LNF Cam adjustment

[stromboli86]

So following these guilds:

Advance intake and exhaust => more low-RPM power, less high-RPM power
Retard intake and exhaust => more high-RPM power, less low-RPM power
Less overlap => lower EGTs, faster turbo spool, less fuel
More overlap => higher EGTs, slower turbo spool, more fuel

Everything you said sounds about right but i would question this section... not that it is wrong by any means but the LNF is not an ordinary engine being a turbocharged/VVT/direct injection engine so.. im confused! time for more research

[CDNITE]

So maximum intake retard is 10*(cam table) or 0*(base) and the maximum exhaust advance is -6*(cam table) or 0*(base).

Does any know the maximum intake advance or exhaust retard?

Stock table has -40 as the max intake advance and 40 as the max exhaust retard.

Also I played with tons of different values in the idle tables and they did nothing for me. I don't know what these tables do but its not cam idle control.

[gmtech16450yz]

Hey guys give it up on trying to change cam timing at idle. The cam actuators are locked in the park position at idle.

As far as the max cam movement, I don't remember the exact numbers but it should be around 20-25 degrees on the LNF. That would mean the editor numbers are in crank degrees, not the 10:1 ratio I've seen talked about.

[CDNITE]

Hey guys give it up on trying to change cam timing at idle. The cam actuators are locked in the park position at idle.

As far as the max cam movement, I don't remember the exact numbers but it should be around 20-25 degrees on the LNF. That would mean the editor numbers are in crank degrees, not the 10:1 ratio I've seen talked about.

Agreed gmtech, the cam position at idle is not adjustable.

If the editor number aren't in 1/10th degree, then there are at least 50* of cam adjustment just in the stock intake table. Could that much adjustment be available?

[gmtech16450yz]

If that 50* is crank degrees, that would be 25* of cam degrees, which would be about right with what I was thinking the LNF actuators would do.

You know the cam stuff would be a lot easier if you didn't have 17 different conversions to do to figure out what the actual position is! Actual, advertised, installed, editor, scanner, GM's scanner numbers, crank degrees, cam degrees, overlap degrees, opening degrees, closing degrees, different degrees for intake and exhaust,,,,,,,, Too many degrees!

Here's a few general theories or common cam timing/tuning approaches...

For higher mpg's, you want to reduce pumping losses. You do that by lowering dynamic compression. The way that's done is by retarding the exhaust and advancing the intake timing. That increases overlap and basically lets some amount of exhaust back into the chamber. This also lowers egt's.

For low end power, you want to advance intake and exhaust timing. That raises dynamic compression.

For top end power (turbo), you want to retard intake and exhaust timing. Later intake valve closing gives the pressurized intake charge more time to fill the cylinder, even if it's into the compression stroke a little bit. If you've got 30psi boost pushing the intake charge in, the piston is gonna have to go up to the point of building 30psi before it could even start pushing the charge back into the intake. Retarding exhaust timing lets the piston start pushing the exhaust out a little before it opens the exhaust valve, which helps if the backpressure in the exhaust manifold is high. (small turbo) Retarding both intake and exhaust at high rpm's lowers dynamic compression again and lets the motor rev out easier. (I learned that on the LS motors with VVT, advance the cam too far on the top end and it simply will not rev out, and knock like crazy! High compression is good down low, it's not so good up high.)

Light loads, if you want power, reduce overlap by advancing exhaust and retarding intake a little bit. If you want mileage, go the other direction, increase overlap and retard the intake and exhaust a ton. The high numbers around freeway cruise in the LNF (and most every other VVT engine without an EGR valve) is for mileage. If you want power, take away a bunch of the exhaust retard, you can leave some of the intake advance, but watch the overlap. The secret here is keep the big overlap RIGHT AT freeway cruise rpm and loads, then close up the overlap right away when rpm's or load starts going up. That way you get high freeway mpg's but a little more on the pedal and it's pulling hard. My freeway cruise is right around 2500rpm and 50% load, so that's where I have the big exhaust retard and intake advance. Right out of those cells and I'm back into power mode. Tricky part here is making sure you don't have too big of a mountain in your cam timing maps. You can make up for some of the dip in power as you go through that mountain with the other torque/throttle control tables. If the power has a low spot on a normal accel, just bump up the throttle in that spot.

