I have a 455 .040 over, 10.25CR pistons, Head and block milled .010", Permatorque gasket .039" compressed, 1970 W30 automatic cam

I am using a Quadrajet carb that was the recommended replacement in 1980 per Oldsmobile.

Distributor recurved to W30 specs and NOS stock vacuum advance, running 10 deg BTDC.

455 runs about 200-205F degrees around town, 205-208F on highway.

I want to keep stock appearance, but had 4 Core radiator rodded out, tested using 195 thermostat(tried other temps, and orifice sizes, antifreeze, water wetter, Olds HD water pump, etc etc etc this is best it can do with stock appearance.)

I am running VP 101 unleaded race fuel only.


When I first start the car and engine is cold say up to 185 , it runs great and NO pings when I jump on it moderately hard or above.

after it hits normal operating temp say 205F it pings like crazy when I jump on it moderately hard or above.

I have been told that the VP 101 should be enough to run without pings and it is running too lean.

I backed off timing to 6 Deg BTDC and it was a little better but still pinging.

So looking what others have done.


Rejet richer?? What primary/secondary jet/rod specifications?


or ???? other ideas


Thanks

Fred

 

You may try a cooler plug. What are you running in it now?

 

Do a compression test. Not that you can change it now but I'm guessing your dynamic compression might be high. Getting it cooler couldn't hurt either.
I know you are trying to keep it stock looking but there are radiator manufacturers who make better stock appearing radiators.
There were no 455's in 1980 so you could be running lean since they were all on SBO during those years.
What is your total timing with vacuum advance disconnected?

 

Perhaps with richer jets and dropping the thermostat to 180° would be beneficial. Running a few degrees cooler will often be enough to tame the pinging.

 

If you are running a stock air cleaner with the heat riser tube. Make sure the butterfly in the inlet of the air cleaner is open to the fresh air side with the engine running. I have seen the bi metal valve (it is basically a air bleed valve) malfunction and cause the butterfly to close off the fresh air side anytime the engine is running. This means all of your air charge is coming from the heat riser tube (off of the exhaust manifold) This would put your inlet air temp in the 350 degree range and will cause pinging.

 

The "W-30 AT cam" is the same as any other 1970 442 automatic cam (285/287). Is this what you have? Which "W-30 specs" did you have the distributor curved to? AT or MT? Did you have the vac advance altered as well? In any case, this isn't 1970 and it is unlikely that a 1970 advance curve is correct for today's gas. Also, are you running ported or manifold vac advance?

 

Fred your running temps are good. How do your plugs read? White, Black or tan? This color will dictate carb jets n rods. I suspect yours are white. If its an off-the-shelf smog era Qjet its likely lean as hell. This could be most of the problem. Determine what jets n rods are in there now (primary and secondaries and the secondary cam & hanger letter designation). Is the secondary (AVS) door opening up when you have it on the floor? That setting could be too tight.
All this carb jargon too much? Get the two Bibles for Qjets and read. Or send it out with all the info on your car and have it set up. They will need your vacuum signal, comp ratio, cam profile, gearing, converter stall, your altitude above sea level, available fuel octane etc...Fix the lean fuel, part and WOT conditions first before moving to timing.

With a true 101 octane gas it should take a bunch of timing at 10.25:1. I suspect the centrifugal advance is coming in too early and is too much? Combine this with a lean carb and there's the problem(s)

As mentioned you need to super-tune the distributors advance curve. Whats the total timing setting and at what RPM does that total come ALL in?

Do you have a set-back timing light? Get a decent one if not...not harborjunk.
Start with 10-12 initial base timing at 6-800RPM warm. Install an adjustable position(not adjustable rate) vacuum advance canister. Set it to obtain 8-10* more timing at idle, warm. Now your total at idle is 18-22*. Make sure the advance canister is plugged into direct intake vacuum, not ported or above the throttle plates.
The centrifugal advance will bring in the rest, say 10-15* for a total of 36-38*, or even more maybe, at the desired RPM. Your desired RPM may be 2600-3200 RPMs. Your areas elevation, gearing, torque converter etc...will all play a part in where exactly everything needs to be dialed in. A dyno will make quick work of this. If not a lot of trail and error is needed. Bottom line is... give it as much timing as it will tolerate once the lean fuel condition is fixed.

 

Don't forget distributor degrees are 1/2 crank degrees when looking at vac advance specs.

 

What size secondary rods are you running? I had the same problem after changing carbs but mine was only bad at WOT. Going to smaller secondary rods completely solve the problem. Before doing this I ruled out what others are suggesting above (timing, etc).

 

initial timing may not be as important as total timing. your distributor may be advancing too much and needs to be recurved. there are some youtube videos on the subjects of recurving distributors and total timing. good luck

 

Thanks guys, found my distributor mechanical advance is way too advanced. like 20 deg over spec!! Tom Lamano is now another on my do not use list...

 

Also went to 44 primary rods in carb per CLiff's High Performance. rest carb is stock specs.. Really helped

 

38 degrees is a lot for an Oldsmobile. My stroker 400 ran best on the dyno at 34 and is was very rich. It has three twos.