Slowing down a modern engine....

[BioHazard]

As much as I would love to have a giant single cylinder gas oilfield type engine they just don't exist around these parts. What I wonder is why couldn't I take a more modern automotive engine and run it down at less than 500 RPMs and still get useful power output?

For example, I have a spare 350 Chevy engine just taking up space. Could I add giant flywheels to this and run it at 400 RPMs or less? How would an eight cylinder compare to a single cylinder of similar displacement for slow speeds? Would the cam profile prevent it from working this slow? Wouldn't the added cylinders help it to run slowly? Obviously one would need a much smaller carburetor for fine throttle control but that can be arranged. I'm thinking at these speeds one could get away with not having a governor if absolute RPM control isn't needed.

I also wonder if the cooling system could be modified to a thermosyphon system thereby removing the parasitic load from the water pump?

Just thinking outloud here...

[Derb]

Hi Bio. You have opened a can here. Common belief is that slow running engines perform better with longer stroke, lower compression (petrol engines) smaller diameter inlet ports and longer intake manifold tracts along with smaller bore and taller carburettor - possibly constant velocity (higher air speed and better fuel vapourisation). Less ignition advance and yeah - good flywheel and crank mass. With regards to thermo-syphon cooling, won't work with an engine designed for a pump - Cooling passages too small and incorrectly configured. Better to go with electric water pump which will only run when required. Cam timing would also have to be modified with a nice long skinny set of headers. What a hoot though - could sound like an old flathead V8!

[Ronmar]

You would need to modify the oil system to deliver higher pressure at the lower RPM.  At the slower speed, I do not think the cam would be so much of an issue, as you have a lot more time for things to happen at the lower RPM.  A carb sized to the available HP would be a necessity for control as you have stated.  I don't think thermosiphon would work, unless the engine heads could be modified to allow the coolant to leave the heads vertically.  As noted the coolant passages are smaller, but so its the ammount of HP you are going to be able to extract from such a beast...  If the design has the coolant flowing up thru the intake manifold directly to a high centeral point, then it could possibly work.  I bet it would be smooth, but I wonder how efficient it would be???  Don't know that I have ever heard of anyone doing this.  Perhaps there is a reason for that:)  

[veggie]

How much power are you hoping to produce?
I doubt the 350 chevy performance curve goes below 1500 rpm.
However, my guess would be that 400 rpm would produce approx. 10 HP
Anyone else care to take a guess.?

Oh yes.....and you will need a HEAVY flywheel.

veggie

[Henry W]

There are ways to do it but lots of parts will need to be changed.
Parts needed:
High volume oil pump
Heads with smaller valves ( like from a 307) with intake ports closed up
Custom Cut Cam
Adjustable cam sprocket
Smallest 2 barrel carberator or custom manifold with a one barrel carb.
ONE LARGE DIAM. HEAVY FLYWHEEL
ECT,ECT.................
Worth the effort???

A better engine would be a Ford 4.9 Liter, 300 ci. straight six. This engine would be easier to modify to run at lower speeds under 1000 rpm. Peak torque on this engine was at 1800 rpm stock.

Henry

[BioHazard]

Worth the effort???

Is it worth the effort to restore an old oilfield engine? It's more "I want to try it" than "I need to do it". I'm thinking it might make a cool PTO to use in my shop, I could have an alternator, welder, air compressor, etc....

I think the hardest part to find would be the flywheel(s)...any ideas? Think I could just have a round peice of steel cut by CNC?

[Henry W]

I think the 350 engine might be a externaly ballanced engine.

The Ford 300 six is a much better suited engine.
The engines peak Hp was rated at 3500 rpm.
Small valves
Small intake ports
Internaly ballanced
Stock cam gives great low end torque.
Almost a 6" stroke
Very cheap to buy

Henry

[Ronmar]

Why smaller valves/passages?  All the slowspeeds I have ever dealt with have rather large valves...

Well low speed, a large diameter section of pipe cut to form the outer rim, and stacked flat plates to form the center...  Or for that matter, just stacked plates to form the flywheel...  OR a truck tire filled with water?  A 24" diameter wheel turning at 500 RPM is the equivelent of 35 MPH...

[admin]

the 350 is an internally balanced engine, the 400 small block was externally balanced

why not give it a try if you have one already.

they run at about 550-650 at idle depending on configuration, and they drive a p/s pump and in many cases an A/C pump
those two things alone require more than 10hp. so it might not be too hard to do...

i would not expect much for fuel efficiency however, probably pretty hard on fuel consumption at that level of operation.

bob g

[SteveU.]

