Hello to all!! I need someone who's sharp at tuning higher compression olds motors. Ideally, I would love to get my car to run on 91 octane supreme.....without rattling to death! I've been at this for awhile now....
I have a persistant problem with my 455 motor in my 1972 442 Cutlass-s. Since I had the engine rebuilt, I have to use mostly racing gas to keep the engine from pinging, when its up to temprature! I'll list the major mods to the engine...
1. bored over .020 thou.
2. higher compression pistons..9.62 to 1, estimated compression ratio.
3. 32 degrees total advance... In an effort to find a possible answer, I took all the vacuum advance away...did I go backward? does the vacuum advance retard at full throttle or advance? is all mechanical better, like I was told by my mrechanic, "drag racing buddy"
4. crane cam...1500 to 5500 power band
5. Comp cams valve train with guide plates and "magnum" roller tipped rockers.
6. oversized valves, ported & polished cyl. heads
7. port matched intake and exhaust
8. "breakerless" single wire ignition module kit in distributor, but It reads 45 degrees with a dwell meter?? I was told that's normal for this electronic kit. wiring connections have been checked and double checked...correct coil side and all. I always thought 30 degrees was the norm for V-8 GM engines. Shouldn't it read the same? electronic or points?
could the factory harmonic balancer be bad..."spun" how do I check alignment on that???
The intake and carb are factory stock units except jet sizing for the correct air fuel ratio. Please help me stop having to take out a loan everytime I want to drive my car!!! I need a place to start diagnosis
THANK YOU!!!

 

You need to run it on 93 octane, sorry. To check the harmonic balancer timing mark, rotate the engine so #1 is at TDC and see where the mark lines up to the scale.

Around 36 BTDC @2800 - 3500 Rpm without vacuum advance connected is the norm for V8 engines. Does your engine ping? Are the valves adjusted correctly?

What ignition brand are you running? Does it require a full 12v? Spark plug gap?

Vacuum advance "advances timing" however depending on your distributor it could be advancing it too far. So yes keep it disconnected for now.

 

Do you have a good/proper cooling system? Beyond that ping is always a compression vs. octane issue as well as sometimes lean jetting.

Since it's been rejetted let's assume it's correct.
Exactly what cam is in there? 1500-5500 tells us nothing.

And that compression ratio was actually measured? By whom? What piston is in it? Unfortunately too many shops really don't know what they're doing when it comes to that.

Oldcutlass is right. You may just have to run 93.
I just built/dynoed a 10.0:1 iron headed 455 with a decent size hyd. roller and on 91 it didn't like anymore than 33* total. Lost hp everywhere at 35*.

Just an fyi.

 

Hi!
1. The ignition "kit" is named..."brakerless" made by B&M Co. Purchased from.. "year one"
2. Yes the engine "pings" when at operational temprature, 180degrees.
3. Spark plugs are E-3 brand and the gap is factory set..E-52's.
4. the camshaft is a "crane" 292-H pwr. band is 1500 to 5500 rpm
5. the valves are set correctly at zero lash..Comp cams "magnum roller tipped" rocker arms with locking type adjusting nuts..."polylocks"
6. the rest of the valve train is all comp cams and is set up just like a chevy cyl. head with guide plates etc.
7. My mechanic (former drag racing buddy) has assembled and "ran" several 455 Olds motors and set the motor up at 32 degrees total advance, no vacuum, all mechanical. We both "guggled" different tension springs in the distributor for optimum staged "tip-in" and is all in by 3500 rpm. He's also the one who did the math, to come up with the final compression ratio. It sounds like Im not alone in this....
Regards to all!!
Denis