how to get deck hight and piston info

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earthmover

earthmover

in the tire smoke
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I know it's been asked before but how do I check my deck hight???from what point to what point ..then is there a way for me to get the info I need to know about my piston that I can check(bme piston they cant help without the piston work sheet if I had that I would not have called them) anyway if I check for the cnter of pin to top of flat and then what it's a dome top..looks just like the trw piston just alot lighter I think with the fire slots...I know my head cc 68cc gasket is going to be fel pro 1008 or 8553 I think that # is right its a stock strock 340 bored 30 4.070 .thanks for any help...Is ther a special tool I need to get the deck hight or can I use a tape meas????? I have a mag. base and the gauge and a old cheap dial ind. thats not very big about 6" i think...:clock:
 
The deck height is the distance between the crank center line and the top of the deck. To figure out what height you need to be zero deck it is:

Deck Height = 1/2 crank throw + rod length + compression height

Rod length is 6.123" on a small block mopar. Compression height is distance between center of wrist pin to top of piston. Check piston manufactures web site for compression height.
 
okay I got the deck hight part but the piston are bill miller dome tops I called and gave them the #on the pistom they told me that was useless unless I have the work sheet form them that tells me what the comp. hight is...thats why I need to fig out how to meas. myself..but as I said they do look just like the trw........thanks for the deck info
 
Take 1/2 the diameter of the pin bore of the piston. Then measure from the top edge of the pin bore to the flat above the top ring. Add those two figures fro your compression height. Compression height does not include any dome or dish. BME does full customs, so short of sending them a piston, you're lost without the spec sheet.
 
hay thanks guys I'm just tring to get a good idea of what to look for on the comp. of this motor this time....as long as I am close I 'll be okay I think..I want to run this thing on the pump gas if possible..........I'll take some meas. and see but as always I'll be back with some more ??????????????????of help thanks:cheers:
 
hay guys I did a little meas. and got a few #'s as far as the deck height I cam up with 9.5 deck height and on the piston I cam up with from the center of the pin to the flat of the piston is 1.5 now it is a dome so I dont have the height of the dome but the dish in the piston for the val. is 3/16 deep.. does that sound right???????
 
I'm just guessing here. But, if you say that the piston has a dome on it. Chances are that the comp ratio will be more than 9.5 or even 10. Most flat top's (no dome) will give you 9.5. Pump gas may be out of the question then.

also,

After looking at BME's site, It looks as though they only make racing pistons for cars that turn left. (sorry not a huge fan of Nascar)

my 2 cents
 
now when I said 9.5 I mean the deck height for the center of the crank to the top of the deck not the comp.....as far as the piston go bme made them for a x block that I had, but I got rid of it a few years back so as far as going left I dunno .....now at the same time I am going to mock it up and see just how far down in the hole the piston are cause I remember them being down in the hole not flat with the deck.....(the flat part of the piston is down in the hole the dome is out of the hole just a little) thanks:-D
 
earthmover said:
now when I said 9.5 I mean the deck height for the center of the crank to the top of the deck not the comp.....as far as the piston go bme made them for a x block that I had, but I got rid of it a few years back so as far as going left I dunno .....now at the same time I am going to mock it up and see just how far down in the hole the piston are cause I remember them being down in the hole not flat with the deck.....(the flat part of the piston is down in the hole the dome is out of the hole just a little) thanks:-D
Click to expand...

I misunderstood your measurement. I have zero deck height on the brain. I'm building a block right now that's using zero height. If you say your using 9.5" minus the 9.6"(stock deck height) you should be .100" in the hole.

You will need an accurate method of measuring the depth when you do your mock up. Like a depth micrometer.


I still think those Nascar pistons are going to make you car pull to the left. :toothy10:
(sorry I couldn't resist)
 
Most LA small blocks will measure in the 9.65 to 9.62 range. Blueprint height is 9.590 IIRC. Which is wht the factory pistons are always down in the bore a little or a lot. If you are coming up with 9.500, the block was seriously decked. For the deck height of what you have, if I read right: 1/2 stroke - 1.655 + rod 6.123 + compression height 1.50 = 9.278. Not even close to right. 340s should have a compression height closer to 1.75-1.800" depending on the piston. My advice... mock it up and see what it does.
 
center line of MAIN to top of block is deck height.crank throw is stroke. i haven't looked at my book for awhile but, stock should be .100" in the hole.andflat tops are gonna be any where from 8:1 to 10:1 as you remove block and head material toward zero deck height and smaller combustion chamber you go up in compression ratio.you can't change that.
 

okay this is what I came up with could be wrong but I dunno...... at the crank it was 2.5/2=1 1/4 now from the deck to the crank was 8 1/4 total if you add this it is 9 1/2 to the deck then I meas. the piston pin it was 21cm I think come out to be 13/16 I maybe wrong then I meas. from the middle of the pin to the top or flat of the piston which was 1 1/16 and I ga:read2::read2::read2:ve it a 16th to be sure......as far as the dome top go I have not had a chance to meas. it but I will on sat. if I can.. now I was told that it was 12.5.1 comp.. but we know better right.......
 
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