Fuel milage question. 383hp 906 head vs aluminum. questions for roadtrip cruiser

[C_stripes]

I am not trying to start a debait about economy and if I'm worried about that.... Blah blah blah...


First question; I am curious though, what would you estimate a 71 B-body w/ 383HP, auto, and 3:23 gears and a little larger than factory tires should get?

Second question; do you think running Edelbrock aluminum heads, intake, mild cam, and carb would help or hurt the mph?

Third question; Would an aluminum radiator with electric fan make a difference?

In theory, this would be for a real long distance, mostly open road and would not be 'racing' the vehicle.

Do you think it would average 15mpg?

[XH29N0G]

I don't know whether the aluminum heads will make a difference in long distance gas mileage.  My guess is that the biggest impact on long distance gas mileage will be the accelerator pump, keeping the throttle steady, tires (type) and tire pressure.  Timing might also make a difference.  I assume the other bolt on components (heads, intake, exhaust, etc...) also have an impact.  I think this is about what I used to get on long trips, although I upped the mileage a few mpg to the 16-20 mpg range with an overdrive gear ratio in a 70 383 at one time.

[Ghoste]

Well of course taking weight away with the aluminum is going to help although I'm not sure it could be measured.  Theoretically some improvements to help engine efficiency could also beused to help mileage versus speed but its a little more complex than this sentence can contain.

[rt green]

do we have a limited mph on the freeway? are there any guide lines we have to follow?  in order to do a debate, a set of rules would be fun.

[C_stripes]

It would be a combo of Interstate, back roads, and mountain roads. Any elevation between 0' to 6000' elevation. Average freeway speed would be between 75-85 mph. Back roads would be 55-60 mph.

With the overdrive unit, would it be better to have 3:55 gears?

Tires would be BFG Radial T/A's set at 35psi.

The trip would be about 15,000 miles in 45 days and would hit all lower 48 states plus DC. (More to come on the road trip plans soon(I will possibly be looking for places to crash some nights))

Would aluminum wheels help with milage or would it make no difference over rallys?

I really want to do this in a 70's mopar vs a new camry or something. I think it would be much more satisfying.

[Ghoste]

Aluminum wheels would help.  Final drive ratio depends on a combination of where the greatest majority of driving will be done and what is the lowest but still highly efficient rpm that your choice of other components require.

[1974dodgecharger]

I run..
Rpm heads
10.5 to one
383
Hooker headers, 3 inch all back
750 dp
Electric pusher, mechanical puller
Manual tranny
31 inch total rear diameter thats 20 inch rim with 295/45/ with 18s up front
3.23 gears

I get roughly 8mpg with hard acceleration (show offing) i get 5 but steady highway cruising i get 10 max.

[Ghoste]

What do you have for camshaft?

[C_stripes]

The car isn't built, or even bought yet. I am just trying to figur out the best options. I may go small block, but the car I have found that I like is a 383hp.

I am trying to find the best options for optimum mpg as well as having performance when wanted. But mostly mpg. The car/s that I am looking to find are 71-3 b-body (prefer four door or wagon) or a cordoba or magnum. I still have a little time to decide and find the right car.

[471_Magnum]

Keeping any of these old cars in the proper state of tune is way more cost effective at improving gas mileage than ANY modification you can make.

Keep your foot out of it and big blocks with highway gears (3.23s or numerically lower) get low to mid teens. You can hyper-mile into the upper teens, but that's no fun.

Small blocks really aren't much better. Mid to upper teens. You might hypermile one to 20.

I'm sure someone will chime in and brag they can do better, but those results aren't typical, or consistently repeatable (if accurate). Run a big block with 2.73s down hill with a tail wind and it can get 30 mpg. Drive it back up the same hill and get 5 mpg.

Run a fat, out of tune car, and fuel mileage takes a dump. Cruise at 75+, same thing.

[Ghoste]

Perfect and precisely.   

[1974dodgecharger]

What magnum said....I say 440....

[odcics2]

Had a 68 Charger , 318 auto with 2.76 gears.   Bumped the timing about 2 degrees. Ran a cold air tube from the air cleaner to the hole in front of the battery.
Dropped the front a bit. (mostly for looks) Moved the acc. pump lever one hole leaner. Had a hotter coil.  Best I ever got was 27.2 on a STEADY 6 hour long 55 mph trip.  Hey 55 was the limit and the Smokies were all over the interstate.    Weighed about 3,350.

