I know the book says .25 however that's bone stock with points. Have any of you played with gaps on upgraded ignition systems? I have my csi electric dizzy and tossing in a 40k volt flamethrower coil. I have both 7 heat range plugs and 8.
In theory if you're running a higher voltage you can run a bigger gap, what this gives you in terms of performance I don't know, but that's a good question for the Prathers on Dyno Day.
I read the further gap takes advantage of the stronger spark. Both performance and fuel economy. How much seems to be a mystery
I currently use 0.035" and have used 0.040" without issues, but haven't a way to measure performance differences.
Quote from: John Gervais on September 11, 2018, 05:39:10 AM
I currently use 0.035" and have used 0.040" without issues, but haven't a way to measure performance differences.
What is your setup?
Also on the subject of spark plugs, anyone side gapping?
Quote from: 94touring on September 11, 2018, 06:11:07 AM
Quote from: John Gervais on September 11, 2018, 05:39:10 AM
I currently use 0.035" and have used 0.040" without issues, but haven't a way to measure performance differences.
What is your setup?
It's a warmed up 998 with 9.5:1 CR, Lumenition Optronic ignition system, KC's small-bore stage-3 head, dual springs, roller tip rockers, 997 camshaft, HIF38, Maniflow exhaust, lightweight flywheel etc., etc., etc. -
EDIT: Forgot to mention that I'm using NGK B6ES plugs.
Regarding 'side gapping', I haven't tried it. As I see it, since the spark will jump the shortest distance between the electrodes (intersting reading in Vizard's TtASE 2nd edition, pages 443-445), regardless of where the negative electrode is physically situated.
Our A-series cylinder heads have good swirl/turbulent combustion chamber characteristics, so the likelyhood of the air/fuel mixture fogging up the air space between the electrodes is (in my opinion) minimal. This is also why we generally don't index our spark plugs. I also think that side gapping would wear the forward edges of the ground electrode rapidly, thus reducing any benefit by effectively increasing the electrode gap.
I think that, as noted on TtASE page 445, if anything, shortening the spark duration would yield greater benefits than side gapping and I would love a set of Nology wires to try this out on the MG shop's collaborator's (the engine builder) shop dyno.
Maybe I put it to the test on the dyno. I have been doing countless reading this morning and finally found a dynosheet on side vs regular... 3% increase. As you say, may not matter on our engines. Even if I make 100 crank that's only 3 ponies, but not insignificant on our little cars.
Interesting dyno plots - 77.gif
I wouldn't mind an extra 2 or 3 horses; percentage wise, 2 or 3 on top of 65 - 70 would be significant.
The "side gapping" reminds me of the Bosche W7DTC plugs I used to use in my old VW and the first few Minis I had. They are a copper core, triple electrode plug and is a direct replacement for the plugs we typically use (NGK BP6ES or Champion N9YC).
Jesse said 30-35 would be good.
Good to know and good to know.
Dan, Have you seen the NGK B7ECS (and B8ECS, B9ECS...) spark plugs?
They tend to run just a wee-bit cooler than the B7ES plugs as the shorter ground electrode design provides a faster path to transfer heat away from the ground electrode, and have the 'oblique' ground electrode. Originally designed for racing, they're more resistant to vibration as well.
I went gapless with some 7 heat range brisk plugs. Expensive suckers but those in conjunction with a 60k volt coil really made the car run smooth.