SPARK PLUG GAP and COMPRESSION CHECK

[mraley]

I have looked everywhere and can't find what the proper gap is suppose to be on my 1966 Mustang 200......Do any of you know?

Also, I bought a compression gauge yesterday, how much compression should I be looking for if I'm good?

 

[ski4evr]

This is from the 1965 Shop Manual for Comets, Falcons, Fairlanes, and Mustangs:

Spark plug Gap: 170-200 cid -> 0.032-0.036 inches

Compression: 170-200 cid -> 155-195 psi @ cranking speed (with no more than +/- 20 psi between cylinders)

Those numbers should be good for a '66.

ski

 

[ski4evr]

Those numbers are for stock. If you've upgraded your ignition (i.e. electronic and/or an aftermarket performance coil) - the gaps can be larger. Also, if the block has been bored / head modified - resulting in a compression ratio change from stock - the compression psi will likely change as well.

A stock 200 has a bore and stroke of 3.68 x 3.126, a compression ratio of 9.2:1 and the compression range of 155-195 psi

A stock 260 has a bore and stroke of 3.80 x 2.870, a compression ratio of 8.8:1 and the compression range of 130-170 psi

Just to give you a feeling for how the numbers may vary if yours is not stock

 

[mraley]

Just finished the compression test. All cylinders were right at 200 except for number six. It was about 195. I take it this is good??????

 

[addo]

If that's PSI, it's excellent. If it's KPa, not so good!

 

[mraley]

addo....Yep it's PSI.....


The only thing left to check is the vacuum advance. I pulled the plugs and checked the gap. No problems

 

[TheDude]

The only thing left to check is the vacuum advance. I pulled the plugs and checked the gap. No problems

What are your gaps set at?

 

[mraley]

I set them at 40

 

[Anonymous]

try them at 50

.040 is not that much of a difference.