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different form sparkplugs for marnel heads


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#1 artinist

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Posted 16 July 2004 - 04:34 PM

i don't know if anyone has paid much attention to this but with the marnel heads, the stock type spark plug protrudes way too much into the combustion chamber.
I will check it on a stock head to see if its the same situation but on my marnel the is about a 1/4" of the threaded portion thats exposed.

Any exposed threads will lead to premature detonation and will take away any advantage gained from combustion chamber work.

Actaully Kelly noticed the spark plugs sticking out right before we were installing my head. he brought up a good point. those thread will also accumilate carbon overtime and when you try to remove them, they will damage the threads on the head.

here is the stock head with a BPR8ES (physically similar to stock plug) plug in it. no threads are exposed at all.


Here it is a marnel when new:


and when ported:


I found some different form factor plugs on www.ngk.com that should work better than the stock type.

its funny, using the application search botton on that site it shows that almost all of the high performance plugs like the (BPR8ES) which some of us here are using, are original applications for Jet Skies.

both of these have regular stock type tips, and the tips stick out almost just as far into the combustion chamber but the difference is that the threaded portion is only 1/2" long. the threads on the stock are 3/4" long

here is the BCPR7ES heat range=7


here is the BPR7HS heat range=7


here is the BPR7HS (left) vs. BPR8ES (right). i didn't have a BCPR7ES to compare it to but its basically the same as a BPR8ES


I just ordered at set of the 7s from NAPA. will post pics when i get them on tuesday. these should pretty much elliminate any exposed threads.

what do you guys think?
-----------------------------------------------------------
88 Starion - 341rwhp@23psi on 91 octane - sold
97 3000GT VR4 - Sold





#2 Guest_silverngray_*

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Posted 16 July 2004 - 05:12 PM

Sounds like a cheap way to ensure more reliability to me. Especially if you are runnin lots of boost! If I remember correctly they didnt stick out on my stock head. Then again my memory isnt the greatest either smile.gif

Rico

#3 eeaston

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Posted 17 July 2004 - 12:20 AM

Art, you hit the nail on the head there.  Exposed threads are gonna be just as bad as if not worse than JV shrouds for detonation.  Plus anyplace carbon accumulates is another detonation hotspot.  I'm glad you posted this, I bought a built engine with a Marnal so I've never seen the combustion chamber.  Please keep us posted on how the new plugs fit.  I don't even know what plugs are in my engine.
Eric-'88 Silver Quest, Blk Leather Forged7.2:1, Ported Marnal, BSE, balanced. Home-modd Magna intake, 750cc matched inj. SS header,tial WG, t3 stg5 .82AR/t04s60-1. Megasquirt Fuel & Ign EDIS

#4 heefner

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Posted 19 July 2004 - 11:24 AM

a side by side comparison would be helpful. Good point though I can see how this could easily be over looked.

86' quest

#5 Dcrasta

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Posted 21 July 2004 - 08:15 AM

Cant wait till you get those plugs in so we can see more pics smile.gif
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#6 artinist

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Posted 21 July 2004 - 10:18 AM

ok pics are up.

so the marnel head defintely positions the plug farther into the combustion chamber compared to stock. I guess the threaded section is shorter.

does anyone have a marnel head thats off the car so they can take a pic of how much the plug sticks out? and maybe get a set of these shorter plugs to see where exactly they end up?

i am pretty sure they were sticking out about 1/4" but it will be nice to have pics.
-----------------------------------------------------------
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97 3000GT VR4 - Sold

#7 ALANFROMPDX

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Posted 21 July 2004 - 02:00 PM

I have a new marnal i could look at later.
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#8 Oscar_the_Grouch

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Posted 21 July 2004 - 08:18 PM

Art

NICE Port job on that Marnel.... Who did that I am interested I have not seen one like that since I had my head done over 13 years ago by an old race shop in Miami.

But staying on topic...
I ussually run NGK's TRAILING endge 1st Gen RX-7 Plugs (Will get number soon) on my car at the track. they are almost 3 ranges colder than OEM so it will run like CRAP till it gets hot after the first lap or two man hold on very nice difference. The thing about these plugs is that they are the Old School version of the "Bosh + 4" It has 4 prongs instead of the ussual one. So this means the spark will jump to 4 different points on the plug rather than just one point. Better Bigger spark But again it will run like CRAP when engine is cold as it is a very cold plug.

