I was reading in the archives and found this THREAD
I have a 6 cylinder engine that is carbureted (Garage Link), this would mean 2 sets of 2 cylinders have their power stroke at the same time. I would think since that was the case I could find those two and somehow rig a device to cut off the intake valve to those two cylinders once I was cruising.
In that thread some of the problems were there computer in the car going haywire over too cold an exhaust, shooting gas into a cylinder cause it doesn't have enough, and other things. The pistons and valves would all still be moving, which is creating friction. Would there be problems with reliability shutting off the air/fuel to a cylinder/pair of cylinders?
The other problem you were talking about was balance, I wouldn't be taking anything out of the engine so no problems there. Since I am going from 6 Cylinder to 4 there shouldn't be any problem with the engine being rough, if anything it should run smoother on 4 instead of 6.
The power strokes all overlap, but no two cylinders have their power stroke begin at the exact same time. A 6 cylinder engine has a power stroke every 120 degrees (720/6).
What your engine does have is that each pair of cylinders (1-2, 3-4, 5-6) share an intake port. It is an older design, but works. Take a look into cylinder head lump porting. The shared port arrangement actually results in intake ports that are too large and reducing port size can help improve intake charge velocity which will improve combustion, response, etc. (I've got a 230ci in a '65 Nova so I've looked around a bit for info on the Chevy six)
If you want to shut down cylinders you would need some way of disabling the valvetrain such that the intake and exhaust valves both stay closed but so that you can reactivate them when you need all six. With both valves closed, the air trapped in the cylinder acts like a spring so there are no pumping losses, just drag from the piston rings.
What you should really look for to improve your car is an overdrive. Back in the day they had overdrive units that bolted to the tail of your trans. You can sometimes find them on ebay but they are hard to come by. Other than that, you would probably want a T5 trans out of a Camaro from the 80's.
Ahh, I see what you are saying. It was a pipedream to disable cylinders anyhow . That aside I like the idea of an add on overdrive unit. Funny I didn't think of that as my brother has a suburban with an under/overdrive unit behind his th400. Not sure that it ever worked though as he couldn't tell the difference most of the time and I think it would be pretty obvious on the highway.
Do you know what kind of modifications I would have to perform to fit in an add-on unit behind my transmission? I am thinking getting a junker would be a better way instead of messing up this car. It is too solid for me to think of cutting up.
What kind of gas-mileage have you been able to get from your nova? I could never find anyone's mileage from a car like mine. And then I run into you here .
My dad had an early 80s red Cadillac Biarritz (I vaguely remember it) with the 4-6-8 engine. He said the concept was ingenious, but his car would keep switching from 4-6 cylinders on the highway as 4 wasn't quite enough to do 70mph. He also said something about the seals drying up because of lack lubrication and/or heat issues. Eventually, he just cut the wires and left it a straight up V8.
The Nova gets about 15mpg pretty consistently in about 50/50 city/hwy driving. It has a 3-on-the-tree as well and a 3.08 axle gear. The previous owner rebuilt the engine, so the cylinder compression readings on the 230 are stock - not that it has high compression by any kind of modern standards.
If you can find an original overdrive unit, there is really not much hacking involved. The overdrive just replaces the tailshaft of the transmission with a two speed planetary gearset. It is my impression that these were a factory option?
Interesting that Peakster mentioned the old Cadillac system, it is probably the best chance for cylinder deactivation! I actually have a set of the special rocker arms that they used in the system. They are very simple - solenoid driven and only two wires. I got them to put on my '70 Sedan DeVille, but if one were adventerous the mechanism might be retrofitted to the Chevy rocker arm system. Look around in junkyards - they were only on '81 Cadillac V8's but they are out there.
Aside from engine rpm/displacement considerations -
Maybe aero treatments like an air dam, belly pan or partial belly pan, and rear fender skirts?
Grill blocking behind that huge expanse of chrome grill?
- (I bet the few inches of grill next to each headlight assembly don't have radiator behind them).
Upgrade the ignition so there's a real good spark every time?
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.