What is the most core shift you'd be comfortable with when boring a factory 400 sbc +.030?

Noticed my cam bore is off by .040" to the passenger side ( .080" more material on the drivers side). Lifter bores seem to be well centered side to side and fore and aft. This would mean the thrust sides of both banks of cylinders are already .040 thin. Just wondering what others have run into when they sonic checked their blocks in regards to how much off center they were and still were able to use the block for performance build up.

The Dart block is starting to look better all the time.

Thanks for any input.

Sonic check it before the 'chinist does anything to it -- that is the only way to tell for sure. You can get some indication by looking at the bottom of the cylinder (from the crank end).

If you are serious about horse power the Little "M" should be your first choice. e-Bay the shifted core block to someone who wants a date correct block for their Monte Carlo SS.


Larger Dave

I have a question for you. If your cam is shifted over .040, won't this affect the amount of cam lift on the one side ? Or is .040 not enough to matter as the size of the lifter is large enough ?

Guys, keep in mind that there are a few pieces to the casting mold for a small block -- I'm not expert, but just cause the front piece is shifted doesn't mean everything is shifted (or it could be shifted worse, who knows until you sonic the thing)

I'm no expert here either, but I'm relatively positive the shift you see at the cam boss is typical throughout the motor for the most part. Thats the reason you visualize shift at the cam, it's the only place you can really see with your eye, and gives a good idea of shift.
The cast pieces of the block were separate but connected solidly I believe, could you imagine if you had .040" shift one way in front and .040" the other way somewhere else? you would have all kinds of wierd clearance issues I would think. Again, not an expert by any means, just going off of memory, which isn't quite like it used to be.....
The best way to go is sonic test the block, or if cash allows go with a little M block, they are miles ahead of the factory block. Just consider what will be spent buying, testing, zero decking and machining a stock block to get it were a Little M is already at not to mention all the other benefits.

Thanks guys for the input. Fitted the splayed billet caps tonight. Like someone already said the stepped register splayed caps are a lot of work to get right. Definitely having a flat cap sitting on a flat register is the only way to do this. It's just time consuming milling a few thousandths at a time and then installing and checking the fit. Also the Moroso pan hits the ends of the new splayed caps, so I had to mill as much as I could from the ends of the caps without getting into the outer holes at the base of the caps and the pan still may contact one side of the pan. Should be ready for an align bore of the caps and cylinder bore and zero decking if the cylinder wall thickness checks okay on the sonic check.

I'm a little more concerned with the core shift knowing that it's skiny on the passenger side of the cam bore. If that translates into the same amount of shift in the cylinders that's bad because it'll effect the thrust surface of both banks of cylinders (inboard for drivers side and outboard for passenger) and the thrust surface is the most critical even with the longer rod.

Dart block is looking better, I've got a great deal within 20 miles of me for a brand new one with 400 bore and 350 mains. Maybe the money for the AFR eliminator heads will need to go towards a decent Dart block. We'll see. Looking like another minor set back if the cylinder wall thickness isn't where I want it to be.

TJS I don't believe it will effect lift running a solid cam once the valves are lashed the lift should be the same. The geometry might be effected and one bank of rockers will sit slightly lower on their studs than the other side, but I don't think it'll change the lift. Obviously as you move side to side with the cam bore the lifters don't contact the lobes in the exact location you'd like which could be a problem, but at .040 maybe not. Also I can see how it could have a slight effect on valve timing as cam is moved away from the lifters you can take up the lash, but I believe the lobe/lifter contact point is slightly moved and moving off the baseline occurs slightly later, but maybe not enough to have much effect? Just thinking out loud here, never considered it before. Good point to spend a little thought on though, how the cam/valve events are effected as the cam moves off the center of the block.

Good point to spend a little thought on though, how the cam/valve events are effected as the cam moves off the center of the block.

Shouldn't make any difference. During ALL machining operations, the block was clamped down on its machining pallet as it passed through the 28-station transfer line, located by two pre-drilled master gage holes - one in the pan rail below the fuel pump boss, and another one in the middle of the starter pad. Regardless of core shift, the cam bearing bores and lifter bores will always have the same relationship to one another. There will be some variation between machined surfaces and cast surfaces as a result of core shift, but none between machined surfaces. The photo below shows the two master gage holes that engaged the precision locator pins on the machining pallet. :thumbsup:

John thanks for posting the information! I've wondered what purpose those two large holes ever served. I was just looking at the forward one Sunday night while working on the splayed caps and noticed daylight through the hole as part of it went through the casting.

It's good to know the relationship never changes regardless of coreshift. So everything I was pondering in the previous post is a non-issue. I've got to hurry up and get this thing into the machine shop and sonic checked. Looks like that's my only question mark left keeping me from going forward with it.

Thanks again.