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Min
Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada
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 Posted: Fri May 25, 2007 1:33 am Post subject: EDIS: Spark plug gap. |
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What are the other guys running EDIS doing for spark plug gap/other modifications. Right now I'm just running normal 924 gapping on mine. Has anyone put any thought into the type of plugs we should be running for a wasted spark application (becuase on the exhaust stroke the spark has a reversed polarity and fires 'backwards' from normal, wearing the other side of the electrode, which is why double platinum plugs were developed apparently)
Min
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Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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Martijnus
Joined: 29 Dec 2006
Posts: 2019
Location: Netherlands
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| Posted: Fri May 25, 2007 5:20 am Post subject: Re: EDIS: Spark plug gap. |
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| Min wrote: | What are the other guys running EDIS doing for spark plug gap/other modifications. Right now I'm just running normal 924 gapping on mine. Has anyone put any thought into the type of plugs we should be running for a wasted spark application (becuase on the exhaust stroke the spark has a reversed polarity and fires 'backwards' from normal, wearing the other side of the electrode, which is why double platinum plugs were developed apparently)
Min |
that's new to me...  is it because of the exhaust stroke that it fires 'backwards'? ...still..the reversed polarity part I don't get.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)
924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment  |
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Min
Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada
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| Posted: Fri May 25, 2007 5:32 am Post subject: |
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Yep, on the wasted spark cycle, the spark is fired backwards. Lots of stuff about it on the net.
I'm thinking about increasing my gap to something like 1.3mm or so rather than stock 924 sizing. And just wanted to see what endwrench/etc were doing with it.
Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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scottc
Joined: 26 Mar 2007
Posts: 159
Location: Manilva, Malaga, Spain
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| Posted: Fri May 25, 2007 5:44 am Post subject: |
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Doesn't spark plug gap depend on combustion chamber shape?
I'll drag one of my books out and read up a bit. |
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Min
Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada
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| Posted: Fri May 25, 2007 5:55 am Post subject: |
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| scottc wrote: | | Doesn't spark plug gap depend on combustion chamber shape? |
Only to the point were the head of the electrode hits the pistons. You want the largest gap that your ignition system can safely spark. EDIS stock gap varies from car to car, but its mostly in the 1.1-1.3mm range.
Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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endwrench
Joined: 07 Dec 2002
Posts: 1631
Location: Victor, Montana
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| Posted: Fri May 25, 2007 6:03 am Post subject: |
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Min's right about the reverse spark on DIS systems. I change plugs pretty often so I'm not too woried about abnormal wear. If I had a daily driver I would definetly go with double platinums though. Stay away from any of these fancy pants iridium e3 2prong 4 prong.... crap. And stay away from Bosch platinums of any sort.
I tried gapping mine wider (.050") and it wrked well up to 6lbs of boost then I started getting some fuzzy looking o2 sesor readings at higher rpms when I went to 10lbs boost. I couldn't really feel a miss but I reduced it back to .035" and the fuzz went away. I just run standard autolites.
Todd
_________________
'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!.... |
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Raceboy
Joined: 01 Mar 2004
Posts: 2327
Location: Estonia, Europe
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| Posted: Fri May 25, 2007 6:08 am Post subject: |
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In normally aspirated situation, you can go even 1.3mm, probably won't cause misfire. On boosted engine, get the biggest gap you can get without having misfires. Same goes to dwell time: have the least needed to prevent misfire under boost. But, you can compensate a bit larger gap by adding dwell time, obviously not too much, it would harm IGBT's and accelerate spark plug wear.
Though on EDIS dwell time can't be adjusted IIRC.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
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-nick
Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA
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| Posted: Fri May 25, 2007 6:27 am Post subject: |
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Is wear such an issue for non-platinum plugs & wasted spark? I was using cheap copper-core Bosch plugs. I have the same in my wasted spark twin motorcycle.
Is there much of a real world difference in opening up the spark gap too? I honestly don't know.
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet |
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Martijnus
Joined: 29 Dec 2006
Posts: 2019
Location: Netherlands
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| Posted: Fri May 25, 2007 6:37 am Post subject: |
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| -nick wrote: | Is wear such an issue for non-platinum plugs & wasted spark? I was using cheap copper-core Bosch plugs. I have the same in my wasted spark twin motorcycle.
Is there much of a real world difference in opening up the spark gap too? I honestly don't know. |
my thoughts too! My motorcycles all have wasted spark and run way more revs than my porsche..and they don't wear much...
Howcome?
