Better gas mileage w/ a 283, 305, or 350 w/ 700R4 [Archive] - Chevelle Tech

: Better gas mileage w/ a 283, 305, or 350 w/ 700R4


Augustboy2009
Sep 2nd, 07, 4:00 PM
Okay guys, I've been doing some searching on engines as far as gas mileage.

I'm planning my next project and really want a mileage friendly engine.

Heres the question; What engine will get better gas mileage with a 700R4 in a 1968 to 1972 El Camino. 283, 305, 327, 350?

I don't need a performance engine, just a daily driver that gets good gas mileage.

The engine must consist of a smooth running cam (hydraulic roller), a balanced rotating assembly, and small 1.94 heads for torque. (possibly E-tec heads).

Any opinions will help tremendously.

pizzi-man
Sep 2nd, 07, 4:14 PM
use fuel injection and you should see a big improvement no matter which motor you use. I personally like the 95 LT1 set up I have with the 2004r. 18 mpg around town and 26 to 28 mpg on freeway.

gnicholson
Sep 2nd, 07, 4:30 PM
what the previous guy said would work well. if i were going to build an engine for a carb i would use a 283 or a 307 would work better i think for the increased low rpm torque. use a good q jet, stock manifold ,about 9 to 1 and a hyd flat tappet cam with about 256-260 adv. on 112. with proper tuning i think you could achieve 25 mpg at 65 mph

pdq67
Sep 2nd, 07, 4:36 PM
I figure that a a stock, 195 2-barrel or 220Power Pack/283 w/ a stock 3-speed stick OD tranny will get about 25 mpg too w/ the correct rearend!

And imho, this is a great engine tranny combination for a DD!

You can't hardly run onna these into the ground, they are that tough!!!!

6500 rpm w/ either the stock, -929 like/if not cam or a Performer cam w/ the hy-lifters lashed out!!

Personally, I'd run this litttle Clevite solid lifter cam!!

PN 229-1998; 258/219/270/229, 114/110, .456"/.479" and need's .022" lash on both sides..

Should be a really mellow little cam!!

pdq67

Robinls5
Sep 2nd, 07, 5:32 PM
I built a 70 Chevelle SS 454 Sta. Wagon, I drive it about 4-5000 miles a year. It has a LS-5 type 454--700R4--3:08 12 bolt. this year from Pittsburgh to Nashville Tn. (CB-07) on the interstate without the air on.
The 454 is turning 1950 RPMs at 75 MPH . I am getting 19.46 MPG. NOTE: with an Auto-Zone rebuilt Q-Jet. Big Cube engines, when you are rolling, do not work too hard. I believe a small block VS B.B. the big block will stay in fourth or loc-up longer than a small block due to the torque factor. J.M.O. Bob

Greybeard
Sep 2nd, 07, 7:59 PM
You might consider a '93-96 Caprice 4.3 V8. Known as an L99 or "baby" LT-1, it looks exactly like a LT-1, and uses the same EFI with smaller injectors. The Impala guys claim up to 30mpg, well, some claim more......you know how that works.

If you wanted, you could go carbed, but it's probably just as easy to use the EFI. Get the harness and ECM, and send it to these guys http://ls1wiring.com/. They can redo the harness and ECM to take out the "body control' systems for the price of a carb. You can find their specials on e-bay under "wiring harness".

I bought an engine with 26,000 miles for $400 complete with harness and ECM. $250 for the wiring and ECM mods, some orange paint, new flywheel and pilot shaft bearing and it's ready. These are seldom cars with abuse. Usually sold to older people and all with automatics. One problem for those guys who don't like long rods, these engines have'em. Find a 350 LT1 block, use the crank and rods from the L99 with 350 pistons and you've got an injected 302 if you like more power.

Augustboy2009
Sep 2nd, 07, 9:02 PM
Interesting, The EFI set up sounds like a combo. I'll have to do my homework and read up on EFI stuff.

fabio
Sep 2nd, 07, 10:43 PM
I would say with the bigger 350 or 383 you would need less throttle to get the car moving. Then when you open that thing up it will run better than the smaller cubes. PLus you want something with decent torque so you won't have to downshift to maintain speeds when climbing little hills etc.

kirkwoodken
Sep 2nd, 07, 11:33 PM
Chevy made a SB truck cam with about 173*@.050" duration with the last three part numbers of 906. It's high RPM limit was about 4500 RPM. Great torque and milage cam if you can find one. Made in the 60's. I'll see if I can find out more if you are interested.

As always, maybe you should give UDHarold a call.

Augustboy2009
Sep 2nd, 07, 11:56 PM
I would say with the bigger 350 or 383 you would need less throttle to get the car moving. Then when you open that thing up it will run better than the smaller cubes. PLus you want something with decent torque so you won't have to downshift to maintain speeds when climbing little hills etc.

