The difference between 305 and 350

[Nima]

What are the pros and cons of each engine?
thanks

[Tx Firefighter]

305 has a smaller bore, same stroke as a 350.

Pros of 305 are noticeably better fuel mileage and cheap cost to buy into.

Cons of 305 are simply less power than a 350 would give.

Overall though, a 305 is a good and decent engine, and all the external stuff off of one will fit a 350, so if you spend cash on a 305 buying intakes, carbs, brackets, and such, it will all swap over to a 350 if you decide to later down the road.

[67_C-30]

Originally Posted by Tx Firefighter

305 has a smaller bore, same stroke as a 350.

Pros of 305 are noticeably better fuel mileage and cheap cost to buy into.

Cons of 305 are simply less power than a 350 would give.

Overall though, a 305 is a good and decent engine, and all the external stuff off of one will fit a 350, so if you spend cash on a 305 buying intakes, carbs, brackets, and such, it will all swap over to a 350 if you decide to later down the road.

I disagree on the fuel mileage part. I've swapped several 350's into cars and trucks that had 305's and always picked up fuel mileage. The small bore chokes them down so much that they work much harder to do the same amount of work. I agree that the 305's are a decent engine, and fine for a daily driver, but I would not say that they have any "pro's" over a 350.

[piecesparts]

Originally Posted by Tx Firefighter

305 has a smaller bore, same stroke as a 350.

Pros of 305 are noticeably better fuel mileage and cheap cost to buy into.

Cons of 305 are simply less power than a 350 would give.

Overall though, a 305 is a good and decent engine, and all the external stuff off of one will fit a 350, so if you spend cash on a 305 buying intakes, carbs, brackets, and such, it will all swap over to a 350 if you decide to later down the road.

I can't support that thought, when I went to a 350 in my truck and ditched the 305; I gained a better power curve and worked the engine less to achieve the same result, and in th elong run got a better gas mileage. It was only a MPG, but it was noticeable.

[Tx Firefighter]

I've swapped a good number of 305's out for 350's particularly in early to mid 80s trucks. At best, I'd say equal mileage between the two. I agree that the reason is that the engines had to work too hard. A lot of 80s era trucks had 700r4 overdrive transmissions and 2.73 rear gears. A big block would strain to pull in those conditions.

In earlier model stuff, with more sane gear ratios, I've seen a couple of MPG better mileage with a 305.

I went through a fetish for mid 60s El Caminos about 15 years ago, and I wound up actually running a good number of 305s in them. When I'd swap a 350 into someone's truck, Id keep the 305 for my personal use.

[67_C-30]

Originally Posted by Tx Firefighter

I've swapped a good number of 305's out for 350's particularly in early to mid 80s trucks. At best, I'd say equal mileage between the two. I agree that the reason is that the engines had to work too hard. A lot of 80s era trucks had 700r4 overdrive transmissions and 2.73 rear gears. A big block would strain to pull in those conditions.

In earlier model stuff, with more sane gear ratios, I've seen a couple of MPG better mileage with a 305.

I went through a fetish for mid 60s El Caminos about 15 years ago, and I wound up actually running a good number of 305s in them. When I'd swap a 350 into someone's truck, Id keep the 305 for my personal use.

Maybe in a car they will pick up just a little, but I just assumed the original poster was referring to a truck. I have had several late 70's and 80's Chevy/GMC truck with a TH350 and either 3.08's or 3.42 gears and when I swapped 350's in place of the 305, they always picked up fuel mileage. The 305 works harder to push a brick down the road! I agree that the 80's trucks with 305's or 350's were terrible with OD trannys and super high gears. You couldn't pull the slightest incline without the convertor unlocking. Any one of those I've ever had I drove them in Drive unless I was on the Interstate because I hate the mushy, gutless feeling they have in OD.

[MylilBowTie]

My 86 is getting 9.5 mpg with th350 and 3.42 gears. Engine looks like it wasn't rebuilt but never know. Has all the pollution control stuff on it. Smokes when it starts up and oil pressure isn't all that great either. It did have a 700r4 that was swapped out for the th350. The 700r4 was acting up pretty funny. Soon it will have a 350 in it (when the 305 dies). I would like to see what kinda mileage I get then.