Hope that helps, it's midnight and I might have gotten something in there backwards! To throw another monkey wrench in all this, if you're making big cam timing changes, you better be adjusting your ign timing and injector timing tables too. Look at the injection timing tables and you'll see numbers in there that were put in to match cam numbers.

One more thing, if you want to see what effect a table has, GO BIG! Meaning don't change a cam timing cell from 36 to 32 and expect to "feel" the difference. Take those cells from 36 down to 10 or so just so you can see what it does in actual driving. Same with what you guys were talking about with the torque management settings, if it's at 100% in a certain row or cell, drop it to 50% and I'm betting you'll be able to see if it does anything or not. If it doesn't do anything, drop it to 10%, if it still doesn't do anything it's a table that doesn't work or something else is over-riding it. There's a few of those.

[gmtech16450yz]

explain this to me......
if intake more negative is advance and exhaust more positive is retard, then how does intake cam - exhaust cam = overlap

now i have a feeling that the camshaft pids are correct but i dont think the current overlap pid is correct ..... someone please explain to me? are you guys saying the more negative the overlap number the less overlap you have and more positive the more overlap you have. cause then i might be able to see that......


i could use some focusin right now.......or that shit from the movie limitless lol

You know I made that custom pid like a year and a half ago, I haven't used it since then! That is wrong, you can't get overlap by subtracting the two.

[stromboli86]

As far as the max cam movement, I don't remember the exact numbers but it should be around 20-25 degrees on the LNF. That would mean the editor numbers are in crank degrees, not the 10:1 ratio I've seen talked about.

If that 50* is cam degrees, that would be 25* of crank degrees, which would be about right with what I was thinking the LNF actuators would do.

the second sounds backwards, isnt it 2* crank per 1* cam? So scanner reads crank of 50*, meaning cam has moved 25*?

[gmtech16450yz]

the second sounds backwards, isnt it 2* crank per 1* cam? So scanner reads crank of 50*, meaning cam has moved 25*?

Lol, what a dumbsh!t. I told you guys it was late! My brain and my fingers obviously were getting some clutch slip between them.

Good catch, I fixed it in my original quote. Thanks. Did I screw anything else up?

[cobaltssoverbooster]

You know I made that custom pid like a year and a half ago, I haven't used it since then! That is wrong, you can't get overlap by subtracting the two.

yea i thought that pid wasnt accurate..... am i correct though that we are adjusting for less overlap like such:
intake cams-
advance = positive numbers
retard= negative numbers which to me explains the dip in the middle of the graph being more negative to advance the cam and lessen overlap for mpg

exhaust cams-
advance = positive numbers
retard = negative numbers and same for the mpg dip in the cam table heavy

i notice in the graph the positive exhaust value matches the negative intake numbers as far as the where the hump is. it only makes sense that they are making the lsa larger in that spot. so positive exhaust advances the cam which brings the closing point away from the intake opening event. and for the intake if they retard it there well that drives the opening of the intake away from the exhaust closing event.

i got messed up because i forgot that cams are read as exhaust first then intake when plotting them on the degree chart.......things i forget that come back to hurt me

[cobaltssoverbooster]

holly crap does this sound right i just imaginated it up? thoughts please....

