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I am working on a 1967 Impala with a factory 327/275 HP motor, 4 barrel,and powerglide trans. The motor is factory stock with 37,500 miles. It has been sitting for 5 years and I recently got it running. I have gone completely through the ignition system changing everything with new parts, checked the timing setting it between 6 and 8 degrees before TDC per factory specs, flushed and refilled the cooling system, opened the heat riser and changed the fuel filter.

I have a detonation issue while under a load. It is driving me nuts. The hotter the motor gets the worse it is. When the engine is cold it does not do it.. It sounds like it is restricted to the passenger side head area. The motor otherwise runs fantastic. I have had all kinds of thoughts from friends and mechanics about different issues that might be causing the problem. The gas in the tank that had been sitting for 5 years was siphoned out and Shell 89 octane was put in about one month ago by the prior owner. One old time mechanic told me this is the issue. He said that octane rating is too low for that motor plus there is most likely a carbon build up.

Research shows the compression rating on this motor is 10:01. The heads are the double hump heads. My thought is to drain ALL of this fuel out and put in some 110 octane racing fuel mixed with Sunoco 93 and then BLOW OUT THE CARBON. Trouble is the tank is 3/4 full...

Any ideas or thoughts from anyone???? It could simply be just this fuel issue and maybe bump the timing down a bit...

Thanks.....Rich

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Water or Seafoam through the carb to blow out the carbon, before draining the gas. If that cures it, you have a cheap fix.

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I'd be surprised carbon was an issue with the low mileage.

Any chance of a pic with the air cleaner off from the passenger side? Just want to see how the distributor is indexed and how the vac advance is run. Is the mechanical advance operating freely?

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Paul, the advance appears to be working fine...

Rich

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i would try timing at 4 or 2 degrees, see if it reduces ping. don't know shell gas down there but i avoid using it here. i had the same 10:1 327/275hp in a '69 impala (transplanted) years ago, it ran like crap on shell fuel, compared to other brands.

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Don't overlook the distributor advance springs. They may need to be replaced with heavier springs to prevent excessive timing advance.

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Is the gas an ethanol blend? Ethanol blends at even 10% can cause that. And Stihl chainsaws will overheat in a heartbeat on a mix with that stuff.

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What's the total timing? How much vacuum advance and how much vacuum to reach full advance?

The factory used rubber bushings to limit advance, and these often get brittle and fall off after 50 years.

Check basic "timing 101" stuff first.

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They like to run on Sunoco 93, retard it a few degrees if it continues. Not knowing what the camshaft specs are, it may not be too suitable for a factory spec tune....Get it quiet, then fine tune it from there.

BIG

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: novadude</div><div class="ubbcode-body">What's the total timing? How much vacuum advance and how much vacuum to reach full advance?

The factory used rubber bushings to limit advance, and these often get brittle and fall off after 50 years.

Check basic &quot;timing 101&quot; stuff first. </div></div>

Rich
All of the above is where I think you should concentrate, JMO, gas alone may not be the fix.
Also what is the total advance at idle with the vac can hooked up ?
Spend some time reading this, very informative.
Vacuum advance and timing

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Sounds like timing and gas. Have been through the new gas blues. It boils easily and causes all kinds of problems. Verify TDC, just maybe it is off on the damper. But timing can build heat and heat will cause detination. Food for thought, the OE timing chain no matter what the mileage is probably not in the best of shape. The plastic breaks down and separates.

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Sounds like timing and gas. Have been through the new gas blues. It boils easily and causes all kinds of problems. Verify TDC, just maybe it is off on the damper. But timing can build heat and heat will cause detination. Food for thought, the OE timing chain no matter what the mileage is probably not in the best of shape. The plastic breaks down and separates.

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Reminds me of the 455HO in my old black 72 Firebird Formula. I could not stop the pinging even with the timing backed off 15 degrees. Pulled the engine out to rebuild it and discovered that someone had installed 12 to 1 pistons in the engine (which was designed for 8.4 to 1 compression ratio).

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Check the outer ring on the balancer, it may have slipped and be giving you a false reading on your timing. Or you can just keep bumping the timing back until it stops spark knocking under load. Then adjust the idle and keep an eye on your temp gauge to make sure the timing is not too low. It is kind of primitive but I've done MANY times years ago.

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Mike, That is an awesome article. I saved it so anytime I need to explain it to someone, I can have at it!
Thanks

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I know you say that it has not tampered with, but are you 110% sure the pointer is original? The posts about the timing chain, balancer ring, and advance springs are all noteworthy, too. Nylon gears are a time bomb, they are gonna go, just a matter of when. You can't tune by the old service manual; conditions now are not the same. Cheap gas then was better than our good stuff now. Just make sure you try changing one thing at a time. If you make all the adjustments at once, you won't know what did or did not work. Try the old &quot;all in by 3500rpm&quot; and see what happens....that will get you in the ballpark.

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Thanks for ALL the GREAT advice!!! I found that it was the frickin crappy gas that was in the tank. I siphoned it all out put in a mix of 6 gals of 110 octane racing fuel and 6 gals of 93 Sunoco Ultra and she is purring like a kitten now!!!

Rich

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LOL. Glad it was something simple!

That happened with my Grandfather's 71 Lincoln monstrosity. It has a 460 with close to 10-3/4 to 1 compression. My dad was putting regular 87 octane in it and wondered why he could never get it to shut off when he turned to key off. It would rattle and ping when running and run on for over a minute (if you let it) after you turned it off. I had to siphon out the entire tank and refill it with 93 just to be able to drive the thing again.

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[img]<<GRAEMLIN_URL>>/biggthumpup.gif[/img] 93 Is the trick...Those 327's want good fuel. What plugs are you running? I know they love a straight 44 and did not like the 45's...I've went down to a 43 in some combo's too. Keep playing with it and you'll ditch the 110 soon...

BIG

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Dyno guy we use warns us to never bring fuel from convenience store (Wawa, Sheets, etc) or other wholesale and value places. Says the premium octane fuels from those places cause detonation or behave like lower octane fuel.

Sunoco 93 was good for us.

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pxtx</div><div class="ubbcode-body">Dyno guy we use warns us to never bring fuel from convenience store (Wawa,) or other wholesale and value places. Says the premium octane fuels from those places cause detonation or behave like lower octane fuel.

Sunoco 93 was good for us. </div></div>

Paul,

Wawa 92 is great stuff. There's a few local street racers going 8's on Wawa 92 with no octane helpers

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WOW ... To be in California and see people talking about WaWa gas ... [img]<<GRAEMLIN_URL>>/haha.gif[/img]