small block performance AND economy

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RzeroB

RzeroB

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I just got done reading the "fuel economy issues" thread http://www.forabodiesonly.com/mopar/showthread.php?t=197268&highlight=fuel+economy+issues and it was kind of ugly - 8-10 mpg out of a 318? That's like big-block fuel "economy" (not!)! At $4 a gallon those kind of numbers won't cut it for me when I finally find a car and get back in the hobby. When I find a car, I would really prefer a small-block vs "the leaning tower of power" Slant-6. Nothing against the 6, I would just like to have the small V-8 and reasonable economy too.

It got me thinking. The last small-block I built was a 318 with a mild cam, headers, Edelbrock SP2P manifold and a Holley 390 four barrel carb. If I recall correctly, I could get 15-16 mpg out of it if I took it easy AND it was surprisingly "lively" when I put my foot into it. Now it's been a while, this was the early 90's, and technology to improve economy and performance has come a long ways since then. So it has to be possible to build a small-block that can be considerably better on fuel economy can't it?

I would think a 273, or 318, could be built with modern aftermarket fuel injection system and mated to an overdrive transmission which together could yield 20+mpg. Read a thread over on Cuda-Challenger.com where some guys are swapping in 500 and 518 OD trans from Dakotas with a little modifications and fabrication http://www.cuda-challenger.com/cc/index.php?topic=75030.msg761753#msg761753 I know you could bolt on an aftermarket OD trans from Keisler or Passon but the cost would probably out-weigh the gain in economy - negative return on your investment.

As you can see it's been a while since I last built a small-block, so I know there are a lot of new things and techniques out there to build a more effecient small-block. So my question is, has anybody achieved sucessful results in improving their economy to around 20mpg or better? If so, where are you guys and the threads detailing your build.

Thanks!
Tom
 
might want to look into efi and an od of sorts....but keep this in mind...if you do not do a ton of driving you may never recoup the funds spent if you go down these 2 roads....
 
At 55mph in the back roads of Georgia, (Southeast corner up to Valdosta & back) I can squeeze 17.5 in my 1973 Plymouth Road Runner 340-A833 four speed-maybe3.55/3.23 with a 600 holley carb on it-food for thought. Someone either rebuilt, re-ringed, or just swapped the cam in it; Rustyratrod said the cam was bigger than stock. The car has exhaust manifolds with dual exhaust (small pipes, maybe 2 1/4??).

I bet in an A-body with 3.23's, an OverDrive transmission, with a well thought out 318 that 25mpg's would be easy on the highway until you got on it-just my ignorant guess though.
 
inkjunkie said:
might want to look into efi and an od of sorts....but keep this in mind...if you do not do a ton of driving you may never recoup the funds spent if you go down these 2 roads....
Click to expand...

X2
I'm convinced the biggest contributor to higher MPG s the gearing.

I have a driver 68 barracuda, 318, Weiand intake, 625 Carter, unknown cam, (previous owner said it was a mild RV cam but it has a pretty good lope) 904 w/ unknown shift kit, 3.23 SG in an 8-3/4, 215-60x15 tires, no A/C, manual steering, aerodynamics of a brick ( not the narrow end, the wide face). Best ET of 14.77 in the quarter. I drove 4 hours each way to Tri-State Dragway on Saturday for the Hemi Reunion. I did NOT get into the secondaries at any time during my 8 hrs on the road, never cruised higher than 65 MPH and had a steady 17-18 inches on the vacuum....er "Performance Indicator", and after 2-1/2 hrs with the flakey gas gauge I stopped for fuel. (gauge was on the E mark) Did a quick calc and came up with a crummy 13.5 MPG. The speedo/odometer are dead on per my GPS. I'll have to do a total trip MPG when I fill it up again later this week. Really, $120 or so to drive 430 miles? I could've taken the Neon at 37-38 MPG.

I actually drive this car, not daily, but 1200 miles or so per year. The Passon 5 speed would be my choice but the payback would not happen in my lifetime. I'm thinking of switching to a known cam that still will have some power but improve the MPG.

It's going to be a couple years before the 5.7 swap happens so I don't want to put much into this 318.
 
I'm confident that a healthy, stock-valve'd 318 with a performer intake, mild cam (210*@50-ish), modest carb (500cfm eddy), A-998 trans, and 3.23's can get 20mpg at 55mph.
 
i am trying to do exactly same to my 318 this winter.

goal is small power gain, mainly low end torque and improve mpg.
od trans, a500, compression up and, ligther rotating engine parts, little bit bigger cam.
Od is coming rest of parts are subject to change till i open up my engine.

