Engine compression 150,125,125,140. MATH QUESTION

[89ARIES]

At nearly 200,000 miles, I am told you can never rebuild a top end without blowing out the bottom end, so you are out of luck either way so every time the top
end starts losing compression, REPLACE ENGINE. Is this a fallacy? I was hoping that maybe all my car might need soon is just a top end job, not a whole block job. My other
question is this:

Is Compression DIRECTLY related to gas mileage and power. Lets do a hypothesis. Please, some tech answer this for me:

Normal Compression: 150,150,150,150=600 lbs
My Compression:150,125,125,140=540lbs

Can two headgasket jobs being part of the loss of compression? It just doesn't seal as well as before? Anyway:

540lbs/600lbs=90% of the power left. So, max speed of 108mph is now really only 108 x .90=97 mph. Gas mileage of 21/26 mpg is now only 18.9/23.4 mpg
At what point will car no longer pass smog? When compression is 100,90,90,95? How many miles will it take for my engine to be done. Hhm. Will it even make 250,000?

[K-CAR_WAGON]

Its not true that rebuilding a top end will necessarily cause the bottom end to fail. Its more a question of does it make sense to spend alot of money/time/effort rebuilding a top end of a high mileage engine when there has to be wear on the low end with 200K. Your car does not have an oil pressure gage so you don't know the extent that you have been losing oil pressure over the years primarliy due to bearing wear. Your rings and cylinder walls are also worn to some extend.

With your engine which is rather common and used on alot of other Mopar cars, from a financial viewpoint, it makes more sense to find a low mileage one from another car - maybe a low mileage wreck that had been hit in the rear. Even, if I was going to have an engine rebuilt, I will probably find another low mileage one rather than use yours as the core.

Yes, compression is related to power and MPG. However, the slightly lower compression numbers that you have should not make any noticeable difference. The difference in MPG that you are experiencing is proably not due to loss of compression - but rather to other issues like timing setting, driving habits, fuel blend, fuel injector control, etc. Most likely your car is just running slighly too rich sometimes for whatever reason.

Forget the max speed - you don't have a race car or peformance car. Forget your simple calculations - its alot more complex. Lots of issues involved with power, torque and achieving max speed in addition to cranking compression: how well the car is breathing, timing setting, fuel delivery at different speeds, computer controlled advance curve being applied, valve sealing at differnt engine speeds, etc. ....

No way to tell when it fail smog or how fast it will degrade to lower compression. With the compression numbers you currently have I expect you would not have a smog problem provided your cat and oxygen sensor are still good.

Headgasket jobs don't cause you to loose compression. Not addressing or fixing all the causes of the reduced compression can result in not getting a compression back to the original design valve. For example, some of the compression loss can be due to valve sealing and/or ring sealing and/or an imperfection in the head surface.

[MyDodgeDip]

If you weren't so busy telling everyone with a beat to hell, average K car that it was worth $3,000, you could have picked one up for nothing by now and had a good drive train to swap into your car...

[89ARIES]

I don't tell EVERYONE they have a $3000 car.

[88 aries]

and not to mention your 1 of 100 crap you pull all the time....Guess what theres a more rarer car...a tucker...if you had one you could say 1of 50..

seriously...where you do get these BS stories? are you some sort of automotive historian guy? We get sick and tired again and again of hearing about your car.. you don't see us complaining about ours...Lets face it your 89 Aries is a $$$$$ piece of crap...with high mileage. the car alone is worth about 400.00-500.00 I dont care if it is the last of the 89's.... So to simplify the subject..YOU ABUSE YOUR CAR!!!!! FORGET ABOUT MAX SPEED ITS NOT A HEMI CUDA!!!!


and mydodgedip makes a good point instead of telling everyone their car is worth 3,000, you could have bought another K that is in much better shape and runs 100 percent better..

[89ARIES]

This was not an abused car. I never ran it over 85 more than a dozen times in 9 years. I did the best I could with what I had. Its a miracle
the car has even made this far, considering all the problems I had.