Just wondering what is all needed to replace a LT1 with a l99 4.3l V8 out of a caprice.

LT1 is in a 1994 firebird but engine is blown and needs rebuild. Have a L99 that I can get extremely cheap and low mileage from a 1994 caprice.


I understand the l99 is physically the same size as a lt1, and it being the same year as my firebird, it should not be a difficult swap. Wiring should be the same and all I need to do is swap the ECU to the caprice ecu.


I am not concerned about loss performance. I purchased the car with the blown engine cheap and just want it as a daily driver. I owned a 3.4l camaro before and was happy with its performance. I assume the 4.3l is a tad better than a 3.8l. Anything is better than my current 91 escort...

 

This post is better off in the V6 forum.

 

May I ask why? Both are V8 engines that fall in the same line of engines?

 

I don't think you would need anything special for the swap. It's a smaller displacement version of the LT1 and not a V6.

 

The 94 Caprice engine will have a vented opti so you might need to adapt the wiring for that but that is an UPGRADE from the unvented opti on a 94 f-body.

You would need to swap the damper hub because the accessory drive depth is different. The b-body got 2 knock sensors, I believe your car only got one so one wont get plugged in.

The L99 has 19lbs injectors just more an FYI than anything. I would NOT try swapping the pcm. I am sure you could get someone to put together an L99 tune for an f-body and then your speedo will be right and everything which it wont be with the Caprice programming. The pcm itself is the same PN.

One thing I am not really sure about is the clearance between the straight plugs and your exhaust be it manifolds or headers, easy enough to test on the engine stand.

I hope that all does not sound like a big deal, it is all minor.
When I bought my 96 it had a L99 in it and it was replacing a 84 with a 305. The 96 is a much heavier car despite the same chassis. As such it felt down on torque compared to the 84 with a 305 BUT it was also clearly up on HP. I think it would be better than the V6.

 

Ok, well I just bought the l99 with 70K miles with the PCM for $200. $700 cheaper than a lt1 in my area.

The engine was pulled from a car with a 2.73 gear ratio, same as mine.

The engine also included everything from oil pan up to intake and fuel rail. Also has the exhaust manifolds.




Now I contacted a tuner in Elgin IL and he said he could tune a pcm for this setup, but if I have the l99 PCM with the l99 injectors, and my car has a 4l60e with the same rear gear ratio, wouldnt the stock tune work?



So all I got to do is change the damper hub which I have on my current LT1.

 

I really don't think the b-body exhaust manifolds will connect to your f-body exhaust.
2.73 would be an odd ratio in a b-body, only ever heard of one before, generally a civilian L99 car was 2.93 and the cop car was 3.23.

I also believe that even if the gearing was the same you still have tire size issues and I thought there was an AC difference in the pcm as well. I would have Ion do a program for you. I have had him repair a pcm and installed his programming in friend's cars and it all went well.

 

also the l99 injectors seem to be 19 an hour from what everyone is saying and i believe lt1 injectors are 24lb an hour so i suggest swapping injectors from the lt1 over, for the tune on lt1 computer won't match the l99 engine set up

 

Well I got the old LT1 and trans out today. Took it out the top and only took a bit under 2 hours. Will have the LT1 and L99 side by side tomorrow.




Im going to double check on the rear ratio, but could of sworn it was 2.73.

I will be using the Fuel rail and Injectors from the 4.3l l99 with the l99 computer.

And on the exhaust, it was already cut so I am having all new piping welded in at a shop.



See how well that does, if the stock tune cant do it, Ill just send in the extra pcm laying around to get programmed.