RE: 4 stroke debate

RE: 4 stroke debate
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RE: 4 stroke debate - 6/12/2007 5:42:08 PM

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quote:

ORIGINAL: blw

Do you have a reference to the claim that 2 stroke engines make 80% more power over 4 strokes?

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.

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RE: 4 stroke debate - 6/12/2007 5:49:32 PM

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quote:

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

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

Mike

(in reply to Scar)

RE: 4 stroke debate - 6/12/2007 5:50:48 PM

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quote:

I borrowed a friend's two-barrel setup until I could get a big Carter AFB and the appropriate manifold.

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.

< Message edited by Sport_Pilot -- 6/12/2007 5:52:05 PM >

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RE: 4 stroke debate - 6/12/2007 5:52:55 PM

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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.

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RE: 4 stroke debate - 6/12/2007 8:45:03 PM

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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.

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RE: 4 stroke debate - 6/12/2007 8:48:39 PM

Hobbsy

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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.

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RE: 4 stroke debate - 6/12/2007 8:57:53 PM

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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.

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RE: 4 stroke debate - 6/12/2007 9:04:41 PM

Hobbsy

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I have a Torque Reaction Dynamometer from American Hobby Products.

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RE: 4 stroke debate - 6/12/2007 10:43:56 PM

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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

< Message edited by chevy43 -- 6/12/2007 10:45:56 PM >

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RE: 4 stroke debate - 6/13/2007 2:00:23 AM

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"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.

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RE: 4 stroke debate - 6/13/2007 5:28:15 AM

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quote:

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...

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.

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RE: 4 stroke debate - 6/13/2007 5:42:45 AM

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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.

< Message edited by blw -- 6/14/2007 1:55:55 AM >

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RE: 4 stroke debate - 6/13/2007 9:49:36 AM

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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.

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RE: 4 stroke debate - 6/13/2007 3:13:25 PM

blw

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

< Message edited by blw -- 6/14/2007 1:56:12 AM >

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RE: 4 stroke debate - 6/13/2007 6:04:04 PM

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quote:

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.

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RE: 4 stroke debate - 6/13/2007 8:20:21 PM

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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.

(in reply to wcmorrison)

RE: 4 stroke debate - 6/13/2007 8:34:04 PM