editor tables we know intake 10 is 0* and exhaust -6 is 0*
so basically if the intake cam we set to 10 then that is tdc crank factory installed position
a value of -20 + 10 for actual position gives you -10 which would be a 2* shift at the cam. well if you apply the crank ratio 2:1 then you have effectively retarded the intake cam 1* of crank rotation..........yess!?!
now if the cam chart was related to crankshaft angle then moving the cam a value of 1 would net a 10* shift on the base cam pid which it doesnt do, it actually does the opposite which verifies the previous statement.....10 value shift related to 1* change on the base cam pid. so therefore the cam charts are all based on camshaft position in degrees of cycle but can still be related to crank shift...

so since we know the camshaft specs from gm direct we know where each cam is installed at and their respectful durations. a value of 0* equals the installed cam chart position and by calculating a custom pid of example: [(intake cam angle/2)-installed lobe center angle(lca) on a 360* plane] & [(exhaust cam angle/2)+ lca on 360*] give us the new lca in crankshaft deg*. now you just apply the new lca to the cam charts and move their respective opening points to follow and viola you can now calculate the respective overlap visually on paper.

either that was an awesome learning point for me or i got sold some good shit....nuff said

[silverbullet08]

If that 50* is crank degrees, that would be 25* of cam degrees, which would be about right with what I was thinking the LNF actuators would do.

You know the cam stuff would be a lot easier if you didn't have 17 different conversions to do to figure out what the actual position is! Actual, advertised, installed, editor, scanner, GM's scanner numbers, crank degrees, cam degrees, overlap degrees, opening degrees, closing degrees, different degrees for intake and exhaust,,,,,,,, Too many degrees!

Here's a few general theories or common cam timing/tuning approaches...

For higher mpg's, you want to reduce pumping losses. You do that by lowering dynamic compression. The way that's done is by retarding the exhaust and advancing the intake timing. That increases overlap and basically lets some amount of exhaust back into the chamber. This also lowers egt's.

For low end power, you want to advance intake and exhaust timing. That raises dynamic compression.

For top end power (turbo), you want to retard intake and exhaust timing. Later intake valve closing gives the pressurized intake charge more time to fill the cylinder, even if it's into the compression stroke a little bit. If you've got 30psi boost pushing the intake charge in, the piston is gonna have to go up to the point of building 30psi before it could even start pushing the charge back into the intake. Retarding exhaust timing lets the piston start pushing the exhaust out a little before it opens the exhaust valve, which helps if the backpressure in the exhaust manifold is high. (small turbo) Retarding both intake and exhaust at high rpm's lowers dynamic compression again and lets the motor rev out easier. (I learned that on the LS motors with VVT, advance the cam too far on the top end and it simply will not rev out, and knock like crazy! High compression is good down low, it's not so good up high.)

Light loads, if you want power, reduce overlap by advancing exhaust and retarding intake a little bit. If you want mileage, go the other direction, increase overlap and retard the intake and exhaust a ton. The high numbers around freeway cruise in the LNF (and most every other VVT engine without an EGR valve) is for mileage. If you want power, take away a bunch of the exhaust retard, you can leave some of the intake advance, but watch the overlap. The secret here is keep the big overlap RIGHT AT freeway cruise rpm and loads, then close up the overlap right away when rpm's or load starts going up. That way you get high freeway mpg's but a little more on the pedal and it's pulling hard. My freeway cruise is right around 2500rpm and 50% load, so that's where I have the big exhaust retard and intake advance. Right out of those cells and I'm back into power mode. Tricky part here is making sure you don't have too big of a mountain in your cam timing maps. You can make up for some of the dip in power as you go through that mountain with the other torque/throttle control tables. If the power has a low spot on a normal accel, just bump up the throttle in that spot.

Hope that helps, it's midnight and I might have gotten something in there backwards! To throw another monkey wrench in all this, if you're making big cam timing changes, you better be adjusting your ign timing and injector timing tables too. Look at the injection timing tables and you'll see numbers in there that were put in to match cam numbers.

