Any major differences between LM4 and LM7??
03-31-2017, 09:01 AM
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Any major differences between LM4 and LM7?? So I'm still trying to find the engine that's going to be my building block for my project, and I'm planning to go look at some junkyards this weekend and hopefully bring home a used but in good shape 5.3, hopefully for cheap.
I have been initially locked in on getting an LM7, but after doing some more research I have found that an LM4 is basically the same thing, just with an aluminum block and 5 less HP. To me it seems worth it to sacrifice 5 horsepower to get some weight reduction up front. I'm just wondering is there anything specific I need to know that separates the 2 that would make it more of a chore to get the LM4 instead of the LM7? I've been looking at pre-2002 5.3s, because I want to avoid the flex fuel options as well as the DOD. The plan is to put on fbody oil pan and water pump/accesories, ls1 or ls6 intake and fuel rail,some bigger injectors, ls9 head gaskets and ARP head bolts, and push 12 psi through it with a T76. Any advice on that set up at all is greatly appreciated, as this is my first swap. This will all be going into a 05 RX8 GT, and will be mated with a T56.
I appreciate all feedback, thanks!
I have been initially locked in on getting an LM7, but after doing some more research I have found that an LM4 is basically the same thing, just with an aluminum block and 5 less HP. To me it seems worth it to sacrifice 5 horsepower to get some weight reduction up front. I'm just wondering is there anything specific I need to know that separates the 2 that would make it more of a chore to get the LM4 instead of the LM7? I've been looking at pre-2002 5.3s, because I want to avoid the flex fuel options as well as the DOD. The plan is to put on fbody oil pan and water pump/accesories, ls1 or ls6 intake and fuel rail,some bigger injectors, ls9 head gaskets and ARP head bolts, and push 12 psi through it with a T76. Any advice on that set up at all is greatly appreciated, as this is my first swap. This will all be going into a 05 RX8 GT, and will be mated with a T56.
I appreciate all feedback, thanks!
04-03-2017, 10:53 AM
#2
TECH Resident
The biggest difference ,in my mind,is the ability to bore the block. I got a LM7 1999 and I can bore it to 5.7 and I will have a iron LS1..I'm not worried about the extra 100 pounds for my truck its going in. To get rid of the flex fuel is not cheap either.
04-13-2017, 02:19 PM
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Besides the aforementioned ability to bore the block and the obvious weight differences, your project goals should be considered. N/A build with just H/C/I? The LM4 is probably fine. If you want to go forced induction there is an argument to be made for iron (LM7) in durability. You should check out Matt's builds on youtube under "Sloppy Mechanics" all of which revolve around junkyard LS Engine combos with boost. A common theme with those builds is the iron block. Good luck with the build.