help with gas mileage, this 67 needs to be on the road more

[The Big Green]

I have a 67 Chevy SWB with a 350 and the gas mileage is about 10mpg with 11 here and there on a good day...lol. I got the truck when I was 17 and I'm 27 next month. When I was 17 and gas was alot cheaper and I didn't pay for gas anyways, I put in a new rearend with 4.11 gears. I don't like the gears now, I mean they are fun in town but I run 3,000 on my 35 mile trip to the city, I live in the boonedocks...lol. I have a 350 probably bored to a 360 with 11.1 popups,300 Lunati cam,282 stock heads with the 1.94 valves. I have a Edelbrock Victor Jr. intake, pulls at 3500 to 7500 I think. I have a crappy 750 holly that I bought and it falls on its face sometimes when you hammer down and it runs really rich, burns the eyes when you stand behind the truck. I wont buy another carb from a place that rebuilds them. How can I get better gas mileage, gas prices are high and I just hate to see these old trucks sit because gas is high. I know the 4.11's are killing me and that 750 and cam and pistons love the 3grand rpm's for 35 miles. My first ideal is a 3.42 gear. What does everyone else think? I know I wont get 20+mpg but 10 just sucks. Oh, and I built this engine about 4 years ago and will be tearing it down for new rings and bearings so it would be a good time to do things different. I don't want to go stock but I will if I have to. These trucks are 5000lbs and its like pushing a piece of plywood down the road.

[Wrenchbender Ret]

I agree the rear gears need to be changed. If that Holley burns you eyes, the power valve is probably bad. They are not hard to put in. Check the float levels through the site holes. Most Holley's have external adjusted floats. If not you can do the primary when you put in the power valve. Holley's are not noted for gas mileage but if set up right they are not that bad. Check your spark advance. Get an adjustable vacuum advance & set it for a low vacuum & hook it to manifold vacuum. When you go into the engine put in a milder cam.

[67ChevyRedneck]

A 3.08 gear and a light foot might get you 13 maybe 14 mpg going 55 mph.

[The Big Green]

Thanks for the help guys. I don't know about a 3.08 gear because its kinda high and I don't want my truck to struggle to get going. You may not tell but your engine may. Also, on the power valve, I know I have never had on go bad but my buddy borrowed my 750 for about 2 months while my truck set because I'm a good friend. I raced him in my 01 dakota and he was in a 350 91 s-10, I beat him by the way, 408 stroker and 600hp will get it done...lol. His trottle stuck WIDE open and he had to kill it, well you know what that would do. It backfired about 10 times so loud that it scared the crap outta me...lol...like a 12 gauge by my ear 10 times and my ears were ringing. I think a power valve could be it but I don't know how they act with a bad power valve because I've never blew one. So what are you guys getting on gas and how often are you on the road? How many miles do you drive them?

[The Big Green]

Oh, and I will probably put in a smaller split duration cam. My dakota is about 500lbs lighter and it gets 12 and its 600hp but has 3.55 gears. I just want my 350hp or so 67 to get better than that atleast.

[Longhorn Man]

Almost 1/2 the ppl who responded on my poll (http://67-72chevytrucks.com/vboard/s...d.php?t=172346) are getting 10 -12 MPG... considering you have 4.10s in back, that's not bad at all!
And this GMC had 3.07 gears, with just a little 350... hell of a cam, and not much else internally... it would stand up and rip outta the hole, then cruise at 2500-ish ROM down the freeway. Yeah it woulda jumped harder with 3.73 or 4.10's, but unless it's a drag truck, I think this would be strong enough.

[67_C-30]

I'm getting 15 - 16 with a basically stock 350 (stock rebuild with flattops instead dished pistons and factory 300HP 350 cam) with a Q jet, TH350 and 3.08's. I'm running P275/60R15's which are 28" in diameter. My truck has no problem spinning the tires and takes off with ease. I've had trucks in the past with 3.08's that seemed sluggish, but with a heathly engine they work great.

[Eddie H.]

Keep the 4;11 gears, fix the Holley, of get a better carburetor. (A good Q jet will get better mileage if you keep your foot out of it), and put in an overdrive trans.

[joedoozer]

Yup, I love Q-jet carbs. I used them all the time when I was younger, because that is what came on the motors I bought. And being young and broke, I used what I had. You can make a lot of power with a Q-jet, and if you do keep your foot out of it, driving around on those little primary's should get you decent mileage.

