Variable Cam Timing. Performance and lower Emissions - IMBOC
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post #1 of 9 (permalink) Old 03-18-2019, 08:15 PM Thread Starter
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Talking Variable Cam Timing. Performance and lower Emissions

Variable Camshaft Timing was developed by Ford, and first made it's appearance in the late 90's 2.0 Zetec engine. The early versions were either on the Intake cam, (improved performance) or the Exhaust cam, (reduced emissions.) The 2008 Bullit has variable cam timing, but since it is a SOHC, the effects on performance and emissions are a compromise. Variable cam timing traditionally operates with oil pressure driven cam phasing controlled by solenoids and the PCM adjusting for factors such as load and RPM. The disadvantage of early systems was the need for higher oil pressure and the resultant parasitic losses.
With the advent of the Coyote engine Twin independent Variable Camshaft Timing or Ti-VCT came into production. This new system provided the ability to advance or retard both the intake and exhaust cams independently. This provides greatly improved performance and lowered emissions, eliminating the EGR completely. The use of Borg Warner's Cam torque actuation (CTA), which uses torsional energy in the valve train to rotate the camshaft instead of traditional oil pressure driven cam phasing was also introduced.
Basically, there is a center lock position with oil pockets on each side and check valves. The phaser directs ratcheting advance or retard (based on load and RPM and...) and the oil pockets stabilize the movement in only one direction at a time aided by the check valves. So the oil pockets act as limiters but do not move the cam timing. The torsional energy of the cams rotation cause movement, and the phaser returns to center lock position for "cruising" operation. This system operates at lower oil pressures because the oil is not driving the timing changes. And, intake and exhaust cams can change timing independently to optimize performance and emissions. There's lots going on here and it requires a lot of computer power to bring harmony to it's operation.
The result of all this technology has taken the 4.6's horsepower of 315 all the way up to 480 HP in the 2019 Gen 3 Bullit Coyote.
What's next? Just read an interesting article on Microwave ignition, which they claim can add 30% more power and reduce emissions by 80%! Wonder if you'll be able to heat up your lunch as well?


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post #2 of 9 (permalink) Old 03-18-2019, 10:31 PM Thread Starter
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Believe it or not, I thought about this for a week, after reading several articles, and this is the elementary explanation of how it works.
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post #3 of 9 (permalink) Old 03-19-2019, 09:14 AM
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Very cool Matt's 08 is throwing a code that i think has something to do with one of these. he replaced the cam sensors hoping that was the issue but it could be the Alt also. it does it intermittent and one time when this happened he said it was knocking a little. when he started it after towing the car the knock was gone. we shall see... Everyone is telling him alt so i am wondering if it is one of the VCTS?

Bullitt 3130 has a few modifications mostly suspension and braking work for the fun twisty roads. and an teenage(16) female Mechanic who is driving and wants to track her car.

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post #4 of 9 (permalink) Old 03-19-2019, 09:30 AM Thread Starter
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Could be a solenoid or phaser? Alternator is an easy check. You'll figure it out.
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post #5 of 9 (permalink) Old 03-19-2019, 11:12 AM

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WOW, Thanks Pat for another GREAT technical article.

I "kind of" knew what these system did but had no details, other than oil pressure somehow controlled the system.

I also had no idea that this eliminated the EGR systems. That (EGR) system was one that was greatly misunderstood. Used correctly, it was something that could help your engine. I know many guys who just yanked they EGR systems off never realizing what they were really used for.


NOTE TO MODS/OWNER, is to possible to create a place that Pat can store this articles so they are in one place??? These are items that people will be referencing for years to come.
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post #6 of 9 (permalink) Old 03-19-2019, 11:40 AM Thread Starter
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Thanks Jack. It's a little different than when we built small blocks and cam timing was like + or - 5 degrees. They had to build wild camshafts with crazy lift characteristics to get the power. Now, just program the phaser for more intake duration.


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post #7 of 9 (permalink) Old 03-19-2019, 02:47 PM

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Thanks Pat, The ability to adjust intake and exhaust timing independently almost boggles the mind. Back in the day, you had to work with a cam manufacturer (grinder) to get cam timing, duration, overlap etc that you wanted. Lots of trial and error. Some things worked and others not so much. Now, you can do this via computer programming.

I guess I can understand why today's engines make so much more than the days of old. Weeks worth of research, assembly, testing can now be done in a matter of hours with computer adjustments.
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post #8 of 9 (permalink) Old 03-19-2019, 05:27 PM Thread Starter
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The Nascar boys still play with it, but at least they've gone to roller cams.


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post #9 of 9 (permalink) Old 03-20-2019, 12:55 PM

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I had VCT on the exhaust side of my 2000 ZX2 S/R. Once you spent time tuning that VCT right you could hear it just wanting to suck in more air. It really made a different in helping to extend the powerband and make the best power possible at every 500RPM interval.
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