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Affect of changing spark plugs (gap & heat range) on existing tune

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I still have the stock plugs in my b18c1 (USDM GSR) though at this point the motor is setup more similar than different to a b18c-R (Type-R). The reason I say this is at this point I’m running Skunk2 Tuner 1 cams which are just a little more agressive than stock Type-R cams but very similar specs just with a longer duration on the high cam. I’m also running the Skunk2 manifold which is more or less a copy of the Type-R manifold with some refinement. I’ve got the Type-R throttle body on it and intake as well.

The GSR stock runs 10:1 CR though mine has been milled a bit and comes in a little higher. The Type-R is 11.1:1 CR.

I dynoed at 173whp on a Dynapack which is a little more than a stock ITR which seems to be low to mid 160s.

All that said, the Type-R runs plugs gapped at .008 tighter and 1 heat range colder than my stock GSR plugs that I’m still running. Given my similar setup and just looking at my plug ground straps (albiet they’ve got 3k miles on them) I think the Type-R plugs may be worth a try despite the difference in compression.

So question is what affect would putting in the tighter gap and colder plug have on existing tune? I understand that the colder plug can create an opportunity for additional timing advance in a knock limited scenario which I am not. But before going and making adjustments to the existing tune I’d like an idea of how I’d expect the baseline to be affected by this change. Would it be better to experiment with the gap change first on my existing plugs and see how that goes before next introducing the colder range so I’ve got some more controlled variables? Would the only way I could measure the results or the change be in additional tuning opportunities provided and reading the ground strap, or is there a way to measure the difference without retuning against my baseline?

My theory is that the change in plugs would not change the results of the existing tune but could provide an opportunity for more power. I figure that gap will still ignite the fuel. For some reason of all the Honda B engines only the GSR had the bigger gap. Both the higher compression Type-R and lower compression non-vtec LS had the same smaller gap. The heat range is more of a question mark to me but with fresh plugs I think I should be able to validate that by reading the plugs after a quick run or would reading the new plugs not be valid unless I also made timing changes to go along with the colder plugs as well?

Hello the plug change will not affect the tune at all any more than maybe able to get a couple of hp out of it. it has no real bearing on fuel mixture or ignition timing other than in a knock limited engine and even then it would be only a slight change may be a deg of timing

As Ross said - of themselves they won't affect the tune, but the tune may affect the sparkplugs.

More power means more heat in the combustion chamber which means the sparkplugs may need to be a colder/harder heat range. With highly modified vehicles, this can be as much as three, even 4 heat ranges - your engine is lighly modified so I'd suggest the Type-R that is one range colder.

With the spark plug gap, in theory largest that will give reliable ignition as it will ignite more mixture, especially if the engine is running lean and/or has poor fuel atomisation. but in practice stock or slightly smaller should be fine for a mildly modified engine - again, the Type-R spec' should be fine.

Thanks guys, I’ll give it a try, that’s what I was looking for.

Curious if either of you could comment on why Honda might have chose the gaps the way they did. Seems odd to me.

Stock Gaps:

b18b1 (LS, no vtec, lower compression, stock ~120whp): Gap = .039

b18c1 (GSR, 10:1cr, has vtec, stock ~140whp): Gap = .047

b18c5 (Type-R 11.1:1cr, has vtec, stock ~160whp): Gap = .039 (same as LS)

I have to wonder why the GSR (or middle child) is the odd man out with the gap or more confusing why the LS has the same gap as the much more powerful Type-R given the middle child is specified wider. In minutiae there are many small differences between these 3 setups that are probably not relevant. The only key differences I can think of on the GSR which I did not list above is that it has a 2 stage intake manifold with butterflies to try and optimize the lower rpms further. They all 3 share the same injectors though though in psi the fuel pressures are: LS = 40, GSR = 48, Type-R = 47.

I have an understanding how gap affects burn and am familiar with the concept the biggest gap you can go before ignition breakdown is optimal. I also understand how if you already have a spark plug why you might increase or reduce gap from what you have, but what I’m not clear on is how you (or Honda in this case) might go about picking a gap out of the blue.

I think the colder Type-R plug was a resounding success. Drove nice and the ground strap coloration pretty much exactly half way wheras the GSR plugs Inpulled out the whole strap looked uniformly cooked. A bit surprised that the coloration looked like white paint. I attached the image for completeness.

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I was suggesting the TYPE-R heat range and gap because the power output is similar to what your engine is now producing, and Honda tech' guys are smart cookies who would have done the testing to see what worked best.

Hard to say for sure, but I suspect it's still a little on the lean side - but time will colour it more.