Okay, i understand this is not how many ov you would do things... but please... humor me. I'm going to do this either way, and i'd like to be armed with some data when i go to my machinist.


How far can you mill a stock 5.9 Magnum (2000 if that matters) before running into sealing/performance issues? I'm firmly in the less is more camp when it comes to this stuff (Ie: i'd rather have a stock bore and more rigid walls than a bigger .060" bore), but my goal here is quench... and tight as possible... WITHOUT rebuilding the engine.

My pistons are around .050" down the hole (.048" to .052"), and this engine is in REALLY nice shape. Can i lop .040" off the deck without any issues? How about .045"? (my worst case scenario).

Obviously, the point is to re-use my existing pistons and a really thin gasket.


I've been quoted $250 to do it, so for what it will gain, that seems a paltry expense. Also going to mill the heads a bit, but not as much.

I take it your short block, or whole motor is still together? No matter what, clearance will have to be checked. Worst case scenario is there are stock weight, standard bore pistons with deep notches available that are cheap. I don't remember the brand or number, but somebody on hear has done it. Brian at IMM would, and could get you a set.
If you are committed to running that big of a cam, you might as well buy it , get some checking valve springs and find out what you will need to do.
What you want to do is the route I wanted to take till I found the extra wear right at the top of ring travel. My plans changed, and after tossing around the same problems you ask about here, I wound up with a 408 stroker kit with forged pistons having deep notches. Also check the CC on your heads, so you know exactly what you are getting into for compression on this deal, if you plan to run pump gas.
I hope this works out for you. Another thing to consider is that the factory got good results out of that big quench distance as it was built! That to me says it might be a small gain is all that will be found in chasing a very tight quench distance.

This engine's pretty damn clean, and it tested out at 175-180 across the board (referenced against a lot ov other Magnums the same wrecker had). Right now its down to the short block, and i CAN stop there if need be... just shave and port the heads, cut the guides and be done with it. I'd REALLY like to try this out though.

Buying new pistons (IF they are actually stock weight and EVERYTHING else, ie: no extra work) would depend on just how cheap... and by that i mean the whole deal (rings cost money too). If they were comparable to paying someone to notch my pistons... well... maybe...

Wasn't going to go quite that big on the cam (was thinking something more Whiplash size), but i found one used, and it will save me a lot ov money. Plus... its gonna be a light, stick car... and i have never had a big lumpy cam. This one's a nice size, plus its easy on lift, so easier on valvetrain.

I'll be cc'ing the heads yes, at least one chamber... that'll give me an idea at least. The info out there (62 to 65cc) leaves a lot ov room for variation... and i dont like that.

I would mill off .030 and be done with it. 030 will be safe, and your pistons .020 in the hole + .020 steel shim gasket gets you to where you want to be. If you start to go more than that you're going to run into issues getting your intake manifold to fit correctly and you will be into it for additional milling to correct.

You will need to mill the "China Wall".

Run a thread chaser down the head bolt holes in the block, for the head bolts will be treading into new unused threads. And chamfer the holes.

You may need shorter pushrods, or may not.

You may also need to run a few extra gaskets under the dizzy mounting flange after milling.

You will need to mill the intake face on the cylinder heads. Refer to the DC book for how much material to take off the intake side, and china wall in relation to the deck surface.

You may find the chart on allpar.com

Upon assembly, check to see if the cylinder head alignment pins are not holding the heads off the block.

I would think .050" off the block should NOT be an issue with head gasket sealing. BUT, have no personal experience with this small block.

X2 on milling the heads, so you can use any manifold (rather than create a special manifold)

Don't know on deck milling limit but as for bore limit, most can handle a .040" over bore safely but as always only way to know is a sonic check. my 410 is a 95 year magnum block bored .040" over and it still had good enough meat to not worry about it.

I was certainly HOPING to only have to mill the face ov the heads. This is going to start adding up...

A new development may allow me to only have to mill .025" off the block (for a .025" remaining deck height). I'm told i can break apart a single MLS gasket and use the steel shims. Both my surfaces will be machined... so it sounds doable? Those are apparently .009". That would be perfect... if it works...

When I did it I did not mill the "china wall" at all. I just made some thin intake gaskets from some thin gasket paper stock from NAPA and I used a bead of "right stuff" sealant on the ends, no distributor shim needed. I did it all wrong but it worked great.