If you dont want to go that far into the cold you can go with the OEM replacements NGK's for 2 Gen Eclipse Turbo's they use a TWO prong plug and the plug is about the same range as ours or a bit colder. But these are like $5.00 a pop from the dealer and I have not been able to get them from anywere else.

These two style plugs are used to aliminate the trouble of "Indexing" your plugs, so this way you will always have a good spark pointing or in the way of the air/fuel mix.

FYI: Just in case some of you are not familiar with Indexing...
Indexing is the name given to the act of beeing able to get the open end of the Electrode and prong of the plug FACING directly into the oncoming Air/Fuel Mix. That way the SPARK will be at its hottest at the heart of the mix. Its been proven to gain power over conventional installation. And NOT all plugs will be able to screw all the way in and have them pointing in the right direction. So going to the alternate plugs with two, three or four prongs will enhance the Indexing effect BUT without the trouble.

Just adding to the conffusion , sorry  ;D

Oscar
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#9 davida.

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Posted 23 July 2004 - 01:04 PM

oscar you really are confusing things so lets clear this up.
if the theory of indexing works as you discribe, by orienting the
prong to be away from the combustion center to expose the
electrode, how in the world is adding more prongs into the mix
going to keep the electrode at maximum exposure.
to me its doing just the opposite.  it shields the electrode further
when the whole ideas is to give the flame room to propagate.

sorry all for deviating from this fine thread.
da.

#10 Oscar_the_Grouch

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Posted 26 July 2004 - 08:33 PM

DA

Well its simple... You "Index" the SINGLE prong Plugs.... The Multy Prong Plugs dont need to.
And the difference between the TWO is that you will get a MORE wild of a SPARK with the multy Prong plugs as the spark "JUMPS" from prong to prong making it simmilar to a Multy Spark situation.

So basically with the ONE prong you can ONLY maximize the spark by indexing.
And with two, three or four you are just INCREASING the spark .

TWO different situations. BOTH with gains in performance.
Hope I cleared that out.
Oscar
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#11 Dcrasta

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Posted 28 July 2004 - 06:10 PM

They have some plugs for the rx7 that are a center electrode and side raised electrode.  I think the 2 and 4 prog ones may get too hot if you run it too lean smile.gif

We dont need high tech plugs in this ole 2 valv head ..  I think we can use motorcycle plugs smile.gif    
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#12 Dcrasta

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Posted 01 September 2004 - 11:47 PM

BUMPITY BUMP

Hey Artinist hows it going on this?
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#13 artinist

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Posted 02 September 2004 - 12:41 PM

they are on the car now. pics of the plug are on first post up top.
i cant take a pic of them on the head since the head is now on the car too. maybe someone who has a marnel off the car can take a pic.
-----------------------------------------------------------
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97 3000GT VR4 - Sold

#14 Dcrasta

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Posted 02 September 2004 - 04:01 PM

So your using the shortys?  They working for you?
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#15 artinist

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Posted 08 September 2004 - 11:12 AM

yea, car works pretty normal.
-----------------------------------------------------------
88 Starion - 341rwhp@23psi on 91 octane - sold
97 3000GT VR4 - Sold

#16 Dcrasta

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Posted 08 September 2004 - 04:18 PM

That is a very sweet port job btw!
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#17 Q

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Posted 08 September 2004 - 09:19 PM

I use EV8 's NGK these are the Gold Palladium plugs . My car has never had such crisp throttle responce and it pulls harder.

#18 BullShipper

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Posted 13 October 2004 - 10:03 PM

I hsve the smaller plugs on as well
car seems fine
but i think i gapped them to low
hard starting

#19 artinist

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Posted 14 October 2004 - 10:51 AM

i don't know who started the trend of the smaller gaps. keep it at stock gap unless the car is missing under high boost which is very unlikely with any new aftermarket coil.

the spark is supossed to be as big as it can.
-----------------------------------------------------------
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97 3000GT VR4 - Sold

#20 artinist

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Posted 14 June 2005 - 12:41 PM

bump
-----------------------------------------------------------
88 Starion - 341rwhp@23psi on 91 octane - sold
97 3000GT VR4 - Sold




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