LM4 or LM7?

2003 CHEVROLET S-10
180,000 MILES • 4WD • AUTOMATIC
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THEDOGSS
  • MEMBER
  • 3 POSTS
Hi. I watched your complete breakdown and rebuild of the LM7 on YouTube and it's perfect. I want to do a 5.3 build and swap it into my 4WD 03 S-10 p/u and I was wondering if a 2003 LM4 might be a better application than a 2005 LM7. I have access to either engine. I plan on doing almost the exact same build as yours to start, and possibly boost in the future. I don't know if the aluminum block would be better because the steel might weigh down the nose of the pick-up too much or would I be sacrificing reliability. Thank you for your help!
Apr 7, 2022 at 12:48 AM
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STEVE W.
  • ✓Experienced Mechanic
  • 15,320 POSTS
The lighter engine is better for the weight as it's only 50 pounds heavier than the 4.3. The iron version is 120 pounds heavier. However, it's not hard to get springs to handle the extra weight as they made them for the trucks with plows on them. The better version is the 05 rather than the 03 lm4, it has a better bottom end with heavier rods and better cam availability. You will likely need a different oil pan to clear and may need to drill the dipstick hole depending on the pan. Plan out what you will be using the truck for, the LS can be set up as a low-end torque monster or a high HP fire breather or in between and getting it wrong can be miserable.
Apr 7, 2022 at 8:57 PM
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THEDOGSS
  • MEMBER
  • 3 POSTS
Hi Steve, thank you for your help. You said the LM7 has heavier rods but I'm going to be doing the build with forged rods. My plan is to keep it fairly simple and make max 500hp and just have a fun street truck. That being said, if I decide to add forced induction to the truck in a year or so, I wanted to have a block that could withstand the added power, which is my worry with the aluminum LM4.
Apr 8, 2022 at 2:14 AM
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STEVE W.
  • ✓Experienced Mechanic
  • 15,320 POSTS
The LM4 has been taken to over 850hp without any issues so 500hp isn't a problem.
Apr 8, 2022 at 12:03 PM
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