Technical Piston help

Building a GMC 302for street only. ARIAS Pistons(.60) arrive but they are 12:1.Head is 2193983. Head has been worked(?).Don't know the cc's of the head. I am only going to put it in a 1/2ton truck. What can I do now ?
Thanks in advance

 

Start by measuring the cc of the head. You need to know where you are to get where you're going.

 

When you find out what you need, maybe Arias can take some off the dome for you ?

DND

 

Will find out head cc weds afternoon. Sent Arias email for options

 

Show me a photo and tell me how high the dome is above the flat of the piston and if the dome is flat. Arias normally put the top ring pretty far done on the piston also. I had to beg them to put mine only .200 down. All this takes away from comp ratio. 12-1 were special order an normally the head had .090-.125 milled off to do it.

 

Why did you buy the 12:1 pistons? No other choices?

 

I was buying from "Patricks's"9:1. He said 5week or more wait time. He gave me this guys number. Didn't know they were 12:1 till I called ARIAS today; when pistons showed up. Glad I did.
Dome is close to half an inch.

 

See the top shape

 

There are online programs that will help you to calculate your true compression ratio. You will need a graduated tube and a dial caliper or depth mike. You will also need to do a little math. The program will do most of it. Then you will know your true combustion chamber size and if your head has been milled. The cost of the tools should be less then your machinist would charge to do the measuring for you. And you will have the tools and experience for ever. Well maybe not the caliper. Once you have done all this you will know how much to remove from the piston dome to bring it down to 9 to 1 or what ever you are looking for. Chuck them in a lathe or mill and have at it.Also. Be real careful putting in the rear main bearing shells. Get them wrong way around and kiss off your new motor.

 

Can't tell from the pics how thick the piston is at the dome, but my guess is you're gonna end up getting different pistons for this mill. Sorry.

 

I would bet the head was milled at one time.I don't have any of those tools so I am leaving it to the machinist.The pistons are with me;but I can drop them off at the machinist.If they can shave them down then great! Just bummed wasn't given correct ones.

 

If you have a ruler, you can measure the approximate thickness of the dome (it will require subtracting the inside measurement, from the outside measurement). If it's less than 1/2" thick then I really doubt you can machine the piston enough to get the compression down to where you want it.

 

I don't think the pistons are hollow dome if I am seeing right on the bottom view, then can mill to flat if necessary...Well hopefully..

 

I can see them being either hollow dome, or solid dome, depending on how I squint. A ruler will tell pretty quickly.

 

That dome is right at a half inch

 

Measured difference is 1/2" . but not sure if worth gambling. Might be able to sell these to recoup some loss and order correct ones.....

 

My GMC was turbocharged and had 9 to 1 CR pistons from Arias. Even they had a slight popup. You may well be able to use these.

 

The key to the head milling is looking at the side of the head where the side panel goes over the push rods. If the bottom of the threads holes are right at the bottom or some are showing (don't worry about this they thread into the head gasket material) then it's been milled .100-.110". stick a set of dial indicators in and see how much you have.

I checked my plaster castings of an uncut 302 head and they are .820-.840" thick so with a .060" head gasket that would be close to .900" of depth in the head for .500" of popup.
The next thing to do is set the piston on a flat surface and measure to the highest point. Then put your scale inside the piston and measure to the highest again. I'll bet it's over 1/2". You only need .200" piston head thickness on a forging anyway especially on the street. So you can take a lot off if it is.

I guarentee you I would not run then in anything the way they are. Forged pistons are not run ready out of the box, You need to round off ALL those corners with may take off 5-10 cc's per piston; those corners are detination points. a good body file will make short work of the edges and then a flapper wheel to finish them off.

When your done with them, get them re-balanced. Lastly if you want to sell them PM me on what you want. I'm sure I have a set in my garage which have about 1/8" popup. Thanks and Good Luck

 

How did you end up with Arias pistons without filling out the order form listing all the specs of your head & block ? When I ordered a set for a 248, Nick sr. helped me get all the info they needed. I made a chamber cast, asked for 9:1 popups to fit that chamber & use 283 Chev rings. A few weeks later they arrived. They're like jewelry.
The domes on yours look like they would be right around 9:1 with an early head for the domed slugs ...

 

I originally went to "Patrick's" and he stated at least a 5week wait. He had a buddy call me. Stated he had .60 over BUT failed to mention they were racing pistons.

 

I called ARIAS and based on the stamped number; he told me they were 12:1 I wanted 9:1

 

You know the auto manufacturers are pushing hard for 100 octane gasoline at the pumps. Some BS about they need it to meet mileage standards and 1/2 the world has 100 so why can't they.

You might have fuel by the time you get it together

 

SWEET!!!!^^ We have Chevron 94(no alcohol), which is already light years better than the slop most of you poor *******s are saddled with. 100 octane would be KILLER!!!

 

They have 100 at the pump at one station in town it's seven bucks a gallon. But if it was common, it would probably only be about 30% more expensive than 91? who knows.

Interesting about the pistons...maybe if you measure the depth of the chamber, you can get an idea of how much the head has been milled if any, and figure out what to do.

I have a 983 head off the 270 in my old school bus, the chamber is what, 110-120 cc? from a rough measurement. It's 3/4" deep at the intake valve.

 

If the they can sonic test a block can't they sonic check a piston then you would know how thick the dome is.

 

All you need is a 2 rulers, or sonic test

 

Dtwbcs...
I have an electronic devices to check compression. .
It's called a whistler..
Same tool used in sprint cup etc..
If you can install one Piston with rings in one cyl..I can tell you te the exact compression ratio..
If I'm close to you..

Sent from my SAMSUNG-SM-N910A using H.A.M.B. mobile app

 

You might want to take a 6" rule and measure the inside of the top forging to the bottom of the skirt

Then measure the outside from the top of the deck to the bottom of the skirt

Then measure the depth of the 2 milled area's on the inside , to see how thick the top is before doing any cutting on the dome

Might wind up with too thin to use ?

DND

 

Those pistons look to be solid dome to me, but, the machining on the inside of the piston under the dome is unusual. Milling the tops would put the thinner part where that inside machining is; probably how they weight matched the pistons. I say mill away. I am Butch/56sedandelivery.

 

I'm waiting for someone to design some user friendly software so that we can use a 3D scanner app like http://www.123dapp.com/catch to work out C.R. Maybe we'll be able to 3D print our own pistons one day.

I need some pistons for my 270 with 302 head about that C.R.