I just installed a cam and cam phaser limiter in a 2012 Chevy 6.2L Silverado. I built a fixture to put around the #2 cam journal and apply air pressure to it so I could measure the travel on the bench. Without pressure to the actuator it locks the cam to no travel. My limiter was supposed to limit the travel to 22 degrees as well. I measured 8.5 cam degrees (or 17 crank) of travel with a degree wheel fastened to the cam and by moving the actuator control rod in and out by hand. I checked the cam install and once I got the right cam (long story) it was installed 7 crank degrees advanced in the parked position (like the cam card said).

Once driving I was able to scan with HP tuners a max of 8.2-8.4 degrees advance in the part throttle areas of my tune. I had to change those valvues from the 22 degrees I originally had in there to 8.4 to prevent from getting a cam actuator code. I ended up putting 5 degrees in my WOT 6000 rpm cells which should give me 3 crank degrees (5*2-7) retard at this point.

I found it hard to believe that GM retarded the cam 52 degrees from the factory and thought the numbers (26 max) in my stock tune were in crank degrees. I am pretty sure from all of this they were in cam degrees. Now with only 8.4 cam degrees of retard in part throttle areas I would guess the fuel mileage benifits are mostly gone but the WOT benifits are all still there.

I played with numbers from 4 to 8 in the WOT cells and saw a small difference in power using a virtual dyno program. 4 degrees was apx 5 to 10 hp stronger than 8 up top in the 4 runs I averaged but I would rather do this kind of testing on an actual engine dyno to really dial it in. IF anyone has that info to share it would be nice but I doubt they will.

 

Im running a similar phase curve now too. IIRC im 4 or maybe even 2 degrees retard MAX rolling in around 5000 from my +4 in the grind.

I can assure you guys that this car will see the dyno ( although probably not this year unless I buy a dyno which I actually have considered and still may do ) but when it does? I'll be posting up my findings.

 

Thanks!! Thats exactly what I wanted and mostly confirms my findings.. In hindsight I wish I'd known some of this as I would have definitely machined my limiter block down to give me more rotation. (I will do that if I ever need to pull the front cover for anything, but not just for that) Even though I'm currently only getting 7deg of cam rotation to your 8.5, it may open up a bit when the springs,etc. all get broken in more, or I settle on a final oil weight that gets me the pressures I want..

(I've haven't been able to do a CASE learn on my motor, and I was worried that it might be limiting me too. Although I read CASE is not important, you never know some of the interactions these new GenIV PCMs have.. I suspect CASE isn't enabling because I don't have my brake switch wired in to the E38 PCM.. Purhaps this Winter it'll make the patch list)

mike

 

I wish I would have opened my limiter up a little too once I figured out I was going from 52 (not 26) down to only 17 degrees retard for the part throttle fuel mileage. I had .198 piston to valve clearance on my exhaust retarded 17 degrees and .168 if I had gotten 22 degrees of retard. I am sure I could have used 30 degrees or more and been fine. May not have made much difference though. Who knows?? I put a blower and smaller top pulley on this truck all at the same time and my customer has commented (not really complained) about getting 3 mph on his display less fuel mileage than before. I doubt he is driving the same so who really knows if he is getting worse fuel mileage or not. Its pretty hard not to put your foot into it now and hear that blower whine.

Does anyone know what gains in fuel mileage there are with a VVT cam working fully vs not having one at all?? Maybe someone with a stock cam could shut off the VVT in the scanner and do a before and after reading in a somewhat controlled enviornment.

 

I don't know for sure, it was something I wanted to test but won't be able to now. By retarding the cam substantially, the pumping losses are reduced and I've seen claims of 5%-8% better mileage.. Since the VVT-2 (in my case) cam has different lobes, lift, and Lobe-Sep, the gain may be further reduced since you won't get as much reduction in pumping loss with the tighter lobes...

 

The cam and crank sensors allows the PCM to know where the base cam setting is and that's "0" position for the tables. The Tables then just rotate (retard) from that value and the cam sensor can tell from the 4 different "windows" and the 58-tooth crank sensor, where the cam is in relation to the base.

 

I have dynoed some big nitrous engines on an engine dyno and swapped cam pin bushings or slid the jesel cam gear and found most of them liked the cams just a few degrees retarded from straight up. They were completely different animals than this however. We didn't care if we lost a few foot lbs of torque at 4500 rpm because all you had to do is bring in the bottle sooner. They did usually show 5 or 10 hp more at 8000 rpm retarded just a few degrees though.

 

Great ideas & info! Thank you! If only there were a good way to actuate the phaser w/ air (or other means) while installed in the block w/ the return spring still in place. That would make it possible to do non-destructive degreeing & PTV checking.

 

How did you measure the .168 if you didn't have the limiter to set it to 22? Did you shim it around or alter phasing through other means? or is that an extimate based on the cam ramp rate?

 

I degreed the cam with the actuator fully assembled in the parked position or fully advanced. The big spring will hold it there.

