I did a test over 3 full tanks of gas including 2 days at the track (16 passes) and I am getting an average of 5 mpg. I used a GPS device to record my Miles.

No Comment graemlins/angry.gif

My 70 gets about 10-14 MPG depending on driving habits...and thats with vacuum secondaries.

Geez Tom, I wish I had a spare 3X2 setup to bolt on for you. 1.) I;d really like to see how it compares to a standard 4 bbl, and 2.) you might get 6 around town! tongue.gif

About 17 driving back and forth to work with 1 or 2 good WOT pulls to 6K on a daily basis. I'd do much better if I had an overdrive or a lock up torque converter. Then again, if I didn't have to hear that "spreadbore roar" everyday I could skip the overdrive! :D

Mike

I get about 9, then it gets worse from there depending on how my foot feels :D

17 if I'm playing, 20 if I baby it. Have had as high as 23, but that's with all ideal circumstances and driving below 65 mph.

mine's getting really bad milage or really good milage, depending on how you look at it......it's not using any gas, but it hasn't moved since March. graemlins/sad.gif it's in the body shop. my 454 would get 10mpg with a 850 dp, 4.10 gears, and 10" convertor. with same convertor and gears and a 750 vac sec, my 355 would get 15mpg. i haven't even run 1 full tank of gas through my 406 yet. got it running just in time to put it up for the winter, and it's been in the shop since there was snow on the ground here.

I get roughly anywhere between 7 and 9 miles a gallon. Depending on driving/cruising, I'll get more around 8 1/2-9, if I'm havein' some fun :D I'll get more around 7 or so, maybe less :confused:

I just drove 327 miles of Interstate today w/ my 68. It has a ZZ502 t400 3.07 rear. Averaged 9.59 MPG.

eight

about 17 here.....if i'm easy on it.
you can guess i get quite a bit worse if im not ;) thats with 2.56 rear gears and a 600 vacuum secondary holley. no overdrive or lock up torque converter. and its a 355.

Back and forth to work everyday, about 18 to 20 miles per gallon. Stock 350 (ATK long block bored .30 over) with a Holley 4 barrel, vacuum secondaries....2.56 rear.

About 6 gallons to the mile :eek: Oops, I mean
about 6 miles to the gallon :rolleyes: and it really, really Sucks right now at $2.45 a gal. for premium. Oh well, I guess I don't own a big block Chevelle for economy, right? :D

Gaz the lead foot graemlins/waving.gif

As I stated in another post, 20mpg on the highway, 454/700R4/2.73 .

BTW, can run 8.50s in the eigth@89mph. Not at 20mpg then obviously! graemlins/waving.gif

10 on a tank with a couple of WOT runs. 383 TH400 3.36 rear.

James, a rat doing 20 mpg and still making good HP. That's impressive!

Depends if I have the brick or the cinder block with me that day!!!! tongue.gif
The Elky about 15 or so...the Chevelle...maybe 5.
Brian

My 69 Elky with mild 350,T56 trans,and 3.50 cogs in the Fab 9 averaged better than 20mpg on the Power Tour legs I just ran. Had two tanks with 24mpg average. The SB in the car is not earthshaking when it comes to power but 1700rpm at 70mph in 6th gear equates to good fuel economy.
Am hoping for 15+ when the BBC is installed.

I used to be up around 10mpg with the old hyd rollers that were about 286 or 296 seat, 230 @ .050, high lift, when I switched to the wide-by-huge with too-wide LSA solid, I am getting 6.5mpg or less.
I have not tried an extended highway trip yet.
I can't fill my tank so my method of calculating MPG is a little, um, well, imaginative.
All I know is that if I plan for an afternoon of driving, even if I park the car for 2 hours in that afternoon, its gonna cost me 15 bucks. I fill to 3/4 tank and have to burp the tank on hot days periodically. it's better than spilling the gas out the tank on hard acceleration (I'm sure the guys at the track loved that.... I'm surprised they didn't use some Henry VIII torture tactics on me that day..)
Aside from still being a <word omitted to save moderators time> about the 3mph I wanted to hit 120, I can deal with the 6 mpg because of how smooth it is.
All things considered, I look at that 8AN line feeding the 750/850 base DP with these gigantic fuel bowls and no return line, and I am like gas mileage what? heh.
EFI I bet I could squeak 10-14 out of the car and boost the power some.
I'd like to know what I get on extended highway trips at 65-70 (2800-3000rpm) but because I can't fill my tank what I do is add up gallons bought over a period of time (say a month, when I get the bill), and miles driven over that period..
So its near impossible (unless someone can tell me how..) to figure out a straight highway session for MPG.
Filling the tank has resulted in the cold gas expanding on a hot day and just pushing itself past my gas cap onto the ground.. so no more full tanks.

