Using this -> http://www.rbracing-rsr.com/comprAdvHD.htm
It says that my little stock longblock iron head LT1 has a DRC of 9.86:1 at sea level. From what I've read in the Advanced Tech Forum here, that should be way too high especially considering the iron heads. But GM built this to run on 87 octane.

Does this calculator really use duration @.050 like it says?

Here is what I put in. 4" bore 3.48" stroke 5.7" rod 10.1CR with 22* ABDC (191/196@.050, 111LSA 106.5 ICA)

When I put in my cam specs for what I was hoping to use, it gives 44* ABDC and with 11:1CR that would bump the DCR up to 9.97:1... I don't think I would have a problem with this... Would I?

 

didnt GM build the LT1 for 91 octane???

 

would they really build an engine specifially for the police and taxis that would only work with 91 or better? I don't think so.

 

I got 8.60 DCR on your base engine using another program. That sounds much more reasonable than 9.86.

You entered 22 deg, the intake opening event instead of 55 or 56 degrees ABDC, the intake closing event. Try 55.5.

 

The site says to use the duration @.050. When I put the stock impala specs in Desktop Dyno, it gave me:
IVO (BTDC)=-11
IVC (ABDC)= 22
EVO (BBDC)=33.5
EVC (ATDC)=-17.5

 

Dear

In most cases I'm familiar with, DCR uses total duration or "advertised duration". After all, with the lifter at .050, that's .075 open at the valve with 1.5rr, hardly a closed cylinder which can contain compression.

By definition, DCR uses cylinder volume @ intake valve closing

This 191/196 @ .050 cam is actually about a 258/264 total duration cam. IMO, the calculator needs total not .050 numbers.


My $.02.

 

As usual, the old stroker said it well. It makes no sense to talk about seat timing and then use duration at 0.050" for the calculations. Discussion of DCR is usually based on seat timing and hence on advertised duration.

Rich Krause

 

Its a typo, use the seat duration instead and you should get more accurate results. Only catch is I can't find the IVC for a stock cam anywhere...

 

OldSStroker, have you measured the stock impala cam to find the seat duration?

ThankSS for clarifying everything guys

 

silly question-


whats "ABDC"

(if anyone answers "trey in 1st grade.... )

 

After Bottom Dead Center

 

ahh, compression questions...the beauty of build up.