well i finally got these dome pistons off my friend from work, there .030 over forged pistons. i compared the domes to my flattops with 4 valve reliefs that came out of my motor and it seems that the pin height is i guess you would say it as lower then the pin height on my flat tops. like if you put them up against eachother with the top of the pistons flat the dome pistons pin height is lower. i can post a picture later tonight to give you guys something to look at and help me out if you can. my flat tops sat flat with the top of my block before i pulled them out and thats with 3.48 inch crank and 5.7 rods so im afriad to say there gonna stick out and smack the head. what do i have to do to use these pistons? shorter rods? i'd hate to think i just wasted my money bucks on these.

 

here is a picture of the dome piston, my flat tops are at the shop so il ****** a picture of them side by side after work. thanks guys.

 

Are you sure they're 350 pistons? Why do you want domes?

 

thats not what i was hoping you would say lol. but they are .030 over pistons for sure and im pretty sure that they are chevy pistons since the pin diameter is the same as the set that came out of the motor and a set of casts i got sittin around to so theyve gotta be chevys right? cause fords pins are different size i read on summit when i was checking to make sure they were not ford pistons.im kinda worried now. and i was gonna use these domes cause there forged and they were cheap and i got a set of 882s to use with them. i know 882s arent that good but theyl be fine for me right now seeing that there ready to bolt on unless i get screw in studs or pin the studs first.

 

A Ford 302 has a 4" bore with a shorter rod and a similar but slightly smaller wrist pin.

A Chevy 327 also uses a 4" bore with the same length rod but a shorter stroke.

Are there any part numbers on them?

You'll still need to calculate the compression ratio with 882s (yuck), those domes are going to eat up a lot of volume.

 

so i can use a 327 crank and be fine is what your saying? il get those pictures and then maybe you can tell better. thansk for the help so far man. gotta go to work.

 

If you used a 327 crank you'd build a 327, not a 350... assuming those are really 350 pistons. A common 327 crank won't fit in a common 350 block, though.

If you can't figure out what they are, get your money back, or cut your losses and throw them in the trash.

 

From that picture, those look like they're made probably for a 5.7" rod and either a 3.48" or shorter stroke if I had to guess. My pistons are for 3.75" stroke, 6" rod, and the wrist pin is really close to the oil ring.

 

I dont think there for 5.7 and 3.48 stroke because compared to the flat tops with 5.7 rods for 3.48 stroke the pin height is lower on the domes if you sit the pistons flat on there skirts.

 

Here is a picture of the dome against a .030 cast stock slight dish 4 valve relief piston. how do i measure to see what the pin height or compression distance i think its called. i need to know if theres anything else i can change, rods or crank to use these pistons or should i just suck it up and buy a another set and give them back if hel take them.

 

also yes they do have a part number on them but i cant seem to find out what they are by it. part number is 48083 and there is a L on 4 of the pistons and a R on the other 4.

 

Measure the diameter of the wrist pin and the distance from the center of the wrist pin hole to the piston face.

The "L" and "R" indicate that the pistons go in the left or right bank. Putting them in backwards would be a Bad Thing.

 

yeah i know the L and R means what bank, but how would i measure from the center of the pin hole if you cant get it exact center? or do you mean take the pin out and measure the top of the pin hole to the top of the piston. the pin is .927 i know that for sure.

 

Measure from the top of the wrist pin hole to the face, and measure from the bottom of the wrist pin hole to the face. Add the two numbers together and divide by 2.

Are you sure it's .927? It looks smaller than the other piston.

 

alright, thanks man il have to wait til tommarow to get my hands on a dial caliper but yeah they are the same pin size. i measured the dome one today at work and it was .927 and i can put either pin in either piston just as tight as the other so i know for sure there the same size.but tanks for your help so far man its greatly appriciated and everyone elses. but are you leaning more towards these being 327 pistons? if thats how they turn out il find a 307 crank and use that just build a 327. if its not a gimmic on e bay i could get a 307 crank with matching bearings for i think 125 dollars and i know people are gonna say its just a stock crank but thats what i had planned on using is my stock 350 crank that is pretty fresh.

 

I wouldn't waste my time building a 327.

 

i know what your saying but if i can use these pistons im going to or il never use them and throw them away so not gonna waste the money lol. he said they were 12.5 to one ratio with 64cc head. now with me thinking that they were 350 pistons i looked them up on i found a dome piston with 12.5 to one ratio with 64cc head so seeing that these are prolly 327 pistons would they still be 12.5 to one ratio? i mean since the pin height is lower does that compensate for the loss of stroke when going to a 3.25 inch crank and will it be roughly the same compression ratio?

 

You're building a disaster.

Throwing them out would be preferable to having to spend more money just to use them. You want to use a dome to make up for a loss of compression with garbage heads, presumably to make more power, but you're willing to give up displacement (ie. power) to do it? That doesn't make sense.

Compression ratio is the ratio of the volume of the combustion space plus the swept volume of the cylinder to the volume of the combustion space alone. If you decrease the displacement, you're decreasing the swept volume, so you're decreasing the compression ratio.

Just because some dome piston gives a 12.5:1 ratio with a 64cc head doesn't mean your piston does, either. You need to know the actual volume of the dome on your pistons so you can use it with all the other parameters to calculate your actual compression ratio. 12.5:1 would be way too much to run on pump gas in any case.


But yes, the wrist pin height changes to accomodate differences in stroke and/or rod length.

 

i was just trying to understand that. im still learing about the more technical aspects of building a motor then just assembling one. i was just using that as a example.but tommarow i will measure the pin height wtih the way you told me to. how can i measure the dome height?

 

It's the volume of the dome you need, and accurately as possible. There are a few ways to do it, the most accurate depends on having a cylinder of the correct bore and a burette. A less accurate way depends on having a graduated cylinder large enough to lower the piston into slowly.

 

well found out today that these pistons have a compression height of 1.80 inches 12.5 to one with 64 cc head. so these are 302 pistons? is there anyway you can use them in a 350. if not il put them on ebay and get my money out of them back and get different ones.

 

Those are a 302 piston for a 5.7" rod.

 

You dont want to use those anyway. Sell them, get the right ones.