I'm not certain if this topic has been discussed in detail before, but I am interested in finding a nice blend of performance AND efficiency. I am modifying an AMC 66 classic convertible from the ground up to look like what could have been done to one back in 60's to hot rod it. I'll be using an early 70's AMC 401, possibly stroked to 434, roughly 10:1 compression, and built for low to mid range power to take advatage of the low gearing (3:15), I'll be using a t-85 3spd(of which the t-10 was built from) with a 2:49 first gear and a borg warner overdrive. This will give me roughly 2000 rpm at 75mph on the highway in overdrive depending on the exact rear tire size used.
I intend to drive this car a goo bit. I have driven 25,000 miles in the past 6 months alone. This car isn't to be my only car here, but I want to feel comfortable using it as much as I want. I feel no need to win any races but I would certainly want it to move out when asked to. I like the idea of using big inches to push a 3500 lb. car around. I have every interest in using a carb, no fuel injection for me...I don't dislike them...there just not for me. I've seen overdrive conversions again and again for obvious reasons, but I have seen very little information of how to build up an older designed carbureted v-8 engine with fuel comsumption as much of a factor. Things such as carb selection and tuning, vacuum advance distributors and set up, ignition choices, head porting suggestions, piston types, cam selection for both performance and efficiency. How about intake manifold selection. Exhaust thoughts.
I think that there are a lot of people out there that are interested in this subject...but most are probably uninterseted in bringing it up and being ridiculed for being a mizer or something. And by the way...as a pre-defense, I know very well how to suck down the fuel. I do also own a 69 firebird with a built 383 chevy, big solid cam, fully ported heads, team G intake, mechanical 750 holley, and 12.5:1 compresssion running 4:10s in the rear. And it runs like a demon on race gas at 6 bucks a gallon!
My goal here is to build a 13 second or so driver that runs strongly, stops pretty well, handles OK, and can pull 20mpg or more on the highway and not be so bad around town. This is something of a challenge for me rather than realistic need to save pennies on gas money here, but I am very interested to make a go of it.
I WOULD REALLY LIKE TO HEAR FROM PEOPLE WHO WOULD LET ME KNOW THE STATS ON THEIR CAR. MAKE, WEIGHT, 1/4 MILE TIME, GEARING, TRANS TYPE, ENGINE SIZE AND MODIFICATION, AND OBSERVED GAS MILEAGE FIGURES, etc.
Any thoughts would be greatly appreciated!
Thanks and great magazine!!!
well, i have a 71 nova with a BB 454. it has 9.25 compression and a smaller cam with a 750 edelbrock (vacum secondary) on top of a factory 396 intake. It has a turbo 350, and 3.08 gearing in the stock peg-legged 10 bolt rear. I cruise 70 at about 2,600. The tires are 205-75-R14's. I pull 12 m.p.g. on a normal day(it shoots down to 9 when cruise to fast). I dont know if that will help, but I hope it does. If you get 20 m.p.g, let me know, i'd like to manage the same, but I dont ever see it happening.
Thanks for the thoughts on the Nova. If it makes you feel any better my 69 Firebird makes your Nova seem economical. I've known of people who proudly proclaim low 20's on the highway with 13 second cars, and not the import kind! All 350 plus cube, carbureted motors pushing 3300lb. plus cars. All that I recall have serious highway final drive, an overdrive tranny for sure. And all seemed to be interested in both performance and fuel efficiency from the get go when laying out their cars' setup. Most getting better than 20 (claimed) on the highway are running around 2000 mph at 75. That is what I come up with calculating my gearing/overdrive/tire size combination.
One guy I met has a 69 camaro with a 10:1 comp 383 and a 700r4 with 3.09 gears that ran a 12.80 (saw it myself, met him at the track) with 255-50-15 BFG radial ta street tires. After talking about his car he told me that he takes it on long trips and using an aftermarket cruise control, claims to regularly get 23 mpg at 70mph on average. He told me that he put the whole car together himself, except for the tranny rebuild I think. He said something to the effect that it is easy to get great performance out these cars, but if your willing to give up 15% of the all out performance potential of your car at the track, you can lay it out to be very comfortable and efficient. Boy do I wish I got his phone number
New corvettes are pushing 29mpg highway(claimed) with final gearing that works out to 1650rpm at 75. Of course fuel injection is widely considered a more efficient fuel mixer compared to an even highly tuned carb with mileage in mind. And clearly the corvette is a far superior aerodynamic animal, but a very impressive number though considering that it's weight, cubic inches, and overall power is not that different from the muscle cars of old.
