The0nlyon3

427ci, LS Next block Brodix BR7 heads BTR ls7 stage 3 cam.
With a 4.125" bore, 4" stroke, 6.125" rod length
4.2" 0.051" head gaskets
-2.8cc pistons combustion chambers are 71cc
BTR ls7 Stage 3 cam with a IVC at 48.24 degrees..

static compression ratio is 11.69:1
DCR is 9.46:1.....

will that DCR too high for pump gas 91?

spanks13

iTrader: (5)

You calculate DCR by using the IVC value at advertised duration not .050" duration. You can email BTR and see if they'll give you the advertised numbers.

Otherwise you're just guessing.


First off though - I'm calculating a different CR. At zero deck I'm getting 11.26 to 1. Do you know how far the pistons are coming out of the bore?

old motorhead

iTrader: (10)

And your DCR is much lower than 9.46. Post your cam specs and I'm sure someone can get you close on the static and dynamic CR.

Edit: Looked up the cam specs and ran the numbers. With the pistons out of the hole .008, I get 11.47 static and 8.37 dynamic. With deck height at 0, I get 11.27/8.22. All that is assuming Cam Motion grinds BTR's cams.

The0nlyon3

Cam sheet

The0nlyon3

Using gofastmath.com I came up with this for IVC @0.050 is 48.5.

My specs with 0 deck

What the calculator came up with for zero deck

This is 0.010” In The bore

0.010” in the bore .

Double06

The close on the cam card is not an actual close you will see they are using a tappet check height of .050 not 0 which is what the DCR is based on. The 48 degrees closing is at .050 tappet lift. Typical cam duration on these are 50-60 degrees beyond the .050 so in you case the 237 is actually 287 to 297 duration at .00 or .006. So if you are say in the middle at 55 degrees half of that is say 27 degrees add that to the 48 and you get 75 degrees. Do you DCR based on 75 degrees and I think you will find you are in the low 8s. Low to mid 8s is where you want to be on pump gas.

Darth_V8r

iTrader: (4)

The go fast math calculator is worth exactly stir-fried ****.

The0nlyon3

Alright now we’re getting somewhere! Thanks so much man I appreciate you taking the time to figure it out and explain it! Guess the calculator I was using is junk lol

The0nlyon3

I love me some stir fried ****.. lol glad to know that, I’ll steer clear from it

Jimbo1367

LOL. I learn something new from you everyday here, man. LOL

Double06

I don't know why these guys can not put the .006 measurements in there cam card is it really that hard to do (its just another line of ink and put a little .006 next to it). They have the info, you just have to call them up. I know, the .050 is the all important number but still it gives you an idea on the starting ramp rate.

old motorhead

iTrader: (10)

Cam Motion told me to add 54* to their duration at .050 to get to duration at .006 on their cams. Comp Cams publishes their .006 numbers for their various lobes in their master lobe catalog. I remember Tx Speed lobes being more aggressive than Cam Motion's, but don't remember the numbers.