What spark plug and gap size?
 

What spark plug and gap size is recommended? I have 2.7L with Webers.

While not an exact answer, here's my .02 cents on spark gap - you want the biggest gap you can reliably spark.

As you start increasing gap, you give the spark more options of getting to ground besides going thru the spark plug. Since the cylinder is under pressure, the spark doesn't really want to go across the plug and is looking for other paths; arcing to another plug inside the cap is a popular path, as is arcing thru the wire insulation. When the plug gap is small, these options don't look attractive to the electricity. But when it widens, they do.

I would imagine .030" (1.2mm) would be a good starting point..

Hope this helps,
Chuck.H
'89 TurboLookTarga, 339k miles

NGK BPR 5ES is usually a good choice for street car with carbs.

My '73 rebuilt to 2.7 has Bosch W8DCO plugs. There's no science behind it for me though, that's what was in it when I got it and it's what I've used since. It's always been a point of curiosity, so I'm eager to see some replies.

I used NGK BPR5ES to tune the carbs

when tuned I run BPR7ES or BPR8ES

if you're running rich or doing low key short drives use BPR5ES

My constant BPR7ES needs 5 miles in summer to clean up carbon from a cold start. In winter they need 10 miles

There's no science behind it for me thoughhttp://www.yono.info/h.jpghttp://www.yono.info/d.jpg

I have been running NGK BP6ES with a .30 gap plugs in my carbuerated 2.7 for a few years with great results. I tried BP7's but they wanted to foul. I also use 87 octance fuel in a moderate climate which should be considered. Hotter climate, cooler plug and higher octane, BTW with NGK plugs the lower the number, the hotter the plug.

David

Do most folks generally prefer the NGK plugs over Bosch?

Are there any advantages to running platinum or multi electrode plugs in the older cars?

My experience is platinum simply has a longer service life. Since I change plugs regularly on the cars, I go with quality inexpensive copper plugs. NGK and Autolite have treated me right.

When I got my racecar (3.2L weber carbs, S cams, 9.8 compression (actually much lower- long story....) single plug) it came with a bunch of extra spark plugs. Almost all of them are Bosch platinum 8 range for what its worth.... Point being is they worked fine with the carbs running high octane (typically 104 unleaded or 110 leaded) and Electromotive ignition with a lot of advance- 35 degrees I believe.

I purchased the NGK BPR5ES, problems with running bad and noisy under load is now gone. Strange things can occur with faulty plugs.