VVT or variable valve timing (VCT in the world of Ford) isessentially an electro mechanical trick to achieve to a much finer degree what hot-rodder's have attempted for decades in seeking higher power levels from their engines.

Where I get this wrong...please correct me as this is a thought experiment!!!

By more precisely timing the ignition and exhaust events in every stroke of the piston VVT seeks to maximize the power of each combustion cycle while also minimizing emissions. In addition a good VVT system can minimize the effects of the bad or lower octane fuels, differences in atmospheric pressure and air density, and probably some other things I'm missing; all through varying the time periods in which intake and exhaust valves are open or closed and the precise moment at which to ignite the air/fuel mixture in the compression stroke to take full advantage of the mechanicaladvantage of the descending pistons force acting on the crankshaft.

While the mechanical aspects of each cylinders maximum compression of the fuel/air charge is fixed, let’s say 10 to 1, the actual level of compression of any individual firing cycle is dependent upon the moment in which the charge is ignited.

If ignited too early by too great an advance that fires the charge while the piston is still rising the engine grenades as the rising piston is forced downward by the explosive mixture. (Given the time necessary for the ignition to actually fire and the mixture to ignite there is a 'sweetspot' prior to TDC that is 'safe' to use to get maximum mechanical advantage. I believe in the Ford system it may be as much as 15 degrees before TDC).

If fired too late as the piston is near the bottom of its stroke as it descends the charge is wasted producing little effective mechanical force. (Again, in the Ford's application I think they can delayignition as much as 45 degrees AFTER TDC) In the case of any ignition that ACTUALLY occurs past TDC the actually compression of the mixture is beginning to fall, and the later the ignition occurs the lower that compression becomes until it's actually not compressed at all and is being sent out the tailpipes during the exhaust cycle. In essence our high compression engines become a low compression low power lawn mowers all in an attempt to control knock and emissions.

There's a lot going on here and damn little time to do any of it since at 6000 rpm each cylinder is firing 3000 times, or 50 times every second!! If something gets out of sequence even a little bit bad things happen very quickly<G>

This next bit is one I stumbled on awhile back and it serves to remind me of how ingenious and complicated engines have become and how little we think about what makes it all possible. I added it just for fun.

DEFINITION OFACCELERATION

"One top fuel dragster 500 cubic inch Hemi engine makes more horsepower than the first 4 rows of stock cars at the Daytona 500.

It takes just 15/100ths of a second for all 8,000+ horsepower of an NHRA Top Fuel dragster engine to reach the rear wheels.

Under full throttle,a dragster engine consumes 1-1/2 gallons of nitro methane per second; a fully loaded 747 consumes jet fuel at the same rate with 25% less energy being produced.

A stock Dodge Hemi V8 engine cannot produce enough power to drive the dragster's supercharger.

With 3,000 CFM of air being rammed in by the supercharger on overdrive, the fuel mixture is compressed into a near-solid form before ignition.

Cylinders run on the verge of hydraulic lock at full throttle.

At the stoichiometric(stoichiometry: methodology and technology by which quantities of reactants and products in chemical reactions are determined) 1.7:1 air/fuel mixture of nitromethane, the flame front temperature measures 7,050 deg. F.

Nitro methane burns yellow... The spectacular white flame seen above the stacks at night is raw burning hydrogen, dissociated from atmospheric water vapor by the searing exhaust gases.

Dual magnetos supply 44 amps to each spark plug. This is the output of an arc welder in each cylinder.

Spark plug electrodes are totally consumed during a pass. After halfway, the engine is dieseling from compression, plus the glow of exhaust valves at 1,400 deg. F. The engine can only be shut down by cutting the fuel flow.

If spark momentarily fails early in the run, unburned nitro builds up in the affected cylinders and then explodes with sufficient force to blow cylinder heads off the block in pieces or split the block in half.

In order to exceed 300 mph in 4.5 seconds, dragsters must accelerate an average of over 4G's. In order to reach 200 mph (well before half-track), the launch acceleration approaches 8G's.

Dragsters reach over300 miles per hour before you have completed reading this sentence.

