390 truck piston cc?

[fomocoguy]

Do any of you know the approximate volume of the dish and valve notches on a stock 390 truck piston? If my 300 project needs to be bored out enough I may use 390 pistons but I need to know the cc's of the dish so I can calculate compression ratio. Thanks!

[hotrodfeguy]

Well, full dish is 9.5 CR, and the flat tops with just the eyebrows are 10.5 hope that answers what your after. The 390 truck pistons are 410 pistons and had lower end of 8.X CR I think off the top of my head the 72 390 was like 8.2 But dont hold me to it but its right around that.

[HOWDY69]

Well Summit says the 381NP has a recess 0.097 inches deep and 2.62 inches in diameter. So that would be about 0.52 of a cubic inch or 8.6 cc if my math is correct. I do not think this includes the eyebrows and each brand is different so YMMV.

http://www.summitracing.com/parts/STL-381NP30/

Mine were cc’ed in the hole which includes the volume above the ring and the depth below the deck but it seems like I got pretty close with the above estimate.

[fomocoguy]

Well, full dish is 9.5 CR, and the flat tops with just the eyebrows are 10.5 hope that answers what your after. The 390 truck pistons are 410 pistons and had lower end of 8.X CR I think off the top of my head the 72 390 was like 8.2 But dont hold me to it but its right around that.

Thanks, but I'm not using them in an FE so I need to calculate it with my specific set up.

[fomocoguy]

Well Summit says the 381NP has a recess 0.097 inches deep and 2.62 inches in diameter. So that would be about 0.52 of a cubic inch or 8.6 cc if my math is correct. I do not think this includes the eyebrows and each brand is different so YMMV.

http://www.summitracing.com/parts/STL-381NP30/

Mine were cc’ed in the hole which includes the volume above the ring and the depth below the deck but it seems like I got pretty close with the above estimate.

That helps! I could probably just go with 9 cc and get a round about figure. Thanks!

[convincor]

Be sure and cc your heads. The C1 castings i used where spec'd to be 68-71 cc and actually are 78cc.
So with my build- block is 4.090 bore, 3.98"stroke crank, 381N pistons, calculates out to 9.37 to 1 compression.
418 cu.in.

[fomocoguy]

Wow, that's a big difference! My head is supposed to have 69cc chambers but I'll have to do that and see. How did you do it? I was thinking of putting a peice of plexiglass over the chamber with a hole drilled in the middle and just pouring oil out of a graduated cylinder to fill it up. Is there a more "correct" way or will that work fine?

[DuckRyder]

There are tools to do it which I suppose one could argue might be "more correct", but the method that you propose will work. Obviously you will have to be very careful not to lose any of the fluid that you are pouring and give it time to "settle" to get accurate readings.

http://www.summitracing.com/search/Depa ... Rank%7cAsc

I'm not sure what most folks use, but it seems oil might be a bit "clingy" where the graduated cylinder and any funnel you might use are concerned. Automatic Transmission Fluid might be less so, and antifreeze much better.

The instructions from comp recommend "a 50/50 mix of water and alcohol with a few drops of dye or food coloring."

http://static.summitracing.com/global/i ... a-4974.pdf

[fomocoguy]

Cool, thanks duck! I think I can pretty easily make one of these kits.