To figure PTV clearance I just measured the valve drop at 10 degrees before TDC with checking springs (or no spring). This is usually when the ex valve is closest to the piston give or take a few degrees. Then I measured the lift at the pushrod only with a dial indicator at 10 degrees before TDC for fully advanced and multiplied that times the rocker ratio and subtracted from the valve drop. To see what it was retarded 22 degrees just rotate the motor to 32 degrees before TDC and measure the lift at the pushrod and do the same math. You could measure it at 62 (52+10) degrees BTDC if you wanted to see what it was at full retard without a blocker.

 

Ah okay. I see what you're doing there.

Assuming 22* (crank deg) cam phasing available, the process for the exhaust clearance would go as follows:
- Install phaser sprung in advanced position (default)
- Measure valve lift at 10*BTDC
- Measure PTV clearance at 10*BTDC by pushing down on the valve
- Rotate the crank to 32* BTDC (10*BTDC +22* phaser travel)
- Measure valve lift at 32* BTDC
- Compare valve lift at 32*BTDC to valve lift at 10*BTDC. Subtract the difference from PTV clearance at 10*BTDC

You could even sweep over a range of crank angles to figure out exactly where your minimum clearance would be for both situations. **** man, that is brilliant. All clearances checked without ever rephasing the cam. Only challenge is understanding the phaser travel, but you could probably do that with a protractor while you're installing the limiter block or do as you did with the compressed air.

Very smart. I'm tempted to repeat my measurements just to see how they compare and also kicking myself for taking apart a perfectly good phaser. Having one of those "why didn't I think of that" moments. Thank you 64c10ls1!

 

Mike, sorry for the hijack.

 

You are close but let me be more clear and I will use the actual number I got with my small 214/228 114+7 cam

Check cam installed ICL with phaser in advanced position (default) **107 ICL
Assuming it is correct procede (They ground your cam right and sent you one on the correct core)
Remove spring
Turn motor to 8 degrees BTDC (thats what I used)
Measure ex valve drop from seat to piston contact with a dial indicator on stem (no rocker no spring) **.385"
Put the spring back on or hold valve up with cloths pin or checking spring
Install dial indicator on ex pushrod tip (no rocker) and turn motor till your on the base circle Push down on the indicator and set to zero
If you want to check PTV at fully advance then turn motor to 8 BTDC
read indicator **.034 .385 - (.034 x 1.7 = .058) = .327 ptv fully advanced
Turn motor backwards (retarded 22 degrees) to 30 degrees BTDC
Read indicator **.130 .385 - (.130 x 1.7 = .221) = .164 ptv retarded 22 degrees

This assumes the rocker ratio is actually 1.7 at all lifts (close probably)
This assumes the small spring in your dial indicator won't collapse your lifter (it won't)
You don't have to block your lifter this way.

You can do you intake this same way but only in the advanced position and at 8 degrees after TDC **.208 valve drop - (.077 x 1.7 = .131) = .077 ptv Intake fully advanced

 

You can just measure the gap from the stop to the vain with a caliper at the outer edge of the actuator. Then measure the diameter of the actuator bore.

Dia 3.294
Gap .246
.246 / (3.294 * 3.14) * 360 = 8.56 degrees

Mike, I also checked it with the block in the wrong chamber and came up with this

Dia 3.294
Gap .213
.213 / (3.294 * 3.14) * 360 = 7.4 degrees

 

Okay, I see you are doing it slightly different from what I said. Rather than ever measuring the clearance directly at a particular cam position, you are mapping out your valve lift, mapping out your seat to piston valve travel, then taking the difference to determine the clearance. One key difference is that with your method you don't need to install the rocker or ever worry about lifter preload (no solids required), which also prevents having to remove the head on an already assembled engine. But you do have to assume a rocker ratio and your measurement errors will add since you are not directly measuring the clearance. You are probably still getting numbers that are close enough.

Your intake clearance seems awfully tight though.

 

Mike it looks like he not only just found your problem, he has also seriously bested me in common sense.

 

Ya I didn't like it but the piston is chasing the int valve unlike the ex. At high rpm when its retarded 10 crank degrees the clearance will be greater anyway. I run less than that on solid roller motors without issue. Problem with hydrolics is you don't want to pump up your lifters.

Ran it several times to 6500 without issue so far. Normally the auto tranny will shift at 6300.

 

Do you mind sharing the specs on the engine? cam, compression, boost, etc?

Now I am just shamelessly hijacking.

 

Stock 2012 6.2L Silverado 1500
Comp cams 214/228 114+7 apx .570 lift
Beehive springs and comp pushrods 7.375 (actually measured 7.4 gurrrr)
Maggi 1900 blower with 3.0 in pulley instead of stock 3.3
Stock E85 compatible injectors because they were bigger than the ones in the kit. Need bigger, at least an LS9 injector.
Has 7.5 lbs boost with small pulley, 5.0 with stock pulley.
LS9 Map sensor

Now you got me thread jacking. lol

 

Ah ha! Someone needs to kick CompCams in the *** and have
Them change their directions from "any" chamber to the chamber
Closest to the pivot. Even then, 8.5 deg is not the 11 deg they're
Advertising.. Class action, class action...

No worries about hijacks, we're still on topic here...