What size plug do I need for the large hole in the front of the intake baseplate (manifold)? It's the one that's under the two smaller holes. I was going to use the one out of my old engine but I can't get it out. Also what's this hole for in other applications?

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Riccioli Performance Motorworks

--RPM Racing--

Getting there.....383 with Super Ram, Bosch 24# SVO's, MSD, Edelbrock 58 mm TB, 700R4 tranny, Eibach springs, Koni 12 way adjustable shocks and struts, and more!! Now let's pray it runs when it's all back together!!!!

 

If they go into the water passage then I can only guess at 1/2" pipe plug. I doubt it's as large as a 3/4" pipe plug and the smaller ones should be 3/8" pipe plugs.

Those holes are usually for heater hose ports and coolent sensors.

 

I don't remember the exact size of the coolant passage hole, but it's bigger than 1/2". I recall using like a 20mm+ sized wrench to remove it awhile back. Probably 3/4".

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1990 IROC 350
Mods: Too busy trying to make it run right to mod it.
Airfoil, Dynomax cat-back, MSD coil, 180 t-stat, Bald Eagle tires,
Hypertech fan switch, Accel 23# injectors, Holley module, ported plenum,
Ported Daytona Yellow stock base, Moroso valve covers, other stuff,
Streetdampr, Ruger P95DC, hot wife, new oil filter, !cats, !TBC, !AIR.
18.0 @ 85MPH since I'm one big-a$$ MF
"It's better to have and not need than to need and not have."