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I was aiming for a pump gas friendly engine with fairly low compression in the first place. Im running iron heads also and really would like to do a mild supercharge if possible. I really didnt want a high compression race engine. My fear was more of having too much compression.
 

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This is where the piston information came from. It discusses how the piston manufactures dont talk about these certain "sucker pistons" or "rebuilder pistons" and how they are difficult to identify.

I`m positive it means .020 off the tops, the silvolite jobs are one in the same, it shows it on there site, however, speed pro has went out of there way to hide it, as there is very little info on any of there piston or parts lines period. sterling, badger and other companies do this as well, there called "rebuilder" pistons, these things are all over Ebay at steal prices, and they advertise them as "10:1 flat top pistons" they don`t mention there`s .020 off the tops, hence the name "sucker" comes in. I didn`t know mine were like this when I got them, all I knew was the engine didn`t have no where near the same power as compared to the TRW forged flat tops I had in there before, what gave me the first clue was when I took the heads off and looked in the bore, I was making sure my timing marks were lined up correctly, so I brought it to TDC and noticed the piston was way down in the bore, and I thought "that don`t look right, what`s going on here?" so I came inside and looked at silvolite`s web site and that`s where it said 1.540 and I said "man, they cut .020 off the tops,,, why? no wonder it hasn`t got any power" and since then I looked at other pistons, the 345NP was one of them as replacements, and found they too had .020 whacked off the tops, all the cheapy replacement "flat tops" are like this, as are the dish top pistons that we recently took out of my brothers 85 vette, they had .030 dish top jobs that had .020 off the tops, that killed the compression to about 7.9:1, the only reason the car had any throttle response was due to the TPI, had it had a carb, it would have been a complete slug. the piston companies are taking people out to lunch with these pistons, and they try to keep it a big secret as if they don`t want us to know, because they don`t want us to know! they don`t even put it on the piston box, and it`s not mentioned anywhere in the instructions. I don`t think there made this way because of a cylinder ridge, anyone can buy a ridge reamer, I think there made this way to get money out of something that`s not worth it, it kills compression and quench, and anyone who knows performance knows these are 2 prime ingrediants in any performance rebuild, so the piston company don`t mention it cause they hope the builder don`t know, and what the builder don`t know won`t hurt`em right?"]I`m positive it means .020 off the tops, the silvolite jobs are one in the same, it shows it on there site, however, speed pro has went out of there way to hide it, as there is very little info on any of there piston or parts lines period. sterling, badger and other companies do this as well, there called "rebuilder" pistons, these things are all over Ebay at steal prices, and they advertise them as "10:1 flat top pistons" they don`t mention there`s .020 off the tops, hence the name "sucker" comes in. I didn`t know mine were like this when I got them, all I knew was the engine didn`t have no where near the same power as compared to the TRW forged flat tops I had in there before, what gave me the first clue was when I took the heads off and looked in the bore, I was making sure my timing marks were lined up correctly, so I brought it to TDC and noticed the piston was way down in the bore, and I thought "that don`t look right, what`s going on here?" so I came inside and looked at silvolite`s web site and that`s where it said 1.540 and I said "man, they cut .020 off the tops,,, why? no wonder it hasn`t got any power" and since then I looked at other pistons, the 345NP was one of them as replacements, and found they too had .020 whacked off the tops, all the cheapy replacement "flat tops" are like this, as are the dish top pistons that we recently took out of my brothers 85 vette, they had .030 dish top jobs that had .020 off the tops, that killed the compression to about 7.9:1, the only reason the car had any throttle response was due to the TPI, had it had a carb, it would have been a complete slug. the piston companies are taking people out to lunch with these pistons, and they try to keep it a big secret as if they don`t want us to know, because they don`t want us to know! they don`t even put it on the piston box, and it`s not mentioned anywhere in the instructions. I don`t think there made this way because of a cylinder ridge, anyone can buy a ridge reamer, I think there made this way to get money out of something that`s not worth it, it kills compression and quench, and anyone who knows performance knows these are 2 prime ingrediants in any performance rebuild, so the piston company don`t mention it cause they hope the builder don`t know, and what the builder don`t know won`t hurt`em right?
http://www.hotrodders.com/forum/heads-21002.html
 

