5.9 Magnum build w/LA heads

[Squishy]

I'm building a .030 over 5.9 magnum block with LA aluminum heads. All machine work is complete, decked .010", .030" over bore.
Parts List:
Block

• Wiseco ProTrue Street flat top pistons
• Eagle I beam rods
• Stock crank
• Balanced rotating assembly

Heads

• Speedmaster heads (Purchased Bare)
• Local head shop prepared
  • SS 2.02/1.60 valves
  • Bee Hive springs, retainers, bases
  • Race valve job with bowl blend.
  • Mancini 1.5 rocker kit for magnum bottom end

Cam is an Oregon Cam regrind 224/230 @ .050"
This is my first Magnum block and after installing #1 piston (no rings) I have a proud piston at .020". Machine shop said they decked .010" from both sides. I understand the magnum deck is shorter than the LA, but has anyone had this much piston out of the hole?
I'll need a .066" Cometic MLS head gasket to get the quench where I would like it, but what sucks is they are $120.00 each!
I know I left out a bunch of details on the engine, but I'm sure I will get questions about it.

 

[Kern Dog]

I went through this, sort of.
I built a 1990 360 in this thread:

The 360 build that has more turns than Willow Springs

Post # 188 shows where I am above deck too. I went with Cometics to get the compression back down into the 9s.
The Magnum series does have a shorter deck...I've read it is .019 shorter than the LA series.

 

[GTX JOHN]

I would buy the Cometic gaskets if it was my engine.

 

[gzig5]

Get the Cometic gasket and get on with life. It isn't just the Magnum block. I was going to have to do the same thing on my 71 340 putting closed chamber aluminum heads on when the stock OEM pistons were .030" above deck. In a five to six thousand dollar build, an extra $100 for what are probably the best quality head gasket you can get, is a drop in the bucket.

 

[Squishy]

I'm not worried about spending the $ for the head gaskets as much as I am about the piston sticking out of the hole .020". I mainly needed some feedback to see if this was not uncommon for a magnum block.
I guess I can stop whining and get on with the build!

 

[NC Engine Builder]

I'm not worried about spending the $ for the head gaskets as much as I am about the piston sticking out of the hole .020". I mainly needed some feedback to see if this was not uncommon for a magnum block.
I guess I can stop whining and get on with the build!

Zero issues with the positive deck pistons, the early 340s were that way from the factory. You could also fly cut the pistons .020 and use the .039 felpro gasket, good qench and cheaper than cometic.

 

[mopowers]

Zero issues with the positive deck pistons, the early 340s were that way from the factory. You could also fly cut the pistons .020 and use the .039 felpro gasket, good qench and cheaper than cometic.

Just curious - what would you charge to cut 0.020" off a set of pistons?

 

[NC Engine Builder]

Just curious - what would you charge to cut 0.020" off a set of pistons?

Probably 75 or so.

 

[Squishy]

Zero issues with the positive deck pistons, the early 340s were that way from the factory. You could also fly cut the pistons .020 and use the .039 felpro gasket, good qench and cheaper than cometic.

Yes, that would be a good option. The only reason I would not choose to go that direction is that the static compression ratio at this time will be at the 10.25:1 range. I don't know how much it would decrease the size of the valve pockets, but it will definitely raise the compression. Also, the whole rotating assembly has already been balanced.
I was already concerned about the compression being too high for the street, but the guy who did all the machine work didn't seem worried about it. With the cam I'm running the dynamic comp comes out around 9:1, general rule of thumb says 8.5:1 with aluminum heads. I'm at 2,700 ft. so that might make the difference.

 

[mopowers]

Probably 75 or so.

That seems cheap. I had a set done about 15-or so years ago and paid twice that.

 

[gzig5]

That seems cheap. I had a set done about 15-or so years ago and paid twice that.

Really comes down to what the machinist is setup to do. If there is a lathe available, trimming the top of the piston is literally throwing it in the chuck or fixture, checking runout and taking the cut in probably two passes max. That's about two minutes per piston with a five to ten minute setup. So less than half an hour at shop rate. If he doesn't have a lathe (or milling machine) so dedicated, there usually is an increase in delay and upcharge for tearing down a dedicated long run setup for something that takes minimal time. Some guys just don't want to bother with small jobs because of the setup and tear down for short runs is a PITA.

 

[GTX JOHN]

Th

Probably 75 or so.

That is a very reasonable price.
If you were closer, you would be doing all my
machine work if you had time!

 

[TT5.9mag]

Using the gasket to set the compression ratio and quench distance on a piston that is out of the deck is the CORRECT way to do it. Why are you opposed to doing that way? Is it just the cost of the gaskets? $120 is nothing compared to the cost of the rest of the engine build.

 

[TT5.9mag]

BTW your results are very typical when using an aftermarket LA piston in a magnum block. Lots of builders do that on purpose to get the compression they want with open chamber heads.

 

[subcom]

1994 Magnum block, same wiseco
piston and rod combo but block is not decked. I use a Felpro 1008 gasket with magnum heads.

 

[Squishy]

Using the gasket to set the compression ratio and quench distance on a piston that is out of the deck is the CORRECT way to do it. Why are you opposed to doing that way? Is it just the cost of the gaskets? $120 is nothing compared to the cost of the rest of the engine build.

I think I was misunderstood with my post. I'm totally good with using the thicker gasket to set the quench, I just wanted to make the point of needing more expensive gaskets. I have spent good money on this motor and I'm not about to cheap out on a couple gaskets!

 

[B3422w5]

Zero issues with the positive deck pistons, the early 340s were that way from the factory. You could also fly cut the pistons .020 and use the .039 felpro gasket, good qench and cheaper than cometic.

That is what I did. My flattops were like 15 out of the hole. Shop cut them to exactly zero deck, so I just run the 1008 fel pro gaskets