I know this has been covered & if anyone can point me to it, please do so. I looked & couldn’t find what I was hunting though. I’m looking for some pointers on making good gas mileage with a SBC for my El Camino. I’ve got a “hot rod” so making big power (or even sounding like I am) isn’t really a concern. Enough to move it efficiently is all I need. This will be something I use around town but I drive quite a bit. Round trip to work is 40 miles and hitting the junk yard & running errands on Saturday can rack up 100 miles easily. 14-16mpg vs. 16-18 mpg isn’t really worth worrying about. 12mpg vs. 22mpg is though. I had a ’69 2wd Blazer once that got 10-12mpg. As cool as it was, I hated it because I couldn’t afford to drive it. I’d like to be somewhere in the 18-22mpg range. I know that gearing makes the biggest difference of all. I’m not sure of the rear end gear in the El Camino but if it is too deep I can change it. I’m planning on using a TH400 trans that Kennedy gave me. If I can get more info on the rear end & trans codes I’ll post it here. …& yes, I know an LS motor makes good power & mileage but I can round up &/or build a small block for almost nothing. I’m on a TIGHT budget with this one. Any thoughts on making good mileage with a SBC? I’m guessing mostly stock internals, lower compression, little cam, carb size suited to the engine (2bbl even maybe?), & timing set accurately. Thoughts on 283 vs. 350? Thanks guys, JH
My thoughts are if you have more power, you will give it less throttle to get going. An efficient motor will make more power. Overdrive will help a lot. A mild cam, intake, headers, good ignition. Its all about the whole package, including tranny rear end and tire size.
In my experience, a good Quadrajet will get you better fuel mileage than a 2 bbl as long as you keep your foot out of the back barrels. The lowest numerical rear gear ratio that was available for the style rear your El Camino came with is 3.08; you may want to consider an overdrive for maximum economy.
The TH400 is not gonna help your cause, a 700R with a lock up will probably get you 25-30% better mileage on the same engine
I dont think you would want a 3.08 gear rear end. it will be harder to get up to speed. I have a 56 chevy with a 350, its got aluminum heads, mild cam, performer intake and sanderson headers. Its been ported and polished. carter carb its a 650. Has a 700r4 tranny and 3.55 gears. I can cruise at 80 mph and have plenty left. Ive buried the needle plenty of times. Will do a one legged burn out into 3rd gear. If im good i can get 20 miles per gallon out of it. But i dont its just too fun.
Harrison Don't lower the compression, detunning one will not make it have better mileage. To make good mileage you have to be running as efficiently as possible. Build your engine and your gear ratio to go with each other. I don't like overdrive trannys so I normally run a T350 or a T400 behind my small blocks. The last one I ran dailey liked to run around 3000-3200 best, so I setup my rear gear to be hitting 3K to 3200 at cruising speed. Prefer Holley carbs so I ran a 600 vac secondary with the spring in the vac pod heavy enough that the secondaries were just ready to start to open @ just above 3200. That way I cruised on the primaries but had plenty of grunt when I nailed it. Get the best heads you can afford. Run a mildish cam, I run L-79s in my street 350s. A good set of headers and with a 350 run your exhaust in 2.5" with free flowing mufflers. On a smaller engine I might keep the exhaust around 1.125 to 2.25. With a little over 400 HP on tap in a 4,000 lb square pickup I was nailing 20-22 on the hiway and 18-20 around town.
I have done a lot of research also on mileage and a good overdrive trans seems to be the way to go. I am leaning toward the 700R4 also, makes the most sense.
O/T 78 El Camino,90's roller cam 305 block with a mild Comp Cams hydraulic roller cam,9.25 compression,Edelbrock 600 carb,Rams Horn exhaust manifolds,aggressive spark curve,wide ratio Saginaw 4 spd,2.73 rear gears.23 mpg on the hiway with surprising power from the shitty 305.A few more MPG could likely be had with some more tuning. As always,a clean areodynamic vehicle gets better fuel mileage.
The only way an OD will work for mileage is if you are geared low enough so that when you are cruising you are in your power band. Here is an example. The Raven has a T-5 behind a small block in his AD truck. He has a 3.73 gear in the truck, the engine doesn't start climbing up on the came until he is in the 2800 RPM range. With the tires he has and the OD that puts him over 80 mph. @ 65-70 where we are most likely to run he gets better mileage running in 4th gear than in 5th. Unless you are building an engine that runs well around 1800-2200 with the average OD setup you are not going to reap any rewards with your OD tranny. All you do is lug it around and lugging one is not how to make good mileage.
