[trailwing]

I had a bad experience with a recent shortblock and decided to start from scratch. One of my goals was to eliminate the chance of detonation, so I dropped the heads off at a reputable porter (to clean up the combustion chambers) and took a standard bore shortblock to a recommended builder. I specifically asked they zero deck the engine but when I returned home & measured it... the pistons are about .020 down in the hole.

Specs:
- '74 455 (.030 over)
- SRP 2-eyebrow pistons
- SCAT rods
- Standard stroke, stock crank
- 87cc Edelbrock Heads
- Edelbrock head gaskets (.038, 4.200)
- Old faithful in UPS land somewhere

So... This puts my compression ratio closer to 10:1 but theoretically hurts quench. Will it matter? Do I need to put my foot up their ass? Piss poor automotive support is beginning to cost me a lot of money.

[critter]

Sounds about right for a block that hasn't been decked. To zero deck they needed your crank and enough pistons and rods to mock up the four corners. Did they ask for those?

[Matt Meaney]

i would think, at this point, it would be much less of a hassel and maybe even less expensive (???) to get a thiner head gasket to get the quench distance you want.

[Tom Vaught]

Originally Posted by trailwing

I had a bad experience with a recent shortblock and decided to start from scratch. One of my goals was to eliminate the chance of detonation, so I dropped the heads off at a reputable porter (to clean up the combustion chambers) and took a standard bore shortblock to a recommended builder. I specifically asked they zero deck the engine but when I returned home & measured it... the pistons are about .020 down in the hole.

So... This puts my compression ratio closer to 10:1 but theoretically hurts quench. Will it matter? Do I need to put my foot up their ass? Piss poor automotive support is beginning to cost me a lot of money.

Factory spec for a Pontiac quench distance (off the line was up to .023") so with you being at .020" distance, I would not lose a seconds worth of sleep over the deal.

I will tell you as a Research Engineer that that zero deck is not all that it is cracked up to be vs .005" down for example. It might make a slight difference in emissions but you could not measure the difference on a accurate dyno, maybe a few more points of BMEP.

Tom Vaught

[trailwing]

They assembled the shortblock, so yes they had the pistons. They also decked the block... just not how I asked them. Detonation (and other stuff) killed my last engine in about 500 miles, so I'm a little sensitive right now.

[trailwing]

Sensitive to dillweed aftermarket support that is... you guys are great.

[Matt Meaney]

Originally Posted by Tom Vaught

Factory spec for a Pontiac quench distance (off the line was up to .023") so with you being at .020" distance, I would not lose a seconds worth of sleep over the deal.

I will tell you as a Research Engineer that that zero deck is not all that it is cracked up to be vs .005" down for example. It might make a slight difference in emissions but you could not measure the difference on a accurate dyno, maybe a few more points of BMEP.

Tom Vaught

hopefully not too far off topic, when i was talking to my local engine builder about what i wanted, i said "zero decked" and he immediately responded "5 in the hole". can you elaborate on this any? from everything i read about quench, it seems that the actual distance between the piston crown and head is what's important not so much where the piston is in (or out) of the block. also, having the piston down a bit keeps the "fire" from being directly in line with the head gasket.

on another note, it was my understanding that the factory had the piston down in the hole about .020 with about a .020 crush steel shim type head gasket. giving about a piston to head clearence of about .040 ish. the op stated his pistons are at about .020 and his gaskets are .038 giving a total of .058 piston to head clearence. still close enough with aluminum heads?

thanks

[b-man]

You asked for zero deck and didn't get what you wanted and paid for.

Take it back and have them make it right.

I've torn down several 'virgin' '73 -'74 455s and all of them were between zero and -.005 deck from the factory, I'm running one of those shortblocks (I left it untouched because it was in great condition) right now in my '64 GTO.

I thought the 455s would have had the pistons down in the hole by about .020 so I was a bit surprised, the 'virgin' 400 engines I've taken apart have all been right around .025 down in the hole.

[PLAY400]

When they 4 cornered my 73 YC 455 nothing was close so I had it 0 decked. I am always concerned about detonation as I run cast heads so I followed the Dude's advice and radiused all edges on the pistons tops and heads and to date have no problem with 92 @ 9.75 compression and 36 advance.