3900 Camshaft spec dilemma

[Guest]

I believe I acquired the following specs from CNCguy:

open close
Int 6 btdc 24 abdc 210
Exh 53 bbdc -19 btdc 214
LSA 112.5

Delta tells me today:

Int -18 atdc 49 abdc 210
Exh 35.2 bbdc 7 btdc 208
LSA 116


The problem is the specs from Delta look like crap in desktop dyno performing about 18% under the previous thought to be stock specs. The 07 G6 and chevy Uplander 3900 use the same camshaft per GM. #12591843.

I'll give them a call and have them check to see if a mistake was made in the numbers I was given because the curve appears to be off a good bit.

corrected the LSA
I wonder if he's reading the lobes in reverse order.

[robertisaar]

this is what i came up with, though i have no idea where my original numbers came from...

[Joseph Upson]

It gets worse when retarded beyond 0 degrees. I recall that my current reground cam when the module is at full stop is only slightly retarded so the stock cam at full stop may not show any retarding of the intake valve at all, that may be the 0 degree mark. I read in a magazine article that in one case the VVT camshaft in a Ford engine goes to full retard in the event of a fault being set regarding its control. Chances are having a negative cam position in Desktop for this cam maybe an error.

The first cam reground by Delta shows almost the exact same curve at 0 deg that the stock camshaft shows at -15 deg, how is that possible?

[CNCguy]

Deleted

[Joseph Upson]

My measurements were taken with the VVT fully advanced. The actuator showed 18 degrees at full advance when I had it measured on a CMM. The numbers below should be at straight up. Retarding my numbers by 24 degrees closely matches Deltas intake numbers. I still have that cam here and will see about getting it measured when time permits.

-18 Deg
Int -12 btdc 42 abdc 210
Exh 35 bbdc -1 btdc 214
LSA 112.5

Thanks, I'll re-enter the specs later. Just to clarify without minus signs, your specs are to be read:
.
int Opens 12 deg After TDC, closes 42 deg after BDC,
exh opens 35 before BDC and closes 1 deg before TDC.

I don't understand the difference in the LSA as that doesn't change with cam position. They don't have the actuator and are treating it as a typical non variable piece.

[CNCguy]

Joseph.... I didn't check the numbers you originally posted and assumed they were mine when I modified them. After your last post, I dug around and found my original measurements. They are quite different that the ones you posted as the LSA is rather large. The measurements were taken at .006", .050" and .260" with LSA checking 119, 120.5 & 119 respectively. Below are my .050" measurements along with the numbers adjusted for 18 degrees retard.

Taken at .050" Lobe Lift
IN open relative to ATDC 1 19
IN close relative to ABDC 30 48
IN Duration 209
EX open relative to BBDC 59 41
EX close relative to BTDC 29 11
EX Duration 210
LSA 120.5


Could the one set of numbers be from Delta when you had the first cam reground? The discrepancy in numbers is surprising. Is it possible there is that much variation in the assembled cams? Surely not. I had wondered if the 120 LSA measurement may be an error but think it is right after reading some articles online. The LS1s have almost 120 LSA according to an article I found.

http://www.chevyhiperformance.com/techarticles/95298_camshaft_lobe_phasing/index.html

"Most factory camshafts use wide lobe separation angles to improve idle stability. The ’98-2000 LS1 Camaro hydraulic roller cam uses a 122-degree intake centerline combined with a 117-degree exhaust centerline to create a 119.5-degree lobe separation angle."

[Joseph Upson]

Not sure what to make of it. Delta doesn't have cam software which makes me wonder what kind of resource they are using for their spec recommendations. There is also the possibility that GM used two camshafts as we've discovered they used two different rod lengths with no mention of it. I have yet to check the part number against the 2006 G6 cam part number. I never received any specs for the first cam, a comment was made about the wide lobe separation but since I accepted what I had in the computer I didn't ask them about it at that time.