Nice looking Burb,the mileage is about what you can expect at that speed. 10mph slower will probably help a lot. The 3.73s probably aren't that bad cause it helps to keep your vacuum up. I could recommend an ankle governor but this is the Hamb.
Here's what I'd check. Crank gear/retarted? Use a gearset for 1967-70 distributor curve/advance/vacuum advance/port or manifold vacuum? If not HEI, convert. Lock up converter for 700R4/working correctly? run carb with smaller primaries
My 37 gmc pickup had a stock 396 Qjet, th400, 3.08 gear with 275/60/15's. I drove it daily for 4 years. On the hwy at 72 mph I averaged 17.5 mpg. Aerodynamics are probably less of an issue on that sub than the cam and carb. I had a 72 monte carlo with a 468, th350, 2.73 gear that got 2 mpg better than when I swapped in an overdrive th2004r for a few months. The OD trans put the engine in the wrong rpm for efficiency for my combo in that car. Yes, the converter was locked up when needed. I do not think that 14 mpg is as good as you can get out of that vehicle. I think if you are willing to swap the cam and or carb for a better mpg tune you will see better mpg.
what's that thing weigh? i bet with all the wood it is pretty heavy. how much stuff were you carrying? hilly trip?
the speedometer is good checked it with gps. i have got about 1500 miles on the truck but it has been on short trips of 50 miles or less i will hook up a tach and see what the rpms are. and check the timming again and make sure the vacum adv is working
The force of wind resistance is proportional to the square of the speed...like this F=r*V^2 where "r" is some constant that I can't be bothered to look up and V is velocity in ft/sec; I think. Anyway a 5 mile/hr head wind can really do you in. and a 5mph tail wind gets you numbers that are questionably good. The good news here is gas is less than 2 bucks a gallon! Kelvin
So really we're just talking numbers here in a kick the sack game. There's not very good, and not so bad, then pretty darn good, and outstanding. When talking Numbers with my Customers I tell them this. Fun costs Money, how much Fun can you Afford? Also, some get a little more Fun out of the same amount of Money spent. Thank God gas is back around 2 bucks a Gallon, now go burn some up. The Wizzard
I have chevy 1997 1500 2wd single cab stepside with the vortec 350, 5 speed, 3.42 posi and 265/60/16. I have a K&N and cat back exhaust. I bought it brand new. I NEVER get more than 18mpg. I get 17ish highway 14 to 15 in town. 14mpg is not that bad.
My little 32 Tudor (Brick) is setup like this: 290 inch flathead Potvin Eliminator cam (used in dragsters) (2) 4 bbl carbs (vacuum secondarys) Stock Ford Aluminum heads (Canadian) Center dump headers Stock front mounted "Helmet" distributor with Pertronix trigger Toploader 4 speed with GV od behind 4.11:1 rear axle (becomes 3.21 in OD) 29" tires Gets consistent 21 mpg on flat ground @ 65-70 mph Gets over 16 in the hills (I live in the hills) I don't think the cam has much, if anything, to do with the mileage as long as the engine RPM is in it's happy range. I'm in the 2400 rpm area @ 65/70. Engine is happy. I'm happy. Gas is not 2 bucks here in CA Best bet for that Burb would be to install a bung in one or both of the head pipes and beg, borrow, or buy an AFR Meter and tune it that way. That's as GOOD as it's gonna get. It does make a big difference...
I find that keeping my foot off the floor significantly increases my gas mileage, but stomping on it significantly increases the smile on my face going down the road. With gas at 1.69/gal here, I'm looking forward to March when I can put my 37 on the road again.
It's all about weight and profile with your Suburban. My '40 Coupe got much better mileage after the chop. At 65mph, I am running 1900rpm's and get 22mpg. I have a warmed over 292 inline with a 270 cam, 3x2 holley/webers, t-5 , 30 " tall tires in the back and 3:55 10 bolt.
I got a 30 over 327 and four speed with 3.5 rear, can't remember the tire size. I got a best 16 mpg highway. And I get the "what kind of mileage does it get?" question all the time. My response is always the same, 21 SMILES per gallon!
29moonshine; Sorry this thread seems to have headed off in left field. I don't read much that's actually helping you determine if your getting all you can or what to do to find that out. Let me tell you what We do to get things to the Best performance level possible. I'm talking Race Car for the most part by my 51 has gone through this and many a Customer car get's the same treatment. Every new motor that comes to me is Fresh off the motor Dyno wet and Loaded ready to just start driving the way you want to. The Dyno tune let's you find the Sweet spot for the full R.P.M. rage. Once in the Vehicle there's No Pussy Footing around of Guess work with a Screw Driver, you just Go. For me it's the Best $$$ spent and if something happens on a fresh motor it's going to be in my Builders hands not a bad conversation between Me and Him. The next Best thing is a Chassis Dyno. The motor is in it's true enviroment, exhaust, fuel, ign power. Hook it up, Stand on it and see what you have. The big screen tells it all. If your using Fuel correctly. When and where your Ign timing is at it's best and just maybe you could use better exhaust. Over all it's $$$ well spent as long as your Dyno guy knows his stuff. With the Race Cars, any Carb, Dist, or Ign control box change the Car goes back on the Chassis Dyno and gets a couple pulls. That verifies we are where we belong and everything is up to the Driver. We never do parts changes or Tune up's in the Pits. (don't mistake that for not doing necessary service) There it's just a matter of keeping things where they belong and a little Luck. As for what I think about your Truck. Make sure your Converter is Locking up at highway speed first then go get a Power Tune. Come back latter and tell us what you got. Brand New parts don't always equal Good parts. The Wizzard
AFR is a small part of the equation. I've been able to get 5 or 6 mpg in a car with an AFR meter showing it running just like it should.
