mcconahay37

iTrader: (3)

I'm about to redo the advance curve in my vacume-advance HEI distributor. With the spring kit, there is a graph with three advance curves. I'm not really sure how to interpret the graph, and I don't know which curve I need. The engine is a 350 with a slightly larger cam, minor head work, Performer RPM intake, Holley 600cfm carb, Comp Cams 1.6:1 roller-tipped rockers, and a Crane HI-6 CD ignition. Also, what should I open my spark plug gap to to take advantage of my upgraded ignition?



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82 Camaro:
350, Erson cam, ported heads, Crane Hi-6 ignition, Accel supercoil, Comp Cams 1.6:1 rocker arms, TH350 tranny with 2500 stall.
SLP 1 3/4" headers

RB83L69

What cam? what compression ratio (heads & pistons)? what gears?

Those are the biggest determining factors for the desired advance curve.

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"So many Mustangs, so little time..."
ICON Motorsports

[This message has been edited by RB83L69 (edited June 21, 2001).]

8Mike9

The graph shows the amount of mechanical advance applied with each spring set vs. engine RPM.

This advance should be added to initial/base timing with the vaccum advance disconnected.

As RB mentioned, several factors determine the curve you'd want to run. Most of us in the "pre-ECM" days did this via trial and error. There's probably dyno programs out now that can get you right where you need to be..or contact the manufacturer for a recommendation..or just post the info RB asked for...he's probably been through it several times before.

mcconahay37

iTrader: (3)

Unfortunately, I don't know the cam specs. I bought the engine from my dad's friend, and he had done the swap but didn't know the specs on the cm. It's a little bigger than stock, but that's all I know. Compreesion ratio is probably about 8.5:1 and I have 2.73 gears. Looks like trial and error will be how I do it, but which curve do you think I should try first?

RB83L69

Start with the red springs. With 8½:1, you'll almost have to work at it to make it ping. It will of course run the best, produce the most power, use the least gas and have the best throttle response, with as much timing as possible without pinging. Set the static timing by advancing it until it pings at low RPM and low vacuum (4th gear at as low RPM as it will stay in high gear at, and a good bit of gas pedal). Once that's set, see if it pings at high RPM with heavy load and full throttle (3rd gear at 3000 RPM, WOT) with the red springs; if so, try the blue, if it still does, try the white. Once you have that set, adjust the vacuum advance until you can go up a hill in 4th gear and lockup at 50 MPH, give it a little gas but not so much that it shifts down or out of lockup, and add vacuum advance until it starts to ping, then back it off until it quits. All of this with the motor fully warmed up or even a little too hot, so you don't get into trouble when it does get hot.

You need more cam than "slightly larger than stock" to work well with the rest of your setup. You might want to look at a Comp XE262H which should work well with the bigger rockers, without killing gas mileage or any of that, or requiring bigger valve springs.

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"So many Mustangs, so little time..."
ICON Motorsports