Thats what I was kind of trying to determine. Is it better to go with a small motor with less of a stroke or go with a larger 350 size to allow the engine to obtain more torque requiring less throttle to get the car moving.

gnicholson
Sep 3rd, 07, 12:06 AM
i had a 283 in a 66 belair that was completely stock with a power glide. it had very good low rpm torque even with the high 1st gear. if you build the engine with the correct parts such as heads with the correct sized intake runners it will get better milage than a bigger engine and still run good .like i said earlier 25 maybe better on the highway. the late model fuel injected setups are intriguing but are more complicated and more expensive. how bout a new ls 2. 400 hp and 25 mpg 30 in a new vette

Augustboy2009
Sep 3rd, 07, 12:11 AM
i had a 283 in a 66 belair that was completely stock with a power glide. it had very good low rpm torque even with the high 1st gear. if you build the engine with the correct parts such as heads with the correct sized intake runners it will get better milage than a bigger engine and still run good .like i said earlier 25 maybe better on the highway. the late model fuel injected setups are intriguing but are more complicated and more expensive. how bout a new ls 2. 400 hp and 25 mpg 30 in a new vette

Yeah, an LS 2 would be very nice but I'm sure they are pricey. Maybe when the time comes I can find decent LS 2 out of a wrecked car.

mnunn
Sep 3rd, 07, 9:59 AM
While you're collecting opinions,

Since "performance" isn't a driving factor here, I'd think torque is the major consideration. As such I like the 305/EFI combo to go along with your TH700 tranny.

My reasoning is the 305 has more torque at lower RPMs than either the 283, 307, or 327 and less volume to try to fill with air and fuel for every revolution while still delivering enough horsepower to get you up a hill or two without needing to downshift. (Not that a 350 wont, it's just that if the smaller engine will, so why go bigger)

If you don't want the EFI "challenges", then a small Q-jet atop a "performer" manifold would IMO be the better induction choice. HEI at a minimum (and an MSD box if resources allow to promote complete combustion).


If you're planning to build the 305 yourself, then I'd choose pistons and cyl heads that'll work together to minimize any tendency to detonate on 87 Octane, and a cam with a wider LSA. 1.94 intakes are plenty big but I'd shy away from the 1.5 exhausts. The roller cam path you want allows you more airflow potential through the head while minimizing overlap. Regarding detonation, It'd be a bummer if you built this engine to save money and then had to pay 20 or 30 cents more per gallon for high test to stop the pinging.

Even without EFI I'm a strong advocate for putting an O2 sensor in the exhaust to watch what the A/F ratio is doing while driving. That'll enable you to jet the carb for optimal fuel mileage when cruising.

For a low RPM engine, I'd save my $ on balancing and spend it on a wide band O2 sensor and gauge, or a towing/RV style torque converter to minimize slippage until you reach lockup speed.

One final thought...Depending on the R&P ratio you have, with the TH700's 30% overdrive you can get too low on your Final Drive Ratio. If the street tires are normal diameter, I'd think 3.08's are about as steep as you'd want to go (thinking alternator and A/C RPMs here and potentially falling below the engine's natural torque curve). I like 3.55's behind a TH700 personally. You say it's a daily driver project. But you'll still need it to take off from a traffic light a little quicker than a city bus. So depending on the weight of the car, shoot for at least a 9.0 or better total mechanical ratio in low gear.

Just more food for thought.

Good luck.

animal69
Sep 3rd, 07, 1:33 PM
Have you considered a 305. An El Camino is a heavy vehicle and the 305 with it's 3.48" stroke would have more torque than a 283 (3" stroke) or a 307 (3.25" stroke). I had one in my '83 1/2 ton (3.42 posi with a 4 spd. OD manuel) and got very good milage (18-20mpg) when just cruising down the highway.

70 beater
Sep 3rd, 07, 2:12 PM
One final thought...Depending on the R&P ratio you have, with the TH700's 30% overdrive you can get too low on your Final Drive Ratio. If the street tires are normal diameter, I'd think 3.08's are about as steep as you'd want to go (thinking alternator and A/C RPMs here and potentially falling below the engine's natural torque curve). I like 3.55's behind a TH700 personally. You say it's a daily driver project. But you'll still need it to take off from a traffic light a little quicker than a city bus. So depending on the weight of the car, shoot for at least a 9.0 or better total mechanical ratio in low gear.

Just more food for thought.

Good luck.

This is good info here,as well as everything else posted.I've got a mixed up combo,performance engine,heavy truck,stock converter 700r4 and 3.08 gears.Not a good set up,almost 80mph at 2000 rpm,way below where the engine starts getting into its' sweet spot,making for poor fuel economy in o.d. and lugs the engine down,does better in drive.I've got to change the torque converter and gear,at least gear at a minimum,to correct it,going to 4.11s.

For a DD build a good low rpm torque engine like these guys are saying.