Spark plugs for racing

[AcecaRacer]

Does anyone have any opinion on recommended spark(ing) plugs for racing an Aceca with D2 engine?  I have heard you should use "cold" plugs for racing and "hot" plugs for general use.
   
   I do realize that it may depend on compression and fuel.  Assume a "gently" race prepped engine with cam and pistons.
   
   Any comments/experiences/recommendations would be appreciated.
   
   Cheers,
   Rob

[Jim A]

Rob:  It has been a long time, but I do remember experimenting with different spark plugs when I got my Ace, with a 100D, in 1960.
   The best plug at that time for running clean around town was the platinum tipped Lodge; I don't remember the heat range and I am sure they are long gone.
   I also remember that the two main Bristol "tuners" in the LA area, Stu Haggard and the other whose name escapes me had very different approaches to various settings, including plugs; they had fairly equal success, however.
   It was cerainly true that the colder plugs used for racing, necessary to prevent detonation, would "load up" in daily use.
   Many of these problems were somewhat solved when NGK introduced "extended range" plugs.
   I wish I could remember more.
   Jim Armstrong
   Mendocino County

[Jim A]

Bill Rudd was the other Los Angeles Bristol tuner in the '50s and '60s.  IIRC, he worked for Rene Pellandini and Lew Spencer at World Imports and later was head honcho at Harrah's collection.

[pls01]

Rob,
   I am running NGK C6HSA in my D2.  I have 9.5:1 CR and a vintage Isky cam.  Never have a problem with knock, but I don't race the car.  I have an old engineering book on design and tuning of competition engines.  It mentions that the Bristol hemi head is very unlikey to knock; the engine design seems very tolerant to heat range, CR, fuel, etc.
   
   One thing about the NGK's is the reach seems a bit short.  When screwed into the head, the electrode is not in the combustion chamber.  It is still recessed in the spark plug hole.  I have a spare head and some old Lodge plugs.  I'll see if they have the same issue.  Anybody know of plugs with longer reach?
   
   Cold plugs were for racing and I remember starting racing engines on "warm-up" plugs and then switching them out to colder race plugs.  NGK has a very good website that goes into detail on plug selection.
   
   A little off subject, but get some Sunoco race gas, it's like crack for a Bristol engine.  There are a couple speed shops around that sell it.  It's 114 octane!  No worries about knocking.  It's weird stuff totally different than pump gas. It also runs $8-$9 for a US gallon.  When I want to give the AC (and me) a treat, I mix it 50/50 with 93 octane pump gas.  It could be a placebo effect, but the engine seems to run much better
   Peter

[AcecaRacer]

When I bought the car, it came with NGK C7HSA plugs and champion Z9Y plugs.  I believe the C7HSA plugs are "Cold"  I don;t know anything about the Champion plugs though.
   
   I would be VERY curious to know about the plug length issue as well.
   
   Thanks to all.

[AC Ace Bristol]

Rob, Jim & Peter
   
   I've never experienced any major problem with NGK  C7HSA plugs, either for road or track.
   I'm running a sports cam, Cosworth pistons and a compression ratio of approx 10.2 :1.
   On the track, sprints or hill climbs I top up the 97 Octaine   with some additive  which gives an  extra 1 or 2 Octaine.
   
   On very long mountain passes I have been known to retard ignition if experiencing pinking.
   
   I know some of the more serious competitors use special high octaine fuels, however their cars are rarely used on the road.
   
   I will measure up some old  Platinum Ten.L100 plugs in the morning and see if they have a different reach to the NGKs. Seem to recall they were long reach, but haven't seen new ones for years.
   
   Keith

[AcecaRacer]

Keith,
   
   Thank you for your reply.  When you say you have a "Sports" cam, could you elaborate a bit more as the previous owner of my car installed a "sports" cam and I have no idea about it's specs.  I also have Mahler pistons.
   
   Have you ever run C6HSA's?
   
   Cheers,
   
   Rob

[AC Ace Bristol]

Rob
   
   Been out in the Workshop and picked up a tray of Old plugs(inhereted when I bought BEX333 along with various spares and back issues of ACtion).
   
   The Old K.L.G  and N.G.K.  C -7HS plugs  and the Modern NGK C7HSA all have the same length screw threaded section.  However upon closer inspection the K.L.G Ten L100 and the K.L.G 80 have exposed Earth Electrode same as every day modern plug.
   
   Whereas the Platinum plugs e.g. K.L.G. P ten 80 and 100   have the Earth electrode shrouded inside the plug. Same as a the Lodge, Champion & K.L.G. racing plugs we used in Lotus Twin Cams and Cosworth BDA & BDBs in the early 70s.
   
   Going back through the grey cells to School and College days.
   (Now don't be cheeky)
   
   In engines with a low compression ratio i.e, in which the combustion mixture is not so greatly compressed, the distance between the insulated electrode and earth electrode is greater thus producing a longer spark.  Since a highly compressed gas presents a higher resistance to the spark the gap is made smaller.
   
   The deciding factor in the choice of sparking plug is it's thermal value, It is determined in a test engine under accurately defined conditions.  for instance, a thermal value of 95 means that the incandescent surface ignition occours in the test engine after 95 seconds. A plug with a high thermal value,i.e a plug which can be subjected to a high thermal load and yet remain cold, has a smaller insulator - so as to proved better heat dissipation.
   
   Sorry to go back to first principles, just trying to explain to some of our non technical , non hands on members reading this thread.(assuming they haven't fallen asleep)
   
   We always used the hotter plugs to start and warm up or for every day road use, and the colder race plugs for events or hard use, these plugs would foul up in heavy slow moving or static traffic, much to our embarrasment in London's heavy traffic.
   
