Highest Compression You've Run on a Daily Driver

[Bad_S55]

Well as the title says, what's the highest compression ratio you've run on a daily driver? At what point does fun just become stupid and expensive?

[RubberCtyRauder]

Notme but my friend had I think was 18:1 compression ratio for his DD...Oh yeah it was 550 Caterpillar in a W900L Kenworth 300" wheelbase :D

[chief455]

Well as the title says, what's the highest compression ratio you've run on a daily driver? At what point does fun just become stupid and expensive?

Engine suicide = going higher.

Depending on n/a or boosted, block, head and piston materials and shapes - will determine what ratio that is.
Keep it safe, be able to buy gas anywhere.
Pretty vague question though...some guys daily drive race cars :D

[Marauderjack]

13.5:1 (I think....1967 Dodge Charger 426 HEMI).....Sonoco 260 or Amoco 100.....1968!!:cool:

[justbob]

12.5:1 I believe. Chevy small block.


Builder Of Badassery

[hotford]

Lexus FRC 12:1 on pump....

[Bad_S55]

Notme but my friend had I think was 18:1 compression ratio for his DD...Oh yeah it was 550 Caterpillar in a W900L Kenworth 300" wheelbase :D

Show off :D


Engine suicide = going higher.

Depending on n/a or boosted, block, head and piston materials and shapes - will determine what ratio that is.
Keep it safe, be able to buy gas anywhere.
Pretty vague question though...some guys daily drive race cars :D

I'm still trying to figure out if I can buy gas anywhere with a 12:1 ratio:rolleyes: I have a low-ish milage Mark VIII engine at my disposal, and figured out I might as well do something with it this summer. By using regular 2V heads on that shortblock, I end up with stupidly high compression, and 300 horsepower on paper!

[chief455]

I'm still trying to figure out if I can buy gas anywhere with a 12:1 ratio:rolleyes: I have a low-ish milage Mark VIII engine at my disposal, and figured out I might as well do something with it this summer. By using regular 2V heads on that shortblock, I end up with stupidly high compression, and 300 horsepower on paper!

Do you have 104-110 octane fuel at your disposal also?:confused:

I ran 12.5:1 in the 90's using Cam2 ($4.75/gl then) and 94 octane. Neither fuels exist here anymore..:alone:

[MOTOWN]

12.5:1 on a Chevy Big block 454 on pump gas , it was also 94 octane Sunoco back then.

[ctrlraven]

Coyote 5.0 motor is 11.0.

My new motor is 11.0.

[Logizyme]

12.5 is pretty common among current direct injection gasoline engines and with regular gas.

It's not the pressure that gets you, its the pre-detonation.

[MOTOWN]

12.5 is pretty common among current direct injection gasoline engines and with regular gas.

It's not the pressure that gets you, its the pre-detonation.

Surely your kidding:confused: what current production vehicle has 12.5:1 comp and uses 87 octane?

[Merrill]

Do you have E-85 readily available? Cheap race gas with the proper fuel system.

[ctrlraven]

Surely your kidding:confused: what current production vehicle has 12.5:1 comp and uses 87 octane?
http://www2.mazda.com/en/publicity/release/2012/201202/120222a.html

The Mazda SKYACTIV-G engine achieves the world's highest compression ratio for a regular gasoline mass production automobile engine of 14.0:1.

[Ourobos]

11.5:1 SBF, 93 octane..

[Bad_S55]

http://www2.mazda.com/en/publicity/release/2012/201202/120222a.html

The Mazda SKYACTIV-G engine achieves the world's highest compression ratio for a regular gasoline mass production automobile engine of 14.0:1.

I remember reading about this. Aren't they direct injection?


11.5:1 SBF, 93 octane..

Now is the octane rating more dependent on how aggressive your cam is instead of how high your compression ratio really is?

[ctrlraven]

I remember reading about this. Aren't they direct injection?


Pretty sure it's DI.