Here is really intresting build:
http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=3944014&page=0&fpart=1&vc=1

better mpg is bossible mine got almost 20mpg when it was stock. but it took REALLY carefull driving
 
Want to get better fuel economy, get an AF gauge and start tuning!

Most cars with performance upgrades are horribly rich on cruise.

350hp 360 with a 750 DP getting 20mpg on the highway, yes it can be done.
 
Gearing is everything. I get about 13.8 mpg (Canadian gallon) out of my 340 Demon with a 6-71 blower as long as I'm not getting on it. That's with 650 to 700 HP available if I want it.

Jack
 
google Hot Rod Dave Super Dooper mileage 318

actually that doesn't work...anyway the thread is on Moparts
web board
 
Thanks for the replies guys! I know some of you guys have to be working on getting both performance AND economy out of your small-block.

I'm a high performance horsepower junkie myself, but the cost was a lot easier to swallow when gas was under a $1 a gallon vs $4 a gallon today. One of the reasons I switched to motorcycles - a lot more bang for the buck. Where else can you be running in the 10's for $6K (02 Suzuki Hayabusa)?

Anyway, someone out there is doing it with the small-block and I want to see their results. I want to get back in the game and not go bankrupt paying the oil cartel in order to drive and enjoy my car.

Keep it coming, I want to hear how you are getting both out of your car.

Thanks!
Tom
 
Coyote Jack said:
Gearing is everything. I get about 13.8 mpg (Canadian gallon) out of my 340 Demon with a 6-71 blower as long as I'm not getting on it. That's with 650 to 700 HP available if I want it.

Jack
Click to expand...

Hmmm? Forced induction with a supercharger, turbocharger or both helps the 18 wheeler big rigs improve their efficiency and power. So I assume it would do the same for any engine wouldn't it? Forced vs vacuum induction increases volumetric efficiency doesn't it? Obviously a turbo or a Paxton type supercharger can increase performance, but can it also improve economy?

Tom
 
I have a 500hp 408 with 4.10 gears and overdrive transmission. If I drive it nice I have gotten 15 mpg, and if I drive it like I normally do I average 11.5 mpg.
 
Mopar to ya said:
I have a 500hp 408 with 4.10 gears and overdrive transmission. If I drive it nice I have gotten 15 mpg, and if I drive it like I normally do I average 11.5 mpg.
Click to expand...

Are you serious? With a 4:10 gear? Oh, wait, the secret is the OD trans isn't it? What OD trans do you have in there? What is the OD gear ratio?
 
O.K. some things from the thread if i remember correctly
You must have high compression...10:1 min
hi or medium lift short duration cam
your maximum lo speed torque must be your cruise rpm
lots of small things help
..weight reduction,tire pressure,aerodymaics or wind resistance,wheel alignment
hi flo air cleaner,small carburetor primary venturi,thin oil ,reduce engine parasitic losses, lean carburetor,engine timing/ tuning.etc...
..Hot Rod Dave was flirting with 30 mpg in a 318 notch.
 
My barracuda was averaged 14mpg. 318, milled 360 heads 1.88 1.60 valves, engle cam 216 at .050 113ls. ported 360 intake, long tube headers, 750 summit carb, 904 with shift kit, and stock converter, but 3.91 gears. I think with 323 gears it would have been at least 1.5mpg better.

if I was to build a mpg 318 I would use kb167, magnum heads, should give 9.6 to 1 compression, a howards 711381-10 ground on a 114ls (711381-14). the wide lobe separation should help bleed off some cylinder pressure. Performer rpm intake, holley 600 with annular discharge boosters. long tube headers, 2.5" exhaust. 3.55 gears, a500 trans, I think would do pretty good.
 
Just to give you another option. Fit a turbo.
This will make the motor more efficient and have more power. Just don't go too big on the turbo.
 
DGC333: 360, 10.6:1 compression, 375hp, 23MPG, a833OD 355. It can be done.

I got 18 with my 5.9 magnum, aftermarket mild cam, a904, 3.73, before the surgery.
 
Don't waste your time with any old engine, drop in a newer Hemi, chevy LS or coyote from a newer car and get 30mpg and make 400 plus hp.
My 5.0 mustang can drive down the road for hours and never drop below 30mpg plus that engine would run mid 11's in a 3200lb A body.
 

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the 'old timer' said...they sure don't build 'em like they use to.
the other said...it's a good thing!
 
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