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#1 |
Blue 67
![]() Join Date: Apr 2004
Location: Western WA
Posts: 1,178
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The difference between 305 and 350
What are the pros and cons of each engine?
thanks
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1953 GMC 3/4 ton: current project 1967 C20: 5.3 voretc with T5 conversion, 4 wheel 8 lug disc brake 1972 Nova: my 4 door sport sedan! 5.3 voretc + T5 conversion. drivable project, FUN!! 1979 Camaro Z28: 5.3 vortec conversion with build TH350: drivable project, Fun to drive 1992 Camaro RS convertible (Z28 clone): 5.3 conversion with build T5: on going project 2005 Silverado 2500, 4x4 Duramax, original owner |
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#2 |
Watch out for your cornhole !
![]() Join Date: Jun 2003
Location: Azle, Texas
Posts: 14,162
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Re: The difference between 305 and 350
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.
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#3 | |
I have a radical idea!
Join Date: Jan 2005
Location: Sweet Home Alabama!
Posts: 6,513
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Re: The difference between 305 and 350
Quote:
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'67 C-30 Dually Pickup 6.2 Turbo Diesel, NP435 ‘72 C-10 SWB , 350 4bbl, TH350 '69 C-10 SWB , 250 L6, 3 OTT '69 GMC C3500, dump truck, 351 V6, NP435 '84 M1009 CUCV Military Blazer 67 C-30 Turbodiesel build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254096 My trucks http://s226.photobucket.com/albums/d...ediafilter=all Member of the 1-Ton Club! |
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#4 |
Watch out for your cornhole !
![]() Join Date: Jun 2003
Location: Azle, Texas
Posts: 14,162
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Re: The difference between 305 and 350
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.
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#5 |
Right turn Clyde
Join Date: Nov 2002
Location: Cincinnati, Ohio
Posts: 2,911
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Re: The difference between 305 and 350
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
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1974 C25 LWB: 454 4bbl Carb / TH400 / 3.73 1992 Camaro RS 305 TBI |
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#6 | |
Parts and more parts
Join Date: Nov 2003
Location: Lebo, Kansas (middle of nowhere
Posts: 6,821
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Re: The difference between 305 and 350
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#7 | |
I have a radical idea!
Join Date: Jan 2005
Location: Sweet Home Alabama!
Posts: 6,513
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Re: The difference between 305 and 350
Quote:
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'67 C-30 Dually Pickup 6.2 Turbo Diesel, NP435 ‘72 C-10 SWB , 350 4bbl, TH350 '69 C-10 SWB , 250 L6, 3 OTT '69 GMC C3500, dump truck, 351 V6, NP435 '84 M1009 CUCV Military Blazer 67 C-30 Turbodiesel build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254096 My trucks http://s226.photobucket.com/albums/d...ediafilter=all Member of the 1-Ton Club! |
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#8 | |
Parts and more parts
Join Date: Nov 2003
Location: Lebo, Kansas (middle of nowhere
Posts: 6,821
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Re: The difference between 305 and 350
Quote:
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. |
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#9 |
Active Member
![]() Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
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Re: The difference between 305 and 350
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. |
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#10 |
Old Skool Club
![]() Join Date: Jun 2001
Location: Benton, AR "The Heart of Arkansas"
Posts: 10,880
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Re: The difference between 305 and 350
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.
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Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was. |
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#11 | |
Parts and more parts
Join Date: Nov 2003
Location: Lebo, Kansas (middle of nowhere
Posts: 6,821
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Re: The difference between 305 and 350
Quote:
Agree with your insight ![]() Last edited by piecesparts; 11-26-2007 at 12:21 PM. |
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#12 |
Registered User
Join Date: Nov 2006
Location: lafayette, ga.
Posts: 832
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Re: The difference between 305 and 350
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
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![]() It must be fought for, protected, and handed on for them to do the same.... Ronald Reagan |
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#13 |
Parts and more parts
Join Date: Nov 2003
Location: Lebo, Kansas (middle of nowhere
Posts: 6,821
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Re: The difference between 305 and 350
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)
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#14 |
Account Suspended
Join Date: Mar 2006
Location: Weaverville, NC
Posts: 718
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Re: The difference between 305 and 350
45....thats the math teacher response...lol
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#15 |
Rottenwood Garage Member
Join Date: May 2005
Location: Marietta, Georgia
Posts: 4,321
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Re: The difference between 305 and 350
The difference between 305 and 350....................EASY
One is junk and the other is not.
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2004 Chevrolet Suburban C1500 2001 Chevrolet 2500HD Crew 6.0 1999 Harley Davidson Electra Glide 1972 Chevrolet C-20 Custom Camper "Dump Truck" 1972 Chevrolet C-20 Suburban "Big Green" 1969 Chevrolet C-50 Wedge Hauler "Leonidis" 1966 C-10 2x4 short fleet 327 4 speed "Race Truck" 1952 Plymouth Cranbrook "Rican" (my grandfathers) 1931 Ford Model A Coupe "Black Beauty" 1930 Ford Model A truck "Club Cab" 4x4 Rottenwood Garage and Speed Shop.....where everything must be racy! It's not just a hobby..It's a LIFESTYLE!!! Thanks for nothing Barrett-Jackson You cant fix stupid or teach accountability! Time wasters, looky Lous and tire kickers are everywhere! |
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#16 |
Join Date: Dec 1999
Location: Eastern - Manitoba Canada, Winnipeg
Posts: 4,369
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Re: The difference between 305 and 350
Math teacher would mark that wrong for no unit of measure...lol.
