OK I have a 4 bolt main block already clearenced for a 383 crank and at a 30 over bore. the problem is there was some water damage to the block due to the machine shop so for it to be cleared up it needs to be taken to 50 over. my question is what advantages disadvantages would this have. Im building this for a blown application, Im planning on making about 550RWHP on 10-11 lbs of boost plus a 75-100 shot. My other question is what crank should I consider? I was thinking of going with a Cola forged piece? But i wasnt sure if it was a better value than the Eagle or if I would need it for only about 550. Thanks for the help guys.

 

Most people generally stop at .060" over on a SBC, so .050" "shouldn't" be a problem. But it's a good idea to have the block checked very closely for cracks and whatnot, especially since you're gonna subject it to boost.

 

The castings these days are very thin. Most "experts" recommned on 0.030" over for a forced induction buildup. I went 0.040" over on my last rebuild (motor was already 0.030" over) and I was apprehensive. It's been ok, but I have a "new" virgin block for next time that's going only 0.010" over. That way I should get better ring seal (and a touch more hp) and have "room to grow".

If it's not out of the question for you to spring for another block, I'd go that route.

YMMV

Rich Krause

 

Rich, what's the point of going .010" over on a new block? To make sure the cylinders are perfect?
Also, isn't a used block usually preferable because it is "seasoned"?

 

Yes, a seasoned block is better. My "new" block isn't new though as GM is not making LTx blocks any longer.

0.010" over has two advantages. Thicker cylinder walls = less distortion under high cylinder pressures = better ring seal = more power. Also, 0.010" over leaves room for subsequent borings without running into the problem of thin cylinders.

Rich Krause

 

Thanks for the replys guys, I do have another virgin block here so I'll try going 10 over on that one. Rich what are some other good ideas to go along with a 10 over bore. For example what stroke and rod length should I use? Oh and rich by the way Im loving that cam you chose. the 224/236 on a 115. It by far has the best idle/power ive seen sofar Thanks again!

 

I think he meant what are the advantages of .010" over compared to no bore at all (leaving the standard bore, finish honed of course). Could be wrong...?

 

On a new production stock block the bore is not done with torque plates in place, the bores are often out of round and may not be properly referenced with respect to the main bores, etc. IOW, boring the cylinders is part of the standard "blueprinting" procedure needed for all hi-po buildups. An premium aftermarket (eg Dart) or OEM specialty block (eg Bowtie) can be purchased already "blueprinted".

On a used block there is usually cylinder wall wear, so to get the proper size, finish, and "roundness" needed for good ring seal boring is indicated (as well as for the reasons above). If you have a block that's already blueprinted with minimal wear, a finish hone may be all that's needed. The problem is that this may result in slightly more than ideal piston to bore clearance.

BTW: most pistons for the SBC are 0.030" over or above. But it's easy to order "custom" bores (though you pay full list). That's how I got my current 0.040" over JE "Extreme Duty" pistons.

Rich Krause

 

I am glad the cam is working out. How much vacuum are you seeing at idle? Where does the power peak?

Please see my previous reply: if you go 0.010" or 0.020" over you may need a "custom" piston. But this isn't all that much more expensive than an "off the shelf" piston of equal quality. So that would not deter me.

I prefer short rods for SC motors. Basically, long rods help an NA motor rev. But short rods decrease the peak cylinder pressure, which is important on a SC application. In addition, the "effective chamber volume" is larger. This results in more mass in the intake charge, and more power. And since you don't need to rev the snot out of a properly set up blower car, there is no downside. 5.7" is fine for a 3.75" stroke, probably 5.875" for a 396 (5.875" stroke).

If I were buying a new rotating assembly I would go 396 (3.875" stroke) for a blower car. Again, the disadvantage of a long stroke (doesn't want to rev) is not an issue for a street or street/strip blower car.

Rich Krause

 

Rich, thanks. That is what I was referring to by a stock block, when you get one from Dart or World Products the bores are already bored and honed and ready to go. A used block will require some work, of course.

 

good post!

 

Rich im seeing about 14 inches of vacuum at idle. Im not sure about where the cam maxes due to some "trouble" with the programming. I have yet to get a clean pull from the car. But I will let you know when I found out.