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Ls1 vs LM7 5.3

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Old Jun 15, 2025 | 11:44 AM
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Default Ls1 vs LM7 5.3

Really wanting to know if there is a noticeable difference between the 5.7 LS1 and a iron 5.3L.

Based on my short research the power difference is about 20HP and 100lbs?

I recently found out the 02 camaro I purchased a few years ago was swapped to a 5.3L and was wondering how much power I'm missing out on.

I do just weekend joy rides so nothing crazy on a track or nothing. The thought crossed my mind to buy a 5.7 LS1 but finding a good one for under $5k is not possible in my area.

Aside from the swap the previous owner put some SLP exhaust on it and the weiand ram air intake. With the 862 heads on the motor. I assumed I gotta be close to 300hp potentially?


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Old Jun 15, 2025 | 12:01 PM
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Factory the 5.3l is 9.6:1 compression and 80lbs heavier than the LS1, so there's that aspect. The Weiand Intake on that is about 25lbs so you're up 105lbs now, it has the same flow of the LS6 Intake but aluminum so you have heat soak which is power loss.

LS1 is 10.2 compresion, bigger bore hence why it's 346ci displacement. The 241 Heads on it flow a hair more on the Intake side due to bigger Valves, but them 862 Heads on a LS1 have been proven to be a gain because they have smaller chambers which make higher compression.

If it was me and you wanted to get into it, two options here that'll work well:

Find a cheap 5.3l shortblock and have that bored to a 3.905 Bore, get the correct Flat Top Pistons for that bore have it all balanced and built, slap some 243 Heads on it with a LS6 Intake. It'll make some power.

Or

Find a 6.0l LQ4 or LQ9, put 243 Heads on it with a LS6 Intake, and let it rip. Putting a small Cam in either will be fun.

Comes down to how much you want to spend on it all and what you want to do.

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Old Jun 15, 2025 | 12:28 PM
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Originally Posted by the_merv
Factory the 5.3l is 9.6:1 compression and 80lbs heavier than the LS1, so there's that aspect. The Weiand Intake on that is about 25lbs so you're up 105lbs now, it has the same flow of the LS6 Intake but aluminum so you have heat soak which is power loss.

LS1 is 10.2 compresion, bigger bore hence why it's 346ci displacement. The 241 Heads on it flow a hair more on the Intake side due to bigger Valves, but them 862 Heads on a LS1 have been proven to be a gain because they have smaller chambers which make higher compression.

If it was me and you wanted to get into it, two options here that'll work well:

Find a cheap 5.3l shortblock and have that bored to a 3.905 Bore, get the correct Flat Top Pistons for that bore have it all balanced and built, slap some 243 Heads on it with a LS6 Intake. It'll make some power.

Or

Find a 6.0l LQ4 or LQ9, put 243 Heads on it with a LS6 Intake, and let it rip. Putting a small Cam in either will be fun.

Comes down to how much you want to spend on it all and what you want to do.
Always the man with the answers. Appreciate all the insight!

I like the thought of the 6.0 and it feels like a cheaper route potentially. Where I'm located I can find these motors fairly easily. I'm hoping to make upper 300 low 400HP for this car, I'm just a weekend driver so I don't need anything crazy.
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Old Jun 15, 2025 | 03:12 PM
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Do have headers or stock manifolds?
Also stock 5.3 cam?
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Old Jun 15, 2025 | 03:26 PM
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Originally Posted by LS1 TJ
Do have headers or stock manifolds?
Also stock 5.3 cam?
I have no clue the history of this motor.

I would assume it's got the stock 5.3 cam. Headers and Manifolds probably came off the previous LS1.
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Old Jun 15, 2025 | 03:55 PM
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Originally Posted by SlimmyJimmy
Headers AND? Manifolds probably came off the previous LS1.
You have EITHER tubing headers or cast manifolds. Not both.
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Old Jun 15, 2025 | 04:02 PM
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Originally Posted by G Atsma
You have EITHER tubing headers or cast manifolds. Not both.
Gotcha, i was confused what you were asking for.

I have the cast manifolds. Looking at Google comparison between LM7 and LS1. These were off the LS1 engine. Definitely not tubed headers sadly.
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Old Jun 15, 2025 | 04:16 PM
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You have the stock LS1 Fbody Manifolds. Like I said in your other thread someone crammed a 5.3l in there because it was a cheap fix. Blown up LS1 out, 5.3l in. Everything else is the same.
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Old Jun 15, 2025 | 10:36 PM
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I believe I have seen that at the crank, there is about a 50hp and 50tq difference between the 5.3s and the later 5.7s that have the ls6 intake. At the wheels it is probably about 40 and 40.
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