smog legal 305 to 350 swap

[rustydread777]

hello new to the site i have a 1987 el camino with a lg4 305 with computer controlled carb smog legal edelbrock intake smog legal edelbrock headers better breathing exhaust rebuilt th200 4r trans and soon a 80 gph fuel pump. well this is what i want to do swap a 350 in, i know that all the things will bolt over no problem i know all that stuff and im not looking for a tire burner i have one of those so i dont need anything crazy this is a daily driver and often haul stuff. the 305 has 260k plus miles it runs ok carb and heads where rebuilt. i want to get a cam with a little more lift and duration no more than .200 at .050 lift and want to keep my stock tq convertor and stay smog legal with the computer carb and distributor if this is not possible i will just rebuild the 305 i have lots of 350 just sitting in my garage. thanks

 

[85GPLef41]

It Sounds like you have your homework done 😀 I did the same thing for the most part.....except leave the computor hooked up. If you plan on doing that get a 350 knock sensor. I also believe you can buy 350 engine chip to get the computor to work at its best.By the way" Welcome!"

 

[rustydread777]

thanks for the welcome and yes i guess i would need to change the knock sensor to control the spark advance. the quadra jet and computer will eventually adjust itself to the engine all i know is that the secondary metering rods need to be changed to better flowing rods the A.U. rods to be exact. i will eventually use an f body serpentine setup for less belt drag and will go to an e-fan setup. know that the 1985 and up 305 had 9.3 or 9.5 to 1 factory and was due to the knock sensor that helps with high compression and timing advance so should i just fresh up the engine and get a decent street cam (daily driver) or just go with a 350. i guess all i can do is swap it and hope for the best. wanted to go with the 400 hp sbc 400 in my garage but thats going in the wife's blazer :|

 

[rustydread777]

hello any info. well so far i did this i pulled several secondary metering rods from cars at junk yard and replaced mine with a good m rod it opens up sooner car would only rev to 4000 or so now will damn near go to 5000 and pulls all the way. so what are any smog legal performance swaps anyone has done.

 

[rustydread777]

ok lots of views and no reply well this is it this will be my final build 305 .030 over comp 12-305-2 world products 305 heads with pocket porting edelbrock intake edelbrock exhaust system corvette air breather with K&N intake modified quadrajet all port matched got the pair of heads for 500 fully assembled brand new i will be doing the final assembly and i will be happy with my little 320 ft lb 290 hp chevy 305.

 

[85GPLef41]

I would just do the 350 swap and use a 350 computer, knock sensor, and related items. Your cam choices would be somewhat limited but if you go with a roller block you have better performance. I thought of doing the same but even the stock 350 was a night and day difference compared the 305. I hate to say to get rid of the 305 and get a 350 but in the end it makes sense 🙂 . Torque is what get's these cars going and the more displacement the better. My stock 350 upgrade has left me wanting more....

 

[AlanB]

Rustydread777,

You probably didn't get a lot of responses because you weren't asking any specific questions really. The 305 to 350 swap has been done thousands of times and is a fairly straightforward deal. Your 305 sounds like a nice build, but I would recommend the 350 swap as well for the extra cubes. It won't cost you anymore to rebuild a 350 and dollar for dollar you will always make more power than a 305. Montecarloss.com is another site with lots of detailed info on this swap.

If you decide on the 350 swap here are some things to consider. You could just drop in a 350 and change nothing else. Lots of guys have done this with good results. In my opinion, you should at least change the secondary rods, knock sensor, and ESC module. I use CV rods with great success. I run a ZZ4 GM PROM, but these are getting expensive and hard to find. Google it and you will find someone selling them. Many have run the 305 PROM on 350s with success. I never tried it.

You car is an 87 so it has a one piece rear main, new intake bolt pattern for 87, and center bolt valve covers. Keep this in mind as you may need to change intake or flex plate depending on the year of block/heads you get. Also keep in mind that the dipstick tube changes from one side to the other over the years. Your stock exhaust manifolds may not clear the older driver side (older) dipstick tube. Edelbrock TES headers clear both sides.

If you found an 87 or newer 350 from say a TPI car or Caprice, you would be able to reuse your flex plate and intake and the dipstick location should match your 305. Another option would be to find a 96 or later vortec 350 from out of a truck and just drop it in. If it were me I wouldn't even rebuild it. Just get a vortec pattern Performer spread bore intake and haul *ss. These motors have vortec heads. The only expensive part with the later model motors is the cam because the factory hydraulic cams are more expensive, around $300, but well worth it.

 

[rustydread777]

hey thanks for the reply and yes i guess i did not ask any questions.i went to an el camino gathering this weekend and got some ideas. well looks like the blazer is going away and i would like to use the fully rebuilt 400 with vortec heads that was going in the blazer my question is now will this work in my el camino. i know that a small block is the same as the next except the internals i could get a quadrajet intake for the vortec heads like you said 300$. will a 350 knock sensor work on a sbc 400 i know that the 400 is strong i will ether build the 200 4r beefy or go to a good 700 r4 build i know the rear end will hold up as long as i don't put sticky tires on it. it curently has a xe 274 cam in it and i would need a larger stall. well i dont know if it will be smog legal unless i bring the cam down change the prong.... ok sorry i went on a rant if i did this would it be easy to just swap in an HEI and use my performer rpm intake with my edelbrock carb or fight the battle with smog if all this crap is going to be to much than i will just sell the 400 and world heads and use the money to pull a 1987 350 rebuild it with a 350 knock sensor prom and rods and get the trans rebuilt and call it a day. what do you think AlanB