crankshaft for lm7 with boost

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Jun 16, 2023 | 10:41 PM

Firebirdboi

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crankshaft for lm7 with boost

so im building an LM7 for my firebird but idk what the best crankshaft to use for longevity is since im going to turbo the motor. any help or suggestions?

Last edited by Firebirdboi; Jun 21, 2023 at 06:52 PM.

Jun 21, 2023 | 02:31 PM

Black_Sunshine_99

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Stock, if its a gen IV motor, reuse the entire rotating assembly.
Gen III can be used as well, just not quite as stout.

Jun 21, 2023 | 06:41 PM

G Atsma

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From: Central Cal.

Quote:

Originally Posted by Firebirdboi

I'm building an LM7 for my firebird but idk what the best crankshaft to use is since I'm going to turbo the motor. any help or suggestions?

If your power level will be 700 or less, the stock lower end should be fine.

Jun 21, 2023 | 06:49 PM

Firebirdboi

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Quote:

Originally Posted by G Atsma

If your power level will be 700 or less, the stock lower end should be fine.

so i’m going for 450-500 turbod, and i was planning on replacing pistons and rods anyway. should i get the crankshaft resurfaced or do i just get it balanced with the pistons?

Jun 22, 2023 | 09:02 AM

Black_Sunshine_99

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Quote:

Originally Posted by Firebirdboi

so i’m going for 450-500 turbod, and i was planning on replacing pistons and rods anyway. should i get the crankshaft resurfaced or do i just get it balanced with the pistons?

450-500whp will be a cake walk using something like a 7875 and could definitely use the stock rotating assembly.
If you're planning on pistons and rods regardless, then you might as well check out Summit Racings 5.3 rotating assemblies.
For a few bucks more you can get a matching crankshaft and all the head room you'll need to turn the power up later.

Jun 23, 2023 | 09:34 AM

ddnspider

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I wouldn't think about a crank until i was north of 1000whp.

Jun 23, 2023 | 10:28 AM

strutaeng

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Quote:

Originally Posted by Firebirdboi

so i’m going for 450-500 turbod, and i was planning on replacing pistons and rods anyway. should i get the crankshaft resurfaced or do i just get it balanced with the pistons?

How does the crankshaft journals look? A lot of folks pull these engines with high miles and the crank journals look really good and slap new bearings. Maybe just a polish?

Only if the journals look bad you'd get it turned or ground.

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Jun 23, 2023 | 11:08 AM

LQ4-E39

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Years of 14-15psi on my stock LQ4 and it's never even had the heads off. I pulled a rod cap once just out of curiosity while the oil pan was off and the bearings still looked great after 200K+. Send it

Jun 23, 2023 | 08:01 PM

#10

Firebirdboi

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Quote:

Originally Posted by G Atsma

How many miles on the engine?
Is it still together? If so, and it's under 200k miles, run it as is unless there are obvious issues.

so the milage is unknown but there is obvious damage to the crank, i don’t know if it can be saved but if it can i’m willing to reuse mine

Jun 24, 2023 | 07:29 AM

#11

strutaeng

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Quote:

Originally Posted by Firebirdboi

so the milage is unknown but there is obvious damage to the crank, i don’t know if it can be saved but if it can i’m willing to reuse mine

Dang, that looks bad. Did any of the main bearings spin on the journals? If so, may be better to start with another better block.

Seems like crankshaft is pretty rough also.

Jun 24, 2023 | 09:29 AM

#12

strutaeng

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Quote:

Originally Posted by Firebirdboi

so the milage is unknown but there is obvious damage to the crank, i don’t know if it can be saved but if it can i’m willing to reuse mine

Dang, that looks bad. Did any of the main bearings spin on the journals? If so, may be better to start with another better block.

Seems like crankshaft is pretty rough also.

Jun 24, 2023 | 12:16 PM

#13

3 window

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Looks like you’re gonna end up getting into it pretty good. Do yourself a favor and clean everything really good while it’s apart. All the carbon from the ring lands, oil gallies, try and get it spotless. It’s obvious that that engine hasn’t been taken care of.

Jun 25, 2023 | 08:40 AM

#14

Firebirdboi

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Quote:

Originally Posted by strutaeng

Dang, that looks bad. Did any of the main bearings spin on the journals? If so, may be better to start with another better block.

Seems like crankshaft is pretty rough also.

so i’ve got bad news, i was inspecting the block further and i found a crack 🙂.
so i’m thinking of getting an lq4?? i’m all ears

Jun 25, 2023 | 09:13 AM

#15

strutaeng

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Quote:

Originally Posted by Firebirdboi

so i’ve got bad news, i was inspecting the block further and i found a crack 🙂.
so i’m thinking of getting an lq4?? i’m all ears

Yes! Well, as long is not in this condition. 🫣

Jun 26, 2023 | 09:39 AM

#16

Black_Sunshine_99

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That looks like boat anchor material to me.
I'd look for an L33 or an LC9 5.3 but that's just me, you're gonna pay a mint for an aluminum 6.0L.

Jun 27, 2023 | 07:08 PM

#17

Project GatTagO

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From: Little Austin

Quote:

Originally Posted by Firebirdboi

so im building an LM7 for my firebird but idk what the best crankshaft to use for longevity is since im going to turbo the motor. any help or suggestions?

Where are you located? I have a low milage Gen 4 5.3L complete rotating assembly. Crank will need a polish (has mild surface rust), but it is way better than what you have.

Andrew

Jun 28, 2023 | 08:26 AM

#18

ddnspider

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Some of you will hate this, but I've bought a reman stock crank from the parts store and sent back my torn up crank as the core. It was cheap and had no issues and the new crank looked good.

Jul 8, 2023 | 11:43 AM

#19

gnx7

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I would get a used Gen4 engine (2005+) which has the better connecting rods, gap the rings for boost, add BTR LS9 head gaskets, head studs, and put in a large enough injector for 1000rwhp on e85 as you are going to quickly outgrow your 500rwhp goals and get bored of it. The Gen3 rods most people say beyond about 600rwhp will bend over time.... the Gen4 rods look much beefier and have an H-beam shape.