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Senior active founding member. 70 3/4 ton GMC Suburban 4x4 250/4 spd. 71 1/2 ton Suburban Chevy 4x4, 350/350 72 Chev 1 ton tow truck 402BB w/Holmes 440 wrecker on propane 2005 FLSTSCI Harley Springer 85 FXSB Harley Lowrider 72 Triumph 650 Bonneville 5spd "Poor people don't have hobbies" Quote from wife. |
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#17 |
Registered User
Join Date: May 2005
Location: PA
Posts: 2,696
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Re: The difference between 305 and 350
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#18 |
Fat Fendered Fleetside
Join Date: Nov 2004
Location: WPB, S. FL, USA, Earth
Posts: 718
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Re: The difference between 305 and 350
hmmm, what about 305 Cu.in -vs- 307 Cu.in.
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71 GMC lwb 56 Big window swb 93 GMC Sonoma (dd) radiused fiberglass fender project for 67-72 |
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#19 | |
Registered User
Join Date: Nov 2006
Location: lafayette, ga.
Posts: 832
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Re: The difference between 305 and 350
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
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![]() It must be fought for, protected, and handed on for them to do the same.... Ronald Reagan |
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#20 |
ENGINE BUILDER
Join Date: Apr 2006
Location: Shortsville n.y.
Posts: 344
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Re: The difference between 305 and 350
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.
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#21 |
Rottenwood Garage Member
Join Date: May 2005
Location: Marietta, Georgia
Posts: 4,321
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Re: The difference between 305 and 350
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.
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2004 Chevrolet Suburban C1500 2001 Chevrolet 2500HD Crew 6.0 1999 Harley Davidson Electra Glide 1972 Chevrolet C-20 Custom Camper "Dump Truck" 1972 Chevrolet C-20 Suburban "Big Green" 1969 Chevrolet C-50 Wedge Hauler "Leonidis" 1966 C-10 2x4 short fleet 327 4 speed "Race Truck" 1952 Plymouth Cranbrook "Rican" (my grandfathers) 1931 Ford Model A Coupe "Black Beauty" 1930 Ford Model A truck "Club Cab" 4x4 Rottenwood Garage and Speed Shop.....where everything must be racy! It's not just a hobby..It's a LIFESTYLE!!! Thanks for nothing Barrett-Jackson You cant fix stupid or teach accountability! Time wasters, looky Lous and tire kickers are everywhere! |
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#22 |
Parts and more parts
Join Date: Nov 2003
Location: Lebo, Kansas (middle of nowhere
Posts: 6,821
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Re: The difference between 305 and 350
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. Last edited by piecesparts; 11-27-2007 at 10:44 AM. |
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#23 | |
I have a radical idea!
Join Date: Jan 2005
Location: Sweet Home Alabama!
Posts: 6,513
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Re: The difference between 305 and 350
Quote:
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'67 C-30 Dually Pickup 6.2 Turbo Diesel, NP435 ‘72 C-10 SWB , 350 4bbl, TH350 '69 C-10 SWB , 250 L6, 3 OTT '69 GMC C3500, dump truck, 351 V6, NP435 '84 M1009 CUCV Military Blazer 67 C-30 Turbodiesel build thread http://67-72chevytrucks.com/vboard/s...d.php?t=254096 My trucks http://s226.photobucket.com/albums/d...ediafilter=all Member of the 1-Ton Club! Last edited by 67_C-30; 11-27-2007 at 11:05 AM. |
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#24 |
Parts and more parts
Join Date: Nov 2003
Location: Lebo, Kansas (middle of nowhere
Posts: 6,821
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Re: The difference between 305 and 350
We all understand that we are talking about engines that are really low on HP, already--Don't we? The GM motors in these trucks were built with a lower compression ratio and their HP ratings were in the 160 to 200 range for the most part. Down grading this will make the engine absolutely enemic and to me worthless in a truck. (My own personal feeling) The gearing was the worst that was done to most of these trucks---OD trannies and a gear ratio around 2.73 to 3.08---I have a 3.42 in my truck, but I run a low profile tire to make the gearing a little more steeper to get the bite that I want. I drive around 21,000 miles a year, so I tried to make it as efficient as possible and get use of every drop of fuel. Mine looses mileage when I get to cruizing around eighty, especially in cold weather. I saw that yesterday coming home from K.C.; I think I dropped a couple MPGs. You have to bless those guys that are in a hurry and give them a 1/4 mile to find that errant trooper using radar.
Last edited by piecesparts; 11-27-2007 at 11:44 AM. |
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#25 |
Special Order
![]() ![]() Join Date: Nov 2004
Location: Mt Airy, MD
Posts: 85,859
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Re: The difference between 305 and 350
The right cam makes all the difference in the world and will dispell all myths that a 305 or 307 can`t 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.
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~ Last edited by special-K; 11-27-2007 at 11:28 PM. |
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