1968 Corvette Distributor Advance Options

[Joseph M.]

Hello,



Basic Operating RPM Range:
1,600-5,600
Intake Duration at 050 inch Lift:
226
Exhaust Duration at 050 inch Lift:
234
Duration at 050 inch Lift:
226 int./234 exh.
Advertised Intake Duration:
288
Advertised Exhaust Duration:
296
Advertised Duration:
288 int./296 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:
0.587 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:
0.610 in.
Valve Lift with Factory Rocker Arm Ratio:
0.587 int./0.610 exh. lift
Lobe Separation (degrees):
107

[Duke W.]

Re: 1968 Corvette Distributor Advance Options

It sounds like the 38@2000 is being measured with the VAC connnected. In order to understand the WOT timing curve, you need to measure it with the VAC disconnected.

I may be able to give you some recommendations, but I need to know the OE centrifugal and vacuum advance specs, which should be in the '68 CSM, and you need to determine what the actuals are. Unless it already has very light springs, the centrifugal should top out at something near 5000.

I also need to know if it has ported vacuum advance (I expect it does) and need to know manifold vacuum @ idle speed and total idle timing (measured with the VAC connected).

IMO that cam has WAAAAAAAY too much overlap, but it's too late now...

For comparison the L-71 mechanical lifter cam has .050" durations (above the tops of the clearance ramps) of 231/231 and the LSA is 114 deg. Your hydraulic roller has similar durations, but a much narrow LSA, so it has a lot more effective overlap, which is not a good way to go for a road engine.

IMO it's tough to beat the OE L-36/68 cam with massaged heads if you want a docile and torquey big block with respectable top end power to 6000 and decent fuel ecomony. High overlap really kills fuel economy and low end torque, but doesn't help top end power.

Duke

[Joseph M.]

Re: 1968 Corvette Distributor Advance Options



Thanks!