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Old 01-10-2009, 02:54 PM
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350 Chevy rebuild parts and machine work

Hopefully this wont get moved.
Just a couple of quick questions. I have just got all my parts for my rebuild, but engine machinist is an hours drive away so thought I'd get some info before driving there and finding out they can't do what I want. I recently purchased a reco'd 350 in parts. Fresh rebore and crank grind etc so was a ood start. Problem is I want the block decked as its not yet. How far can you deck the block. using flattops, but Ive heard some people say 25 thou and 45 thou. Also I got a set of new pistons and rods that some guy changed his mind on but they are balanced for a different crank he wouldn't sell. Can they also get rebalanced to suit my crank? Can I get away with using a new stock oil pump or will I need hivolume, (380-400hp), and is there any advantages of a mechanical flat cam over hydraulic or is it to tough on a street engine. Thats all, should be answered with one question. Thanks

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Old 01-10-2009, 03:23 PM
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Depends on too many variables to give one simple answer.
People often say "Zero decked" but that's a relative term.
You need to know rod length, stroke, piston pin height, and what clearance you want before you can accurately do it.
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Old 01-10-2009, 03:40 PM
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gidday, rod length s stock 5.7, stroke is standard 350, 3.48? or whatever it is, all I know of piston is 1.56 comp height, running old school 462 heads, stock length valves and pushrods, 500 lift cam, heads havent been milled yet, was seeing if I could get away with just milling the block, just gotta sort out whether I can take 10 20 30 or 40 off it, so I can drive too the nearest machinist and tell him what I want done, as they aren't really in the know over here about chevy v8s.
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Old 01-10-2009, 03:43 PM
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If you want the piston flush with the top of the block, it would need to be decked to 9.002" deck height, which equates to about .025"-.030" off the stock deck.
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Old 01-10-2009, 03:48 PM
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Alright, thats sounding better. So if I get them to mill 25 thou off it should be safe. Will that make much difference to the compression or not enough to notice. As I can't find any information on the pistons I am using nd I am trying to get to 10.5 so every bit helps. Also can I re balance pistons that Have been balanced already
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Old 01-10-2009, 03:53 PM
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It will make a difference in compression. With nothing done to the heads, and .041 head gasket, you'll be at about 10:1 compression.
http://www.kb-silvolite.com/calc.php?action=comp
Take about .030" off the heads and you'll be closer to the number you are looking for, along with the block decking.
When I'm figuring compression, I was using 7cc for 4 valve relief flat tops, not sure what you actually have.
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Old 01-10-2009, 04:09 PM
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Good to know, so I can take upto 30 off the heads as well. Our pump gas goes up to 98 octane so Iam hoping 10.5 will be in the boundaries and also high enough for performance too. My pistons are a 4 relief valve type, but cant find out anything on the net about them. They are an old piston. Speed pro (when it was actually a big brand) forged 30 over number 6000p. Noone knows anything about them that I have talked to. Now finding a gasket in that size is my next job.
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Old 01-10-2009, 04:11 PM
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By the way that website you provided is good. pity I musta stuffed up as it came back in the 11's. haha. where it says piston head cc is that just of the one piston or all 8.
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Old 01-10-2009, 04:46 PM
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Each of the measurements are just for one bore/piston.
I'm not sure what you have available there, but the typical fel pro gasket should be about .041" thick, and 4.166 bore. That's typical rebuilder stuff, so even if you don't have that brand available, they should be similar.
Typically, stock heads CC at larger than the factory says, so your 64's would likely measure 65-68CC's.
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Old 01-10-2009, 04:58 PM
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If the rods have not been shortened much when resized and the crank is standard. Your piston deck height will be 9.00". I believe that is the dimension the machinist will use to determine how much to take off your block.

A SBC from the factory is suppose to be 9.025".

I would not tell him how much to take off as all blocks are different. They are usually a bit taller toward the back of the block.

My figures say 10.5:1 compression. I used .035" for the gasket, 64CC as combustion chamber size, and 6CC for the piston head volume. Flat tops with 4 valve reliefs?? I think 6CC is right for them?

