I'll tell you why they don't exist. If the testing raised the price of a model engine by so much as $1, 95% of the modelers would object to it as a an unwarranted expense.
We use prop/RPM comparison data to determine power levels, always have and probably always will.

Check out the tachometer forum to see how it works...............

Boy, does that bring back memories. In 1966 I bought a brand-new Carter AFB (Buick, by the Part Number) and stuck it on my '57 Ford 312. I kept that convertible from 1965 until 2005, auctioned it and my folks' place that year in November. The Ford still had that AFB, and ran great. I probably kitted it twice in that 40 year span.

Our troller / original poster has failed to get us going on engine debate here. No one has mentioned the real difference : 2 strokes scream, 4 strokes growl. I'm happy with either, on a given day!

Cheers,
Dave Olson

I didn't make that claim, ask jeffie8696. However, I believe it is a generalization. I am sure some two strokes may produce that much more power.

Scar, I think you have pretty much nailed it there.

Mike

Odd, I also once had a 55 Chevy with a 327. Except it was bored to a 333, had 30-30 Duntov cam, double camel hump heads, headers, Eldebrock manifold, and a beautiful Holly four barrel. I think it was 750 CFM. Without posi traction it would burn out as long as you kept the throttle down, well almost. Had a Carter carb and the Holly is much easer to maintain and make fuel adjustments with. But outside of that the Carter is a good carb. The later Rochesters that came in the large late 60's early 70's Buicks were also good carbs, but also hard to make adjustments with.

I concur about the scream VS growl statement. I to enjoy both.

If our engines all operated at peak RPMs all the time it would be moot but as we know most of us use the throttle to control the plane. An engine with more average power should perform better than one that has all its power in a very narrow RPM range. This is accomplished many ways through engine design, fuel etc. I think we all deserve to know the numbers.

The only difference I notice at the field is I fuel my plane, a 4S saito, clear the carb, and fly while many of my 2S buddies are tweaking carbs every time for their first flight, and some at every flight to get that mighty scream that they seem to find necessary to get all the power they can.

Jeff, here is a perfect example, I flew this Webra .91 Diesel conversion on a slab tailed Hangar 9 UltraStik for a while, I don't know of anybody who would have claimed it lacked flying power. It turns that Graupner 15x8 at 8,700 rpm, but that probably doesn't compute to much hp. I just mounted on the JossStik today.

I wont say I have a preference for either form each has its own merits. I would just really like to see quantifiable data to base decisions on.

I have a Torque Reaction Dynamometer from American Hobby Products.

I think a big part of what makes a two stroke have less than twice the power of the same size 4 stroke is:

All the breathing of a 2 stroke has to take up the bottom parts of the stroke! What that means is that the power stroke has to be cut short compared to the length of the power stroke on a 4 cycle.

Once the ports open the power stroke is over! 4 strokes get a whole stroke for intake and and whole stroke for exhust - yes there is some overlap but not nearly as much as a two stroke...

I love engines with no preference of either.

I do love two stroke detroit diesels!!! They scream like all two stokes

"Drive it like yer mad at it" Doctor Detroit (me). Got the nickname in college since I had a way with em, you just have to hold your mouth right, circle the engine clockwise 3 times, bark at the moon, etc etc. LOL.

The poppet valves of a four stroke also open well before the piston reach's top and bottom center. The exhaust valve opens before the piston reach's bottom dead center, though maybe not as much as a two stroke, At top dead center the amount the intake valve opens is not that much differant than the ports of the two stroke.

Any conventional engine can only empart power effectively to the crank just after TDC and just before BDC all other forces applied to the crank are just wasted. 2S engines put max power in the smallest package and even though you can get a 4S engine to run well and make a lot of power the physics just aint there.

At the beginning of the sportsman pattern season I was faced with a 4 or 2 stroke decision and ended up getting the 91FX. The OS91FX with a tune pipe was about the same price than an YS110.
The 91FX with tune pipe weighs 28 oz (795gm) and the YS110 without muffler weighs 27.4 oz (776gm). So there’s little difference. I run the 91FX at 10500 with a 14X8 APC and 15% Cool Power. From what a hear you can run the YS110 at about 9500 with a 15X8 prop, so power is very much the same. So you get a bit more toque but you need to run the YS on 30% nitro, you can not hand start it and even with a starter it can be troublesome, then it needs regular maintenance. You also need a very strong airframe to withstand the four-stroke vibration. The two-stroke is a fuel, fly and forget engine. Just what you need then you want to concentrate on your flying.

There are advantages to 4 strokes over simple power from high RPMs.

Then explain why the two storke dirt bike has more torque than the same sized four strokes? I think that having two power strokes every four strokes adds more average torque for the same time, however the peak torque for the two revolutions are higher with the four stroke. But that doesn't translate to beter performance for dirt bikes.

If you'd like to see some amazing Kawasaki's both 2 and 4 stroke just google Allan Millyard!
Dave :^)

Wow, how did you get your hands in there. 327s came along long after the era for a 55 Chevy. I do recall a chap that had a 327 with normal asperation that blew everybody away. He done great until he blew the engine. After that he had to resort to twin quads or three duces to do the same times. Seems to be that would have been about 1065-66. I was busy being a Lieutenant in the USAF.

Cheers,

Chip

My 68 vette with the 350 horse 327 ran fantastic. All it had was a nice set of headers. Nothing compares to my 04 Mach1 though. Even though it is a 4 stroke. LOL

Field experience confirms that twostrokes are no more than 15-20% stronger than fourstrokes. If you want more power out of a twostroke engine then a tuned exhaust systems must be used.
Running the same fuel a 46 sized twostroke is like a 52-56 fourstroke or a 25cc twostroke is about egualy strong as a 30cc fourstroke.

More like a 46 sized two stroke is like a 70 sized fourstroke. My .46 TT seems much stronger than the 52 through 60 fourstrokes.

I agree with you that it takes a .70 four-stroke (or better) to equal a good .46 two-stroke. But, that's why we have horse races, I suspect. <G>


Ed Cregger

-----------------


This was in 1964, right before Holley became popular. In fact, at that time, Holley carbs were avoided by the unenlightened (me).

I would have been infinitely better off with just one of those Rochester four-barrels on a good manifold than even with the Carter AFB carb, which turned out to be too big for my engine. Something that flowed about 650 CFM would have been about perfect.

To another gentleman that mentioned not much room for the 327 in the 55 Chevy, believe it or not, the block was physically about the same size as the 265 CID that the Chevy came with originally.

What I would give to have that car right now and in the same condition as it was when I bought it. It had been customized and repainted by the original owner. He had even modified the suspension and it was a great modification. I've owned nearly half a dozen 55 Chevies and not one of them handled like the beauty with the 327 on board.

Anyway, it sure would be nice to drive to the flying field and carrying models in that car today. Talk about a conversation starter. Youth is wasted on the young.


Ed Cregger

Yep same size, but there was plenty of room under the hood, putting in a 427 was a popular mod just had to modify the firewall. The Tim Taylor method was to bash the firewall back with a sledge hammer. There were kits that moved the radiator foward instead, in fact I think there was a 426 Hemi kit.