Engines > Your Own Design
1/4 scale Porsche 917 180 degree V12 Build
steamer:
This is the beginning of a new build! A 1/4 scale Porsche 917 180 degree V12 or Flat 12.
This engine was instrumental in the victories for Porsche at Leman in 1970. This engine also would go on to dominate in the CANAM series in the early 70's in its turbo form. However, this build will be of the engine in the Leman endurance racer format as shown below.
Specifics:
Bore: 0.845" ( 21.5mm)
Stroke: 0.692" ( 17.6mm)
Displacement: 76.7 CC
Air cooled
Engine block 2 piece split at the crank for a right and left half per the prototype.
DOHC with 2 valves per cylinder with 12 individual heads sharing a common cam box.
Gear driven camshafts as was prototypical, with a timing Vernier at each camshaft
Camshaft: Individual hardened inlet and exhaust cams pinned to a common shaft driven by a gear as per prototype.
Ball bearing Crank with hardened throws
Plain connecting rod bearings of 6.7mm diameter.
Pressure Lube
Scavenged dry sump
Carbureted ( Original was fuel injected)
Ignition will be via glow plug for initial running and debug.
Dual Distributors
Fuel E85 Gasoline with synthetic oil mix
I'll be following the prototype where ever possible. The output shaft will be prototypical, and be gear driven off the center of the crank.. The cooling fan and the distributors will be driven from the top counter shaft also driven from the center of the crank.
Features where I will be departing from the prototype
Connecting rods will be 7075 T6 Aluminum, with bronze bearings ( the originals were Titanium with shell bearings)
The crankshaft will be for the sake of durability and reliability be a ball bearing built up crank. As popularized by Shilling. The crank throws will be hardened A2 tool steel.
The Oil Pump and Scavenge Pumps:
The oil pump and scavenge pump were driven by a pair of spur gears off the lower output shaft and were mounted directly to the engine block and fed oil to the engine with internal passages. This is the proper thing to do on an endurance racer. The best way to avoid a broken oil line is to not have oil lines in the first place! However, the only way to access these pumps, is to split the case. For the sake of maintenance simplicity, I've elected to mount the pumps off the front of the engine, directly driven by the output shaft. This will allow easy removal of the pumps.
The output of the oil pump will feed 6 nozzles via a cross drilled hole in the left engine block. These nozzles will be aimed at each connecting rod pair.
Scavenge will be taken from the sump from two sump pickups connected vis cross drilled holes in the right engine block.
Now running some oil in the fuel is a common way to lubricate the bottom end on 4 stroke Model engines. That would preclude the need for a oil pump and a scavenge pump....but all of that will get sorted out once it's running.
I've made a start with the rotating assemblies. I'll post up my progress shortly.
Link to the Design Thread. https://www.modelenginemaker.com/index.php/topic,6259.0.html
Dave
Vixen:
And so another epic build begins. I for one, will be following each and every step. In some ways I feel very close to this one. Maybe it's next on my list.
Dont forget to reference your readers back to the 917 design thread from time to time.
Mike
crueby:
Carton of fresh popcorn: check
Comfy chairs for me and shop elves: check
bibs to control drool: check
Ready! :popcornsmall:
Vixen:
Did you notice the caption on the second to last photo "porsche-917-racer-could-be-yours-for-a-cool-20-million.jpg ".
Now we can see why Dave is building his own, rather than buying
Mike
steamer:
--- Quote from: Vixen on September 06, 2021, 10:24:31 PM ---And so another epic build begins. I for one, will be following each and every step. In some ways I feel very close to this one. Maybe it's next on my list.
Dont forget to reference your readers back to the 917 design thread from time to time.
Mike
--- End quote ---
I can only imagine it's because you and I have been talking about the design of it for 5 years!! :cheers:
Life certainly got in the way of this one....My daughter's cancer....twice!.....the surgical reconstruction of my right quadricep, and a global pandemic!...... There! that's three! NO MORE.
8)
Dave
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