1FastBrick

iTrader: (17)

My understanding is that the alluminum L33 5.3L Uses a flat top piston Instead of the common Dish piston in the regular old iron 5.3L. That is were you see the bump in compression. BTW The flat top in the L33 5.3L is the same flat top used in 4.8L The GM part numbers interchange between them... Zippy Looked this up at the dealer he used to work at.

The only diffrence between the two heads (862 - 706) was the casting process they use

zippy

Wow, quite a bit of guessing and not direct info going on in here. Not meant at all of you, but a few. Not all of the aluminum 5.3L's were an L33. The Trailblazer, Envoy, Rainer, and SSR also had aluminum 5.3L's that weren't an L33. The L33 if it is a true L33 will have 243 or 799 castings on it. The only difference between them and the heads on the LS6 are the valves and valve springs. They get the standard length valves and they aren't sodium filled. They also get standard truck valve springs. Other than that they are the same casting. As one fast brick posted the compression difference was made up for the larger cc combustion chamber of the 243/799 head over the 862's by using the 4.8L piston. The L33 came in 05-07 classic extended cab 4x4 1500's only and they were the only aluminum block used in the half ton trucks until the new body style. If you want to make big power from the 5.3L, use the original L33 pistons (look them up for a 4.8L if they are hard to find), and use the 862 heads. Only use the 862 heads if you spend the extra little bit to have the intake valve changed to the 2.00" valves and mildly port them. If you do this you will have one bad *** 5.3L that with the right cam will run with a 5.7L or 6.0L in stock or cam only form.

old motorhead

iTrader: (10)

Thanks for clearing that up. The heads difinitely didn't fit what chevy described. The camshafts looked to be the same on the iron 5.3 vs. the aluminum block. The pistons were also dished on both motors. Looks like we didn't have an L33 after all. It's history now so I guess it really doesn't matter what it was. Learned a little though.

1FastBrick

iTrader: (17)

Zippy It is intresting that you say to use 2.0 valves. I wish I had the money to do actuall Dyno testing. Richard at WCCH said that when he tested these small bore heads with a 2.0 valve on the flow bench, He was seeing shrouding issuse with them. My first thought was that it may be do to the combustion chamber design. As the valve comes off the seat it is really close to the cumbustion chamber in these heads. I bet it would be no big deal if you enlarged that area and milled the heads to help compensate and maintain around the same CC... of course By the time you reinvent the wheel here I guess your probally not far off from a set of 243 castings any way... all well whats a few more paper wieghts around the garage. I got a couple sets and they were cheap enough

zippy

There is certainly a shrouding issue, but I feel that there is still a small gain even on the small bore with going to the bigger valve. I plan to test that this year some time. In a case such as this though if you are rebuilding the engine and possibly going with an overbore it will help with the shrouding issue. If I recall correctly, since the 2007 NNBS trucks came out all of them with 5.3L's and 4.8L's are using the 243 style head. Even with those trucks being heavier they are outstanding fast with just a few mods. I can only assume that the new heads are helping in some way.

1FastBrick

iTrader: (17)

Yes, I believe it has to do with the Heads combustion chamber... look at were it's at around the Valve on the 243 Vs. the 706 / 862. To me it does not apear to sit as close near the valve... The 243's were designed for the flow with the larger 2.00 Valve... Whats your thought on it???

1FastBrick

iTrader: (17)

In other words... Yes, I do agree from a performance stand point it could use the 2.00 Intake Valve, But I think for it to work properly with out hendering performance you would have to "clean up" the area around the Valve on the head so that the air can flow better around it and minimize it's chance of shrouding...

zippy

The chamber on the 243 is larger for sure. I agree that it was designed that way for a reason. I think that part of the benefit of the larger chamber with the 243 head is keeping more room around the intake valve to keep the flow smoother. If you go with the larger valve in the 862's there is still gain, but a little work in the chamber and some milling works out well. The 5.3L heads have been very popular for the F-body guys and they make very nice power with them.

1FastBrick

iTrader: (17)

They sure do make some nice Power... Would be nice if some one put the time in to do a stage 2 program for Us truck Guys... Maybe I will work on another set of heads after I get my new Motor together... I got a set of stage 1.5's from richard @ WCCH for my new 5.3L

hog

Also watch out for the LS4 5.3 that was used in the FWD apps.

Zippy;s info is correct.

the GEN3 (2004 and older) 5.3 alum. block used in SSR(300hp/335 lb/ft), Buick Rainier, Trailblazer EXT, Envoy XL,
were RPO LM4 and were rated from 290hp/325 lb/ft torque.

the GEN IV,RPO, LH6 and newer 5.3 alum block Chevrolet Trailblazer, Trailblazer EXT,GMC Envoy, Envoy XL, Envoy XUV, Buick Rainier, Saab 9-7X, Isuzu Ascender was rated at 300 hp and 330 lb/ft torque



Someone previously mentioned that the LM7/L59 iron block 5.3's cam was the same as the alum block L33 310 hp engine.

It is not, it has slightly more lift than the standard LM7/L59 5.3. There is another cam difference but I cant remember it off the top of my head.

peace
Hog