The potential for advanced cam timing....

[takza]

This isn't something I've done...but something I probably will. I'm putting it here so the info won't get lost and so any informed comments will collect.....

Basic info:

The single most important valve timing event when considering an engine’s desired operating range is the intake closing event. The reason for this is that there is only a given amount of time to complete any process within an engine at a given speed; as engine speed either increases or decreases, there is a corresponding increase or decrease in time available for properly filling the cylinder. Therefore, for increasing engine speed, the intake valve must be closed at a later time due to the decrease in time given for completion of cylinder fill.

(Retarded cam timing) However, closing the intake valve at a later point in the cycle will hurt low end performance to some degree because of the fact that there is not enough charge velocity at low engine speeds to maintain the high inertia needed to completely fill the cylinder. The result is a certain amount of reversion of the charge back into the intake manifold at low engine speeds, which results in lower signal across the carburetor and poor idle and throttle response characteristics.

(Advanced cam tming) Conversely, if an earlier intake closing point is selected, the engine will have good idle characteristics and tremendous low speed throttle response and torque. The trade-off in this scenario is that as engine speeds rise, the valve will close before cylinder fill is complete, resulting in a decrease in power at these elevated engine speeds.


Finding out how the 3AC is setup:

<a href='http://www.iskycams.com/degreeing.html' target='_blank'>http://www.iskycams.com/degreeing.html</a>


CHECKING VALVE OVERLAP WITHOUT DEGREE WHEEL OR DIAL INDICATOR

When installing a camshaft, or when an occasion arises where it is necessary to make a check on valve timing and no appropriate instruments are available, the recommended Isky procedure is as follows:

Insert the camshaft and mesh the timing gears on the stock marks. Do not as yet install the timing gear cover.

Adjust the valve lash of the intake and exhaust valves of the No. 1 cylinder.

Using a long wrench or lever, turn the engine over in the normal running direction. Use enough leverage to get an even, steady movement instead of a jerky motion. Rotate until the intake and exhaust valves of No. 1 cylinder are in the overlap position (both valves opened slightly). Stop exactly on T.D.C., which is marked on the harmonic damper.

Now loosen and back off the rocker arm adjusting screws until the intake and exhaust valves are just barely closed. Lock the adjustment screws so that the intake and exhaust valves are at exactly zero clearance.

Now turn the engine over exactly one revolution of the crankshaft to T.D.C. on the harmonic damper. You are now at T.D.C. on the compression or firing stroke.

Take Notice! Now there is a large space between the rockers and valve stem tips. The space indicates the actual amount the valves were open at T.D.C. of the overlap period (less valve lash, of course).

We will measure this gap space by probing with common feeler gauges of various thicknesses combined until we determine the gap space.

After computing the gap, record the figures for both intake and exhaust in your notebook. If the amount of gap on intake and exhaust is exactly the same, you have a perfect split overlap.


Various comments on results from advancing cam timing:


"I really liked the cam in my Cougar 351W when I had it advanced (by
mistake) a WHOLE tooth on the chain.... It made for GREAT stoplite power
and even good mileage.... but ran out of poop at 4500 or so..."

"By advancing the cam, the valves open and close earlier. Duration and overlap remain unchanged. Advancing raises the cylinder pressure (due to earlier valve closing) This improves low end and mid-range torque at the expense of some top-end power. The result is similar to using a shorter-duration cam since the intake valve closing point is more critical than its opening point.

Trial and error is usually the best method when advancing or retarding a cam to alter performance. Our experience indicates that cam advance of 2' to 6' should give the best overall performance.

Advancing and retarding a camshaft will move valves closer to the piston. Valve-to-piston clearance must be checked after advancing or retarding alterations to prevent possible engine damage. Also, changing the cam timing will also change ignition timing, which must then be reset."

"Just installed Mikes 10 Degree cam sprocket on a 90 metro this weekend. Engine is basicly stock. It is without a doubt worth every penny. The car has a lot more power and pep. It brought the idle up approx 75 - 100rpm. The midrange power is really noticable. Mileage on the highway has actually increased a small amount. 1 - 2 mpg. City seems to be about the same as before. With some pedal to spare."

"The main thing I noticed is the ability to "lug" the engine, and no more detonation. NONE. (Found out by accident doing a 2nd gear start.) At about 10 mph I can shift into 4th gear and slowly climb up to 55 without any spark knock at all. That is really awesome! And everyone knows how easy these 3 cyls will ping when loaded down. This valve train likes the 10 degree advance over the stock gear."

