I'm going to build a basic 430hp 6in rodded 383 and I want to use a street fill of hard blok. Do I need to bolt a head on when I fill the water jackets or will it not really matter? My understanding is that most bore flexure occurs in the top 1 inch of the wall. The block fill will be well below that. What do you guys think?

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82 z28 350cid, vortec heads, comp 262h cam, Holley 600cfm carb, 2in twice pipes, MSD ignition, turbo 350 trans, 3.73 posi, manly b&m megashifter

 

you should only be filling the bottom inch or so for the street. that'll stiffen up the bottom of the cylinders and if you break through when you grind it for clearance it'll keep it from leaking.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

I plan on only filling up to the bottom of the core plug holes. I'll be fine won't I?

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82 z28 350cid, vortec heads, comp 262h cam, Holley 600cfm carb, 2in twice pipes, MSD ignition, turbo 350 trans, 3.73 posi, manly b&m megashifter

 

Yup, make sure to set a level on the deck to make sure it's level in both directions and fill it to the bottom of the freeze plug holes. when that hardens up do the other side... The inside of the water jacket should be very clean before doing this so it adheres well. I've found that hydrochloric acid solution works great to eat the scale off. Or have the block tanked or oven baked...

You sure you need to do this? At +.030" you should be OK unless you are asking alot from your motor (700+ HP)

I guess it can't hurt as it increases the oil temp and keeps the walls straighter longer.

 

How does it increase the oil temps? I don't see how. The reason I want to do it is that I have never done it before and want to give it a shot and I think trying to find 1 horsepower in 10 places is easier than trying to find 10 horsepower in one place.

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82 z28 350cid, vortec heads, comp 262h cam, Holley 600cfm carb, 2in twice pipes, MSD ignition, turbo 350 trans, 3.73 posi, manly b&m megashifter

 

It insulates the bottom of the block where all the oil galleys run through. Usually the coolant would pull the heat out of the oil which isn't a real good thing. Actually hotter oil makes more horsepower (overheating it isn't good either) but basically 220 degrees on the oil and 170 coolant temp is pretty optimal, but almost impossible w/o block fill.

Running conventional oils over 230 isn't a good idea, but synthetics could take alot more without breaking down.