One more thing, if you want to see what effect a table has, GO BIG! Meaning don't change a cam timing cell from 36 to 32 and expect to "feel" the difference. Take those cells from 36 down to 10 or so just so you can see what it does in actual driving. Same with what you guys were talking about with the torque management settings, if it's at 100% in a certain row or cell, drop it to 50% and I'm betting you'll be able to see if it does anything or not. If it doesn't do anything, drop it to 10%, if it still doesn't do anything it's a table that doesn't work or something else is over-riding it. There's a few of those.

Ive done a little playing with the cams using your theries here for the LNF. I noticed if you lowered dynamic pressure too far in the cruize area it was difficult to maintain a certain speed. You had to keep your foot in it or get a little boost built to cruiz steady which in turn killed milage. -25 and 18 was a pretty happy medium for me.But I did this by retarding the intake and advancing the exhaust. Did you get this backwards in your post here? Or have I been doing it wrong this whole time? Or was it that negative intake timing was advancing and positve exhaust timing was retarding? I need to wrap my head around this again to get back in the game.

[cobaltssoverbooster]

camshafts are read in order of sequence per the crank direction of rotation so you would have to read them as exhaust actions first then intake actions. thus retarding exhaust and advancing intake gives us overlap.

[gmtech16450yz]

camshafts are read in order of sequence per the crank direction of rotation so you would have to read them as exhaust actions first then intake actions. thus retarding exhaust and advancing intake gives us overlap.

Exactly. Retard exhaust and advance intake make the overlap larger. Advance exhaust and retard intake closes up overlap.

The thing that makes this confusing is the numbering in the scanner, editor and what the cams are actually doing. To keep it simple and making sense try thinking of it this way...

The cam actuators can go both directions (advance and retard), but for all intents and purposes they only really go this way...

The exhaust cam actuator is only going to RETARD the cam timing.
The intake cam actuator is only going to ADVANCE the cam timing.

So the "hump" in the center of the tables, right around freeway cruise is ADVANCING intake cam and RETARDING exhaust cam. That lowers dynamic compression, lowers pumping losses and reduces EGT's and NOx. It also makes the gas mileage increase, meaning higher mpg's. You can gain torque by reducing the amounts of both cams movements in that area, but you will hurt mileage. If you reduce (let it have LESS retard) the exhaust cam more than you reduce (let it have LESS advance) the intake, you'll gain torque without killing mpg's as badly. I think that's what you were talking about with your -25 & 18 numbers Silverbullet.

I'm glad you guys are brainstorming on this, I haven't thought about it for quite awhile. I know what numbers do what in the scanner and editor as far as cam adjustments go, but I haven't messed with making better cam PID's in over a year. If you guys can come up with some custom PID's that make sense and work better, that would be awesome! I know they can be made, it just takes time to think it through.

On the overlap part, the reason why you can't really get a good calculation on it from the scanner or editor numbers is because it's based off of the END of exhaust duration and the BEGINNING of intake duration. The duration's aren't the same between the two cams.

[stromboli86]

I hope i got this right, feel free to edit, doodle, tell me its all wrong... lol



smaller than i expected! Here's a decent read as well: http://www.carcraft.com/techarticles...e/viewall.html

[cobaltssoverbooster]

you need the .050 lift values which i have posted on here before but the only problem is i didnt have the lifters shimmed up to 0 tolerance like the hydraulic lifter would be so the values are wrong for measuring at the valve.

i am going to be swaping motors here probably late this summer....i know it is far away but im putting in a crate from gm so that means i have a whole motor to use for r&d... even if someone goes and does it before me i dont care ill do it again to verify what i find.

[gmtech16450yz]

OK, it's late again, and I sucked at math in school, BUT I THINK I FIGURED OUT HOW TO LOG OVERLAP!!!

This is gonna take a little bit to explain, but I think it works. At least it seems to and the numbers make sense. I not only figured out how to log it in the scanner, I figured out how to show it in the editor. Let me know if it was too late and this is all a bunch of cr@p.

First off, here's the custom pid...