Sorry for the long post..
Matt

I drove from Davenport, to Waterloo {iowa}, 130 or so miles, with 4.11 gears in the Nova @ 3,200-3,700 RPM and did it with gas to spare in my 16 gallon cell, but i drive a stick. Fuel factors include, the 302/310, 268/278@.050 solid cam and my 750 mighty demon, mechenical secondary, and that i got on her pretty hard twice in Davenport.

Some of the Corvette guys on Corvetteforum.com just got 19 and 20 with a 540 and a carb and a 454 with EFI with 3.08's and a tremec on the highway. Pretty amazing.

Gear and converter will kill mileage with any engine.

5 to 6 mpg....

OK, I can't help myself. It's a sin to gloat ain't it? 439 ci mechanical cammed HUGE port rat rat running through a 5 speed and 3.31s, 3300-ish cruise rpm = 15.X mpg. Have logged as high as 16 on a steady 62-65 mph ( 3200 rpm) highway run. Motor is a bit mild I suppose, but strong enough to get the car to 118 mph in the 1/4 mile/91 in the 1/8, with full 7000 rpm capability ( and I think there's more there with a better fuel system and race-tuning the trips which I haven't had the time to fiddle with much).).

If I could go 55 mph ( 2900), Old Red would sqweak out near 17-18 I suppose. Not bad for an ol 435HP 427, eh?

At first I thought the hotter and tighter LSA UD cam had an impact on milage, but now with 4000 miles under its belt, I can't see any difference between it and the old 114 lsa Crane LS6 cam. Well, until you hit the loud pedal.

TRIPOWER BABY!

Wish those Vette moneyboys hadn't bid the price of admission so darn high. Dang, I'd set them up for ya'll for free. Really a simple blueprint, sourcing some old GM parts, and a check to Holley custom shop for $777 for 3 carbs delivered. ( although I don;t know much about the stock vacuum secondary deal - we use the old Ford/Mopar mech setup).

Yet, it will take me many, many runs to Nashville ( CB) to recoup the cost of the setup. But so far, with a 5 mpg differential and nearly 4000 miles logged JUST to CB and back, figure I've saved over 100 gallons of fuel just in the CB trips. Ten more years of going to CB,and I'll have the whole setup paid for! tongue.gif

A friend has a 32 Ford with a blown elephant on alcohol. He showed up at one of the Friday nite get togethers with it. I asked him how he was going to get home (about 5mi) He said his son was following him with a van with fuel in it. The 32 had a 10 gal tank but he couldn't go 10mi in it with out filling the tank.

Gene,
Why wouldn't you think you could tune a 4 bbl to get the same, or close mpg as the tripower. I'm not saying you can or can't just asking.

I get about 16mpg with my new 355 but I have a heavy foot and smoke the tires up the on ramp going to work and usually drive 80-90 mph on the freeway :rolleyes: I also have 2.73 gears and a th350 graemlins/thumbsup.gif

Originally posted by 427L88:
James, a rat doing 20 mpg and still making good HP. That's impressive! I have been amazed!!!

I've done everything I could to ruin the milage, put a lighter spring in the secondaries, upped the primary jets 2 sizes, added a secondary metering block with huge 88 size jets, and I also carved the choke housing of the Holley. Not to mention the 280/288 cam and 2.19/1.88 valves in the heads!!!

Things that are helping the milage though are the 700R4, 29" tall tires and 2.73 gear. I also have an air fuel ratio gage installed and a manifold vacuum gage. The A/F gage is a must to tune the carb and I drive with one eye on the vacuum gage when crusing, high vacuum=good milage!

James, absolutely, I find the vacuum gauge invaluable. For effecient crusing, for telling me when a valve isn't lashed right, etc.

Doug, I suppose you could. I mean it's only a 2300 2 bbl running the motor at cruise, same as the front of a 750, so theoretically you should be able to. But , you won't have the loud pedal effect. With the 750 and a GM 163 it was around 14, with an 850 it had a bunch of top end snot, like now, but mpg was ridiculous. I did try fiddling with that one, 105 PV and jetted down to 76s etc, but nothiong really helped. Oddly , the 750 is/was setup just like I have now, 72/73 jets in the primary, and PV-blocked 78s in the secondary.

Having said all that, the 3X2 mani is a unique creature with a small/tall runner dual plane off the center carb, and pretty much straight shots at the intake valves off the outboards. So you're dealing with a crude version of the modern Honda V-Tech variable runner manifold in a sense. Small runner 180 on center carb, short, big runners, 360 open off the outboard carbs. The center runners sort of "spider" into the open secondary runners.

