dallasite21

I have a 1971 Cutlass with a rebuilt 455 with Edelbrock 3712 Cam Kit, Ga Heads, .40 over bored cylinders, high compression pistons, I beleive the Federal Mogul 369P pistons, a Mallory HEI distributor, Quadrajet carb, and AC delco plugs. Compression Ratio should be 9.5:1. My plugs are currently gapped at .42, but it is not running right . Rough idle, and vacuum in the 14 to 16 in/lb range. I have searched for leaks and found none. Car also diesels when you turn it off even though my timing is fairly close although not perfect. Also runs a little hot.

What should my gap be set to for a set up like this? Anything else not sound right about this configuration?

Here are the specs for the cam kit

Edelbrock 350-3712


Intake Valve Lift (in.)
0.448
Exhaust Valve Lift (in.)
0.472
Int. Duration @ .050 in. (Deg)
204
Exh. Duration @ .050 in. (Deg)
214
Int. Duration Advertised (Deg)
280
Exh. Duration Advertised (Deg)
290
Lifter Type
Hydraulic Flat Tappet
Engine Make/Size
Olds 307-403
Usage
Street/Performance
RPM Range
0-6750

DeltaPace77

Doesn't sound like a spark plug gap problem, but possibly no spark to a plug at all. May be a valve train issue, as had a hydraulic lifter pump up on me before, taking the pushrod and rocker arm with it. Running hot could be a cooling system problem, to much intial timing or, or lean carb jetting. Your cam doesn't sound very big for a 455, so doubtfully that. Good knowing the LSA spec though. Far as the shut down dieseling, could be cylinder carbon build up, low octane fuel, or again lean carb jetting. Probably check each plug for spark first(auto parts stores have cheap testers), followed by a look at the valve train.

Allan R

Your gap is pretty much bang on. Should be .040, but with HEI it can be pushed to .045. With an HEI you can prolly advance your timing a fair bit - it will run cooler. Adjust your fuel mix to correct that rough idle; I had the same problem my engine would run rough because it was set too lean. (what DeltaPace said)