"My car now has a unique ability to lug the engine like crazy, (rolling 4th) without pinging. It’s really weird but it can. It pulls really great in 3rd gear now. I can now hold 5th gear on some hills, where before I would have to downshift to 4th. The true testimony of Superflys gear happened this week when my wife HAD to drive the car. (She hates it, or use to) It has been over a few months since she last drove it. “It’s too slow, I can’t get going with the other cars “. After she got back from her little trip she asked, “what have you done with the engine in this thingâ€Â

[GTSSportCoupe]

I wonder if the 3AC uses the same cam gear as the 4age? There are lots of aftermarket adjustable cam gears available for the 4age. Performance adjustable cam gears allow a pretty wide and continuous range of adjustment.

Here is one on ebay:

<a href='http://cgi.ebay.com/ebaymotors/ws/eBayI ... ename=WDVW' target='_blank'>http://cgi.ebay.com/ebaymotors/ws/eBayI ... me=WDVW</a>

I think that there are a couple of companies that make aggressive aftermarket cams for the 4AC. I believe these cams will fit in the 3AC too. Between the cam and cam gear you could probably gain 15hp. With a better carb, the 3AS exhaust manifold, and 2" exhaust piping with a high flow muffler and cat, you could probably gain another 10hp. This would put you at a whopping 85-90hp .

[Adelard of Bath]

My volvo has a hotter cam, but I have less torque at the bottom...people here seem to have a grasp on it, but it's funny the number of people I hear who don't realise that an engine can only do so much, and changing to a "higher HP cam" that power has to come from somewhere...

This topic came up on my volvo board not very long ago, everyone seemed to agree that advancing the cam a whole belt-tooth was way too much, so they recommended getting the adjustable gear

[GTSSportCoupe]

My volvo has a hotter cam, but I have less torque at the bottom...people here seem to have a grasp on it, but it's funny the number of people I hear who don't realise that an engine can only do so much, and changing to a "higher HP cam" that power has to come from somewhere...

Different cam profiles basically just shift the peak torque of the engine higher or lower in the rpm range depending on their duration and lift (which affect flow velocities/volumes of the intake charge). A 'hot' cam looks like it makes more power because it is optimal higher in the rpm range and hp = (torque*rpm)/5250, thus a higher hp # is produced. Many people don't realize that hp is just a product of torque. Torque is what moves a car. Some of those big new diesel pick-up trucks have 600-700ft/lbs torque, but only 300-350hp. They may only have a hp to weight ratio of 88hp/ton, but they have a really high and broad torque band. These trucks can out accelerate many a sports car that has a higher hp to weight ratio.

I was sort of joking about the hot cam/exhaust/etc in my post above. These would not be appropriate modifications for a 4wd. For a sports car operating in the upper rpm range yes, but not a low rpm 4wd.

[Adelard of Bath]

If someone was actually serious about offroading and dedicated enough, they could do what they could to move the curve to the lower speeds as much as they could...

Actually, to me, I prefer the feeling of being able to skyrocket away from stoplights, rather than have alot of power at speeds that are illegal...so i've never got into the whole cam swap thingie

basically though the engine is only a certain size, and thus can only hold a certain amount of air, which can only support a certain charge of fuel, and there is a certain amount of energy stored in the fuel, and there's nothing you can do about. Unless you start compressing the air, super-charging the...well the charge.
heh

but here we are preaching to each other about things we already know.

cool.
heheheh

[Typrus]

Drop in a V-Tec.. Why have 1 cam profile when you have one that changes equivalent profile at speed? Maximum lowend efficiency meets maximum high-end horsies.
Just look up how V-tec works.. Very smart.

[GTSSportCoupe]

Drop in a V-Tec.. Why have 1 cam profile when you have one that changes equivalent profile at speed? Maximum lowend efficiency meets maximum high-end horsies.
Just look up how V-tec works.. Very smart.

Variable valve timing and lift/duration is pretty awesome alright.

I had a really good idea for the ultimate head design with infinitely adjustable timing, duration and lift (where as now, only the timing is infinitely adjustable). My idea would also massively reduce rotating mass of the engine, giving better throttle response. Actually, it would eliminate the need for a throttle completely.

