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I apologize if this is a dumb question, but when CCing heads would it be worthwhile to screw a bolt into the spark plug hole to as near flush as possible before taking the volume? I know it will be stated the heads live with the spark plug in there, but what is the true volume of the combustion chamber? Does that small volume in the spark plug make any difference?

I do usually overthink things but in this case, I just want to make sure I get an accurate combustion chamber volume so I can calculate an accurate static compression ratio.

H2OSB

I would CC the heads with the plugs you're going to use,when the engine running in the car. Try using a hotter plug & a colder plug, to see if it makes that much of a differences.

Yeah, it does. Aim to use the actual plug you’ll be running.

VIPERGREEN76 wrote: ↑Wed Oct 02, 2019 7:12 pm I would CC the heads with the plugs you're going to use,when the engine running in the car. Try using a hotter plug & a colder plug, to see if it makes that much of a differences.

This will be my first T4(actually, my first aircooled engine build), and the engine is currently in the form of parts, so I'm not even certain what spark plugs to use.

H2OSB

The W7DTC is a good plug. They seem to be NLA now, but can still be found on ebay etc. I was lucky enough to buy cases very early on.

Anyway, they're M14x 3/4" long with triple grounds. The heat range is one point colder than stock, so it'll work best with mild compression ratios that take advantage of 91 octane. Not sure what cam you'll use, but if you have a C35 for example, you'll want around 8.8:1. A C45: 9.3:1. Stock: 8.0:1.

I'm pretty sure I'll be around 9.2:1 and I am thinking C45, but I'll soon know exactly what my static CR is. I have to finish getting the combustion chambers free of carbon deposits for the most accurate volume measurements.

Can anyone suggest a spark plug that will be a good stand in? I think, however, I will try to acquire a set of the W7DTC that were suggested.

H2OSB

NKG B6ET is a similar spec plug and a popular choice.

Oh, are you in our group? Did I just send you cc plates? You need some W7DTCs?

Heh, you're Tabari? Lol, yep, this is John. I know your name over on the Samba, but didn't realize this was you in over here.

Yeah, I'll email you about a set of plugs

H2OSB

I seem to have no problem buying W7DTC on line. There are millions out there. A couple yeRs back I was buying them on ebay by lots for about $1 a plug. They are still out there. I have about 6 sets of them. Ray