LM7 800whp+ build, best options?
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Teching In
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LM7 800whp+ build, best options? So i have a 2003 lm7 longblock with 150k, i got it for $30(!!) My goals are to go with an all out build of the motor, im a college student in an engines program and have access to a full facility to do all the required machining myself, saves me money. I also own 799heads and live in the same city as Katech (they will be porting and polishing the heads). My question is, what is the overall best route to achieve 800-1000hp? max displacement of 383ci with a fully forged rotating assembly, cam, heads obviously, and a heavy shot of wet? or should i go back down to a 4.8 and boost the **** out of it with e85 (i live in Mi, e85 is extremely accessible) orrr could i bore the cylinders to 3.903-3.905 give or take and destroke with a 4.8 crank with the same boost formula, this way it gets the power gain from the larger bore but also the smaller crank for higher revs, higher revs = potentially more boost. Maybe im completely wrong on that one and it wouldnt be worth it. What would be my best shot (no pun intended) at getting to my target goal of 800-1000hp?
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Teching In
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You can keep the bottom end as-is if you’d like. Lots of guys out there running this very setup making 1k and more to the wheel. You don’t have to throw any money at the short block if you don’t want to. Sure, the 4.8 arm is stronger because of the shorter stroke, but not necessary. You got a great price on the long block, no doubt. If and when this one craps the bed, grab another long block and do it again. I know that your a student currently in an engine program and this route seems boring to you most likely…which is why I don’t have a boosted build…I’m an engine guy and it’s just toooo simple to make 1k wheel with a turbo and I get bored very easily, but honestly there’s no tricks involved in this type of build. Heck, with a $30 long block, I’m not sure I’d even put headbolts in it. Your out nothing but time when it goes. The oil your gonna put in it cost more than the engine.
Now…being as how you have access to machining and such, in the meantime, you could always be planning a boost-friendly project at the same time. Go ahead and boost what you have for sure, and use it for a learning platform. Get the tuning right and play with boost control setups, get the fuel system right, etc. BUT in the meantime, plan yourself a boost build with maybe an iron 6 liter block, forged internals, quality fasteners, heads built to handle heat (good valves) and focus the second build on a more long lasting deal. When the LM7 goes, throw the better bullet in there, and with the right tuning, turn it up for more power. I’m just thinking out loud here of course. If you need a “class project” type of thing, this would be a good way to go. Turbo builds will require lots of lessons learned, and patience. Over build the crap out of the fuel system. You’ll thank me later. Learn to tune or invest in a really good tuner with boost experience. Tuning is everything here if you want longevity and/or power.
Sizing the turbo is something you’ll need help on from someone else besides me with turbo experience. I’m not very keen on what size turbo makes X amount of power, but there’s plenty of folks here that can quote that stuff because they do it all the time.
Now…being as how you have access to machining and such, in the meantime, you could always be planning a boost-friendly project at the same time. Go ahead and boost what you have for sure, and use it for a learning platform. Get the tuning right and play with boost control setups, get the fuel system right, etc. BUT in the meantime, plan yourself a boost build with maybe an iron 6 liter block, forged internals, quality fasteners, heads built to handle heat (good valves) and focus the second build on a more long lasting deal. When the LM7 goes, throw the better bullet in there, and with the right tuning, turn it up for more power. I’m just thinking out loud here of course. If you need a “class project” type of thing, this would be a good way to go. Turbo builds will require lots of lessons learned, and patience. Over build the crap out of the fuel system. You’ll thank me later. Learn to tune or invest in a really good tuner with boost experience. Tuning is everything here if you want longevity and/or power.
Sizing the turbo is something you’ll need help on from someone else besides me with turbo experience. I’m not very keen on what size turbo makes X amount of power, but there’s plenty of folks here that can quote that stuff because they do it all the time.
TECH Fanatic
Joined: Jan 2018
Posts: 1,251
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From: Dade City, Fl.
I agree with @Che70velle . use the LM7 and boost it pretty much as is to learn with. Cam plus injectors. When it "goes away" or you grow tired of it start your next build with a 4th gen 5.3l. No need to go through all the maching work and ported heads to get 800 wheel. $ spent where it isn't needed.Use that money for the trans,rear,suspension and...TIRES 
On The Tree
Joined: Jun 2019
Posts: 184
Likes: 66
From: HTown, Texas
I would look to swap out in internals for Gen IV 5.3L stuff if 800-100whp is your goal. The rods are stronger and use full floating pins, plus the crank will have the 58x wheel. On E85, you're going to be limited to about 15psi with a 24x crank and 411 ECM, whereas a 58x crank with the p59 ECM will let you get up to almost 30psi. If you use an aftermarket ECM, then it won't matter obviously.
