Building LM7
Thread Starter
Teching In
Joined: Feb 2025
Posts: 22
Likes: 4
From: Chicago
Building LM7 Hey guys I am looking for some help with my build I have a 2003 Silverado 1500, 5.3 LM7 Today I went out to my car and when I started it, I heard lifter tick. Came out of nowhere. Any recommendations on new ones? Upgraded. I already have a set of brand new JEGS 243 Heads laying in my room.I was told I will need to mill them down 0.025inches to keep stock compression.I am looking for around 400whp NA I am looking for recommendations for my build. Here is what I have in mind, let me know if some things don't work together for what I'm looking for. This is the first LS family engine I am working on so any help is appreciated. Build : • Head - JEGS 243 0.025 mill (Comes with Valves and Springs)• Headgasket -BTR MultiLayer 0.51" (BTR98544)• Lifters - Haven't Picked Yet• Pushrod- BTR OnePiece OE7400-16• Camshaft - Sloppy Mechanics Stage 2 with their gasket kit for the cover etc Or should I just get the whole sloppy Mechanics stage 2 KIT for 750$ which includes the pushrods and new springs and pushrods As far as everything else. I think i know what route im taking, TBSS intake manifold. Wont get a huge throttle body for no reason. I'm gonna stick to around the 87mm TB size. Along with the 34lb TBSS injectors. I shouldn't have a problem with 400whp out of this engine build
Stock Throttle Body will be fine for all that the 5.3l doesn't move enough air through it to need bigger. Price the kit out compared to individual prices with shipping see what's better.
Thread Starter
Teching In
Joined: Feb 2025
Posts: 22
Likes: 4
From: Chicago
S = Stock J = Jegs
S Exhaust Valve 1.55in
J Exhaust Valve 1.57
S Combustion Chamber CC 64.5
J Combustion Chamber CC 69
TECH Fanatic
Joined: Dec 2019
Posts: 1,129
Likes: 478
69cc combustion chamber? You're going to lose a noticeable amount of power and torque. Those heads would be a downgrade for you.
Going from a 61.15cc head to a 69cc head will lower your compression ratio to 8.8:1.
Stock vs stock on a mild 5.3, the stock 706/862 heads have been proven to outperform the 243 heads.
You should consider selling the heads and rethinking your whole combo.
Going from a 61.15cc head to a 69cc head will lower your compression ratio to 8.8:1.
Stock vs stock on a mild 5.3, the stock 706/862 heads have been proven to outperform the 243 heads.
You should consider selling the heads and rethinking your whole combo.
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Thread Starter
Teching In
Joined: Feb 2025
Posts: 22
Likes: 4
From: Chicago
69cc combustion chamber? You're going to lose a noticeable amount of power and torque. Those heads would be a downgrade for you.
Going from a 61.15cc head to a 69cc head will lower your compression ratio to 8.8:1.
Stock vs stock on a mild 5.3, the stock 706/862 heads have been proven to outperform the 243 heads.
You should consider selling the heads and rethinking your whole combo.
Going from a 61.15cc head to a 69cc head will lower your compression ratio to 8.8:1.
Stock vs stock on a mild 5.3, the stock 706/862 heads have been proven to outperform the 243 heads.
You should consider selling the heads and rethinking your whole combo.
It would also lower the cc to around 64
I just thought I got some nice durable heads and wanted to work around them. I mean if all I need to do is mill them down .025 to match the 706 head then all parts would just be direct swap from 706 to 243. Same length pushrods Same size head gasket .051 etc.
I thought it was a good choice to build around them as it has bigger intake and exhast valves than the 706 heads at like 1.85 vs 2inch
But I am just learning in the LS world, I come from Jap crap and germans before this so thank you for the advice. I might consider selling them.
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Verdad Gallardo TECH Fanatic
Joined: Dec 2019
Posts: 1,129
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Even if you milled them down to the stock 243/799 chamber cc, you would be at 9.2:1 compared to the factory 9.5:1.
Here is a dyno comparison of stock 5.3 heads vs 243 heads on a cammed 5.3. The stock 5.3 heads outperformed the 243/799 heads everywhere on the graph, with the exception of maybe 1 small blip, in an engine with a greatly increased airflow demand. It would be a shame to have machine work done to your heads just to lose power.
Here is a dyno comparison of stock 5.3 heads vs 243 heads on a cammed 5.3. The stock 5.3 heads outperformed the 243/799 heads everywhere on the graph, with the exception of maybe 1 small blip, in an engine with a greatly increased airflow demand. It would be a shame to have machine work done to your heads just to lose power.
So .025 shorter Pushrod.
And that's if the Jegs Heads are the same Pedistal height as the stock GM LS Heads. Regardless, if you put a Cam in it you need to measure anyway so there's that.
Thread Starter
Teching In
Joined: Feb 2025
Posts: 22
Likes: 4
From: Chicago
69cc combustion chamber? You're going to lose a noticeable amount of power and torque. Those heads would be a downgrade for you.
Going from a 61.15cc head to a 69cc head will lower your compression ratio to 8.8:1.
Stock vs stock on a mild 5.3, the stock 706/862 heads have been proven to outperform the 243 heads.
You should consider selling the heads and rethinking your whole combo.
Going from a 61.15cc head to a 69cc head will lower your compression ratio to 8.8:1.
Stock vs stock on a mild 5.3, the stock 706/862 heads have been proven to outperform the 243 heads.
You should consider selling the heads and rethinking your whole combo.
also was recommended that the Truck Norris Stage 2 cam would probably be best for my application.