1962 340 hp pistons
Anybody know without doing a lot of reseach if the 1962 factory-installed, 340 hp pistons (compression 11.25 to 1) were aluminum or forged or cast steel? Thanks, Larry
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Re: 1962 340 hp pistons
Today a lot of car owners are switching to flat top pistons because of the gas situation. My 63 the LWC had flat tops the first time it was restored in the early 80's and a local NCRS judge said to me. Fred said there is just something not right with the sound of your engine. It just doesn't sound right. Well the old boy was right. Flat tops and the forged aluminum are a world apart in sound and performance. The flats lack the deep throaty sound. Right Clem??? JD
P.S. The 2nd time around the engine got the Forged jobs and now it sounds original.Comment
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Re: 1962 340 hp pistons
forged pistons do have that "klunk,klunk" sound when cold till they expand because they are set in at .005 piston to wall when cold.Comment
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Re: 1962 340 hp pistons
I wonder what static compression ratio a flat top engine will yield with a solid lifter cam and late closing inlet valve. I would think this would make a torque shy motor even worse with a 3-- something gear and close ratio trans.Comment
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Re: 1962 340 hp pistons
Thanks to all for their input. I definitely want to achieve as much of the original sound and performance as I can with the engine rebuild.Comment
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Re: 1962 340 hp pistons
They are still available. Federal Mogul Speed Pro L2166.... The actual CR with double .018" shim gaskets as implemented by GM during '62 production is about 10.7:1 with 61 cc head chambers and nominal deck height.
Search archives for more info.
DukeComment
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Re: 1962 340 hp pistons
Duke, Are you saying that with the double 0.18" shim gaskets, the actual CR for the 340 hp engine was 10.7:1, not the advertised 11.25:1? My '62 was built on/about June 22, 1962. I know that the availability and cost of high octane gasoline are issues to consider when rebuilding a HP engine today, but my car will have limited road miles, and if I have to use aviation fuel or high octane additives, I am willing to do that.Comment
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Re: 1962 340 hp pistons
if the block is not "decked" and the heads are not cut to the AMA cc specs the CR is lower than posted. just make sure there are no sharp edges left in the combustion chambers and on the piston tops. sinking the valves during a valve job lower the CR. to get a true 11.25:1 CR takes some machine workComment
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Re: 1962 340 hp pistons
You can always tell an early Vette that has a replacement or de-tuned engine in it by the sound. I haven't been wrong yet, even with those that have taken a lot of pains to disguise it. These old ears are hard to fool. Then too, I have had old timers ask me to start mine up just so they can hear the solid tappet sound - music to our old ears.
Stu FoxComment
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Re: 1962 340 hp pistons
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I've referenced an online CR calculator a zillion times along with recommendations of how to get more power and revs from SHP engines without affecting judging appearance or recognizable operational characteristics like the idle characteristic. Run the numbers yourself with difference gasket thicknesses -.025" nominal deck clearance, 61 cc chamber, 5.3cc piston dome.
Do you know what the first mandatory operation is before you disassemble the existing block? If not you need to research the archives.
If your late build engine has never been touched the gasket thickness should be about .036". You can measure with a feeler at any corner of the block head interface with the heads installed. What do they measure?
I recommend you massage the heads and run the LT-1 cam. The limit with this configuration is about 10.5 true. If you stay with the Duntov cam limit the CR to 10.25.
The chamber relieving along with a little valve sinking should increase chamber volume about 2 cc.
It's not worth pushing the CR a to the point of detonation and having to blend in high octane fuel. The difference in power between a true 10.5 and 11:1 is about 1-2 percent. Observe the above CR limits and you should be okay on unleaded premium.
DukeComment
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