spark plug reccomend....

[rewguy]

3/4" reach tapered seat, for 10-1, 383 fastburn engine.....

[ProPower engines]

3/4" reach tapered seat, for 10-1, 383 fastburn engine.....

What application?? What other particulars on the engine?
Street Drag Oval track Marine?? How much compression??Carb??

They should use a 5/8""Hex gasketed type plug.NGK has a good selection of colder type plugs for race or extended full throttle situations such as marine use.

[CGT]

Its actually .708 reach tapered seat. NGK TR6 would be a decent starting point for a 10.1 comp street/strip engine...provided you can use a projected tip..which I assume you could with 10.1 on a 383.

[rewguy]

street, 10-1 compression, holley sniper fuel injection, should make roughly 485hp

[rewguy]

Its actually .708 reach tapered seat. NGK TR6 would be a decent starting point for a 10.1 comp street/strip engine...provided you can use a projected tip..which I assume you could with 10.1 on a 383.

gm performance page states 3/4 reach specifically?
https://www.gmperformancemotor.com/parts/19300955.html

[CGT]

Its actually .708 reach tapered seat. NGK TR6 would be a decent starting point for a 10.1 comp street/strip engine...provided you can use a projected tip..which I assume you could with 10.1 on a 383.

gm performance page states 3/4 reach specifically?
https://www.gmperformancemotor.com/parts/19300955.html

Hmmm...Well, now you got me researching that. That head always used to call for AC FR3LS or MR43LTS plug which is 5/8 hex .708 reach. Can't see a spark plug number recommendation by GM anymore. .750 5/8 tapered isn't common. Im gonna look through some old catalogs. Weird

[FC-Pilot]

Heck, as of ten years ago autolite did not make a .750 tapered plug. I know .708 is very common. I know other gm heads also used the .708 depth of that era. My money is on CGT that it is .708.

Paul

[Charliesauto]

Its actually .708 reach tapered seat. NGK TR6 would be a decent starting point for a 10.1 comp street/strip engine...provided you can use a projected tip..which I assume you could with 10.1 on a 383.

gm performance page states 3/4 reach specifically?
https://www.gmperformancemotor.com/parts/19300955.html

Hmmm...Well, now you got me researching that. That head always used to call for AC FR3LS or MR43LTS plug which is 5/8 hex .708 reach. Can't see a spark plug number recommendation by GM anymore. .750 5/8 tapered isn't common. Im gonna look through some old catalogs. Weird

There are no .750" reach tapered seat plugs. If a head is machined for a tapered seat .708" reach then a .750" gasket plug will end up the same place in the chamber. They are interchangeable, assuming the head is machined with a countersunk lead in at the top of the threads to accommodate a tapered seat plug. If the head is not machined for a tapered seat plug then .750" gasket is the only choice.
When heads will accept I either, I prefer the tapered seat.