[fairlane347]

My MM is 12:1 and I run 93 pump gas. no problems with it, of course its tuned for it.

[chief455]

Now is the octane rating more dependent on how aggressive your cam is instead of how high your compression ratio really is?
pretty much everyone rates required octane based upon static compression ratio.
A cam with a lot of low lift duration, valve overlap, can bleed some compression off - but not enough to run lower octane fuel.

So many variables - head chamber shape and finish, valve seat angles, piston top surface, valve pocket reliefs, aluminum vs cast iron, etc, etc

I'd advise Google 'compression ratio and octane' then read as much as you can ;)

[Logizyme]

Surely your kidding:confused: what current production vehicle has 12.5:1 comp and uses 87 octane?

Many engines equipped with DI that are N/A have CR's in that range
The 2012+ Ford Focus 2.0L has a 12.0:1 compression ratio.

Cams, and more specifically valve timing can make a huge difference in dynamic compression. With various forms of variable valve timing(usually in the form of variable cam timing) being pretty much universally standard on current gasoline engines, a common strategy is retard valve timing when regular fuel is used and advance it when premium fuel is used, as an example the 5.0L engine used in the 2012+ Mustang, which can run on regular but will produce 30 or 40hp more on premium.

Direct injection is catching up with variable valve timing as becoming industry standard, together making higher and higher static compression ratios common, even on regular gas. Camless designs have been in a select few production models for a few years, giving even greater flexibility over dynamic compression and engine performance, notably the Fiat 500s and Dodge dart's equipped with the multi-air engine, which uses oil pressure actuated electronically controlled solenoids on each intake valve to control valve timing, however still uses an exhaust cam so its not completely camless, BMW has also produced engines using camless or semi-camless designs. Pretty interesting stuff.

[MOTOWN]

Many engines equipped with DI that are N/A have CR's in that range
The 2012+ Ford Focus 2.0L has a 12.0:1 compression ratio.

Cams, and more specifically valve timing can make a huge difference in dynamic compression. With various forms of variable valve timing(usually in the form of variable cam timing) being pretty much universally standard on current gasoline engines, a common strategy is retard valve timing when regular fuel is used and advance it when premium fuel is used, as an example the 5.0L engine used in the 2012+ Mustang, which can run on regular but will produce 30 or 40hp more on premium.

Direct injection is catching up with variable valve timing as becoming industry standard, together making higher and higher static compression ratios common, even on regular gas. Camless designs have been in a select few production models for a few years, giving even greater flexibility over dynamic compression and engine performance, notably the Fiat 500s and Dodge dart's equipped with the multi-air engine, which uses oil pressure actuated electronically controlled solenoids on each intake valve to control valve timing, however still uses an exhaust cam so its not completely camless, BMW has also produced engines using camless or semi-camless designs. Pretty interesting stuff.

Very interesting , but not exactly what i was referring to.

[lifespeed]

12.5:1 in a 454 Chevy with iron rectangle port heads. Had to use 100 low lead from the local airport, really couldn't be run on 92. Rebuilt it to 10:1, much more practical. Not much loss in horsepower either.

Edit: ran 12.60 in the quarter with both motors (same except for pistons). Compression made no difference.

[chief455]

12.5:1 in a 454 Chevy with iron rectangle port heads. Had to use 100 low lead from the local airport, really couldn't be run on 92. Rebuilt it to 10:1, much more practical. Not much loss in horsepower either.
This is closest to what the OP was asking = at what piint is high compression, and the required fuel, wasting money.
As I stated before, build, or buy, engine with compression suited to readily available fuels.
You can make up power, equal to or more, than if higher compression were utilized.
I changed a cast iron head motor with ~11:1 running race fuel turning 10.33 e.t at the track. I dropped it down to 9.3:1, by using higher flowing heads with a larger, polished combustion chamber, different low lift cam duration and lobe seperation angle, used 93 octane pump gas and ran - 10.20.
my only goal was to make the car pump gas friendly.