Which Spark plugs to use?

[Mudhog1974classic]

Hi Guy's,

I'm about to change the plug's on the Mudhog and was wondering what others are running. The Hog's set up is as follow's:

3.9 V8 motor out of a 1996 Disco
Classic front engine cover
SU carbs with custom air box
8mm eagle HT leads
1996 Disco Electronic ignition
Lpg and Petrol

I have been running NGK BPR 5ES-11 and the truck has had a miss on Lpg down low in the rev range under load!

Petrol has been fine.

[discopete]

For both my lpg vehicles I use NGK Iridiums. Get them when they are 20% at sale time. I had a similar problem with the miss when using V-groove ngk changed to iridium and problem masked for a bit. Eventually found cracked rotor.

Pete

[Reads90]

Champion are the ones land rover use. Remeber that the engine you are putting them in is from the 60's so new arty farty spark plugs as the v8's don't like them :)

[chazza]

Champion are the ones land rover use. Remeber that the engine you are putting them in is from the 60's so new arty farty spark plugs as the v8's don't like them :)

I have had heaps of Champions fail on me before the service interval is up!

Since changing to NGK Iridums and Gasmaster HT leads, no misfiring at all and what appears to be better economy.

[Blknight.aus]

I like the NKG range, the iridiums I think are a little much but the do last well if your engines on tune...

[discopete]

Just remembered, I used 1 plug colder for lpg which is bpr6 range. That's the norm when running lpg and if not using iridium plugs, which don't ever need gap adjusting, close the gap a bit.

Pete

[Mudhog1974classic]

Thanks Discopete,

I think I might try the Iridium plugs, will look for stockest tomorrow and order some.

Thanks for the info everyone that helped:D

Cheers
Brett

[LOVEMYRANGIE]

The 1.1mm plug gap might be a little too big as std gap is only 0.8mm. You will get a better flash using smaller gap.
I run a std 3.9 on dinojuice and ditched the resistor plugs in favour of your std NGK BP5ES plugs and KV85 Magnacor leads.
Iridium plugs will give you a longer life and an emptier wallet, but performance wise it wont increase anything.

There are some people who are 'excited' by the Bosch Super 4 range of plugs. Again, not so much of a performance increase, but technically they are better due to 4 ground electrodes positioned horizontally increasing exposure the spark gets compared to a normal plug. Bosch pt # WR91

[Tombie]

Super 4 plugs quench the flame front and are crap.

Iridiums dont soot up on the 3.9s and work the best.

Champion - Never had a vehicle running champions that didnt have issues.

[LOVEMYRANGIE]

Super 4 plugs quench the flame front and are crap.

How do they quench it? The spark is fully exposed??

[chazza]

Iridium plugs will give you a longer life and an emptier wallet, but performance wise it wont increase anything.



I disagree; when talking about running on LPG. Performance drops off quite noticeably using conventional plugs during a service interval, necessitating changing them every service, or misfires will occur.

Since I changed to Iridium, the car has been through three services and still running beautifully on LPG.

I remember calculating that if the Iridums last 50 000 km, they will be cheaper than running conventionals; but it is an easy calculation to make as my memory is probably wrong.

Cheers Charlie

[LOVEMYRANGIE]

I disagree; when talking about running on LPG. Performance drops off quite noticeably using conventional plugs during a service interval, necessitating changing them every service, or misfires will occur.

Since I changed to Iridium, the car has been through three services and still running beautifully on LPG.

I remember calculating that if the Iridums last 50 000 km, they will be cheaper than running conventionals; but it is an easy calculation to make as my memory is probably wrong.

Cheers Charlie

OK.... I will re phrase this.... You will not GAIN extra horsepower by using Iridium plugs. They may allow your engine to run at its optimum on gas, ULP, PULP, methanol, Avgas or what ever, therefore making use of all the ignition capability the engine has but a sparkplug alone will not add to your engines horsepower. If your engine runs considerably better with new plugs then obviously your old plugs were stuffed or just not very good to start with, Champion proves my point.
And before many of you follow in with "derrr Freddie.." spare a thought for all the suckers that believe advertising.
The benefits of an Iridium plug is the very small tip on the electrode. This produces a spark that is not bigger, but more concentrated and gives a higher arc intensity and hotter flash and a more reliable burn.
Subsequently with such a small point, the electrode needs to be made of something considerably more durable than your standard plug.
But as i have no need to empty my wallet to pay for a bunch of fat tossers to sit around a boardroom in Corporationland and fondle brochures of their $1m boat in one hand and the latest advertising brochure for a sparkplug that gives you 15% better fuel economy and increases horsepower, forgetting to tell you that the tests are based on an untuned car with 100,000km old sparkplugs that has actually dropped 40% of its power from new...... well you know the rest!!:)

[Tombie]

Flame propagation from an iridium plug is far better and less shrouded.

I did back to back tests with +4, V-Spark, Normal and Iridium plugs on my supercharged discovery at Turbo Tune some 8-9 years ago.

The +4 were worst, then conventional, V-Spark then the best being iridium tip plugs.

The spark is no more intense as any spark only arcs from a small point on a plug, just like a plus 4 will spark on the tip to whichever point has least resistance electrically (this includes pressure etc in the chamber)

Emissions from the iridium plugs better flame propagation was lower then the others...

Sorry, but hard evidence supports this, I'll see if Turbo Tune kept the data next time I'm in town.

[LOVEMYRANGIE]

Tombie, check out the link here. The point I made on spark is explained in paragraph 3. Remember that it is "required voltage". Available voltage ultimately intensifies it.

http://www.ngkspark.com.au/pages/bulletins/T01-7.htm

i havent used the +4, but i have used Golden Lodge back moons ago in a 2.6 Bitsaremissing with a T4 Garrett and twin DCOE45 Webers. Went liek a shower of proverbial! These stopped misfiring although the tips ended up wearing out like a + sign!

[LoveMyV8County]

NGK Iridiums FTW. BPR6EIX if I recall correctly.

Definitely improved my V8's running on LPG. Despite the longer life I suspect they were more costly to use than standard plugs, but I experienced improved performance (compared to Bosch).

No improvement in economy though because I then drove faster.

[Mudhog1974classic]

NGK Iridium BPR 5EIX -11 plugs fitted today

Miss down low still there!

A friend ask if I had an engine earth strap, I said No.

Could this be affecting the spark on Lpg?

Brett

[LOVEMYRANGIE]

NGK Iridium BPR 5EIX -11 plugs fitted today

Miss down low still there!

A friend ask if I had an engine earth strap, I said No.

Could this be affecting the spark on Lpg?

Brett

Possibly. If you dont have an earth anywhere on the engine to the battery or if you have a bad connection, you wont get good current flow and your earth is THE most important.
I have a strap between the head to the block to the chassis on each side.

However, the 1.1mm gap will most likely be too large. Unless you have an aftermarket HEI ignition and they specify using 1.1mm gaps, it takes considerably more voltage to jump the spark gap. End result is a weaker spark and with gas, thats a misfire. If your not getting a good earth, it will most likely compound the problem.
The only thing you should change is the thermal range of your plugs and use a colder one for gas. In the case of NGK Iridiums, BPR6EIX if you normally use a BPR5E**.