i got my block at the machine shop now where it has been hot tanked and magnafluxed.... the machinst measured the bores(its currently .020 over). and i was gonna get it bored another .010 to make it a total of .030, and more importantly clean up the cylinder walls...BUT the machinst said it looks like a piston overheated and expanded the walls at one point and he says he doesn't think another .010 will get rid of it....He suggests another .020 to be safe(for a total of .040), but i was wondering if that is not safe in another way...

main question: How much more risky is a 408 then a 406? i'll be using a 6.0 rod...the block is a 4 bolt...

 

Probably the only way to know for sure is to have the cylinder walls sonic tested.

 

I'd stick with the additional .010" if at all possible, for a total overbore of .030".

Have him bore the cyl in question, even though it may cost a couple of extra bucks, and see if it cleans up. It's going to cost a couple of extra bucks no matter what you do, unless you just go straight ahead and do the bull in a china shop thing, and punch it to the max no matter what like a production line rebuilder. Remember, once that metal is gone, it's gone; there's no putting it back, short of sleeving it. $$$$ compared to one extra bore step on one cyl.

It's a 400, in whatever overbore; not a mutation size. Don't worry about this "make it a 408" type of talk, it makes one look illiterate and inexperienced.

Piston selection is far greater for a .030" oversize than any other.

 

We have gone .040 over on the 400's, but I do suggest having it sonic tested as variances in castings can become an issue. Worst case, have it sleeved.

 

so whats a rough guess at the price of having it sleeved?

i think i am gonna do what RB83L69 said, and get him to bore the bigger cylinder first to .010 and then see if its still not enough, and if it isn't, then i'll get it sonic tested and if all goes well, then it'll be .040 over total...

i really don't wanna go to .040 over though, because the more costly this becomes, the longer it will take me to put it together... and if i could mangae to just go to .030 over total then summit has a nice "complete package" for pistons(wiesco forged 4.155 bore pistons with the moly rings and piston pins), but i don't know if its offered in 4.165 bore..

 

You may also experience some overheating in the end so expect to need a good cooling system. I had a friend that bored to the limit of the block and he said it would overheat after like 10 minutes of driving and that was with an electric push fan.. It ended up being a trailer queen just to get to the track until the whole engine finally let go after a while. You could also search the yards for a better block.

 

If the 1 cyl. doesn't clean up but all the others do, maybe you could just sleeve the one that doesn't. This way you'd be left with the good selection of +.030 parts & more metal between the fire and the water. Might even be cheaper than going +.040 (when you factor in the piston $$)?

Just an idea.

 

i was talking to him again today and he said he thinks i am better off going .040 over. and he said how very little difference there is in the extra .010 between that and .030 over and he figures the extra few thousanths of an inch shouldn't make much of a difference with over heating.

are you sure your buddies had the steam holes drilled in the heads? what woudl you call "bored to the limit"?

 

If there is not much core shift in the block, .040 over will be fine. I've built a number of 4.165 bore, stock block, engines that's logged 40,000 plus miles,, including one of my own. Steam holes in the heads and a good cooling system is imperative whether it's a standard bore or 4.165" bore. I do however consider .040 over as the limit on a minimal core shift stock block.

The most economical forged 4.165 piston is a dished TRW piston (L2352F - $245???) that delivers around 10:1 compression with 64cc heads and works great if you plan on running cast iron heads,, even on pump gas. It's for 5.565" rods, but there's not nearly the advantage as most believe in moving up to 5.7" rods unless you plan on making over 500 horses.

Most higher end pistons can be found in .040 over applications,, although the choices are not as plentiful.

I would ask the guy to give it a try at .030 over, but would not loose a minute's sleep over going .040 over,, as long as core shift is within reason.