Help me understand cam timing (LNF)

[oldskool]

I think the overlap that you are calculating is the change in overlap about the base cam. The other parameter is the effective amount the cams are advanced or retarded.

That's what I was trying to get at - change in overlap relative to the hardware specs. I wasn't trying to calculate the actual overlap; i couldnt' guess on how to do that. Thanks

[ChevyHighPerformance]

That's what I was trying to get at - change in overlap relative to the hardware specs. I wasn't trying to calculate the actual overlap; i couldnt' guess on how to do that. Thanks

This may help visualize what is happening from a traditional cam perspective:

I = intake cam angle from the table
E = exhaust cam angle from the table

Relative Lobe Separation:

(I - E)/20 = change in lobe separation angle in degrees

where:
A positive value means more lobe separation (less overlap)
A negative value means less lobe separation (more overlap)

The change in the lobe separation value gets added to (or subtracted from) the stock lobe separation to get the effective lobe separation. Since you may not know the stock cam lobe separation, you can convert your cam tables, like you did, and see if the overlap is increasing or decreasing and by how much.

Relative Cam Advance:

(I + E)/20 = change in cam position in degrees

where:
A positive value means the cam is retarded
A negative value means the cam is advanced

I'm guessing the cam is run straight up so the cam advance that you calculate may be the actual effective cam advance or retard.

The durations and lift of the cam is not adjustable.

[oldskool]

This may help visualize what is happening from a traditional cam perspective:

I = intake cam angle from the table
E = exhaust cam angle from the table

Relative Lobe Separation:

(I - E)/20 = change in lobe separation angle in degrees

where:
A positive value means more lobe separation (less overlap)
A negative value means less lobe separation (more overlap)

The change in the lobe separation value gets added to (or subtracted from) the stock lobe separation to get the effective lobe separation. Since you may not know the stock cam lobe separation, you can convert your cam tables, like you did, and see if the overlap is increasing or decreasing and by how much.

Relative Cam Advance:

(I + E)/20 = change in cam position in degrees

where:
A positive value means the cam is retarded
A negative value means the cam is advanced

I'm guessing the cam is run straight up so the cam advance that you calculate may be the actual effective cam advance or retard.

The durations and lift of the cam is not adjustable.

Thank you for posting this! I just have one question - where did the "divided by 20" come from? I would have thought the numbers would be relative to 360 or 180. Could you go deeper with the math? Thanks again.

[oldskool]

Ok, using that formula for calculated change in lobe separation angle (CCLA) in degrees, i get a (-0.75) to 1.20 range. These seem like minimal changes...
However, what you explained makes sense because in general, the CCLA becomes more positive as RPM increases (less overlap).

Looking in specific at the higher load and higher RPM cells, the CCLA tends toward negative again (more overlap?). Is this contributing to the drop in powerband up top? Is there a specific reason for this?

Thanks for your patience with me - I fully understand now why there are entire schools devoted to performance engineering

[ChevyHighPerformance]

The equations are based on specifying a cam based on the intake lobe ATDC and the exhaust lobe BTDC. The 20 in the denominator is made up of 2 times 10. The 10 factor converts the number in the cam phssing tables to degrees, and the 2 factor comes from the lobe centerline-to-overlap equation.

Here is a good discussion of cam terminology to understand where the 2 factor comes from.

http://www.compcams.com/Technical/TimingTutorial/

Cam phasing is new to me too. What helped me is downloading a free engine analyzer program like Engine Analyzer. Then I ran the program with the default engine and cam. For RPMs of 1000, 750, 3000, 4000, and 5000, I went through and optimized the torque (or HP) for each RPM by only changing the centerlines for the intake and exhaust cams. In a spreadsheet, I kept track of the overlap and the total cam advance for each RPM. Then I plotted the optimum overlap and the total cam advance versus RPM. (I also plotted the optimum torque and torque with just running the cam as is versus RPM to see the difference.) You can see for low RPM more cam advance and more overlap was optimum and at high RPM the less overlap and less cam advance was best.

However, idle quality and vacuum will suffer with more overlap. So for idle RPMs, you need less overlap (for idle quality) then as RPMs increase the overlap increases. Then the overlap has to decrease again as RPMs increase.

For my car, the delta overlap is -0.4 degrees at idle, -3.9 degrees at 2500 RPM, and then -1.25 at 6500 RPM.

I'm rambling so I'll shut up.

[oldskool]

For my car, the delta overlap is -0.4 degrees at idle, -3.9 degrees at 2500 RPM, and then -1.25 at 6500 RPM.

I'm rambling so I'll shut up.

