mycarisfasterthanyours

Please help me figure DCR for my setup. I have a lot of unknowns, so I was hoping you guys could help me by using your experience to input the "averages" or common measurements. I understand there is no way to tell for sure without tearing the engine down and measuring stuff, but I would like to get a rough idea. I also don't have the cam card, so I don't know all of the specs for that aside from what is listed.

383, 4.030x3.75
Fel Pro head gaskets
Flat tops w/ 5cc valve reliefs
Stock LT1 heads that have been "minimally" milled (don't know for sure how much)
LT1 block has been decked "minimally", again though, not sure how much.
6" rod
XE 236/242 dur. @ .050, lift of .555/.576 with 1.6 rockers, 112 lsa


Also, since I am pretty sure that the DCR is going to be too high, any recomendations on how to lower to a good pump gas (91 octane) level while still being "streetable"? Thanks in advance.

toby

according to my calculations your dcr is going to be about 9.2 which is pretty high. you could get a bigger cam or have you combustion chambers reworked to incrrease the size and lower the cr.

brian

1racerdude

How much is the cam advanced? Is the ICL on a 112 or a 108?

GetaZforgetGT

This website will give you the variables you need to know and will get you in the right ball park.

http://www.kb-silvolite.com/calc.php?action=comp

mycarisfasterthanyours

Toby, thanks for the help. Can you please tell me what assumptions you used to arrive at that DCR?

The cam is installed "straight up" meaning I didn't advance or retard it myself. I don't know what the intake center line is because I don't have the cam card. It wasn't a special grind or anything if that helps. However it typically comes?

Thanks for the website...I actually already have that, but didn't know all the assumptions to put in there.

Does anyone know how going to say a gm847 would affect the DCR?

1racerdude

Ya don't know what your DCR is now soooo how ya gonna compare to anything.
Ya can't find out the DCR if ya don't have ALL the inputs. Ya can't GUESS.
Look up your cam on the manufacturers site and get the ICL and go from there. If ya give me ALL the info I will figure it for you.
That KB calculator isn't the best,it will just get ya close.

toby

i used a deck clearance of .010, cc volume of 54cc, and a cam adv. of 4 degees which is typical. these are just guesses so you would have to measure everthing to know for sure, but 9.2 is probably close. i have a comp catalog to get the advertised duration of that cam.

toby

also according to those same measurements your static cr is 12.2.

brian

1racerdude

[QUOTE=toby]i used a deck clearance of .010, cc volume of 54cc, and a cam adv. of 4 degees which is typical. these are just guesses so you would have to measure everthing to know for sure, but 9.2 is probably close. i have a comp catalog to get the advertised duration of that cam.[/QUO


I will need the ADVERTISED numbers and the IVC=12 +/- what?
Ya can't figure DCR with @50 numbers.

toby

intake=288 exhaust=294 ivc=72 abdc

1racerdude

Now I need the IVCL=intake valve centerline---- the 112 +/- number is it 108* or 112* or D: OTHER?

1racerdude

Your static is 12.266 your DCR is 9.188.
If ya had a tighter quench I would say it was OK but ya need to cut it down to about 8.5-8.8 with your quench.
Ya can do it by cutting the valve reliefs deeper or cutting 2 more and make it a 4 eyebrow. 4 more CC's will cut it down to 8.74DCR and a 11.65 static. That would be 2 more valve reliefs just like what ya have but on the other side of the piston or have the combustion chambers opened up which is do able.
Or go with a bigger cam(more duration). A 298/302 advertised duration on a 112LSA+4 will get ya 12.26 static and 8.756DCR

toby

or retard the cam 4 degrees that would put you at 8.8.

brian

1racerdude

When ya do that it takes bottom end and mid range torque out of the motor and ya cain't do that on an LT1 with an opti without getting the tables in the computer changed.
Ya would have to get another cam.Soooo just get a slightly bigger one and retain the HP

mycarisfasterthanyours

Thanks for all the help. As you can probably tell, I've been fighting detonation since I put this whole thing together. At the time I built it I was living in a city with a mile high elevation and 92 octane was readily available. Now I live in the Phoenix area and most of the gas stations carry 91 octane. Now that I have a little more information I will be able to make a more informed decision as to the route I want to go.

1racerdude...you say the KB calculator isn't the best...which one do you use?