Has anyone tuned a 6.2 with Variable Valve Timing? If so, what challenges does the VVT present?
Has anyone tuned a 6.2 with Variable Valve Timing? If so, what challenges does the VVT present?
Also would like info on this..Originally Posted by 2xLS1
So far on my L76 engine, I've had to fight with the variable cam spark table. The truck had a Diablo tune in it but over 4,000 rpm it would ping so much it could be easily heard. I'm still learning myself and still fighting to make everything ideally perfect, but so far just taking a lot of the timing out of the variable cam spark table and adding more in the high octane table has worked pretty well.
Has anyone made sense of the numbers presented in the VVT tables? The numbers appear to be too big for intake centerline degrees.
Should be degrees of advance from the intake centerline.
Jaime
It may be degrees but I don't think it is referenced to the intake lobe centerline.
The reasoning behind my opinion is:
Normally, a cam can be made more aggressive or higher torque by advancing the timing around +4 degrees.
Peak torque usually happens when the lobe is installed at the lobe separation angle (LSA or 0 degrees).
Highest HP can be prolonged on the RPM curve by retarding the cam around -4 degrees.
Looking at the L99 VVT, there is no cam retard after 4300 RPM peak torque - in fact, the table calls for +8 degrees. There is way too much advance during low airflow conditions which I think is the AFM zone. And, there is no advance for the RPM range below peak torque.
Therefore, I think there must be some offset reference like 0 on the table is actually -5 degrees on the intake lobe centerline.
you still need to factor in any advance or retard ground into the cam. cant assume the intake centerline is "zero"
Jaime
I think I have the VVT thing figured out. I modeled the L99 cam in EA Pro. I used the cam specs straight up (no advance, no reatard) for the first pass. Then I retarded the cam 8 degrees (-8) for the second pass. I assume the VVT system uses oil pressure to hold the cam advanced. The ECM would then modulate oil pressure to allow the cam to retard naturally with load.
From this routine I think all the numbers in the VVT intake cam table are negative - meaning degrees of retard (LSA minus table value for intake lobe centerline position).
You would be correct
It is degrees of retard...
"For the 6.0 liter (LY6, L76) and the 6.2 liter (L92) engine, the Park position for the CMP actuator and camshaft is 8.5 degrees before top dead center (BTDC) or 17 crankshaft degrees BTDC. The engine control module (ECM) can only command the CMP actuator to retard the valve timing from the Park position or advance the valve timing back to the Park position. The total range of valve timing authority is 31 degrees camshaft rotation, or 62 degrees of crankshaft rotation. The control range is from the Park position of 8.5 degrees camshaft or 17 degrees crankshaft BTDC, to 22.5 degrees camshaft or 45 degrees crankshaft after top dead center (ATDC)." --according to ALL DATA's description.
So yes, if the park position is +17 degrees of crank position, 21 on the cam position would be -4 degrees. This makes a whole lot more sense to me now. That is if the HPT variable cam tables mean degrees of crank position.
I'm just trying to understand this a little better... The table only allow's values of 0-128 so what value is retarding the cam? or is 0 technically 17 in the table and 0 in the table is 17* retard or have I got this all wrong...???
James Short - [email protected]
Located in Central Kentucky
ShorTuning
2020 Camaro 2SS | BTR 230 | GPI CNC Heads | MSD Intake | Rotofab | 2" LT's | Flex Fuel | 638rwhp / 540rwtq
2002 Camaro | LSX 427 | CID LS7's | Twin GT5088's | Haltech Nexus R5 | RPM TH400
You are correct. 0 on the table is the park position (which is 17 degrees ADVANCED). The higher the number on the table, the more the cam is retarded. Whatever number you see on the table just subtract that from 8.5.
example: 0 = 8.5 advanced, 4 = 4.5 advanced, 12 = 3.5 retarded
I like to do everything in crank degrees instead of cam degrees to keep it simple. So just to confirm my understanding is the table done in crank degrees or cam degrees? Are these examples accurate?
7table = 10*advance
17table = 0*
27table = -10*retard
James Short - [email protected]
Located in Central Kentucky
2020 Camaro 2SS | BTR 230 | GPI CNC Heads | MSD Intake | Rotofab | 2" LT's | Flex Fuel | 638rwhp / 540rwtq
2002 Camaro | LSX 427 | CID LS7's | Twin GT5088's | Haltech Nexus R5 | RPM TH400
Why is the cam retarded from the factory so much at the bottom end and almost none at all (advanced .5 in fact) up top? Wouldn't you want to advance it down low and retard it up top???
Anybody working with positive results on this table?
From what I have read, the cam is retarded significantly at cruise speeds for fuel economy.
Where did you read it? I want to read, too.
It seems to be advanced up top. What about that?
"A CMP actuator dynamically changes valve timing events relative to piston timing by controlling camshaft position. This is sometimes referred to as variable valve timing or camshaft phasing. Variable valve timing or camshaft phasing does not change duration or lift.
* By advancing camshaft timing, an improvement in low end torque can be achieved.
* By retarding camshaft timing slightly, an improvement in high end power can be achieved.
* By retarding camshaft timing significantly, an improvement in light load fuel economy can be achieved."
source is from All Data. I would send the link to you but you need to have access to the site.
What vehicle are you looking at that seems to be advanced higher in the rpms?
2011 Silverado 5.3
It seems like the major retard is higher than a normal cruise speed, 6th gear over 2000 RPM?? That is like 80 MPH, I believe.
What would happen if I increased the 4K and up column drastically to like 20?
What would happen if I increased the numbers quite a bit in the 1500-2000 cruise load area and zero'd the rest all around it?
This is under the assumption that the numbers are 8.5 - X.....
Zero would be the most advanced you could get, 8.5 and the the bigger numbers are more retard away from 8.5.....
Last edited by Higgs Boson; 03-17-2011 at 12:46 AM.
Those numbers are retard, not advance.
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