4 Cylinder to 2 Cylinder Project

[dfeldt91]

I have been dissecting the ECU code for my 2001 Volkswagen Passat for a while now and am going to start a new project.

I am going to rewrite the ECU to turn my 4 cylinder 1.8 turbo motor into a 2 cylinder .9 liter turbo motor. I tried removing coilpacks and unplugging the fuel injectors for the third and fourth cylinders on another Passat I had but it ran really rough and wasn't drivable.

I am going to rewrite the software to ignore the O2 sensor, change the boost tables, write out two of the fuel injectors, write out the knock sensors and tell the ECU to ignore the misfires it will detect.

I am going to get the camshafts ground down for the extra cylinders, remove the valves and weld closed the hole, then modify the intake manifold so it does not have a passage to the cylinders. I'll also have to weld together a new exhaust system that only receives exhaust from two working cylinders with the nonworking cylinders being essentially open to suck in and push the air out of the exhaust side.

Has anyone done this before successfully? Either mechanically or using modified software as I am doing?

[Frank Lee]

Thought about it a lot.

I don't think all that welding is necessary. What if it sucks and you want to go back to four?

[Ecky]

My guess is that 2 cylinders won't be enough to maintain speed on the highway out of boost, depending on your gearing. You're probably better off regearing it and leaving all 4 cylinders enabled.

What RPM are you running at 50mph? My Insight's 1.0L 3 cylinder is practically WoT at 75mph at just about 3000rpm, but I have electric assist to make such a small motor drivable and give passing power. Granted, I practically never drive faster than 55 and it has plenty of guts at lower speeds, but your car weights almost exactly twice as much and has significantly worse aerodynamics. If you're frequently downshifting, you're going to ruin you economy as you'll be in a poor-BSFC range.

Honda's solution was, instead of reducing displacement, to run the motor lean keep the throttle plate open and reduce pumping losses, while keeping power on tap that doesn't require revving the snot out of it. I get the best economy at about 1750rpm with an air:fuel ratio of ~22-25:1.

[LittleBlackDuck]

Originally Posted by dfeldt91

I have been dissecting the ECU code for my 2001 Volkswagen Passat for a while now and am going to start a new project.

I am going to rewrite the ECU to turn my 4 cylinder 1.8 turbo motor into a 2 cylinder .9 liter turbo motor. I tried removing coilpacks and unplugging the fuel injectors for the third and fourth cylinders on another Passat I had but it ran really rough and wasn't drivable.

I am going to rewrite the software to ignore the O2 sensor, change the boost tables, write out two of the fuel injectors, write out the knock sensors and tell the ECU to ignore the misfires it will detect.

I am going to get the camshafts ground down for the extra cylinders, remove the valves and weld closed the hole, then modify the intake manifold so it does not have a passage to the cylinders. I'll also have to weld together a new exhaust system that only receives exhaust from two working cylinders with the nonworking cylinders being essentially open to suck in and push the air out of the exhaust side.

Has anyone done this before successfully? Either mechanically or using modified software as I am doing?

I see a number of holes in what you are planning:
Firstly you need to kill off cylinders that are firing 360 degrees apart. This means either 2&3 or 1&4 based on a normal inline 4 cylinder. This will ensure that the engine fires evenly.
Secondly, there will be a huge amount of remapping required to get the engine running correctly because of the changed intake and exhaust flow dynamics.
Thirdly, the turbo will be way too big as you have halved the engine displacement. This will mean staff all boost till you rev the guts out of it.

Welding up manifolds will achieve nothing on the intake side. On the exhaust side, leaving the ports open will cause these cylinders to run stone cold and potentially cause large amounts of distortion in the block and head as well as wasting lots of heat that will require fuel to be burnt to keep the engine at temperature.

Removing the oxygen sensor will cause the engine to run in open loop, again wasting fuel and polluting much more.

If you are really wanting to reduce fuel consumption, consider keeping the engine operating mechanically as it should and look at how Toyota has used the Atkinson cycle - mod the cam timing on the intake side, up the compression and possible reduce the stroke by swapping in a shorter stroke crank.

I would suggest looking at newer, smaller VW petrol engines that can be swapped in as a better platform for tinkering.

Simon

[Bill the Engineer]

It is going to run like a garden tractor, very rough and sputtery. Using only two cylinders in a 4-stroke engine is not dynamically stable. It creates a lot of rocking force in the engine that you will feel as a strong vibration in the car. To make it run properly would require a larger mass flywheel to keep up the crank speed between the widely spaced power strokes. It is not like a 2-stroke engine that fires every revolution. Each cylinder fires once every TWO revolutions.

