Quest for the best milage from a C-10

[diggertodd]

Ready to start a new project - to outfit the highway hot rod with a new engine for the ultimate milage. I currently have a TCI 4L60E trans installed with a mostly stock 355 with edelbrock carb intake and headers. Tweaking and tuning has my besy highway at 14.1 mpg. I travel lots of miles on business and my wife and business partner would like to see fewer gas recepts.

No V6 or diesel - have my hot rod pride

My thoughts are a late model 305 roller cam block with small runner aluminum heads and the new Comp Cams/FAST elecronic fuel injection unit that bolts on like a carb with no manifold modifications. Have lots of friends at Comp for actual cam specs.

Any other suggestions?????

My engine builder for my dragster thinks a 383 combo would actually do better if I control the shifts lower with the 4L60E and will push the brick down the highway better

Any other suggestions?????

[67_C-30]

An EFI 350 is hard to beat. I have never really seen a 305 or a 383 (or 400) do any better overall than the 350 in a truck. A 327 might, but I've never seen many of them retrofitted with EFI for the street. In stock form, the 327 is a little better than the 350. The 305's 3.75" bores choke it so much that it can't breathe, and the long 3.75" stroke of the 383/400 sucks the fuel. The thread below contains various combos and MPG.

http://67-72chevytrucks.com/vboard/s...d.php?t=208202

[Ackattack]

what gears you running? I think with a 4L60E 3.42 or maybe 3.23s would be the optimal gearing for mileage. 3.08s and OD is too high of gearing.

You might also look into some of the OEM fuel injection. I know some of the TBI 305 camaros could put out some decent MPG. I'm partial to TPI, but it may give up a mile over TBI.

Of course you could really step up to the plate and put in a gen III 4.8L and you'd probably be 22+ with the proper tune....but that is a tad more than a bolt on deal

[Gray Ghost]

Stick with the 350 idea....305's have notoriously bad bottom ends after 90k and you won't save any gas in the process.

[Jim_PA]

I agree. I've never seen a 305 out gas a 350 in a heavy vehicle.

[Morgsie]

Originally Posted by Buffalo Elk

Stick with the 350 idea....305's have notoriously bad bottom ends after 90k and you won't save any gas in the process.

This is odd considering the 350 HAS THE SAME BOTTOM END as the 305. Perhaps you are thinking of the soft cams that GM used from the mid 70s to the mid 80s. I also disagree with not saving any gas using the 305 compared to the 350.

[special-K]

I think smaller displacement(283/307),RV cam,open breathing/flow,hot spark,and EFI or small 4bbl.

[67ChevyRedneck]

I have a carburated 350 with a 700R4 and 3.73 open rear axle and I get 16 mpg if I keep it around 60 and 15 mpg around 70-75mph. As has been asked, what's the rear axle? 4.10?

You currently have a great set up.

Have you checked to see if your odometer is even accurate? Mine is off 9%.

[diggertodd]

The big dummy that I am, I did not count the gears when I replaced the cover this spring - I was too hell bent on getting it running, I'm going to make an educated guess it is a 3.73. With the 4L60E in OD and converter locked... I'm at 1850 RPM at 65 MPH. I am not afraid to throw a new Ring and Pinion in her.

You're talking me out of 305, but there are lots of decent looking 283 cores that can be had on ebay for a couple of hundred bucks. But now your all talking me into sticking with a 355.

[mnunn454]

Hardware wise, I too think you have the best combo already:
355
4l60E (make sure the lockup converter is working)
3.73 rear gears
less than 2000 RPMs @ highway speeds.

1st I'd work on the air fuel ratio with an O2 sensor and an a/f meter/gauge. (There was a neat article a couple of years ago in CHP magazine called "old school meets new school" [or similar] where a techie tuned the idle circuits of a Demon carb on a LS powered weekend warrier Gen 3 Camaro to get 25 MPG. )

Then I'd call the comp cam friends of yours and make sure your current cam's LSA isn't creating too much overlap for those low engine RPMs/Torque requirements. Your engine may actually be turning below its optimal efficiency point.

Another dimension of this argument would be the size of your intake runners (manifold and head both). If they're too large for the miniscule CFMs you're flowing at 1900 RPMs, then the intake air velocity could be too low causing the flow to start/stop every time the intakevalve opens and closes and the fuel droplets to attach to the port walls and intake valves.