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Thread Starter
Teching In
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Thank you guys so much for the informative replies. That is a great point for practicing tuning with it, as I want to get into that ballpark as well. Perfect opportunity to learn and blow it up without too much hurt feelings haha. Also I never knew that the 24x was limited for boost. Thank you for that insight. Gen IV internals sound like the ticket, the forged and max displacement build can wait for a ls2-3/lq4/lq9 to come around. 400+ cubes seems like the starting point for a NA/nitrous build.
Thread Starter
Teching In
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You can keep the bottom end as-is if you’d like. Lots of guys out there running this very setup making 1k and more to the wheel. You don’t have to throw any money at the short block if you don’t want to. Sure, the 4.8 arm is stronger because of the shorter stroke, but not necessary. You got a great price on the long block, no doubt. If and when this one craps the bed, grab another long block and do it again. I know that your a student currently in an engine program and this route seems boring to you most likely…which is why I don’t have a boosted build…I’m an engine guy and it’s just toooo simple to make 1k wheel with a turbo and I get bored very easily, but honestly there’s no tricks involved in this type of build. Heck, with a $30 long block, I’m not sure I’d even put headbolts in it. Your out nothing but time when it goes. The oil your gonna put in it cost more than the engine.
Now…being as how you have access to machining and such, in the meantime, you could always be planning a boost-friendly project at the same time. Go ahead and boost what you have for sure, and use it for a learning platform. Get the tuning right and play with boost control setups, get the fuel system right, etc. BUT in the meantime, plan yourself a boost build with maybe an iron 6 liter block, forged internals, quality fasteners, heads built to handle heat (good valves) and focus the second build on a more long lasting deal. When the LM7 goes, throw the better bullet in there, and with the right tuning, turn it up for more power. I’m just thinking out loud here of course. If you need a “class project” type of thing, this would be a good way to go. Turbo builds will require lots of lessons learned, and patience. Over build the crap out of the fuel system. You’ll thank me later. Learn to tune or invest in a really good tuner with boost experience. Tuning is everything here if you want longevity and/or power.
Sizing the turbo is something you’ll need help on from someone else besides me with turbo experience. I’m not very keen on what size turbo makes X amount of power, but there’s plenty of folks here that can quote that stuff because they do it all the time.
Now…being as how you have access to machining and such, in the meantime, you could always be planning a boost-friendly project at the same time. Go ahead and boost what you have for sure, and use it for a learning platform. Get the tuning right and play with boost control setups, get the fuel system right, etc. BUT in the meantime, plan yourself a boost build with maybe an iron 6 liter block, forged internals, quality fasteners, heads built to handle heat (good valves) and focus the second build on a more long lasting deal. When the LM7 goes, throw the better bullet in there, and with the right tuning, turn it up for more power. I’m just thinking out loud here of course. If you need a “class project” type of thing, this would be a good way to go. Turbo builds will require lots of lessons learned, and patience. Over build the crap out of the fuel system. You’ll thank me later. Learn to tune or invest in a really good tuner with boost experience. Tuning is everything here if you want longevity and/or power.
Sizing the turbo is something you’ll need help on from someone else besides me with turbo experience. I’m not very keen on what size turbo makes X amount of power, but there’s plenty of folks here that can quote that stuff because they do it all the time.
Yes especially with e85 where you are running richer by default. I've seen/heard max duty cycles on stock and even upgraded fuel systems running e85. Good point and healthy reminder
I would look to swap out in internals for Gen IV 5.3L stuff if 800-100whp is your goal. The rods are stronger and use full floating pins, plus the crank will have the 58x wheel. On E85, you're going to be limited to about 15psi with a 24x crank and 411 ECM, whereas a 58x crank with the p59 ECM will let you get up to almost 30psi. If you use an aftermarket ECM, then it won't matter obviously.
I would look to swap out in internals for Gen IV 5.3L stuff if 800-100whp is your goal. The rods are stronger and use full floating pins, plus the crank will have the 58x wheel. On E85, you're going to be limited to about 15psi with a 24x crank and 411 ECM, whereas a 58x crank with the p59 ECM will let you get up to almost 30psi. If you use an aftermarket ECM, then it won't matter obviously.
On The Tree
Joined: Jun 2019
Posts: 184
Likes: 66
From: HTown, Texas
I'm talking about the different operating systems available for the stock ECU's. The 411 ECU's can use a truck OS to enable flex fuel for E85, but are limited to a 2bar VE Table. The P59 ECU can use an OS with flex fuel and a 3bar VE Table.
I might be wrong in that you might be able to use a P59 ECU with a 24x crank, but the wiring is different as Gen III cars with 24x cranks normally use the red and blue connector and the 58x cars usually use blue and green.
I might be wrong in that you might be able to use a P59 ECU with a 24x crank, but the wiring is different as Gen III cars with 24x cranks normally use the red and blue connector and the 58x cars usually use blue and green.