[dc_malibu]

I have a 3951511 stock bore 2 bolt 400 that has stock dish pistons,crank and rods. I want to build this for a nice street manners motor . I would like to change the pistons to Speed Pro hypereutectics H615cp which have a comp. hgt. of 1.425 and change the rods to 5.7 . The block has not been decked; so I'm assuming I have 9.025 deck height.I want to see if I'm calculating this right so bear with me.
Stock stroke:3.75 /2 = 1.875
Comp.hgt of piston: 1.425
Rod length: 5.7
____
Total: 9

Should leave me .025 in the hole right?
Piston's have a .135 dish w/4valve reliefs. Will run cast iron Darts w/64 cc chambers.
Any experts out there let me know if I'm correct . Thank's in advance for your help. Don

 

[Busted Knuckles]

If it'll clean up at .020, I have a new set of reverse dome Keith Blacks that I'd make you a deal on...
What Dart heads? I'm building a 400 with some of the new big Bowtie Vortecs, hope to have some numbers soon.

 

[rich1978]

Don, what you really need here is a CC value for the pistons, if you want to calculate compression ratio -- You've got the rest of the info you need, ASSUMING you're right about the deck height. Everyone will tell you to measure to be sure, but you're probably pretty close there. That said, the pistons you list are on this page:

http://www.flatlanderracing.com/trwchevy400.html

And it says 10.0:1 with a 64cc head and 9.0:1 with a 76cc head. Not sure what they are using for deck height, but that gives you a ballpark number. In CC terms, you're comparable to a 20cc dish or so, the 18cc pistons I have (for a 400) are rated at 10.2:1 w/64cc heads and my new 22cc dish are rated at 9.8:1 with 64cc chambers.

 

[trmnatr]

I have a 3951511 stock bore 2 bolt 400 that has stock dish pistons,crank and rods. I want to build this for a nice street manners motor . I would like to change the pistons to Speed Pro hypereutectics H615cp which have a comp. hgt. of 1.425 and change the rods to 5.7 . The block has not been decked; so I'm assuming I have 9.025 deck height.I want to see if I'm calculating this right so bear with me.
Stock stroke:3.75 /2 = 1.875
Comp.hgt of piston: 1.425
Rod length: 5.7
____
Total: 9

Should leave me .025 in the hole right?
Piston's have a .135 dish w/4valve reliefs. Will run cast iron Darts w/64 cc chambers.
Any experts out there let me know if I'm correct . Thank's in advance for your help. Don

PM me

We are in your area and have 7 pistons with rods, the other piston is good but i would replace it being that cylinder cracked

.065" quench, 62cc head = 10.96:1 so depending on your heads and all they would work good. We ran 10.40's with them for years, KB hypers with 5/64" rings

 

[RB69SS396Conv]

The SpeedPro Hypers ALMOST NEVER (I would say "never", but that's a very dangerous word to throw around...) have the same compression height as stock. That is, they are "designed to fit" an engine with a nominal compression height of 1.425", which is NOT the same as saying their CH is 1.425".

Nearly all of them add the usual "rebuilder" .020" of deck clearance, since it's alot less of a problem for a rebuilder if the motor comes out with slightly lower than stock compression and works, than it is if they have to deck the block to repair a blown head gasket scour or something, and then the pistons hit the heads.

Note that their compression spec is lower than you get when you put .025" deck clearance into whatever "calculator" you're using. Instead, it matches what you get when you put .045" deck clearance into the calculator. That should be a red flag to you that the CH is NOT 1.425".

Measure with a mic between the top of the pin bore and the top of the piston. From that number, subtract half of the pin diameter of .927", which would be .4635". If the pistons are REALLY 1.425 CH, the measurement will therefore be 1.425" - .4635", or .9615". More likely, the measurement will actually be .9415", indicating the extra .020" of deck clearance, or about .045" "down in the hole" at TDC.

 

[70 ELK]

Many thanks to Don and the rest of the posters, as this thread is right on point for me. I'm hoping to build a Dart SHP small block with AFR 180cc heads and hypereutectic pistons. May even go with Dart's short block, which includes them. In any event, the info posted really helps me in considering--during planning stages-- a ballpark compression ratio before purchase of any parts to measure.

My question is whether I should hold off buying the heads to see what the real measurements are on the SHP short block(If I go the short block route)?

Thanks, again!

 

[rich1978]

John, you should be able to get the exact measurements from Dart as to what pistons they use, what the finished deck height is, etc. They can probably tell you what CR you'll have with a given CC chamber head and compressed gasket thickness...