The shop should be competent enough to tell you exactly what you need otherwise I wouldn't trust them with the install.

 

Revo and 4D05G35:

I really can't understand why you keep saying bore size has nothing to do with compression ratio? That is totally wrong. If all variables stay the same and bore size is all that is changed, your compression ratio will absolutely change. I will write out an equation if that is what it takes. But before I do...

Here is a link I found at the top of a google search explaining everything I don't feel like typing. http://www.e30m3project.com/e30m3per...comp_ratio.htm
Make sure you read the part where it says:

"Even if the volume of the combustion chamber (V2) is kept constant, we can increase the compression ratio simply by increasing the stroke and/or the bore size."

Also here is a link to a compression ratio calculator I found online with another simple search. Without writing out an equation for you, it will show by changing only the bore size field, your compression ratio is altered slightly. http://www.csgnetwork.com/compcalc.html

If these examples are still not able to change your minds, then please enlighten me on how all this information, as well as everything I have said could possibly be incorrect. Also, make sure you site some sources or provide some links of your own so that there's no confusion to others that may be reading the incorrect information you are posting up here.

Additionally, just to be clear, this isn't a pissing contest. I have no hard feelings toward either one of you. If I am wrong I will gladly admit it if that is the case, however from everything I know and can find, that isn't the case. I'm not trying to call anyone out, I just want to correct any mis-information that may be here, weather that is mine or anyone elses.

 

There are sources on the internet that say evolution is BS...just cause you find it on the internet doesn't make it true.

Ok, in the grand scheme of things, your compression ratio will not be EXACTLY the same because the heads are not perfectly edged cylinders, but rather more of a dome shape, but you can bump out your cylinder 1 or 2mm and your compression ratio will not change more than .01, which is nothing in the grand scheme of 10.3:1.

 

Silver tiburon.
I am still reading up on this. I am limited on the searches I can run while at work, so it will have to wait until im at home and free. So far I have found a few forums that support what you say. I have also found that it's not as cut and dry as the math indicates.

No hard feelings here either. The last thing I want to do is spread misinformation.

 

i say just trade it in for a newer g35. It'll probably be cheaper since you can finance any lost over 5yrs versus paying cash upfront to fix the engine, plus down time on the car. Engine build never go exactly to schedule and never cost exactly the amount you budgeted. They usually cost more then what you budget and take longer then you spec out.

 

I stand corrected.

I have been struggling with this concept, but It finally makes sense to me. Initially I was thinking that all things alike and the only changes being the cylinder bore diameter and the piston diameter that the CR would remain the same. When the cylinder is bored the walls are parallel so with the larger diameter the piston can draw in more air at BDC, but it has more room up top now due to the larger bore so the CR would remain. Basically you just have the same set-up (81mm bore vs 84mm bore) just on a larger scale, but thats not the case.

The ratio between the higher volume of air the larger bore can draw at BDC and the slight increase bore (where the air/fuel is compressed) diameter at TDC is not equal.
The volume increase at BDC is greater than the volume increase at TDC so it results in a higher compression ratio. The increase is not drastic, but enough worth mentioning.

 

This is a perfect simple explination of what I have been trying to say all along. Well put. In the end all that matters is that everyone understands compression ratio will change slightly with bore size where everything else is constant. And as you said, the change is minimal but definitely worth mentioning.

 

Now that we've discussed CR....A new OE short block with good headwork/valve job and cams would be ideal for what you want once you've discovered what your current engine issues really are.
Gary

 

Piston diameter? Who said anything about piston diameter? Piston diameter is directly related to bore size, and bore size is directly related to calculating volume which you posted in your equation above (which is missing a few things). I'm not sure what point you are trying to make other than what I have already said is true. I'm not sure why this is such an arguable topic when it is seemingly very cut and dry. I'm done arguing this point as it has already been proven in theory and mathematically. After all, this isn't evolution we are talking about as Revo remarked.