Sorry to bring this back from the dead, but i have more questions Based on the formula you stated earlier, i'm getting -0.05 degrees change in lobe separation angle on the stock main warm tables in the 120% load 6000rpm cell. Are you saying that at -1.25 you are actually requesting MORE overlap than the stock tables? I thought we wanted less overlap at high rpms.

[SSpdDmon]

<< still waiting for someone to help the rest of us understand how to make the right changes to the intake & exhaust cam timing tables to optimize the stock turbo's output.

[cobaltssoverbooster]

the major players are more keeping it a secret its very easy to mess this up

[oldskool]

the major players are more keeping it a secret its very easy to mess this up

Hmm that's too bad because when i figure it out i'm going to share it with EVERYONE muhahahahaha. I have the formula from ChevyHighPerformance and a working spreadsheet to figure change in lobe separation angle and cam advance/retard.

I guess I just have to experiment...

[|V3nom|]

hopefully you get this figured out, i could use a good tune lol :P.

[ChevyHighPerformance]

Sorry to bring this back from the dead, but i have more questions Based on the formula you stated earlier, i'm getting -0.05 degrees change in lobe separation angle on the stock main warm tables in the 120% load 6000rpm cell. Are you saying that at -1.25 you are actually requesting MORE overlap than the stock tables? I thought we wanted less overlap at high rpms.

My numbers and strategies were for an NA engine not the LNF engine.

Let's say my stock overlap is x degrees.

At idle, my overlap would be x - 0.4 degrees

At 2500 rpm my overlap would be x - 3.9 degrees

At 6500 rpm my overlap would be x - 1.25 degrees

Your LNF VVT strategy will be different than my NA strategy; I didn't make this clear in my previous post.

[jimbos'ss]

subd, good info

[boostking]

This may help visualize what is happening from a traditional cam perspective:

I = intake cam angle from the table
E = exhaust cam angle from the table

Relative Lobe Separation:

(I - E)/20 = change in lobe separation angle in degrees

where:
A positive value means more lobe separation (less overlap)
A negative value means less lobe separation (more overlap)

The change in the lobe separation value gets added to (or subtracted from) the stock lobe separation to get the effective lobe separation. Since you may not know the stock cam lobe separation, you can convert your cam tables, like you did, and see if the overlap is increasing or decreasing and by how much.

Relative Cam Advance:

(I + E)/20 = change in cam position in degrees

where:
A positive value means the cam is retarded
A negative value means the cam is advancedI'm guessing the cam is run straight up so the cam advance that you calculate may be the actual effective cam advance or retard.

The durations and lift of the cam is not adjustable.

in bold what is advance, the intake or the exhaust and how do you change the the math for the other cam.

the more you advance the more overlap you will have if you don't change the exhaust side. but when you change the exhaust to more positive or the sooner you open the valve before BDC this reduces overlap but with the math in bold it also reduces the advance. the advance on what?????

I know in higher rpm you want less overlap to allow the cylinder to fill with as fresh of air as possible. but at normal operating conditions its good to have some overlap for improved mpg and overlap also creates an internal EGR effect which is also good for emissions etc... but again the math in bold will reduce the advance of somthing..... need some help figuring out what this math is talking about.

so for now I am opening my intake valves sooner or closer/slightly sooner than tdc and opening my exhaust valves closer to bdc to reduce overlap in the upper rpm range. but when you are in spool up you would want the most exhaust possible to spool the turbo so you would want the intake valves a little less advance than if you were at full boost because you need to keep the exhaust valves closed as long as possible so with the intake valves opening a little later than if you were at full boost this would help reduce overlap but there would still be some due to the late opening of the exhaust valves. you want the exhaust valves to open later so when the exhaust valve do open there is peak pressure/temp going out the exhaust and helping spool the turbo.

Right?????

[oldskool]

Boostking, I thought of the value you are discussing as if you were advancing or retarding a single cam motor - for example with an adjustable cam gear. It's a measure of the entire event not just the intake or exhuast cam.

I could be wrong, but we should be able to achieve more with tuning overlap on this system than tuning overall advance/retard of the cam.

[boostking]

Boostking, I thought of the value you are discussing as if you were advancing or retarding a single cam motor - for example with an adjustable cam gear. It's a measure of the entire event not just the intake or exhuast cam.

I could be wrong, but we should be able to achieve more with tuning overlap on this system than tuning overall advance/retard of the cam.

I agree with you.

[ovenroastedlnf]

bump an old ass thread lol

any new info on this? Still trying to learn it

[BackyardTurbo_FTW]

There are threads now with cam tables that will gain mileage. So far there has been no gain in power on the stock turbo with modifying the high load areas. On bigger turbo cars I have made substantial gains tho!

[viceroykarl]

Check this thread. Some vvt talk for lnf lsj and le5
http://www.hptuners.com/forum/showthread.php?t=35092