I picked up 2 5.3 long blocks, one is a gen 4 with the Tbss style intake and 243 heads. The other one is another aluminum block with 243 heads but it is the gen 3, is this the L33?

I got a long list of parts and I will add part numbers soon. I ordered head bolts, ls7 lifters, head gaskets and also have the lunati dual valve springs. I don't want a race truck. I'm plan on putting this motor into my '85 C10 and use the gen 3. I was wondering what the compression on the aluminum 5.3 with 243s will be?

 

Casting Number 243
Head: 2001 LS6 5.7 Liter Passenger Car
Material: Aluminimum
Part Number:
12564243
Combustion Chamber Volume: 64.45cc
Compression Ratio: 10.5:1
Intake Port Volume: 210cc
Exhaust Port Volume: 75cc
Intake Valve Diameter: 2.00 inches
Exhaust Valve Diameter: 1.55 inches

Stock Head Flow Numbers
Chamber 64.45 cc-------0.100---0.200--0.300--0.400---0.500---0.550---0.600
Intake 210 cc------------62------126----184----224-----251----256----257
Exhaust 75 cc------------57------108----143----163-----176----180----183


What you need to know:
The LS6 cylinder heads is essentially a tuned-up version of the LS1 head. At 65cc, the combustion chamber is slightly smaller and more efficient than the LS1. The more efficient design shortens burn times and ultimately means less ignition timing advance is required to produce the same power. And because less timing allows more efficient combustion, the Ls6 heads allow the engine to produce more torque. The exhaust port is a unique D-shape that improves flow. LS6 heads are the best choice only when all-out power is needed. Be prepared for a big price tag at the dealer or steep core charge from your head porter.


should be pretty close to that compression wise... and yes it sounds like a l33

 

The compression on a L33 is ~9.9:1 IIRC, but it can usually run on 87 octane. Like the Gen4 5.3s the L33 actually uses flat top pistons. That is a great motor.