Hello to all:
The Speed-Pro brand piston I would like to inquire about is part#H859CP30.
It is a D shaped dished, aka. (reversed dome) piston.
 There is very much conflicting information concerning the dish volume.
I have seen them advertised as -12cc, -23cc ,-25cc. dish volume.
I personally have a set and on the end of the packaging Speed-Pro box is printed ,-25cc recess.
I would really like to have this issue definitively cleared up.

 I am building a 383 stroker and need to keep the C.R. down to prevent detonation.I am using 64cc vortec heads.

 You have no idea how much your help would be appreciated.
I am going to thank you in advance.

I have contacted Federal Mogul via email and hope they will answer.

I know some of you hard-core chevy guys can answer this one .  

As far as I can see, that is a 12cc dish piston. Are the pistons still in the box/out of the motor? If so, could you post a picture of them. The best course would probably be getting a buret and measuring them yourself, that way you could be sure of your compression ratio. It would surprise you how compression can vary from cylinder to cylinder or just from an estimated value.  

Thanks for the reply.
Yes, I guess volume measuring would be the way to go. The pistons are brand new in the box.Most all the advertisements advertise 12cc volume.I have emailed Federal Mogul which manufactures these pistons and sells them under the Speed-Pro name. I hope they will take time to answer.

The box they came in states 25cc recess.  Would recess have the same meaning as volume? These are D shaped recesses in the piston.

I would like to get the compression down by using a dished hypereutectic piston.
There are plenty of dished, FORGED pistons out there. They are expensive and not necessary for my application.

I believe this has always been a challenge to find a suitable inexpensive hypereutectic dished piston. I'm not real hot on KB pistons either.

If anyone has a solution to get the C.R. in the 9.1:1 to 9.5:1 range ,I would sure appreciate some advice.

.030 oversize
3.75 stroke    64cc vortec L31 heads
1998 350 L31  Block (roller)  

Frankly, you don't want a 25cc dish. You're going to well under 9:1 with that large of a dish. I really recommend measuring the volume yourself since domes and dish volumes are usually a little mis-stated to prevent excessive compression. If you have a piston that's supposed to -12cc, maybe you'll measure -15cc and then get 9.3:1 compression, even if it is really 12cc then your compression will be 9.6:1 unless the block is heavily decked...  

I have some clarity on the Speed-Pro pistons as of late. I was confusing two different Speed-Pro pistons.
The H859CP30  (.030 oversize,) has a 12.5cc dish volume.
The H890CP standard 4.0 bore has a 23cc dish volume.

With a 3.75 stroke, 4.0 bore (377 *** the H890CP yields an approx. 9.1 : 1  C.R. (64cc heads)

With a 3.75 stroke,4.030 bore (383 *** the H859CP30 yields an approx. 9.7:1 C.R.(64cc heads)

I have seen "all around" that one needs to be below 9.5:1  with cast iron heads to prevent detonation.

I would very much like my truck engine to be "pump gas friendly."

I think 9.7:1 might be pushing the limit.(actually a little over it.)

I believe I will take your advice and measure the pistons I already have and see how true the advertised 23cc is. I was going with a 377C.I. but the machine shop did a terrible job on my block , now I have to go .030 oversize.(383) Pistons won't work so I'm "shopping" again !

Any comments or suggestions VERY WELCOME. thanks

I just want to get it right the first time.  

Why not just go with some good 9:1 flat top pistons instead? Or are you planning to add a turbo or blower to this motor later on?

If you stay below 9.5:1, and have a hot enoguh ignition system, you should be able to run 87-octane gas, at the most 91 octane (mid grade). One of the big keys is going to be the ignition system, and making sure you have a hot enough spark.  

Kudos to you for doing it but if you're going to be so critical of your static compression you're going to need some very precise measurements to do so. Such as: head gasket volume, crevice volume, piston to deck volume, a MEASURED crown volume, etc, etc. Then you're going to need to do your own calculations, don't use advertised numbers. I made an excel spreadsheet to do this math for me so I don't have to flog dozens of numbers everytime I want a accurate compression ratio reading.

Something is fishy with those numbers, a .030" overbore could not make a 11cc swing. Even speed-pro must be making a typo here. The only way you can be sure is to get a buret and measure them yourself. I don't think they will be too difficult to measure. Since there is still quench area you can grease the glass there and just rig up something to hold the piston level.