Next, I'd try a set of skinny hard tires to see if rolling friction is taxing things too much, plus check to ensure the brakes aren't dragging.

Last, I'd try a smooth surfaced topper the same size as the cab, or remove the tailgate, or add a chin spoiler etc to improve the aerodynamics a little.

To encourage you a little, I once got 25 MPG in my ugly as sin 61 Apache stepside. It had a 3 speed tranny, 3.90 rear gearing, 16" military tires, a 283 with small headers and a tiny Rochester 4 barrel carb and manifold. It was a 100 mile R/T test run (about 20 city, 80 highway) so I took off real easy, kept the RPMs low and stayed under 55 MPH.

It can be done.

Good luck.

[57sailplane]

well,

i have thought about building somthing like this a long wile for the boys truck. my idea was to use a small jug block like a 283 or such, then stick a 400 crank in it. small cubes yet enough tork for some highway gears. with the more torque you can run lower rpm. anyway this was just an idea not sure if its realistic.

[mnunn454]

Originally Posted by 57sailplane

well,

i have thought about building somthing like this a long wile for the boys truck. my idea was to use a small jug block like a 283 or such, then stick a 400 crank in it. small cubes yet enough tork for some highway gears. with the more torque you can run lower rpm. anyway this was just an idea not sure if its realistic.

Actually, that idea could work fairly well if you could use really long connecting rods. But since the deck height to crank distance is fixed, the short rod ratio of the 400's crank would negate most of the efficiency you'd pick up with the 283's smaller CID (IMO). Also, I've heard severely stroked engines tend to be sensitive to detonation requiring either more expensive fuel or lower compression ratios. This has the same overall effect of raising cost or lowering output.

All this gets me to thinking about an article I read a few years back called (I think) "The engine Chevy should have Built". It was the 377 (400 block with a 327 crankshaft I think). While it didn't have much more output than the 400 (no replacement for displacement), it came real close even though it was down about 30 cubes. It used 6"+ long 6-cylinder Ford rods, revved higher and could run higher compression ratio/lower octane fuel/more timing than a 400 and still not detonate. All this made it a more economical alternative for delivering about the same performance. Besides the scarcity of 400 blocks today, the main drawback of building one from parts today is the 327/400 crank to block main bearing diameter differences (hard for us to solve, but would have been real easy for Chevy to use 327 cranks with extra large diameter main journals.)

Fun food for thought. Thx, Sailplane

[Brad]

Originally Posted by mnunn454

All this gets me to thinking about an article I read a few years back called (I think) "The engine Chevy should have Built". It was the 377 (400 block with a 327 crankshaft I think).

I thought the 377 was a 400 block with a 350 crank.

[Jim_PA]

Originally Posted by mnunn454

All this gets me to thinking about an article I read a few years back called (I think) "The engine Chevy should have Built". It was the 377 (400 block with a 327 crankshaft I think). While it didn't have much more output than the 400 (no replacement for displacement), it came real close even though it was down about 30 cubes. It used 6"+ long 6-cylinder Ford rods, revved higher and could run higher compression ratio/lower octane fuel/more timing than a 400 and still not detonate. All this made it a more economical alternative for delivering about the same performance. Besides the scarcity of 400 blocks today, the main drawback of building one from parts today is the 327/400 crank to block main bearing diameter differences (hard for us to solve, but would have been real easy for Chevy to use 327 cranks with extra large diameter main journals.)

Fun food for thought. Thx, Sailplane

It was actually a 400 block with a 327 crank --

http://67-72chevytrucks.com/vboard/s...d.php?t=164908

[mnunn454]

Originally Posted by diggertodd

............My engine builder for my dragster thinks a 383 combo would actually do better if I control the shifts lower with the 4L60E and will push the brick down the highway better

diggertodd,

Are you running an aftermarket controller for the 4L60E? Or is it an OEM unit and feeding it TPS and MPH data somehow?

Assuming it's aftermarket, how much more work to upgrade the controller to a OEM ECM and TBI setup? Though certainly not easy, the ECM/TBI path would ensure an efficient 14.7:1 a/f ratio.

[Brad]

OOPS- I could have sworn it was a 350 crank. It seems I've heard of someone doing just that, but maybe I'm mistaken.

