:help: What is the differents between a J-motor and a C-motor?

some one wiser than i can straighten me out but i think it is just the emmission systems. my half ton has the egr and other goodies they thought that was required to keep deq off there backs . all the three quarter tons and one tons didn't have any add on emmissions like that.

Welcome to the forum!

It's all about government emissions standards.

All civilian vehicles with less than 8000# GVWR were equipped with C-code engines which had EGR (Exhaust Gas Recirculation) and EPR (Exhaust Pressure Regulation) systems. Basically, the vehicles that fall into this category are mostly 1/2 ton pickups, Suburbans, and Blazers, although a few 3/4 ton trucks got C-code engines (such as mine, which comes in just short of 8000# GVWR).

The purpose of the EGR was to feed a some of the exhaust gases back into the intake. The idea was to reduce combustion temperatures and thereby reduce NOx emissions. The purpose of the EPR system was to create some exhaust backpressure by restricting the exhaust to so the EGR would work properly.

Both systems are only active at throttle openings less than 8 degrees measured at the injection pump throttle shaft (in other words, at idle). They are operated by vacuum and controlled by electric solenoids.

Another peculiarity of the C-code engine is that it has different intake and exhaust valves.

The downside of the EGR/EPR system is that it cuts horsepower a bit. The EGR valve restricts the intake, among other things. The different intake and exhaust valves do not affect power very much, oddly enough.

J-code engines were used in civilian vehicles above 8000# GVWR and all military vehicles. These vehicles were exempt from emissions laws. They had no EGR or EPR systems and they had slightly larger valves.

Hope this helps!

So if I buy a chevy m1008 what code engine will it have ?

The M1008 will have a J-code engine since it is a military vehicle.

Ok thank you