Difference between 2000-2003 and 2004 - 2006 +10hp 5.3 LM7 L59

[Burban22]

Anyone know what the difference is between these two generations?
What was changed on the later versions to increase +10hp and +5tq. Intake? Cam? Just the tune?
I have an 03 Burban early build with 8th digit T = LM7 so I got the 285hp LM7. I did get it blackbear tuned which definitely woke it up.

2000 - 2003
285 hp@ 5200 rpm
325 tq @ 4000 rpm

2004 - 2006
295 hp @ 5200 rpm
330 tq @ 4000 rpm

 

[Marky Dissod]

Besides switching from a mechanical fan attached the crank, to a pair of detached electrical fans?

 

[Fless]

2004s still came with a fan clutch. Electric fans didn't come in the Hoes until 2005.

 

[Burban22]

Yea I still have mechanical fan which I don’t mind having.

In addition to Blackbear tune I also replaced the stock muffler with a magnaflow 12588 which is nearly a direct swap (needs to be welded). Also added a AFE 54-74101 intake.

I’ve done the easy bolt-ons and will prob stop there for now.

Wondering if anyone knows where the 10hp gain came from in 2004.

 

[Burban22]

Muffler and intake pics attached

 

[Burban22]

2004+ 10hp gain due to flex fuel capable?

 

[Fless]

The LM7 isn't Flex Fuel, is it?

 

[Burban22]

Correct LM7 isn’t flex fuel compatible and that’s the main difference between LM7 and L59 according to multiple posts.

• They are 99% the same. I realized this past weekend that I've had an L59 the whole time I thought it was an LM7. Only differences are more injector flow (33 lb/hr vs 22.5-28, depending on the year iirc), different fuel injector connectors (EV6, I believe, vs minitimer), and a few differences in the ECU. Depending on the year, it got a sensor to detect the ethanol content of the fuel, and also depending on the year, it kept return rails longer than the non-flex fuel motors did.
  
  Besides that, it is literally the exact same motor.

L59 Vs. LM7 Engine : What’re the Differences? | Rx Mechanic

Distinguishing two engines having similar physical looks from the same manufacturer can be tricky. In this L59 Vs. LM7 debate, get both engines reviewed.

rxmechanic.com

The factory L59 injectors were rated at 33-36 lbs. and support about 435 hp at the wheels. Note the 2001-04 return style fuel system cam with 33lb injectors running at 50 psi, while the 2005-07 engines were returnless and had 36.6lb @ 58psi injectors. The easy way to know which you have is the 2002-04 rails were plastic and the 2005-07 rails were stainless.

L59 5.3L Engine Upgrade Guide: Expert Advice for L59 Mods to Maximize Performance

[Editor’s Note: This L59 engine upgrade guide is part of a series of LS engine upgrade guides assembled by a team of LS experts at Summit Racing that we are sharing at …

www.onallcylinders.com

 

[Burban22]

But different injectors shouldn’t account for the 10hp difference unless L59 was tested while using e85 but I’d think that would be more than +10hp difference.

 

[Fless]

Correct LM7 isn’t flex fuel compatible and that’s the main difference between LM7 and L59 according to multiple posts.

• They are 99% the same. I realized this past weekend that I've had an L59 the whole time I thought it was an LM7. Only differences are more injector flow (33 lb/hr vs 22.5-28, depending on the year iirc), different fuel injector connectors (EV6, I believe, vs minitimer), and a few differences in the ECU. Depending on the year, it got a sensor to detect the ethanol content of the fuel, and also depending on the year, it kept return rails longer than the non-flex fuel motors did.
  
  Besides that, it is literally the exact same motor.

L59 Vs. LM7 Engine : What’re the Differences? | Rx Mechanic

Distinguishing two engines having similar physical looks from the same manufacturer can be tricky. In this L59 Vs. LM7 debate, get both engines reviewed.

rxmechanic.com

The fuel pumps are also different, gas vs FF. FF has slightly less pressure but more flow, IIRC.