I have a 1989 Trans am. I just took out the 305 TPI to replace most of the gaskets while replacing the head gaskets because they were blown. While doing that I found that they front bearings (the ones around the crank where the timing chain is) are done and so are the rob bearings. I also was going to replace the rear main seal, which I also found that the guy that "rebuilt" my transmission (it's still messed up) removed the bolts around the seal and has caused it to leak and go bad. Anyways, I have found a 350 that I would like to replace the 305 with considered I need to rebuild the 305 and I don't see the point in putting my money into that engine' I would rather have a 350. The 350 has been rebuilt. It is out of a 1976. With a SCAT crank (don't know what one), JE 10.5-1 forged pistons, the heads were rebuilt, stainless steal valves were used, elderbrock intake (don't know which one), Holley 750 double pumper, and it has also been bored 30 over.

I am wondering what power gains, hp & tq, will I be getting from this swap; how much mpg drop? What all will I need to do to convert to a carb'd engine. I know that I will need a fuel pressure regulator (Mallory 4309 was suggested). But what about wiring? I have a vacuum advanced distributor, if it doesn't already have one with the engine. Do I need to keep my ECU to run my lights, dash, fuel, starter, etc? Also I had just bought a new flex-plate right before I took the engine out and a new mini torque starter for that plate, will I be able to just bolt those onto the new engine?

 

Lots of unknowns to accurately guess your HP with the 350; which heads are on it/valve size, which cam is in it.... Most likely you will see some kind of HP/TQ gain and MPG drop.

To switch to a carbed engine, what do you want to keep? electric fan, in tank fuel pump? No you don't need your ECU to run any of that stuff. You will need to retain your wire harness, but it can be thinned out to remove everything you don't want/need anymore. A lot of this will depend on what you can do on your own. It's time consuming and not for a novice, but definitely doable.

I kept my in tank fuel pump, electric fan, all gauges and interior/exterior lighting still function. The car is just like it was with FI.

 

Yeah, I know there's a lot of unknown things that would help to determine the accurate figures. I just figured it would be worth asking.

I would like to keep my fuel pump since it is a new one, which is why I would need need the fuel pressure regulator; correct? I do have the dual electric fans that I would like to keep as well. And of course having the gauges and lights inside and out would be nice to have. Haha.

Would it be easier to switch to a 350 or 327? And which one would be a better semi built engine? In your opinion that is.

 

Yes you need the regulator to bring the fuel pressure down. Keeping all that stuff isn't too tough if you can read a wiring diagram and use a volt meter. A 305/327/350 are identical to swap, its just the internals that are different (this is generally speaking, so i dont get hit with specifics). You need to use the right oil pan, use your 305 pan. You need the correct flexplate for your engine/starter/trans combo. Flexplates are different between 1 and 2 piece rear main seals, as well as tooth count for the starter.

 

So as long as I make sure the new engine I get is also a 1 pc rear main seal then I can switch my flex plate over to it? If I choose to keep the ecu for the time being would it mess up my engine running or anything until I get the time to start removing and rewiring?

 

A '76 is 2-piece rear main seal. A 153-tooth flexplate is something like $35 new (just ask for a '85 'Bird 305 automatic application flexplate at the parts store).

Leaving the ECM in place won't affect anything if you go non-computer carb & distributor (you have to do both - non-computer carb and computer distributor don't play well together).

 

So my 153 tooth flexplate won't work? Well that's fine, not a big deal.

 

'85-older were 2-piece rear main seal. '86-up were 1-piece rear main seal. The bolt patterns were deliberately made different so you couldn't put one on the other.

If you look at the 2-piece RMS crank, you'll see a counterweight cast into it in the back, outside of the oil pan. The back of the crank had to be redesigned to allow a 1-piece seal to slip over it to the sealing surface, so the counterweight was moved to the flexplate/flywheel. Since the 1-piece flexplate/flywheel has this weight on it, and the 2-piece RMS flexplate/flywheel doesn't, you don't want it to be possible to mix the crank and flexplate/flywheel types. So, the factory made it Murphy-proof.

 

Alright, thanks. That's good to know.

 

So it turns out that I didn't get that engine after all. I ended up getting a 1972 350 carb'd. He had it all rebuilt 300 miles ago. I believe that everything is stock and cleaned/polished up. He said the compression is either 7 something or 8 something to 1? Is that correct? Well the machine shop cracked the block for him and won't fix it. But I went out and found another '72 engine with the block and heads only. It had a couple burnt valves and a few broken rocker arms or rods? So I'm only going to use it for the block only and reuse everything out of the other rebuilt engine. I'm wondering about the compression currently and the best way to raise it up from the 7 or 8.. I'm looking for 9 something to 10.. I know the pistons in both blocks are dish ones and I have read that I can go get flat ones for it and it raise the compression. I also read that getting 6" rods will increase power and efficiency? Well I'm not replacing the rods at this moment but just wondering. I want to get the good block cleaned and bored .040 over, new flat top pistons, and maybe a really mild cam that doesn't require new rockers or anything. Can anybody help me out on what I need? Thanks, Bradley.

 

I would like some help with this, what all do I need to do? Can I get rid of the engine bay wiring harness? If I do that, what all wires will I need to run for the engine and fans?

 

I didn't get rid of the harness, i just cut out everything that wasn't needed anymore. You will have to look at a wiring diagram to figure out exactly which wires to keep, since they vary between engines and years. You will want to keep the big red and purple wires coming off the starter, keep the wires for the fuel pump and cooling fan relays, coolant temp sensor, oil pressure sensor, power to the coil, tach, alternator and there may be a few others since you have an automatic trans. A wiring diagram is going to be your best friend though....... and worst enemy when you realize it has the wrong colors like mine did lol.

 

Do you know where the best way to find a good wiring harness for my car? But how hard would it be to not have to cut the wires out and to unpin them or run new wires?

 

Try looking for a carbed harness on the sale boards, but that will require repinning to work with your connector at the firewall, and may require new pins to be added.
The reason i suggested cutting is if you want a clean look to your swap. You can leave everything there if you want a ton of useless wires laying around the engine bay.

Edit: I also just found this in the Carb forum, may want to get ahold of Pocket
https://www.thirdgen.org/forums/carb...-new-carb.html