What year 350 would I need to find to drop in to replace an LG4, without all of the emissions systems, and still be able to pass the IL emissions test??

 

Maybe I'm missing something here, but i don't understand how you can lose all of the emissions-control systems and still pass smog.

Now, if you want an engine that is smog legal, GM used to make a kit that included a 350, a nice dual-cat exhaust, etc., etc. GM discontinued the kit, but sd and gmpartsdirect.com might have some in stock. If this kit is installed as instructed, it is smog legal in all states. If the kit is no longer available, you can still piece most of it together, although it will be much more expensive.

And then there's GM's new 383, which seems like quite an engine.

 

I started out with an '86 LG4. I have strict inspection and enhanced dyno sniffer to pass. The sig shows what I did - everything would work just as well on a 350.

The keys to clean running exhaust are good tuning and a good cat. A.I.R. helps the cat work, but if not required by a visual inspection, you can get by without it (see "good tuning and a good cat" above). However, the factory feedback-type induction and ignition make passing sniffer a whole bunch easier.

When building an engine to pass emissions, the main thing to avoid is "too" - as in, too much cam, too much carb, etc. However, simply going from 305 to 350 isn't "too" much of a deal.

Suggestion: Get a 350 block. Rebuild it as required, use flat-top pistons with 4 valve reliefs. Put good heads on it - most '70's 350 heads and a good number of late-'80's-on 350 heads are junk. A good choice would be World Products S/R Torquer heads with 64cc chambers. Chose a cam that is computer-compatible, such as the Crane Compucam series, or Comp of a similar type (if you go with one as "big" as mine, you're going to need a higher stall torque converter as well). Add emission-legal headers with y-pipe such as the Hooker 2055, cat and on back for '86-'90 TPI single cat application. Put all that in with all your existing LG4 equipment, including all the emissions systems (except the single snorkel air cleaner has got to go - see the Tech Articles on this board for how to make a better one), and you'll have yourself a good running, powerful, driveable, efficient, clean-running ride.

 

I'd go with what 5-7 is saying. As for heads, if you do not want to go aftermarket, a set of 416 or 601 heads from an early (pre-centerbolt) 80s 305 would work good too. They have 58cc chambers though, so for a 350 you'd need slightly dished pistons to not have "too" much compression ratio.

A system like TPI will make passing MUCH easier than a 4bbl will though.