Actual cam timing

[K44]

I'm really struggling with where the cams are in relation to TDC or BDC

IE, is -20 on the on the intake cam 20 BTDC? 40? or what?

What are the separation angles at the widest and narrowest points?

Has anyone figured this out. I have searched for months and cannot find any answers.

This is for gen 2 but I am assuming gen 3 is the same.

Thanks in advance

[engineermike]

This is my take on it, but DO NOT take this as gospel. I took the cam angles and put them in "old school" terms of lobe centerline angles, lobe separation angle, and cam advance. I can transpose these into event relationship to TDC if needed.

In the gen3 tune, and I believe the gen2 to be similar, it lists the intake valve open at 340 and close at 599. The difference of which is 259. Information online seems to indicate gen1 and 2 were 263 duration but this could just be a small difference in how it is measure (cam vs valve and duration@? lift). It also lists exhaust valve open at 369. If we assume the same exhaust duration as intake, that puts the exhaust valve open at 110. All this assumes these are the values when the cam phasers are neutral (0, 0 in terms of the mapped point and OP cam angles).

This means that in old-school terms of cam centerlines, LSA, and advance, it would be described as follows at 0, 0.

Intake centerline: 259/2 - (360-340) = 109.5
Exhaust centerline: 259/2 - (369-360) = 120.5
LSA: (109.5 + 120.5)/2 = 115
Advance: 115 - 109.5 = 5.5
This sounds about right to me, knowing the characteristics of the engine running the phasers neutral.

Now we throw TiVCT in there and look at the extremes. The exhaust cam can only retard from the neutral state, but can move 50 deg. The intake can advance 20 or retard 30.

Max overlap case:
The intake centerline can be brought from 109.5 down to 89.5.
The exhaust centerline can be brought from 120.5 down to 70.5.
Resulting LSA is (89.5 + 70.5)/2 = 80 (!)
Resulting advance is 80 - 89.5 = -9.5
It gets close at WOT in the mid-range.

Min overlap case:
The intake centerline can be increased from 109.5 to 139.5.
The exhaust centerline can not be increased beyond the 120.5 because it can only retard.
Resulting LSA is (139.5 + 120.5)/2 = 130
Resulting advance is 130 - 139.5 = -9.5
This is used for "optimum stability" modes such as idle and coast-down.

Both cams full retard case:
The intake centerline can be increased from 109.5 to 139.5.
The exhaust centerline can be reduced from 120.5 to 70.5.
Resulting LSA is (139.5 + 70.5)/2 = 105
Resulting advance is 130 - 139.5 = -9.5
This is used for "optimum fuel efficiency" at light loads and low speeds in order to simulate the Atkinson cycle (extended power stroke and reduced compression stroke, also described as expansion ratio > compression ratio).

Both cams full advance case:
The intake centerline can be reduced from 109.5 to 89.5.
The exhaust centerline can not be increased beyond the 120.5 because it can only retard.
Resulting LSA is (89.5 + 120.5)/2 = 105
Resulting advance is 105 - 89.5 = 15.5
This combination isn't used in any tune I've seen.

[Grim5.0]

to echo Mike, here is the gen2 specs plugged into a shared gen1 cam visual that another member created. slight difference ive found with compcams spec cards is centerline at 109 parked for the intake/123 for the exhaust for the gen2. Gen 1 is 139 for intake and 123 for exhaust. same duration, less lift. the tune shows the same 259 for the duration though as the gen3 in the gen2.

gen2 parked at 0/0 in the tune is
Valve events @ Park (no adv/ret) @.050":
IVO: 3.5 ATDC
IVC: 34.5 ABDC
EVO: 48.5 BBDC
EVC: 17.5 BTDC

GEN2 valves.xlsx

[SilverFrostLSC]

Does anyone know gen3 f150 specs vs gen3 mustang? Is it just firing order thats different?

[engineermike]

What do you mean by specs? Most of what’s posted above is in the tune.

[K44]

Thanks Mike and Grim5.0

[K44]

Ok I've been mulling this over.

If I am correct at park the intake valve closes at 60 degrees after BDC or 120 degrees before TDC

Finally numbers I understand.