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It figures. Why do you bother going to "other" web sites for information?
That guy is a flaming internet idiot.
His explanation that .020" after the piston number means that these are "sucker" piston shows his total ignorance and lack of experience.
He makes up a wild conspiracy story to cover the fact that he stupidly installed 1.540" CH pistons.

These would work perfectly with a 9" block with a 3.5" stroke and 5.7" rods and a .038-042 gasket OR a 9.010" block and a .015" gasket or any combination of gasket/quench possibilities.

If he installed them in a 9.025" block a 3.48" stroke and 5.7" rods his compression would indeed be in the toliet...which is where his head ought to be.

Always beware of internet "experts" that talk about their older brother's 'Vette.
 

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Paul Wright said:
It figures. Why do you bother going to "other" web sites for information?
That guy is a flaming internet idiot.
His explanation that .020" after the piston number means that these are "sucker" piston shows his total ignorance and lack of experience.
The only reason it seemed plausible is because of this remark.

A guy at Silvolite told me their cast (not KB) pistons for a Chevy 307 were .013 too short. The Federal Moguls were .020 too short.
I dont know why Silvolite would lie about such a thing.

no wonder it hasn`t got any power" and since then I looked at other pistons, the 345NP was one of them as replacements, and found they too had .020 whacked off the tops, all the cheapy replacement "flat tops" are like this
The hyper pistons are advertised as 1.560 compression height and teh as cast are 1.540 compression height piston.
 

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The 345NP piston the guy talks about is Federal Mogul Sealed Power piston.
The 345NP piston is on the NHRA list of accepted replacement pistons.
On the FM web site it clearly shows the piston CH is 1.540.
They also have a piston available in sets that's 345NCP with a 1.56" CH. It's no conspiracy, though it's possible to get the two confused.
Just a quick check of available piston CH showed:
1.54"
1.55"
1.56"
1.563" (the L2256F piston)
1.57"

They make pistons with different CH's for a reason and it's not to "sucker" ignorant unsuspecting engine assemblers. Some classes allow tolerances to factory specs. This means that a stroke that's nominal 3.48" could be within tolerance if it was +-.020". A smart racer would grind the crank so it was on the high side of that tolerance or 3.5".
Same is true of decking. Since they allow some machining it's better to whack the block to 9". That way you have minimum quench with a .039" gasket, a few more cubes, higher compression and still factory "stock". A 1.54" piston is also useful for the rebuilder that has milled the block out of neccessity but doesn't want to raise the compression.

If your engine requires a 1.56" CH don't buy a piston with 1.54". I do agree that buying pistons on Ebay is a crap shoot. I'm finding a lot of the "new" stuff must be seconds or poor quality counterfeits.
I had to buy more than a couple Ebay sets to find ones that were acceptable for Kev's engine. The best thing to do is buy good pistons from a reputable dealer that stands behind the sale. Yes, it will cost more that way but if for some reason it's wrong you can return them.

If a piston is listed as 1.56" and it comes as 1.54" then it's machined wrongly or wrongly labeled or the web site/catalog is wrong. Either way send it back and tell them they have a problem. Make sure you've measured it right or you'll have egg on your face.


My point in all this is I've posted everything you need to know. Formulas, how to do it, what to use.... and for some reason some idiot on another site still has more credibility than I do.
I may be thought of as mean and rude but I know more than that guy does.
Hey, I don't care. Really.

You are the one ultimately responsible for your engine. You need to learn how to measure and calculate stackup, compression, quench and clearance. If you won't do that and instead prefer to look for shortcuts from the internet BS monkey's then I can't help you.
Good luck.
 