Any others want to put their two cents in?
when you order a cam tell them what your desires are. as for getting the 20+ miles per gallon you are going to have to get a gear vendors bol on overdrive or a kiesler five speed stick both expensive options you may also look into a custom fuel injection setup and a very mild gear set like 3.42 or smaller but then this is going to kill you 1/4 mile time so you are going to add forced induction or nitrous
I already have an overdrive. I'll be using a t-85 3spd( what the t-10 was built from) with a borg warner .7 overdrive tailhousing and either a 3.15 or 2.87 rear. That leaves my 70mph cruise at 1700rpm. My first gear will be a 2.99...that should help overcome some of the gearing along with an AMC 401 with considerable bottom end torque. I am not so concerned with the 1/4 mile times for this car. Have a 69 firebird with 383 solid lift cam chevy with 3.91's in it for that. I want to be able to mash it at 20mph and take off and still be able to cruise on the highway. This car is to be my DRIVER. Lots of driving, including plenty of highway miles. I'd like to stay away from fuel injection if I can help it...just not my thing, old fachioned I guess. I have considered the nitrous option though if I feel the need for more speed.
Is anyone out there putting down some respectable power and still getting decent mileage with an old school v-8?
I have a 1970 chevy camaro with a 350 and a tremec tko five speed with 3.42 gears and a 27.5 inch tall tire. I am running a holley 750 dp and on average out of my 18 gallon tank I get 320 miles per tank so just over 20 mailes a gallon. I use this car as my daily driver and have a tendency to punch it alot from the lights and on the freeway.
You might want to recheck your math.
320/18=17.7777 or slightly LESS than 18 MPG.
Thanks for the info. Regardless, 17.7mpg for all around driving with some heavy footing is not bad at all. 27.5 in tires at 75mph in a TKO tranny overdrive at .7(or there abouts) comes in at 2200rpm. Nice highway engine speed. I'll be running more cubes (409) so it should not be a problem to run a lower cruising (engine) speed as long as the motor is set up for it from the start. A new corvette runs in the 1700 range at 75 with a small block. My aerodynamics certainly won't be as clean, far from it, but I intent to be putting out more power, he he, especially torque.
Anyone else want to put their 2 cents in?
Do I hear 20mpg in an old school v-8?
20MPG shouldn't be that hard to achieve with a light throttle foot, relatively high compression (10:1) and a cam, carb,intake and exhaust system optimized for economy.
Super Chevy magazine did a project "Econo-Performer" '70 Monte Carlo many years ago, when Doug Marion seemed to be the only person on staff at that mag. (think 1980s--yes, the entire decade)
They were able to get the car into the 13s and still got 20+ MPG, but it was kind of bogus if you ask me. They ran a tight convertor on the street, but swapped in a looser convertor for dragstrip runs. 1 1/2" primary headers on a small block 350, tall gears (2.73 or 2.56) rear gears, etc for highway cruising, god knows what gear was used for strip testing.
IIRC, the engine was a mildly warmed-over 350 with an "economy" cam & Holley Dial A Mile electronic carb.
If you're really concerned about fuel economy and driveability, get a q-jet that matches your combo as closesly as possible. Then tune it until it matches perfectly. Much easier and cheaper than screwing around witha Dial-aMile, if they're even still available.
A stick shift trans, with OD, as you've suggested will eliminate the convertor swapping that SC was saddled with.
Even a primitive feedback FI system will put an electronic carb. to shame when it comes to drive-ability and economy.
Go with an aftermarket FI system, or thoughtfully cobble together your own TPI system using mostly GM parts from the junkyard if finances, wife, personal objectives don't have a problem with it. The cheapest of these systems cost only a few hundred dollars more than a functional electronic Cabruetor and they are MUCH easier to tune.
Good fuel economy comes from the best possible use of the spark when it enters the combustion chamber. Ideally, all fuel will be consumed at exactly the right time, resulting in great fuel economy, a smooth idle, and low emissions.
An MSD-6A may also make a marginal improvement in fuel economy.
I'm pretty sure SC magazine claimed 22+ MPG with their project "ECONO PERFORMER" You might want to check your local public library. I'm sure the project is full of "dos and don'ts" that still apply today.
Thanks for the thoughts. I will look up the "econo performer" article. There was also an article recently in one of the mags that claimed 24mpg or so using a 302 with I believe a procharger belt driven blower in an early el camino set up for the power tour. I'm looking at much bigger inches and I haven't much interest in the blower route so I never read into it that much.
Any other thoughts, experiences?
