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Engine Detonation 350 Oldsmobile with Quadrajet

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Cliff Ruggles:
Right to start with you do NOT have enough camshaft in the engine so it's going to be octane sensitive.  252 seat timing is WAY too small for a 350 CID engine over 9 to 1 compression.  The tight 110LSA just makes it worse closing the intake valve WAY too soon which narrows up the power curve and spikes dynamic compression pretty high early in the RPM range.  Olds engines also use dished pistons (most of them) and crappy combustion chamber shapes.  Between the bathtub chambers and too much quench area they tend to run hotter and ping easier than other designs.  A LOT of quench area is NOT your friend with these things BTW.

I'd yank the cam and tink it off the nearest dumpster and install a cam with about 20-30 degrees more seat timing and wider LSA.  Summit sells a 214/224/112 cam that will work much better than the tiny little Comp Cam you are currently using.

I've ran into EXACTLY the same issues you are several times with engines in the 9 to 9.5 to 1 range pinging with any heavy load on them and I couldn't pull out enough timing to make them stop.  Every single time they had a short seat timing Comp Cam in them on a 110LSA......FWIW.

As far as Comp Cams valve train parts, specifically their "roller tip" rockers.....absolute and complete JUNK!  I have yet to remove a set from on engine that weren't blue or even black where the poor fitting grooved rocker balls were wearing heavily into the bodies.  The grooved rocker balls and poor fit to the bodies are also a design flaw.  Instead of the oil "pooling" and running out on the tips of the rocker arms to get atomized for cooling and lubrication it runs straight down the studs and back to the sump....duh?

I'm also NOT a fan of their heavy retainers and they recommend WAY too much spring pressure for their tiny little flat camshafts which is really hard on everything in the valve train and a big contributor to all the wiped out lobes we read about every time we log on to a Forum related to this hobby......FWIW......

rhinosoft007:
Thanks for the updates guys, sorry I missed the replies on this post, may have forgotten to tick the correct notification button.

Cliff, thank you for your comments, will go down that track.

Check my latest post, now its the carb, related maybe.?

Graeme

Cliff Ruggles:
Once you get the right cam in that engine your detonation issues will go away.  Carbs and distributors aren't going to get you there.....IMHO....

Jeff K:
 I didn't see weather your running a vacuum advance. I know Cliff is pro vacuum advance but I've had  :) trouble with them.
 
 In 1974, I blew up a real nice GTO 389 with dual quads because I connected the vacuum advance in the points distributor to the ported vacuum in the lower left corner next to the air  fuel screws on the front AFB. This vacuum outlet was for the Roto Hydra-matic (Slim Jim) equipped Catalinas and Grand Prix equipped motors.
This was in a real strong 1964 2+2.. It had a 1966 389 with 092 (10.5) closed chamber heads.

Cliff Ruggles:
Vacuum advance is a load sensing device.  It only adds timing at very light engine load.  Any heavy or full throttle it's not adding any timing.

Doesn't matter if you hook it up to manifold or ported vacuum.  The only difference between manifold and ported vacuum is that the VA is applied at idle and coasting with a manifold vacuum source. 

Using ported vacuum it's only applied at light part throttle or when you are driving very gently.

Neither scenario will contribute to detonation at heavy engine load.  If you experience any pinging at light engine load it's telling you that the engine doesn't need as much timing as that VA is adding, but it will not destroy the engine. 

If you run in to that scenario simply modify the VA to add less timing or find one that does.  You can measure the travel in the VA or use a timing light to find out how much timing it adds.  A drill bit makes a good measuring device for VA units.  They are also easy to modify.  Here I use a MIG welder and round file to fine tune them to add the amount of timing desired.......

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