Stroker and Bore suggestions?

[adas]

Aloha, I have my evo with Yasuni 16 and don't much like the setup. Yes it screams, but I am not keen to drive 13,000 rpm all the time. So I am going to build a torquer low revving 9000 rpm engine and need suggestions. I know Mexiicano and Tiba and Browni have been discussing and making big bore/stroke engines, so what is the verdict?

1: I want to use some Taiwan parts to keep the cost down

2: I also want to use my LC setup and rear disc Aprilia cases

3: 54mm bore 47mm stroke is a good one?

4: So what is the best setup and to find a variator (spline sixe) to work as well as which pipe?

thanks frank

 

[cantdrive55]

One of the few LC stroker cylinders that I've seen is a 53mm Koso. Then you can get the 47mm crank. It uses the large spline 16mm variator... Then look into the Koso 100cc pipe. Its a chrome stroker pipe that is amazing.

 

[tiba_karotsu]

here are some of my suggestions if you have some cases lying around;

FRC 53mm modular head cast iron cilinder kit
Tong-Ti 45mm stroker crank or a CMR 44mm stroker crank
V8 street power pipe

the Tong-Ti crank has a 16mm splined driveshaft but the CMR crank has a 13mm splined driveshaft so you can still use your old transmission & vario.

you have to overbore the cases to fit the cilinder & crankshaft so if you're willing to bite the bullet & do the necessary mods it'll be worth it.

 

[adas]

Aloha. Do all the quad ATV 90cc-100cc parts fit. Such as Eton Kasea, etc? I am seeing a lot of items for sale on ebay, as well as inexpensive sites in the USA for these Quads
heres some
http://www.hyper-tuned.com/index.html

http://www.lakesmotorsports.com/

I know my 42mm crank for the Eton Quad fit the same as my aprilia lc 50

What do I watch out for?
If I get the 54 LC cylinder will the 47 cranks be matched so I do not need base spacers, and make the port timing too long. etc?

frank

 

[rydah]

brah did you try cycle imports, they get all the parts you listed.

 

[dynomec]

Well if you try to import the parts then they will increase the cost. You should go to nearest vendor they will help you in better way.

 

[adas]

Getting back on topic here.....

Aloha. Do all the quad ATV 90cc-100cc parts fit. Such as Eton Kasea, etc?

Are the big bore kits just the Jog 90's and derivatives?

Is is better to stay with the 13mm or is there good varios avaiable when using the 16mm.

Is the stock Jog 90 crank OK or cheap ones like the Riuma OK?

thanks Frank

 

[Big B NRG]

Will a 47 mm stroke crank fit in a 39.2 mm stroke engine?
You have to mill the crank 3.9 mm around.

Do you have enough space left to make the engine seal airtight?

 

[rydah]

Will a 47 mm stroke crank fit in a 39.2 mm stroke engine?
You have to mill the crank 3.9 mm around.

Do you have enough space left to make the engine seal airtight?

you can machine the stock block to fit the 47mm crank. my friend did that to his malaguti block.

 

[tiba_karotsu]

i think 47mm stroker crank will fit a standard 50cc Minarelli carter, with 2F4R 44mm crank it still has enough thickness to support a bigger crank.

 

[Big B NRG]

Ah oke, because I have seen piaggio engines, milled out for 44 mm cranks and there was little room for more stroke

I prefere btw a big Bore instead of a big stroke, because of the piston speed.

 

[tiba_karotsu]

Ah oke, because I have seen piaggio engines, milled out for 44 mm cranks and there was little room for more stroke

I prefere btw a big Bore instead of a big stroke, because of the piston speed.

yes but look at the customer GP bikes like the Honda RS125 they have an almost equal bore & stroke (54mm bore x 54,5mm stroke) b'coz this lay-out gives the most port area for a given displacement, even the legendary NSR500's have this same bore & stroke lay-out.

the CR85 dirtbikes have an almost equal bore & stroke (47,5mm x 47,8mm) & they make 26hp stock, they key is port area, let's compare a 2F4R set-up (47,6mm x 44mm) vs an MHR Team bored out to 80cc (50mm x 39,3mm), with the longer stroke you have more area per every degree of port timing as opposed to an overbored cilinder where you need to raise & widen the ports to achieve the same port areas like the 2F4R kits have.

