Why not higher compression ratio??

[Boss302]

ok basic principal of power the more violent the explosion the power power that is going to be made. period. now whether that power can be harnessed is another thing. so to increase the intensity why not go to a higher compresion ratio and high boost at the same time or high compression and little boost. why is the trend 8.5?

 

[IJ.]

Detonation on pump fuel.

 

[MDCmotorsports]

Yup. If you could cool the intake charge and not be limited to pump gas you could run 12:1 compression engine etc etc with X lbs of boost without problems.

 

[Nick M]

8.5:1 is unecessarily low in my opinion. If you are forged, I would experiment with higher static numbers. And I had money to burn.

 

[Boss302]

well race gas should remedy that problem ay? 93oct. is a little low ain't it?

 

[MDCmotorsports]

Unless the engine is tuned, you run race gas all the time, and you have a very large and efficient intercooler I would say no.

10:1 to higher compression with boost requires a build engine also, and exotic race fuel such as 115 race gas, alcohol, or toluene.

 

[Boss302]

not even 110? what kinda intercooler would yall recomend i'm currently looking at some from drift motion.

 

[whenmunkysfly]

i thought you lowered the compresion so you could get more air and fuel in the combution chamber because since its on boost the more room=more fuel and air= more burning and more compression. but hey im not a boost expert i've never even had a boosted car til i bought the supra and its not even running yet.

 

[Boss302]

no that applies to anything internal combustion you want that cylinder as cramped and full as you can get it. the more room the lower the compression because it is a ratio. if you have a hole that is 3ft deep filled with air with a plugger that has a recess in the head of 2ft. vs. one that has a recess of 1.5, which one is going to have more force and resistance? the 1.5 cause there is less room for the air to move to.

sorry for the typo's my dad was tripping and rushing me.
i'm pretty sure i got all that right though as far as teh concept goes.

 

[MDCmotorsports]

Boss: slow your typing down. I can't even read what you just wrote.

 

[mickyg]

Something about a hole filled with hair. Gross...

 

[koulee]

no that applies to anything internal combustion you won't that cylinder as cramped and full as you can get it. the more room the lower the compression because it is a ratio. if you have a whole that is 3ft deep filled wit hair with a plugger that has a recess in the head of 2ft. vs. one that has a recess of 1.5 which one is going to have more force and resistance? the 1.5 cause there is less room for the air to move to.

He lost me at "no"

 

[mattjk]

also attributed to poor combustion chamber design.

 

[Adjuster]

Ok, here are some simple facts every engine has to deal with.
Most pump gas will detonate at CR's over about 12.5:1, and considerably less on our engines due to advances in the design of the newer motors.
Some NA's might be able to run that ratio, but not that I know about.

When your at low rpm and boost is not being provided yet, all you have to run on is the engine displacement and static compression ratio. (The higher the ratio, the more power the engine makes to a point.)

When you start to force air into the chamber, you can pack more air and fuel into the same space, so you get more power. At some point however, the air and fuel become so dense, they produce their own heat, and you get detonation. (Diesels are designed to run this way, and have CR's of about 18:1 to heat up the air so the fuel will burn.)

If you lower the static CR, then you have more "space" to fill, so you can make more ultimate top end power on full boost, but your extra space lowers the CR, and makes the engine more sluggish off boost.. and at some point the CR is too low to even run correctly since you have to compress the air/fuel mix to get it to burn anyway. (correctly that is.)

So, short answer?
Yes, you can run 9:1 CR and have a nice reponsive 7MGTE. (I do it every time I drive my car.)
I would not run this without thermal coatings on your pistons however. (Everything in my motor is coated where possible.) It only takes a few moments running lean or detonating to ruin an engine.

 

[IJ.]

Dynamic Compression Ratio!

Timing will also affect this as it can raise cylinder pressures to the point where mechanical failure happens.

None of this is "magic" xx octane will detonate at xx pressure you need to accept this and make your choice from there ie: Low Static + High Boost or High Static + Low boost.

 

[cruzinbill]

or direct port injection... you know where the injector injects into the firing chamber... reallllllllllllllllly helps against detonation

 

[Boss302]

i know there's a point where it's just stupid to attempt just wondering where the danger zone could possibly begin round about i figured 9.5 is the best i could do with out going crazy.

 

[Junior]

or direct port injection... you know where the injector injects into the firing chamber... reallllllllllllllllly helps against detonation

no dude, DPI INCITES detonation, just it does it at the same time that you'd normally be sparking, so it's impossible to "pre" detonate, since the fuel isn't in their yet. this lets you run CR's as high as you want. infact you often HAVE to run high CR's since the mixture has to reach a high temp in order to ignite the fuel when it's injected.

This is the reason diesels have glow plugs.

 

[IJ.]

Diesel 7M's ? :wtf:

 

[cruzinbill]

you do know alot of new non diesel vehicles use direct port also..... alot of mazdas if i remeber correctly