The 305 in my Camaro getting really good gas mileage I think for what it is. Its about 17-18 city and almost 25-26 hwy. 305 tbi, 700r4, 2.73 gears, 235-60-16s

[piecesparts]

Originally Posted by MylilBowTie

My 86 is getting 9.5 mpg with th350 and 3.42 gears. Engine looks like it wasn't rebuilt but never know. Has all the pollution control stuff on it. Smokes when it starts up and oil pressure isn't all that great either. It did have a 700r4 that was swapped out for the th350. The 700r4 was acting up pretty funny. Soon it will have a 350 in it (when the 305 dies). I would like to see what kinda mileage I get then.

The 305 in my Camaro getting really good gas mileage I think for what it is. Its about 17-18 city and almost 25-26 hwy. 305 tbi, 700r4, 2.73 gears, 235-60-16s

OUCH, my truck now has a 385 stroker motor in it and with the 3.73 gears and the 700 R4 modified tranny, I get 15 MPG.

My son's 86 hada 350 with 3.08 gears in his and after we installed the 700 R4 it was getting mileage like yours. We installed a 3.73 12 bolt posi rear end and gined 3 MPG in his driving. The trick is to get the RPMs in the power range and the truck does NOT have to work hard ot overcome the small inclines and acceleration issues.

[68gmsee]

Too many variables can go plus or minus in the mpg's in either engine. The engine condition, timing, carburetor, intake/exhaust manifold, tire size, truck weight, rear axle ratio, trans., exhaust, ignition, etc., etc., can increase or decrease your gas mileage.

Some years back, my brother and I had similar trucks. I believe he had a 292, not sure, and I had a 350. I got better gas mileage.

As for my choice, I'd go with the 350 with extra hp and popularity over the 305.

[ChevLoRay]

The argument of cubic inches has been going on for years. Whether it's "There's no substitute for cubic inches" or "Speed costs money, how fast do you want to go?", there are on-going arguments.

Another way to look at it, as I was once reading, is like the amplifier that you use for the speakers you have. I bought a Sansui 2000 receiver/amp when I was overseas. It put out 32 Watts RMS, per channel, continuous power. The speakers I bought were rated 16 watts continuous RMS, but good for 32 peak watts. The analogy was that the amp would make the speakers sound better with lower output, than a set of speakers that were matched to the amp. It was like putting an L-79 small-block in a Chevy II. I'm gonna guess that the L-79 engine in a heavier vehicle gets worse mileage than the Deuce.

[piecesparts]

Originally Posted by 68gmsee

Too many variables can go plus or minus in the mpg's in either engine. The engine condition, timing, carburetor, intake/exhaust manifold, tire size, truck weight, rear axle ratio, trans., exhaust, ignition, etc., etc., can increase or decrease your gas mileage.

Some years back, my brother and I had similar trucks. I believe he had a 292, not sure, and I had a 350. I got better gas mileage.

As for my choice, I'd go with the 350 with extra hp and popularity over the 305.

Agree with your insight . A person can build to the type of driving that you want. If you are pulling the stumps out of the ground, then the highway will suffer. The 292, that you refer to was built for torque and geared as such to make it work the farm and ranch. On the highway it was not strong enough to go all out at highway speeds. I used one to pull my trailer and my 68 truck home and it gobbled gas like a 454--all the while a little Old Lady was passing me on the hill. I would not buy one for anything. The 350 is the GM all around workhorse and it allowed a lot of different alignments for use. High gears and OD trannys is a bad squirt in the pot--they don't REALLY work together, as one would think they should. As I stated, I get dang fair mileage for a 400+ HP stroker motor in my truck and I drive it where I want to go with it. (trailers are for wussies and shiney museum pieces) I keep my RPMs in the 2100 to 2500 range and that appears to be the so called "Sweet Spot" for it. I can also "walk" a Mustang when I want to. I also run a shorter tire design than most to get the truck to respond the way it needs to.

[mnunn454]

Originally Posted by MylilBowTie

My 86 is getting 9.5 mpg with th350 and 3.42 gears. Engine looks like it wasn't rebuilt but never know. Has all the pollution control stuff on it. Smokes when it starts up and oil pressure isn't all that great either. It did have a 700r4 that was swapped out for the th350. The 700r4 was acting up pretty funny. Soon it will have a 350 in it (when the 305 dies). I would like to see what kinda mileage I get then.

The 305 in my Camaro getting really good gas mileage I think for what it is. Its about 17-18 city and almost 25-26 hwy. 305 tbi, 700r4, 2.73 gears, 235-60-16s

Mylilbowtie: I'd say there's something bad wrong with the 86 truck 305/TH350 if it's only getting 9.5MPG. I have a cammed up 454/TH400 with 3.73 gears and get 10-11 MPG. Is your O2 sensor off line, the ECM removed or missing some valuable sensor information for efficient combustion? I know my 82 Pontiac 305's MPG fell like a rock when I removed the air inlet temp sensor out of the air breather snorkle.

