9:1 compression..Will I be ok?

[jaredgsx]

I am buying all of my parts for my rebuild this comming up winter and here is what i was thinking.

I want to run 9:1 compression. I know that with increased compression the head in the cyclinder goes up as well as the chance for detiontaion. Well I will also be running a better Alky injection system with a progressive controller that sprays an increased flow from 1psi-on up. With running 93 octane, the alky injection, and a huge front mount, would this be stable as in would i blow my motor faster than someone who was just running stock compression?

 

[GVR4592]

It will probably be fine. If you had dsmlink you could remove some timing and be able to run high boost still.

 

[BaddAssGst]

Any reason you want to run 9:1 as opposed to a 7.8:1 or 8:1 piston? I would think you would be better off running more boost as opposed to less boost and more compression. Is this a street car, track car?

 

[98eclipseRS]

Well let's see, I currently am running an estimated 9.4ish compression. The problem I find is tunning with pump gas. It makes the car, or at least mine(every car is different) very much knock happy. Even with a fmic. however, I am runnign on piss 91 octane cali gas which is half of my problem. However, I also made 402whp on 91 octane only it just takes alittle mroe time with tunning and the car has to get tuned a little more to the ragid edge than with lower comp pistons.

The benefits I see with higher comp ratio is that you get better spool up, and more power under the curve. Also when running race gas/alky/meth injection the gains in power are much larger over that when running a lower comp ratio, say an 8:1 or 7.8:1. If you plan on running alky injection you will be more than fine with running a 9:1 comp piston. FWIW running a 75/25 meth to water ratio(by volume not weight) it is very similar to running on high octane race gas when mixing it with 91 octane. Don't forget if you are going to use aem for tunning that their timing values will read lower than say with dsmlink or the stock ecu because of the way it reads the signal from the CAS.

 

[GVR4592]

Well let's see, I currently am running an estimated 9.4ish compression. The problem I find is tunning with pump gas. It makes the car, or at least mine(every car is different) very much knock happy. Even with a fmic. however, I am runnign on piss 91 octane cali gas which is half of my problem. However, I also made 402whp on 91 octane only it just takes alittle mroe time with tunning and the car has to get tuned a little more to the ragid edge than with lower comp pistons.

The benefits I see with higher comp ratio is that you get better spool up, and more power under the curve. Also when running race gas/alky/meth injection the gains in power are much larger over that when running a lower comp ratio, say an 8:1 or 7.8:1. If you plan on running alky injection you will be more than fine with running a 9:1 comp piston. FWIW running a 75/25 meth to water ratio(by volume not weight) it is very similar to running on high octane race gas when mixing it with 91 octane. Don't forget if you are going to use aem for tunning that their timing values will read lower than say with dsmlink or the stock ecu because of the way it reads the signal from the CAS.

Do you actually see improved spool with just a change in compression?

 

[98eclipseRS]

Do you actually see improved spool with just a change in compression?

if you were to somehow go from a set up with 7.8 compression and then somehow instantanesiouly go to the same setup but now with 9.1 compression then you would see a difference. Problem is when you change the pistons compression you are usually changing other thins in the set up at the same time and that seriously effects spool up as well. It does feel "faster" driving around town to me but that can be contributed to alot of things with my set up.

 

[jaredgsx]

Well let's see, I currently am running an estimated 9.4ish compression. The problem I find is tunning with pump gas. It makes the car, or at least mine(every car is different) very much knock happy. Even with a fmic. however, I am runnign on piss 91 octane cali gas which is half of my problem. However, I also made 402whp on 91 octane only it just takes alittle mroe time with tunning and the car has to get tuned a little more to the ragid edge than with lower comp pistons.

The benefits I see with higher comp ratio is that you get better spool up, and more power under the curve. Also when running race gas/alky/meth injection the gains in power are much larger over that when running a lower comp ratio, say an 8:1 or 7.8:1. If you plan on running alky injection you will be more than fine with running a 9:1 comp piston. FWIW running a 75/25 meth to water ratio(by volume not weight) it is very similar to running on high octane race gas when mixing it with 91 octane. Don't forget if you are going to use aem for tunning that their timing values will read lower than say with dsmlink or the stock ecu because of the way it reads the signal from the CAS.

Thanks for the good info. Around here there is a gas station that has 103 at the pump, so if need be i will just shell out the extra cash. I do intend to run 75/25 mixture.

 

[GVR4592]

if you were to somehow go from a set up with 7.8 compression and then somehow instantanesiouly go to the same setup but now with 9.1 compression then you would see a difference. Problem is when you change the pistons compression you are usually changing other thins in the set up at the same time and that seriously effects spool up as well. It does feel "faster" driving around town to me but that can be contributed to alot of things with my set up.

I was just curious, I've never heard of anybody decreasing their spool time with higher compression. Usually they just notice the off boost torque more. I'm going high compression on my next engine, so I was just curious.

 

[JOEY A]

Im currently having my motor built with weisco .20 over and eagle rods and the compression is going to be 9.1 for better spool later on when im on a bigger turbo etc. I should see alot faster spool with my Wee EVO3 should be a fun car....

 

[98eclipseRS]

I was just curious, I've never heard of anybody decreasing their spool time with higher compression. Usually they just notice the off boost torque more. I'm going high compression on my next engine, so I was just curious.

If you took my reply as offensive then I am sorry I did not mean to come off that way at all. I was just giving and example of where you would actualy see increased spool, whereas when most people do high comp pistons they change their entire setup which kinda fudges the results.

 

[GVR4592]

Nope I didn't take it that way, I was thinking the same thing though. I was hoping you didn't think I was being a jackass when I asked about the compression changing your spool time. The internet is great that way, it's really easy to misunderstand people.