Is your 350 engine trashed or something? Otherwise, your decision isn't sensible. Let's see if we got this right. You want to spend a lot of time swapping from a 350 to a 305, with the hopes of saving what, maybe 2 mpg? Then, you want to spend money back on the 305 to punch up the h.p.? Does this make good sense to you? It doesn't to me.

 

76 305 IS one of the bad years for Cams. If the motor has an original cam in it chances are it will need replaced. I don't want to **** off any 2nd or 3rd gen guys but the 70's-mid 80's 305's are not good motors. I can not tell you how many I have pulled and discarded. They are worth scrap weight.

 

I won't spend no time swapping the engines out the guy will swap both engines out an hook everything back up on mine no prob. An the swap is a even swap no money an he built the engine up some. An the whole reason for the swap is I know some people that have the 350 that is carb & fuel injected an they all say the same thing time to sell an get 4 or 6 cylinder engine 350 is way to hard on gas. Plus I have had several people say you don't want a 350 for a daily driver it will drink the gas go with the 305 or something like that. So thats what I am doing. I don't know nothing bout Chevy engines I have a 74 Ford truck. Either I go with 305 or 302 Ford engine an drop in it.

 

If you plan on putting a ford 302 in it....good luck. The mounts would need to be custom made, and you would end up using something like a C4 trans, thus needing new a crossmember and most likely a custom cut driveshaft. Not to mention the fact that a C4 may not fit in the tunnel. removing the 350 is not a sensible option. If you are looking for MPG and power at the same time go with a 4th gen V6.

 

We explained but you have alread made up your mine. The 305 is a weak motor. You "build" it and run it hard it will not hold up long. There is nothing magic about a 305. If you build a 350 it will take a pounding for years. If you back it up with the right gears it will get almost as good.

Let look at some facts.
1992 z28 305 automatic is rated at 16/25 MPG
1993 z28 350 Automatic is rated at 17/24 MPG

THe 350 has 70 more HP. Seems to me to be well worth the price

 

I don't see what the debate is. The 305 HO was rated at 190 horsepower and its going to be lower with those 350 cylinder heads. The guy with that 305 is trying to rip you off. There's a reason as to why no body builds 305's Why build one of those when you can build a 350 and get much more power potential? Its a no brainer IMO.

 

You asked for advice, but it seems you want to use the 305 is spite of our advice. Makes no difference to me what you use, but just keep in mind that the 350 will only use more gas if you use the extra power, otherwise the consuption will be equal. As stated previously, 350 heads on a 305 will result in very low compression which in turn increases fuel usage.

 

The guy is already set to swap it out in like a day or so. We were set to swap engines before I posted this. An the people I talk to around here say go with 305 not 350 that the 350 is harder on MPG than the 305. An the people on this site say go with the 350 not the 305. I don't know nothing bout Chevy just what I hear an everybody is saying different bout these engines but the deal is done on the swap. The guy said basically the only thing changing is the block & the heads. I am told the 305 is a 350 block an I have heard the 305 is a 305 block so I don't know bout that either. Will the parts off of a 305 fit a 350? I could check bout getting a 350 an have it checked out an put the parts the guy has on the 305 on the 350 would that be better? He says it has a 283 parts in it an a RV cam. I can get another 350 block no prob an maybe use the parts from this 305 on it an come out with a good engine should I do that? I had newer car this 80 Camaro is the first old vehicle I worked on back in 03 with a 350 in it. I did not know nothing bout engines till I started in on this Camaro & based the 360 in my Ford truck off this 350 Chevy engine so these are the only two engines I know anything about. I don't know a lot about them but some. I am planning to go with either 273 or 308 rear gear an Hooker headers & a manual trans with the car. Another thing is the 350 that is in the car was run hard an abused it would not surprise me if the block don't have problems. The engine smokes like a freight train an the trans that was with the engine in the guys truck was almost totally gone an he would run the truck in a low gear in a manual trans an see how fast the truck would go. The 305 I am getting is a good clean engine with a lot of usable parts. I am planning to check later bout a 350 block get one in good shape an build it for easy on gas an use the 305 for now just to make sure this 305 is what he says it is an that is a good engine. We did the deal on the engines not ever a hour after getting the car. The guy that had the car was just talking bout how fast this engine is an the horse an all that an how he would run the engine in his truck 2 minutes talking bout that engine he abused it an probably junked it. That is why I am doing this deal.

 

From your first post: "I have a guy who wants to swap me a 305 high output with 350 heads an all that for the 350". You didn't word it as a "done deal" then, which is why we were trying to steer you in the right direction. You're also listening to some wrong people on your end, based on some of the advice you've been given.
No, the 305 is not a 350 block, the bore is smaller. Yes, the 305 is a 305 block.
Knowing your 350 engine smokes helps, the 305 at least will make the car drivable, to get you by......provided the 350 heads on it don't have too big of a chamber size, and provided that 305 is in fact a solid engine.
The 350 can be harder on gas mileage, if you're harder with the gas pedal. Drive either one modestly, and difference in mileage should be negligible.
Parts that are interchangeable are the external accessories, not the internal mechanics.
What gears depends on your driving; city, highway, or both. 2.73's are high, 3.08's are fine for the highway. But if you want gears for combination driving, you may want to consider going lower still, like maybe 3.42's.

 

You keep saying you know nothing about chevy engines, but if you know about a ford engine, the basics are still the same. No, you can't compare the ford 302 with a GM 305, but most things are the same. If you've made up your mind, cool and best of luck, but it really sounds like a bad thing. If the block is cracked thats one thing, but if not, it sounds like you are giving up the better platform. There is a reason why this guy wants to do this swap. I would be more understanding if the 305 was stock, but with 350 heads and an "RV" cam which more than likely is a stocker, or just junk, do not expect that vehicle to run correctly. I hope your area doesn't require emissions testings.

Not every guy on here has a 600 horsepower car, some have stockers that are head turners, and some guys have done wonders with the V6's. I think the advice you have been given is to help you get the most enjoyment and reliability out of the car. Best of luck