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Discussion Starter #1
As you know my dad and I started building my 302. Well we put the #1 piston in all is well. Try to put in the next one and it won't even go in the bore! I micked out every piston and the one that fits the bores is only 4.025 and there is another one in my piston set that is that size. The rest are all 4.030. They are speed pro hyper pistons with the coated skirts. The machine shop lied to me and told me the compression ratio is 9.8 and my dad and I figured it to be around 9.1. He said my chambers are 56 cc's. My dad and I cc'ed them 4 times and came up with 61 cc chambers. So now I have to get different pistons and I am going forged I think. The bore on my motor is 4.025 shouldn't a .030 overbore be .030? I want my compresison ratio right around 10:1 but I don't want to buy a $500 piston set to do it. So does anyone know of any pistons that are either hyper or forged that have a compression ratio close to that for between $200-$250 or cheaper? The block has been zero decked. I know that the chambers have to be 61 cc. Man I am pissed, I payed my machine shop $850 for the labor and I told him about 100 times that I want a 10:1 compression ratio, now I find out he lied to me just so it would be easier for him. Man I am pi$$ed! Can someone help me find a affordable piston please. I am power hungry. The funny thing is I am only 18 so I don't know if he thought he could get away with it or not? Hope he knows I ain't paying for ****ty pistons that aren't even the same diameter right out of the box! Please help me! I am going insane. I just want to drive my car again! :: :: :: ::
 

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It sounds to me like the block was bored, but not honed. Usually they bore it out to around the correct size, and take the remaining material off by honeing them out. .005 of an inch should be an easy hone job. I would take the block back to the guy and tell him he needs to check his work, and you need the cylinder bores at .030 over for your pistons to work. Before you buy new pistons, maybe it would be better to have the heads milled to raise the compression? Also, maybe they have already been milled and you and your father arent adding that into the equation.
 

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The bore on my motor is 4.025 shouldn't a .030 overbore be .030?

Can't explain that one but agree with you.

Typically, the pistons run .002 to .005 smaller than the nominal bore size. I tend to run looser piston clearances in racing engines due to the expansion characteristics of the piston skirts so my clearances would be at the upper end of the range. The bores on a .030 nominal overbore usually end up at .0305" to .032" depending on piston size and make. Each piston is fitted to its individual bore and are numbered. These are the instructions I give to the racing shop which has handled my machine work as I don't have the specialized tools in my shop. Sometimes we horse-trade *G*.

As to compression ratio, please list the model number and/or dome/dish volume of the current/prospective piston. Also list the year (if applicable) and model (engine type or aftermarket manufacturer number) of the cylinder head being utilized. If OEM, list any modifications made to the valves/chambers. The range you mentioned is pretty normal for the engine you're building. FWIW, early 289's with flat-tops should end up around 10:1, especially with larger valves and typical decking/surfacing. Note any materials removed from head and block deck as well.

Other VMF'ers are up on current pistons to recommend. I'd just get some Silvo-O-Lite KB HE pistons and call it good. You can always have the block re-honed to fit them, if necessary. Unless you're running a big camshaft, having high compression isn't really necessary for a street engine. For racing though, SBF's, IME, like all the compression they can get. 13:1 isn't uncommon.
 

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Discussion Starter #4
Yes the heads have already been milled .020, but the machine shop ground out a whole bunch of material to "unshroud" the valves and they are also set down, therefore making the chambers back to their original size again, even though the machine shop swears that they are 56 cc chambers they way they are. The heads are 351w heads, casting number D00E-C. I know he is lying for a fact! If I buy a matched pistons set, shouldn't they all be the same diameter? Not off by as much as .005? Yes they cylinders have been honed. This is the 3rd motor I have build. My dad has been a mechanic for 28 years, so I know I can trust what my dad says. We are just plain being screwed, but little does he know, I will not take it! :: The pistons are part number h273cp. I am running a pretty decent cam. The specs are: 224 degrees of duration at .050 on the intake and 230 on the exhaust, 110 lsa, and .509 lift intake, .512 lift exhaust. Are those kb pistons a good quality piston? I was looking at those, I was also looking at trw forged pistons (part number L2482) The motor is a 69 casting. The block has been decked .010.
 

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A good shop will match pistons to the hole . When you get them back they will be marked as to what cylinder they belong to . Every piston is a little different in size so matching them results in a more balanced compression ratio across the board . Most of the time the bores will be over the 4.030 when done , as the pistons need expansion room . If they were exactly 4.030 and the pistons are exactly 4.030 when the engine warms up the skirts will swell and drag the sides of the bore ..... shortly after locking up .
 

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If I buy a matched pistons set, shouldn't they all be the same diameter?

Typically, yes. The TRW's and Speed Pro's I've used usually measure within .0002 to .0007" across the skirts and pin bosses, although the two dimensions are different due to cam grinding of the skirts.

the machine shop ground out a whole bunch of material to "unshroud" the valves and they are also set down, therefore making the chambers back to their original size again

Please post a picture of this, along with the information I previously requested. IME, it's nearly impossible to reclaim territory lost to the grinder, unless a bunch of material comes off the deck surface of the head. Larger valves must be properly positioned for correct stem height and geometry and the quench area around the spark plug must retain a certain shape for proper flame travel. Unshrouding valves must be done very carefully. I developed templates from sectioning heads to balance the pros and cons of this operation. I've found the chamber shape of the early W heads to be a really good compromise between the variables of compression and flow.

As your father is a mechanic, he likely knows some of the better shops in your area. I'm sorry to hear this one let you down. Perhaps a trip to the race track and some bench racing might net you a better referral. Racers know who does consistently good machine work. IME, in the past when I've had trouble with a shop, rather than hammering away at them and creating a bad aura around the building process, I've taken the monetary losses and moved on to a more positive situation.

Hope everything works out for you folks!
 

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Discussion Starter #7
How do I post an image? I can get a pic with the digital camera, but I haven't learned how to post them yet.
 

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I can tell you that D00E heads are typically 62-64cc stock, before milling. That 5x cc stuff is just not true. D00E heads on an otherwise stock 302 block will get you about 8.5-1 CR, which is why flattops and/or a typical mill job is needed to reclaim the compression.

Id say get those bores honed and go from there. Its a pain but I know what you mean: I had some D00E heads tapped for studs once and the shop, which I checked around about and was assured by many that it was top-notch, apparently gave my heads to the 'summer intern' and he proceed to break into the water passages in TWO seperate places for no reason other than incompetence.

however, the shop manager was apologetic, he fixed them for free and threw in a set of guideplates for free for my trouble, so not all was lost ::

Bottom line is, I have just about given up on getting correct machine-shop work the first time thru. I EXPECT to go back at least once to fix something they screwed up, and I budget that into my project time *sigh* :(
 

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First, process and compress you pix into jpeg format. File sizes of 50-100K are sufficient for high resolution full screen pictures if compressed properly. Then, upload your picture to web space. If you don't have web space, send it to me and I'll host it and post it to the thread.

Lastly, read the FAQ about using UBB to post images and image links (preferable).

Good luck!
 
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