Spark Plugs tapered or not??
 

i have been reading through and am a bit confused.. LOL i have a 78 trans am with a 72 400 block with a butler stroker 461 rotating assembly. xe274 cam, qjet. stock intake.. 6x -8 heads from original 78 400 engine. head and intake have been milled now roughly 94 cc.. my question is.. what type spark plugs should i be using.. tapered or gasket? also i have been looking at the ngk plugs and want to stay towards a cooler plug. i saw some of the info with a spreadsheet that was discussed but im mostly confused if i need tapered or not.. lol.

also i did pick up ac delco R44TS.. are these wrong??

Tapered seat.

With the early heads that are machined with the flat for the crush gasket you can use the latter taper seat plugs also if your playing around with tip lenght for better flame travel and combustion, or if you just in a pinch and can't get the plug you need.

I ran TS plugs in my first set of '71 no, 96 heads with no problems

R45 TS (taper seat) or R45 TSX(Taper Seat Extended tip) for the 0.060 factory gap on a 78 motor.

Just a thought but in my experience before about 1991 Delco ignitions were marginal at .060 and more reliable at .045.

NGK ur5 should work and use the smaller gap.035. Taper seat. Are they dished pistons? Flat tops would give 9.5 compression. Prolly need pretty good fuel with that cam. I have similar combo with ram air 4 cam and still need at least 89 octane and a good spark curve

Neill, how are ya?

yes flat top with a 6cc valve relief.. also i made a typo on my chamber size they are around 96 cc not 94.. but yes agree should be 9.3-9.5 range on compression according to multiple calculators i used.. yes.. i run 93 sunoco.. im thinking at some point i might do an msd ignition. but dont know if i will really benefit from it..

Don't run a 45 plug. Alcohol in fuel makes engines run Plenty hot enough. If
you have AC I would not go over a 43 .
Running a tapered seat plug in a flat gasket seat really limits the seal contact area.
" S" are extended tip plugs and are typically used where a recessed piston is used.

Hmm, i have found suffix T is tapered seat, S is extended tip and X is extended gap.

/\ THIS /\

OK I stand corrected-just never seen T plugs just TS or TSX.

Regardless an AC 45 TSX are what is on my spec for my original 78 6x-8 180 HO motor.

The 'T' plugs are mostly used in trucks or heavy-duty applications.
 

I've never had very good luck with them. They seem to foul much sooner - probably because the center porcelain is completely hidden inside the shell and there is no turbulence to clean it off.

Here is a pic of both styles, courtesy of my Uncle Rock(auto):

All Pontiac V8 engines uses plugs with extended tip from factory, suffix S.
Added suffix T for 1972 and later heads, added X for extended gap used with HEI ignition.

Suffix T alone not for Pontiac V8 engines.

So...AC 43 TSX or AC 45 TSX on a 70 400 with HEI??

There were some late in '71 model production "66" casting 455 heads which took tapered seat spark plugs.
Have yet to run across the same situation on other late production '71 D port heads, but would not surprise me.

On a 70 400, unless you've changed the heads to a later model, that engine should take an AC R 43 S Which is a larger 13/16 plug with a gasket and the extended tip. Pick your heat range, 43-44-45


The "T" is the taper seat small 5/8 plug for the 71-72-ish and later stuff.

No, 1970 heads uses plugs w/o suffix T, as in Tapered seat", since in 1970 Pontiac uses plugs w/gasket.
If you need plugs with extended gap for HEI usage in 1971 and earlier heads use plugs with suffix SX, then you´ll get plugs with gasket, extended tip and extended gap needed for usage of HEI ignition.
SX plugs usually has .060" gap that may need to be adjusted to .045" in other than "smog"-applications.
Also, you may get by with S plugs having .035" gap adjusted to .045".
If you are using 1972 or later heads you need to add the T suffix to either S or SX plugs.
If you for some unknown reason need plugs with .080" gap, extended tip and tapered seat there is plugs with suffix TS8.

Hope this makes some sence.

Thanks, seems like there is always exceptions to the rule.
Lots of design changes appeared going low compression in the "smog"-era.