I'm not buying that one Jim. Certainly there is more to tuning than just the AFR, but I've never seen it harm an engines performance or economy. Just my experience Jim
Jim nailed it. Dive the wheels off what you have and be happy. You could POSSIBLY nail down 16/17 MPG with a late model 6 speed. Really though, you're pushing/fighting a lot of air in that rig.
i am going to drive even if it only gets 10. i just thought it should be a little better than 14.. i will check the timing and make sure the vacum adv is working and the trans is locking up when i get back next week. i want to drive it to tampa in march
I was thinking the same thing. Converter stall isn't a constant figure, it varies according to the torque the converter sees. So, at 60mph the aerodynamic resistance is relatively low, and so therefore is the torque at the converter: chances are the converter is well stalled at the corresponding rpm, even if that is lower than the converter's advertised stall speed. At 70mph the aerodynamic resistance is much higher, so though the rpm is 17% more, the torque at the converter is more like 36% more - which might be enough to raise the stall speed to a point where the converter isn't stalled any more. That's why you need the lockup converter.
Read: http://www.oldsmobility.com/old/carlife_apr67.htm Also, consider the use of the stock, temperature control, air cleaner housing. i know---it may not look cool, but it might help out mpg-wise.
Yes... Recommended reading. Some interesting approaches to efficiency being taken. And look at the observed mileage figures at 50-60mph and above. Thanks for the link...
My 37 was a pretty tame street rod by most accounts - 302 Ford, 500cfm 4bbl, C-4 (no overdrive) and a 3.08 rear with around 28" rear tires. I built it to look good and travel well. But 18-20 mpg was about average. I think I got 22 once or twice, but who knows why. I also wished for more. I'm very sure the Rosta cruise helped mpg greatly on the interstate. So, get a little bigger rear tires first, if you can fit them, if you can't also afford a rear gear change at the same time. If you travel a lot on freeways, get a cruise control too! I put a lot of my 37's 30K+ miles on it over the interstate. Think how much further you could afford to go these days, with the cost of fuel at the moment! Gary Unsolicited opinion department: I can't stand to piddle along at the posted interstate speeds. I drive my hot rods like I drive my modern daily. Why have a hot rod and be over taken by 18 wheelers, old ladies and lawn service trucks? If you're not going 5-8 mph over the posted limit on most interstates (still under most state policeman's irritation level), you'll be run over by every one. You won't be the fastest a little over the limit just one of the herd. At that speed, you make better time and even relax a little because you don't have to keep one eye on the rear view mirror for over taking farm vehicles. Country roads are another matter, there's more to see and do. But still need enough poop to get around the old ladies and farm equipment.
Kool suburban, thinking 14mpg is not that bad, as a ref, 2002 suburban, 5.3 engine, OD trans, 3:73 gears, all modern technology, best ever 19/20, usually 17/18 @ 70/75. Also have 2001 Ford Expedition, 5.4 OD trans, 3:90 and 15 mpg is its best, usually 13/14 @70/75. When I put my enclosed trailer behind either, Chev 10+ , Ford 8+, on windy day even worse, So.... Considering, you're pushing a aerodynamic brick with all old tech, 14 sounds pretty good. This reminds me of a fellow rodder that built a 41 willy, big tire car w/ blown 502 and constantly bitched about poor gas milage 6/8 when cruising, I thought that was good for what he had and when asked what he expected, got PO over question.
Maybe I am in the minority here but I have lots of ideas on this topic: Swap out the engine with a very OT clean running DOHC 4 cylinder. If that is too much work, you might just rip those big old wind grabbing fenders off, that would be good for a few MPG. Honestly, if you cut the roof off not only would you eliminate a lot of drag but it would cut down on weight as well. Of course all those ideas would destroy a really cool rod. Maybe you could just sell it to someone who couldn't give a rat's ass a bout a couple MPG and buy a Prius. Is that too harsh?!
Lots of helpful comments hidden among the useless ones, it sounds like you have an idea of where to start. Most threads like this just fade away, make sure you actually come back and let the few who were interested know what's going on. Fwiw, if you go through the suggested vacuum advance check, ignition timing fiddling, mild carb adjusting, and make sure the converter is locking up properly, don't be scared to take it somewhere to get tuned by a pro. A lot of street rod shops and performance shops have the knowledge and equipment to get these cars dialed in.
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