Simple: Have electronically controlled valves. Use solenoids to open and close the valves. Sure it will use lots of current, you'll need kick ass solenoids, and I'm sure there will be other issues, but the technology is there, and it would be way better than all the complicated expensive mechanical components currently used for vtec/vvti/etc. The car would be completly drive by wire. At idle, the valves would barely open, just enough to keep the correct idle speed. Through the entire range of operation of the engine, all cam characteristics could be varied infinitely according to a 'cam map', similar to injector duty cycle on a fuel injected engine. This would be AWESOME for racing applications. It's like having the perfect cam. Imagine the torque curve of the engine...and the high revving ability without valve float etc.

Yet another idea with no money to develop...although I've heard rumor that some automanufacturers are working on something like this.

[Pegger]

I think that's a pretty good idea.

The economy, power, throttle response torque and power at a much wider RPM range ETC...

However I'm not sure an electric solenoid would be fast enough to be the actuating components behind the valve movement.

I don't know much about solenoids, but I do think they are generally a slow operating device...

Not pooping on your idea... it's great.

I think electronically controlled hydraulically actuated might do the trick... It's used on modern fly by wire aircraft and as far as I know it's next to instantaneous response...

Guy

[Chris]

I was wondering if anyone knows how many different cam profiles are available for the 3-A/3-AC engines. I know of two off the top of my head.

[Gasoline Fumes]

Drop in a V-Tec.. Why have 1 cam profile when you have one that changes equivalent profile at speed? Maximum lowend efficiency meets maximum high-end horsies.
Just look up how V-tec works.. Very smart.

Variable valve timing and lift/duration is pretty awesome alright.

I had a really good idea for the ultimate head design with infinitely adjustable timing, duration and lift (where as now, only the timing is infinitely adjustable). My idea would also massively reduce rotating mass of the engine, giving better throttle response. Actually, it would eliminate the need for a throttle completely.

Simple: Have electronically controlled valves. Use solenoids to open and close the valves. Sure it will use lots of current, you'll need kick ass solenoids, and I'm sure there will be other issues, but the technology is there, and it would be way better than all the complicated expensive mechanical components currently used for vtec/vvti/etc. The car would be completly drive by wire. At idle, the valves would barely open, just enough to keep the correct idle speed. Through the entire range of operation of the engine, all cam characteristics could be varied infinitely according to a 'cam map', similar to injector duty cycle on a fuel injected engine. This would be AWESOME for racing applications. It's like having the perfect cam. Imagine the torque curve of the engine...and the high revving ability without valve float etc.

Yet another idea with no money to develop...although I've heard rumor that some automanufacturers are working on something like this.

Yeah, a few auto manufacturers are working on it. At least they were a few years ago, I haven't heard much lately. One problem was getting the valves to close slowly like a cam lobe can. The solenoids tend to just let the valve slam into the seat too hard, causing damage or accelerated wear. By the way, some BMWs don't have throttles. They have variable ratio rockers instead. Maybe it was the 7-Series or M5?

[takza]

Next timing belt change or whenever I get inspired to do it...I'm going to try moving the gear one tooth advanced and test it using the 30 to 55 MPH power test.

First I can see if 9 degrees advance is livable...and test any resulting power and MPG improvements. Or see any downside.

I won't mess with another cam cause it's relatively expensive and risky to replace a functioning cam...while moving the cam vs belt one tooth is free...except for the labor involved.

For my purposes...9 degrees might be about right...I could count to both hands the number of times I've hit 5K with the Tercel....though it will wind up there real well. The fact that it will...tells me that torque will benefit from advanced cam timing.

I want more grunt power offroad, better MPG, and better usable power in everyday driving. Combining advanced cam and ignition timing...MIGHT increase the tested "power" of the 3AC by maybe 35%? Advanced ignition gains at least 20% by my testing.

Anyone that happens to have their car apart can feel free to test this out before I do........ :blink:

[Retroloc1]

You can slightly change your timing when you mill your head to an hotter CR.

You generally finish between two teeth and so have to choose: 1/2 tooth sooner or 1/2 tooth later ?

[Adelard of Bath]

In college I had an IC-engines class and we talked about the whole solenoid thing, pretty sweet, also things like multiple valves, well everybody does that now....multiple sparkplugs, anybody run that anymore? or was that a failed technology...you could cut your flame propogation time quite a bit if you did it right

[Thereminator]

Takza,I think the 3-AC is a non-interfearance engine so you dont need to worry about valve-piston clearance...Right? B)

[takza]

One site listed it as an interference engine, but when my belt went...I had no problems. Another site listed it the other way.

I guess that with most engines...10 degrees wouldn't cause a problem even if it was interference.