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EFI 125cc 2 stroke

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Finally had some success.

GP cyl, top end, VP113,

125 cc rotory valve, throttle

body, straightline ign, no PV

...some tweaking of the map

and it peaked at 48+ hp rwhp

Next is a better cyl, with PV,

try a programmable ign,

and maybe a different pipe

Its being posted in yamaha

2 stroke, since a same

or similar cyl is going on a

yz125 bottom end, and the

FI could end up on it, or a

yz250

image.jpg

image.jpg

Edited by yamaha7442
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Am I wrong in thinking something looks fishy with that dyno? 13,000rpms, and the power is showing no signs of peaking?

maybe it rev's to the moon!   :jawdrop:

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The gp engines rev that high. I I read somewhere that the ktm 125cc gp put out 55hp @ 13k so it is possible bit these engines are made to run high rpm all the time but very impressive power per cc.

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This one is just a dyno engine,

and was peaking around 13,500

...it will hopefully get more runs

/ tweaking on the map asap

There are some higher revving

kart motors. Some of the newer

ICA 100cc stuff hits 19 to 21K

... a similar one, with a 58mm

bore, and longer stroke was

tested at a local track recently,

and revs to 15+K

image.jpg

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copy and paste " pcr 100cc "

onto the youtube search bar

...you can hear what 19 to 21K

sounds like

Edited by yamaha7442

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Did a bit of remapping on the EFI 125,

...now its time for a cyl with PV,

and another Ign

Tried uploading a short vid,

no luck

max is 8MB.

...will have to make it a bit smaller

Edited by yamaha7442

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The newer PV cylinder, and

programmable ign helped the

curve quite a bit, ...time to try

some different comp. ratios,

pipes, and maybe a bit of porting.

Hopefully, it will get in the 50+ hp

image.jpg

image.jpg

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The newer PV cylinder, and

programmable ign helped the

curve quite a bit, ...time to try

some different comp. ratios,

pipes, and maybe a bit of porting.

Hopefully, it will get in the 50+ hp

 

Thats a interesting project you have going on. In your pic its pretty blurry to see the Rpm scale. If you would can you repost the pic or set the scale numbers for us. I know the GP engines rev very high so what are you looking to accomplish with this engine?? Motocross?? Just curious if you have room in that cylinder for a a pair of finger ports as it would add a few more Hp and more torque.

Edited by Zrt1200

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These are some other dyno runs,

tuning in the mapping. Will try to

bring up the runs / new pics to see

the scale better- phone pics.

Would have to change the cyl design

a bit for finger ports.

This is more of an excercise to see

what a small bore can do, as well as

EFI a 2 stroke. Boats, sleds, aircraft,

etc have working efi 2 strks, ...why not

MX ? We'll see.

Have driven 125 / 150cc karts with this

kind of power / rpm, and its fairly insane.

Have also ridden a Tom Morgan AMA

pro KX 125, which had crazy power / rpm,

...probably the fastest mx bike have been on.

image.jpg

image.jpg

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I here ya about a MX EFI bike and why not. I have a efi 700cc twin 2T sled engine with a PCV programer on it and it runs pretty dang well. I think for a MX'er you will need to bring the Rpm curve down a touch or at least widen the band out while gearing it way down for the added Rpm's. I have ridden peaky MX'ers and they are fun if you can keep them in the power band. As I see it now you are getting a pretty decent curve just the rpm scale is pushed a little high for MX. Have you tried retarding the timing in the upper rpm curve??

Edited by Zrt1200

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Ign timing and fuel mapping is all

linked to CP, so small changes

can be made instantly.

Tuning efi is getting better, filling

in and fine tuning the maps.

Next up is a full race spec cyl,

then try other pipe combo's.

Once a max hp number is hit,

then maybe back it down a bit

for a broader spread.

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Hey there!

 

This is awesome what you are doing!  I apologize in advance because I don't know that much about EFI two stroke setups but considering my stock yz 125 engine produces around 34hp, what are the factors, if any in addition to the EFI, are there that allow you to make 48hp from that engine?  Would it be ridiculous to assume that I could get the same numbers out of my little 2006 yz125 platform if i were to convert to efi?

 

Appreciate any information you provide to help me better understand what's going on here :)

 

Thanks! 

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Here is some thing else to play with the next time you are running it on the dyno. Make up some stinger diameter reducers and put them in. On our1000cc 3 cylinder drag sled engines we have found up to 12HP by making 1/2mm change in stinger diameter. Some pipes like a lot of reducing and other dont. You just need to try it. We also have welded a 1/2-13 nut to the stinger at the end of the cone and just crank in a 1/2-13 bolt to increase back pressure. Its the same as reducing stinger diameter for all practical purposes and easier than changing reducers.

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Non of this stuff should impress anyone. Until it's put into a dirt bike chassis it's useless. The only 2 EFI dirt bikes I have seen in use are a YZ 250 and a CR 500 in a YZ 450 chassis.....

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Hey there!

 

This is awesome what you are doing!  I apologize in advance because I don't know that much about EFI two stroke setups but considering my stock yz 125 engine produces around 34hp, what are the factors, if any in addition to the EFI, are there that allow you to make 48hp from that engine?  Would it be ridiculous to assume that I could get the same numbers out of my little 2006 yz125 platform if i were to convert to efi?

 

Appreciate any information you provide to help me better understand what's going on here :)

 

Thanks! 

 

This is 100% just an experiment to this point, and only have a bit of time each week to do testing.

The engine is based off of some GP 125 roadracing parts, so thats where most of the power / rpm

comes from, and not much, if any yet, from the EFI. The best part about the EFI is instantly changing

the mapping ( which is like changing a pilot, needle, or jet ) anywhere on the rpm curve

to richen or lean it.

The GP carburators on the roadracing bikes are work of art by themselves, and

not sure if any of them were even running EFI.

 

If anything, this setup would probably start getting tested on a kart 1st, before a dirtbike,

...and even thats a while away.

A GP cyl without EFI will eventually be fitted to a YZ 125 bottom end, just to see if it works,

...never know til ya try, lol

 

So, no, ...this probably wouldnt help much on your bike.

 

The best mod i did to my YZ 125 ( 144 ), was putting on a PSI jetless carb back when

they were being made. The throttle response was instant, and it revved out faster and higher.

The APT or Lectron might be a good choice if you're looking for some bolt on performance.

Dirtrider Magazine did a comparison / video of a stock vs APT carb on a KTM 300, and the dyno

results looked really impressive.

Edited by yamaha7442

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