is it ok to deck block .065 to get to zero??? I am rebuilding the engine in my '71 455 conv. and I just talked to my machinist who is working on my engine and he is concerned about having to remove so much material to get to zero on the deck. He has trued the surface and installed the pistons at the 4 corners and says it will still take .065 to make it zero. Is this ok? How much is normal? I keep hearing about how important it is to zero deck the block but I want to verify this before it is too late. Thanks, Randy
I had mine done so the pistons were .003 in the hole and I believe they took .050 off of mine. No complaints or problems that I'm aware of.
What pistons are you using? Different makers have different heights. You may want to make a piston swap to keep from having to deck so much.
block decking Decking the block that much will also necessitate milling the intake side of the heads and the use of adjustable push rods or roller rockers.Better to get a different piston height to get the compression and squench area your lookin for.Then mill the block the minimum to true em . gary
Wouldn't offset grinding the crank for a +.050" extra stroke be another alternative? Then deck the block the other .012"-.015".
Yes, mine did require mocking up the motor and grinding to make the intake fit right. I also do run adj. pushrods.
Randy, When I did a mock up assembly to take some initial measurements the stock piston/rod/crank/unsurfaced block combo measured out at .070" in the hole as well. After some research, etc I decided to bump the compression up and went with the Hypereutectics. After another mock up it measured out at .040" in the hole. This may be an option to look at if you are a little antsy about decking the block that much. With this combo you'd only have to deck the block around .030" Near zero deck clearance seems to off much more for an engine than just compression. Just a consideration.
Hi Jim, Thank you for your reply. I have TA's #1607 cast alum. pistons .030 over . They are supposed to be 10.0 to 1. Is it possible that they sent me the wrong comp. ratio pistons? I am having the machine shop compare the pin location with the stock pistons that came out of the engine. Unfortunately, almost all of the machine work has already been done and the rotating assy has been balanced with the new pistons. It would be difficult to make any major changes at this point. Is there any other info needed? Thanks for all the feed-back, Randy
I talked to TA and they said I did get the right pistons. They said to get the true 10 to 1 ratio I will have to deck the block to near zero. I am thinking I will leave the piston in the hole .005 to .010 and go from there. Does anyone have any different thoughts on this? Thanks, Randy
What heads are you running. I have '67 430 heads. I had to open up the chambers to, if I remember right, about 70 cc's or so. And pistons were 24.4 cc's. I used FelPro blue head gasket. I also polished the combustion chambers and removed casting point. I also removed casting "button" on pistons and polished the top of it. My true compression is 10.03 to 1. Without the polishing job, compression was 9.73 and I had to run a 110 octane mix of about 1/3 to not have pinging at full throttle. Now with the polishing and cleanup, I can run 92 to 93 octane and no pinging at all. I would highly recommend this process. It will take an hour or two per combustion chamber, but well worth it in the long run. The machine shop can do the pistons quickly and inexpensively. Also, I checked my paperwork and found that my pistons were .038 to .035 in the hole before decking the block, so .032 was taken off after block was trued up to zero deck, not .050. Sorry.
I hear this subject brought up a lot. Whats the purpose of zero decking the block? Is it really worth all the time and money the machine shop will charge to perform this procedure?? How much of a difference does it make on the average 455??
Hi Phil, I am running the stock '71 heads but they have been ported and polished and matched to the intake manifold. The flow #'s are real good. I am concerned about pinging also. I have told the machine shop to leave the pistons in the hole .008 to .015 and mill off the rest. They will have to mock it up and see what will have to come off to make the intake and heads match up now. Randy
What would happen if a fella just put in 11:1-1 ratio pistons and didn't deck the block? At .050 or so down in the hole would this allow a reasonable compression ratio? I understand this sounds like the cheap way out but many people don't deck, shave or linebore and run fine for years. You get what you pay for but cost is usually a factor, or we would all drive Hummers with 455s and golf on Wednesdays. --Disclaimer: This is comming from a guy that still thinks you can build a reliable engine for under $2,500.
I had mine zero decked. I don't recall how much was removed, but it was a lot. The intake wasn't at the shop when they mocked it up, and therefore didn't remove enough off the intake side of the heads. I had to have the intake shaved and use a belly pan gasket in order to get the intake bolts to go on. Many of us zero deck the block. It raises the compression ratio. Just be sure the shop has your choice of intake gaskets and the intake when the mock it up.
The way it was explained to me at a bar one night (DISCLAIMER!!) was that by zero-decking the block you create a chamber that is as close to half round as possible by eliminating irregular surface area ie. corners/sharp edges etc. This promotes the clean and even burn of the fuel mixture for max power.
OK, I'm starting to uderstand this better now. But my question is how much is gained by doing this? I mean, if it only makes 10 more HP, but cost an additional $500 in machine work, then whats the point?? I am going to be building my 72 455 soon,and this is one of the things I am going to have to decide whether or not to do! Oh,the $500 for machine work is just a guess. I really don't know how it cost. How much did it cost you guys??
Oh ya, if you don't deck the block and get it down to about .035 with head gasket (piston top to bottom of head) you would loose quench area and have detonation problems. As I understand it with quench you can run higher comp. ratios without problems of det. probably 9.5:1, without the quench, you may have to back it down to 8.0:1. Now if I only knew what's the highest compression ratio you can run on the street with the 75/76 non quench heads using regular fuel? Does any one know? (I want to use the smog heads on the street and save the quench heads for the strip)
I've got 11.0 Ross pistons and haven't bored yet but I'm wondering if I should go thru the trouble of zero decking since that'll put me out of pump gas range. I was considering leaving the pistons .020 in the hole for this reason. Is this a good idea?
