I have heard that most evos are getting around 175psi. the manual says the lower limit is 163 psi and that the cylinders should not vary more than 10%. How true is this? and what are the consequences if your not within these parameters.

Next, with a 2.3L stroker and/or 2.4L block(not stroker) how should the compression change should it be higher, lower or same and by how much?

Next, with the above question, is it normal for the compression to be lower before break in as I have heard that the rings need to seat? If this is the case what should be a range of change from start, to full break in (assuming break in is between 500-1000miles), like 5, 10, 20psi etc difference with each cylinder.

Is it true that you should not use synthetic oil for break in? and WHY? and please don't give some stupid answer like you'll get engine failure or something like that. I want to understand what is really going on. like what differences in compression you would get if you did synthetic vs. dinosaur(JK, regular)?

I would really like some educated input. thanks, ahead of time.

 

Damn, are Evos running tubine-jet engines for turbo now?

 

question #1. compression will end up being a bit higher since the piston will travel a greater distance, hence end up compressing more air/fuel.

question #2. no matter how you build your engine, you will need a very carefull break in.

question #3. Synthetic oil is "too good" and won't set your rings in as quickly as natural oils.

 

That number is average for a stock EVO. Most important is cylinder balance, which more or less indicates the condition of each with respect to the others. A leakdown test is usually more useful in this regard than a compression test.


That depends entirely on piston selection. So long as one chooses a stroker piston with the same compression ratio as he had in the initial setup, the static compression will be unchanged. Changing the displacement of the engine only changes the volume of air being compressed, not the pressure.


The answer to that question will likely vary depending on specifics having to do with engine parts selection and details of assembly.



A large consensus of thought asserts that synthetic oil may prolong the break-in period.

 

NOT BOOST! Compression. read the thread

 

The whole purpose of "ring" breakin is the process of the rings removing the peaks in the cylinder wall from the honing process. When you cut the cylinders with a hone you are cutting a cross-hatch patern that will allow oil to be suspended along the cylinder length to lubricate the rings on the wall. This honing process leaves peak (bad) and valleys (good). If a plateau hone (removed peaks but doesn't cut wall) is used then relatively all the peaks would already be removed. This is the best situation as there is basically no breakin period.

You are not trying to wear the rings to the cylinder walls! They are not brakes.
The downside to using the rings to cleanup the cylinder wall is it causes the peaks to roll over and smooth out. a plateau hone cuts the metal off instead of sliding against it and smoothing it out. Often times no matter how well you break in an engine, poor machine work will ruin cylinder wall condition.

For your break-in process you should be putting the car into boost often but not rev'ing it over say 5000-5500 rpms regularly.The boost will force the ring out into the wall to remove the plateaus more effectively then no boost. You do not want to pussyfoot around for 500 miles, it is smoothing out all those peaks and destroying the condition of the cylinder wall and the rings.

Even though it should be obvious, you do not want to lug or accelerate from a low RPM at anytime, whether it is break-in or not. This is very bad for the bearings and will cause galling on the bearings. This creates a significant load on the engine and at a lower crank speed will cause the crank to smack against the bottom half of the bearing. This explanation is not great but this type of damage is undeniable when you diassemble an engine.

 

Oh, I forgot my point. Synthetic oil on breakin is a function of the quality of the machine work and has nothing to do with the actual break in process.
A properly machined cylinder wall, especially if it is plateau hone after the honing process will do just fine on synthetic. A block honed by Billy Bob who has no concept of stone tension and just cuts the cylinders to size would ultimately do better on standard oil because it has less adhesive properties then synthetic and will aid in the removal of the peaks do to the lack of lubrication.

 

Good description.

 

timzcat, i don't think you know what your talking about. the rings seat to the cylinder walls determined by your surface finish and break in method. if you get a good break in the face of the ring will fully be shiny, if not the face of the ring will usually be half shiny and half dull. the dull part is the the original face of the ring that never made contact with the cylinder wall during break-in. if the rings don't seal properly this will show up in a leak down test. the main and rod bearings never make contact with the crank except at startup and when detonating. if they are contacting its usually from improper clearancing,burrs, or rod bolts stretching.