Pinging - Team Camaro Tech
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post #1 of 12 (permalink) Old Jan 4th, 02, 11:08 AM Thread Starter
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Let me try to make this short...I bought my car, the tank was near empty, I filled it up with regular 87 octane gas. It started pinging so I retarded the timing from 13 to about 7 before it stopped pinging. I ran a few tanks of high octane through it before I advanced my timing back up to 10. My bottom end power is great,I can floor it and get no pinging. But when Im on the highway and punch it, I get a lot of pinging. It never pinged when I test drove it, however I never drove it on the highway. I hate to retard my timing more than I have to, but unless I can get some suggestions from you all Im going to have to. My engine is a 383, Holly carb, 700r4 tranny. I dont know if you need any other info? Your help is appreciated!
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post #2 of 12 (permalink) Old Jan 4th, 02, 01:40 PM
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Pinging and pump gas have been the biggest nightmare for a lot of folks...
Depending on where you live the octane is different...
Here in AZ and CA... 91 octane is the highest available from the chains... use to be 92..
In the East... Sunoco has 94 and Amoco has 93.
Try to use only the highest octane sold..
Here are some things that need to be checked.
First thing is to make sure the 0 degree mark TDC is properly indexed to the balancer mark... use a spark-plug piston-stop .... I have seen these marks way off many times..
The next thing to verify and check is the vacuum advance ...use a hand-held vacuum pump connected to distributor and with timing light check that this is working...when this hose is connected to MANIFOLD vacuum you should see the timing jump up by 6 to 8 degrees approx...
Next you need to make sure the carb is set-up properly and not leaning out...
Look at the plugs porcelean...they should not be bone white...the ideal color is the color of a light brown egg ....
Make sure the CORRECT spark plug numbers are installed....a too high heat range can cause extra combustion temps and pinging...
Last resort is to move down in heat range like 2 sizes to see if this helps..keep an eye on the plugs to make sure the colder plug is not glazing...
If the car is equiped with emmissions items like EGR , PVC..ect and they are not working properly ..this too can cause problems...eliminating these features can help reduce these problems..
Regards
Chris


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post #3 of 12 (permalink) Old Jan 4th, 02, 07:02 PM Thread Starter
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Thank you! those are excellent suggestions. I was wondering about the vacum advance, but wasnt sure how to test it. I also wondered about it leaning out, but I thought I would have to buy an air fuel meter to verify. I still would like to buy one, but this should get me buy. THANK YOU again!
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post #4 of 12 (permalink) Old Jan 6th, 02, 03:36 AM
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I would like to make a couple of other points over the excellent post that cerrem made. Great points!

Engine operating temperature will have a dramatic affect on detonation as well. A cooler thermostat and outside induction air will help to alleviate these symptoms.

You did not mention what type of ignition that you are running. Stock HEIs are known for too much advance and have to be either mechanically limited or have a limiter installed on them. I have run across this problem in droves. The symptoms that you have expressed are exactly what the HEIs do. High loading under accelleration and too much advance from the distribor is the problem. Crane, of all manufacturers, makes a limiter for your HEI if that is an issue.
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post #5 of 12 (permalink) Old Jan 6th, 02, 05:36 AM Thread Starter
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Its a mallory distributor, electronic points and regular vacum advance. I do have a cowl hood, but its non functioning with just a regular air cleaner. Im sure I could fabiricate something that would help. Anyone have pics of custom cold air induction set-ups?
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post #6 of 12 (permalink) Old Jan 6th, 02, 05:40 AM
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One modification to cerrems info... Most vacuum canisters will pull in as much as 20 or more degrees of vacuum advance. You will need to limit mechanical movement in the vacuum canister or get one of the adjustable vacuum canisters to get just 6-8 degrees out of it. I suspect your vacuum advance is pulling in more advance than you want. To prove this out make a full throttle pass and a part throttle pass (speed up from 45mph to 60mph). If it pings at part throttle and not at WOT than it's too much vacuum advance.

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...Dennis
"The '69, the '96 & the club"
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post #7 of 12 (permalink) Old Jan 8th, 02, 01:40 AM Thread Starter
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How do you test what the vacum advance is set at?
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post #8 of 12 (permalink) Old Jan 8th, 02, 06:24 AM
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You need a dialback timing light or a dampner that is degreed to do it. They make a tape that will degree your dampner, just be sure to install it correctly if you use it.

Now to check how much advance the canister adds is easy. Disconnect the vacuum advance, plug the source and check your timing at part throttle say bring it up to 2500rpm and write down the amount of advance. (Let's say you read 30 degs) Hook the vacuum advance back up and check the timing again at the same rpm. The reading will be higher if your vacuum canister is working. (Let's say you read 50 degs with the vacuum) Subtract the first reading from the second and you will know how much vacuum advance is added. (In our example 50-30=20)

In low compression smog motors it was common to see the initial at idle set to 4degs btdc with 40 mechanical coming in well past 3000 rpm and at part throttle as much as 60degs with the added vacuum advance. Compare that to what we do with our 10:1 compression mills today running 10-16 or more degrees initial at idle, 32-38 degrees total mechanical and as little as 6-8 degrees of vacuum advance for part throttle totals of 40-46degs.

Total timing is the the key here and with that 383 of yours 32-34 is about all you should want. Try to have it all in before 3000rpm. Depending on how much mechanical advance is built in to the dist you may end up with the inital too retarded and have a slight overheating problem when ideling at long traffic lights. If so a re-curve is in order.

A generic target to shoot for with your 383 would be 34deg's total advance all in by 2800rpm. 14degs initial at idle (both these with the vacuum advance disconnected and plugged) This equates to 20 degs of mechanical advance built into the dist. Then add about 6-8 degs of vacuum advance.

I hope you find this info helpful


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...Dennis
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post #9 of 12 (permalink) Old Jan 17th, 02, 09:14 AM
 
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You've probably got it solved by now...the previous posts were right on. I just solved the same problem on my 454. Vacuum advance was too high and also switching to full manifold vacuum vs ported vacuum helped. Had to install an adjustable vac. can (Moroso) on my MSD GM type HEI. I've got 8 degrees initial....about 20 degrees mechanical all in at 2600 rpm and about 8 degrees vacuum..Wa-lah...no more pinging at highway speeds and partial loading. Before all of this...I was pulling over 50 degrees total at 2600 RPM. Good luck.
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post #10 of 12 (permalink) Old Jan 17th, 02, 09:43 AM
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ssfrebo,

Do you realize that you now have only 28 degrees of total advance at full throttle??
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post #11 of 12 (permalink) Old Jan 17th, 02, 10:58 AM
 
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Actually it looks like my post is a little off. Should be 25 degrees mechanical and about 8 initial....so about 33, which is about right....maybe a little on the low end. I'm keeping it on the low end for hot starting reasons. I think most of the related posts I've read say for BBs that 32-34 is about right (Ref. Ignition Man posts in this Tech forum). Good catch though...
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post #12 of 12 (permalink) Old Jan 18th, 02, 04:44 AM Thread Starter
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I haven't changed the vacum advance yet, but I haven' driven it much lately. I did switch to manifold vacum and in the process, found an open port in the carb. Thank all of you for your responses! This place is great.
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