Hello,
I need help with selecting the spark plug.
The marine long block, carbureted vortec head 10141279, 100cc, on a 7.4L which spark plug for ignition thunderbolt IV, about 9.5:1 compression.
The cam is 0.51 lift on both I/E.
Going in an old 1988 pachanga 22 thats about 3500 lbs. + gear + and bravo 1 outdrive
thanks in advance, all input is very appreciated, including
a) initial timing,
b) spark plug gap,
c) spark plug,
d) ...
thanks!!! I did search and search,
regards
Lief
new build 7.4 vortec

Go with original spec MR43T, .035 and 8*

Thanks!!

As for timing it depends which module you have.
Set to 32-34* at full in timing

Whooa, hold off if doing today.
i could swear the l29 heads you say you have, take longer reach plugs than the r43t’s.

I don’t have the time to look this afternoon but i saw this and needed to say something before you proceed.

The heads are the larger oval ports.
I have the 24 ignition module. So max offset is idle initial timing + 24 degrees max.
Waiting...
Thanks for your input
Lief

Spark plug combustion chamber

10141279 Are the L29 Vortec heads.
They take a longer reach plug
like the NGK TR5 or the AcDelco mr43lts.

Always double check free advice, which mine was too

I'd start with 8* base timing which should keep total to around 32*. Total advance with a V8-24 is around 3750rpms. Verify the total advance as there can be some variance with modules

The reach on the AcDelco mr43lts seems correct to the depth I measured. Thanks!!