The key with Q-jets are the secondary metering rods. Here is a nice chart I found. http://www.hioutput.com/tech/qjetrod.htmlThey are very easy to change, and can give you a run of the mill 4 bbl, or something very aggressive in fuel delivery. This giving you the chance to do daily driving as a 2 bbl, and a dump a lot of fuel (if you want), when you need it.

Q-jets can be complicated, from what people tell me. But with the internet, and boards like this, I don't see a problem. Get a run of the mill Q-jet and install it. Get a few different sets of secondary metering rods. And swap them and test drive for a week. Monitor performance and mileage. Choose the ones you find best. Just make sure you get the air valve adjusted right, so they don't come in to early or late. Air valve is the choke plate looking thing on the secondary side.

[Mint68]

I'm suprised at the 10-12, I normally only get 7-8. I have a stock blazer with 3.08 gears and 31x10.5 tires. I hope the odometer is just counting wrong, it seems odd I get so bad of gas milage.

[68gmsee]

It all depends on what you want... power/speed or economy...

Most young guys I know (includes my nephews) want the power. And it's nice to have, but with that comes the price of low mpg's.

I have a stock 350 with a quadrajet on my 69 Chevy with a turbo 350 and 3.08 rear end. On the highway, when it was running, I would get a respectable 14-15 mpg (no AC).

As far as power, it had all I needed. I've pulled a flatbed trailer loaded with a full size tractor and bushhog plus other equipment and had no problem.

It may not have been fast on take off but cruising was fine.

[The Big Green]

I really appreciate all the help guys. First of all that red truck may need tires after that burnout...lol...good job man. Maybe 10mpg isn't that bad but I'm thinking I can pickup 3 or hopefully 4 more with a new carb thats not a 750 with a screw in it, my uddy did that before he gave it back to me,its a vacuum secondary carb so I could take that out but I hate the hesitation that it has. Quadra-junk...lol...thats what my friends family always called them and after 12 years I just don't know. We have always went Holley but back when gas was like 80 something cents we didnt care to have a good Holley doublepumper. Im not talking bad about Q-jets but in 12 years of driving I've never owned one but I've had a Edlebrock once and they are very easily taken apart and cleaned. I may get a new carb and not rebuilt and go with a 650, its plenty enough for anything under 400hp thats just driven and not raced. I'll go smaller cam eventhough I have heard good things about the Lunati 300,515. I can't decide on gears but if I want to pull my 01 dakota cc to the racetrack I can't go 3.08, so I guess 3.42 it is. Oh, I may be getting worse or better but everythings broken, gas gauge, speedo, nothing works. The gas tank was full and I drive about 35miles to the city and then I drove about 10 miles maybe in town but I drove pretty hard at times and hit 6 grand maybe 7 a couple times and I put 6 gallons in. I may be freaking out because I have to shake the truck to hear what gas I have left. I'll fill up and drive to town, 8 miles and I know this and then fill up and see what I get for sure while driving 55 all the way.

[oldsmobilekindofguy]

drop in a diesel and convert it to cooking oil and make a deal with a local fastfod place to pick up their grease, then you just screen it and dump it in the tank

I wish it were that easy or at least they make it seem that easy on TV

[joedoozer]

Q-jets are complicated. They have quite a few adjustments, including all the little linkages you can bend. Most people get lost trying to tune a Q-jet.......explaining the name Quadrajunk. Most people can't tune them. I was forced to learn, because I couldn't afford a new carb. Do some research on them. A spread bore carb is just what you are asking for. Small primarys for driving and big secondarys for power.

[The Big Green]

I don't want to smell like a big frenchfry driving down the freeway of setting at a redlight in town, having people say I smell good...lol. I would like to get 14mpg or where I can't see my gas gauge go down when I takeoff, its broken now but if it worked I wouldn't want it to. I had a 650 Edlebrock when I was younger and I couldn't afford a different one at the time and I really liked it and if I'm not mistaken they offer a spreadbore carb.

[67ChevyRedneck]

Originally Posted by Mint68

I'm suprised at the 10-12, I normally only get 7-8. I have a stock blazer with 3.08 gears and 31x10.5 tires. I hope the odometer is just counting wrong, it seems odd I get so bad of gas milage.

