I recently purchased a 1971 442 convertible.and have a few questions that some of you may be able to help me answer.

I received the car from Wisconsin and we filled it with 91 octane ethanol free gas prior to shipping the car to Texas. It ran fine when it arrived, but once I went through the WI gasoline and filled it with 93 octane with 10% ethanol purchased in the DFW area, the car began to ping. I added a can of O'Rielly's octane boost and it did nothing. Except for the pinging the car runs good in 100 deg F heat with the AC on and does not overheat. The engine is a 455 cu in but is modified with Edelbrock aluminum heads, performer manifold, carburetor. It also has a high lift cam and forged pistons. These items were purchased from Mondello Performance Products back in 2005 with an engine rebuild around that time.

The cam specs are: lift (in) intake/exhaust .512/.523
duration (deg) intake exhaust 274/280
lobe separation 110 deg

Cylinder heads: 77 cc combustion chamber, 2.072 in/ 1.68 in valves.

We conducted some timing and vacuum checks and obtained the following:
intake manifold vacuum = 12-13 in Hg. best is 13 in Hg when adjusting idle mixture screws.
timing = 10 deg BTDC at idle, 45 deg total BTDC (advance) at 3000 RPM with 20 deg of that advance is vacuum advance.at 3000 RPM.

I am being told that 45 deg total advance is way too much. So my questions are:

1. What should the total advance be for the type of gasoline available (93 octane with 10% ethanol) in the DFW area? I am looking for good drivability, not to race the car.
2.are there any tuning shops in the DFW area that can work on Oldsmobile's? This is a concours restored car so I am not looking for a butcher shop.
3. I would like to eventually replace the high rise intake manifold with a low rise unit because the ram air top assy currently does not fit under the hood. What low rise intake manifold do you recommend? Would a repro W-30 manifold work? any porting needed?


thanks,

Todd

 

My learning has been total timing is initial + mechanical, and vacuum is separate from that. With your numbers, the total timing is 25 degrees which is extremely low.

Anyway, you can limit the vacuum advance to 10 degrees or so with a limiter, either home made (like I made) or with a commercially available one.

 

Id recommend you find locally available not ethanol gas, or have the carb modified by a performance Q-Jet builder to handle the ethanol

 

thanks, I have a limiter on order from ACCEL and will try that first.

 

With a concours restoration, you’re likely still using springs and weights for the advance / retard processes. These parts can wear and throw timing off and indeed you may want to start playing around with swapping in different springs to advance or (more likely) retard the timing in particular RPM ranges to stop the pinging. 10 degrees initial is about right, unless it pings at part throttle or is hard to start. If either of those conditions are present, consider dialing back the timing.

I’ve said it before, this is not an endorsement, but go have a look at Progression Ignitions Bluetooth HEI distributors if you’d like to go beyond weights and springs into software controllable advance which you can use to adapt to whatever gas you’d like to use. My big cars have no advance below 900 RPM as part of the Progression design, then when the engines fire they idle at about 16 degrees and are completely advanced with a further 30 degrees by 3,000 rpm.

If you dig concours and stock, ignore my paragraph above and go find Lars Grimrud’s articles and part numbers for various GM distributors which may help you.

Cheers
Chris

 

Chris, your comments made me realize the descriptions used are a bit misleading. I suspect the body is restored whereas the engine was modified.

 

Timing will change with altitude if you are going closer to sea level retard the timing. I would go in 2 degrees increments until it quits pinging. You don't want to drive it and let it ping it's not good on the motor.

 

That cam is strong for a driver, and really doesn’t support power brakes.
What is timing @3000 rpm?

 

Timing @ 3000RPM is 45 deg.

I think that is high. I will start changing weights and adjusting vacuum advance one I receive the limiter.

 

Loosen the distributor, and with the vac advance line plugged, @3000rpm adjust the distributor to achieve around 32*. You'll never get their with different springs.

 

Per his post above, the initial + mechanical is 25 degrees, then there's 20 degrees of vacuum advance. I would simply disconnect the vacuum advance.

 

So it didn't ping with 91 non ethanol, but then you filled up with 93 with 10% and it started pinging? Are you still running a points distributor? Have you tried running without the vac advance connected? Most distributors keep advancing past 3000 RPM unless modified.

 

There is nothing wrong with 45 degrees of total timing at part throttle cruise, assuming the timing curve is correct.

This is my method for dialing in ignition timing. It’s time consuming, but it works.

Start by disconnecting and plugging the vacuum advance. Get a dial back timing light, or do the math to create a new timing mark at the 36 degree point on the balancer. Last option, timing tape.

Start the engine, rev the engine to 1000rpm and note the timing. Rev the engine to 1500, mote the timing again. Rev to 2000, 2500,3000 and so on until the timing stops advancing. That’s your timing curve.

Next, rev the engine to the max timing speed, and set the timing at 36 degrees. Let the engine idle, note the initial timing. Take the car for a drive, while listening carefully for pinging or detonation. If you hear none, great. You could try a couple more degrees of timing just as an experiment, but more than likely 32-36 will be the “happy place”.

If it rattles, back off the timing a few degrees and drive it again. Keep playing around with it until you find the best setting. Ideally, you would adjust this on a dragstrip or some other controlled environment, but you can find a good compromise if your patient.

Once you’re happy with how it runs, how does it start? If the cranks slowly with the engine hot, you will need to limit the total timing by creating a timing stop or welding the slots closed in the distributor. The idea is to limit the centrifugal advance so you can back off the initial, resulting in the same amount of total timing. Once the engine runs and starts well, note the initial timing.

Once everything is set, it’s time to dial in the vacuum advance. DO NOT MOVE THE DISTRIBUTOR to solve a pinging condition from this time forward. You have the timing curve optimized, now you need to tailor the vacuum advance to work with it.

Connect the vaccum advance to a manifold vacuum source. Take the car for a drive, while listening carefully for rattling, and specifically WHEN if rattles. If it rattles all the time, you need to limit the amount of vacuum advance by installing or creating a limit stop. Crane Cams and accel use to sell the limiting cams for about 10 bucks, I don’t think they sell them anymore. Keep in mind, limiting the vacuum advance also increases the amount of vacuum it takes to get the timing plate to move. Since it also moves the pickup coil pole piece, it also changes the initial timing. Reset the timing to the previous “happy place” before driving it again.

You can play around with the rate the advance comes in by using an adjustable vacuum advance canister. I know ACCEL offers them, if it rattles only at light throttle but stops when you begin to crown the throttle, increase the spring tension. There is nothing wrong with LIGHT pinging at part throttle that stops once you step on the gas further.

Once all of this is done, you can dial in the carb, which might necessitate playing around with the timing again, then go back to the carb, it depends on how picky you are. Use the gas you normally use, and be a little conservative. That way if you have to use fuel that’s not quite up to the usual standard, the engine will still be somewhat happy.

 

Thanks everyone for the advice. Yes it is pinging on TX gas but did not ping on the 91 octane ethanol free gas. I am basically "stuck" with the gas blend that is available in the DFW area.

I will start playing with the car again in about a week. I have an ACCEL vacuum limiter arriving tomorrow. I really appreciate the detailed instructions and will let you all know how it turns out.

 

Think about where you got the last gas. When I lived in the Houston area some of the cheaper stations claimed their gas was 92 octane but my Cutlass ran like crap on it, but with another station’s 92 it ran fine.