Engine pinging? - Team Camaro Tech
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post #1 of 8 (permalink) Old Jul 23rd, 12, 09:35 AM Thread Starter
Shane
 
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Engine pinging?

Hello, im new on here and i was wondering if you guys could help. I have a 1980 Z28 with a rebuild 350 in it. It has a torque build on it so most parts are upgraded ie. Flat top pistons, moly rings, high performance cam, headers ect. but nothing too extreme. Its just used as a daily driver. Heres the problem, When the engine warms up, it begins to ping under load. only when its warmed up though. Its not the fuel. I have the ignition timing at 8. What i think it might be is the spark plugs. I have AC Delco R45TS's in gapped at .045. just stock heat range. What i was wondering is if i should get one heat range colder plugs? What would you recommend and what gap? Any other thoughts on why it pings?

Thanks for any help in advance
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post #2 of 8 (permalink) Old Jul 23rd, 12, 10:09 AM
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Re: Engine pinging?

Hi Shane,

Don't go changing your plugs heat range just yet. Knowing your timing is set to 8 is just part of the info you need and pinging under load has little to do with what your timing is at idle when you set it.

Timing basics;

Mechanical Timing: (also called centrifugal timing) is the amount of timing built into the distributor. It could be 20 or more degrees of timing.

Initial Timing: you set this at idle with the vacuum advance disconnected and the vacuum port plugged off. I assume that is the 8 you have set.

Total Timing: add the initial you set to the mechanical to get your total timing. A typical 350 ci Chevy likes about 36 total.

Vacuum Advance: is supplemental advance that is dependant on the engine vacuum to add additional timing providing better fuel economy and driveability.

Your part throttle pinging is probably a combination of too much vacuum advance and too fast of a mechanical curve. I provided this in another thread, see if it can help you figure out your timing...

Quote:
Originally Posted by DjD View Post
There is no reason to have your total all in lower than 3000 on the street IMO. You want a curve for driveability and when you start bringing it all in too low you might as well lock it out like they do on a drag car.

Here's how I would approach this, In this order:

1 - figure out what total you engine likes; based on an educated guess set it then go make a few wot passes on a hill in the hottest part of the day and listen for pinging, use an overdrive gear if you can but nothing lower than a 1:1 gear. Depending on results add or subtract 2 degs and re-test. I like to run 1 degree below the the point where audible pinging goes away.

2 - figure out your initial; by trying different initial settings (no more than 2 degs change at a time) find out the lowest amount of initial before your idle temps start going up. With that number set your idle and make sure the engine doesn't run-on when you shut it down. If you have run-on increase the initial and close down the throttle blades to drop the idle and eliminate the run-on. Run the lowest initial you can and still get the engine to idle, not raise idle temps and so you don't have run-on on shut down.

3. now you know where you want your initial and total so curve your dist to give you the numbers you are looking for. If your engine likes 12 initial and 36 total build in 24 mechanical....

4. finally bring in the vacuum advance and test for cruise to part throttle pinging. Again find a hill during the hot part of the day and cruise at a low rpm in a high gear and roll on the throttle a bit. Use the most vacuum advance you can without part throttle pinging -1 deg and you'll be good to go.

Make sure your timing curve doesn't start until at least 200-300rpm above your engine idle and that's it. Keep in mind initial timing and vacuum timing (on a manifold source) will effect your idle and you may need to adjust both the throttle blades and the mixture once your timing is set.

Once you have your curve dialed in then take on the carb circuits associated with the symptoms you are having. Cruise surge is usually lean primary jets, stumble when you jump on it is typically the accl pump, pump cam and squirters...

Hope that is a help.

...Dennis

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post #3 of 8 (permalink) Old Jul 23rd, 12, 12:47 PM
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alex
 
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Re: Engine pinging?

Shane all of what Dennis said plus you did not mention the carb size and jetting you might have to richen it up a ta to go along with all the upgrades. 2 we should also know the rest of your build heads cam ignition system etc so we can help you better . Alex
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post #4 of 8 (permalink) Old Jul 23rd, 12, 01:16 PM
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Re: Engine pinging?

Quote:
Originally Posted by DjD View Post
find out the lowest amount of initial before your idle temps start going up
I'm interested in this part as I thought one wanted as much initial as can be had before it starts lugging the starter?

Assuming ones cooling system and t-stat were working properly, and one was working on a car at operating temp to start with,, wouldn't it be hard to tell when the idle temp was being affected by too little adv? Or am I misunderstanding the instructions?

Thanks,
Tom
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post #5 of 8 (permalink) Old Jul 23rd, 12, 01:53 PM Thread Starter
Shane
 
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Re: Engine pinging?

Quote:
Originally Posted by ss27 View Post
Shane all of what Dennis said plus you did not mention the carb size and jetting you might have to richen it up a ta to go along with all the upgrades. 2 we should also know the rest of your build heads cam ignition system etc so we can help you better . Alex

ok so I got a little more info on the engine. Its a block cast # 3970010, Heads are just standard heads (#333882). The carb is a 600cfm. the Jets and rods on the carb are the stock ones. All i could figure out about that distributor is that its a Delco Remy. the camshaft part# on the build sheet is E517219-16 (it just says H.P. Camshaft). The engine has a .040 bore, .020 rod and .010 mains. I couldnt find any #'s on outside of the intake.
Thats all i could figure out about the engine from the chicken scratch build sheet and looking around.
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post #6 of 8 (permalink) Old Jul 23rd, 12, 02:04 PM
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Re: Engine pinging?

