Low Compression - 10:1 // 9:1
 

Hi Everyone,

I was curious about something - hopefully someone can shed some light.

What would happen if you changed the current compression ratio, 12.5:1 to 10:1 or 9:1 but still kept the FRS/BRZ as NA. What would happen/what changes would occur? Any benefits? Or is it only applicable when using Forced Induction, so it would essentially be a waste?

You would lose power and mpg across the board. You would also want a tune. The sole benefit would be the ability to run cheaper gas.

^^ what he said.

It would basically be the worst thing ever and would make about as much sense as a hot air intake or just sanding all of your paint off.

This is how it goes when you lower the glorious 12.5:1 CR on our cars:

Loss of power->loss of mpg->more fuel->less money->less bitches->less life.

The only reason to lower the cr would be able to run more boost in FI situations

You can offset this by hella flush = more bitches.

Ohhh!!! I spy a GTS-V vorsteiner Front bumper!! :)

OOoo Oooo, I wanna put my two cents in! :P

Like everyone else has stated previously, you would loose a lot of power. The higher compression helps with engine response, low end torque and efficient fuel managemant. If you look at how a diesel engine is designed you will notice that the compression ratios are a lot higher than the FRS/BRZ/GT86. Furthermore, the engine is effected by the compression ration and the octane of the fuel. Higher compression engines will not do well on low octane fuels under boost and has a chance for knock (misfire).

This is the understanding I have for my engine build by muiltiple sources including Full Blown Motorsports (@FullBlown, my engine builder). Plus, keep in mind I am not doing NA, I'm boosted with a Greddy Kit.

~10:1 ratio is a good choice for those aiming to use higher amounts of Boost (PSI) through forced induction, safely. It is recommended for those planning to stay in the higher octane range (91 with 10% ethanol, 93, racing, E85). It will be less susceptible for knock versus the 9:1 ratio with stright 91 all day. Example: 10:1 is good if you want to run 10 PSI of boost on 91 octane safely or 18 PSI of boost on E85. Furthermore, you will still have higher torque and power on the lower RPM band versus a lower compression ratio. This will help with turbo lag.

~9:1 ratio is a good choice for higher boost on lower octane fuels like 91. You will have a bigger window for knock control. However, you will loose a slight amount of power in the lower RPM range including torque. With a small turbo that spools up quickly will greatly benefit getting some of the lost power back versus a big turbo. If you plan on big gains and rather have high horsepower with high boost this is the best option for you.

I'm still learning about all of this information but this is the research I've found usefull so far. Personally, I just want a fun car so I am going with a 10:1 ratio so I can cut my turbo lag down. I wouldn't recommend a lower compression ratio if you are staying with a non aspirated (NA) engine.

Edit: Also, since a lot of fuels today have the added ethanol (like 91 +10% and 93 +10% ethanol) it is beneficial to a higher compression ratio with forced induction (FI). 10:1 is a good chice with the added ethanol if tuned correctly. :)

but to be hella flush you need money and this is counterbalanced by the "more fuel part".. = less bitches :P

hahahaha

Don't forget the most basic equation of all: "less money = less bitches" so don't spend everything on the car, no matter how gorgeous, faithful and fun it may be.

bahaha...