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The missing long-stroke 92mm bore VW Type 1s: 2234cc and 2287cc

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Vigilant1

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In another thread I mentioned this, but I'll post more here to avoid derailing that thread.

Right now, the commonly available "stroked" VW sizes are in black below. Are the sizes in red also worth a look?

Possible advantages of these 92mm bore Type 1s with 84 or 86mm strokes:
- Maximum HP is available at lower RPM than with a 2180cc VW. This lets us turn a longer prop which is more efficient, especially at lower speeds (climb). This would be the main advantage of this version, in my opinion.
- Slightly higher maximum HP than a 2180cc engine. The cooling of the head would still be the same as with a 2180, so 75 HP or so might still turn out to be the continuous HP available from any of these engines, but if we need 80 HP short-term (takeoff, emergency climb, one cylinder failed, single engine climb in a Beetlemaster, etc) it would be there.
- Uses the durable thick-wall 92mm cylinders, avoids the thin wall 94s.
Disadvantages:
- Need to use an 84 or 86mm crank, associated conrods, (different pistons?), do the needed case clearancing, etc. Scott Casler sells a 94mm bore by x 86mm stroke "2400" engine (2387 actual), so I assume he already has an 86mm crank that works with the Force One hub.

Observation: Any improvement in prop efficiency (more thrust per amount of fuel burned) allows us to go farther for each bit of fuel. Maybe more important, each HP gained through better prop efficiency is coming at zero increase in CHT. We're getting more thrust while burning no additional fuel= no additional heat load on the heads.

Maybe these longer stroke come with additional problems. I really don't know how the changed geometry affects stresses on wrist pins, main bearings, piston skirts, etc. Whatever camshaft Revmaster is using in their 94mm bore x 84mm stroke 2331cc engine appears to move the peak HP to 3200 RPM. Maybe the same cam would work for a 92mm x 84mm stroke 2234cc engine. That 3200 max RPM would allow a 2" longer prop and even higher prop efficiency (72.5%).



Opinions?

Engine (Displacement)
Bore
Stroke
Horsepower
Comments
2180cc
92mm
82mmm
76 @3600 max (per GPAS)
70 @3200 continuous
GPAS, Hummel/Casler, Aerovee
Prop efficiency at max HP and RPM: 71.4%, 53.4" diameter (54.2 HP out)*
2234cc
92mm
84mm
? 80 @ 3300 max
? 73 @ 3100 continuous

Not shown among listed offerings of GPAS, Hummel/Casler, Revmaster
Prop efficiency at max HP and RPM: 72.2%, 58.2" dia (57.8 HP out)*

2287cc
92mm
86mm
? 82 @ 3300 max
? 77 @ 3100 continuous

Not shown among listed offerings of GPAS, Hummel/Casler, Revmaster
Prop efficiency at max HP and RPM: 72.0%, 58.2" dia (59.0 HP out)*

Revmaster
"R2300" (2331cc actual)
94mm
84mm
85 @ 3200 RPM max (per Revmaster)
80 @ 3000 RPM continuous (per Revmaster)
- Uses Revmaster front bearing
- Prop efficiency at max HP and RPM: 72.2%, 60.0" dia (61.4 HP out)*
"2400" (2387cc actual)
94mm
86mm
85 @ 3600 RPM max (per Hummel)
- Uses Force One bearing and hub
- Prop efficiency at max HP and RPM: 70.6%, 53.4" dia (60 HP out)*

*Prop efficiency estimates above are from Jan Carlsson's "Propeller Design" program for a prop optimized for 100 MPH at a max tip speed of 850 FPM using the MAX RPM and horsepower for each engine. Efficiency differences/differences in thrust produced between long and short props would be greater at lower airspeeds.
 
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Pops

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I think you will find on the larger VW engines that 75 HP is also about the limit for long term reliability from the magnesium cases. The aluminum cases are 17 lbs heavier than the magnesium. I have never used an aluminum case but from all the VW hotrod sites there is a lot of talk of the aluminum cases being weaker because of the walls of the case being to thin in several areas. Then there are some that have no problems. Maybe not having problems because of using a smaller HP engine. ??

I do think you are going in the right direction. Being able to swing a larger slower turning prop for better efficiency is the way to go. IF you can come up the the engine being strong enough to take the added stresses.

The 1834 VW engine in the SSSC is swinging a 60"x26" pitch and starting the takeoff roll the acceleration is shoving you back in the back seat cushion. WOT rpm is 3150/3200 and cruise at 2650/2700 rpm.
 

Vigilant1

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Pops,
Thanks. My objective was to get some of the lower-RPM peak torque of the Revmaster R2300 engines, but using the thick-wall 92mm cylinders (which I believed were preferable to the 94mm cyls). I agree that there's no improvement to be had in continuous HP unless we find an improved head with better cooling. Longevity of any of the large engines will probably depend on good baffling, good instrumentation (esp an MP gauge and CHT senders near the exhaust ports), and the accompanying discipline to operate the engines responsibly. I'd like to have the >option< to overheat an engine to avoid the treetops, but I sure wouldn't blame the engine if I did that.
Some sources indicate the 94mm cylinders are almost as thick as the "thick 92" cylinders, but I can't find numbers.
BTW, Revmaster also upgrades the #2 bearing in their R2300 engine. They apparently replace it with the larger bearing of the same size used in the Type 4 VW engines. Apparently, they found that that the stock bearing wasn't holding up to the pounding of the longer stroke/bigger displacement. Hmmm.
 
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Pops

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Most of the reasons for a magnesium case needing line boring is the pounding out of the #2 bearing magnesium saddle and losing oil pressure from between the saddle and outside of the bearing starving the #3 rod journal on the crank of oil with the failure of the #3 rod bearing on the crank. This is were a well balanced engine really helps on the life of the engine.

In building the large cc engine for more torque at prop rpm's both the heat limited heads and the limited strength of the case is a factor that develops about the same HP output of the engine. For a continuous HP, I believe it's about 75 hp, and anytime above that HP will be helping in limiting the life of the engine in both head temps and case stress.

I was trying to do the same thing in building my 1835 cc VW engine. Building a much larger engine with as much torque at lower rpm's and putting it in an airframe that could fly and have a good ROC on a lot less HP.
In cruise the engine is developing about 33/34 hp of the rated 60 hp and I have all the extra HP to use on taking off a short strip or needing to clear trees at the end of the strip with all of the extra HP and ROC on tap when you need it. With still having an VW engine with high reliability and long life.
 

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