To Zero Deck or not

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xring

xring

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FABO'ers:
I'm starting a 340/416 build with '72 340 block; Eagle forged crank; Eagle I-beam rods and dish Ross pistons. Along with aluminum Edelbrock heads. With this piston I will need to deck the block 0.017" to get zero deck and take advantage of the closed-chamber heads; as well as machining the heads to reduce the combustion chamber volume to get my desired compression ratio.

I've read everything I can find about quench but haven't seen this addressed without custom pistons.

So, should I cut the block to achieve zero deck; and my quench distance will be about 0.040" (head gasket thickness)?

Thanks!
 
I like a zero deck for high performance engines. It can be tuff on the street with todays octanes or suffer retarded timing. Aluminum heads help a bit. But I'd do it if need be.

I don't remember the need for custom pistons though. Deck heights vary from block to block. I have had a zero deck w/OOTB slugs and no deck milling.
 
I plan on doing a test fit after the block is cleaned and bored to check the deck clearance. I don't believe my block has been cut previously, and the piston specs are 0,017" in the hole; but I might get lucky and not have to cut the block. My other thought was to use a thin head gasket, but how thin can you get a custom gasket? Also don't want to cause any sealing problems.

Thanks.
 
It needs to be square decked. Not the same as just decking which is simply milling the surface. Square decking makes it parallel with the crank centerline so you have that nice quench accross the whole deck surface. Otherwise you will be off some on some cylinders. I bring those pistons proud of the deck .010 so the quench is .030 with the performance gasket...
 
I'll talk to my machine shop about the square decking. I wondered how you were supposed to account for the cylinder-to-cylinder variance.
I want to do as much of this build as I can rather than have the shop do it. So I want to do the test fits and measurements (such as how far the pistons are in the hole) and then tell the shop what I need. I want to end up with a good engine, but the fun part of this project is learning all the details like this.
Thanks guys.
 
Xring, the thinest gasket I know of off the shelf is the Mopar thin head gasket @ .028 IIRC. This is something you do not want to use in this build as I see it going.
MEasure up before final fitment.
 
I'm not sure why you want to machine your new Edelbrock heads to acheive your desired complession ratio. With the deck squared and the correct pistons and head gasket thickness, you can custom tailor your CR without having to resort to machining your heads. As soon as you do that you open up another can of worms with pushrod lengths, intake manifold fit, etc.
 
I would zero deck it, even bring the pistons above a few to get you a .035 to .040 quench, it will run better on 93, quench helps with low octain. With those heads and good quench i would shoot for 10.75 to 11.0 cr if you can get good quality 93, in a lighter car, with a stall and freash air intake. Hell i'm running 11.25 cr in a 360 with factory j's and 205 cyl psi on 93 octaine!! with no quench and it has guys running big blocks scratching their heads as to why they lost to a small block with stock heads ...

ebay 019.jpg
 
In this case, you may not be able to measure the block well enough to get the info for them. You can measure one of the edges, but not accross the deck. Ask to look a tthe block machining equipment. If it uses a round cutting head on a long heavy arm, find a new shop. If it looks like a drill press on steroids, and the cutting head is a T shape, ask if they have a BHJ fixture or equivolent. If they do, they can properly square deck the block and all you do is tell them you need it at 9.60 or 9.580 or whatever. For the Diamond dishes I use its 9.580.
 
OldVart said:
I'm not sure why you want to machine your new Edelbrock heads to acheive your desired complession ratio. With the deck squared and the correct pistons and head gasket thickness, you can custom tailor your CR without having to resort to machining your heads. As soon as you do that you open up another can of worms with pushrod lengths, intake manifold fit, etc.
Click to expand...

I will avoid or minimize cutting the heads if I can. Won't know for sure until I CC the cylinders and heads. Basically I picked the pistons on style (dish) and weight and ended up with the Ross -21cc pistons.
Thanks!
 
moper said:
In this case, you may not be able to measure the block well enough to get the info for them. You can measure one of the edges, but not accross the deck. Ask to look a tthe block machining equipment. If it uses a round cutting head on a long heavy arm, find a new shop. If it looks like a drill press on steroids, and the cutting head is a T shape, ask if they have a BHJ fixture or equivolent. If they do, they can properly square deck the block and all you do is tell them you need it at 9.60 or 9.580 or whatever. For the Diamond dishes I use its 9.580.
Click to expand...

Actually what I was going to do was do a test fit after the block is bored and measure the compression height directly from the piston to the deck. Then have the shop deck the block the required amount, not to a certain height.

Will this not work? Does the block need to be square-decked before boring/honing?

Thanks.
 
No, the boring and honing can be done at any time. But, the good machines will bore and deck without ever resetting the block. That's to make sure none of the critical relationships get screwed up as a result of setup or machine type. The honing is done on another machine. There is a big difference between decking and square decking as I said. If you are at all concerned with having a properly set up quench-utilizing engine, it needs to be square decked so the entire deck surface is exactly flat and parallel to the crank centerline. I find it's easier to simply tell the operator "I need 9.580 deck height". You simply add up 1/2 stroke + rod length + compression distance of piston. Rather than to take the block back, mock it up, then bring it back, and say "cut .***" off it" and then mock it up again to see where it ended up.
 
moper said:
... You simply add up 1/2 stroke + rod length + compression distance of piston. Rather than to take the block back, mock it up, then bring it back, and say "cut .***" off it" and then mock it up again to see where it ended up.
Click to expand...

10-4! I come up with a deck height of 9.582" with my combination, using published specs for the stroke, rod length, and piston compression height.

Thanks!
 
I did a similar build (360/408) and just bought the right pistons to get the CR with the selected head (assuming zero decking). IIRC Eddy has 2 different SB heads. I would not mill the heads.

ps I used Cometics but you have to have the right surface finish on the block and heads (smooth - can't remember the RMS#'s)
 
I believe for Cometics and any MLS type gaskets they want an Ra of 30 or smoother. Most RPM type heads are low 30s. Most shop-milled iron heads are 40-45 unless you specify the ultra-smooth finish (and pay extra) and they have the equipment that can do it. Felpro Blues I believe are rated for any Ra from 30-60 something.
 
What is the problem with having the heads milled? Valvetrain geometry?
 
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