Short answer - I donnow. But it never got this type of open road milage with the single Holleys on it. And this motor would run the 750 out pretty quickly, although the math didn't indicate it should. Come to find out I was spining it much faster than 6500-6800, more like 7200-7300. Still think the amswer lies in that old Winters casting, NOT in the carbs themselves. Like I said, my 750 DP is set exactly like the triples are ( except for squirter size obviously), so there is really no difference there at all.

Couldn't you guys cast these things for around $350 or so cost?? A true "dual action" manifold. Kripes, it rivals EFI on the economy front.

How many of these responses are actually calculated, and how many are just guesses or educated guesses?

Originally posted by -SS454-:
How many of these responses are actually calculated, and how many are just guesses or educated guesses? Mine is calculated and confirmed by comparing miles driven and fuel stops with my friends and thier cars. We travel to events together following in each others tire tracks and fueling up at the same time. I'm killin 'em!

my z28 with a bbc 396/414 got 18 mpg with 2.41 gears ,2100 stall and my 3310-2 jetted at 68 front and 72 rear........good for 14.40's @ 98mph in the 1/4

now with my current changes it has fallen to 15.x mpg with 2.73 gears,2800 stall,jetted up 72/76,and redone heads with the cam 4 degrees advanced with new exhaust system........

im sure it would have been slightly better if i would not have ran it hard the few times the speedo went into triple digits,

my truck (86) gets 17 mpg with a 302 fuel injected motor with headers and cold air induction set up

I'm amazed how bad some of your milage is!! :eek:

My 632 big chief over .800" lift roller with a 1350 dominator and locked out timing gets over 10 mpg around town! (I measured while preparing for the pump gas drags)

My saving grace is that i have a VERY tight converter and 3.70's. Cruise around town at less than 2000 RPM much of the time.

My '72 Camaro with a 454, T56, 3.73 12 bolt, 275/60-15 BFG's, averaged over 20 mpg, and as high as 24 mpg on a road trip from Seattle to Dallas, mostly in 5th gear at ~65-70 mph.

Ran 8.20 in the 1/8th at 90 mph with the BFG street tires, easy launch (2.1), and almost granny shifting.

Originally posted by Big James 4XL:

.....upped the primary jets 2 sizes....
Things that are helping the milage though are the 700R4, 29" tall tires and 2.73 gear. I also have an air fuel ratio gage installed and a manifold vacuum gage. The A/F gage is a must to tune the carb and I drive with one eye on the vacuum gage when crusing, high vacuum=good milage! Big James 4XL,

Question: So when you installed the A/F gage you determined that you needed to go up 2 jet sizes?

High vacuum=good mileage? Are you talking about vacuum at idle, installing jets that give you the best vacuum at cruise, or driving while watching the vacuum gauge to help you keep an easy foot on the throttle? I found that you will get max vacuum with a rich (~14.0 - 14.5:1) primary metering setup. By going a little leaner, your vacuum will go down, but your mileage will increase. That also agrees with what I've found running fuel/spark curves at the dynamometer laboratory. Case in point: I have some Qj's that will get me almost 18" hg at expressway speed. I leaned one out to where I get ~16" hg. That is the one that gives me the best mileage.

Mike

Thanks Gene,
I'd be curious to put a wideband oxygen sensor on your car and see what A/F ratio you are at.

Your mpg and performance is impressive with your car.

Making a cost effective trips (that also performs) idea is interesting. The new BG setup is $2300+.

The casting is the bugger Doug. Your custom shop took three reman 2300 and did the carbs up. I think you could come in around the same , if not $1999.99 for a rat, if you could copy the GM Winte4rs casting. The 2300s are big enough for a rat, although I'd be a bit uneasy using that much carb on an SBC. Have to line them to shrink the venturi.

Boy, sure be neat if your folks saw a market for it.

I've never had any sort of dyno/AF or any other test equipment hooked to the engine. It does run a tad lean judging by the plugs, if you can actually judge by that. I tried fattedning up the secondaries to a 79 adn 80, but it got soft. I was told to drop the jetting to 75-76 for best pwoer, but I have to worry about ping too , at 8.6 DCR.

Jake, that's really impressive! Kinda wish I had a 6 speed now with a .68 top gear!

Beat by a friggin Ranger -- AGAIN! smile.gif graemlins/thumbsup.gif

Originally posted by Unclepennybags:
</font><blockquote>quote:</font><hr />Originally posted by Big James 4XL:

.....upped the primary jets 2 sizes....
Things that are helping the milage though are the 700R4, 29" tall tires and 2.73 gear. I also have an air fuel ratio gage installed and a manifold vacuum gage. The A/F gage is a must to tune the carb and I drive with one eye on the vacuum gage when crusing, high vacuum=good milage! Big James 4XL,

Question: So when you installed the A/F gage you determined that you needed to go up 2 jet sizes?