Bill the Engineer

[Frank Lee]

My CB450 parallel twin runs smooth enough.

[MPGeo]

I have to agree with most of the comments already posted...

You would have to select the correct cylinders timing wise...
Eliminating the O2 is not beneficial...
Eliminating knock would do absolutely nothing since the remaining two cylinders would never knock under your proposed scenario...
Turbo lag would be ridiculous, and changing boost tables does nothing for you in this department...
Besides that, the reduced power output would still have to absorb the power requirements to move those two, now useless, pistons up and down for no reason.

But if you are like me, and won't take no for an answer until you try-it on your own, then I have a few suggestions before you cross the path of no return...

You don't want to grind the cam, simply remove your lifter/rocker mechanisms and you the lobes should not contact anything. You still should visually ensure that's the case, but I'm very confident that will be the case. That way you can re-assemble if need be without having to buy it/them again.

You really don't need or want to weld you valve ports shut. No need because your valve springs will make sure that those ports are properly closed unless your valves are not seating properly from wear or carbon build-up. But still you don't want to do this because if you maintain these passages closed the useless pistons would be fitting your other two working pistons in a perpetual compression stroke...

If I was to do this at all, I would remove the lifter/rocker mechanisms leaving the valves of the selected pistons closed, then I would remove the unused pistons... This would be the best option since it eliminates the parasitic losses created by those two useless pistons, and also allows you to not have to modify or even change either of the manifolds at all... at least not during initial testing phase.

But if removing the pistons is out of the questions then I would remove the valves for those unused pistons, and instead of welding anything shut I would leave both intake and exhaust ports fully open to the atmosphere. Simply because that would create the least amount of power loss, but this would require modified manifolds... Or I would remove only the exhaust valve so that I can still use my factory intake manifold without any modifications and only have to deal with the exhaust manifold... and this would do what you stated, pushing and pulling air out of the exhaust port.

Good Luck on your project!

[Ecky]

Originally Posted by MPGeo

snip

But if removing the pistons is out of the questions then I would remove the valves for those unused pistons, and instead of welding anything shut I would leave both intake and exhaust ports fully open to the atmosphere. Simply because that would create the least amount of power loss, but this would require modified manifolds... Or I would remove only the exhaust valve so that I can still use my factory intake manifold without any modifications and only have to deal with the exhaust manifold... and this would do what you stated, pushing and pulling air out of the exhaust port.

snip

I disagree. This way, OP will still get pumping losses. Plenty of manufacturers offer systems to close valves completely and quit firing several cylinders when cruising at low load, because the air inside acts as a spring, rather than simply sapping power by being pumped through.

https://en.wikipedia.org/wiki/Variab...der_Management

[Frank Lee]

FWIW I'd disable the valves on cyls 1 and 4 and pull the non-working pistons and con rods. Then I'd have to plug the oil ports on those two crank pins. I'd want cyls 2 and 3 to be the working cylinders because the rocking couple would be minimized. I don't think I'd try it on a turbo engine unless as someone said earlier a right-sized turbo was fitted. Stock flywheel should suffice. Stock manifolds too. O2 too. I'd put resistors equal in resistance to the injectors on injector leads 1 and 4. Might be naive but if ECU listens to the O2 sensor the mixture richness should be fine in spite of the reduced air volume moving through? It should be able to highway cruise just fine, although acceleration will be glacial vs stock. Fuel economy should be improved but not doubled; my WAG estimates better than 15% but less than 50% improvement. Mind you I haven't done this but this is how I'd start off.

[redpoint5]

My WAG is 0 MPG as the thing won't move.

This isn't the craziest idea to come out of Salem though. My dad hauled a 5th wheel camper with a 1965 Chevy stepside and a receiver made out of 2x10 boards with a semi-circle notched out in both. He captured the ball between the 2 semi-circles in the boards that were then bolted to the bed rails. His safety chain was a come along wrapped around the ball. We needed a landing strip to stop the thing at freeway speeds. The full tank of fuel got us to Portland and all but 3 miles back to home.

Dang camper is still sitting in the same place 25 years later. I have a feeling this VW would move a similar amount after the "upgrade".

Wouldn't the extra load on the 2 remaining cylinders cause premature wear? VW isn't known for reliability in the first place.