I would Sonic check the bores before doing anything, especially 7 and 8 all the way around.

 

I’m not sure on the 400 block that the torque plate makes all that much difference since the siamese connection between the cylinders forces a hot deformation of those walls anyway.

If you run a chrome face ring they need a coarse hone if you run moly rings they are better with a finer grit hone. A current hone method that is popular is the plateau hone which is running a fine grit over a coarse grit this works exceptionally well on either of these rings.

I think you need to get actual bore dimensions as this is going to affect piston to wall clearance and that varies by piston material type low alloy cast or 2618 forged will tolerate a wider clearance if not need it where hyper eutectic castings and 4032 forging are suitable for tighter clearance so actually knowing the bore dimensions against the piston type and their actual across the skirt dimension would be helpful before touching the bores with a hone.

I think your general inspection plan is good adding in magnaflux and sonic check of the bores there is good reason to be sure there aren’t problems lurking in the block.

Your head choice is good, as usual the deck clearance to piston is going to drive gasket selection or the reverse of that. Sounds like a race motor which might benefit from stainless O rings and a flat copper head gasket which in turn might drive a taller compression height piston rather than carving more off the head deck.

The really critical thing with heads is breathing beyond .5 inch. Most competition cams, in fact the whole category, is tending to faster lift rates and more lift where many ports are topping out flow improvements at .5 inch or so. My feeling on this is once the port is maxed in what it will deliver add more lift only serves to degrade the valve train. Example is 300 CFM at .5 inch lift and 305 CFM at .6 inch lift hardly is worth the effort to keep things together at .6 inch of lift. So knowing the flow profile of the port to lift of the valve is a good design constraint.

Bogie

 

Plate honing a GM 509 block is very important for ring seal in my opinion. It'll still work without it just fine, it's just plate honing helps quite a bit.
It doesn't hurt anything to have a second opinion but beware the new shop will want to do things their way so it's likely they will find something.

 

Plate honing a GM 509 block is very important for ring seal in my opinion. It'll still work without it just fine, it's just plate honing helps quite a bit.
It doesn't hurt anything to have a second opinion but beware the new shop will want to do things their way so it's likely they will find something.

Maybe that's why my current engine Puffs a little bit of smoke out the breathers while it's running.
It's a 509 block also 030 over. I took it to the same machine shop I will take this one to, and they did a light hone on it. I didn't even ask if they used a torque plate or not..
This one I want to do a little better job on, and it's going to get forged pistons for sure. Probably D dish, and I'm going to shoot for 10.5 to 1 compression. That 11 to 1 is on the ragged edge!

 

I'm with Johnsongrass1....the 400 block's .125" bigger bore puts all the head fasteners .062" closer to the actual bore wall, so the bolts tend to distort the block more than on a 4.0" bore block.
I'd call torque plate honing vital and mandatory on a stock block 400 build beyond just a mild hotrod deal that is mostly stockish..

i consider that one of the bad things about shopping for stock 400 blocks....i want them bare and clean, magnaflux checked, and standard bore.... so I can have it machined right from the start. I don't want it already machined.

if you can sonic check and it comes out good I'd seriously look at going .040" over.

Problem with torque plate honing after the fact is that the fastener torque load pulls the bore wall back leaving 5 pucker spots around each cylinder that the hone will not even touch unless you've got room to hone it oversize at the current bore and not go outside your piston-to bore limits.

if you're up against this pucker situation at the current fresh .030" bore, you might consider Racetec/Autotec for pistons and they should be able to make you an .035" oversize set....file-to-fit rings and then a fresh torque plate hone and you would be set.

 

4.160 or 4.165 is doable for me. I was already planning on going another .010 over on my current truck engine.
I need to get rid of the hypers eventually, and he said he could hone it to spec, and 4.165 is usually safe. I will make sure they use the plate.
What are yalls thoughts on stuffing a 3.875 crank in there? Is it worth it for another 15 cubes, or just stick with 3.75 stroke?

 

A 406 can easily be build to exceed the strength of the stock block

 

The 3.875" stroke makes for less cam-to-rod clearance, along with more block clearancing necessary at bore bottoms and pan rails.
The clearancing can sometimes get you into water jacket, and the cam situation puts you into a small base circle grind.

There was a company, I think K-1, that made 3.875, 3.935" and 4.00" stroke cranks with a 2.00" small journal, and a 2.00" small journal rod that was actually smaller in overall size on the big end rather than just a large journal rod blank left .100" small on the bore. The dedicated forging smaller rod really helped with clearance.
I haven't seen anything on them in at least 5 years, so I don't know if they are still making them.

For the added clearance hassle and cost of parts, i don't think it is worth it in a stock block. If it breaks, you just tore up rather expensive stuff.

 

Skip White 3.75 rotating assembly it is then!
I am really thinking of putting my Speier 205 Sfactor heads, and Jones solid roller on this if the block checks out.
I haven't assembled the top end yet, so I have a pretty stout top end to put on one of these small blocks.
The 383 short block is assembled already, but I would rather have another 406/408.
So I will send this 400 block out soon to checked out!