Hey All, I've been researching for hours and I can't seem to come to a conclusion on what I have. If anyone can help I'd appreciate it.

I just bought a 98 blazer with what I was told is a 5.3L out of a 2007 Silverado in it. It runs fine and idles smooth. (so there are no problems) I'm trying to fact check this thing and all of the clues I read only make me more & more confused. And who knows... maybe its a Frankenstein build?

Here is what I do know:
Iron block / aluminum heads
853 number on drivers side head
EGR port on passenger side / front of intake has home made blockoff plate
Aftermarket tube headers w/o identification.
Coolant neck is angled at about 45deg
Valve covers are NOT perimeter bolt pattern.
Coil bodies are round. (cooling fins on top of coils are mostly square shaped)
Intake manifold is plastic and looks tall and bulky.. not the smooth cross ram types that is on vettes and F-Bodies.
TB is cable operated
Fuel system has two lines. (one is smaller than the other so I'm thinking its a old school return system)
The AC compressor is very low and on passenger side. it has a little belt tensioner between it and the crank pulley.
Tranny is a 4L60e
Has 5.3L emblems on the doors.

Thanks for any help you guys can give.
If there is anything else I can check please advise!

Regards, Rich

 

If any part of it is 2007, it's a mash-up of parts. Not necessarily a bad thing though. 853 heads are LS1 heads. Larger intake valve but also larger combustion chambers, lower compression ratio on most early 5.3s. Early 5.3 intake setup..drive by cable, return-style fuel rails, etc..that says 99-2002 truck to me. If the return-style rail fits it and it doesn't look like someone customized it, then it would only fit the earlier truck intake(pre-2004-ish). I am in the process of fitting my 2000 fuel rail to a later truck intake and it's taking a little cutting and welding. That's not saying that the short block couldn't be later. That's the standard location for A/C compressor. Have you had the intake or any other parts off?

It's definitely not a complete 2007 motor but that's not the end of the world. The earlier 5.3s are quite capable. I'd be interested to know about the head/shortblock combo..if you put LS1 heads on an early 5.3, you get very low compression.

 

Thanks Mercier,

It runs well and makes good power down low. I've not had a chance to check compression yet or even get out and play with it at higher rpms. (just got plates yesterday)

The previous owner didn't know much other than the "tune" turned off security and allowed for no cats. He seemed confident it was out of a 2007. But.. the 853 heads has me thinking not.

As best I can tell the whole install was not a hack job. Everything that was done looks to have had a reasonable amount of attention. The pre-TB piping is a bit simple. But it works. MAF, TPS, and fuel pump are new. MAF is about 82mm inside diameter.

The fuel rails look factory stock and perfectly match the intake. All in all (other than the round coils) I'm thinking its a 99-2000 5.3L out of a truck.

 

That sounds like a reasonable assessment save for the 853 heads. Are you sure they aren't 862? That or 706 is what would be factory stock for early 5.3/LM7. Those heads would give you more compression and might even run better with that early intake(which BTW will not do much for you over 5000RPM). The later trucks have an intake that flows better at higher RPM. If they really are 853s then perhaps they were milled to get you some compression back..but I wouldn't bet on it. The 853 has a bigger intake valve which will improve flow a bit, but the loss of compression is likely more than cancelling that out. Good news is factory heads and intakes are cheap and plentiful so you have affordable upgrade paths within the factory parts.

 

Thanks Mercier, Are there numbers on the block that would be of use?

 

Yes..maybe. There are casting numbers. See the following chart. It might help.

https://summitracing.custhelp.com/ci...974/1164656520