ZACK could you post a link showing the kit you have? As Camaro 69 has said you must know what you have in the engine before you can make the call on the head chamber size. Together the parts you choose/have will determine the compression ratio. Are the pistons flat tops domed or dished? The camshaft design needs to work at a determined static compression ratio... togetherthey will determine the dynamic compression which helps determine the octane fuel you need to run. We need more info

 

You can see the exact parts I bought on MY EBAY feedback, heres a link, just click "view item" it should be the last 5 transactions from the seller discountperformanceparts. I did not relize at the time they offered a kit so I bought the parts individually, but they sent the kit. http://feedback.ebay.com/ws/eBayISAP...ab=AllFeedback
My pistons are flat top SPEED PRO's.

 

thats good info but we need a few more components... we need to find deck height, do you know if the blocks been decked? Do you know the part number of the pistons, if not do they have four eyebrows or two per piston? The reason I ask is that some replacement style pistons are actually made to account for decking to achieve a stock deck height ie .020 further in the hole.
If you do not have the info we will need to measure the top of the deck to the top of the piston, to get real accurate you can measure the volume of the piston to deck but I dont think it is necesary and with flat top pistons we can estimate the eyebrow volume. items to note the stock deck height in a smallblock is 9.025 taking off .025 leaves you with the so called 0 deck, the squish distance(distance between the piston top and the flat part of the cylinder head) should be between .045 and .035 this is the place to be for combution chamber effeciency. Because your engine shortblock is already done the only thing you can do to adjust the squish is the head gasket thickness. All this info goes into calculating the compression ratio. The increased stroke of the 3.75 inch crank will also increase the compression over the 350 3.48 inch crank. Let me know if all this makes sense because its goning to be needed later on in the calcs.

 

The top of the pistons have two eyebrows andread:
H860CP
218-03-02-C
Ido not believe the block has been decked, the piston is nearly flush with the top of the block. I hope this info helps, let me know what else you need to know and I will do my best to answer them. Thanks

 

On the passenger side of the block on the deck infront of where the head goes is there any show of numbers stamped there?

 

Piston Specifications:




Part
Number
Dome
Style
Comp.
Height
Dome
Vol.
Compression Ratio1
Ring
Size
Pin
Style

64cc
72cc
76cc

H860CP30
Flat 2VR
1.425"
-5cc
10.3
9.53
9.17
5/64 5/64 3/16
Press or Float

 

I am fairly sure the compression ratios given are for a 350 the 383 will be higher. Do you have access to a machinist rule? If not a very straight metal rule or something and a set of feeler guages I want you to double check the deck height(not the best way but to confirm it will work. A dial indicator with a magnetic base would be a great help. The piston need to be at top dead center(the highest point in the stroke) once you get there you will notice a slight spot of no movement on the dial indicator that is the dwell at the top of the stroke once you are there put the straight edge across the bore and measure the distance from the straight edge to the top of the piston with the feeler guage record the number if it is close to .025 it hasnt been decked. What octane fuel are you wanting to run, compression builds power but requires higher octane? Iron heads are less tolerant to high compression and usally need .5 to1 point less compression than aluminum heads to stay out of detonation. Vortec heads are actually a little more tolerant I am not sure about the SS heads. anyways check the clearance and let us know. I am going to pull the camshaft specs and run some dynamic compression stuff to help with the fuel octane requirements.

 

The calculator I used says about 9 to 1 compression for89 octane. I was just thinking a friend of mine son had a set of dart iron eagle heads with the 72?cc chambers for sale a few months ago I know they were not on the engine very long Id bet you could get them for less than $500 if he still has them. They are a better head than the SS ones. He is in Eau Clair Pa.

 

At 10:1 with the spec cam 383

Your corrected Compression Ratio with boost and altitude is 9.80:1.
Your camshaft specifications call for an inlet valve closing of 35.5 degrees ABDC measured at .050.
At 5500 RPM your intake valve is considered closed at 50.15 degrees ABDC.
Your chamber volume is 79.98 cc's. With this camshaft and RPM your dynamic, or effective stroke is 3.26 inches. Your dynamic compression ratio is 8.52 :1 corrected for cam timing, rpm, and rod length. Your dynamic cylinder pressure, corrected for cam timing, rpm and rod length is 199.28 PSI. Your dynamic volumetric compression ratio, reflecting static c.r., cam timing, rpm and 90 % VE is 7.67 :1. at 5500 RPM
Your minimum suggested octane is 93

 

9:1

Your corrected Compression Ratio with boost and altitude is 8.80:1.
Your camshaft specifications call for an inlet valve closing of 35.5 degrees ABDC measured at .050.
At 5500 RPM your intake valve is considered closed at 50.15 degrees ABDC.
Your chamber volume is 89.07 cc's. With this camshaft and RPM your dynamic, or effective stroke is 3.26 inches. Your dynamic compression ratio is 7.65 :1 corrected for cam timing, rpm, and rod length. Your dynamic cylinder pressure, corrected for cam timing, rpm and rod length is 172.32 PSI. Your dynamic volumetric compression ratio, reflecting static c.r., cam timing, rpm and 90 % VE is 6.89 :1. at 5500 RPM
Your minimum suggested octane is 89