5.3/4.8 question

[scampbell2x]

Howdy all,
I just bought a LM7 from a 2004 GMC Sierra out of a junk yard. I didn't check the vin like I should have, so when I got it home I tore into it to see if it was a 4.8 or 5.3. It wasn't until I had the oil pan off that I read that there are tabs on the head gaskets indicating what size the engine is. 4.8 stamped clear as day. I was a little bummed, I figured I would check the crank casting number anyway. casting # 12552216, 5.3 crank.........Has any one else ran into this? It seems like the HG tab isn't an accurate way to ID a LM7!!

 

[350runner]

Only thing diff in the two is rid, stroke, and bore size all else is the same. The 4.8 will be a peppy snapy one... I raced my bud with one and we were neck and neck

Sent from the dust in front of you!

 

[350runner]

I'd do a single exhaust on it tho it'll keep up the torque. Wanna boost up the power? Google turbo 4.8

Sent from the dust in front of you!

 

[MadOgre]

LS BASED GEN III DISPLACEMENT INFORMATION


RPO VOL CID CR BORE STROKE BLOCK OE APPLICATIONS
LS1 5.7L 346 10.2:1 3.898" 3.622" ALUM 97-04 Corvette, 98-02 Camaro/Firebird, 04 GTO

LS2 6.0L 364 10.5:1 4.000" 3.622" ALUM 05-07 Corvette, 05-06 GTO, 07 CTS-V
LS3 6.2L 376 10.7:1 4.065" 3.622" ALUM 08-09 Corvette
LS6 5.7L 346 10.5:1 3.898" 3.622" ALUM 02-05 Corvette Z06, 04-05 CTS-V
LS7 7.0L 427 11.0:1 4.125" 4.000" ALUM 07-09 Corvette Z06
LS9 6.2L 376 9.1:1 4.065" 3.622 ALUM 09 Corvette ZR1 (Supercharged)
L92 6.2L 376 10.7:1 4.065" 3.622" ALUM 07-11 Escalade, 10-11 Silverado/Sierra, 07-11 Yukon Denali, 08 Hummer H2

LQ4 6.0L 364 9.4:1 4.000" 3.622" IRON 99-Present Full-Size Trucks
LQ9 6.0L 364 10.1:1 4.000" 3.622" IRON Escalade, Silverado SS, Full-Size Trucks
LM4 5.3L 325 9.5:1 3.780" 3.622" ALUM 04-Present Full Size Trucks, 04 SSR/Trailblazer/Envoy/Bravada

LM7 5.3L 325 9.5:1 3.780" 3.622" IRON 99-Present Full Size Trucks
LR4 4.8L 293 9.5:1 3.780" 3.267" IRON 99-Present Full Size Trucks
LSA 6.2L 376 9.0:1 4.065" 3.622" ALUM 2009-2011 CTS-V, 2012 Camaro ZL1

All LS based engines have a 9.240 Deck height, unless it's an LSX block, which is available in a 9.26" and a 9.70" deck

 

[scampbell2x]

Thanks for the replies! I'll start a build thread soon, this engine will be going in my 86 K10 soon!

The crank casting number is a solid way to determine displacement, correct?

 

[MadOgre]

Well the 6.0, 5.7 and 5.3 all use the same stoke of 3.62 so I don't know. Still learning about these engines my self.

The 4.8 has flat top pistons and the 5.3 does not. And because they use the same bore they can be swapped into a 5.3 for better compression and the added benefits of flat top combustion.

If it is a LM7 it should be 5.3 as the LR4 is the 4.8

 

[350runner]

More so the stamp on the motor

Sent from the dust in front of you!

 

[bucket]

And because they use the same bore they can be swapped into a 5.3 for better compression and the added benefits of flat top combustion.

Ah, this has been discussed here before. The pistons can swap because the 4.8 and 5.3 use different rods, correct?

 

[350runner]

Yup you can bump up the compression

Sent from the dust in front of you!

 

[MadOgre]

Ya the two have different strokes so you have to swap just the pistons. The rods can not swap.

 

[scottybaccus]

Hot Rod just posted a great article about what you can and can't do in boring the LS, and Hot Rodding did a destructo test recently on a 5.3, making over 60 1000+ HP pulls on the dyno, only to find out it was a 4.8. Find that article and check out what they did with only a cam swap. You'll be all giddy.

 

[scampbell2x]

This engine is indeed a 5.3, well, kinda. It's been punched out to 3.898. My next concern is that there is quite a bit of carbon buildup on the inside of the oil pan, on the screen to the oil pickup, and in the driver's side cylinder head. The passenger side head is squeaky clean. I heard the engine run before I bought it, sounded fine. Good crosshatch in the cyl walls, valve seats seal perfectly (tested on bench with fluid). Any ideas why there would be so much crunchy buildup inside this engine?

 

[350runner]

Sounds like a lil blow by. Might just be able to get rid of that with a couple hard runs to better seat them rings ;-)

Sent from the dust in front of you!

 

[firebane]

This engine is indeed a 5.3, well, kinda. It's been punched out to 3.898. My next concern is that there is quite a bit of carbon buildup on the inside of the oil pan, on the screen to the oil pickup, and in the driver's side cylinder head. The passenger side head is squeaky clean. I heard the engine run before I bought it, sounded fine. Good crosshatch in the cyl walls, valve seats seal perfectly (tested on bench with fluid). Any ideas why there would be so much crunchy buildup inside this engine?

**** oil.. **** oil filter.. Not driving it hard enough.. Not driving it long enough.

 

[MadOgre]

I would check compression cause it sure sounds like blow by to me