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Unread 07-12-2010, 05:39 AM   #16
tjkj2002
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Originally Posted by tommy2399 View Post
In most of the U.S., regular gas has an octane rating of 87, midgrade gas is 89, and premium is 91 or 92. (Octane ratings are lower in the mountain west due to the effects of thin air on internal combustion.) Contrary to widespread belief, the octane rating doesn't indicate how much power the fuel delivers; all grades of gasoline contain roughly the same amount of heat energy. Rather, a higher octane rating means the fuel is less likely to cause your engine to knock or ping. Knock, also known as detonation, occurs when part of the fuel-air mixture in one or more of your car's cylinders ignites spontaneously due to compression, independent of the combustion initiated by the spark plug. (The ideal gas law tells us that a gas heats up when compressed.) Instead of a controlled burn, you get what amounts to an explosion--not a good thing for your engine. To avoid this, high-octane gas is formulated to burn slower than regular, making it less likely to ignite without benefit of spark.

The majority of cars are designed to run on regular gas, and that's what the manuals tell the owners to use. Higher-performance cars often require midgrade or premium gas because their engines are designed for higher compression (higher compression = more power), and regular gas may cause knock. If your car needs high-octane gas, the manual will say so.
Higher compression does not equal more power.The most powerful engines put in a vehicle only has 7:1 compression ratio and puts out over 7000HP with only 500 cu in displacement.

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Unread 07-12-2010, 06:10 AM   #17
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Originally Posted by tjkj2002 View Post
Higher compression does not equal more power.The most powerful engines put in a vehicle only has 7:1 compression ratio and puts out over 7000HP with only 500 cu in displacement.
yes it does, that 7:1 motor you refer to must have a blower or turbo to get the air/fuel into the motor to make that kind of power. however i have a 125cc dirt bike making 22+hp with between 6&7:1 compression ratio but spins 14,000rpm to do it. the more air/fuel you get into the motor the more power you get out.
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Unread 07-12-2010, 05:42 PM   #18
tjkj2002
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Originally Posted by scottunangst View Post
yes it does, that 7:1 motor you refer to must have a blower or turbo to get the air/fuel into the motor to make that kind of power. however i have a 125cc dirt bike making 22+hp with between 6&7:1 compression ratio but spins 14,000rpm to do it. the more air/fuel you get into the motor the more power you get out.
Yep,but with lower compression.

Like stated high compression does not equal more power.
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Unread 07-13-2010, 03:44 PM   #19
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Originally Posted by tjkj2002 View Post
Yep,but with lower compression.

Like stated high compression does not equal more power.
a turbo or super charger increase actual compression ratios, while not being fed air it is 7:1, being force fed air can increase real compression into the mid teens or better. a rough limit for "pump gas" is in the 14.5:1 range with a good intercooler keeping air charge temps down, that translates to about 20psi on a 7:1 motor, give or take.
drag cars will run 6.5:1 compression and force 60+psi of air into the motor.

higher cylinder pressure=more power. you can either stuff air into it with a fan or increase compression on an n/a motor to achieve that result.

you can force feed a higher compression motor, but due to the nature of air density you can't push more than a few extra psi at it depending upon the strength of the motor's components.

"premium" gas used to have detergents that regular and mid grade didn't have. the times of those formulations are long past and all gas has some level of detergent in it.

if you're concerned about carbon build up you can either use seafoam or mopar combustion chamber cleaner, or if you're experienced you can use water mist to steam the carbon from the inside(this type of cleaning is for people very experienced with their motors only, it can kill your motor if done wrong).
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Unread 07-14-2010, 02:39 PM   #20
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Originally Posted by ratmonkey View Post
a turbo or super charger increase actual compression ratios, while not being fed air it is 7:1, being force fed air can increase real compression into the mid teens or better. a rough limit for "pump gas" is in the 14.5:1 range with a good intercooler keeping air charge temps down, that translates to about 20psi on a 7:1 motor, give or take.
drag cars will run 6.5:1 compression and force 60+psi of air into the motor.

higher cylinder pressure=more power. you can either stuff air into it with a fan or increase compression on an n/a motor to achieve that result.

you can force feed a higher compression motor, but due to the nature of air density you can't push more than a few extra psi at it depending upon the strength of the motor's components.

"premium" gas used to have detergents that regular and mid grade didn't have. the times of those formulations are long past and all gas has some level of detergent in it.

if you're concerned about carbon build up you can either use seafoam or mopar combustion chamber cleaner, or if you're experienced you can use water mist to steam the carbon from the inside(this type of cleaning is for people very experienced with their motors only, it can kill your motor if done wrong).

