Potential engine mod? Otto to Atkinson conversion

[freebeard]

http://http://en.wikipedia.org/wiki/Scuderi_engine

Originally Posted by Allch Chcar

The 1.3 liter 4 banger used in the Festiva is the smallest 4 banger I've seen

VW shipped a 1.1 liter four-cylinder engine starting in 1936.

[Teemo]

So with Atkinson conversion it again comes to tradeoff: more mpg vs. power.
As I understand it Atkinson conversion can be made without cam timing adjustment. Instead it can be done by raising the static compression ratio and limiting the throttle opening. Throttle opening limit dependent of the engine revs. But this is not safe, because if one accidentally opens the throttle full, he will blow up his engine.

-raise the static compression ratio
-limit throttle opening (dependent of engine RPM, lower the rpm --> less max opening)

[Hugh Jim Bissel]

In this post on the Prius engine swap thread I was wondering about how easy swapping one of the Prius engines (1nzfxe) for the engine in my 03 Pontiac Vibe GT (2zzge) would be. This got me to wondering if since my current engine has 2 different cam profiles (1 for regular operation, and the 2nd for high rpm power) if by taking manual control over the switch between profiles would I be able to selectively "derate" my engine?

Almost certainly this could be done with a new/recut camshaft, but I was curious if my existing cam could do the job. Looking at the numbers (copied below) from this pdf it seems the intake stays open later, but I'd like to get the opinion of someone who actually knows about this as to how they think my engine would behave if I switched it to the 2nd cam profile at 2500-3500 RPMs (abt55-75mph in top gear). Pictures in the pdf make it look as if both profiles are on the same cam, so while one profile can't be rotated relative to the other (without regrinding), I believe intake can be rotated relative to exhaust if that will make a difference.

2ZZ-GE Valve Timing Chart

.	.	Exhaust	.	.	.	.	Intake	.	.
.	Open BBDC (CA)	Close ATDC (CA)	Lift (mm)	Duration (deg)	.	Open BTDC (CA)	Close ABDC (CA)	Lift (mm)	Duration (deg)
Low	34	14	7.6	228	.	-10 to 33	58 to 15	7.6	228
High	56	40	10.0	276	.	15 to 58	97 to 54	11.2	292

All data from PDF linked above, with exception that duration is from Wikipedia

The goal of this would be to get my throttle open more when cruising at highway speeds: since at 65ish I'm already pushing 3000rpms I'm at a very low throttle opening, by switching to a "modified atkinson" cam profile I cut my power produced, resulting in a wider throttle opening, less pumping loss, and higher mpg at the same speed. Right now the 2nd cam profile dosn't kick in till above 6000rpms, and I never go up that high in daily driving.

[beachmezz@gmail.com]

A quick question 'could the same effect (A reduced fuel/air charge) be accomplished by simply closing the intake valve earlier before the cylinder is completely filled?

[Angel And The Wolf]

The purpose of the Atkinson cycle is to allow more travel on the power stroke(30% more in the Prius engine) to extract more of the energy from the burning expanding gasses, and the same 30% more travel to push the (now lower pressure) exhaust gasses out.
The late closing intake valve looses that extra 30 % of air, before compression begins, so in the 1.8L Prius engine, effective engine size is reduced to a 1.4L engine for compression purposes, with an extra .4 ltrs of travel for expansion and exhaust.
This captures more of the power, and eases the energy needed to exhaust the spent fuel.

Closing your intake valve early would create a lower pressure in your cylinder which your piston would have to fight against in order to continue to descend.

Your best bet would be to regrind your intake cam for a longer duration open time, (starting at the same degree, but remaining open more degrees after BDC) realizing that whatever portion of the former compression stroke your intake valve remains open would reduce your effective engine size and power, while also decreasing it's pumping losses.

Don't forget to reprogram your fuel injectors for less fuel per stroke, and to not spray during the open intake valve period.

If you are worried about losing power for passing, you can install an electrically driven supercharger coupled to a Wide Open Throttle (WOT) switch for when you want acceleration rather than economy.

[zonker]

I'm bringing this post back from the dead. I'm seriously contemplating doing this with a Geo Metro 1.0 3 cyl.

So far what I have learned is the Miller and Atkinson engine designs are similar by limiting the intake cylinder fill by either closing the intake valve before TDC (miller cycle) or closing the intake valve after TDC (atkinson) in order to limit the amount of cylinder fill. The advantage to this comes in less volume and effort required to compress the air/fuel mixture while giving it a full amount of stroke to expel all the exhaust gases.

Since most all hybrid applications have been using the Atkinson principle, I think I will stick to that design.

My understanding is that it will be an absolute slug off the line so that is why it is integrated with the torquey electric motors of a hybrid.

A 25% power reduction can be expected when comparing Otto cycle to Atkinson so my 55 hp Geo motor will reduced to 41 hp. I can live with that if it means a 65mpg runabout with a 75 mph top speed.

So... am I the first adopter here at ecomodder or has someone else tried this before me? If so, I'd love a little sound advice.

Rob

[Angel And The Wolf]

I'm not sure if this would increase your economy, as the engines which use the intake valve type of Atkinson cycle have about 30% longer power stroke than effective compression stroke. Your engine will have the standard stroke, without the extra length at the bottom for extracting the full energy from the expanding gases. (See my post from 2013) Maybe if you shave the deck to obtain 13:1 compression ratio, AND re cam your intake valves to close when the pistons are 30% of the way up, (or, alternatively, you could have your exhaust valve open for that 30% compression stroke. I'm not sure which is best.) Yes, your intake volume (and power) will be 30% lower, but your compression ratio will be the same as stock, (rather than 30% lower) with a longer power/exhaust stroke. For occasional full power, you could add an electric turbo to turn on when your accelerator pedal is fully depressed, to restore your full intake volume for acceleration needs.

https://www.youtube.com/watch?v=7a_J2X88fSE

[Angel And The Wolf]

Originally Posted by zonker

Since most all hybrid applications have been using the Atkinson principle, I think I will stick to that design.

Just curious, how will you do that?

[cRiPpLe_rOoStEr]

Originally Posted by Angel And The Wolf

Closing your intake valve early would create a lower pressure in your cylinder which your piston would have to fight against in order to continue to descend.

Wasn't exactly this what Volkswagen tried with its "Budack cycle" engine?