1. Cut weight as much as possible (weight is the #1 variable in fuel economy).
2. Tighten up aero package (block off grille as much as possible without overheating, restrict air flow under the car, smooth out the "hic-ups" (e.g. bumper ends, flat moldings, big mirrors, air-grabbing fender openings).
3. Velocity, velocity, velocity in the intake/cam/exhaust tract at cruise (look at the m-i-l-d cam specs for LT1, LS1, look at ram tuning intake & exhaust (longer, smaller tubes).
4. Run slowest engine speed you've got torque enough to pull (a 6 or 7 liter engine should be able to pull a .5 overdrive on a 3.08 or even a 2.73 gear)
5. Synthetic lube in all components
6. Cruise lean-- Use wideband O2 sensor to lean out cruise mixture--cover it with other carb circuits (accel pump, secondaries, etc.) Not as good as EFI, but . . . . Note: lean running causes NOx emissions problems and can burn up parts.
7. Compression, Compression, Compression--low compression wastes fuel. Low compression and big cam is even worse. Aluminum heads, electronic ignition timing w/ knock sensor and coatings on pistons, valves, and on combustion chamber in the heads can allow increased efficiency and more margin for tuning errors. Atkinson or Miller-cycle cam timing can increase expansion ratio efficiency (but at some expense of power)
8. Use a mild power adder that doesn't hurt cruise efficiency (a small shot or low boost turbo (or even a supercharger w/ part throttle bypass (see GM 3.8 V6)) can gain back some of the losses from mild cam and long ram-intake and exhaust. Need to balance this against compression, though.
9. Temperature-controlled electric radiator fan
10. Use cruise control whenever possible
11. Skip shifts when possible (GM T-56s make you go from 1 to 4 at low load for a reason) and shift at lowest rpm the engine will pull without lugging.
12. Monitor manifold vacuum
13. Anticipate stops and lift early
14. Reverse flow cooling w/ proplyene glycol coolant
15. Windage scraper and accusump (to safely lower oil level in the pan)
16. Lowest possible backpressure in the exhaust (if you're burning valves, then the tune is wrong) but keep velocity high in the scavenge portion.
17. Extra credit for the truly ambitious: get some of that new hybrid-electric junk out of a salvage and figure out how to simplify and adapt it into a legitimate V8 rod. Somebody will do it. Why not be first?
If its not TURBOCHARGED, you're not finished yet . . . .
In 1977(?) Hotrod mag did a story on the new Z28 and built it for MPG. They got 20+mpg. Q-Jet, Edlebrock SP2P intake, Isky(?) mileage cam and headers. Ran quicker 1/4 mile times and got good mileage. Pooped out above 4800 RPM
I'm running a 305 Chevy in a '48 Plymouth coupe. With a Q-jet on a '82 Camaro intake with 2:73 rear gears I was getting 20+ MPG. Changed to a Performer intake and lost 4 MPG. Changed to a 600 Holley and lost 2 more MPG. I cruz at 70 MPH at 2000 RPM
Found a SP2P at the swap meet last weekend for $20. Will get a new Q-Jet or Edlebrock 500 cfm AFB and get my MPG back.
For power with fuel economy EFI is the only way to go. Putting EFI on a AMC will take some effort, but Turbo City has a kit to add a 2 bbl throttle body EFI to any car. Multi point is better, but will take some fabrication (welding) to an intake to accept injectors, but can be done.
Getting 20+ MPG out of a mildly built carbureted V8 in a 3500lb vehicle isn't too difficult, you just have to focus on building an efficient drivetrain with components matched to acheive a good balance and work in harmony to produce power AND mileage.
This is where torquey engines and mild gearing rule the day. Hairy cams with poor idle characteristics and the related speed parts to support such a camshaft work against you in the fuel economy department, but efficient V8 mills with mild cams and related speed equipment will deliver power you can use around town...AND go easy on the fuel consumption!
Remember the old "Fuel Economy" gauges that GM and some others used to install in passenger vehicles back in the 70s? They were nothing more than vacuum gauges rated to show "good", "fair" or "poor" economy depending on what the manifold vacuum reading was. High vacuum designated "good" fuel economy, and low vacuum (foot to the wood!) indicated "poor" economy. Hook up a vacuum gauge in your ride, especially the older Autometer ones with color-keyed sweep readings and watch it as you drive. Note your vacuum readings at highway and city cruise speeds.
To gain better fuel mileage, you want to make your engine more EFFICIENT. This will drag better performance along with it, so your car will actually be faster, AND more economical than it was in stock form!