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Im just saying compare the compression heights to the advertised compression each piston gives you.

I think it's the other way round, because if you look in Jeg's, h345 np which is the Hypereutectic is said to produce 9.5 with 64cc heads and 345npstd is said to produce 10.2.
 

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They're just advertised compressions for people that are too lazy to measure. It's so some silly guy on the hotrodders forum can say, "I've got an 11 and a half to one Chevy 302 with camel humps that will rev to 9000 rpm and eat big blocks for lunch." If you don't measure, it's a crapshoot.

Kev
 

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A piston manufacturer can't compare CH to CR because they wouldn't know what the block is decked at. Also, they wouldn't know how big the chamber of the head is, gasket thickness, etc. There are many factors that go into CR, not just the pistons. Piston, as well head manufactures may list a possible CR, but they can't state it for certainty. They are general numbers, not exact. If you want to achieve exact numbers, it has to be measured!
 

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Well ok thats a better explanation since this was just an observation. I know for my situation I will eventually check for piston depth at tdc and go from there since I have no info on my pistons what so ever. Oh and of course thanks because i feel educated now.
 

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Paul Wright said:
My point in all this is I've posted everything you need to know. Formulas, how to do it, what to use.... and for some reason some idiot on another site still has more credibility than I do.
I may be thought of as mean and rude but I know more than that guy does.
Hey, I don't care. Really.
I took all you had to say whole heartedly and was just trying to understand why the compression heights differed so much from the advertised compression. I havent sensed you or anyone in this thread to be rude but just offering good info to learn off of. If I dont ask I wont learn.
 

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I get frustrated sometimes because it takes time to draft a response, type it up and edited to where I think it gives the correct answer to a question.

I don't mind a student who asks a question but a student that doesn't listen to the answer is irritating.

You seem to have difficulty understanding the difference between piston advertised compression ratio vs the compression height. Then this guy got you convinced that piston makers are lying to people (he doesn't explain why they would do that) about it.

The key thing to remember is there are people that observe and make up theory's about everything. It's a faulty leap of logic that piston manufacturers are going to the trouble of milling off exactly .020" ( a crazed and yet still accurate machinist?) and purposely selling them as 1.56" CH pistons to "suckers".

Just because someone says he talked to a guy at Silvolite about making "short" pistons doesn't mean he did.

What if I said I heard from Santa Claus that the Easter Bunny is handing out eggs infected with bird flu? At least I've named my source!

How about if I said those evil Chinese are copying Silvolite pistons so well, the only way you can tell is the CH is a metric 40 mm or 1.544"?

Hey, I just made that up but it sounds plausible!

The internet is full of this kind of hearsay, rumor and innuendo. That's why this site is better than most because the moderators diligently monitor for BS and slander.

I realize that even my credibility has to be earned. I can't just say I'm an expert. I have credentials (ASE master machinist is one, 21 years at Roush might count)
Hopefully my answers have been right a lot more times than wrong but there's a "check and balance" built in.
This forum uses peer review just like the scientific community does. If I say something that is false, misleading or flat out wrong, it will be caught by one or many of the other smart people in our 4,000 and growing members.

Go ahead and ask a question. Then all you have to do is listen to the answer.
 

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Doesn't bother me one bit. The Nova's at home, I'm finishing up a paper at Pitt and the Rex still needs a patch panel or two before I start driving it everywhere.

Next weekend perhaps? I was thinkin' of maybe running the little rotary thing for sh**s and giggles. Or maybe I'll bring the Nova down and see how it runs with the weight reduction and new wheels, just to isolate some variables for when the big PW350 hammer goes in. It's been feeling a little sluggish lately, though. I think it might be dying. I'll run a compression check before I take it out to make sure it's not gonna blow up on me.

Kev
 

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They say engines alwyas run best just before they blow. You might get your 13.99 or get into triple digit mph.
 
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