2G 6 Bolt or 7 Bolt Block Question

[Mham2k]

How much pressure can a 6 or 7 bolt block hold before cracking? 40psi? 50psi? 70psi?

I'm not referring to internals I'm referring to the actual block itself.

Trying to understand what they can handle before they have to be filled.

 

[motomattx]

They don't usually crack, they distort and there is no set number where it will happen, it has alot to do with fuel type and detonation control, people have made over 1000hp with an unfilled block, how much do you plan to make?

 

[bastarddsm]

From the data I've collected over the years, I'd say anything over 40psi on a 0.020" motor and you are subject to cracking a cylinder wall.

Certain piston designs can help and hurt. Ratchet ass tunes obviously hurt things, if you need 1/2" head studs and a mls to keep it sealed at 40psi, you are going to be more prone to trouble.

Higher compression motors hurt it too.

 

[Mham2k]

They don't usually crack, they distort and there is no set number where it will happen, it has alot to do with fuel type and detonation control, people have made over 1000hp with an unfilled block, how much do you plan to make?

Right now just wondering for the future. Couldn't find a clear answer on it.

Some fill some don't, haven't seen anyone say they cracked one.

 

[1990TSIAWDTALON]

My son cracked a 7 bolt cylinder wall in the exact fashion that @bastarddsm describes. He said 36psi, but I know my son, was probably at 40 on a .020 7 bolt block. #4 cylinder cracked. Was tuned professionally, just didn't like the boost pressure, is my thought. He wanted to throw his internals into another block but his are .020 pistons so he said he would rather buy new pistons for a standard block. Food for thought.

 

[Mham2k]

My son cracked a 7 bolt cylinder wall in the exact fashion that @bastarddsm describes. He said 36psi, but I know my son, was probably at 40 on a .020 7 bolt block. #4 cylinder cracked. Was tuned professionally, just didn't like the boost pressure, is my thought. He wanted to throw his internals into another block but his are .020 pistons so he said he would rather buy new pistons for a standard block. Food for thought.

Gotcha, how do you get away with new pistons for a non new Standard block. Find one with decent cylinder walls, hone, and drop in?

Sounds like it more safety than really allowing much more boost.

 

[Mham2k]

From the data I've collected over the years, I'd say anything over 40psi on a 0.020" motor and you are subject to cracking a cylinder wall.

Certain piston designs can help and hurt. Ratchet ass tunes obviously hurt things, if you need 1/2" head studs and a mls to keep it sealed at 40psi, you are going to be more prone to trouble.

Higher compression motors hurt it too.

This is exactly what I was looking for, thanks

 

[1990TSIAWDTALON]

Gotcha, how do you get away with new pistons for a non new Standard block. Find one with decent cylinder walls, hone, and drop in?

Sounds like it more safety than really allowing much more boost.

Yep, I had an old 7 bolt block that I tore down for him. It was standard bore but had been left outside for a number of years and it had some rust pitting in one cylinder that would never hone out so he needs a standard bore 7 bolt block and needs to buy a standard set of replacement pistons.