LS3 donor vehicles

I understand that there are some different variations of the LS3 engine in various cars. For instance, the LS3 that came with an auto trans in the Camaro is better known as an L99 and has the dumb stuff like VVT and AFM that nobody wants for a swap with a manual trans.

However, I understand that this L99 engine didn't come in Corvettes with the auto trans and that version of the LS3 is okay to use. Aside from having the ECM reflashed for use with a manual trans, are there other complications of using an engine from an auto trans donor car?

All help much appreciated!

It depends on how easy you want to make your conversion. You will find that an engine out of a Camaro or Firebird will fit easier in the 944 than a Corvette engine. The front end belt drive system clears the frame rails better and a stock Camaro intake manifold will allow the hood to close without excessive modifications. Any LS engine will at least need the PCM re-flashed to eliminate the theft deterrent system so I wouldn't worry too much about if the donor vehicle was an automatic transmission or not. All the changes to the programming can be done at the same time.

really it all comes down to your end goal and how much the engines cost. accessory drive is a big thing to consider, either camaro engine (l99 or ls3) use the longer truck offset accessory drive, however i would think that stuff should work, just rad clearance is something to consider (do some research on if this drive setup fits in these cars, i couldnt tell you). the corvette ls3 uses the shortest drive offset, but the alternator is way to far out and wont fit in the car. typically most run the f-body accessory drive setup, its a mid offset.

as for the rest of the motor, l99 vs ls3, that comes down to the cost difference. the ls3 would be a ready to go engine, the l99 i would 100% be deleting the afm, vvt could be kept if you want it. deleting the afm requires pulling the heads and swapping lifters. if you want to delete the vvt that does require a new cam. now if you want to put an aftermarket cam in your build anyways, if the l99 is significantly less money than an ls3 it would be worthwhile to go this way, do the new cam and lifters, a set of valve springs and you can have close to 500hp (flywheel). really it just comes down to what you want in the end.

anything can be done with the stock gm computer to make either engine work, auto or manual doesnt matter. if you buy a complete dropout engine thats fine, however the way i see it i wouldnt pay to get a stock gm computer. the cost of the ecm, then add in the cost of a swap harness, then the cost of unlocking that ecm and getting a basic tune put on, and then not being happy with that tune and having a dyno tune done, id just go with an aftermarket ecm. stick something like a holley terminator x on it.

all previous insight is dead on. for reference i put a '99 corvette 5.7L LS1 in mine, BUT it was previously swapped in an rx7 so it already had the f body accessories done on the front for it to even think of fitting.

i did have to do a but of chop to my front hood latch for the tight 90 to even think of squeezing in which seems to be much tighter than others swaps.

highly recommend kent's ac kit to get it tightly hugged into the block which will avoid any hammering of the frame to make it fit. The original compressor and bracket i bought off of rock auto would never ever have fit.

great points on vvt and afm.

we ordered a new LS3 from chevy performance and the stand alone install kit with fuse block wiring drive by wire pedal and ECU. because covid was in full swing and after waiting over a year having supply chain problems we still never received the new LS3 engine.
we ended up finding a low mile corvette engine. the problem with the vett engine is it's a semi dry sump. in no way did it fit with the semi dry sump. 1st the oil pan and then no place to put the oil tank.
so the engine had to be converted to a wet sump. then with the alternator on the vett being mounted high on the left side this wouldn't fit under the hood. so also a relocation for that is needed.
we are lucky as this build is a track car so no AC is needed.
ICT has had all the engine parts we needed to swap to the wet sump and relocate the alt and things. the down side is with the vett engine the money saved when buying it was lost to swap over to the wet sump.

Thanks for the replies, guys. My swap will be a tad more complicated as I'm attempted a CA-legal swap, but I made an acquisition today that should make it a lot easier. Picked up a wrecked 2005 Corvette with an LS2, 88K miles for $7K. Planning to part out everything I don't need. Seemed like a pretty good deal.

Shown with my tow vehicle in front.

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I have bought many salvage vehicles ( cars and motorcycles ) for parts I have needed and then sell off every thing from it I didn't want. it always worked out for me really well doing so.