(([PID.2172]+10)+([PID.2178]+6)-16)/2

Yeah, don't ask me how I got to that, I probably couldn't remember already! I tried about a hundred different functions before I figured this one works.

So here's the basic premise- The intake cam only advances, that means any numbers in the editor and scanner are degrees of ADVANCE. (I'm still thinking that they're crank degrees so you'd have to divide them by 2 to get cam degrees. Right? I'm pretty darn sure the LNF's actuator authority is 25 degrees so the tables going from -10 to +40 would make sense- 50 divided by 2 would be 25 degrees cam movement.)

The exhaust cam only retards, so again, that means any numbers in the editor or scanner are going to be degrees of RETARD. Since the cams are only moving in those directions, that means ANY numbers higher than the park position in EITHER intake or exhaust cam tables or scanner readings are going to be INCREASING overlap. Meaning a -30 number in an intake table cell, and a 30 number in an exhaust table cell would mean the cams are widening the overlap. If the numbers were -30 and 0, the overlap would still be widening. If the numbers were 0 and 25, the overlap would still be widening.

So here was my theory- the sum of those two numbers would tell you the overlap CHANGE from the park position. That's a biggie right there, I'm only talking about logging and showing overlap changes from the park position. I know the advertised overlap is supposed to be 10 degrees, but I have no idea what the actual installed overlap with the actuators in the parked positions is. It doesn't really matter anyway, we just need to see the changes relative to the park position.

So simply adding the values together won't get you numbers that make sense, you have to modify the calculations a little bit. Since the tables, and the scanner doesn't start at 0, I had to factor in the -10 and +6 numbers. In other words, if the scanner or editor shows the intake at -25, the CHANGE from the parked position is actually -35. Likewise, if the exhaust cam shows 15, the change is actually 21. Everyone still with me? lol.

After compensating for that, the overlap now read -16 at the park position, that's no good. So I put a -16 in the function and it comes out to 0 at the park position. The numbers come out looking reasonable I guess, high overlap numbers are in the 40's and 50's which if you add the advertised 10* it would mean highest overlap would be in the 50's or 60's.

[gmtech16450yz]

Page two- showing the overlap in the editor...

So this one might be a little tricky to follow, but again, it looks like it works. Here's the steps...

Start with the intake cam table, select the entire table and subtract 10 from the whole table. Then do the exhaust table, but on that one add 6 from the whole table. Next select the entire exhaust table and copy it, then paste it onto the intake cam table as "paste special- subtract". Last step is to divide the entire table by 2 by putting .5 in and multiplying. What you have left is the overlap that both the intake and exhaust table numbers in your editor end up giving when they're in the car.

Try it out guys and let me know if it works for you. It looks good so far on my end, but again, it's late and I'm tired of thinking.

[stromboli86]

my eyes are burning way too much to comprehend that haha, iv been using PID's to display the actual cam values, as seen on the adjustment tables and the further apart the 2 lines get on my scanner, the larger the change in overlap like you were saying...

You got me thinking earlier when you said that there is no adjustment for the cams at idle but i kept thinking back to when i first started messing with my car. i had always had issues getting it to listen to what i typed in the idle tables, like i wanted them parked at 10 and -6... but eventually i realized i had typed -10 like an idiot, then as the car warmed up it slowly made its way towards being parked! I just reviewed those old logs and tunes and the numbers i was seeing at idle were corresponding with numbers in the catalyst heating tables even tho it was disabled! So that being said and noted, im thinking some of those tables are either miss labeled or my car just likes to mess with me. Im going to change a bunch of the tables around soon and see how it responds

[cobaltssoverbooster]

the ideal overlap pid will do everything in one....or i can waste a weekend making an excel file that shows overlap angles for entire cam charts both cobalt/hrr and soltice since iirc the soltice has a few extra rpm cells on the y axis.

based off of technical cam spec paperwork from gm we can say the camshafts are installed and parked at value X of lobe center angle. you know the total duration at advertised open there fore you divide by two and you now know the exact angle at wich it opens and closes at advertised duration. now we have a installed and parked intake open angle* and exhaust close angle*. we will call them "I" and "E" for the intake and exhaust cams natural position value of valve close and open for the later example.

now for every crank rotation in deg* or (intake/exhaust cam actual sesor position/2) you would add or subtract that shift from the installed angle thus telling you exactly where the new close and open angle* is at.