Back to the poster's question regarding the Pro/Cons of a 305/350:

If you ignore for the moment GM's goals for each engine to meet emissions targets, I think it mostly boils down to cost over performance ($ per HP and $ per foot pount of TQ) and availability of parts. 350 has more parts available for it than almost any other engine on the planet.

Using the cost equation, I think you'll find a 350 (both stock and modified) is often a more cost effective choice than a 305.

Anyone see that ad in this month's CHP Mag for a 351HP /400TQ 350 for $4,000 from Monster transmissions? That comes to about $12/HP ($10/foot pound) plus there's free shipping, no core charge, and a 2 year warranty.

Also there's a Year-One ad on page 98 for a dyno tested 4-bolt main 350 with a roller cam producing 400HP. It sells for $3,000 with no core exchange. That's $7.50 per HP (plus shipping I assume) and comes with whatever warranties they didn't put in the tiny ad.

While you can find many a 305 for less than $3000, you probably won't find one in the 300+ HP range for $7.50/HP.

Were it me, I'd go with the 350 for almost any SBC project unless the 305's in just too good a shape to get rid of. I would never set out to build/rebuild a 305 when for virtually the same price you can add 15 to 30% more output by going 350 and not negatively affect your gas mileage.

Finally there's the resale value aspect. If you ever sell it, I think you'll find more of a market for it with a 350 in it than a 305 (IMO).

Just my thoughts. Some may argue otherwise.

Good luck.

[72BLUZ]

I Swapped A 305 For A 350 In My 92 P/u I Only Get 15 Mpg The Diff Is The 350 Block Is Bored 40 Over. Everything Else Is From The 305 Oem

[piecesparts]

Originally Posted by 72BLUZ

I Swapped A 305 For A 350 In My 92 P/u I Only Get 15 Mpg The Diff Is The 350 Block Is Bored 40 Over. Everything Else Is From The 305 Oem

So you are saying that you are running a 350, with the 305 computer program and injectors? There are things that you can do to improve the perforemance and mileage on that truck. I took my 91 5.7 / 3.42 geared rearend truck from 16.5 MPG (when I purchased it in 2000) to a steady 20 MPG daily. I cleaned up the air filter (using a standard 14" X 4" K&N air filter setup, shorty headers with a dual 2 1/2" exhaust, a TBI spacer, MSD ignition, Hypertech chip w ith a 180 degree T/stat, and the best change of all---electric fans instead of the factory clutch fan (the fan removal made a 1 MPG change)

[72BLUZ]

Originally Posted by piecesparts

So you are saying that you are running a 350, with the 305 computer program and injectors? There are things that you can do to improve the perforemance and mileage on that truck. I took my 91 5.7 / 3.42 geared rearend truck from 16.5 MPG (when I purchased it in 2000) to a steady 20 MPG daily. I cleaned up the air filter (using a standard 14" X 4" K&N air filter setup, shorty headers with a dual 2 1/2" exhaust, a TBI spacer, MSD ignition, Hypertech chip w ith a 180 degree T/stat, and the best change of all---electric fans instead of the factory clutch fan (the fan removal made a 1 MPG change)

I HAVE THE K&N AIR FILTER WHICH GAVE IT 1 MPG. BUT THE OTHER THINGS YOU MENTIONED I HAVE NOT DONE. I THOUGHT ABOUT IT. BUT HAVE TO MANY IRONS IN THE FIRE RIGHT NOW. IF YOU NO WHAT I MEAN! CURRENTLY BUILDING A NEW ENG FOR 72BLUZ AND HAVE A 88 P/U THAT POSSIBLY NEEDS A HEAD WHICH THE 88 IS A SHORT WHEEL BASE I HOPE TO MAKE THE EVERYDAY DRIVER

[jim zag]

Here is something to think about. If you want better mileage put in a smaller camshaft! A smaller cam lets less air flow through the carb, drawing in less fuel. How about a 350 with a 305 cam? I know it would make less HORSEPOWER but if you want better mileage I think it would be worth it. A 350 would make more Torque at lower RPM set up this way. Better yet put a stroker crank in a 305 block and have 334 cubic inches. The OEM's are building the newer engines with smaller bores and longer strokes to get more torque out of smaller displacements. When gasoline gets past $4.00 I think I just might have to do some R+D myself.