Quote:
Originally Posted by Dosperado View Post
I'm interested in this part as I thought one wanted as much initial as can be had before it starts lugging the starter?

Quote:
find out the lowest amount of initial before your idle temps start going up
Assuming ones cooling system and t-stat were working properly, and one was working on a car at operating temp to start with,, wouldn't it be hard to tell when the idle temp was being affected by too little adv? Or am I misunderstanding the instructions?

Thanks,
Tom
Watch your gauge Tom, if you are running the factory 4degs btdc that was so typical of a sbc from back in the day and you are seeing 210 deg temps, as you increase the initial to say 12 degs btdc you might see the temp drop to 180 and if you were willing to take the time you could probably chart the temp go up as you retard the timing... That's an example, you probably won't see 30 degs difference.

Now why would you want to run as much initial as possible up to the point just before it starts lugging the starter? Timing is all about timing; think quarterback leading the receiver with the pass, his "timing" has to have the football at the same spot as the receiver, too much timing and he over throws the ball and it can't be caught. Spark timing is the same thing, you want the spark plug to fire at the right moment, not too soon and of course not too late. Too soon is retarded timing and too late is too advanced. Doesn't matter if you are talking initial, total or anywhere along the timing curve.

That said re-read all of #2 (not just the clipped quote) and you'll see I include all the variables necessary to find the best initial timing for your engine. What you quoted was just part of the whole it was not a standalone statement, the last sentence sums it all up. You don't want it to over heat from retarded timing, you don't want run-on cause by opening the throttle blades to compensate for retarded timing and you want enough timing for your cam profile to allow the engine to idle yet you don't want so much advance that it effects starting...


Quote:
2 - figure out your initial; by trying different initial settings (no more than 2 degs change at a time) find out the lowest amount of initial before your idle temps start going up. With that number set your idle and make sure the engine doesn't run-on when you shut it down. If you have run-on increase the initial and close down the throttle blades to drop the idle and eliminate the run-on. Run the lowest initial you can and still get the engine to idle, not raise idle temps and so you don't have run-on on shut down.

...Dennis

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post #7 of 8 (permalink) Old Jul 23rd, 12, 02:36 PM
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Tom
 
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Re: Engine pinging?

Thanks, I was planning to read it a few times after work

I've never before heard a good explanation, but what you say makes sense, I'll be breaking out the timing light again!

As for why you would adv timing until the starter lugs? Just hear it so much, even here recently, and from so many "mechanhicks", it seemed about as reasonable as all the other "we don't need no stinkin timing light!" advice

nothing scientific, but you here something like "advance until it lugs the starter, then back it off two degrees, then find a hill, listen for pinging, if none, good to go, else back it off two degrees and climb the hill again", etc.

Of course the results always backed up with data from the old "seat of the pants Dyno!"

Kind of like "No torque wrench? Just tighten until it strips, then back it off a 1/4 turn"
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post #8 of 8 (permalink) Old Jul 23rd, 12, 03:45 PM
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Re: Engine pinging?

Quote:
I have a 1980 Z28 with a rebuild 350 in it......When the engine warms up, it begins to ping under load.
Bit of background..
Does this engine still have pollution stuff, egr etc on it?
What dizzy is in it, the orginal 80s or post mid 70s?
Is the detonation at WoT or low mid loads or both?
And at what rpm range is the ping?
Do u have a choke on the carb?

post mid 70s dizzies have to be converted to pre polution curves..in most cases the there is enough in the post 70s dizzy to convert with a little bit of compromise, but in my experiance reading what u are doing u have a dizzy the may need more than that in the curves.
If have a choke, at cold then engine runs rich... even without a choke runs a little richer till warms up... If the carb is close on tuning limits / mixture requiements it may need jets or powervalves (depending on rpm range and load it pings in) looked at

Quote:
Now why would you want to run as much initial as possible up to the point just before it starts lugging the starter?
I can see the logic in that....more intial (not idle intial+Va) the more load put on the starter....more load higher current drawn...And yes I have seen big ampmeters used to watch starter loads and ID intial and starting issues... Factory can be anything from a few degrees before TDC to just under 10 degs depending on the vechile/engine...When one watches the amps, getting up over 10 they start climbing, get over 12 and climb fast, and varies as to cam profiles.

Ball park
This is a basically stock + a bit engine so keep that intial 10 or below...
Idle (intial+ VA) in the 14 to 18 deg range
Total (intial +cent) between 32 and 36 degs around 3200 rpms...
Keeping everything below 40/42 degrees (intial+cent +VA)
Have the cent come off around at least 300 above idle in N rpms...better for a street around 1100 to 1200 ....if around the 1100 this means will have resonable springs in.
From there if still pings the chances are the carb is too lean.
1st check for vaccuum leaks including things like secondary butterfly gaps and the mixture/ idle sped screws are aprox 1 1/2 turns +/- 1/4 turn.

My Spelling is not incorrect...it is creative

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