Spark plug "indexing"?

[alloyboy]

I overheard a couple guys talking about indexing the spark plugs on an engine they were building.
I, not being familiar with the terminology, butted in , and asked for an explanation.
They explained that with all the plugs being lined up in a multi-cylinder engine,ie: all the plug gaps being situated,
"indexed" to a common location in the combustion chamber, a gain in power will be attained.
I suppose this is a form of "super tuning". I was not impressed!
Have any of you heard of this, or use this technique, and am I behind the times?

 

[idano]

a similar post is also on the board.

There are some very small hp benefits from plug indexing...but very small.

Conical/radius seat spark plugs are the "funnest" to index as there are only about two of three thickness conical gaskets availiable. on multi electrode plugs like the Bosch 4+ there would be no advantage tho....I'm thinking on a HSC (high swirl chambered cylinder head) there wont be any to be had also.

But if you flog ten items each having 1 hp up, then you have magically picked up 10 hp....(or was that just misread figures on the dyno)...hmmm.

 

[patprimmer]

Plug earth strap indexing gives barely measurable results in some engines, and no result in others.

I have doubts about the repeatability of such results as some tuners index to a different position than others.

The more popular and plausible theory is to aim the open side of the gap towards the exhaust valve as this is the hottest spot in the chamber, and therefore the easiest to ignite, and more likely to get slightly faster flame spread.

I class it as a trick rather than a technique, and I am pleased to see my oponents useing it, as while they are chasing that 0.1% increase, they are overlooking a 1% to 2% increase somewhere else.

One VALID reason to index plugs is to prevent the earth strap hitting piston domes on very high compression engines, but a better technique is to notch the piston dome. That way plugs can be changed without needing to check that the piston is not at TDC.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[alloyboy]

idano,patprimmer: Thanks for your responses.
I use "surface gap" plugs in my racers so I'm not really concerned about this procedure. I was only curious.

 

[motorcyclemac]

The only reason I have ever done this was on a Harley Davidson Ironhead Sportster that uses a very high dome piston that created a "pocket" on the side opposite the plug. I did note that when the gap on the plug was "aimed" at the "pocket" behind the piston... it was easier starting and seemed to foul plugs slightly less on start up. Not really a honest solution to a poor engineering problem in my opinion. The real answer for that engine in particular is to dual plug it.

Cheers..
Bill

 

[evelrod]

In the mid eighties I crewed an IMSA GTO Pantera for a couple of races. That particular Ford had a terrible habit of closing up the plug gaps if they were not correctly indexed. Replacing the plugs with a side gap or surface gap style plug would have, IMO, solved the problem. I never got the chance to implement the solution as the car was destroyed in a practice accident with the death of the driver. I would like to have tried the new plugs to see if there was a power output difference. I now use extended core plugs (NGK) in my four cylinder race engines with no effort at indexing as it seems to make NO power difference on the dyno.
Just another thought---In the late 60's a street plug would barely last a race but the NGK side gap plugs could last a "season" without problems---'nowadays' a street plug is often found in race engines functioning all season without any apparant problems. ??? "They sure don't make 'em like they used too"---thank goodness!!!

Rod

 

[alloyboy]

evelrod, I don't think the plugs are to blame as much as the fuel and low ignition voltages of years past.
These two items caused the bulk of plug deteriation and failure in my opinion.

 

[MaxRaceSoftware]

NGK side gap plugs could last a "season" without problems---'nowadays' a street plug is often found in race engines functioning all season without any apparant problems. ??? "They sure don't make 'em like they used too"---thank goodness!!!
Rod
====================

NGK makes a great plug

Happy New Year .. Rod and to all , and to
GregLocock =>"Bob's your Uncle "

Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers

http://www.maxracesoftware.com

Support Israel - Genesis 12:3

 

[motorsportsdesign]

In Pro stock drag racing engines the reason to index is piston to plug clearance, adding the clearance to the piston gives away valuable compression.

