Finally getting ready to button up my 383. Need alittle help figuring this compression thing out. Heres what I have.

3.905 bore
4.0 stroke
6.125 rods
-5 cc pistons
pistons out of the hole .005
Comp 287 cam, XER lobes, 238/240 dur on 112, no advance. I dont have the cam card for the rest of the specs.
AFR 205's milled to 62cc
Cometic .040 gasket 3.910 dia.

Looking to finish this up this week if someone can check my SCR/DRC for me.

 

11.4:1 SCR. Not enough info for DCR. Everyone makes way too much stink out of DCR. I personally wouldn't worry about it.

 

watch out for that dish/dome thingie (+/-) on these spreadsheets, but assuming pistons are dished,

on both counts, but if you're interested, i got a DCR of 8.27 with a rod length of 6.125"

possibly a little too safe....

 

 

added alittle more info. What else do we need to know besides the cam specs?
I'm trying to find out if it will be ok on 91 octane. Thats about the best we have around here besides E85.

 

Well i just punched your numbers into Pianoprodigy's calculator and it came out to 11.63 SCR, 8.48 DCR. Granted this spreadsheet is not "perfect", but is pretty damn close and super easy to use. If you retard the camshaft 2 deg it would drop your DCR to about 8.3 or so, allthough you would most likely be ok with the 8.48 on 91 octane. I guess the general consensus is 8.7 or so is about the upper limit for 93.

 

can anyone else check the numbers?

 

What answer are you looking for? Static compression ratio is a mathematical equation that if figured correctly with all the correct variables yields a single correct answer. Based on your inputs, the correct SCR has been indicated above.

DCR is a whole different ball game. There are multiple methods to calculate it and they all come out different. To complicate it even worse, there are multiple schools of thought on the applicability of any DCR measurement to engine performance. Many on this site argue it's a major contributor to performance and others argue that it doesn't mean much. So knowing that there isn't a universally accepted method of calculation or a method to apply this factor, what does knowing this information provide?

 

Dude, 2 of us have provided you with an answer and they are within .10 on both the SCR and DCR. You are not going to get a much better figure without actually measuring and CC'ing every component. If you still do not trust the answers, here is the link to the DCR calculator/spreadsheet I used, you can punch your numbers in and get your own figures:
https://ls1tech.com/forums/showthrea...&highlight=dcr

Good luck.

 

Really sorry I asked to have the numbers checked. I'm just not real sure I have a decent setup or not.