Bigger tires will cause your speedometer to read "slow." Get a friend with a somewhat new vehicle with an accurate speedo and match their speed, get on a cell with them and ask what speed their going. That's how I determined my 67 was 9% on the slow side. This has been confirmed with a couple different police speed thingys too (the things they put up to "warn" you about speeding.)

[68gmsee]

Originally Posted by joedoozer

Q-jets are complicated. They have quite a few adjustments, including all the little linkages you can bend. Most people get lost trying to tune a Q-jet.......explaining the name Quadrajunk. Most people can't tune them........

Took the words right out of my mouth... I've always had them on my vehicles and trucks except for an AFB Carter once. I still don't profess to understand them.

I've never really had a lot of problems with them, either. Once they're mounted and working the only parts I've replaced is the standard kit (gasket, needle valve, float and filter).

[jonnybravo]

my 68 had a quadrajet that took a crap when i was using it as a dd so instead of rebuilding it i went and bought a cheap edelbrock 600 or 650cfm cant remember. a little over 200 bucks took me from 9 mpg to 11. didnt take too long to pay for itself. any increase in mpg when you start with that low of a number is significant.

[The Big Green]

Quadrajets are good carbs if there adjusted right but with a good Holley or Edlebrock,if you buy them new there great, but I bought rebuilt and its crap. I'm going to a different, new carb asap, when I go thru my engine in a couple weeks. I'm going with a extreme energy 284/296dur 507/510lift Lunati cam, and a new rebuilt pair of Bowtie heads with 185 runners,fully ported, 555 lift spring,comp guideplates, and 205 valves...lol. I should get the same if not better gas mileage and be faster because they will breathe so much better than the 882 heads I have now but they were are cheap heads. I'm going with the 3.42 gears and look for a 700r4 tranny with the overdrive which I could use. Gas will NEVER go down or back to 80 cents a gallon ever again and the prices wont keep me off the road, I can care less. Face it, if gas hits $5 a gallon there will still be just as many people on the highways only thing is is that there are no hotrods anymore really. There are still cars and trucks, brand new ones getting 12 in town and 16 on the highway and thats not much better than us. The new Trailblazer SS with the 6.0 gets 12t and 16h and its fast but not faster than my dakota od chevy and the dakota gets 12mpg and it will run circles around the trailblazer.


Whats everyones opinions one the my Bowtie heads? I can still trade my buddy for some 041 heads with a bowl port and 194 valves. What carb would everyone run on this, cfm size? I will run a flat top piston and prolly like 10.1 with the 63cc close chambered 301 bowtie heads and stay 11.1 with the 64cc 041 heads.

[Pont406]

With 284/296dur you will always smell gas.

[Cannon007]

what size torque converter u have?get 3.73's and a built Overdrive tranny with a 3k converter and your golden. As for the engine look into making it a full roller cam and match up a good intake and carb for it.

If your on a budget I would just get 3.73's and a 2600 converter and a new carb, and do some good tuning on it.

[The Big Green]

Well, this engine was built about 4 years ago and if I'm not mistaken its a 3000 stall. I'm kinda set on the 3.42 gears but if I can find a good 700r4 I'll go 3.73's because of the overdrive it will still run at lower rpm's on the highway. Right now my truck smokes when I startup which is valveseals but with the 301 63cc heads that are built that will take care of that problem. It smokes when I hammer down which is a bad carb and it falls on its face when I first hammer down which I could use a new powervalve. I got a few small problems but its all good. I don't want to go to a full roller, if I do that it will be to newer ls7 aluminum engine but until then it can stay the way it is. I want to fix this engine and run it for a while and then sell and go injected.

[SCOTI]

Your 'new' cam choice still seems a little big for a 350 that's trying to squeeze mpg's. The 2.05 valves might be overkill for the application too.

Try something around a 268 duration cam, the OD trans w/a decent convertor, some 3.73's & a 28~29" rear tire. Maybe some of the Edelbrock E-Tec series heads or Vortecs that flow decent for the money spent.

[The Big Green]

I'm not rebuilding my engine right now, I'm just going to bolt thoughs 301 heads on, if I have flat tops if not I'm going in. I really love that 300 though but if I go in I going bigger...screw gas prices.