Doesn't the TH400 require more HP to turn the pump than any other tranny? I agree with the folks saying not to de-tune. Build the 283 and blueprint it. You are after efficiency, so making it as right is possible is key. You want as few reductions to the VE as possible. Build the motor for low rpm torque as best you can with a 283. A mild cam, heads ported and polished, exhaust sized appropriately per the cam and head builders recommendation, index the plugs, etc etc. There isn't anything wrong with a 3.08 gear if you build the motor to perform down low. Once its rolling, make sure its easy to keep rolling. A narrow tire, proper tire pressure, you know the drill. I had a '69 Chevelle, 307 automatic, for several years, that routinely got 24-26mpg on the interstate and 20-22mpg around town. I never set any 1/4 mile records with it, but it sure got by cheap on gas. Relatively speaking of course.
Used to have a Police Interceptor, 351W, AOD & 3.08 Milage wasn't bad & it was fast enough for the cops. A 350 would be better getting going with 3.08s than a 283. Back in the late 70s Popular Hot Rodding did Project Econo-Performer. Got an impressive increase in MPG & some gain in performance. Mostly common sence things. Headers & duals, spread bore carb. RV cam, low restriction air cleaner, low rpm intake, nonretarded timing set. An AOD would have been on the list if there had been any.
X2.... TH 400's have the highest parasitic loss of any of them out there. From a racing perspective they consume >80 hp and have the heaviest rotating mass but are damn tough ! Way tougher than most 300+ hp engines need. The TH 350 and 700r4 are in the 40 hp parasitic loss range and you get the low 1st gear with the extra .73:1 gear reduction in 4th with the 700R4. The 700R4's can be built to handle 500+ hp w/no electronics. Powerglides have the lowest overall parasitic loss and lightest rotating mass but obviousely only have 2 speeds. 2.70's - 3.50 rear gears and a 700R4 is the perfect combo !! Happy motoring !
700R4, 10.25 to 1 cr, aluminum heads so you can run that cr, Q-jet carb a good choice, and an RV cam. Use this http://precisionsite.com/auto-x/tools/ to calculate your rear end ratio needed to be able to cruise 70 mph at 1950 to 2050 rpms, and you will have a mileage king that with the much lower 1st of the 700R4 will get its heavy butt off the line in good shape. BTW, I have a hot rod that will turn a low 11 second 1/4 and get 30 mpg, so been there done that.
I'm planning on doing some light aero work to my '61 Suburban to pick up some mpg this summer. There's better than a foot of air between the core support and the front cross member, and air piles up under the hood... you can see the center of the hood flex from wind pulsing. New vehicles have a cover that goes from behind the front bumper to the cross member, to keep air out of the engine bay. I'm going to do that, and add a short shin spoiler well back from the front bumper to plow air out from under the truck. I just wrote a feature story on a '46 Plymouth for the One Lap, and he picked up 40 miles per hour around Daytona's track by putting a splitter/air dam on the front of his car, and a partial belly pan like I just described above. That definitely translates to mpg on a street car. The hole in the front grill panel, behind the grill but ahead of the core support, is about 18 inches wider than the opening in the core support for the radiator... allowing air to back up against the core support. I'm going to close that off so any air coming through lines up against the radiator, rather than stacking up on the sides of the radiator against core support. I've also noticed that the rear bumpers protrude beyond the quarters, as most vintage vehicles do. It's no secrete that tucking the bumpers flush or even recessed into the quarter picks up mph, because it stops parachuting the air. I'm going to fabricate a neat little filler panel between the quarter and the end of the bumper. It'll look like a factory add-ed on piece of formed sheetmetal, tucked right behind the leading edge of the bumper end. I will probably also make a very limited partial belly pan coming off the bottom of the gas tank and running to the rear bumper, to stop air from getting scooped by the bottom edge of the rear bumper. What will all these do? Dunno... but it can't hurt, and with gas prices climbing, I'd rather do some hot-rodding to get my daily driver a little more efficient, than park it and drive something else. -Brad
I would do a 350, parts are cheap. Do an efficient short block, clearanced for 5-30 oil, cast crank (lighter than steel), flat top's with low tension oil rings, standard volume oil pump. Iron heads for sure, something aftermarket that are small (180 intake) like SR Torker's. If you don't want to spring for aftermarket heads, some camel hump's will work (they are small good torque heads by today's standard's). RV/Towing style cam. Dual plane intake with a Q-Jet (dont get into the secondaries a lot). As others have said, 700R4 Is the answer. 3 something first gear will get ya off the line and you'll have overdrive high gear. Painless and TCI make a kit to wire a toggle switch to lock up the converter at will.