[67_C-30]

Originally Posted by jim zag

Here is something to think about. If you want better mileage put in a smaller camshaft! A smaller cam lets less air flow through the carb, drawing in less fuel. How about a 350 with a 305 cam? I know it would make less HORSEPOWER but if you want better mileage I think it would be worth it. A 350 would make more Torque at lower RPM set up this way. Better yet put a stroker crank in a 305 block and have 334 cubic inches. The OEM's are building the newer engines with smaller bores and longer strokes to get more torque out of smaller displacements. When gasoline gets past $4.00 I think I just might have to do some R+D myself.

If you put a smaller cam than stock in a 350 you'll lose effeciency which will in turn make the engine actually work harder. That's the problem with the 305. You'd be better off going with smaller cube small block like a 283 or 307. The 3.875" bore of the 283 and 307 is just big enough to truly flow effeciently with SBC's valve spacing. The 305's valves are shrouded by the small bore and bigger valves have no effect on power. Flowbenches have even comfirmed that bigger valves actually hurt port flow on a 3 3/4 bore. The new engines with smaller bores have heads designed to work with smaller bore and better designed combustion chambers. Forget a 334, they are definitely not going to be a economy engine. The 283, 307 and even a 327 are Chevy's best economy engines in regards to old scholl small blocks. That would be your best bet for a good combination of fuel economy and power.

[1972Ryan]

45....thats the math teacher response...lol

[72freak]

The difference between 305 and 350....................EASY

One is junk and the other is not.

[Jim_PA]

Originally Posted by 72freak

The difference between 305 and 350....................EASY

One is junk and the other is not.

Agreed. I wouldn't run a 305 if it were given to me. The 305 in my 84 z28 was consistently spanked by my FRIEND'S DAD'S... Honda accord.

You just can't polish a turd.

[LMN8UR]

Originally Posted by Jim_PA

Agreed. I wouldn't run a 305 if it were given to me. The 305 in my 84 z28 was consistently spanked by my FRIEND'S DAD'S... Honda accord.

You just can't polish a turd.

True, You can't polish a turd. . . But you can spray paint em! ! !

[Rod]

Math teacher would mark that wrong for no unit of measure...lol.

[Mordachai]

hmmm, what about 305 Cu.in -vs- 307 Cu.in.

[72freak]

Originally Posted by Mordachai

hmmm, what about 305 Cu.in -vs- 307 Cu.in.

Although most of the purists on the board would probably argue the fact that the 307 is a good engine....... I will just say that junk might be too harsh word to describe it also.

If I was in a situation where I had to choose between a 305 or a 307 I would take the 307 in a second.........and start saving money to buy a 350 as soon as I could.

[piecesparts]

Originally Posted by Rod

Math teacher would mark that wrong for no unit of measure...lol.

One is a 50% junk and 45% parts to be reused, with 5% salvageable fun. The other is 100% upgrade. Which if calculated on the linear scale is an exponential growth of enjoyment.



Quote: I HAVE THE K&N AIR FILTER WHICH GAVE IT 1 MPG. BUT THE OTHER THINGS YOU MENTIONED I HAVE NOT DONE. I THOUGHT ABOUT IT. BUT HAVE TO MANY IRONS IN THE FIRE RIGHT NOW. IF YOU NO WHAT I MEAN! CURRENTLY BUILDING A NEW ENG FOR 72BLUZ AND HAVE A 88 P/U THAT POSSIBLY NEEDS A HEAD WHICH THE 88 IS A SHORT WHEEL BASE I HOPE TO MAKE THE EVERYDAY DRIVER


Take alook at things that you can do that are cheap or simple. You can upgrade to a better set of sparkp[lugs and plug wires and gain change in performance. Use standard Delco brand plugs, but spend a little extra money on the plug wires. Look for ones with a very low resistance rating. I picked the MSD 8 MM wires, and that definitely helped. I also backed that up with one of their high performance coils. There is some money spent here, but you get your money's worth back. (You did say that you were only getting 15 MPG and that is at approximately $3.00 a gallon--) The payback is slow, but not as slow as it was a couple years ago. I see that Summit Racing shows the replacement chips to be around $129.00, and that sounds expensive, so that would be a later item to consider. The TBI spacer was worth a great change in my low end torque and the dollars spent for the change was worth it in my truck. for about $70.00, you can get a better acceleration curve and use that fuel more efficiently.