Ok, back to my L6.

[Jim_PA]

Originally Posted by Brad

OOPS- I could have sworn it was a 350 crank. It seems I've heard of someone doing just that, but maybe I'm mistaken.

Ok, back to my L6.

Yeah, it's done, 400 with 350 crank = 377 (destroked)

400 with 327 crank and ford rods = 350 (even more de-stroked I suppose)

[68C15]

Originally Posted by Jim_PA

Yeah, it's done, 400 with 350 crank = 377 (destroked)

400 with 327 crank and ford rods = 350 (even more de-stroked I suppose)

doesnt that come out to be an actual 348 ci? I know a speed shop in Ill. who had one in his stock car. the power band started at 4500!!

as for MPG, have you thought about throwing an EGR into the mix? you can run higher compression for full throttle power and have it lean the mix out some for cruising.

[Brad]

AHA! I didn't think I was that crazy!

[Andy4639]

I have a complete 305 HO motor 700-R4 transmission out of a camaro with 4:10 gears and I get 18 on the open road. The same thing is the problem with my 07 Tahoe to high of gear kills the milage. 3:08 gears keeps the Tahoe in the wrong RPM range all the time sucking gas.
If I drive the 71 at 55-65 I could probably get over 20 just can't make myself drive that slow. Oh I have over 200,000 on this setup that I installed back in 1989. It's my daily driver too!
The 305 has performed well with no issues.

[watahyahknow]

a smaller engine needs to work harder in the truck and therefore wears faster and suckle more gas
about the 400 crank in the little bore block : yes it could work but i dont think it will make mush power since the bores are still shrouding the valves
about the 350 327 crank in a 400 block :crumpy jenkins made a lot of those engines they rev like mad , he solved the problem with the smaller diameter of the mains by putting in a set of old 400 bearingshells and pin them down , then he would line bore the lot and put 350 bearning over the 400 ones

[diggertodd]

Yes, I have the TCI 4L60E trans controller - it works fantastic, you can plug in a laptop and move upshift and downshift points as easy as a multiple choice/ chart. There is also an optional program where you place a simple grounding toggle switch on your dash and you can move the shift points and shift firmness (mine is set with a 10% increase) with the flip of the switch.

As far as the different cranks in different blocks, my magazine relationship with different companies such as Ohio Crankshaft, the new blank crankshafts they can use have enough material to pretty much grind any journal or rod diameter and with your desired stroke without the need for spacer bearings, But I cant get them to agree on what combination would be the most efficient to push the ultra aerodynamic and lighweight C-10 around. I am going to throw the 377 thoughts at them.

------

www.dragnews.com

[jkaylor68gmc]

I am running a 305 0.30 overbore, iron heads, flat top pistons, Edelbrock performer aluminum intake, 500cfm carb and of course A/C on the '47 which weighs about the same. It is hooked to a TCI 700R4 with lock-up converter, 20-inch rear wheels 9Unsure of rear tire height and stock '65 Chevy truck manual gears ( i believe are 4:11s) and I get 20mpg. The lock-up converter really helps.

[69face]

just put in the engine that goes with that transmission you have. the lq9! 6.0l vortec! 5.3l vortec! 4.8l vortec!

[Ronin8451]

I have a '70 LT1 350 with a small solid lift RV cam, Holley Strip Dominator intake, a Holley SA770 carb leaned out by drilling air bleeds all backed by a 700R4 and 4.11 gears turning 28" tall tires in my '64 long bed step and it gets 19.2 MPG @ 70-75mph on a good day. I am right at the brink of pinging all the time and have to run a bottle of 104+ octane booster every 2 tanks ( I fill up at half tank to keep it mixed as long as possible). I bought the truck with the engine/tranny already installed and put the SA770 carb on it along with a new HEI ignition. I am playing with the ignition curves to help get rid of the pinging. I may try some 1.6:1 roller rockers to get a little more duration out of the cam to bleed off a little cylinder pressure. I also have headers with 2 1/4" exhaust and Flowmasters turned down in front of the axle. The high compression is a big factor in efficiency at the 2600RPM it turns @ 75MPH . I may swap the intake out for a Performer RPM to get more low to mid-range TQ. out of it .

Rick

Rick