pls help me find my compression ratio

pb_paulie_b

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May 19, 2001

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Chaptico, Maryland

Oct 9, 2005

#1

• Oct 9, 2005

• #1

i'm putting together a 69' block 383 w. i need a lil help finding my compression ratio. heres my combo, 9.5 stock deck 69' 351w, 4.030 bore, 3.750 stroke, 6.250 rods, and -27cc reverse dome pistons. i'm using the tri-pro heads with a 60cc combustion chamber. also plan on using cometic gaskets if that matters. hopefully i'm not leaving anything out? i'm pretty excited about it all! thanks for any help...PB

 

pb_paulie_b

Founding Member

May 19, 2001

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Chaptico, Maryland

Oct 10, 2005

#2

• Oct 10, 2005

• #2

anyone?

 

P

primetime1267

New Member

May 19, 2005

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Sarasota, FL

Oct 10, 2005

#3

• Oct 10, 2005

• #3

tryy going to your pistons company website. Thats what I had to do on my 414W ..I went to Probe and figured it out..

Hope this helps.

 

pb_paulie_b

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May 19, 2001

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Chaptico, Maryland

Oct 10, 2005

#4

• Oct 10, 2005

• #4

i'll goto je's site and check it out. thanks for taking the time primetime...PB

 

pb_paulie_b

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May 19, 2001

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Chaptico, Maryland

Oct 10, 2005

#5

• Oct 10, 2005

• #5

i check je's site and there is nothing on the subject. i also tried probes site and found nothing? i did find lot of compression ratio calculators on google but they trip me up when they ask for the deck height. i need to know so i can order my cam from comp. and it would help me know how much boost i can run...PB

 

Rick 91GT

Mustang Master

Nov 29, 1999

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Oct 10, 2005

#6

• Oct 10, 2005

• #6

I assumed a o deck height, meaning the piston is fluch with the deck surface and a piston with a Compression Height of 1.375"

* 383 cid *

Bore Size: 4.030
Gasket Bore: 4.100
Piston Top Land Dia: 3.995
Stroke: 3.750
Connecting Rod Length 6.250
Compression Height: 1.375
Deck Height: 9.500
Ring to Top of Piston 0.250
Gasket Thickness: 0.040
Valve Notches Volume: 27.00
Dome Volume: 0.40
Volume Head: 60.00
-------------------------------------
:COMPRESSION RATIO: 9.152
-------------------------------------



calculation variables:

Piston to Deck: 0.000
Crank Throw: 1.875
Vol. Above Top Ring: 0.90 cc
Piston to Dec Vol.: 0.00 cc
Gasket Volume: 8.65 cc
Volume Clearance: 96.16 cc
Cylinder Volume: 783.85 cc
CID: 382.517


(notes/messages)

× Piston Flush with Deck

 

pb_paulie_b

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Oct 10, 2005

#7

• Oct 10, 2005

• #7

rick you are the f'in man Thanks for the breakdown!...PB

 

pb_paulie_b

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Oct 10, 2005

#8

• Oct 10, 2005

• #8

would it matter that my comp. height is 1.350?

 

Rick 91GT

Mustang Master

Nov 29, 1999

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Oct 10, 2005

#9

• Oct 10, 2005

• #9

Paulie, is the piston to the top of the deck? If not where is it, in or out of the bore and by how much.

Yes that will effect it....

Based on a 1.35" CH the piston is .025" down in the bore if the block is 9.50"

Bore Size: 4.030
Gasket Bore: 4.100
Piston Top Land Dia: 3.996
Stroke: 3.750
Connecting Rod Length 6.250
Compression Height: 1.350
Deck Height: 9.500
Ring to Top of Piston 0.250
Gasket Thickness: 0.040
Valve Notches Volume: 27.00
Dome Volume: 0.00
Volume Head: 60.00
-------------------------------------
:COMPRESSION RATIO: 8.703
-------------------------------------



calculation variables:

Piston to Deck: 0.025
Crank Throw: 1.875
Vol. Above Top Ring: 0.88 cc
Piston to Dec Vol.: 5.23 cc
Gasket Volume: 8.65 cc
Volume Clearance: 101.76 cc

 

pb_paulie_b

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Chaptico, Maryland

Oct 10, 2005

#10

• Oct 10, 2005

• #10

the pistons and rods and crank and stuff are in boxes i need all the parts together to build it...PB

 

pb_paulie_b

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Chaptico, Maryland

Oct 10, 2005

#11

• Oct 10, 2005

• #11

thanks again rick!

 

Rick 91GT

Mustang Master

Nov 29, 1999

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Oct 10, 2005

#12

• Oct 10, 2005

• #12

the way you figure out deck height on the assembly is half the stroke + the rod length + the CH of the piston.

1.875 + 6.25 + 1.35 = 9.475

So to acheive the first number I posted you need to deck the block till it is 9.475", the second numbers I calculated were with a 9.50" deck.

If you need any more help let me know. I mock up every assembly first and take my own measurements, then the shop who machines my stuff has a nice set-up that uses lasers and goes off of the crank and cam centerlines to accuratly measure deck height. Then they deck it to what ever spec I ask

Measure all your parts, very important!

 

pb_paulie_b

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May 19, 2001

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Chaptico, Maryland

Oct 10, 2005

#13

• Oct 10, 2005

• #13

rite on. i need compression to be as boost friendly as possible so if i got things right, i should not deck my block and keep it at around 8.7. thanks for dumbin it down for me...PB

 

Rick 91GT

Mustang Master

Nov 29, 1999

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Oct 10, 2005

#14

• Oct 10, 2005

• #14

Where is Chaptico, is it on the Eastern Shore?

 

sunil6784

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Mar 31, 2005

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Oct 10, 2005

#15

• Oct 10, 2005

• #15

http://www.csgnetwork.com/compcalc.html

Searched on google for compression ratio calculator...theres quite a few out there.

 

pb_paulie_b

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May 19, 2001

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Chaptico, Maryland

Oct 10, 2005

#16

• Oct 10, 2005

• #16

Rick 91GT said:

Where is Chaptico, is it on the Eastern Shore?

Click to expand...

it's in St.Marys, where the wicomico and potomac river come together. i live about 10 miles from M.I.R.