Conflicting plug gap size

[Vsantoro]

I asked a plug question and got some mixed results, also checked my book and the corvair site with digitized books. Got a ton of mixed info.

I have a 1962 monza 900 convertible. Its not a turbo. Anyone know the exact plug gap size ?

My book says .035, corvair site shows .030, the plugs were .028 (which said they were pre gapped for this vehicle.)

Im going through trying to fix some popping thats happening in the carb since I have done a few things and plugs were one of them, so want to make sure the gap is perfect.

Thanks,
Vic

[NMVair]

Thers probably a bit of a bread basket to work in but run .032

[Vsantoro]

Hmm. Thanks but that’s neither one , I’m going to try it wish I knew the right size

[bbodie52]

A spark plug gap of 0.030" meets the needs of just about all Corvair engines. A wider gap is more difficult to fire reliably with a standard ignition coil voltage output. Higher cylinder compression ratios or a turbocharged engine generally has higher combustion chamber pressures — making the high voltage needed to create the ignition spark reliably greater. The Corvair engines rated at higher horsepower levels generally had a higher 9.0:1 compression ratio, This can make the combustion chamber pressures higher. The turbocharged engine has a lower compression ratio of 8.0:1, but the turbocharger boost and increased horsepower output increase combustion chamber pressures, which again makes a reliable spark more difficult to achieve. For these reasons the Corvair shop manuals specify a reduced gap of 0.030" in all but the lowest horsepower engine.


1964 Shop Manual Tune-up Specifications


1965 Shop Manual Tune-up Specifications








How To Set Spark Plug Gap

https://knowhow.napaonline.com/how-to-s ... -plug-gap/

[Vsantoro]

Thanks. Well, I will tell you, Im learning with these cars, small stuff counts. I was having some rough running, popping carb issues after putting in a new cap and rotor, new plugs, and new wires.

I bought the NGK BR6HS plugs as recommended by multiple people. Its pre-gapped to .028

I just pulled all the plugs and gapped them to .032
Put them back in and wow what a difference, no popping and sounds a hell of alot better. I still have a valve lash issue that I need to fix but this little change made a huge difference.

Thanks again to all the folks here. A few more week and I might be able to get this thing NYS inspected

Vic

[Lane66Monza]

I would consult the 61 manual, since it is the basic manual for your car. The 62 manual is a supplement for changes, they made to the 62 model year.

Ir seems the 61 model is correct. Editors changed it for some reason in 62-63 supplement, but got it right again in 64 supplement.

[bbodie52]

You missed a critical difference between the 1961 Corvair base shop manual engine specifications and tune-up data, and the 1962-63 Corvair Supplement specifications...

LEFT-CLICK EACH CHART IMAGE TO ENLARGE FOR EASIER READING...

1961 Corvair Shop Manual - Engine Specifications

1962-1963 Corvair Shop Manual Supplement - Engine Specifications

As I stated earlier, the engine cylinder compression ratio has an impact on the combustion chamber pressures encountered by the spark plug electrodes. In 1961 ALL of the Corvair engines had the same 8.0:1 compression ratio. In 1962 and later Corvairs, the optional engines had increased horsepower — primarily due to increases in the compression ratios or the addition of a turbocharger, as well as some changes in the camshaft specifications. When the combustion chamber pressures increased due to the increase in the compression ratio from 8.0:1 to 9.0:1 (or the addition of a turbocharger on the 150hp engine option) the spark plug gap on those high performance engines decreased from 0.035" to 0.030". The ignition coil output voltage to the spark plugs remained the same, so the design engineers reduced the spark plug gap specification to facilitate a reliable spark plug firing under the increased cylinder pressures encountered with a 9.0:1 compression ratio (or with the turbocharger).

This revision of the spark plug gap specifications remained for all model years through 1969.

[Vsantoro]

see what I mean. its definitely conflicting info. I set it to .032 and it seems to be running good. Eventually I'll bump it .035 and see what that does. I know that at the plugs pre-gap .028 it ran like crap.

[Lane66Monza]

So the next question in order to make the complete circle of information, what engine HP is in the car? The original 84 hp or did someone swap in a 80 hp engine in the past 62 years?

I haven't found anywhere in his posts, what engine hp or the engine number being reported. Critical piece of info for any engine diagnosis.

Can you let us know the Engine Number and its HP as you know it.

Here is some info to help you ID your engine.

[Frank DuVal]

I use .030" for all but the lowest HP engines (they get .035"). Yes, OP needs to know what engine they have.

I do not know why a small change from .028 to .032 would really affect engine popping.

[Vsantoro]

Everything is fixed now , between the plugs (yes the gap change made a difference) then we just adjusted the timing and then adjusted and synced the carbs, and now she runs like a dream