Converting 4cyl Nissan Altima to 2cyl - removing pistons and connecting rods

[cr45]

Originally Posted by Frank Lee

I think those are fails.

Please elaborate!

[Frank Lee]

All those things still are net absorbers of energy vs piston deletes.

[Goldenstate]

Any chance of raising the compression ratio on the two remaining cylinders to gain some efficiency during the modifications to the motor?

[gumby79]

Have you considered doing a 5 stroke?
You have 2 pairs 180 from each other. 1342

#1 ehxsost valve feeds into # 4 intake valve then out to the manifold. Theoretically you should be able to use the same cam. A regrind would help. . New intake/ehxsost and crossover manifolds would be needed . .

Five-Stroke Engine Works and Might Enter Production - autoevolution

This consept has ben put through Proof Of Concept. Useing 2 into 1 for a total of 3 cylinders ,not 1 into 1 totaling 2 cylinders as I'm suggesting.
Dreem big chisel down to reality

[Ecky]

My opinion - regearing is a better idea than cylinder deletes.

As I understand it, frictional force goes up with higher RPM, so friction increases in a non-linear way, and a 2 cylinder running at 4000rpm would have greater total frictional losses than a 4 cylinder at 2000rpm. If you can drive the car in the same gears as before with half of the pistons removed, great, but if you find yourself upshifting to make power where you wouldn't have previously that's counterproductive.

[Fingie]

I got a idea once that the cyl 5 on a inline-5 would compress air to the remaining cylinders, but it would require an entirely different crank in order to time it.

[cRiPpLe_rOoStEr]

Originally Posted by Anatoly Kishinevski

I am a Russian

Oh, really? I could never have figured it out

This thread is about a modifying a car engine to half of it's original displaced volume with the goal of increasing fuel efficiency drastically while maintaining driveability of the car (safely).

I have been planning the conversion of a 4 cylinder car to a 2 cylinder car for about 2 years. I recently acquired a rust free 2000 Nissan Altima with a 5spd transmission and 2.4L KA24 engine. This car is going to be the machine to which this modification and test is done. The engine is favorable because it has a very long stroke to bore ratio.

I've already considered to convert 4-cyl cars to 2-cyl, but I'd rather resort to a motorcycle engine. You know, some custom/cruiser motorcycles are set to RPM bands more comparable to car engines than to other motorcycles, so they could be suitable to your project, and at least for me it sounds more advantageous. Fewer dead weight, a more compact engine, and most likely to also decrease internal frictions and inertia too. BTW when my dad had a Subaru I've already considered to replace its flat-4 with a Harley-Davidson Twin-Cam.

[cr45]

Originally Posted by cRiPpLe_rOoStEr

BTW when my dad had a Subaru I've already considered to replace its flat-4 with a Harley-Davidson Twin-Cam.

Subaru would make an ideal conversion as you could run it as an opposed piston twin. This would result in perfect primary and secondary balance and hence this conversion would be considerably smoother than a straight 4 conversion.

[cRiPpLe_rOoStEr]

Originally Posted by cr45

Subaru would make an ideal conversion as you could run it as an opposed piston twin. This would result in perfect primary and secondary balance and hence this conversion would be considerably smoother than a straight 4 conversion.

I know flat-twin conversions based on the Volkswagen boxer are quite common for ultralight aircraft, but it would be more complex to do in a Subaru engine. If I were all for a flat-twin I'd rather get a BMW R-series engine or doing something based on the VW boxer instead of messing with the Subaru engine.

[George Tyler]

Originally Posted by cr45

If the compression ratio in the "air spring" cylinders were to be lowered I suspect that you might get a useful efficiency gain.

One way to do this might be to remove the inlet or exhaust valves and then block the port downstream from the valve.

Another option would be to fit pistons with a lower piston pin to crown height.

The lower compression ratio would allow one of the compression rings to be removed thus reducing mechanical friction.

part of the remaining loss would be air leakage, specially in an old engine, effectively the "spring" is stronger on the compression that on the expansion stroke as some air has leaked out. Also, the compressed air at the top of the stroke is hot, and heat is lost there, so on expansion the colder air has less pressure. removing valves to lower compression would help but there is also some increased loss from increased surface area absorbing more heat, and pumping loss.
How about removing rings completely, cut the crown off the piston? this would remove all compression and also lower friction loss as there are no rings and piston friction is also reduced as this is controlled by side thrust due to downward thrust on the crown being translated into side thrust by the angle of the connecting rod.
Ultimately, a smaller engine transplant may be better, like the 3 cyl diesel one on this forum. But I guess this would be cheaper. also consider adding a turbo with this mod to get power back to where it was, you will still get the efficiency gains.