Start with your cam. Be conservative when selecting your new bumpstick. If you're going with a poked & stroked 401, let the displacement and the stroke do the work for you, and keep the cam profile towards the tame side of the spectrum. You could probably balance power and economy best if you stick with lift numbers in the .480" to .505" range, and keep duration @ .050" down to about 221 degrees. That's pretty tame for a 434 cubic inch engine, but it will be strong where you want it to be...down in the lower RPM ranges where you will spend the bulk of your time. Also, invest in a dual pattern cam...you can sneak a little more lift and duration in on the EXHAUST side, but don't get TOO carried away.
Headers and a free flowing exhaust system come next. SOME back-pressure is actually a good thing in a street cruiser, but you still want to expel the spent gasses to fill the cylinders with a fresh charge for maximum performance. Stock manifolds and small pipes with restrictive mufflers will hurt you here, so ante up for good tubes and pipes!
Induction system design will also play a major role in your quest for a somewhat fuel-friendly tire fryer. Go with a dual plane intake manifold, and a Holley 750cfm vacuum secondaries carburetor. Lots of people like the Edelbrock/Carter carbs...but I've always gotten more power out of the Holleys without giving up mileage. (The secret is to tune the carb to your engine...and I could write a small BOOK on how to do that! However, it will be damn close to the money right out of the box, you can experiment with tuning from there).
Now, you need to light the mixture. The GM HEI distributors do this the best, and aftermarket versions for non-GM engines are now available. Seek one out for your AMC application and you'll be happy with it.
(The old Delco points distributors found on many early 70s AMC motors work good too if you prefer a breaker point ignition system).
Add an Accel Supercoil, good plug wires and an adjustable vacuum advance unit to your ignition parts shopping list, and that will be all the fancier you need to get in the ignition department! Mind the advance curve, though...most aftermarket distributors can be ordered with curves already tailored to your application if you provide the vehicle and engine specifics to the manufacturer, so take advantage of their expertise in dialing in distributors. You can tweak it to eek out the last bit of mileage/performance, but having it close right out of the box is well worth the added effort on your part.
With an engine built as I've outlined above, moderate (highway friendly) gearing won't hurt your acceleration too much...as the engine will be strong in lower RPM ranges, making enough torque to accelerate the car without spinning into the stratosphere to do so! You'll need good tires, because if you break loose with highway gearing...you'll spin the tire(s) halfway into the next county! It impresses bystanders, but doesn't do a thing for lowering your ETs!
(Highway gearing keeps torquey engines in their most efficient RPM band longer...allowing them to either accelerate the car harder...or smoke the tires endlessly as the motor muscles it's way through the powerband!)
The bottom line is, that increasing an engine's efficiency in the RPM range that you will use it most, automatically gives you better performance AND economy. Building a motor that makes peak power at 6000 RPM and then lugging it down with 2.73 axle gears is only going to give you a nasty sounding idle coupled with a slow and thirsty slug! If mileage and power are your goals, then keep those things in kind when you engineer a smart combination of parts and systems to work together towards meeting those goals. Concentrate on making low end power with the types of parts I've mentioned above, and you'll be happy with your end result.
(I had a 396 Chevelle with 3.90 gears, a four speed, Holley 780cfm vacuum secondaries carb, Engle cam, Holley intake and a stock HEI distributor with a curve kit thrown in. The car was gutted for weight savings and ran high 12s/low 13s on slicks and open headers, and delivered 17-21 MPG with a light foot on the street. If I had known better at the time, I could have tweaked it to get even MORE mileage without slowing it down much, but I was very happy with it as it was! I've also built other street machines that ran 14s and got mileage figures in the low 20s, so it's certainly possible if you work at it.)
This may be completely off what you want to hear, but I'll say it for the sake of saying it. My uncle( he's about 60 by now) told me about an experiment him and a friend did in the late 70's. They took a 70 nova with a straight six and made it get 100 mpg. go ahead, throw up your B.S. meters, but this is what I remeber of how he said they did it. They took the fuel and ran it to a big heat coil. basically it was a cylinder surrounded by copper tubes that were heated by the anitfreeze(the tubes that would usually run to the heater). Then, they had a fuel line at the top of the cylinder that collected the vapors created would funnel into. From there, you used the carburator like a well, a carburator. It controlled the vapors going in. he said they only tried it twice because they were scared a backfire would kill them. but if a chip were made that could detect the backfire and shut down the fuel line, it might be worth it someday. I would try it sometime, but i dont have a car to spare if it did backfire. just food for thought.
And to think Honda and Toyota spent billions on hybrid technology . . .
BTW, they didn't try this little "hot vapor" experiment while they were making a coast-to-coast record run in 24 hours, did they?
This story reminds me of a former coworker who swore her stock 307- powered '71 Nova would do 160 m.p.h.