By builder recommended to use standard .051 mls GM gaskets. But the only ones I find are 4.020 bore, and these at 4.080 bore, which are listed as ls3 gaskets. I know the ls3 is a gen4 if I am not mistaken, so will these 4.080 ls3 gaskets be ok to use on a 4.030 gen3 block?

http://m.summitracing.com/parts/nal-12610046

 

I don't know why they wouldn't work.

I'm using the similar Cometic gaskets on my .005"-over stroked 6.0l.

 

I'm using the LS3 gaskets on my .005 6.0 block too, but in my case it's because I'm using LS3 heads, so they are the best choice. My only concern would be whether the larger gasket would have a negative impact on quench, which could potentially cause detonation. You may want to do some homework on that. If so, you may want to find an aftermarket MLS gasket with a diameter closer to the 4.040-4.050" range.

 

I was in a hurry when I posted earlier, I am pretty sure the gaskets physically fit, I just don't know how critical the bore size of the gasket in relation to cylinder bore size is. A flattop .030 over 6.0 with 243 heads shaved .025 may be pushing it for compression on pump gas, and I don't want to deal with detonation.....that is what killed my 383 after all.

 

using a thicker gasket to lower compression isn't always going to provide the results that you may want. The problem with using taller gaskets is that it will ruin the quench, which can actually cause detonation. You really may want to look into having the combustion chambers on the heads ported to get some volume back.

 

I was concerned that the gasket bore size being too big could cause detonation, but after researching last night, I didn't find any complaints of it. The cometics come with a 4.060, which I think would be better, but found quite a few threads with them leaking coolant, sometimes I to the oil, so I am going to give the 4.080 GM MLs ones a shot. Builder specified to get .051 gaskets to get the desired quench. I do agree, thicker gaskets are not usually a good direction to go.