GaveUpOnTV

How much of a difference are there between engines (in the extreme cases) with the same mods that have different results?
I know the MPG can be different for the 'same' engine, but WHY? (I know 'why ask why') I'm just curious, trying to learn something How much of a difference IS there? (in the bigger cases) TIA.

omaharam

I can't answer your question, but here is some absolutely mid blowing info I learned a few weeks ago. It is unbelievable how much variance there is in these trucks and here is my example.

Long story short...I had a cracked piston. Floor It diesel called Cummins to order a replacement piston and told them it was an 04.5 5.9 600 engine in a Dodge Ram. The guy asks him what the stamped number is on the piston. He says, I don't know. I can go check. Why would you need that? The response was that there are several different pistons for the 5.9s and they VARY IN SIZE! To make sure it has the correct diameter and rings(rings come with the new piston), we need to replace it with the same piston number.

John has also seen a few trucks that apparently have a glitch in the ecu from the factory and don't do any backdown or torque management.

XLR8R

No bombed CTD is sane.....

jrussell

Wow...thanks for sharing that info.

Sounds a little similar to what I found when pulling my injectors.

CRXsi

This can be quite common for many brands of engines as they use the sizes differences to account for machining tolerances on a day to day basis during manufacturing. I have seen the same thing working for different dealers with injectors as well. They match injectors based on machining tolerances and that way can have a matched set in a particular vehicle. Did they mention what the variance is in sizes based on the number on the piston? Usually it is like 0.001" or less (usually less) difference in size (injectors I have seen 0.0001-0.0005" tolerances requiring the different part numbers to match them more closely). Often the number can be a batch code so they match the batch code to a size reference and then match the new injector/piston/etc to that size reference so sometimes the 2 numbers don't even match but it is the size tolerance. The tolerance usually comes from using a particular bit during machining, once it wears or is replaced the batch number changes as so will the minute machining tolerance. Usually this kind of clearance tolerance is only done on high quality or high performance type companies/products so we should feel privileged that Cummins goes to this detail.