You've heard of varaible valve timing?

How about variable compression?


Now just about everything is adjustable: spark timing, mixture, valve timing, turbo boost, and now compression. Thanks to powerful computers…


We recently had a thread on this subject.
I’ve read articles on it, but until/unless it hits the streets I have mixed emotions. Added complexity to squeeze and itty-bitty-bit of extra mileage out of ICEs seems to me to be looking for problems in the long term.

I wonder what we’d get of we mixed variable compression with variable valve timing, stop-start systems, and direct injection. I have to wonder if it’d be reliable in the long term. Or affordable. Or worth it. Only time will tell.

It’s on the streets, the new Infiniti QX50 has it now.

Saab developed one 18 years ago. GM wasn’t interested.

High compression for efficient part throttle driving, lower compression with turbo boost for more power.

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It’s funny, driving an old vehicle, and having had issues with variable spark timing, I’m not excited about adding more complicated systems like variable valve timing and variable compression to my future cars.

Give me a simple small underpowered car and engine and I’ll be happy to accelerate through the curves and turns while the larger vehicles have to slow down in the same curves and turns. It’s more fun than only being able to accelerate in a straight line under massive power anyway.

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Does adding complexity to a system really make a difference anymore? Everything in cars is so complex from a systems perspective. Heck, even on my 11 year old Acura the climate control isn’t just an air conditioner and heater, it’s a voice-activated dual zone temperature-select system with a sun angle sensor that makes the side of the car facing the sun blow harder than the other side, which it accomplishes by talking to the navigation system.

God help me if that thing ever breaks. I ain’t fixin’ it. It’s actually kind of a miracle I can still do my own brake jobs and spark plug changes.

When the prospect of the heater not working means a bill that looks more like the money for an engine swap, I think we’ve gone beyond rationality from a complexity perspective.

I’ve almost gotten to the point where I’m not sure I should care enough to get upset about overly-complex developments with internal combustion engines. They’re in their death throes. Electrics are going to take over sooner than later, which will be nice from several perspectives, not the least of which being that an electric motor is a whole heckuvalot simpler than even a 4-banger from the 1980’s.

Ooohhh agree with that. If compression ignition gasoline engines catch on - Bye bye, spark plugs plugs

If electric calipers ever become a thing - and there are more than a few working on it - you might not be able to change pads without a computer.

Brave New World…

We’re looking at two different perspectives here.

I’m driving a car with a busted and air conditioning system and a radio that barely works because the volume knob is worn out, and I don’t intend to replace or repair either system. A car that can run 300,000 miles without any major engine failures appeals to me. I’ve chosen to live without air conditioning rather than continue to replace the compressor every 2-3 years and use a bluetooth speaker rather than replace the radio and speakers.

You’d probably have dumped my car and moved on to the next one years ago. I decided to buy a new motorcycle instead and keep driving my clunker. If things keep going well, I may keep it until it turns over 400,000 or 500,000 miles.

I look forward to things getting simpler. Migrating to a plugin electric lawn mower has been great. However, before that happens, hybrids and internal combustion engines are getting more complicated, not less. I’m just glad I can still buy a motorcycle that has a relatively simple internal combustion engine, and I also look forward to someday commuting on an electric motorcycle.

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My limited experience with valve train complexity is that it works like window panes or shaving blades. There is a big improvement when you go from single pane to double pane, or single blade to double blade, and less and less benefit as you go from double to triple or quad.

My 1997 328i BMW has VANOS only on the intake cam. This significantly improved the power delivery across the RPM range and helped the mileage. Other than needing to replace the VANOS O-rings every 10 years or so as they get old and hard, it is a very robust and reliable system. This 5 speed stick gets 30 mpg highway and now has 337k miles with no major repairs.

My 2004 325i BMW has dual VANOS. Performance improvement over single is not noticeable. Still pretty reliable needing only O-rings every decade or so. This 5 speed stick gets 26 mpg highway. Where is the benefit?

My 2013 328i BMW has dual VANOS and adjustable valve opening. This is WAY more complex and troublesome than just VANOS, and increases the labor for a routine valve cover gasket replacement from 1 hour to 6 hours. This car gets 24 mpg highway. Where is the benefit??? I will admit that this engine runs silky smooth, but if I were interested in silky smooth, I would have bought a Lexus. Can we go back to what worked and lasted forever?

What you’re describe is a phenomenon called “diminishing marginal return.” It’s part of the reason Continuous Quality Improvement isn’t really continuous. You eventually reach a point where the gains aren’t worth the effort anymore.

The thing about variable timing is that it has dual benefits. It gives you better fuel economy, but it also gives you an aggressive lobe profile on the camshaft when you mash the accelerator, making the valves open and close at points in the combustion cycle that maximize power. Then, when you’re cruising at 70 MPH using the cruise control or with the throttle barely open, it switches to a lobe profile that maximizes fuel economy. In the end, variable timing ends up adding a fun aspect to how the car drives when you mash the throttle. @bscar2 knows this pleasure. He has described the experience of “the VTEC kicking in.”

The difference is that VTEC is, or at least was (I’m not sure how they’re implementing it now) one of those brilliant ideas that was actually pretty simple. It was actuated by oil pressure. High RPMs would make the ECU open up an oil pressure solenoid, and the oil pressure would move a pin that locked the rocker arms together which made them use the high-lobes on the camshaft.

Pretty much as long as you didn’t let the oil level drop too low, VTEC worked. There are ratty old Preludes and Del Sols running around that haven’t seen the inside of a shop other than Jiffy Lube in over 50,000 miles, and the VTEC still works fine.

I doubt we’ll be saying the same thing about @Manolito’s 2013 BMW, which is unfortunate because it would be nice if BMW would start building solid cars again instead of rolling gadgetfests.

I second that, for their motorcycle line.

I haven’t had VTEC anything in almost 10 years.

Me neither, but then I haven’t owned anything made by Honda in over ten years. VTEC is a Honda trademark.

My 99 Civic was the last Honda I owned, and that was just before I bought my CX-7 back in 2010.
Maybe if @Whitey would care to elaborate on why he tagged me for it, I could better understand.

Since you are here , is the Mustang GT all taken care of now ?

I posted in the thread I made, but, yeah, everything is in order, I even have the title info to get my plates now

I thought I remembered you mentioning it once. Maybe I was mistaken.

I have owned a VTEC, it is a kick in the pants. A bit like the secondaries opening up on old 4 barrel carburetors. Flawless on a car with 107,000 miles that never had any internal engine work done.

Variable vale timing is something else entirely. My last 2 Mustangs have had variable valve timing that allowed about 50 degrees of camshaft timing change. Just 2 cams on the '07 and 4 on the '13. Totally seamless operation.