High vacuum=good mileage? Are you talking about vacuum at idle, installing jets that give you the best vacuum at cruise, or driving while watching the vacuum gauge to help you keep an easy foot on the throttle? I found that you will get max vacuum with a rich (~14.0 - 14.5:1) primary metering setup. By going a little leaner, your vacuum will go down, but your mileage will increase. That also agrees with what I've found running fuel/spark curves at the dynamometer laboratory. Case in point: I have some Qj's that will get me almost 18" hg at expressway speed. I leaned one out to where I get ~16" hg. That is the one that gives me the best mileage.

Mike </font>[/QUOTE]The A/F gage did in fact tell me I had a lean condition just off idle to about 2000RPM. I had a slight stumble as well, and the bigger jets cured it, the A/F gage then started showing a tad toward the rich side above 2000 RPM but dead on at cruising RPM(1800). I was not tuning for gas milage at the time. I was trying to cure the stumble and relieve a detonation problem I was having at the time. It took a cam change(276/286 to a 280/288 UD/Lunati)to cure the detonation, but my milage also improved! :confused:

And yes, I keep an eye on the vacuum gage to help keep an easy foot on the throttle. At my normal cruising RPM I can easily lighten up my foot and have 15"hg and better at times. The trick is to stay aware of the gage reading and let off the pedal as much as you can. After a while it becomes second nature, and I have no doubt it has saved me many many gallons of gas. So to answer your second question I use the primary jetting to get good vacuum at cruise. I've noticed that with my present combo the throttle(pedal)only needs to be pushed say 1/4" once I'm in overdrive and the converter locked up to run 70mph, what I'm trying to say is it just doesn't take a lot of throttle to go down the road and it has enough torque I don't have to stand on it to go up grades or pass other cars.

Gene,
That trans has a .50 6th..

But I was runnign in 5th most of the time, following the 24 ft Uhaul..

The Camaro had 461 cubes, the Uhaul had 427...
The Uhauls was hauling over 20K lbs of truck and stuff.
Tha Camaro was usually hauling one adult and one kiddo.

Uhaul=7mpg
Camaro=20+

LOL
At the time it had a Q-jet, factory iron oval intake, HEI, 236/248 solid lifter cam with 106 LSA...

I have a '90 model extended cab dually, 454/TH400. If I Fred Flintstone it at the lights (open the door to push myself to get going), I get 9.4 mpg. With the price of gas as it is, I've learned to baby it quite a bit. Sure wish I'd known gas would get this price when I bought it!

BTW, my mpg's are all calc'd. The only fuzziness is in how much the tank is full. Old cars tend to "pop off" the pump early.

And to add to the high compression/VE/mpg issues, although I beleive the engines DCR helps efficiency everywhere, my engine's 8.6 DCR is too high. Just picked up a bad batch of Sun93 and had to go to the local airstrip and top off with 100LL. It's that close. Bad batch of gas, and I have to pull the vac adv off( until the fuel is correct), which, of course, isn;t going to allow anything like 16 mpg at 3200 rpm. Old Red rides on a razor's edge at 93 octane and 35 total timing ( + 9-10 additional at cruise).

ANd lastly, a correcetion. Tom ( mc71540 ) I ASSUMED you meant ride with me, but then remembered you have a 69 in the wings. Did you mean drive down with me? Is the 69 going to be a driver? Pure show?

Gene,

The '69 is going to be a completely stock appearing and will be driven, but will be at least 3 years before it is ready to go...But then I will drive down with you.. graemlins/thumbsup.gif


My '72 Buick GSX Clone on the other hand will be out of the paint shop in about 3 weeks, it is Black with GSX Equipment minus the stripes.

Tom, I ran into a guy today at a car show who has a bunch of Buick parts for sale. Let me know if you'd like his number.

My 2003 Silerado 2500 crew cab, over 40,000 miles has an average of 19.6, has gotten 24 plus and will get 17 or better towing :D :D

That Duramax and Allison trans are a wonder, 6800 pounds just for the truck and it has a 3.73 rear.

Originally posted by Wally:
My 2003 Silerado 2500 crew cab, over 40,000 miles has an average of 19.6, has gotten 24 plus and will get 17 or better towing :D :D

That Duramax and Allison trans are a wonder, 6800 pounds just for the truck and it has a 3.73 rear. My 04' duramax/allision doesn't get anywhere near that mileage. Mine's fully optioned extended cab 4x4. I get 18 on the highway and ~15 around town if I keep my foot out of it. When I tow I usually drive between with the air on I get between 13.5-14 mpg. I had an 03' 2wd before this one and it got 2-3 mpg better on the highway.

Originally posted by 10sec69:
Tom, I ran into a guy today at a car show who has a bunch of Buick parts for sale. Let me know if you'd like his number. Jim, Yes I would..Thanks..