[lt1tyrell]

Hahaha ok you win, you are right...more compression=less power...

[bradbb2005]

Originally Posted by tjkj2002

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.


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.

Fist of all, there is no difference in the way an I6 and a V8 work, they are both combustible gasoline engines.

Second, let's analyze this, if you compress the gasoline/air in an engine which do you think will explode with greater force, the one compressed more or less? ....still don't know?.....think of a musket, if you dont pack the powder in tightly the projectile will not travel very far (the piston rotating the crank), but if you do pack it tight it travels farther (the piston pushing harder and the crank rotating faster).

Third, you now start to "kinda" agree that compression is directly proportional to hp.

[tjkj2002]

Originally Posted by bradbb2005

Third, you now start to "kinda" agree that compression is directly proportional to hp.

No kinda agree,just increasing the compression will not give you more power,you must do other things to get more power from increasing the compression ratio.It is also fact that without those tuning mods more compression reduces HP,just look at the advertising for the Hyundai Genesis,200 some HP only if using premium gas,makes less on regular gas since the PCM has to adjust timing and such with the higher compression ratio.


The I6 is nothing like the V8,a inline engine has distinct characteristics then a V8 and responds differently to engine mods.

[95BadBoy]

OK folks - this thread has went way south. Back to the OP's question......... or drop it. But me thinks the octane thing has been discussed. Take it to PM's.

[bradbb2005]

Originally Posted by tjkj2002

The I6 is nothing like the V8,a inline engine has distinct characteristics then a V8 and responds differently to engine mods.

I didn't say they were the same, I said they operate the same, from a theory aspect of how an engine works.

I love it when some people will argue a point on and on until everyone gets sick of arguing and gives up and then they are right, its like winning a race because the other guy didn't show up to the track.

[T-birdJunkie]

Originally Posted by bradbb2005

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

the HO 4.7 makes most of its power from a different cam profile. Your argument is invalid.

[oldMountainMan]

Originally Posted by pt2005

Hi,

I've been using 87 on my KJ since day one. Heard from some friends (I am not mechanically inclined as you may tell ) that sometimes switching to a full tank of 91 will help clean the fuel system and give it a boost. Thought it a good advice; however, I remember vaguely the KJ manual says something like the car is designed for 87 and using high octane gas may harm the engine. Thats why I never used 91.

Another question I have is: I've been swinging between Chrevon, Shell, Mobil, 76 (and sometimes Arco). I noticed 76 seems to give me the highest mpg. But I am not sure if I am right because I don't have any data to back up. Any advice on the best gasoline name to use?

Thanks a bunch

Higher octane gasoline won't hurt anything but your wallet. It also won't help anything. Octane rating measures knock resistance, and nothing else. The 91 octane has the same cldaning additives as the 87 . Using higher octane than the engine needs just wastes money.