Recently came in possession of an 84 Cutlass Supreme 305. 85k original miles. Building a car in my fathers memory who passed last year. He loved Gbodys and loved fixing them up. Unfortunately I have no mechanical experience other than what I’ve learned from studying this engine and reading various forums and watching YouTube videos. I’m very determined to finish this project for my cruiser. Initially the engine was overheating due to corroded radiator, and failed intake manifold gasket. After changing the radiator and taking the carburetor and intake off I noticed one of the intake bolt hole was cracked. A new intake is not very expensive at all, but I’m curious if the 305 is worth the time and money to fix up, or if I should consider swapping to a 350. Found a crate 350 online for 3k but I’m not too sure what is required for the swap. Any help along the way on my first Gbody build would be extremely helpful and greatly appreciated.

 

Patrick,
I am assuming that the 350 you found is a Chevy engine. It should bolt right in where the 305 is with pretty much no modifications.

But I will say that the 305 is really a decent little engine. I had an 85 K-Blazer with one and it actually moved that big thing around pretty nicely. If you are not wanting a hot rod I would say just fix the 305 and keep driving.

 

Yeah it would just be a weekend summer cruiser. I had just read so many bad reviews about the 305 I had considered just swapping. That’s very helpful. Other than the cracked bolt hole in the intake the engine would run strong. Might have some air/ fuel problems, it would idle rough and stall after overheating which I figured was the intake manifold gasket failing and sizzling. Other than the new intake. What else would you think would be a good addition to the 305 in terms to making it have slightly more power and sounding better?

 

Are you sure it is a 305 and not a 307? 305 is a Chevy engine. 307 is an Olds engine. Pretty sure the original engine would have been a 307, though it is possible someone swapped in a 305.

 

305 I had thought. It might be the 307.

 

Easy way to tell: is there an oil fil tube on the front of the engine?

 

Yes

 

Then it is an Olds V8. Likely the 307. A Chevy V8 will require a bit of work to swap in. You'd have to replace motor mounts, accessory brackets, exhaust manifolds, flexplate, starter, etc.

If you just want it running, an intake is relatively cheap (needs to be an Olds small block intake though). If you want a hot rod, there are better starting points.

 

This is the only one I could find. Looks like that’s the one.

 

Patrick,
​​​​​​
Sorry for the loss of your Dad.

What is your goal with this car? Once we know that we can help steer you. Since it is an Olds 307 it will be easier to stay Olds due to bracketry, exhaust and transmission already fitting.

Good luck!!!

 

The only thing that’s not the same is the slot on the left side for the choke. Would that matter?

 

Intentions are just to have it running good and smooth for a weekend/ summer cruiser. Relatively low miles so I figured it has a decent amount of life still in it. Not a hot rod but I’d like it to sound nice. Still learning my way around everything but I’m enjoying it very much. Like I said very determined.

 

Do a compression test, monitor oil consumption if they're both good do a tune-up leave the 307 and enjoy the car. Could have an exhaust shop do some custom work to change the sound.

Good luck!!!

 

The 3711 has those features:

https://www.summitracing.com/parts/edl-3711?rrec=true

 

Good advice. However, if the 307 doesn't prove to be healthy, an upgrade to a 350 will probably be a better way to spend your money.

 

Just to clarify, you would need an Olds 350 and not the “crate 350” that you originally posted about. That one is a Chevy engine.

 

^^^X2^^^
If the 307 needs major work then go to an Olds 350.

 

Unfortunately, the Edelbrock intake isn't much of an improvement over the factory A4 intake. Where is it cracked?

The 307 won't make a lot of power, period. Maybe throw some long tube headers on it, remove the smog equipment (distributor and carburetor), plug all the unnecessary vacuum lines, and run it. A rear axle gear change (3.73) would provide much more speed than the 307 could ever provide.

If you really want more power, a running 350 or 403 shows up every once in a while for less than $1,000. Oil pump, 7111 intake, cam, roller rockers, and maybe heads if they are 73 or later has proven to make a good ~300hp cruiser.

 

Cracked on on of the bolt holes on the right side

 

If you are talking about this notch, that's how the manifold is made. It's normal. That one bolt is in a relatively tight tolerance slot that locates the manifold front-to back on the block. All the other holes are oversize to allow for manufacturing tolerance stackup. Compare the diameter of the hole to the left vs. the width of that slot. It has to be a slot so that the manifold can adjust for different head gasket compressed thickness or if the heads need to be milled.