Help me make sense of my dynamic compression calculation
08-29-2022, 07:43 AM
#1
Teching In
Thread Starter
Help me make sense of my dynamic compression calculation So, I just recently learned about DCR and with my current setup it may be way too high at 9.5:1.
I tried a couple different online calculators that use cam specs at .050 because the TSP cam card didn’t give specs at .006.
my setup:
LM7 with flat top pistons (sealed power hyperutectic .030 over bore)
Texas Speed 212/218 .550/.550. 112 LSA 110ICL
.048 head gaskets
static compression 10.8:1
how I entered my information into the calculator:
bore: 3.809
stroke: 3.622
head cc: 61 (stock 862 castings)
piston dome vol.: 0
head gasket thickness: .048
head gasket bore: 3.835
deck clearance: -.006 (pistons are .006 out of the hole)
rod Length: 6.098
IVC: 36
coming up wit 9:44:1 dynamic.
Yet, and this is where I’m kinda confused, If I punch in all the specs for a bone stock 5.3, I come up with 8.5:1dynamic which if I understand correctly is absolute max you would want for premium pump gas? But a stock 5.3 runs fine on 87?
I picked my cam because I was wanting more low and midrange for my truck.
going to more duration would push the operating range farther up into the rpm’s right?
one thought I had was to change pistons to the 7cc dished version of what I have now and they would get me to 8.66 DCR.
that still a bit too high? Would the tuner have to pull too much timing to we’re that would be a issue.
If along with the dished pistons if I retard my cam 4 degrees I can get right about 8.5.
what are y’all’s thoughts?
I tried a couple different online calculators that use cam specs at .050 because the TSP cam card didn’t give specs at .006.
my setup:
LM7 with flat top pistons (sealed power hyperutectic .030 over bore)
Texas Speed 212/218 .550/.550. 112 LSA 110ICL
.048 head gaskets
static compression 10.8:1
how I entered my information into the calculator:
bore: 3.809
stroke: 3.622
head cc: 61 (stock 862 castings)
piston dome vol.: 0
head gasket thickness: .048
head gasket bore: 3.835
deck clearance: -.006 (pistons are .006 out of the hole)
rod Length: 6.098
IVC: 36
coming up wit 9:44:1 dynamic.
Yet, and this is where I’m kinda confused, If I punch in all the specs for a bone stock 5.3, I come up with 8.5:1dynamic which if I understand correctly is absolute max you would want for premium pump gas? But a stock 5.3 runs fine on 87?
I picked my cam because I was wanting more low and midrange for my truck.
going to more duration would push the operating range farther up into the rpm’s right?
one thought I had was to change pistons to the 7cc dished version of what I have now and they would get me to 8.66 DCR.
that still a bit too high? Would the tuner have to pull too much timing to we’re that would be a issue.
If along with the dished pistons if I retard my cam 4 degrees I can get right about 8.5.
what are y’all’s thoughts?
08-31-2022, 07:29 AM
#2
TECH Fanatic
I think you should install the camshaft and not worry about it. Firstly, you really need those .006 numbers to calculate it. Secondly, DCR is way overblown on the internet.