4 Cylinder Inline Engine

[Nerd1000]

Hi Ray,
Just something from my "Car maker" experience. The 2 inner manifold pipes would normally come from further away - not the nearest - holes in the plenum. Makes the inlet tracts nearer to the same length as those to the outer cylinders. In fact a lot of work went into making the inlet tracts the SAME length to eliminate differences in "resonances": I.E. 2 outer cylinders with longer tracts could at some resonant point in the rev range take ALL the mixture effectively, leaving a transient depression (or pressure!) for when the next inlet valve opened, which if an inner cylinder with shorter tract length was not resonating and unable to cope with the different manifold pressure... so not getting the right mixture and causing a flat spot at the resonant engine speed... instead of the expected "boost".
Simply, when all the inlet tracts are the same length there is only one "potentially problematic" resonant speed to manage especially - instead of 2, when there are 2 sets of inlet tract length.
Longer tracts also resonate at a lower speed, - usually within an engine's rev range, but shorter tracts sometimes resonate above the max engine speed.
Racers use resonances to get extra power. The "common man" driving his mass produced car doesn't want to feel a resonance that can give a sudden surge of power, but sometimes these are tuned to suit other factors. E.g. if an engine is on an automatic transmission that normally runs the engine at a fixed rpm (max. torque rpm). then the inlet tract length (and maybe exhaust lengths) will be tuned to resonate at that length to get the natural power boost available.
For a "bench idling engine" it matters not a jot - except to passing "rivet counters".
I like the clear pipes? What material have you used? - My supplier doesn't do clear metal...
Ken

This resonance for performance business is very common on modern cars, in fact it isn't uncommon to find cars with manifolds that have multiple runners of different lengths and shutters that can open and close them, so that the engine can have two or more optimal resonant speeds.

Think you'll find those tygon tubes will flutter and close up to a degree on running.

The automatic inlet valves should reduce that effect somewhat.

 

[Rdean33422]

This has been the easiest first time startup of any of my model engines. I haven't changed the valve timing or the ignition timing settings that I made while engine assembly. The carb main needle factory setting was close right out of the box. My counter weight on the throttle lever works even better than I had hoped. Throttle response is good and reliable. All cylinders are firing and pulling in equal strength. The fuel flow can be seen in the lines and seems to the same on all cylinders. I will be using this design on any future engine builds. My distributor is working just fine but the miter gears are a little noisy. The gas tank holds 1/2oz of fuel and is good for 3 to 5 mins of run time depending on the engine speed. The atmospheric intake valves have not been a problem at any speed. Low speed idle has been recorded at 900rpms but I think it can be lower when broken in. Highest temperature recorded was 175 degrees at the exhaust port on number 3 cyl. The engine block is so massive that it acts as a heat sink to keep the temp down. I let it cool off completely between runs.

I want to thank everyone who left comments and likes along the way it is appreciated.

Thanks for looking
Ray

 

[Sparky_SC]

Story goes that the whole is equal to the sum of its parts. You did such a fine job on all the parts I am not surprised how easily and how well it runs.

 

[kuhncw]

Very well done, Ray. Nice runner.

Chuck

 

[Steamchick]

Well done Ray.
Success speaks for itself. Excellent work.
You have made a very interesting story of your build. Most entertaining! And it raised some interesting discussions.
Thanks!
K2

 

[Rdean33422]

Thank you Sparky, Chuck, and K2 for the kind words.

Ray

 

[Niels Abildgaard]

Thank You for an enjoyable trip back in time.
In 1965 I rode a Nimbus in danish army and in 1974 I learnt and was tested sidecar driving with another Nimbus.
Four throw crankshaft hung in two ball bearings and a single OHC camshaft and visible valve springs.

Nimbus history link
Nimmer

 

[ninefinger]

Nice result. I like the translucent intake runners, I wasn't expecting to see little puffs of fuel mixture in them but seeing is believing. Adds an extra visual detail to the other externally exposed bits like the crankshaft and the camshaft

 

[olf20]

Nice result. I like the translucent intake runners, I wasn't expecting to see little puffs of fuel mixture in them but seeing is believing. Adds an extra visual detail to the other externally exposed bits like the crankshaft and the camshaft

Great job! I enjoyed your build and learned several things that
I can / will use!
Thanks
olf20

 

[minh-thanh]

Ray

Runs Great, Sounds Great..
You make the engine very easy
You make an engine no plan, 4 cylinders, 4 atmospheric valves :
Congratulations, Thanks for sharing !

 

[Rdean33422]

Thanks Nimmer, ninefinger, olf20, and Minh it is appreciated.

Ray