Alright guys I'm, like a literal ton of other people, planning on doing a 305 to 350 swap. I just got a 91 firebird with the tbi 305. My problem is that I'm actually finding too much info about this. I feel like this shouldn't be all that complicated but there is just so much info out there that I feel lost. This is gonna be my first engine swap, and I wanna make sure I get it right.
So what I want to do is give you guys an idea of how I think this should work, and have you shoot it down and correct me if I'm wrong about anything.
I know that all chevy smallblocks should be interchangable. so the exhaust, the intake, the engine mounts, the tranny, and any other hardware should just bolt on.
From what I've found, I need to change the fuel injectors, the prom, the ecm, the knock sensor, and possibly the fuel pump.
Fuel injectors should be easy to do.
I have no idea where to even find the PROM and ECM on the car. Or where to buy them. This is probably my biggest concern about this swap.
the knock sensor I think should be simple enough.
And the fuel pump is up in the air for me. This car has been driven pretty rough, and has pretty high mileage. however, I don't know if the fuel pump is necessary for this swap.
Any thoughts about this? does it look about right? Am I missing anything?

 

The PROM is locating inside the ECM (engine control module) which is the big metal box under the passnanger side dash. Check out the DIY prom board for more info in tunning the computer.
The knock sensor is a simple swap, the new one goes in the same spot as the old one. The only difference is the new one will be the correct one for a 350.
Changing out a fuel pump isnt all that hard. If you think youre pump might be near the end of its life, go ahead and change it. While its not necessary since youre staying TBI, its just good insurance. You can swap to a higher flowing pump (which wouldnt be a bad idea)

 

alright awesome that helps a lot. So will the knock sensor fit onto any 350 engine? or are older blocks not equiped with a spot for one. I have an early 70's 350 sitting in my garage, but I don't know if anything that old will work on this car (with the knock sensors and electronics, not to mention the serpentine belt that's on the 305). Would I be better off scrapping this 350 and finding a newer one? Or can this be made to work? I only have it because it was free, but if it won't work then I dont really want it just taking up garage space.

 

Knock sensor will go into the block on pass side - just about under the #6 spark plug - just look at the block and see if there's a hole there.

If the heads have accessory holes in the fronts, then your serp belt system will bolt on fine.

 

Ive got a 70's 350 in my car (not really a 350 but a 350 block). a lot of things interchange. Just be aware, the dipstick could be on the other side of the block. Nothing major though. I like my driver side dipstick better anyway.

 

thanks for all the great help guys. I'm gonna end up scrapping the 350 in my garage. No spot for the knock sensor on it, and I don't think the holes on the heads will match up to the serpentine system. Oh well, time to find a new engine I guess. Saves me the trouble of rebuilding this one. My friend actually told me the knock sensor didn't really do anything crucial though. Is this true? I always thought it was pretty important.

 

The knock sensor retards the timing if it detects spark knock. Its needed to run any sort of fuel injection, not needed for a carb.

 

That's what I thought. alright well thanks guys. I'll keep everyone updated. I found a guy who said he can do the body work for cheap, and I've almost got the original 305 out. I'll try and get pictures up soon.

 

Nonsense. Every small block Chevy that's been made has the spot for the knock sensor. It's called the water jacket drain plug.

Your friend doesn't know what he's talking about.

Correct.

Not true. The factory used knock sensor on many different carb applications, including '85-'87 f-bodies (and the '84 full size van we used to have).

Of course, the "not needed" part could be argued. Personally, if it was available to me, I'd keep it.

 

I'm doing the exact same thing your doing. I had to change the waterjacket plug for the knock sensor (probably need a torch and wd40 or something), the dipstick side is on the driver side, buy headers and a flexible dipstick if your 305 was passenger side: (http://cgi.ebay.com/ebaymotors/SBC-CHEVY-FLEXIBLE-ENGINE-OIL-DIPSTICK-PRE-79-5002-_W0QQcmdZViewItemQQhashZitem51976b87dbQQitemZ350432757723QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories)
If your heads don't have the holes to bolt in your air conditioning and what have you, you can get them drilled at a machine shop, shouldn't be expensive at all I bet. Oh and use the crank pulley from your 305 and I think the water pump too because the belt grooves are different.
AND, I think the 70's 350's used a flat tappet camshaft so you'll need some zinc additive on every oil change, this should last you the whole year:http://cgi.ebay.com/ebaymotors/4-ZDD...Q5fAccessories

You could also use your 305 heads on the 350,that would take care of the hole drilling. make sure the pistons are the smog dished type, but if you do that you'll probably need premium gas. Should get some more torque but your power will drop at like 4500rpms or something. Hope I helped.

 

I should have been more specific, "not needed for NON CC Carbs "

 

True. But, that '84 van was non-CC carb.

At any rate, if you're starting with TBI, no carb is emissions legal (regardless of where you live in the U.S.).

And, I must have missed where the OP said anything about converting to carb.

 

He didnt. It sounds like hes keeping the TBI. I just just throwing it out there that is needed for his application, but not ALL applications.

 

I think I'm still gonna ditch the 70's 350. Even if it could be done, it sounds like more work then I'm up for. Plus it doesn't run, so it would take a full rebuild. I'm just gonna keep shopping for something newer, and find something with everything I need already.
Another thing that I saw, however, and that I have a question about. I know I need to change the ECM for my 350 swap, but what I'm worried about is that this will screw with my VATS system. Is it true that the little chip on my key is tied to the ECM? will I have to get new keys or anything like that? or will the VATS system itself still work with the ECM changed.
Also, thanks for all the great info guys. It is really helping me a lot. Like I said, this is my first swap, and I want to take it slow, and get it right the first time. I don't want to have problems because I didn't understand something, and was in too much of a rush to check beforehand.

 

Another question about this swap. Will the radiator that was in the car with the 305 be sufficient, or will I need something bigger or more efficient? Also, I've been hearing that cars older then 25 yrs old aren't checked for emissions control. Is this true? I think swapping to carb could be a LOT easier, as I am having so much trouble figuring out the specifics of the computer (ECM/PROM) and what specifically needs to be changed. I have never had to do emissions tests because its not required where I live, but there is talk of them starting to be manditory, and I dont wanna be running an illegal carb and get caught on it.

 

look for a lt1 or an ls motor .... still gonna be some work but it would be worth it

 

Flywheel/flexplate also as the older eng. is a 2 pc RMS and the current one is a 1 pc.

 

thought I would give everyone an update. went ahead and bought a good-running 305 for simplicity.(didn't feel like dealing with all the changes, let alone learing how to program a PROM) I tore it down, put all new seals on, new oil pump, new thermostat, simple stuff, just your basic overhaul. It's now reassembled and ready to be put in the engine. been a couple of months in the making, but shouldn't be much longer before she's running for the first time since I bought her. It's been going almost too smooth, and I'm just waiting for something to go wrong. But I've got my fingers crossed. wish me luck guys.

 

the bird's running now. sounds great, runs great, and only a couple minor problems to fix before its good to drive.