Jonathan T. Schmidt

http://www.motorsportsdesign.com

 

[evelrod]

Well faint and fall over---Happy New Year, Larry. I had just about given up on hearing from you again. Glad to see you back. Hope all is well and you haven't been washed out into the Gulf.


alloyboy---I used an electronic ignition system developed by Howard's here in SoCal in the late 60's used on F-5000 V8's and F/B Cosworth BDA's(SCCA Formula Atlantic/Toyota these days) that developed very high peak output so I doubt that, in my case, the ign was ALL of the problem. I still see quite a change in spark plug quality, overall. I have boxes of NGK B8 and B9 racing plugs from the early 70's (they were a sponsor then) and I have no doubt that they would still function adaquatly even though they are substantially different in concept to the NGK racing plugs of today. I no longer get free plugs so I use off the shelf street NGK's w/MSD 6ALN and they last all season in my Mini Cooper vintage race car! In the 60's I raced an Austin Healy Sprite that, with a one race 'cheater' engine made ~100hp @ 7000rpm---that same type car with a 'legal' engine is making close to 130hp @ 9500rpm and living to tell about it. Yep---I am sure glad those 'good old days' are just a memory. I could not afford to race these days if I had to do it that way again. Happy and prosperous 2004.

Rod

 

[alloyboy]

evelrod..... 'nuff said.Mutual wishes to you and yours.

Best wishes to all in '04.

 

[ShaunT]

We all appreciate curiosity.
Hey Larry Meaux: Got tons of your customers. Know Ronny Mallett? There are also a few who visit us on Eng-Tips.

C'ya,

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

 

[MaxRaceSoftware]

Shaun TiedeULTRADYNE/LUNATI Arl,TX

just heard Ronnie sold his Race car ????
Ronnie let someonelse re-port the heads i ported
for him... he slowed down about a second ET

Thats probably why he was trying out different cams
to try and make the engine respond to his new head work ?
Probably thought he didn't have the correct cam
for the new head work ??

i'm guessing there was a flow-separation problem
occuring at the short-turn when they reported the
cylinder heads . The heads were flow tested on a
homemade vacuum-cleaner flow bench that probably
could only pull 5 to 8 inches of H2O depression
out of that Aluminum BBC head ??

Flow that might appear better at 5 to 8 inches
can be entirely different at 28 to 48 + inches H2O

Air speed that slow can follow a bad curve,
but as air-speed increases , it can't stay attached anymore ,
and flow drops dramatically in a live engine !!
..yet it looks great at low test pressure

i've had Racers and other head-porters send me heads
they couldn't figure out ...they look great on their
flowbench , but won't run fast 1/4 mile,
such as , example=>i've been sent a few ported LS-1 or
LS-6 SBC heads that look great at 28 inches ...
but take a 5 to 8 PerCent dive at 36 inches at .500" Lift and above .
its easy to pick those heads 2-3 tenths and 3 to 5 MPH gains
fixing that problem . Sometimes its a short-turn problem
other times its a velocity or flow-direction problem
or a combination

during the course of porting and flowtesting heads,
i double-check the flow at 36 to 48 inches,
to make sure its real flow .

So far, its been my experience that when FlowTesting at
36 inches , i have not been fooled by flow bench numbers
as long as i also check port velocity and other things
at that speed as well . Everything i see at 36 inches
shows me quicker ET / MPH during actual live DragStrip run !

i definetly can't say the same thing for 28 inches or less
FlowBench test pressure.

Anyways , my new Website = maxracesoftware.com
should be up and running by Feb 1 , 2004
will have a bunch of .MPEG movies of engine dyno testing
and a ton of Hi-resolution pictures of cylinder porting
and dyno testing , as well as , many new DragRacing
simulation computer programs , some free to public
as well as source code in Visual Basic 6 for Windows and
VBDOS 1.0 and QuickBASIC 4.5 to 7.1 source code / files .


Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3