View Full Version : static vs dynamic cr and octane rating

11-03-2009, 03:52 AM
ive been working on a build for quite a while now and since most of my planning ends up falling apart due to lack of information or misleading information ive ran into my biggest problem so far...

the motor im attempting to build is a hybrid 5sge and im aiming for a static cr of around 11:5:1 or 12:1, despite the massive amount of research ive been doing i still havent found any way of figuring out the maximum static or dynamic cr i can run on pump gas...

any ideas?

11-03-2009, 03:57 AM
If anyone can help you it would probably be Sang, Mr. Turrari, or Nuclearhappiness

11-03-2009, 04:07 AM
I have run 10.5:1 on premium. From back in my hotrodding days, we would stay on pump gas until around 11.5:1 or 12:1. That is pushing it, and you will have to play with your timing to keep the ping at a minimum. I would try to stay around 11:1 if it were me.

11-03-2009, 07:50 PM
a static 12:1 is fine on cheap gas as long as it only idles...
if you want to make any power you'll need premium and the higher the RPM (depending on cam choise) the more timing you'll have to pull out to keep her from knocking apart. during a build it's hard to creat a dynamic compression number. you need to build the engine to a certain goal with a good solid static compression. dynamic compression changes dramatically during coarse of RPM.
example my motor:
static 8.2 :1
dynamic at full boost at 6400 rpm with stock 232 cams 25:1
dynamic at full boost at 6400 rpm with 24 cams 26:1

11-03-2009, 08:08 PM
My RSX has 11:1 CR and it runs on premium.. revs all the way to 8,500 too

11-03-2009, 08:28 PM
dynamic compressions a little hard to figure out... and im working on finding the stock numbers then adjusting them for what im changing in the motor... from what i understand of na motors dynamic compression will never change unless it has vvti or some form of vtec since dc starts once the intake valve is fully seated... since my setups na i have no clue how it would function with a turbo but im aiming for around 8.2:1 dc which if im trying to get a 12:1 cr then the math invloved at that point is in trying to find cams that will work in this setup... besides im not to worried since the 5s has a knock sensor which should help out...

damn... as long as i dont end up detonating on premium and much to my surprise 110 octanes all i can run i think ill be happy...