The difference between 305 and 350

[67_C-30]

Originally Posted by special-K

The right cam makes all the difference in the world and will dispell all myths that a 305 or 307 can move a truck well enough to gain mileage.I overhauled what my`71 K/20 had in it one time.With an RV cam,450 cfm spread bore,headres/duals,HEI,and 1.94 heads in a 4.57 geared 14.50/37 tired utility bed equipped work truck that weighed a good 7,000# I got 13+ mpg avg mileage and hauled that load like any 350 would on more fuel.
I hear of better mileage out of 305s than I`d ever expect to hear from a 350.

Are you talking about a 305 or a 307. Two totally different engines. I've had many 305's and I was never impressed by the fuel mileage on any of them except one I had in an '89 RS Camaro. I got 24 - 25 MPG on the highway, but my buddie's '91 Z28 with a L98 TPI 350 gets better mileage than my RS did, so there again I can't the 305 was any better. I get 11 and 12 out the 383 in my car hauler which has a Xtreme 4X4 cam, 600 Holley and Aerohead 76cc heads with 1.94"/1.50" valves. It has a SM465 with 4.10's and 235/75/16 tires which measure around 31". My truck weighs 8800# without me in it, so its rolling over 9000# down the road. I promise you there isn't a 305 alive that will outpull this puppy! I have a broken Eaton HO72 rearend, a Dana 70 yoke and 2 driveshafts with the ears broken off that will stand by that statement! I pull junkers out of fiels and woods sometimes that are full of rocks, logs and ruts. I have to be real careful in first gear because if the truck ever bumps around hard enough to make me stab the throttle just a little bit, it will break stuff if it doesn't spin the tires.

[special-K]

Thanks for clearing that up.I never knew the 305 and 307 were different motors.Did you ever have a 305 in a truck?What cam?As I said,"the right cam makes all the difference in the world",to quote myself.I`m only speaking facts based on personal experience.The motor I mentioned wouldn`t be the same in a heavy car hauler that would gross at over12,000#.That`s unreal mileage,BTW.Especially for a Holley 600 on a 383 with that cam and a motor that eats HO72s.I`m impressed.And,thanks again,for great info.I didn`t know a 383 would out pull a 307 or a 305 in that weight range.
As far as your seperate discussion with modern Camaros goes,the differences in fuel delivery systems makes as much differences as differences in displacement.We`re getting beyond apples to apples vs apples to oranges and more into apples to cucumbers.It`s a long way from a light Camaro with a 305 to a 3x heavier empty truck that a 305 was never offered in or intended to give service in.We`ve gotten far away from talking about what the thread starter was needing to know.
In a light truck with a small load and proper gearing for the cam a 305 will get better economy.LT1s with o/d can get as good of mileage,but that`s not an even comparison because of different fuel delivery system.If that was the specific question,my answer would have been different.I took it to be asking the difference in the same design/different displacement in the same truck.

[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! ! !

[jgrh64]

which ever you decide on, use the later model vortec heads more effecient all around. (not all centerbolt cover heads are vortecs)

[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.

[MylilBowTie]

Guess I forgot to say my 305 has about 250k on it. I also have metallic oil in it. Still runs really good for what it is. My truck doesn't have an O2 sensor on it. Still has the original catalytic convertor, air pump, egr and all that stuff.

There will always be 305 supporters and haters. Im on the fence about it. I used to hate on them but they are not that bad.

[capev86]

i like both the 305 and the 350. i would choose a 305 with a 400 crank over a 350. a stroker 305 with good air flow (preferably mpi setup) should make for an economical powerhouse. a truck is for hauling heavy loads. my dad put a 70's monte carlo 305 in his 72 suburban to replace the tired 350. he installed an rv spec cam and a camaro oil pump. it did a fair job pulling our 6,000 pound 1971 holiday camper.