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Forced induction and cylinder deactivation

11K views 8 replies 6 participants last post by  Telco 
#1 ·
I've got both turbos and superchargers down pretty well, for one who has never actually had one.


However, cylinder deactivation has me thrown for a loop on this. Does anyone know how well forcing an engine that can shut half the cylinders down randomly works? I actually come from the GM world (my Charger is the first Dodge I've ever owned) and over there they just shut the cylinder deactivation down in the computer.


My question is, has anyone worked out how to force feed their engines and keep cylinder deactivation too? One of the things I've always enjoyed on cars with cylinder deactivation is to try and keep it in 4-banger mode as much as possible, on the other hand I LOOOOVE the feel of being pushed back in the seat when I punch it. My first cars were either high output small blocks or high output big blocks, and I loves me some power. What I'd really love though, is having my cake and eating it too.


If it's not possible then at some point in the future I'll probably just stroke and bore the existing engine to get the big punch. The advantage here is the car would stay in 4cyl mode longer when cruising. I'd just like something now, like in the next year.
 
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#2 ·
I'm sure others who have forced induction will be able to help you better but, from what I've read on here, any engine upgrade (cams, etc) mean that the MDS lifters have to go. They aren't designed with strength in mind and will fail when pushed too hard.

And, the cylinders aren't shut down randomly. It's a function of speed and throttle position. I've had my car go into 4 cylinder mode at 30 when cruising through town. Mine is easy to tell when it does because I don't have a factory exhaust anymore.
 
#3 ·
I know the cylinder shutdown is a programmed function depending upon sensor input and from the computer's standpoint it is a set, predictable operation, but its effective operation is still random. Hit a hill it shuts off, top the hill it comes on. What the supercharger, which is pumping X amount of air in, is going to see is an engine that suddenly cuts its size in half. Same for a turbo. I'm just not sure if a blowoff valve would be able to keep up, or how well it would run when flipping modes, or even how it would sound.

If the specialized lifters won't handle it though, I guess that makes it a moot point. Thanks, appreciate it.
 
#5 ·
Maybe I don't understand it properly, but doesn't MDS just shut off spark & fuel? So technically you'd still be forcing the air through the same amount of displacement, just no ignition. The other 4 cylinders would just effectively be an air pump.
 
#6 ·
I think the lifters are shut off by a solenoid, so that the valves stay closed. Your engine then becomes a V4, with 4 pistons just bouncing off the air cushion trapped in their cylinder. I dont see why it wouldnt work, and long as MDS can be tuned to never come on under boost
 
#7 ·
Yes, fuel is shut off but the valves are also closed off. The computer uses a solenoid to control oil flow, which is what activates/deactivates the valves. You'd think compressing the air would steal power from the engine, but as it was explained to me the air acts as a spring and puts almost all of the energy taken off the crank to compress the air, back into the crank as the air in the cylinder decompresses.

I'd only be interested in doing this if I could keep the MDS system working. In any case, won't be touching it until the warranty goes.
 
#8 ·
You will want to replace the MDS lifters when putting on a blower. Replacement is also recommended for high lift Cams. I do not know of anyone that keeps the MDS with FI. I have been told they will fail with boost .

CompCam even recommends to replace the MDS lifters with their cams.
 
#9 ·
Heh heh, thanks, but I want to keep MDS. I like that system and it's one of the reasons I went with the Charger. Otherwise I'd be in a Chevy SS. I'll be honest, I like the Charger but if the SS had come with AFM, VVT and direct inject heads I never would have looked Dodge.
 
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