120 4-STROKE engine is equivelent to what 2-stroke?
Is there a conversion table I could use?

Thank you

A normally aspirated 120 4-stroke is equivalent to a 91 2-stroke. The YS 120 4-stroke is equivalent to a 120 2-stroke, maybe even slightly more powerful.

Not to mention that the 4-stroke has a much better torque delivery at lower RPM's.

The "grin" factor of a 4 - stroke is equivelent to all the 2 - strokes in the world - PRICELESS

A Rossi 91 2 Stroke engine will have more power than a YS 120 4 Stroke.

Really? So, we could put an 18x6 prop on that Rossi, and have it turn more RPM than the YS would? No way. Don't be misled by advertised horespower claims. Torque is what turns the prop, and a YS 120 will eat a Rossi 91 when it comes to torque.

The only "Official" equivalent was the AMA standard of several years ago. By that, a 1.0 four stroke was considered the equivalent of a 0.6 two stroke. That same ratio was applied to all classes. For example a 50 four stroke was legal in class "B" where a two stroke had a 0.30 max size.

With modern four strokes the average two stroke still has a slight edge over the same size four stroke, but it's pretty much up to you now. An 80 two stroke or a 90 Four.

Bill.

Now I am not sure about what I said. But I know the Rossi 91 is made to swing a 14-6 prop.. but I don't know how many RPM's it will swing this prop.

How about a Webra 120 (2 stroke) versus a YS 120 ?

.

A Ys 120 is comfortable swinging a 18X6 prop? Never heard that before. What type of plane and what rpm? A scale WWI plane?

Fourstrokes have come a long way, I have an old Saito .40, one of the first to have rocker arm covers and a fairly new Saito .30. The .30 has very nearly the same amount of power as the old .40. The .30 has the advantage of being equipped with one of William Robisons Thermodynamically Enhanced cylinders. How's that sound Bill?

Ok,

I have to ask.

Hobbys,

What are you talking about? (Thermodynamically Enhanced cylinders)

Dave:

That shore do sound high brow, don't it?

It's is a treatment all my four stroke engines get, and sometimes I'll do a two stroke also.

Really, it's nothing more than black baked enamel on the ouotside.

Bill.

Sorry about that Sky, I was just having a little fun with my good friend William. This is the engine.

A coat of paint will make it perform better? Won't it act as insulation? I have heard that special dark coatings will disapate heat better than bare metal.

There has been a debate or two here about that issue but it's never been proven one way or the other.

Brian:

Done properly, the engine runs cooler with the black enamel. If you put it on too thick it does no good - it can act as an insulator.

Bill.

A thermocouple attached to the glow plug will show the difference. To a lesser extent, the exhaust gas temperature will be affected.

Measuring the outside surface temperature of the cylinder tells you only that the outside surface is hotter or cooler, says nothing about the internal temperature. The Glow plug measurement is the best way we have to check it.

Bill.

Even if you don't accept it helping the engine run, you have to admit the engine looks better that way.

Haw.

Bill.

And that's simply a black enamel Bill? Not a chemical blackening?

Minn:

The Saito "Factory"black cylinders are anodized and polished before machining. If you pull a GK apart you'll see the inside is also black where the casting has not been cut. Since anodization changes the dimensions of the part, I've never tried any chemical blackening.

Going all the way back to Vincent motorcycles, I've been using a good quality "Stove" enamel and giving it a couple hours at 140F to set it. The baking is not necessary if you're careful, the first couple runs on the engine will take care of it.

The enamel requires careful thinning to get the coverage without getting thick, currently I'm trying fuel proof black spray paint. Much easier. Hobbsy's engine has the spray, the engine I'm doing now for a local fellow will get the spray also. We'll see how it works. Coating thickness is a lot easier to control with the spray too.

Bill.

Here are some shots of the "Real" GK, and one of what I sometimes call the "White Knight."

First shot is inside the front of the case, black arrow pointing to the ring that's not machined, showing the black color. Second and third show the GK rocker pedestal and the WK pedestal, the WK is still natural aluminum color.

Bill.

Wow! This went all the way from power comparison of 2-stroke and 4-stroke engines to what paint to use when coloring your engine. I love it!!!

Every post is a diverse learning experience.

doubledee

What would the new Saito .82 fourstroke be equivalent to , it has more horsepower than the 90 Saito but not quit as much as the 100. sooooooooo

Jon, I have an almost broken in Saito .82a, it turns a 14x6 APC at 9,350 richened down from 9,520 and I suspect has a couple of hundred more to be gained. That is on WildCat 10% Premium with 16% 80/20 lube and a H9 SuperPlug.

Jon:

The FA-82 is a departure for Saito, it's the most "Oversquare" of the line. Where the other Saito singles are happy never getting over 10K rpm, the 82 comes alive at 10K. The FA-80 does very well on a larger plane than the FA-80 would be happy with, on a smaller faster plane the FA-82 would be the better choice.

Can't really call an equivalent for any of the 4s engines, just generalities.

Bill.