Hey just stack up standard manual transmission flywheels. Trough drill out the pressure plate mounting holes and through bolt to the engine mounted flywheel. back side drill for the pressure plate dowel/alignment pins to take the sear stress off of the thru-bolts.
I think you will find with the complete power overlap on a V-8 you will not need that much added flywheel weight. The cumulative ring drag from those eight cylinders though are going to give you a lesson in why for fuel efficiency the less cylinders the better for this aspect. Ever have to fuel one of the V-10's?? Piston speed, bore/stoke relationship will be related to the characteristics of your intended fuel type, speed range and even running loads. Only way to make something like this fuel cost practical is with really cheap propane or natural gas. Neither of which is "native" to the PNW. We have water, wind, wood and solar and a smidgen of only so-so fossil coal. EVERYTHING else is imported in including Nuke.

All my own opinions
Steve Unruh

[XYZER]

I believe you could thermosiphon a 350 running at 500-900 rpm. The heat disapation won't be the same as a smallblock producing 275hp ....heat rises. Why a high volume oil pump if you are only trying to lube 15hp or there abouts. I would find a small downdraft single barrel carb and play around maybe water injection and lean the heck out of it...? (no experience there)I have never tried this but I'm sure if one does with a used 350 you won't be out much and what a story! 

[LowGear]

I love it when the Chevy 265-350 is referred to as a "Modern" engine.  I used to sleep with a 265 when I was in high school.  How about pulling four of the pistons out while we're at it?

Casey

[BioHazard]

Good ideas everyone. I think I want to turn this into a "how slow can I go" project. I agree the 350 isn't going to be fuel efficient but I do get lower commercial gas rates at my shop.  I think it would make a great welder with the right head, I need a new one anyway.

Practical? Hardly....but this is america I don't have to be practical.  I kinda just want to hear the noise it makes...

[WStayton]

  A few words of warning from a ex-automotive engine engineer of the same period as this engine.

1) There ain't no-way/no-how that you will make a thermo-siphon work with this type of engine.  As previously noted, cooling passages are quite "tight".

2) Also as previously noted, you will need a high volume oil pump to provide enough oil for lubrication at such a low speed.

3) The camshaft will have to be retarded, at least, for the engine to function - and, maybe, you will need a custom cam to make it work.

4) Fuel economy will be horrible, no matter what you do - of the order of 1.50 BSFC - There are just too many sliding surfaces to be amortized over too little output.

5) A much smaller carb is definatly required.  I THINK that some of the early 4 bangers used a one barrel carb but there are a couple of problems, both related to the fact that these carbs were for quite high speed engines, so they are not as tiny as a direct comparison would lead you to expect.  The other problem is that even with a small carb, you will still have it dumping into a sewer pipe of an intake manifold, so even if you have reasonable velocities in the carb, you will have near stagnation in the manifold.  Not such a problem for a stationary engine, but cold-starts will still be a BEAR! <smile>

  CAN you do it?  Yes, definately!  SHOULD you do it?  Only, you and your banker can make that decision!

  Even the Ford 300 CID six cylinder would have many of the same problems/challenges when you are running it outside of its design range, though I would expect them to be less since it is not SO far from its torque peak

My opinions, which are worth exactly what you paid for them! <grin>

Regardz,

Wayne Stayton

[Henry W]

Wayne explaned it very well. I just did not have the time to get into it.
Highlighted in blue are some things Wayne went over:

Also as previously noted, you will need a high volume oil pump to provide enough oil for lubrication at such a low speed. The small block Chevy engine oiling system can handle upwards to 500 hp stock but at low speeds below 500 rpm the oil pump will not develop enough oil pressure.

A much smaller carb is definatly required.  I THINK that some of the early 4 bangers used a one barrel carb but there are a couple of problems, both related to the fact that these carbs were for quite high speed engines, so they are not as tiny as a direct comparison would lead you to expect.  The other problem is that even with a small carb, you will still have it dumping into a sewer pipe of an intake manifold, so even if you have reasonable velocities in the carb, you will have near stagnation in the manifold.  Not such a problem for a stationary engine, but cold-starts will still be a BEAR! <smile>
A small one barrel carb would be best but a big problem is the stock intake manifolds and intake ports in the heads. The fuel will pool in area's. This was exectly the problem that Ford had with the Boss 302 and Boss 351 Clevland. The ports and valves were too large for normal street use. The intake velocity was not enough to atomize the fuel at lower speeds.

The camshaft will have to be retarded, at least, for the engine to function - and, maybe, you will need a custom cam to make it work.Camshaft will need to be custom ground.


Henry