hit the Mountains any **** way!!!

lol, i knew it would fly over a few heads, that's why i posted the pic.

****, I miss Squaw, Northstar, Sugar Bowl, and Sierra. **** I miss Tahoe. Used to go at least twice a month when I lived up in San Jo.

Sorry to get off topic. I still wonder what happened to mm64. Mike is still around, just taking some time off. PSWS and ADA know's their sh*t though.

Yo Blah,

Nice to see that somebody else is doing a bit of research. I guess that if you want to go fast without spending big wedge, then learn how a two stroke works. My analogy has allways been that it's like a trombone, shorten something and it sings at a higher frequency (revs) lengthen something (intake tract, exhaust tract, swept area of cylinder) and it sings lower. Hopefully handles a bit better though. (Not as well as an oboe?!)
Got burned last time I made this analogy so I'll be ready with the extinguisher.

Cheers

when running the stroker i think if you put a 3mm spacer and made sure the port timing was correct, and you keep the 39cc piston you would have the best gains. You would have to use a removeable dome kit but this is what i plan on doing with my bike. I want to add a boost port to the stock cylinder head but it looks to thin to me. How big are you guys going on the boost port and are you taking it even with the transfers or higher?

Blah, absolutely brilliant as usual. As you know I was in the process of doing those calcs for my little experiment here anyways. The rest of you guys should really read that again and follow along with the calcs b/c it lets you see what the results of changing your port timing will be. I've always like that Macdizzy site too. As for skiing/boarding, I wish we would have never sold our timeshare in Breckinridge,CO... ****it!

Blah I would agree with you if the squish were not set on the stock or stroker crank set up.
But think of this, If the top of the piston were set to .5 mm with a stock crank (no gaskets) verses the top of the piston were set to .5 mm with a stroker crank (base spacer or gaskets). The jug (Cylinder head and transfer ports) have been shifted up. With the stroker crank installed the transfer port duration increases because the port hieght has effectivly increased (due to shimming) and surface area exposed increases due to the increased downstroke.
I'll run some rough numbers.
What really concerns me is the vibration issue and how to compensate for the increased mass of a BBK piston.

Blah using your calculator and base numbersStroke = 32
Rod Lenght = 60.2
port hieght = 10
duration = 151.26

now sub
stroke = 35
and
port hieght = 13 (because the hieght of the head has to be shimmed)
duration = 167.32

16.06 deg increase in port timing

HMMMM maybe that is why everyone selling the stroker crank has porting specs that include raising your ports, alright, they don't talk about the transfers but they all say to raise your exhaust port or did you guys not notice that? Anyway I am glad that some people on here know what they are talking about, I have seen a million "ported" cylinders being sold and I am just not sure how they are ported because when you ask the seller about how they changed the port timing and area their reply is always "they are bigger", I don't think any of them actually have a degree wheel or know what they are doing.

I'm glad some of the people reading this actually followed it, i didn't waste my time after all. We do have to adjust the port height to match where the piston lands. Probably would not shim 3mm higher, with a 3mm stroke increase the piston would be 1.5 higher and 1.5 lower, also the transfer duration would be a bit long for fixed gearing engines i reckon. There's a few assumptions in our posts and i welcome hindsight to find them for us
I guess it would be best to know the rod length before making assumptions, especially when doing calculations in a public forum.

Sadly, i have not got my hands on a stroker crank yet, iv'e given up. I guess that's the thing about living squillions of miles away from where the action is. We have to make most things ourselfs and this requires a bit of learning and doing. lol, when they tell you the ports are bigger ask them if John Holmes ported it

Do u have any idea's what the durations should be increased too, around 180* for 11grand?

You give me $11 grand and i luv u long time.

Sorry but only 11,000 rpm

It's not just the duration, if you had at least pretended to look at my earlier post you would know that. the information you seek can be worked out yourself if you read these pages
http://www.macdizzy.com/cyl_primer.htm

There is not one answer, you cant just get a magic number. The engine is a lot like a cake baking a cake, you mix all the ingredients together in the right proportions and the result can be good, but if you add too much of one ingredient or too little the cake can turnout pretty bad, don't you agree?

also consider this, you may want a bannana cake but someones given you a chocolate recipe, well the thing taste like a great chocolate cake but you don't like chocolate, you like bannana.

to be honest what type of freak doesn't like chocolate? Man, what's wrong with chocolate? you should just go and get a banana cake from someone who bakes cakes, sure it wont be as good as a home baked bannana cake but it will be better than no cake at all.

mmm, cake

BTW, thanks Blah for diving deeper (technically) than the spinner and this is the sheet posts. Now if we could only find unbiased dyno runs for all these mods there would be real meat to chew on (sorry no cake, watching the carbs).
Alas due to loose tolerances even with hard dyno data results will still vary. What would be a good base line for evaluating mods? (In theroy) Maybe someone has the blueprint specs from the Blata bluebird motor. At least this would be a constant baseline to model from.