a more oversquare engine lay-out will favor a 4stroke engine b'coz you need big or many valves in order to feed the engine with the airflow required at high rpms, we also have tested both lay-outs in the 55cc class where a big bore lay-out (42mm x 39,3mm) vs long stroke lay-out (41mm x 41,5mm) & the longer stroke lay-out beat the big bore lay-out everytime in a 400m dragrace.

why would you think Fabrizi came out with a new FHT 84cc with a 47mm stroker crank? he could've just gone with a 50mm x 44mm to get an 86cc displacement, maybe he knew what the manufacturers like Honda, Yamaha etc. were on to & decided to follow suit.

 

[Big B NRG]

*Story*

What I mean is this. With a shorter stroke, it's easier to do revs.

My philosophy is that you want your poweroutput on the highest rpm possible, because you get your speed out of your RPM and your meters/miles per RPM comes from your torque.


So I prefere it this way:

15k RPM and 11NM instead of 13.5K rpm and 12NM torque.

For sprinting, torque is the less important factor on a scooter, atleast that's what I think.

You are right on the square engine thing, but for me it's not an option because of the rules.

 

[mt5-ronken]

You are so right o the square vs oversquare thing.
An other thing which favours square or under square (stroker) engines is that you have lesser area on the pistoncrown in which heat can pass through, so you will have a little less energylosses to the pistoncrown.

But sadly on a two stroke there isn't really a substitute for revs when talking about maximum power output.
It's sad cause you push the engine to an extent that can cause large problems with relayability.
And what´s more sad is that larger bore often means heavier pistons, which makes more stress on the pistonbearing and conrod at a given rpm.

 

[tiba_karotsu]

with today's technology & advances in metallurgy even with a 47mm or 50mm stroker crank you can make it rev to 19,000+rpm like the go karts do, the only problem is that the basic scooter carter is of a compromised design where packaging more than performance is the goal but with some ingenuity, dexterity with a grinder & some epoxy it can be fixed.

hp is also dependent upon torque output at high rpms, a linear torque curve that extends at overrev will net you more hp, for sprint racing especially in shorter distances torque is much more important in accelerating from a stand still, sure you may give up some rpms with a stroker crank but you can make it up by tuning the vario & changing gear ratios.

in dragracing peak hp isn't very important, what's important is to have a fat, linear powerband that extends from 9,000rpm all the way up to 15,000rpm, most of the time dragraces are won or lost at the starting line so you need torque to pull you out from the starting line as quick as possible, over here acceleration up to 50m is just as important as top end power, the quickest 70cc, 90cc & 125cc dragscooters over here have only a difference of a few kmh in topspeed but the biggest factor is the acceleration in 0-50m & the 125's accelerate like a fighter plane hooked on a steam catapult on an aircraft carrier, that acceleration you can only get with a lot of torque.

look at where the trend is going, most tuners are no longer satisfied with just 70cc they want more bang for their buck, the 2F4R 78cc & FHT 84cc are filling up that niche, way before the only course was to convert cilinders from 85cc dirtbikes & fabricate a custom crank to fit into the scooter carter, if the demand goes up maybe manufacturers will start making race kits with much bigger displacements, at the moment the FHT 84cc is starting to look pretty good, with a custom pipe it should make around 28hp to 29hp with gobs of torque in the midrange, maybe after we complete the 2F4R project we'll get us a set of FHT 84cc race kit to build another dragscooter.

 

[rydah]

my friend has a couple of those fabrizi kits sitting in his showcase right now.

 

[tiba_karotsu]

my friend has a couple of those fabrizi kits sitting in his showcase right now.

tell me is it the one with the 44 or 47mm stroker crank? is the exhaust port of the cilinder a butterfly shape or the one with auxilliary exhaust ports.

 

[rydah]

its the one that goes with the 47mm stroke crank and i am not sure what exhause port it has, i am thinking its the butterfly one, but i know he has only one of the cylinder heads that take the 2 spark plugs. this guy knows the owner of fabrizi so they hook him up. one of the kits is for his bike and the other kit is for cruza's aprio. if you look at the exhaust from the outside its like square and the header part of the pipe is square to match up. kinda weird.