Project LS Swap LR4 4.8L

Reusing the plum crazy truck from the website I decided to build a LS swap truck using a truck motor. I thought I was getting a deal on a  2003 LM7 5.3L motor with 4L60E trans  but not only was the transmission near death when I got it installed but the 5.3L turned out to be a 4.8L LR4 motor and the ONLY way to really tell the difference is to remove the oil pan and windage tray and look at the number on the crankshaft.  When I recently pulled this motor for replacement for project plum crazy, I looked at that number and big 482 stamped in crank which = short 3.267 stroke crankshaft rather than the 216 casting 3.622 stroke in all other LS engines.  Which not only makes this engine a tiny 293ci 4.8L motor rather than a 325ci 5.3L motor but that short stroke really affects the torque which is what raised the red flag during those dyno pulls.

At the time of the install i was unaware this was a 4.8L engine.  Too trusting I guess.  I put a LS1 hot cam in like I did the dark nite project truck which sounds good and is VERY streetable and I have changed the gears to some 3.73 gears and the Auburn Pro series posi that I acquired. I

I am just going to run stock exhaust manifolds and run 2.5″ pipe to the Flowmaster FLO-Y250300 collector that was on the truck from the last project and should handle the power output just fine.

 For valve springs, I used these beehive springs from Scoggin Dickey Chevrolet.   price is reasonable and I am not going to go thrashing this thing over 6000 rpms so I believe they will be just fine.

For motor mounts I am going to use these adapters from summit racing.

Click here for more information about part# TRD-4572

For the AC, I should have new brackets manufactured based on the modified set that I made for the dark nite project which should make running TBI AC on a LS truck motor pretty much a bolt on deal.

Once again, I will be getting to work over the throttle body. They are going to bore it out to 77mm and shaving the throttle shaft to get me some more air flow from the 6.0’s throttle body as the motor had drive by wire so I upgraded the 6.0L to 80mm and using the 77 on this project.

I will be running 2 electric fans on the radiator to give me that extra little bit of power from this engine and they were about the only things left over from the black magic project.

When it comes to wiring this computer system I will try to list the resources for that wiring and let you know how hard it was and how it turns out.  There is a lot of swap information on

Now for the wiring, I have found a company to do custom wiring harness to run any LS based engine with a LS1 computer which gives me idle control as well as a nice clean easy to install wiring harness that matches my injectors which has a mini delphi plug instead of EV1 that LS1 cars use as well as my motor came with a nice 5 wire MAF that I wanted to utilize instead of the 3 wire the LS1’s use. If you need help getting the wiring you need for your engine, I will be glad to help you determine what you need and order the harness which is around $550 and looks great.  If you mark the wiring that you cut as you remove your TBI harness it should be really easy to drop this harness in with your engine.  You will need a TACH converter box from as the LS1 computer outputs a different type of tach signal than your older GM tach is looking for so it can change the signal type as well as calibrate the tach if your upgrading a 6cyl truck/tach to a V8.  I pained my way through modifying the stock wiring harness to run motor and it was NOT painless and didn’t look good so I ordered the harness below which looks awesome and has a LOT less wires due to the unnecessary crap we are not using on this swap and gives me all the stuff I need to control the engine and transmission for reasonable money.   When I started the 6.0L project I couldn’t find a harness under $800 so when I found these that added nice webbing over the wiring for a nice clean look. I abandoned my mess and went this route.

When I finally hit the dyno with this project and the numbers came out pretty close to what I expected. I was hoping for a little more but I was running 87 octane fuel which is what I plan to run in this truck as well as just the stock iron manifolds instead of headers and such so its pretty basic swap.  Motor you can see on the graph pulled 272hp and 255lb of weather corrected torque as it was plenty hot and humid when I did that dyno pull.   Considering a stand 20% drivetrain loss for it being an automatic that equals 340hp and 320lb of torque which is same torque as the plum crazy TBI project truck pulled and but  it took 5000rpms to get that peak torque number where the TBI motor got its 255rwtq by about 3000 rpms.  now the horsepower flew past the old 350 TBI plum crazy horsepower at 3000 rpms to climb on up to a pretty decent number.

Bottom line: this 4.8L motor needs to turn more rpms to run well and that is why this truck now sports a 3.73 gear instead of a 3.42 like it did as a TBI truck and really needs about a 3000 rpm stall converter.  Once you get the rpms up the truck will fly and it doesn’t do bad for towing but a well built 350 TBI motor can walk all over it on the bottom end.  Bang for the buck, I have about $2500 in this whole engine project including the wiring and such and wasn’t the easiest installation but not terrible bad.  Would I do this to another TBI truck, maybe.  Most likely an S10 that doesn’t need as much torque. But the truck is pretty quick and would be a lot quicker if I were to put a higher stall converter in the thing and who knows I might snag one off ebay or something but that won’t affect those dyno numbers just helps me get into that motors powerband quicker.  Truck does knock down 20mpg pretty consistently though.

So what did I learn from this projec, check the engine out before you hand over cash and I learned that even a modest cam like the LS1 hot cam could make a GOOD 70hp over the tuned project stocker truck with actual 5.3L engine.

GM fuel injection for the average guy