L67 / L36 timing set interchangeable? - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 10-31-2007, 04:01 PM   #11
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OK, digging up a semi-old thread for a potentially stupid follow-up question...

Quote:
Originally Posted by 95naSTA
They are not. Well, the cam gear isn't. It retards the L67 cam a couple degrees.
OK, so if an L67 cam timing gear retards cam timing by "x" degrees, and I put an L67 cam timing gear on an L36, would this be exactly the same thing as going into the PCM timing tables with the tuner and retarding timing across the board by "x" degrees?
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Old 10-31-2007, 04:03 PM   #12
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Cam and ignition timing are seperate. You'd need to do both to supercharge an NA, right?
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Old 10-31-2007, 04:22 PM   #13
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Quote:
Originally Posted by J Wikoff
Cam and ignition timing are seperate.
Yep.

The L67 cam gear is made to statically retard the cam a couple degrees of crank rotation. (since the the crank spins twice as fast as the cam)
The intake and exhaust valves just open a tiny bit later which raises the powerband a little bit.

I haven't personally verified that the L67 cam gear actually does retard the cam. I've seen it posted that it does. And from what I've seen, it does look different.
I wonder how much it actually does retard the cam, since I've never seen the actual number in crank degrees.
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Old 10-31-2007, 04:38 PM   #14
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Quote:
Originally Posted by J Wikoff
Cam and ignition timing are seperate. You'd need to do both to supercharge an NA, right?
I knew it was a stupid question Brain fart on my part, sorry!

I'm not looking to supercharge; but I am looking to cam my L36.

Thinking I'll want to swap in a new timing chain and dampener, I bought a whole new stock timing set / dampener (that turns out to be a takeoff from an L67 crate motor).

I am wondering about these things because if my current cam timing sprocket looks worn, I want to know if I can use the L67 cam timing sprocket...but now I need to consider whether using the L67 cam timing sprocket would be beneficial (or detrimental) performance-wise.
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Old 10-31-2007, 04:49 PM   #15
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I'm sure you could re-use your original cam timing sprocket. They aren't really a wear item. It'* more so the chain and tensioner.

I have 90k stock cam plus 40k on the GT1 cam with stock timing gears.

I've even got a 80k old L36 timing gear laying around somewhere. It looks perfectly fine. It'* yours if you want it and I can find it.
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Old 10-31-2007, 06:22 PM   #16
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Quote:
Originally Posted by 95naSTA
I've even got a 80k old L36 timing gear laying around somewhere. It looks perfectly fine. It'* yours if you want it and I can find it.
I think I'd like to have that gear...at the least, I could compare it to the L67 gear and see if I can figure out the cam degreeing difference. If you find it, PM me.

Thinking more about the performance aspect of this...

So, I think I understand that retarding the cam timing hurts low end by causing later intake valve closing, leading to lower dynamic compression ratio (heck, camming does this, which is one reason to mill the heads for greater static compression ratio).

But, how (if at all) could retarding the cam timing help high-end power? Improved scavenging perhaps?
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Old 10-31-2007, 07:04 PM   #17
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I'll take a look this week.

Quote:
Originally Posted by agrazela
But, how (if at all) could retarding the cam timing help high-end power? Improved scavenging perhaps?
At higher engine speeds, the intake valve isn't opening as early as it should. Much like ignition timing, it needs a head start. Retarding the cam is just that, giving the valve opening a head start.
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Old 11-01-2007, 03:38 AM   #18
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Alright, further research suggests that the L67 cam gear advances cam timing versus the L36:
http://www.thrashercharged.com/tech_...-L36toL67.shtm

(If true, perhaps this could be part of what makes the stock L67 torque peak at 400 lower rpm than the L36?)

Looking at photos of said cam sprockets on Rock Auto website suggests to me that the L67 gear might indeed move the cam clockwise a few degrees versus the L36...but that is kinda hard to tell just from photos

I'm really looking forward to comparing these sprockets side-by-side.
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Old 11-02-2007, 11:34 PM   #19
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i remenber on small block chevy in the late 70 to 80'* the cam gear where retarded 4 degrees and that would lower the static compression and the low end power but would give more top end we would buy multiple key way sprokets and install the cam where we had the most compression
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Old 11-06-2007, 08:25 PM   #20
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The mystery is solved!

(Thanks to Mike for sending me an L36 cam gear.)

Comparing them side-by-side, and measuring three different ways, my conclusion is that the L67 cam timing sprocket advances the cam (clockwise) versus the L36 sprocket.

The teeth, dot and camshaft position sensor magnet are in the same relative places, but the camshaft keyway is 2 degrees advanced (clockwise) on the L67 gear.

(OK now, help me out on the automath: does 2 degrees on the camshaft sprocket equal 2 degrees of cam advance, or am I supposed to use some factor like "multiply that by two and call it 4 degrees of camshaft advance"...)

Perhaps I'll use the L67 cam sprocket when I cam, to get a little extra low-end grunt
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