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Old 04-14-2009, 11:21 PM
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pinging? help

Hey i just recently rebuilt a chevy 400 with keith black pistons with 9.1:1 compresson and gm vortec iron heads with .040 quench, with a 60101 lunati voodoo camshaft and a 750 edelbrock carb.

Under heavy acceleration at about 2000 i get this loud rattling noise. I figured it was ping so i retarded the timing to 2 degrees retarded but this didnt help any then advanced it to 4 degrees before TDC but this didnt effect it at all. So then i plugged off the vaccum advance and still it didnt change a thing, i just recently switched to a colder plug and just filled it with 91 octane(was using 89) and havnt had a chance to test it fully yet.

But it seems that no matter what i do i cant stop this noise no matter if the engine is cold or hot it does the same. But on the interstate i can floor it without a noise or at idle i can revv it without this noise...any help would be awsome..i cant figure it out.

Thanks,

Mike

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Old 04-15-2009, 12:20 AM
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Mike it seems to me, that you are a PERFECT candidate for dyno tuning. tune the engine, with it loaded as you are driving it. The spark curve becomes proper as does the carb jetting.

Google a dyno shop in your area.
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Old 04-15-2009, 06:54 AM
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try colder spark plugs.... More fuel...... Have the dist advance recurve.
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Old 04-15-2009, 06:58 AM
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Sounds to me like you have a lean condition. I agree, hit a dyno or at least put a gas analyzer on it and see what is going on.
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Old 04-15-2009, 07:56 AM
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sounds good, does this mean i have to pull the engine? and how much does that cost?

im also using a HEI distributor from GM performance parts..they say its the same one that they use on the 572. is there a chance that if i change back to the original distributor this could cure my problem?


Thanks for the advice..
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Old 04-15-2009, 08:13 AM
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Barring a weird vacuum leak, you need to re-jet your carburetor most likely. As long as the engine has parts that like each other, the fix should be simple and not require a pull out/tear down.
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Old 04-15-2009, 03:02 PM
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Quote:
Originally Posted by SBCfan04
Hey i just recently rebuilt a chevy 400 with keith black pistons with 9.1:1 compresson and gm vortec iron heads with .040 quench, with a 60101 lunati voodoo camshaft and a 750 edelbrock carb.

Under heavy acceleration at about 2000 i get this loud rattling noise. I figured it was ping so i retarded the timing to 2 degrees retarded but this didnt help any then advanced it to 4 degrees before TDC but this didnt effect it at all. So then i plugged off the vaccum advance and still it didnt change a thing, i just recently switched to a colder plug and just filled it with 91 octane(was using 89) and havnt had a chance to test it fully yet.

But it seems that no matter what i do i cant stop this noise no matter if the engine is cold or hot it does the same. But on the interstate i can floor it without a noise or at idle i can revv it without this noise...any help would be awsome..i cant figure it out.

Thanks,

Mike
I guess the first thing to tackle is to determine if the rattle is detonation/preignition in cause or is a mechanical noise.

.040 quench is pretty tight mechanically, that means the pistons (at speed) are closing to within .040 inch (less than 3/64th of an inch) of the head while this is effective in producing squish/quench, it doesn't leave much space for flailing parts to miss each other.

Bogie
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Old 04-15-2009, 03:11 PM
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Are the pistons flat top pistons?
You're not the first one from the Midwest US with issues concerning the real octane of the pump gas there. Seems to be a trend.
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Old 04-16-2009, 07:13 AM
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actually the pistons are keith black hypereutectic 30cc dish pistons. if it would be a mechanical noise would the spark plugs show this? because i replaced my plugs with a colder plug and the old one looked good. i have had problems with gas quality here also but i didnt know the octane could be off?
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Old 04-16-2009, 07:47 AM
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that is a very small cam 256/262 degrees. 256 on the intake makes some serious cylinder pressure with 9:1 cr.

But the good news is......vortec heads don't need much timing. they can get by with 32 to 34 degrees total timing at wot.

15 degrees at idle with 34 total should be enough. Can you measure the total timing???

then get an adjustable vacuum advance canister, and set the vacuum advance to add another 10 degrees. accel makes an adjustable vacuum advance that will bolt to your hei

I would say you need to use at least 91 octane in this engine. or install a bigger cam.
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Old 04-17-2009, 07:45 AM
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i took the inspection cover off yesterday and the noise got louder and i hear a click every time i accelerate a little...could one of the flywheel bolts or torque convert bolts be loose? and would this make a noise like i described?
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Old 04-17-2009, 08:37 AM
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Quote:
Originally Posted by SBCfan04
Under heavy acceleration at about 2000 i get this loud rattling noise. ...i retarded the timing to 2 degrees retarded but this didnt help any then advanced it to 4 degrees before TDC but this didnt effect it at all. So then i plugged off the vaccum advance and still it didnt change a thing
If it does it cold, this lessens the chance that a hot spot in the comb. chamber is causing pre-ignition- but doesn't totally eliminate it, either.

Does it sound like more than just one cylinder is pinging?

If premium gas and retarding the timing hasn't at least helped some, you may have too much compression for the cam you have in it.

BUT- with a 30cc(!!) dished piston, you must have abysmally low static CR anyway. You need to double check the piston's spec's, IMO.

Unless there's mechanical (metal to metal) interference happening- which you should hear all the time, not just at a certain RPM- you might have a hot-spot in a chamber.
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Old 04-17-2009, 10:23 AM
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Quote:
Originally Posted by SBCfan04
i took the inspection cover off yesterday and the noise got louder and i hear a click every time i accelerate a little...could one of the flywheel bolts or torque convert bolts be loose? and would this make a noise like i described?
Yes, or it could be kissing the starter gear. Now your stating to get at where I was going which was can you tell if its a mechanical noise opposed to detonation/preignition. Not always easy to do but the changes you made to timing, etc kind of pointed away from combustion issues.

The SBC starter needs about .050 inch clearance between the top and bottom of engaged teeth, this is set by shims between the block and starter thru the bolt face. The starter gear also needs to retract clear of the ring gear. The ring gear has been know not to be in plane all the way around which could cause it to clip the starter gear at one point. The starter needs a bracket between the block and the front side of the starter. It appears to be an inconsequential piece which is frequently over looked. Without the bracket the starter can get a little bit sideways enough to upset the gear to gear alignment and position.

None of the above is to say that the flexplate isn't tight on the crank nor to say it isn't sitting square to the crank centerline. This is to say, start with the simple issues and work up in difficulty.

Bogie
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Old 04-19-2009, 10:56 PM
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thanks for all the advice..

im going to check the bolts to the flywheel and the torque converter and go from there.

thanks again
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Old 04-19-2009, 11:43 PM
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Ahhhh! Across the parking lot from me, they have a (it looks like a 1972) 'K' series Chevy truck. The tranfer case is making this same noise, it's chain is loose. They thought it was timing, or a cracked flywheel. (something else to check)
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