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engine conversions

Old 08-28-2015, 10:35 AM
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M3220
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Is there a chart for engine conversion of 2 cycle to 4 cycle, 4 cycle to gas, gas to electric and sorts.
thanks
Old 08-28-2015, 01:21 PM
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Gray Beard
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Are you asking about size? Like a 1.20=20 cc or 2.4=40cc.
Old 08-28-2015, 04:12 PM
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yes information like thatwill help
thank you
Old 08-28-2015, 04:38 PM
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I have never seen a chart but there may be one out there. Where all the confusion was for myself years ago was with gas engines. With glow engines a .91 two stroke is the same in either two or four stroke but with a gas engine a 2.4 is a 40cc engine. It's either 2.4 cubic inches or 40cc so you just need a conversion chart. I have a couple I found on line. cc is just cubic centimeters or metric and the 2.4 is cubic inch displacement and used in the US. .91 cid, 1.20cid. Without my conversion chart I would only know a few myself off the top of my head. The US is the only country I can think of that doesn't use the metric system. We gave it a try but all the older folks went a bit nuts trying it. It was given up and now most of us old farts that learned the metric system in the 60s can't remember it.
Old 08-30-2015, 01:36 PM
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Thank you gray beard
m3220
Old 08-30-2015, 02:40 PM
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Originally Posted by M3220 View Post
Thank you gray beard
m3220
I was about to post the chart I have but it doesn't have Cubic centimeters to cubic inches. Conversion charts are all over the net though. my wife has one for centigrade to Fahrenheit due to a lot of her gaming friends in different countries and they freaked out when she said it was 110 degrees one day.
Old 08-30-2015, 06:28 PM
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There really aren't exact equivalents. With 2 stroke to 4 stroke, the rule of thumb is to go with 50% more displacement. So a .46 2 stroke would become a .65-.70 4 stroke. But that's only a rough figure, because the power production between those 2 engines is so different and the props you need to run are so different. Take my .40 size Cub for example. It started with an Evolution .46 engine and flew ok with it. Top end speed was more than the Cub needed, but takeoffs required some skill and it wouldn't vertical for beans with any prop I tried. I switched it to a Saito .72 that made less horsepower but a lot more torque. Takeoffs are effortless now because that power combination pulls so much better, and with the big prop turning about 2/3 the RPM than I used to get with the 2 stroke I also see a lot better vertical performance. So the rule of thumb gets you close, but going from one power type to another means taking into account the quirks of each one.
Old 08-31-2015, 04:47 AM
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I agree, it would be nice to see a chart of what engines are equivalent when using different fuels and strokes.
This is the first time I've heard the 50% Rule for 2 stroke vs 4 stroke.
I know gasoline and diesel will be different still.

I hope someone publishes one.
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Old 08-31-2015, 08:13 AM
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You will never see that type of chart, there may be a size conversion chart out there? That old rule of thumb is a hold over and no one has paid any attention to it in a decade. It's from the time that four strokes first came out. They were very under powered and low on RPM. Over time they have caught up to the two strokes, they will never be the same but that old rule no longer works unless your like me and rebuilds a lot of the old ones. I no longer rebuild anything except the YS so the rule still doesn't work for me.

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