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?
*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.
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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