The gen 2 specs showing the intake opened at 340 then closed at 239 threw me for a loop.

Thanks again

[engineermike]

Kinda crazy to think that ivc could be anywhere from 40 to 90 deg abdc!

There was discussion on another thread about where you might park the cams if you didn’t care for vct, mainly regarding part throttle. I suggested MP23 (15,15), but MP14 (0,0) might be ok too based on old school cam figures. Then again, old school is based on 2-valve stuff.

[K44]

Mike, or anyone, do you have a math for logging cam events? Open /close in degrees. I can't come up with one that works.

[K44]

I've noticed some tunes run less intake advance and more ign timing in the 4500 and lower ranges.

[engineermike]

I actually put together math for all valve events, Soi, eoi, and spark timing and had them plotting on one scanner graph for a while but later realized it really wasn’t that useful. What are you trying to do?

[K44]

What are you trying to do?

I'm trying to balance intake closing with ign advance.

If you still have that math could you post it or PM. Thanks

I want to pop this into my engine software and I need actual event timing for it to work.

[engineermike]

At 0, the IVO is 340 ATDCf I believe, which means 20 deg BTDC. IVC would be 259-20=239 ATDC, or 59 ABDC, or 121 BTDCf. If BTDC is what you’re looking for then the math would just be “121 - intake cam position”.

However, I don’t think this will be a ton of help determining spark timing. I’ve found it much more useful to rely on the oem mbt table and find borderline using the knock sensor feedback.

[K44]

That is what I'm doing , trying to get MBT, but thought it might be faster and use fewer flashes if I plugged cam timing into my engine sim.

That and it would be cool to see the graph. I'll try some more. I'm not an engineer LOL.

[K44]

I tried again with the scanner and I can't get any numbers I understand so I'm using graph paper.

[engineermike]

What reference are you trying to graph against? Btdc or atdc, firing or overlap, intake or exhaust cam? Keep in mind these numbers I THINK are at .050 lift.

[K44]

I'm trying to find all of it. I think what I'm going to have to do is find a coyote and put a degree wheel on it.

From reading the several posts about the cam cycle on these (the atkinson thread)I think the overlap is on the ATDC side of the stroke. I'm wanting to verify where it is. If overlap is indeed after TDC I wonder if an offset key would make more power.

I was under the impression the listed open and closing events were somewhere around .006 lift.

I've been playing with the cam timing in OP and have got pretty close to MBT, not sure if it makes any more power but at least my theory follows reality, at least on pump gas.

I'm probably pissing in the wind, but it keeps me active.

[engineermike]

My mistake, the cam timing numbers are definitely NOT at .050.

You don't need a degree wheel. All of the information needed to determine all valve events is listed above. I just don't know what you are trying to determine. You want to know when IVC happens, but based on what? BDC, TDC, before, after? What load and speed? I need to know what you want them referenced to and in what operating condition.

When at light load and low speed, it simulates atkinson by fully retarding both cams. This puts overlap after TDC. But in the neutral position, they are both somewhat advanced. At WOT the intake cam goes to full advance in the midrange, so you can't assume it's using atkinson at WOT at all. In fact, it's the opposite.

Also, you shouldn't be moving cam timing to try to achieve MBT. You'll lose more from airflow dynamics than you gain from timing. That is, unless you are WAY off of MBT, where small movements towards MBT yield more power than you lose from non-optimal cam dynamics.

[K44]

I had to put it on paper to grasp it.

I have found some throttle response by getting more spark advance. We have shit gas in the summer here in Ky and I was getting 20 degrees max timing on 93 pump. I filled up in central Indiana a week ago or so and it immediately went to 28 degrees. So I retarded the cams a bit and now I get in the 26 degree range with the crap gas. It has improved my throttle response.

[engineermike]

If it's spark timing response you're after, then you'd be better served by modifying your borderline spark tables to get the initial value closer to the knock limit. I've spent a ton of time doing this on mine. I increased my borderline tables on average 5 deg then limited knock advance to 2 deg. It almost never knocks now and I get more spark timing sooner. However, modifying cam timing in order to achieve a desired spark timing response is not the way.