LOL at that comment!!! I'm feeding about 50lb of boost through my 16to1 compression engine in the Dodge I have.........LOL!!!!!!..............So much for the theory you pose that says you can't force feed air into a high compression engine.
don't hate on me, I'm just teasing
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Unread 07-15-2010, 07:47 AM   #21
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and it's a coal burner, whole other ball game suzie.
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Unread 07-17-2010, 07:02 AM   #22
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I can GUARANTEE you more compression equals more power! (To a certain point of course).
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Unread 07-17-2010, 07:58 PM   #23
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Originally Posted by lt1tyrell View Post
I can GUARANTEE you more compression equals more power! (To a certain point of course).
False..............

The early 3.7 V6's in KJ's had 9.5:1 compression ratio with 210hp and 235lbs-ft of torque.

The newer 3.7 V6's in KJ's have 9.7:1 compression ratio and still the same 210hp and 235lbs-ft of torque.


Granted it's only .2 more but that is more with zero HP and torque gain.
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Unread 07-18-2010, 11:43 AM   #24
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Well I am not going to argue with you, the reason they have the same power still is just the way the engine is tuned and/or rated... I have built a few v8 chevy engines and I will tell you if you use higher compression pistons or cylinder heads with a small combustion chamber they are WAY more powerful (in combination with other parts of course) but compression and power go hand in hand. Yes the most powerful engine in the world might be 7:1 but that is because it will have forced induction which is also another form of HUGE compression. But I am done because this is off topic and going nowhere...
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Unread 07-18-2010, 12:37 PM   #25
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Originally Posted by ratmonkey View Post
and it's a coal burner, whole other ball game suzie.

How did you know my name?.........LOL!!!!!
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Unread 07-19-2010, 10:23 AM   #26
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Originally Posted by lt1tyrell View Post
I can GUARANTEE you more compression equals more power! (To a certain point of course).
almost true, more combustion pressure=more power. this can be achieved through compression ratio, forced induction, or to a smaller degree timing advance and cam duration.
Quote:
Originally Posted by tjkj2002 View Post
False..............

The early 3.7 V6's in KJ's had 9.5:1 compression ratio with 210hp and 235lbs-ft of torque.

The newer 3.7 V6's in KJ's have 9.7:1 compression ratio and still the same 210hp and 235lbs-ft of torque.


Granted it's only .2 more but that is more with zero HP and torque gain.
you don't even understand what compression is all about let alone being able to tell the real differences between these two motors.
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How did you know my name?.........LOL!!!!!
i'm psychotic. i know everything.
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Unread 07-19-2010, 08:15 PM   #27
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Originally Posted by ratmonkey View Post

you don't even understand what compression is all about let alone being able to tell the real differences between these two motors.

Yeah I kinda do,been doing this **** for 24 years.Probably built more engines then could imagine,mostly Cummins and Detroit Diesels though.
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Unread 07-19-2010, 11:08 PM   #28
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Haha I can't believe I am replying to this but you are still wrong! I dont care if you have put together diesel engines, you still do not know what you are talking about. Once again more compression will give your engine more power!
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Unread 07-20-2010, 07:52 AM   #29
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Like stated high compression does not equal more power.
Description
_________________4.0L I-6____ 4.7L V8 ____ 4.7L V8 HO
Displacement______ 4.0 L ______ 4.7 L______ 4.7 L
Compression Ratio _ 8.8:1 ______ 9.0:1 ______9.7:1
Power (SAE net)___ 195 BHP ___ 235 BHP ___ 265-270 BHP

'Splain Lucy.

source: Jeep Grand Cherokee WJ - Engine specifications
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Unread 07-20-2010, 09:03 AM   #30
tjkj2002
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Originally Posted by lt1tyrell View Post
Haha I can't believe I am replying to this but you are still wrong! I dont care if you have put together diesel engines, you still do not know what you are talking about. Once again more compression will give your engine more power!
No it does not,just increasing the compression ratio on a engine will not gain more power,actually you could loose HP.Tuning and the correct fuel is needed to gain the HP from a compression ratio increase.

Quote:
Originally Posted by bradbb2005 View Post
Description
_________________4.0L I-6____ 4.7L V8 ____ 4.7L V8 HO
Displacement______ 4.0 L ______ 4.7 L______ 4.7 L
Compression Ratio _ 8.8:1 ______ 9.0:1 ______9.7:1
Power (SAE net)___ 195 BHP ___ 235 BHP ___ 265-270 BHP

'Splain Lucy.

source: Jeep Grand Cherokee WJ - Engine specifications
let's see the I6 is a I6,not a V8.There are tuning that takes advantage of the .7:1 compression on the V8's HO engine.



So like before higher compression does not automatically increase HP,you need to tune it and run the correct fuel to see any HP gain.
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