What to gap plugs at?

[cHz]

I just bought some new NGK BPR7ES plugs and I'm putting them in with some MSD wires. Mods are in my profile, I'm running 15psi right now, but when I go to the track Friday, I'll be turning it up to about 20psi, what should I have these gapped at?

 

[-TunedDSM-]

.028

 

[4BangR-x]

.028-.030

 

[JayRolla]

.028 agreed

 

[cHz]

Alright, will do. Thanks. I have another question, sort of noobish I guess, but are like MSD wires universal? At my Autozone, they have a set of 8.5mm MSD wires I was looking to buy and I was wondering if I needed a certain type or if they were universal?

 

[Lordpaxin]

you would be better off getting a specific application wire.

 

[JayRolla]

Yes lord is right but if they are in stock, measure yours and then measure the msd's and see how close they are. If they are too long it makes the motor look cluttered and if to short they of coarse wont work.

 

[4BangR-x]

Yes, chances are they will just be longer then necessary. They should work fine though.

 

[Piranha451]

Everyone seems to agree on a gap of .028-.030 but NGK states the gap should be .032. I'm not a tuning wizard, so please explain to me why the somewhat smaller gap preference? Thanks in advance!

 

[MrBoxx]

A spark plug part number might fit hundreds of engines and, although the factory will typically set the gap to a pre-selected setting, this may not be the right gap for your particular engine. Insufficient spark plug gap can cause pre-ignition, detonation and even engine damage. Too much gap can result in a higher rate of misfires, loss of power, plug fouling and poor fuel economy. It is always best to check the gap against the manufacturer's specifications.

Another consideration that should be taken into account is the extent of any modifications that you may have made to the engine. As an example, when you raise compression or add forced induction (a turbo system, nitrous or supercharger kit) you must reduce the gap (about .004" for every 50 hp you add). However, when you add a high power ignition system (such as those offered by MSD, Crane, Nology) you can open the gap from .002-.005".

^ Taken from NGK's FAQ site.

Also, from a different site:

Something many do not know, is that with Higher Compression ratios and Superchargers as well as Nitrous, in many cases smaller spark plug gaps must be used as well as the use of a much hotter ignition system (see above). These higher cylinder pressures require more energy to jump the spark plug gap.

 

[Smokin80]

the smaller gap is because of the relatively large amount of boost you are running...20 psi has the ablility to "blow out" the spark and cause all sorts of neat issues. smaller plug gap will help stop that. probably oter reasons but that is my .02

 

[Defiant]

Air is one of the few things whose resistance increases when it's put under pressure.