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)
924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment |
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Min
Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada
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| Posted: Fri May 25, 2007 6:50 am Post subject: |
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| endwrench wrote: | | I tried gapping mine wider (.050") and it wrked well up to 6lbs of boost then I started getting some fuzzy looking o2 sesor readings at higher rpms when I went to 10lbs boost. I couldn't really feel a miss but I reduced it back to .035" and the fuzz went away. I just run standard autolites. |
Apparently the double platinums have been known to have the platinum bonded electrode come right off .....
I've got some standard 924 bosch coppers, I guess I'll try puttin them in at 1.3mm and seeing what happens, also considering filing the tip of the electrode down a bit (.20 or something) so its not in the way of the flame kernel (old hot rodder trick apparently?) which is supposed to help.
Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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Min
Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada
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| Posted: Fri May 25, 2007 6:53 am Post subject: |
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| -nick wrote: | | Is there much of a real world difference in opening up the spark gap too? I honestly don't know. |
If you change your spark plugs when you change your oil, I doubt there will be a problem, platinum plugs arn't recommended in any forced induction situation. Platinum plugs are for lazy folks who want to change their plugs 3 times in the full lifetime of the motor.
There is definately some real work difference in opening up the spark gap.
Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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!tom
Joined: 28 Aug 2006
Posts: 1941
Location: Victoria, BC Canada
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| Posted: Fri May 25, 2007 8:01 am Post subject: Re: EDIS: Spark plug gap. |
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| Martijnus wrote: | | that's new to me... :o is it because of the exhaust stroke that it fires 'backwards'? ...still..the reversed polarity part I don't get. |
I've also heard this referred to as "dual fire."
It seems strange to me as well that the polarity would be reversed on the wasted sparks, since this would tend to dictate a different spark plug design to compensate for it. I suppose they figure running the arc backwards will replace some of the electrode that gets erroded on the regular polarity arc.
It's not reverse polarity because of the exhaust stroke -- it's either because of the above reason (to try to make the plug last more than half as long as it would in a system without wasted sparks), or it's a side-effect of the way the coil is built. There would have to be one coil per pair of plugs, and if there's one plug at each end of the coil, then they'd see opposite polarity.
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78 924 NA
5-lug |
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Min
Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada
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| Posted: Thu May 31, 2007 12:55 am Post subject: |
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bought some ngk plugs, side gapped them, gapped them to .055 definately a noticable improvement in how the car runs, idles better, throttle response is better. Definately good.
Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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scottc
Joined: 26 Mar 2007
Posts: 159
Location: Manilva, Malaga, Spain
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| Posted: Thu May 31, 2007 1:08 am Post subject: |
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Sorry Min, Forgot to come back to you.
Read that spark plug gap is inversely proportional to Compression ratio. As at higher compression ratios its harder for the spark to jump.
The Zetec engine (which uses Edis) has a comp of 10:1
So you might get away with a larger gap???
Good news though! |
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RC
Joined: 25 Mar 2007
Posts: 2637
Location: Australia
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| Posted: Sun Oct 16, 2011 7:39 pm Post subject: Re: EDIS: Spark plug gap. |
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| !tom wrote: | It seems strange to me as well that the polarity would be reversed on the wasted sparks, since this would tend to dictate a different spark plug design to compensate for it. I suppose they figure running the arc backwards will replace some of the electrode that gets erroded on the regular polarity arc.
It's not reverse polarity because of the exhaust stroke -- it's either because of the above reason (to try to make the plug last more than half as long as it would in a system without wasted sparks), or it's a side-effect of the way the coil is built. There would have to be one coil per pair of plugs, and if there's one plug at each end of the coil, then they'd see opposite polarity. |
!tom`s logic is spot on here. Whatever stroke is irrelevant, it is the coil design. One of the two plugs will ALWAYS fire in reverse polarity.
What this means is that half of the plugs, that`s 2 plugs on a 4 cylinder, 4 plugs on a V8, will always have a weaker spark. Not just the "wasted" one but the firing spark. Also half of the plugs will wear considerably more at a quicker rate than the rest.
Ford was clearly aware of this problem and on some cars fitted copper or single platinum plugs to half the engine and platinum or double platinum to the other half that burned up faster. The bean counters triumphed over the engineers in this case. Possibly it was decisions like this that kept Ford`s hands out of the back pockets of the US taxpayers? 
_________________
World`s quickest 924 2L slushbox
| Allan @ DTA wrote: | | I have no issue with superchargers, they are for guys who want to drive a car rather than talk about horsepower with their baseball cap on backwards |
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