Top fuel engines turn approximately 540 revolutions from light to light! Including the burnout, the engine must only survive 900 revolutions under load.

The redline is actually quite high at 9,500 rpm.

Assuming all the equipment is paid off, the crew worked for free, and for once NOTHING BLOWS UP,each run costs an estimate $1,000.00 per second.

The previous top fueldragster elapsed time record is 4.428 seconds for the quarter mile (11/12/06,Tony Schumacher, at Pomona, CA). The top speed record is 336.15 mph as measured over the last 66' of the run (05/25/05 Tony Schumacher, at Hebron, OH). SpencerMassey 3.728 seconds June 2012 and Spencer Massey again 332 mph (1000') April2012

Putting all of this into perspective:

You are driving the average $140,000 Lingenfelter 'twin-turbo' powered Corvette Z06. Over a mile up the road, a top fuel dragster is staged and ready to launch down a quarter mile strip as you pass. You have the advantage of a flying start. You run the 'Vettehard up through the gears and blast across the starting line and pass the dragster at an honest 200 mph. The 'tree' goes green for both of you at thatmoment.

The dragster launches and starts after you. You keep your foot down hard, but you hear an incredibly brutal whine that sears your eardrums and within 3 seconds, the dragster catches and passes you. He beats you to the finish line, a quarter mile away from where you just passed him.

Think about it, from a standing start, the dragster had spotted you 200 mph and not only caught, but nearly blasted you off the road when he passed you within a mere 1,000 foot long race course.

...... and that is ACCELERATION!"

Do the math. At 200 mph your 'Vette is covering 220 feet per second so in 3.728 seconds you've covered 820.16 feet while Spencer Massey's dragster covered 1000 feet in the same amount of time from a dead stop!!!

 

As far as VVT goes, I understand it to be that the solenoids actually change valve timing. At low speeds it gives you the same timing as say a 1966 Cadillac profile. When it shifts it moves up the timing to be like a 1970 Camaro SS barely able to idle but runs beautifully at high RPM's. The people on other forums have said the car would barely run when a solenoid goes out. Kinda like it gets stuck in the '70 Camoro mode..

 

There are a few types of VVT, the simplest just alters cam phasing in relation to the crank at different speeds, nothing is going to out sequence. I guess as always sophistication comes at a cost, but this all seems to work pretty well as the VVT engine in my truck is still going fine after 400k kms.

Top Fuel faster than street sedans? you bet , but the fuel consumption is just terrible, and cornering best not discussed

 

My only knowledge of Cadillac's was my dad's '59 Sedan De Ville and it's 390 V8 produced some 345hp and gobs of torque because it had to move 5000lbs of car to at least freeway speeds sometime before tomorrow morning<G> On the other hand my 73 Camaro with it's small block L48 350 put out a measly 175 hp due to emissions restrictions but the car was lighter and with the 3spd.manual and a 2.63 rear it had fairly long legs.

So yes VVT tries to give us the best of both worlds.

 

Back in the early 70's and the first fuel shortages when finding a gas station that would sell you more than 10 gals. at a time and most were closed on weekends (I know because I was there and searching along with everyone else) the average big sedan was lucky if it could give you 10 miles to the gallon and had more than 250 hp out of it's fairly large V8. The papers were full of stories about how the IC engine was a dead dinosaur walking and the first crude electric cars were being touted as the next big thing.

Today we have small V6's putting out well over 300 hp while delivering fuel mileage in the mid-20's (and some approaching 30) and in some areas exhaust air that's cleaner than what they take in.

All of that and more is because of the advances in fuel and air management achieved through the use of things like VVT and other electronic magic along with engineering and assembly that makes most of today's engine's built to the standards of a Swiss watch. In the late 60's it was fairly common knowledge that the near legendary small block Chevy engines could get an additional 50+ hp simply by balancing and blueprinting their parts so they actually achieved their design specifications and more; even without the use of whiz-bang injectors and computers.

Some might remember the Chevy 409 and it's advertised 409 hp. out of 409 cubic inches but today Jaguar and plenty others are getting that much out of engines hardly half that large and making them run on 92-93 octane fuels instead of 104-110.