Boost and spark plugs

[FatXJ]

Let's talk about boost and spark plugs...

I am planning a supercharged stroker and am looking at some of the finer details.

First what I know:
When you add higher compression like a N/A 11:1 ratio or adding a Supercharger or turbo you need to lower the heat range on the plug to prevent pinging. You may also need to lower the gap on the plug to prevent spark blowout which occurs with higher cylinder pressures, especially at higher RPMs.

So with me planning a 4.7L motor running 7-9psi supercharger should I need to go to a colder plug. I am thinking yes but I have yet to build and run this project so I don't know?! I know theres a lot of what if's but let's just keep it simple for now.

Anybody running a similar setup have any info?

thoughts, opinions, general stupid comments?

 

[tealcherokee]

im working on a turbo stroker, 4.5 pushing 1 bar. im going to be running stock plugs, prolly gapped around .050" (my stroker NA runs well at .060)

ill also be running MSD BTM to retard timing while under boost

 

[XJtoy]

Well I haven boosted a Jeep yet but on all the turbo Hondas that I have built I would say yes go with a colder plug on my Honda i run a 2 steps colder plug and run up to 25psi as far as the gap goes I would go as big as you can and if it starts cutting at higher rpm adjust your gat until it stops cutting out i gap my plugs to 0.025.

Dose anybody have a motor pic of a super charged jeep?

 

[WheelinJR]

Well I haven boosted a Jeep yet but on all the turbo Hondas that I have built I would say yes go with a colder plug on my Honda i run a 2 steps colder plug and run up to 25psi as far as the gap goes I would go as big as you can and if it starts cutting at higher rpm adjust your gat until it stops cutting out i gap my plugs to 0.025.

Dose anybody have a motor pic of a super charged jeep?

I've boosted about 20 hondas, and the colder plugs are honestly just a tuning bandaid.

If you're running good engine management, and know what you're doing stock plugs gapped down work fine. stock gaps were .044" on those, and I would take them down to anywhere from .028" to .022"

If you're running a basic fuel controller type setup, you could use colder plugs to make it work

 

[tealcherokee]

just remember, if youre doing something other than running higher octane gas to cure a knock, youre robbing power

 

[CSaddict]

Colder plugs are an absolute must with any kind big power increase. Jason talk to JD about it on HMT. He went on and on with me about dropping a heat range on my LS.

 

[FatXJ]

I've boosted about 20 hondas, and the colder plugs are honestly just a tuning bandaid.

I don't believe this for a second. Colder plugs are not a bandaid they are a necessity for one reason

compression=heat
heat= preignition

running higher octane than needed is a bandaid, and colder spark plugs is the fix.

 

[8Mud]

I guess this falls into the other stupid comments catagory.
On my Dodge (360) I ran low to moderate boost with a Dyers pump, a colder plug, octane enhancer, retarded the timing (pretty much a must in that motor), made sure it was never fuel starved, ran it a little on the rich side and used a 8.5 to 1 compression. A cam recommended by Dyers.
Had a friend with almost the same setup, that had continious problems with his, like notches burnt into the pistons, head cracks from detonation and other stuff. He tuned for maximum horsepower, I tuned for that sucker to last. He likely had 50 more horses, but that kind of becomes academic after a certain point. I bent my tranny input shaft, collapsed the bushing in the diff. and had other driveline foibles, from the horses I had and never once popped the clutch.
I also put in a Toronado radiator (huge) and made sure I kept it a little on the cool side.
I was running mine with high end gears, so the torque strain on the motor did play a roll.
I talked with Granatelli at Paxton and Dyers, before I even began the project and listened close.

 

[badron]

running higher octane than needed is a bandaid, and colder spark plugs is the fix.
=================================================
Timing, boost, and what ever octane work together to make Max horsepower. No one of them is a bandaid. Drop the boost and you may add a little timing or lower Octane. Push the timing you may need to drop the boost or run the high price spread. ETC, ETC, ETC. The plugs heat is then worked out to work with best combo of things above. Almost always lower.
By the way the things above are just the easy variable to change. General used for fine tuning. Other idem that also come into play but are harder too change are.
Compression ratio and shape of piston top.
Cam profile AND cam timing
Type of fuel system but FI is the only way to go in my book. Intercooling or the lack there of.
Type of transmission.
Gearing
How big of a boat (car/truck) your going to push with this huffer and how it is to be used. By the way most DD boats run a lot less boost.
Last but not least how you drive it. Is a major factor in fine tuning you over sized hair dryer.
All the above ADDED together is why you maybe breaking with 10 inches but your buddy is going strong at 20.