Had a 74 318 Charger SE, 318 auto 2.71 gear. Hooker headers, Holley 450 and intake. Chucked the bumper guards and the AC compressor. Lowered the front.
Best I ever got was 25 on a highway trip.    I guess the extra 500 pounds and lower compression hurt.     Weighed over 3,800 lbs.

Both cars ran Ansen Sprint wheels with Goodyear Rally GT tires, G-60-14.

Had a '68 225 Slant Six, auto Dart that got 25 ALL the time.   It had a Holley Econo-master carb since the original one wore out the throttle shaft! It was entirely stock, other than the carb.    Weighed 2,750.    On the highway, you could feel that blocky car pushing the air.

Overall, get a light car, tune for the highway range, don't move your foot!!   Good Luck!   

[C_stripes]

Thanks everyone.

A few more questions. Does a sure grip change the fuel economy? odcics2 mentioned a cool air intake of sorts, would that really change the MPG? Would a hotter ignition such as running MSD? I am not trying to make a 30mpg big block, though it would be kind of fun to see if it could be done.

Regarding exhaust, Headers bump up the engine compartment heat, but they flow better. What effect might they have (good or bad)? would it be best to run 2.5" or 3" exhaust?

We are all in agreeance that aluminum wheels are better and that the car needs to be tuned properly.

What 4bbl carb would be recommended for durability and mpg and is it true you can actually get better milage with a 4bbl vs 2bbl if you keep a light foot?

I think this thread is kind of fun.

[Ghoste]

2.5 for the exhaust and yes on the four barrel but keep it small, say 650.

[cudaken]

  4 Door, yuck. OK now that I got that out of my system.  

With my old 69 Charger R/T motor I was able to get 16.5 on the highway if I was careful. I had a 650 Holley leaned out with leaner power valve, MSD 6, Eddy Medium Riser intake, 74 A/C Water Pump (fewer vain worth 5 Free HP = MPG) stock Magnum exhaust manifolds with H pipe, 2.5 exhaust pipes, Cagier SS wheels, 255/60/15 on the rear with 2.76 sure grip rear end. I was running the stock distributor, up graded might have gave me a tad more, but I kept mine tuned well.

If you where to use small tube headers, X pipes, better ignition, fuel injection, stock Magnum cam advanced 2 degrees (moves the power band down) or a off road cam (for RV's and 4X4 off roading) I could see you getting 19 to 21 MPG and still be a blast to dive using the tips I gave in the first section. Even with 2.76 my old Charger engine shocked a few people with it launch.

Far as OD,play with this site.

http://vexer.com/automotive-tools/speed-rpm-calculator

While it does not have a OD option you can factor it in.
265/60/15
3.91 gears at 70 MPH = 3372 RPM's X 70% = 2360.40
3.23 gears at 70 MPH = 2785 RPM's with no OD.

You don't want the RPM's to low.

All so look at car weight!          

Cuda Ken

[odcics2]

You want a carb with dinky primaries and large secondaries, which you will rarely open, since you are driving for max mpg.
Think Thermoquad or a Holley equivalent.  Small primaries give better velocity through the nozzles for higher atomization.

Have a good wheel alignment. It costs $$ to drag tires that aren't pointing straight.

Keep in mind that you can spend thousands to save hundreds.  Not a good rule of thumb if you are going for economy.   

Plenty of idiots driving expensive hybrids around that cost so much more over a regular car that it'll take 10-15 years for them to break even!

[Homerr]

C_stripes we are thinking alike.  I'm 5-7 years out on a massive road trip and don't yet have my car.  (Just bought a house this summer with a 20'x30' garage to build my car!)  I've been watching WHITE_AND_RED_69's threads as I like his car a lot.

Over at moparts a guy named HotRodDave has an interesting thread about mileage and the experiments he has been through on a '68 Cuda notchback.  http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=3944014&page=0&fpart=1&vc=1

Somewhere else I've seen someone say that higher vacuum in the engine equals lower throttle input which equals better mileage.

The '69 Charger I had 20 years ago had a 383/727/3.23 Sure-Grip and 14" 235 series tires on road wheels.  Carb was stock AFB, stock bore, backyard mechanic ported heads, stock intake/exhaust manifolds, hi-po oil pump, windage tray, some sort of cam that was 'hi-po' (but I think it sucked all the torque out of the setup), hardened valve seats, trans shift kit, and 2.5" exhaust with burnt out glasspacks.  Mileage around town was about 6, best ever was 11mpg on the freeway.  The car was fun and flashy but lacked an overall quality that I was hoping for and I sold it to buy a house after a couple of years.

