305 to 350 swap 1983, SC, manual trnas, 4bbl
 

Well...after using the search function and browsing around, I couldn't find a direct answer to a question, so if I missed a thread I apologize in advance.

I'm restoring my 1983 Sport Coupe. It originally came with an LG4 305, manual trans, and a 4bbl, nothing special. I no longer have to original motor, but I do have the original ECM, intake, carb, etc...

I would like to install the commonly available GM Performance 195HP 350, and all of the original smog equipment, as well as the ECM, distributor, and feedback carb. What needs to happen to make it work?

Will it just work? Do I need a new PCM? Should I have the carb modified?

Thank you in advance.

Re: 305 to 350 swap 1983, SC, manual trnas, 4bbl
 

Change the knock sensor.
Yes.
No.
Tune it.

Re: 305 to 350 swap 1983, SC, manual trnas, 4bbl
 

Thank you! I appreciate it.

Do you any idea which knock sensor I would need? I have the ECM and harness, I just need to figure out where all the plugs go. I have a diagram so hopefully I'll have it nailed down soon.

Any other tips?

Re: 305 to 350 swap 1983, SC, manual trnas, 4bbl
 

Knock sensors are different depending on bore size and ECM / ignition system.

If an 83 Caprice ran the same exact ECM with a 350, that knock sensor application would more than likely be correct for your 83 ECM and the new 350. It's also possible some of the 85-up 4.3 V6 applications ran the correct knock sensor for your swap, as their bore size is the same as a 350.

I've seen healthier (read: more power) 350 and 400 engines run with stock ECMs successfully. Matter of fact, I bought an 83 G-body with swapped-in L31 that ran great and pulled > 25mpg highway, stock ECM and PROM. I hate to see you limit yourself to the 195hp 350 unless that's just exactly what you want. I'm also a fan of 86-up blocks due to the 1pc rear main seal and 87-up blocks due to factory roller cam provisions.

Read, read, read posts about Q-jet tuning. Damon and some other fellows have good information here. And Doug Roe books are good too. Your stock carb can work great with the 350. Something minor like secondary rods (easy to change) might help WOT tuning.

Re: 305 to 350 swap 1983, SC, manual trnas, 4bbl
 

^^^^ :yup:

Re: 305 to 350 swap 1983, SC, manual trnas, 4bbl
 

Thank you the information. I'm mainly limiting the engine due to the trans...it's a T-5. I don't have the type of money it would take to upgrade.

Re: 305 to 350 swap 1983, SC, manual trnas, 4bbl
 

I'm fairly confident that the lg4 did not have a knock sensor in 83