............................ That'll be neat to see, Brad.................Streamlining a brick!!!..............But, every little bit helps!!!!
David Vizard had a book " Performance with Economy" that talked about a lot of these things. Good discussions on maximizing HP without it being a gas hog. A little older book, some of the stuff is out of date now, but worth the read for what you are after.
A friend of mine had a '63 Bel Air with a late 70's junkyard 305 2 bbl., 200-4R and 3.08 gears with 235/70-15 tires on the back. He put a Summit 1102 cam in it with a cast iron intake, Q-Jet and 2-1/4" dual exhaust off the stock Ram Horn manifolds. It wasn't fast but it could cruise all day long at 60 MPH with 4 adults in it at 20-21 MPG on 87 Octane. I'd say a 305 Vortec shortblock with the stock Vortec roller cam and early 305 HO or 283 Power Pak heads with a cast iron intake and a Q-Jet; 200-4R and similar gears should be able to better that and run a little better. A 390 or 450 Holley 4150/4160 on a '66 327/300HP Holley/AVS iron manifold would also be a good mileage carb and you could fit it with dual feed bowls and tell everybody it's a 780. I'm doing a similar 355 for my '88 C1500. It currently has a tired roller cam 305 TBI out of an '88 Camaro, 700R4 and 2.73 gears. It pulls a little over 18 MPG with mostly Hwy. driving at 60 MPH. The 305 is working a little harder than a 350 would to pull it with those gears but when I tried running in Drive instead I lost 2 MPG. I'm building the 355 for maximim TQ from an idle through 4,000. It will hit peak TQ around 1800, cruise RPM at 55 MPH in OD is about 1350. It will use the Vortec roller cam, 21.7cc D-Cup blower pistons and 305 HO heads to aid low and mid range mixture velocity for low end TQ and throttle response. Of course it has the advantage of EFI but it's still a big heavy brick. If an oil burning 305 can pull 18 in it you should be able to get a lot better from one. It's in for a tranny overhaul right now and with the anticipated increase in low end TQ of the 355 we're switching to a 1200 stall converter from a 454 to help mileage a bit more. It will be all out of steam by 4500 but that's fine for my needs. I originally intended to use Vortec heads but they give up too much on the bottom end and don't really shine until 4,000 or so. Just about when this engine will be all done. I'm not saying Vortecs don't work on the low end so don't everybody get their panties in a twist but there are other heads that work better under 2,000 where my engine will spend 90% of it's time.
I was gonna say 305 as well. We had one in a wrecker we used for towing passenger cars around Houston all through the 80's. Unloaded it would easily get around 18 in town and better on the highway. It did have some large 16.5 tires on the rear though. That was the best truck we ever had. I say a 305 or 350 with an RV cam, stock heads, Performer intake and a single 4bbl with an HEI would probably get you right at what your shooting for if you had a higher rear end gear. I'm guessing 3:42 or higher?? If the trans is working I'd run it and play with the rearend gear.
back in the late 70s or early 80s Super Chevy magazine had a series of articles called project Econo performer. it was a 70 monte carlo with a 350 th350 combo and they litterally wore out the bolts changing and comparing every part looking for the best economy along with performance. I think i remember them getting almost 20 mpg out of that barge and i think their et was around mid 13s
Lots of interesting and mostly good advice on this. I'd have to agree that you need to build an engine that is as efficient as it can be while being built to haul that 4000 lb Elkie around. That means that everything between the air cleaner nut an the drain plug needs to be picked to work together to achieve the desired fuel mileage. I was thinking about what it would take to build an engine that would pull decent mileage in one of my Chevy AD trucks this afternoon and pretty well decided that the base for it should be a roller cam block and go from there. I love turbo 400's but they really don't work all that efficient and that has been a point of discussion for the past 45 years. Great and rugged trans if you are racing or towing but there are a lot better choices for fuel mileage in daily driving. Along with the right engine, trans and rear end combination a guys has to pick the right tires for fuel mileage and probably plan on running aluminum rims to save a few pounds. Then work on the aerodynamics of the truck a bit with maybe an air dam under the front bumper an a cover over the bed to cut down turbulence out on the freeway. It isn't going to be easy but it should be doable.
