Printable Version of Topic

Click here to view this topic in its original format

914World.com _ 914World Garage _ Indexing Spark Plugs

Posted by: Highland Jan 26 2023, 03:11 PM

I just randomly watched a YouTube video on indexing spark plugs. The video says one should have the open end of the gap facing the intake valve. He goes as far as adding spacers so the plug torques at the correct location.

I've never seen anything like that on all the threads here. Does anyone here index plugs? I'm asking this question for any Porsche/VW air cooled engine, but my application is for a 2L 039... head.

Posted by: 914werke Jan 26 2023, 03:14 PM

perhaps at the 99th% of extracting performance of an race engine but for the avg street motor...no

Posted by: Root_Werks Jan 26 2023, 05:04 PM

with Rich, not worth it on any street engine.

If you can find them, both Bosch and NGK make exposed gap plugs. I think Bosch uses the "DTC" in the part number:

Attached image(s)

Posted by: Arkady Jan 26 2023, 07:20 PM

The idea of indexing is to orient the spark plug's grounding electrode so it does not shroud the spark from the majority of the combustion chamber's volume. This photo is of an indexing tool made by Moroso. Years ago I used this tool for getting a bit more power from my small block Chevy for local drag racing.

When the cylinder heads are off, screw the spark plugs into each combustion chamber until one is positioned so the plug's grounding electrode is near the chamber's roof. Then remove it and screw it into the tool. Stamp the cylinder number into the tool where the grounding electrode 'points'. This tool allows you to then choose subsequent spark plugs that will correctly orient in each cylinder when the heads are back on the engine. There is a finite amount of combustible fuel in each cylinder for the power stroke. Spark plug indexing's intent is to maximize that combustion. The photo shows 1 through 8 stamped for each cylinder of my V8.

The amount of benefit you'll get depends on the configuration of the combustion chamber. I found it made about a 10 HP difference in a 400+ HP small block Chevy. A hemispherical combustion chamber engine probably wouldn't get that much of a bump. I'm new to Porshe 914's and the Type 4 engine (one was given to me if I could get it out of the woods) and I haven't even removed the engine yet.

Indexing is easy to do when the cylinder heads are off and it can't hurt...

Posted by: brant Jan 27 2023, 07:10 AM

Done it on the race car for years until we went to a twin plug head