Pistons..

[thesnafu72]

I am rebuilding my 318 and need pistons. I am not really looking to take my block to a machinist and increase the bore of the cylinders; I'd much rather just find some stock replacement ones. I have had a lot of difficulty doing this though, until yesterday when I stumbled across a set of Keith Blacks on Summit. Here's the link:

http://www.summitracing.com/parts/UEM-1266-STD/

My goal is a compression ration of 10:1 but I am not trying to be too picky. This is my first car I have ever restored (72 swinger) and I am looking to do it right. Would these pistons be a good choice? If not, where would be a good place to go ? I have a pretty tight budget and these are priced pretty reasonably.

 

[omahamoparguy]

No, those pistons will never get you to 10:1. See the part that says 1.74 compression heith. This is too short. You need the KB 167 pistons. their compression heigth is like 1.81. This is the part that sucks with the 318. to gain compression it is gonna cost you some $. (although the KB 167's are a good deal @ summit racing)
youe final compression ratio will depend on some other factors, head cc, deck heigth, head gasket etc. Do the math, (ther are some good books called "auto math hand book") I got mine at barne & noble.

 

[omahamoparguy]

BTW, a true 9:1 (maybe a little more) compression is jus fine for the street.
then you could get by with 89 octane.

 

[thesnafu72]

Hmmm. This is much to think about. I definitely will look into getting that book. What kind of compression will those pistons i listed get ? And what do you mean get by with 89 octane..?

 

[1970Duster]

He means you can use 89 octane (pump gas) without a problem.

 

[rick360]

I am rebuilding my 318 and need pistons. I am not really looking to take my block to a machinist and increase the bore of the cylinders; I'd much rather just find some stock replacement ones. I have had a lot of difficulty doing this though, until yesterday when I stumbled across a set of Keith Blacks on Summit. Here's the link:

http://www.summitracing.com/parts/UEM-1266-STD/

My goal is a compression ration of 10:1 but I am not trying to be too picky. This is my first car I have ever restored (72 swinger) and I am looking to do it right. Would these pistons be a good choice? If not, where would be a good place to go ? I have a pretty tight budget and these are priced pretty reasonably.

The only way your gonna get 10:1 compression is if you get get the block bored to .030 or .040 over just increasing your bore size will give you a higher compression size by itself and then there are more pistons available on the market at the oversize to choose from, Keith Blacks for one. Look at what is called the compression height of the pistons they determine how close the piston will come to the combustion chamber and "squish" the mixture into a smaller area. Your ratio is the difference between what the displacement in a cylinder is at Bottom Dead Center than to what it is at Top Dead Center. The smaller the displacement at TDC the higher the compression ratio will be. There are other factors such as how thick your Head Gasket is and the volume of your combustion chambers. Get a book called "Auto Math" it should be on Amazon.com it has all kinds of formulas so you can figure things out. Your going to have a hard time getting that kind of ratio with stock pistons. On my 318 I am getting 9:1 pistons available from Mopar that use the stock cc on the combustion chambers and increase the ratio to 9:1 from a stock 8.5 :1 by increasing the compression height from around 1.741 to 1.759 but they are .030 over pistons also. The only way to get a higher compression with stock pistons would be to shave the block down the amount needed for 'zero deck' or have the heads shaved to decrease the cc on the combustion chambers. You'd need quite a bit shaved to do that. 9:1 compression would be a more obtainable and cheaper ratio to go after. Punch it out .030 over and get those pistons I mentioned they are available on a website called 1stChryslerparts.com Part# P4529419. About $130 for the set and about $200 to have 8 cylinders bored out.

 

[moper]

I''m curious why you believe you need pistons if you don't want to bore it. IMo, either do it right (which means balancing and boring/honing), or simply do a ring and bearing deal to repair it for now.