How do i tell the differece between a C code and a J code engine apart from the obvious air intake?

Injection pump will have a different number, different pre cups in the heads.

Not much way, in an older or used engine - WYSIWYG - no telling what-all has been changed\mixed-up for expedience.

The EGR tower on the intake is a good indicator, tho.

Internally, it's the pre-cups, even if it has a J intake.

Compression and everything else is same - block, heads, pistons, rods, crank, cam, etc.

Maybe power as well, from what I have read, the J codes pull harder and looking at the dyno charts, it would appear to be true. My C code is soft in the midrange and up top, it just falls down. I am putting on a J code injection pump so we'll see what happens. A member on here did the swap and couldn't believe the difference in power.

Thanks for the replies, I'm looking at buying an early 80's blazer for the engine as mine has a really annoying knock that i can find.
The Blazer is supposed to be ex Military so should be a J code? i have a re built J code pump on mine now, made such a differance, it's like a different truck now and will just about spin the wheels, not bad for a 6.2 Dually eh :o)

Just a note to say, that blue dually in your avatar looks mean!

I like it!

Clem

I'm probably waaaay outta my league offering advice on this forum BUT...I was reading an article the other day and they said that sometimes on these engines when the harmonic balancer starts to come apart the pully will rub on its bolts and sound like rod knock. Maybe I have no idea what I'm talking about here but sounds like a simple thing to check before you tear your truck up. Really nice looking truck BTW.

Hi, i've checked my balancer and all is ok with that, think i've got a bent valve :( glad you all like my truck though :)