amazing little 50cc going to park some bigger ones!

[Street Ryderz]

wow! 190 psi! surely that'll removing your chrome from your cylinder pretty quick? i like that tester though where did you get it if you dont mind?

comp gauge came from princess auto here in Canada but it's the same as harbour freight in the states!Not sure what to tell you in Ireland but I'm sure it could be found on ebay.As for the chrome we'll see how it holds out so far it still looks mint this cylinder was done quite well compared to many of the ones I've done previously so I thought why not see if it can handle it.rebuilding this engine only cost me a total of $30 so it's a pretty cheap experiment!

 

[Street Ryderz]

Glad you found that case you were looking for.

I wish I'm still looking for a pair of cases for the 66-70 that take the 17mm crank and 6203's and not having much luck! I dont want the super rat ones for the intragrated cdi though!older plain rat engine or star fire 70 or the early zeda ones are best suited imo for doing up as race engines!

 

[gary55]

Corrected and uncorrected compression ratios calculator
Bore: mm 40
Stroke: mm 40
Height over exhaust port, top of port to top of barrel mm 25
head volume (head cc) 6 cc

uncorrected 9.38 :1
corrected 6.24 :1
This is how I came up with the comp ratio that I posted it's from lambretta's port timming calculator.And it seemed a little odd to me aswell!because the comp gauge is mint and kept in it's box when not in use and it reads correctly on other engine's!And yes it reads 190 p.s.i every time and I checked it three times. When doing a comp check I'll kick it over three times to make sure it hit it's peak .Oh yeah I look at the plug while it was out for comp check and just as I thought just about right now with the jet drilled out to 72 it seems alittle lean in the bottom end and almost perfect on top mind you thats with stock ignition and stock plug lol so I guess thats not bad!

I just checked mine with this calculator.
Bore mm 47
Stroke mm 40
Hgt. over exh. 28.5
Head vol. 8cc
uncorrected 9.68 to 1
corrected 7.18 to 1
My PSI is a steady 135
I know you know your s**t bro when it comes to these engines, but I still can't figure out how the 6.24 to 1 can give 190 psi. I know you will get a extra 25 psi over me due to lower elev., so I guess the rest comes from the smaller volume.

 

[Street Ryderz]

I just checked mine with this calculator.
Bore mm 47
Stroke mm 40
Hgt. over exh. 28.5
Head vol. 8cc
uncorrected 9.68 to 1
corrected 7.18 to 1
My PSI is a steady 135
I know you know your sh*t bro when it comes to these engines, but I still can't figure out how the 6.24 to 1 can give 190 psi. I know you will get a extra 25 psi over me due to lower elev., so I guess the rest comes from the smaller volume.

Im not sure etheir It seemed a little odd to me too!when kicking it over you can feel the comp is a bit more than normal but not bad still starts and runs well so im going with it!lol

 

[gary55]

Im not sure etheir It seemed a little odd to me too!when kicking it over you can feel the comp is a bit more than normal but not bad still starts and runs well so im going with it!lol

I would too. Ya gota love a engine that sings. I just started looking into this altitude stuff out of interest in how much power loss I was realizing from less oxy. and atmos. pres.
interesting stuff. If I took my bike to Phoenix from Prescott I go from 135 to 158 psi and gain around 16%. Plus I gain more cause with more oxy. I can add more fuel.

 

[Street Ryderz]

I would too. Ya gota love a engine that sings. I just started looking into this altitude stuff out of interest in how much power loss I was realizing from less oxy. and atmos. pres.
interesting stuff. If I took my bike to Phoenix from Prescott I go from 135 to 158 psi and gain around 16%. Plus I gain more cause with more oxy. I can add more fuel.

What is the elavation change between the two? 16% change is huge would require re jetting I would think lol!

 

[Street Ryderz]

You might want to check that comp. gauge. I'm guessing you are around 600 abv. sea lev.. So 190/14.37=13.2 to1 comp ratio.. 6.25 to 1 would be 14.37X6.25/1=89.9, oh now I see. It's 90psi not 190psi.. Had me scratching my head for a second.

I went to wiseco. com and used their calc and it said the same as you 13.2 to 1 so im confused thats race fuel comp levels !

 

[Street Ryderz]

Engine Item MM Inches Measurement
Engine Bore 40mm
Engine Stroke 40mm
Deck Height * .25mm
Combustion Chamber CC's 6cc
Your Compression Ratio is 9
Number of cylinders 1
Your Displacement is :50 cc
This one is from cb performance and seems more realistic but now im lost and going to have to do all the math myself to know for sure what it is.

 

[gary55]

There must be more to it than I am seeing. I see variables in 4 strokers with valve timing, but the two stroke should be steady. My still on the learning curve way of understanding it is 9 to 1 is squeezing normal pressure of 1 till it is 9 times greater. So if normal is 14.37 psi at 600 ft. then it's 9 X 14.37=129.3

 

[Street Ryderz]

Enter Bore/Stroke Designation Type
1 = Inches 2 = Millimeters
2

Enter Cylinder Bore Size
40

Enter Piston Stroke Length
40

Enter Head Gasket Bore Diameter
40
Enter Compressed Head Gasket Thickness
.75
Enter Combustion Chamber Volume In CCs
6
Enter Piston Dome Volume In CCs Negative For Dished Pistons (Use '-')
2
Enter Piston Deck Clearance Negative If ABOVE Deck (Use '-') :
-.5
Calculate CR Calculate Total Volume Calc Combustion Chamber Volume

Calculated Engine Compression Ratio
12.651280088584452 :1

Total Displacement Volume
4.31415923495779cc

this calc I beleive is correct in that it takes into account for piston deck height,the piston dome volume and the gasket thickness all of witch are required to truly get a proper answer.And this works out to 182 p.s.i witch is possible if the gauge is out a bit! I would think though if the gauge was out it would be negative givin the task it preforms!