LM4 vs Lm7 for swap
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Joined: Jul 2017
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LM4 vs Lm7 for swap Hello all, Im sourcing an engine for my f100 project. I just pulled an lm7 from the junk yard only to get it home, and find out its got 201k on it, and seems to have missed a few oil changes. Bottom end is black, cent see cross hatching in the cylinders. So im looking to get another one. There is a few more lm7s in yards around here, but all unknown shape/mileage. There is an lm7 that is in a rolled 00 suburban that looks pretty clean, it was at auction and im going to see if i can find the mileage. In another yard there is an 04 trailblazer with the lm4 with around 125k on it. Im trying to decide if itll be worth it to spend the time pulling it vs pulling the lm7. the trailblazer calls for over 20 hours to r&r the engine vs the suburban calls for about 10 hours. Is the 80lb weight savings worth it? Is it higher compression, better heads on the lm4? Im not sure what direction im going to go with the engine, as far as na or boost but i want the option to boost it if i want. I cant fine much info on the lm4 strength compared to the lm7. Im open to everyones opinions. For reference, its going into a 68 f100 that im putting on a crown vic chassis. Initially i would like around 400-450 to the wheels.And maybe boost it to 6-700 down the road. sorry for the long post, i like to be thorough.
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Joined: Jul 2017
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another note, the lm4 has a pretty solid mileage number, i found an oil change sticker that said what mileage it was due next and it wasnt due till last month so i know its around there. the lm7, while it looks pretty clean, im not sure if ill be able to get a solid number for mileage, and id hate to spend the time in the 100+ degree heat pulling another engine that has a bunch of miles on it.
Staging Lane
Joined: Apr 2015
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From: Knoxville, TN
I just completed an LM4 swap into my car and the 80lbs was a huge consideration for me. 80lbs over the nose of a small car makes a pretty big difference in the handling characteristics.
I bought an 03 Envoy with 211k. I could hear the engine run and even got to drive it around the guys yard (it was wrecked so no highway driving). I pulled the motor and harness and sold the remainder of the Envoy for more than I paid for it. I wasn't planning on rebuilding the motor but I had enough to install an LS6 cam/springs and have a shop re-ring and bearing slap the block.
Not sure why the LM4 costs more to rebuild than a LM7. My local shop rebuilt my short block and did a valve job for $800. I assembled the heads and long block.
I bought an 03 Envoy with 211k. I could hear the engine run and even got to drive it around the guys yard (it was wrecked so no highway driving). I pulled the motor and harness and sold the remainder of the Envoy for more than I paid for it. I wasn't planning on rebuilding the motor but I had enough to install an LS6 cam/springs and have a shop re-ring and bearing slap the block.
Not sure why the LM4 costs more to rebuild than a LM7. My local shop rebuilt my short block and did a valve job for $800. I assembled the heads and long block.
TECH Addict
Joined: Oct 2016
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From: PDX-OR-USA
You'd have to swap the parts over.. If your going boost, the LM7 is a cool choice, but if I was staying normally aspirated,
I'd never add the 80 to 100 lbs , the Rainier is relatively light compared to some rigs, you will feel it in the corners, under braking etc.
I'd prb pull the original motor ,, see what stuff looks like then decide on the replacement.
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Joined: Nov 2021
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Depends on why you want the LM7? Doesn't your Rainier have the Oil pan with the axle passthrough?
You'd have to swap the parts over.. If your going boost, the LM7 is a cool choice, but if I was staying normally aspirated,
I'd never add the 80 to 100 lbs , the Rainier is relatively light compared to some rigs, you will feel it in the corners, under braking etc.
I'd prb pull the original motor ,, see what stuff looks like then decide on the replacement.
You'd have to swap the parts over.. If your going boost, the LM7 is a cool choice, but if I was staying normally aspirated,
I'd never add the 80 to 100 lbs , the Rainier is relatively light compared to some rigs, you will feel it in the corners, under braking etc.
I'd prb pull the original motor ,, see what stuff looks like then decide on the replacement.