   So to answer your initial question the plug lengths are the same when comparing the original exposed electode plugs with modern N.G.K C7HSA. Racing plugs have earth electrodes inside the plug body.
   
   I haven't tried the C6HSA plug for comparison as I've been satisfied with the 7s, I will have a word with Tony Byford my engine builder, In the meantime ...   ...  Your views  [?]
   
   Phewwwwwww...... I'm going back to bed.  [|)] ZZZzzzzz
   
   Keith

[pls01]

Rob,
   It looks like I run one heat range hotter than most.  With NGK, the lower the number the hotter the plug.  I run C6HSA while many others run C7HSA.  My plugs look good and the car doesn't knock.
   
   As for the reach, the following pictures show the difference between the original Lodge and current plugs.  Actually, Champion N9Y is shown but its the same geometry as the NGK's. I also had some of the old KLG's that could be disassembled and cleaned, but can't find them right away.
   
   
   
   
   
   Both plugs are recessed from the combustion chamber.  I realize piston clearance is important, but they seem deep in the hole.  I don't know of any longer reach plugs
   
   
   
   

[Robin A Woolmer]

I understand NGK do 26.5mm thread lengths as well as the shorter 19mm, long thread lengths aid plug heat transfer.

[AcecaRacer]

Outstanding info gentlemen.  Pictures to boot!
   This is very helpful.  I am curious about the plug length as you show and suggest Robin.  It seems to go to logic that a plug recessed in the head would not be nearly as efficient OR effective.
   I definitely find that I am currently loading up when driving at lower RPM's with the C7's.  As I mentioned before, I have the Champion plugs as well.  I may try them.
   
   My problem is, I can't find a decent comparison chart of NGK products for love nor money.  Further, NGK has a "racing plug" line of products.  Why wouldn't we try them as well?

[pls01]

Rob,
   Did some web surfing and found the following.
   
   A cross reference chart showed the NGK 6 heat range is equivalent to a Champion 9 or 10.  The NGK 7 heat range is equivalent to Champion 7 or 8.  Apparently, NGK's cover more heat ranges than Champion with one design.  If you are loading up some Champion 9's may work better. You also may want to check for over rich mixture or oil fouling.
   
   The NGK racing product line seems oriented to motorcycles.  The closest plug I could find is R0045J-9.  The size is right but the hottest available heat range is 9, several steps colder than your current 7's.  It's a semi-surface discharge plug with poor low speed performance and short service life.  Sounds like a screaming bike plug to me!
   
   Robin's comment got me to looking for longer reaches.  Actually the NGK chart says the C7HSA is 12.7mm reach.  The "H" is the reach.  We may really want a C7ESA which is "E" reach, 19mm.  However, I could not find that NGK actually makes the C7ESA.  I did find that a Denso U22ESR-N is made.  The right heat range, 10mm thread, and 19mm reach.  I may get one of these and see how it fits in the head.  Note in the pictures, the spark plug hole is not threaded through.  There is an insert.
   Peter

[AcecaRacer]

Outstanding info.. This is why we have forums like this!  I will try my Champion plugs and see what if any change occurs.  I do believe that my carbs are running rich as well, so need to do some work their too.
   Very curious to hear how the denso plug works out.
   
   Thanks again!
   Rob

[AC Ace Bristol]

Hi
   
   
   Had a business meeting today within 1 mile of NGK / NTK  head office, so called in and spent 10/15 minutes with Ron Merralls
   (Technical Services Supervisor.)
   
   NGK Spark Plug heat rating :- The lower the number the hotter the plug (Softer).
   
   As stated earlier I am running C7HSA 12mm reach, these can be up graded to Iridium plugs which are more efficient and  therefore more expensive.
   
   They are coded as  CR7HIX ( R = resisted &  I = iridium electrode)
   
   To go even colder you could use either  C8HSA  or  CR8HIX. (12mm reach)
   
   The longer plugs you referrred to earlier on this thread are 19mm reach.......  the 7 temperature grade units are coded C7E or CR7EIX for the more efficient  precious metal " Iridium " plugs. As the threaded section in the head doesn't go through to the combustion chamber, one could run a tap through and cut more thread, However would that then create a hot spot [?] .  Also be aware that clearance between top of piston gets a few thou closer to the valves/ plug and combustion chamber as the Con rods will stretch at 6000+RPM.
   
   Iridium IX plugs are used by some of the worlds leading race teams and as original equipment in many high-performance road and off-road vehicles.  Quote  "  Enhanced Ignition Efficiency.  Better Accelareation.  Faster Starting and Smoother Running.  Longer life and Improved Fuel Consumption."      www.ngkntd.co.uk
   
   When comparing the temperature coding please note NGK coding  ..... Higher the number.... Colder the Plug (Harder) ..... which is the opposite to that of Champion.
   
   I will try to get Nik to post page 75 of the Latest NGK Spark Plug Catalogue (2009)  Which explains the Design Symbols / Coding of their general range.  Hopefully this is of use and interest to all AC owners.
   
   AC Cobra from 1965 to 2002 are covered by 6 or 7 variants from the NGK Range, again I will email data sheet to Nik and request he post on the Cobra section of our Forum.  []
   
   I must learn to use Photo Bucket... ... thanks for your services Nik... I O U a few pints by now. []
   
   Keith

[nikbj68]

quote:Originally posted by AC Ace Bristol...Page 75 of the NGK Spark Plug 2009 Catalogue...[] Keith

   
   
   Click for larger image. []