Doing more research and building what I want this time around I'm hopeful that I'll get in to the upper teens for the eventual road trip.  For me, I'm pretty much settled on a 440 (close to stock), manual transmission (probably a 5-speed unit), probably a '70 Charger, and whatever is the easiest EFI setup at the time I build.  EFI may help a bit in the mileage department but I also want trouble-free starts and better driveability.

[rt green]

any thoughts on a properly tuned six pack? I know it uses all idle circuits, but if you kept the speed constant ?

[C_stripes]

If you had a six pack, could you really keep your foot out of it?

[471_Magnum]

Took my 6 pack Challenger on the Hot Rod Power Tour running 2.76 gears. Pretty much a stock motor. Got a best of about 16 mpg. Averaged 14 mpg for the entire trip. That car did not have vacuum advance on the distributor, so there were a couple of mpg left on the table. Otherwise, that car was tuned up really well.

Low was 9 mpg, which included a 100 mile stretch running 85+ when I had to double back to rescue a buddy. Demonstrates pretty clearly the impact of driving habits, and what happens when you tap the outboard carbs on a six pack.

Six Packs are a PITA to tune. Due to fuel distribution challenges, they typically have to be tuned a bit rich for driveability. Factor in a non-stock cam, and they really can be a challenge. Not the best choice for economy (or ultimate  performance).

[Todd Wilson]

My only experience with a long drive were in my 69 Charger 318 along side a 70 Charger 383.  Both stock. Running on the interstate at 70mph.   The 383 was getting 18-20mpg and my 318 was getting 22mpg. After Chryco adjusted the tuning the 318 got 25mpg on the return trip. I've never really paid attention to my 71 Charger 318 and have never really taken it on a long trip but its sitting around 15mpg and its not stock.

Mileage will be all over the place with these old cars. Weather and where you are at as well as driving style. I would plan for 15mpg in the fuel budget and if you get better its a bonus. If you are going to tour all the 48 its gonna vary a lot depending on where you are at. That's something these modern vehicles are good at with the computers is keeping the perfect tune on the engine in all conditions.


Todd

[1974dodgecharger]

ken,
is that programs purpose to show you your rpms at what speed?  I keep looking at the 1/4 mile estimate and man that thing over estimates?  Its saying at 4500 rpms in 4th gear for me I should get 10.85 secs at 125mph lol....

4 Door, yuck. OK now that I got that out of my system.  

With my old 69 Charger R/T motor I was able to get 16.5 on the highway if I was careful. I had a 650 Holley leaned out with leaner power valve, MSD 6, Eddy Medium Riser intake, 74 A/C Water Pump (fewer vain worth 5 Free HP = MPG) stock Magnum exhaust manifolds with H pipe, 2.5 exhaust pipes, Cagier SS wheels, 255/60/15 on the rear with 2.76 sure grip rear end. I was running the stock distributor, up graded might have gave me a tad more, but I kept mine tuned well.

If you where to use small tube headers, X pipes, better ignition, fuel injection, stock Magnum cam advanced 2 degrees (moves the power band down) or a off road cam (for RV's and 4X4 off roading) I could see you getting 19 to 21 MPG and still be a blast to dive using the tips I gave in the first section. Even with 2.76 my old Charger engine shocked a few people with it launch.

Far as OD,play with this site.

http://vexer.com/automotive-tools/speed-rpm-calculator

While it does not have a OD option you can factor it in.
265/60/15
3.91 gears at 70 MPH = 3372 RPM's X 70% = 2360.40
3.23 gears at 70 MPH = 2785 RPM's with no OD.

You don't want the RPM's to low.

All so look at car weight!          

Cuda Ken

[Ghoste]

Mileage will be all over the place with these old cars. Weather and where you are at as well as driving style. I would plan for 15mpg in the fuel budget and if you get better its a bonus. If you are going to tour all the 48 its gonna vary a lot depending on where you are at. That's something these modern vehicles are good at with the computers is keeping the perfect tune on the engine in all conditions.


Todd

Good advice and thats a fact, the altitude changes alone will drive your tuning nuts.