If your machinist is not knowledgeable is SBCs, my question is, where has he been? Might want to find a better machinist.
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Old 01-10-2009, 05:31 PM
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so going by that no more than 25 thou.. well i have to travel to a town an hour away to the nearest machinest and being new zealand not many chevy's around and they race 6 cylinders and new holden gm v8s mainly up there. 10.5 is all I want so will mill block and heads and try get a thin gasket and should be right. the piston sits higher in the deck the basic 345np so sounds about right. i would know more about the cc of piston head but as I said earlier cant find nothing out about them. but thanks, its all be good info
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Old 01-10-2009, 05:34 PM
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If you're milling the block to near flush, I would not run the thin gasket.
And if you just tell him the deck height you need, he should be able to make measurements and get it to that height regardless of how it came from the factory.
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Old 01-10-2009, 11:37 PM
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STOP.

Bolt the block to an engine stand. Install the main bearings and the crank. Snug down the main cap bolts. Install #1 cylinder piston/rod assembly into the bore without piston rings. Install rod bearings. Snug down the rod cap bolts. Rotate the crank so that #1 piston is at top dead center. With a steel rule standing on edge, span over the edge of the bore at either 3:00 O'Clock or 9:00 O'Clock as you're standing at the side of the block. You'll want the rule to be within 1/8th inch to 1/4 inch of the edge of the cylinder bore. Using the blades of a feeler gauge, stack blades together and slide them between the edge of the steel rule and the top of the piston crown. Change blades thicker and thicker until you get a snug fit. Rotate the crank a couple of degrees each way after you find the tightest fit to make sure the piston is at top dead center. Once you have satisfied yourself that you have the piston exactly at top dead center and that you have found the tightest stack of feeler gauge blades that will fit, add up the blades and write the dimension down. This is the piston deck height of #1 piston. Disassemble the rod from the crank and move it to #2 cylinder. Repeat the process. Disassemble and move to cylinder #7, then #8. When finished, you will have the piston deck heights of all four corners of the block. You will know your information is correct because you used the exact same piston and rod assembly to do each corner, so there will be no error like there might have been if you used four different piston/rod assemblies. I generally use a solvent to de-grease the block decks and write the piston deck height right on the block deck beside the cylinder I'm checking with an indelible ink marker.

Now, what you want to do is to determine the squish you will use when building the motor. Most commonly, it is set at somewhere between 0.035" and 0.045". This tight squish will allow the fuel mixture to be "jetted" across the chamber toward the spark plug and will allow more static compression ratio without detonation using pump gas.

It will only be by the Grace of God if your block is level corner to corner. If you find it level after your measurements, run out immediately and purchase a lottery ticket. This measurement exercise is not only to set the squish, but also to equalize the piston deck heights so that you get the same squeeze from cylinder to cylinder. I have found block decks off by as much as 0.008" front to rear and others on this board have reported even worse.

Knowing the corners will allow you to instruct the machinist how you want the decks to be cut for being parallel as well as for setting the piston deck height. You can use a taller piston deck height with a thinner gasket or you can use a shorter piston deck height with a thicker gasket and get to the same place. In other words, if you told the machinist to cut the decks so that you had 0.010" piston deck height on all cylinders, you could use a Victor Reinz #5746 gasket that is 0.025" to get to a squish of 0.035". Or, you could instruct him to cut the decks to 0.015" piston deck height and use the 5746 gasket to arrive at a squish of 0.040". Or you could tell him to cut the decks to zero piston deck height and use a gasket that is 0.040" thick for a squish of 0.040".

If you don't understand what I'm saying here, please speak up. You need to know how to do this.

I'll also add a for-instance. Let's say that on cyl 1, you find a piston deck height of 0.023" and that on cyl 7, you find a piston deck height of 0.017". Let's further say that you have decided you want to cut the block for 0.015" piston deck height and use a 0.025" gasket to arrive at a 0.040" squish. You would mark the block for the machinist to angle the block in his mill and take off 0.008" on the cyl 1 end of the block and taper down to 0.002" removal at the cyl 7 end of the block. Let's say that the other side of the motor just happened to be level end to end with 0.022" piston deck height on cyl 2 and cyl 8. You would instruct your machinist to set the block up level and remove 0.007" of material equally front to rear.

Last edited by techinspector1; 01-10-2009 at 11:52 PM.
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Old 01-11-2009, 11:03 PM
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Your thread title has been edited. We're editing the subject line on threads to strengthen the search database, we know you're here with a 'question' and/or for 'help', stating that isn't necessary, being more specific in the title betters the chance of more hits in a search and more responses to your post.

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Old 01-14-2009, 11:13 PM
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Yes, think I understand. Didnt think it would be level anyway but also didnt know how to measure like that so good to know. Will get it down over the weekend and hopefully take the block in next week, and get the project rolling. Thanks for the help., especially with the gasket thickness in relation to how much i get milled..
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