Well if you have a 4x4 there the biggest problem . A 400 trans is a huge gas sucker as well . If you have bigger tires then that will use more gas to turn them . I am sure you have a 4 bbl so there is another problem area . If you have a 4x4 then unlock the front axles and free them up ! Trans wise an overdrive will really help . Anything besides a 400 ! Change the carb to a 2 bbl if you have a 4 bbl . Headers always helps with straight exhaust with small straight thru mufflers . You can also upgrade the cats to better flowing ones too . Good straight air flow to the carb with a good flowing K&M filter . Don't carry anything in the Blazer if not needed that time of usage . Use synthetic oil and good oil filter . Get good high grade spark plugs , wires , cap , rotor and change the fuel filter . Use stock size tires and keep them properly inflated . Check the front end alignment . Get some under drive pulleys that will also help . Electric fans will help better that a belt driven fan . Learn to take off from a stop easily and a good vacuum gauge will help with that area . Stop slowly when possible . Any speeds over 55 will use more gas too . Use the proper grade of gas that the manufacture says to use . If you use a less octane fuel than the company recommends that will hinder the gas milage also . I fewer starts and stops will help with gas milage so maybe a different way to and from work with less stops and starts will save gas even if you drive longer with in reason . Make sure the trans is change gears at the right places and is in good condition . These are some of the things that will add up over a tank of fuel . Still the Blazer with a 400 trans and a 350 w/4bbl is going to be a gas hog , bottom line . Just a thought ! Retro Jim
From what I understand about GM FI systems, they run a hot thermostat, and then make the engine run hotter by leaning it out more after all operating temps come up. So how far do you push your luck with a carb with that kind of science? Higher compression ratio makes an engine more efficient. Low octane makes that more of a challenge. E85? Flex fuel capable carb? Gotta ask questions to get proof(s). It's like algebra.
Do you know how many miles you have to burn to even break even on a transmission swap? I know gas prices suck, but it's like going out and buying a new compact car to get relief from gas prices. At $400/mth for 5 yrs, what is the breakeven point of just running the paid for daily driver?
I would suggest at least running a stock cam. Your idea of running "no cam" will result in no oil pressure and a very inefficient motor since the valves won't be moving. Sorry. I am the guy that likes to ask people if their stock engine has a cam in it.
Back in 89 I had an 83 Pontiac Grand Prix, that I swapped a bone stock 350 sbc (dished pistons/76cc smog heads) and th350 for the v6 it had in it, I believe the rear gear was probably 2.41 ish. Ran a 750 QJ and fiddled with the secondary rods for mileage, stock HEI, Headers, 2 1/2 exhaust, turbo mufflers, no A/C, no smog.....it was a cruiser, and had no prob getting 24-26, and actually got 28 a few times if I kept it right at 63 mph. Then California in all their wisdom wanted to smog it.......it got junked, yup California hates efficiency.....
Yes I do, when starting my trans swap from a Muncie M21 to a Tremec TKO 600 5 speed with fuel at $3.20, it would take almost 7 years. This doesn't take into account the savings on wear and tear on the engine, nor the enjoyment of having a lower 1st gear and quiet, low rpm cruising in 0.64 OD. But now with 91 octane in California going for $4.15, drops it to 5.25 years. I think fuel will climb even higher till car dealers start having electric cars in inventory.
I would run a 4bbl over a 2.. The 2bbl will leave you, with your foot in it more frequently, searching for more. I would run 2" exhaust, also. 350 is a gas hog and 283s are sluggish with out gears, out back. 200 & 700R4s are quite nice, too. you're gonna have to shorten the drive line any-whoo! Sell that 400, you don't need it(for this project) I'll shut up now
I put 6000 miles on my Fairlane with the Hot 331 driving to Bonneville last year. In full max Hp tune I was getting 9mpg, Just taking out some jetting I was able to get it up to 14mpg. Mind you this was running at 80-90mph for 100-120miles at a time. I was running a 3500rpm stall converter, 3.55 gears and a 27.5 tall tire. my car runs 3000rpm at 60/3500rpm at 70/4000rpm@ 80. The best mpg were at 80-90mph. What I can tell you about that is picking a cam that runs in the rpm you want to spend most of your time driving at makes a big difference. For real world tuning an air/fuel meter would be real nice. Leaning out the air fuel mixture as far as you can go always helps. Timing and octane are another issue. I dyno tuned mine on 93@38deg. made 462.6 hp@6900. With 91 I dialed it back to 32deg and there were no issues, but I lost mpg, and lots of hp. . It is fun to play with, but not when fuel is 3.50 + a gallon. I am still wondering why my new daily driver f100 has a built 390 FE
My daily 81 el camino gets 25 on the hiway 283, L-79 cam, t400, headers, 69 z-28 manifold, holley 650, ect... And as overdrives go, they burn MORE power than something that had rearend gears geared to the same rpm at hiway speed, meaning possably WORSE milage.
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