Ex1: (installed camshaft angle intake valve opening * value "I") - (actual intake cam sensor position/2) (using subtraction because in a 360* wheel intake retard would be smaller thus giving me subtraction)

EX2: (installed camshaft angle exhaust valve close * value "E") + (actual exhaust cam sensor postion/2)

that should give us the new open and close positions for the valve events that you can plot on paper.

going into my vast excel knowledge i would make a chart that does two calculations per 1 cell which will take time but all you need to record in the scanner would be cam position sensor actual/2. copy and paste results to excell chart.

ill explain:

if there is overlap and you use a 360* wheel chances are the intake is opening before 360* or 0* (tdc) so the number in degres will be small for example 4*
well when in less overlap you have the chance to be after tdc thus entering high deg* numbers for example 356*.

knowing the installed * value of "I"/"E" we know how far the cams are at max overlap cause we pegged the phaser out.
now for my excel example:
we will only look at the intake cam for this because the exhaust is just oposite of the intakes math.
i will give "I" a dummy value of advertised opening at 5* BTDC

cell block math #1 will say for numbers before 0*/360* TDC you will subtract the (sensor acutal value/2) from the position "I" and install a limit of a value of 5 as a stop.

cell block math #2 will say for numbers results of (sensor actual value/2) equal to or greater than 5.1 you will be using following formula 360-(sensor actual value/2)
the reason is now you have a value for exactly where the valve is opening on a 360* clockwise rotating degree wheel.

this comes in hand like soooooo.........make a new excel tab and label it overlap graph. now make a custom paramater circular style graph that has 360* of values in a minor label of 1* and a major label of 90*,180*,270* & of course 360*/0*. now you just have the chart result values from the conversion listed above plotted and you will have a perfect chart showing overlap. you will have to use colors im sure and possibly copy and paste the graph a few times to have a nice clear graph for a few cells but overlap will have a visual representation.

and if you want it in a numerical chart then you have option two see next post...

[cobaltssoverbooster]

option 2 excel overlap visualized as a chart with cells so the whole table can be converted with overlap visualized as a value.

take value"I" of 5% BTDC

5* of retard will equal 0* and 6* retard we let go over and read as -1*

now we have a number we can use to convert by simple math adding and subtracting


results will have to be related to zero so neg numbers are a representation of deg* ATDC and positive are representation of deg* BTDC

with the results of formula ("I" - [cam actual sensor value/2]) and ("E" + [cam actual sensor value/2]) we plug that into the simple formula of:

New Exhaust cam shifted value - New Intake cam shifted value
and the results would be as follows...... negative numbers for results equals deg* of overlap and positive numbers equal deg* of seperation

now using numbers:

fixed example result numbers say for formula ("I" - [cam actual sensor value/2]) the end result was a value of 3* (BTDC)
and formula ("E" + [cam actual sensor value/2]) the result was -3*(ATDC)

simple formula of exhaust location - intake location
-3-3=-6 so you have 6* of actual overlap

now for seperation....
("I" - [cam actual sensor value/2]) the end result was a value of -3* (ATDC)
and formula ("E" + [cam actual sensor value/2]) the result was 3*(BTDC)

exhaust location - intake location
3-(-3)=6 so you have 6* of actual seperation

i will try and make the pids tomorrow and then make the excel charts to follow so just be patient and give me a few days and it will all be easier to understand with the visual aid. just need factory cam values spec sheet first.


this is a late night discovery that i believe is what we were hunting for so before you go trashing i ask to give me a shot to show my final product and then descriminate 8D lol