Hi guys! I would like to solicit some advice from the engine gurus. I have a 65 L79 with the following symptoms. On occassion, I get a lot of smoke out the exhaust at start up. The odd thing is that most of the time I get very little or no smoke at start up. The condition has appeared while starting engine cold or warm. Also, sometimes see a little smoke in the rear view mirror under hard acceleration (strictly obeying all applicable traffic laws of course! ). The exhaust spits soot at start up, although adjusting the choke to 3 notches lean has improved condition but not eliminated. Motor was rebuilt around 1990 with previous owner. I have run about 1K miles this summer and burned over a quart of oil. Car runs very strong and starts right up, however I had to bump the idle up to 900 - 1K to achieve smoother idle. Original carb restored about 3 years ago, and tuned to max vacuum and RPM at idle. Engine pulls steady 18 Hg of vacuum at idle (seems a little high). Timing set to 36 total w/o vacuum advance. Vacuum advance apears to work fine. Distributor recently rebuilt, and installed Breakerless SE ignition. After 1k miles, the R43 plugs show some oil only around the threads, some carbon, and a little carbon build up at the base of electrodes. Compression ranges from 210 - 215 (seems a little high). Car experiences occassional run on with 94 octane. I use lead supreme 130 to increase octane by about 2 points, which has eliminated the run on. I'm guessing that my next step is to have a leak down test done, but I wanted to get some opinions first. Thanks everybody!
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Re: Engine Condition
For starters, I would get rid of the 43 plugs. Put in R45 or R45S. Check the float level of the carb and make sure it is not dribbling gas in the engine instead of coming through the metered orfices like it is supposed to.
If the Carb is off (and you fix it) and you change the plugs to the hotter heat range, you may get rid of your smoke (black) at start-up. You should also be able to slow the idle speed down to around 600-700. This may stop the run on problem you have.
If you have blue smoke on start-up or on acceleration after coasting, it may be a case of failed valve seals.
1000 miles on a quart of oil? That's around a buck fifty to two dollars it will cost you for oil this year. If that engine was mine with that kind of vacuum and compression readings, I wouldn't touch it internally. Not for a long time.
It's easy to get spoiled with today's engines that go 5-10,000 miles without using a quart. -
Re: Engine Condition
Spitting soot at startup is normal - that's condensation in the mufflers being blown out. The OEM mufflers had a 3/32" hole at the low point of the front bulkhead of each muffler as a condensate drain to extend the service life of the mufflers.Comment
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Re: Engine Condition
The oil is probably getting past the valve guides. Do you know exactly what was done to the head when it was rebuilt in terms of valve guide restoration and sealing? Some methods don't last that long.
Assuming the car sits for days or weeks between drives, oil probably slips down the guides, which accounts for the occasional blue smoke at start-up, and some oil/carbon residue is building up in the exhaust pipes that can be can be spit out with the condensed water when the engine is cold or at WOT when high flow can break away deposit buildup and cause a little visible smoke.
Your oil consumption and smoke is not enough to worry about at this point, and unless you become obsessed with the "problem", leave it alone.
As previously stated, get rid or the R43s and replace them with R45s. Delco heat range "5" is suitable for ALL SB street engines, regardless of horsepower, and heat range "3" is about right is you spend a day hot lapping a race track, but is way too cold for the street and will quickly build up fouling deposits.
DukeComment
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Re: Engine Condition
Thanks Duke, John, and Mike. Unfortunately, I don't know what all was done or not done with the last rebuild. I just haven't seen an intermittant smoking problem like this before. This is also the first one I've had with side exhaust, and I think that is making the sooty garage floor more noticeable. I think I'll just throw in a set of R45's and invest in some extra oil - a lot cheaper than reworking the heads
Any thoughts on the vacuum and compression readings? They seem a little high.
Thanks again!Comment
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Re: Engine Condition
Don You might also want to see if there is any fuel leakage down the carb throat after shutdown. If you had to step up the idle, there may be a rich fuel conditon which could be due to a variety of carb problems... leaking needle valve, leaking valve seat gasket etc. In my case it was leaking by the seat gasket and was noticable by a rough low speed idle which smoothed out at higher speed. I also had excessive fuel smell after shutdown, and gas leaking from the venturis.Comment
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Re: Engine Condition
Don you mentioned that your carb was rebuilt about 3 years ago and that you now have to raise the RPM to get it to idle. Another check that you can do is check your Holley's power valve. If the power valve is bad it will affect idle and provide a richer fuel use which could contribute to the plug problem. Power valves can be bought as a separate Holley product along with separate purchases of fuel bowl and metering block gaskets.Comment
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Re: Engine Condition
When I bought my '67 with an L-79 engine, the acceleration and performance was outstanding. The engine had recently been rebuilt by the previous owner. I noticed the engine had AC-46 plugs. I checked the owners manual, which called for AC-45 plugs. I bought some AC-45 plugs, installed them and noticed a significant drop in performance at driving around town speeds.
From my view AC-45's may be OK for high speed highway driving but AC-46's perform a lot better around town. My 2 cents. PTComment
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Re: Engine Condition
When I tried to buy AC46 plugs lately I was told they are no longer available.
VerleComment
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Re: Engine Condition
Patrick,
Aren't AC46 plugs too hot for a stock small block? Will they burn the pistons? Maybe Duke can shed some light on this.
Just a thought.
DonComment
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Re: Engine Condition
I don't think you can get any non-resistor plugs now. The R45 and R46 were available a few months ago at Advanced Auto Parts and Pep Boys. The R43 is also available. Those paying the big bucks on eBay for any R plug except the R44 is acting eBay crazy as you can buy them local.Comment
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Re: Engine Condition
Don,
I question the AC46 plugs also. I think that's going way over what was intended for these engines. If an original 327 can't run for a long time on the correct original AC44's, something is definitely wrong. I've had the same set of 44's in my 63 FI car for the last 15 years and it never misses a beat. They have probably 5000 miles on them.
The idea here is to select the coldest spark plug that will live in the engine without fouling. In a previous post here, it was recommended that hotter plugs be installed but the original complaint was not the fact that the engine was missing, just running differently and idled slower than normal. (a sign that the mixture had richened) The engine had R43 plugs in it at that time and the recommendation was to switch to 45. That would not be a fix for that particular problem and would probably just start a new problem. A plug that is too hot will promote detonation in the cylinder, especially if there is oil present due to valve seal leak or worn valve guides.
The reason "S" (extended tip) plugs were not recommended for Corvette was the fact that under heavy acceleration, the negative electrode would wind up red hot and cause pre ignition. The boys at GM engineering knew what they were doing when they made their recommendations.
If all driving is off/on a trailer or parades, then I would go up as far as AC45 but that's the top. If they foul, it's time to look elsewhere for the real problem within because it's not the spark plug heat range.
MichaelComment
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Re: Engine Condition
AC heat range "5" is best for normal street and highway driving in all SB powered Corvettes. A "6" is hotter, but unless you have to pull long steep grades, tow a trailor, or are racing, they will probably not overheat.
Just the same, I've never used a heat range "6" as "5" proved to be ideal for normal street and highway driving.
Back when I used to hot lap race tracks with the SWC I used heat range "3", which was just right for that application. I would install them the day before the event and remove them the day after.
DukeComment
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Re: Engine Condition
i think the condition of the plug is more important than the number. run them awhile and pull them out, black = too cold, brown or tan = just right, and white = too hotComment
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