Advancing the cam timing

[Blue 300]

I installed the cam "straight up"
I degreed the cam per Comp Cams instructions for Intake centerline.
That is, to note degree wheel @ .050 before make lobe lift and .050 after. Add the two degrees and divide by 2.
The result was 106.5 which is close enough to the 106 on the cam card.
Then I used the "advance 4 degree" slot on the crank gear.

Checked the degree again and i'm at 103 degrees. What gives? is this correct? Because I was expecting 110 degrees. Am I looking at things backward?

 

[CBODY67]

What are the cam card specs for "straight up" timing? What engine size?

Why do you feel you need to advance the cam timing? Just curious. Many would retard it to bleed off a bit of low end torque and get better top end power, from such a change.

Thanks,
CBODY67

 

[Lefty71]

Have you checked that timing gear set against a known set-up?? Could be a crappy one.

 

[Cazman]

The answer to your question is that it is correct. To advance the cam the number will go down. You should get more low-end power doing this and 4 degrees advanced is not un-common.

 

[70bigblockdodge]

That is correct number goes down. You are advancing the point where intake valve closes trapping most pressure in the cylinder. More cylinder pressure equals more torque down low. If you have a older engine and the compression is higher you can retard the cam (close intake valve later) increasing the scavenge time and allowing more rpm up high.

 

[Blue 300]

Thanks guys,
I'm pulling a small vintage camper with my '68 300, and I think that advancing will be in my best interests. I put a new Comp Cam with .470 lift and 262 dur
21-222-4(Single Bolt) - Xtreme Energy™ Hydraulic Flat Tappet Camshafts
I also have a bag of comp cams degree offset bushings. Here's another question. If the ICL is 106 how far advanced do you think is ideal for my 440?
Stock 440, auto highperf castiron magnum ex manifolds, dual exhaust, with edlebrock 600 cfm carb and electronic ignition. 2.77 rear gear.
Using the adv-4 on the crank gear is super easy, unless you think that I should go only a degree or two, then I could use the offset bushings.

 

[Cazman]

From what I have always been told you use 4 degree increments. I guess 2 degrees is not that noticeable. If it were me, I would call Comp Cams though.
I got a custom grind from Dwayne Porter and he wants it advanced 9 degrees.

 

[CBODY67]

I suspect the new cam will have a good bit MORE cylinder pressure than the stock cam. Using the multi-keyway crank sprocket is a good way to do things, just as the cam bushings can be too, just depends that if you want to change things, the bushings would be easier to do if you have a two-piece front cover.

The OTHER thing is that unless you have the engine on an engine stand, use a dial indicator to verify TDC on the balancer, you don't know if what you have is correct . . . how the key way is cut in the crank nose. To ensure that everything is as it should be.

I like the rpm range of the cam, which might end up being a few hundred rpm lower than spec'd with a 440 than with a 383, depending upon which engine they did that rpm range for. Still, it'll be making power/torque a hair under the torque convert's stall speed, which I perceive is "good". In that respect, I'd leave things like they are and focus on getting the distributor advance curve "better" with that 110 LCA (one thing I had to do with my '77 Camaaro 305 when I put in a 110LCA cam).

Considering how the distributor drives off of the camshaft, how does such a change from "straight-up" affect the displayed spark timing reference point? Just curious.

Just some thoughts,
CBODY67

 

[furious70]

Timing doesn't change, dizzy is put in relative to TDC regardless of where the cam lobes are

 

[CBODY67]

Timing doesn't change, dizzy is put in relative to TDC regardless of where the cam lobes are

So something other than the advanced/retarded/"straight-up" camshaft drives the distributor? OIl pump doesn't care, I suspect.

IF the base spark timing was set at 10degrees BTDC. Then the front cover was removed and a 4 degree advance bushing was put into the cam sprocket. The front cover and such reinstalled, where would the base timing be after the change? Distributor body position not changed during the cam bushing installation.

It just seems to me that if the camshaft phasing relative to the crankshaft is changed, then the base spark timing setting would also change, proportionately. Which would require a tweak after the bushing was installed, to maintain the existing base timing setting. That's the theory I'm following in this deal.

Other question would be "How much more torque would such a 4 degree advance situation add to the existing torque level? Aside from the torque increase from the upgraded camshaft.

Thanks,
CBODY67

 

[70NEWYORKER]

If you advance the cam the spark timing will also be advanced. The spark advance degrees measurement is in relation to crankshaft's postion. Zero degrees or Top Dead Center is when the number One piston is all the way up.
If you advance the cam you will need to retard the body of the distributor.