Help with internals!
TECH Senior Member
Joined: Jun 2016
Posts: 22,291
Likes: 3,616
From: Central Cal.
My first thought: Spend money on a good oiling system over anything else. A completely stock bottom end will get you 7000+ RPM, it's the valvetrain that needs to be upgraded, especially for sustained high RPM. A 5.3 isn't the best engine to start with, as the longer stroke and smaller bore can inhibit high RPM breathing. This is why the smaller 4.8 liter engines love to rev, even though they share a bore size with the 5.3. If you're going as far as to put together a forged rotating assembly, why even keep the LM7 iron block? That's going to slow you down and amplify understeer by making you nose heavy. If you want to keep it, have it bored out to LS1 size and it will be a 5.7 liter, which will easily meet your 400 HP goal ( I'm assuming you meant RWHP ). One thing to note, a 4.8 and a 5.3 that are fitted with identical cams, heads, valvetrain and intake manifolds will make within about 10HP of each other, but the 4.8 will peak out around 1200-1500 RPM higher than the 5.3.( the 4.8 makes quite a bit less peak torque, however ). If revs are what you're after, going slightly smaller will make that easier to accomplish. If it were my build? I'd go find an L33 or LH6 aluminum block, bore it to LS1 size and install a 4.8 crank. Install Summit ProLS domed pistons and H-beam rods, then mill a set of 706 heads to 58CC and have them CNC ported with lightweight valves. 312 cubic inches, about 11.7:1 compression, and 8K RPM ability. Should also make over 500 crank horsepower with ease. I'm sure others with more experience in the road race realm will chime in.
Thread Starter
Teching In
Joined: Sep 2024
Posts: 17
Likes: 6
My first thought: Spend money on a good oiling system over anything else. A completely stock bottom end will get you 7000+ RPM, it's the valvetrain that needs to be upgraded, especially for sustained high RPM. A 5.3 isn't the best engine to start with, as the longer stroke and smaller bore can inhibit high RPM breathing. This is why the smaller 4.8 liter engines love to rev, even though they share a bore size with the 5.3. If you're going as far as to put together a forged rotating assembly, why even keep the LM7 iron block? That's going to slow you down and amplify understeer by making you nose heavy. If you want to keep it, have it bored out to LS1 size and it will be a 5.7 liter, which will easily meet your 400 HP goal ( I'm assuming you meant RWHP ). One thing to note, a 4.8 and a 5.3 that are fitted with identical cams, heads, valvetrain and intake manifolds will make within about 10HP of each other, but the 4.8 will peak out around 1200-1500 RPM higher than the 5.3.( the 4.8 makes quite a bit less peak torque, however ). If revs are what you're after, going slightly smaller will make that easier to accomplish. If it were my build? I'd go find an L33 or LH6 aluminum block, bore it to LS1 size and install a 4.8 crank. Install Summit ProLS domed pistons and H-beam rods, then mill a set of 706 heads to 58CC and have them CNC ported with lightweight valves. 312 cubic inches, about 11.7:1 compression, and 8K RPM ability. Should also make over 500 crank horsepower with ease. I'm sure others with more experience in the road race realm will chime in.
Joined: Apr 2006
Posts: 3,890
Likes: 1,137
From: Grand Rapids, Michigan
Honestly, I just came up with that combo off the top of my head. Knowing what works with LS engines and engine design in general, I felt that would be a stout combination. I know zero about road racing ( although that's going to change with my new daily, a 2013 VW GTI ) so I don't want to make any road course specific recommendations. One thing I can tell you is, Summit makes their H-Beam rods in a 4.8 liter length ( approximately ), so the engine would have a killer rod to stroke ratio as well.
Thread Starter
Teching In
Joined: Sep 2024
Posts: 17
Likes: 6
Honestly, I just came up with that combo off the top of my head. Knowing what works with LS engines and engine design in general, I felt that would be a stout combination. I know zero about road racing ( although that's going to change with my new daily, a 2013 VW GTI ) so I don't want to make any road course specific recommendations. One thing I can tell you is, Summit makes their H-Beam rods in a 4.8 liter length ( approximately ), so the engine would have a killer rod to stroke ratio as well.
Joined: Apr 2006
Posts: 3,890
Likes: 1,137
From: Grand Rapids, Michigan
I get all my machining done through Steve Morris Engines, but he's local to me so it's easier. His work is top notch, however. I know there are a few builders on the site here, I'm sure if you make a feeler post someone will reply.
Thread Starter
Teching In
Joined: Sep 2024
Posts: 17
Likes: 6
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