spark plug gap for headswapped cars

CanadaStang · Nov 14, 2004

RysRed96GT said:
my car detonates slightly as it is now. platinum plugs gapped at .054 . maybe this would help me out some.

Hate to be a pain, but could you let us know how you like the coppers with the .40 gap. [ if it's still pinging a bit etc.]
Also, what coppers did you get, 22's ?

CanadaStang · Nov 14, 2004

Are the test results back yet?

RysRed96GT · Nov 14, 2004

CanadaStang said:
Are the test results back yet?

i didnt even buy the plugs yet

tomustang · Nov 14, 2004

RysRed96GT said:
my car detonates slightly as it is now. platinum plugs gapped at .054 . maybe this would help me out some.

what octane rating do you use?

HIGDON · Nov 14, 2004

Well I'm running the autolite 764's at a .40 gap. Right now I think my exhaust leak is keeping me from getting a full feel down low, but up in the RPMs it runs just fine. Wish there hadn't been 2 weeks between the start and end of the swap so I can really compare it, however it is definately a LOT faster now.

RysRed96GT · Nov 14, 2004

tomustang · Nov 14, 2004

HIGDON said:
Well I'm running the autolite 764's at a .40 gap. Right now I think my exhaust leak is keeping me from getting a full feel down low, but up in the RPMs it runs just fine. Wish there hadn't been 2 weeks between the start and end of the swap so I can really compare it, however it is definately a LOT faster now.

you break the gasket when you reinstalled the h-pipe too?

CanadaStang · Nov 14, 2004

RysRed96GT said:
i didnt even buy the plugs yet

Oh Ok, no pressure

tomustang · Nov 14, 2004

ryan how can you tell if it detonates slightly ?

RysRed96GT · Nov 14, 2004

tomustang said:
ryan how can you tell if it detonates slightly ?

it did it before i installed the midpipe, now i cant even hear **** anymore, just exhaust.

it did it under load sometimes at low rpms, sometimes high. though it seemed to be doing it more sincei removed my airbox. i might fabricate a heat shield for it

CanadaStang · Nov 14, 2004

CanadaStang · Nov 14, 2004

If I drive along at 60 mph and slowly press on the gas, I can hear mine pinging.Not very loud, but it's audible. During the day, when the temp. is warmer, it pings considerably louder.
I wish there was somewhere to get 93 octane around here.

tomustang · Nov 14, 2004

if i throw 93 in it, it almost clears all up.

CanadaStang · Nov 14, 2004

tomustang said:
if i throw 93 in it, it almost clears all up.

Did gapping your plugs at .40 have any effect on pre detonation?

tomustang · Nov 14, 2004

CanadaStang said:
Did gapping your plugs at .40 have any effect on pre detonation?

none whatsoever

CanadaStang · Nov 14, 2004

tomustang said:
none whatsoever

Awww Rats

RysRed96GT · Nov 26, 2005

i'm going to bump this old thread again, as i realized i never responded as to whether i was still pinging with the smaller gap.

well, i forgot if it went away. it was over a year ago.

equally saddly, is i havent changed my plugs in that time.

im noticing some detonation under load at low rpms and sometimes at high rpms. i already changed out the fuel filter, no change. here are my suspicions...

1. Bad plugs - havent changed them in a year. they're autolite coppers.
2. Dirty injectors - I havent had a chance to pick up some seaform to run in the gas tank, but i have some STP that i'll try later.
3. Bad gas - i THINK it started since i filled up with Crown 93 octane that was discounted to midgrade prices (they do that every thursday).

My O2's are only about 5 months old. my MAF is clean. I get no check engine light at all.

Anyone have ideas?

I'm hoping its the spark plugs. Usually i hear some detonation during the hot summer months, but not when its cold. I'll finally let you all know in the next few days!

tomustang · Nov 26, 2005

damn i miss GT even more now

mrvax · Nov 27, 2005

RysRed96GT said:
i heard in another thread that a smaller gap size, like .40ish, would make more power. supposably another guy in the thread confirmed it but i want to make sure. would i make more power with a smaller gap with my higher compression?

After my headswap, I had a fairly well known speed shop owner swear by gapping the plugs to .035. He claimed he tried multiple gaps and tested this at the track. So I ran with .035 (blower and nitrous setting.)

When I replaced the plugs I gapped them at about .053. HUGE difference. Yesterday I replaced the plugs again and gapped them to .055. HUGE difference.

My personal experience is that .035 is NO FREEGIN GOOD for a N/A Stang. When I gapped the plugs to the factory setting, the car ran MUCH better. I'm sticking with .053-.057.

If you're not sure, try .040 for a month. Pull the plugs and re-gap to .055. You will see a noticible drivability difference in favor of the larger gap.

Also, if you use the correct plug for your car and gap down to .040 or .035, I don't like the way the plug's electrode tip has to be bent to achieve that small gap.

BTW: I use NGK TR-55 plugs (copper for performance.)

RysRed96GT · Nov 27, 2005

well, i just cured the detonation problem! turns out it just had bad gas. i went to sunoco, put in some 93 and poured in a bottle of sea foam (just in case). all cured!

anyway, i still need to do my plugs. i actually recall now that when i gapped them smaller, it made a better difference. i remember it was smoother going up the rpm range under load. i recall being suprised when i drove it after being gapped smaller.

still, i will let you all know when i get to it.

spark plug gap for headswapped cars

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