 

[MudDawg]

OK...the OLD FART speaks....Often times the misled and uninformed think that "hot" or "cold" has something to do with the "power" or "heat" of the spark.....NOT SO....spark plugs (more properly called igniters) are made in "heat ranges" ....to understand how this works, one must know how a plug works....first the obvious....an electrical spark jumps the gap between the center electrode and the side (or ground) electrode....If the temperature of the electrodes and the ceramic insulator are too cool....fuel deposits will accumulate and the plug will short...(no spark).....if the temperature of the electrodes and the ceramic insulator are too hot....they will erode away or just melt....the construction difference between a "hot" or "cold" plug has to do with the LENGHT of the INSULATOR....long, deep insulators have a long heat path to the head (where the heat is dissapated)....short, shallow insulators have a shorter heat path....the easier it is for the plug to cool, the lower the operating temperature at a given combustion temperature.

The trick is to pick a plug that runs at the proper temp for YOUR application. Generally speaking, the higher the engine output, the higher the combustion temperature MUST be (because heat is the driving force) the colder the plug needed while under "boost" ....but if the engine spends most of the time off boost and short periods on boost, it may very well be possible that a stock range plug will do....I run stock plugs in my ET bike....it's only on juice for 3 seconds...if I make a full pass at 100%....i change 'em down two notches to avoid preignition and the resultant...KABOOM!!!

 

[lighthouse jim]

The trick is to pick a plug that runs at the proper temp for YOUR application.

Hey MudDawg, where can I find info regarding plug comparisons? I'm running a basically stock 91 4.0 h.o. and want to optimize performance. I figure that there is a LOT of experience out there that I can tap into to avoid trial -and-error method of choosing. I've started searching, and it led me this far...

 

[8Mud]

Cold plugs and hot plugs. Basically a hot plug sits a little lower into the cylinder and a cold plug sits a little higher. The burn starts (highest oxygen content, hottest part of the burn) either a little farther from (cold) or nearer (hot) to the top of the piston. Other factors come into play, but that is the basics.
If your pumping more air fuel mix in there (with a pump of some sort), it is likely to get hotter during ignition. Moving the ignition point away from the piston top a little can help with longevity. Most manufacturers, recommend forged pistons after a certain boost. Lowering the compression ration, can also lower the boom factor some, for various reasons, one is the actual amount of mix pressed into the piston and another is the amount of compression, is directly directly related to the amount of heat generated by the compression. Compress a gas and it makes heat, equal and opposite reaction, decompress a gas and it absorbes heat.
Other factors are, exactly when the spark occurs in the piston stroke, timing. And the octane of fuel, higher octane actually slows the burn and makes the better use of (less wasted or unburnt) fuel. A faster burn can produce more torque, a slower burn more horsepower, but the graphs of the two actually cross at only one point and are interelated.
Like mentioned, the shape of the piston top and the final fuel to air ratio, also play a roll. Basically the more *air*, the hotter the burn (or stronger the explosion) and likely more horses and torque. The more oygen in the ratio, the hotter more explosive the burn.
Quench, the atomized fuel, vaporizes and adsorbes some heat and can lower the mix temperature some. A slightly rich mixture has some cooling action.
Ideally you want a controlled burn, that doesn't explode and/or generate so much heat it melts your piston and/or the cylinder walls and/ro your valves. And you don't generate stresses, way beyond the design parameters of the motor internals.
Also likely is hot spots in the motor that reach way over the 270 degrees required to boil your coolant and RPM's that exceed the oil cooling capabilites of the oiling for the mains and cam bearings.
Intercoolers are good, compressors and turbos generate heat of there own during compression of the air.
Heat is your enemy, as is (near) explosive ignition of the air fuel mix.

 

[MudDawg]

My picks for plugs for a stock 4.0 HO....Standard plugs....NGK #7252 aka FR-5 Autolite #985.....Platinum (longer lasting) Autolite #APP985.....Iridium....(longest lasting but expensive) Autolite # XP985.

My experience over the years is the NGK's and Autolites are good quality plugs. And also ND (Nippon Denso) are good plugs...they are associated with NGK...

Standard 2 bux a pop NGK's keep the fire lit in my dragbike at 10K+ rpm under a 75hp shot of nitrous.....get the picture???

 

[MudDawg]

8Mud brings up some good facts too.....the short of it is plug selection should suit the engine and the state of tune.....no plug will cure problems with a poorly engineered package....there is a point at the far end of the envelope where the engine will in "normal" operation consume its self....the best possible example in a top fuel engine....very seldom do all eight cylinders stay lit for the entire 4.5 or so seconds of full boost...the cylinder pressures are beyond imagining....can you say 600+ hp PER CYLINDER???

 

[8Mud]

My picks for plugs for a stock 4.0 HO....Standard plugs....NGK #7252 aka FR-5 Autolite #985.....Platinum (longer lasting) Autolite #APP985.....Iridium....(longest lasting but expensive) Autolite # XP985.

My experience over the years is the NGK's and Autolites are good quality plugs. And also ND (Nippon Denso) are good plugs...they are associated with NGK...

Standard 2 bux a pop NGK's keep the fire lit in my dragbike at 10K+ rpm under a 75hp shot of nitrous.....get the picture???

The ignition systems are set up to throw a hot, short duraton, crisp spark. They are likely tuned or maufactured with the recommended plug in mind.
Electronic igniton systems may be resistance, sensitive. I know my Renixs seem to be so and my Chev's.
I've resistance measured a whole bunch of different kinds of plugs and gotten wildly variable results, mostly by manufacturer.
But in the end, all they got to do is ignite a mix of gas and air.

 

[8Mud]

8Mud brings up some good facts too.....the short of it is plug selection should suit the engine and the state of tune.....no plug will cure problems with a poorly engineered package....there is a point at the far end of the envelope where the engine will in "normal" operation consume its self....the best possible example in a top fuel engine....very seldom do all eight cylinders stay lit for the entire 4.5 or so seconds of full boost...the cylinder pressures are beyond imagining....can you say 600+ hp PER CYLINDER???

The difference between building a motor you can have some fun with for awhile and building a firecracker. is all in the tuning.

 

[lighthouse jim]

thanks

 

[FatXJ]

the best possible example in a top fuel engine....very seldom do all eight cylinders stay lit for the entire 4.5 or so seconds of full boost...the cylinder pressures are beyond imagining....can you say 600+ hp PER CYLINDER???

More like 800hp per cylinder and the spark plugs are only there to get it running. Once it reaches temp and the gas pedal is pushed the fuel will ignite just from the pressure in the cylinder. This is why you often see a lot of unburned fuel coming out when they roll to the line.

compression+air+fuel=heatbang just like a diesel

 

[Flash]

More like 800hp per cylinder and the spark plugs are only there to get it running. Once it reaches temp and the gas pedal is pushed the fuel will ignite just from the pressure in the cylinder. This is why you often see a lot of unburned fuel coming out when they roll to the line.

compression+air+fuel=heatbang just like a diesel

I'm not quit sure that is true. just speculating here but thay are alway talking about taking the timeing out of it to get over a slick spot or a bump in the track.


but then again the first thing thay do (after pulling the shoots) is to pull the fuel shut off.:dunno: like a diesel.

 

[MudDawg]

Sorry, the ignition system IS REQUIRED for a fuel motor....it IS possible that overheating in the combustion chamber can cause the engine to diesel...that does frequently happen.....but most of the engine explosions occur BECAUSE the ignition on one or more cylinders failed...the cylinder then hydraulics from the massive fuel load and something has to give.:explosion And the actual hp a fuel motor makes is an estimate anyway...no dyno will handle one...and it won't run under boost long enough to get a pull.