My truck is a 79 E350 dually ambulance. I have converted it into my race car hauler (legends car fits inside). Id like to get 10mpg if possible
It has a 460, C6, dana 70 -4.10 gears. It has about 80K miles. Currently gets about 5-6 mpg. The loaded weight is about 9000lbs.
It runs well. I recurved the ditributor, rebuilt the carb (4180) new EGR, smog pump blocked off, no vacuum leaks, exhaust leaks etc.
I plan on putting the stright up timing gears in.
I have a 1970 CJ intake for a quadra jet as well as a new in box 1969 qjet for a buick with a 455. this is a non-egr intake. I think the ports are a little bigger than the stock intake.
Should i use the CJ intake/qjet (i like qjets...good milage/performance comprormise); should i stick with the holley or buy an edelbrock on the stock intake?
I am also planning on going to 3.54 gears (thats the highest available for the d70)
I dont really want to change to an E4OD or an overdrive. I only drive 2-3K miles a year, so its not worth a huge investment for 1-2 mpg
any input is appreciated
Sean

 

Read my post "Fix or repair daily" for igintion upgrades. While the truck is idling take some water and pour it on the intake manifold right where it meets the head if it stumbles and clears up the manfold gasket needs to be replaced. Open air element air cleaner. Dist vacuum advance to ported vacuum, set timing to 12 degrees. Free up your exhaust, run a single 3" no cat system with high flow muffler. Change your timing chain to advance 4. When you change your rear gears you will lose a bit of tourqe which u know so the single exhaust instead of dual and the timing chain will help you regain the lost tourqe Jason

 

With the box on there you will be lucky to get 8 mpg. My '84 F250 heavy duty (1 ton rear end) 460 with recurved dist.(got me out of the 5-6 range and up to 8-9 mpg), C-6 and 4.10 rearend with my camper onboard gets 7 mpg (7.7 mpg twice last fall) on the flats but no faster than 55 mph.

 

Thnaks Jay/Brad
I have a no-cat single exhaust. I was thinking of replacing the muffler with a better one...looks like an old cheepie.
I think the truck has plenty of power to pull the 3.54 gear, since i wont be pulling a trailer.
I guess my biggest question, was whether or not to use the CJ intake with the Qjet or if teh CJ intake wont match up well to the stock heads and therefore offset any gains

 

that cj intake wont do much by itself

however i would highly reccomend the qjet....buy an adapter and bolt it on....i love my q-jet....

 

Kubota, did you put the qjet on a stock holley intake with an adaptor? The secondaries dont line up too well. I have an aluminum adaptor. is that the kind you are using.
When i switched from a holley to a qjet on my camaro, the milage went from 15 to about 20 (cruising),

 

i have a performer rpm intrake...which will take spreadbore and squarebore carbs...so i didnt need an adapter....


i have two friends who i have helkped install q-jets on their trucks.. just using the adapter is fine...the pre 75 ones flow up to 750 cfm, like the one you have, so you should be fine with the adapter

 

The Q-jet is an emissions and mileage carb, so could help. But I worked on so many of them off boats that I hate them worse than I hate M16s.

 

I have a '79 F-350 DRW flat bed that tips the scales just over 6800lbs. I have a slightly modded '71 429 in it with a 4spd, with a Holley 600cfm 1850 vacuum secondary carb. Driving conservatively (sp?) I get 16.5mpg. I also have a '73 F-350 DRW that's a little lighter with a stock '76 460 and C6 that gets about 8mpg driven the same way. Stock mid-late '70's 460's are low powered pigs, put them in front of C6's and they are down right ugly.

IMO 460's need to make at least .65 hp per ci to be efficient. Just flat top pistons alone would get you close to that. True 2 1/4 duals with turbo mufflers would help too. I'm not big on headers on trucks. IMO they don't wind up enough to use them.

Make sure you have the carb tuned to the motor, not just rebuilt.

I see the gear change as being a good choice. That alone, should put you up about 1.5mpg (estimating). I can't stress enough how much of a difference driving under 60 makes on these older trucks. It's like night and day doing 58 instead of 68. Yes, time is money, and at these fuel prices, a few more minutes on the road is a few bucks saved at the gas station. Even when gas was much lower, I still never went over 63, between gas and wear and tear on the motor, it just isn't worth it IMO.

 

The CJ intake although it will bolt on has a huge port mismatch with the standard heads and many people that have tried to run htem end up with intake gasket leaks so I wouldn't use it. But That intake will sell on ebay if it has the correct casting numbers which I assume it does (people pay stupid money for things like that) Then put a wiend stealth intake on there although if you want to run hte spread bore you will need an adaptor.
I know you said you don't want to switch to the EAOD but may I suggest either switching to the EAOD gear set in the C6 or just buy the wide ratio kit (much easier to do with the kit no machining required that way) and put that in with the 3.54 gears this will help bring back some of hte low end in first and second but still give you the higher gears in third. that wide ratio changes first gear from 2.46:1 to a 2.71:1 and second from 1.46:1 to a 1.71:1

 

Go with the Q-jet. Best thing for milage without sacrificing power. But since you are doing all this work, try to get a manifold with matching ports and made for the spreadbore.

Also, if they are available, get Tri-Y headers and run 2.5" dual exhaust w/free flowing mufflers. Tri-Ys are made for torque, not high rpm.

Set your front end with 0* camber and 0* toe-in and run narrow high load, high pressure tires. Also check to insure that you have no brakes dragging.

Run the lightest allowable lubricants in diffs, etc.

Get rid of big mirrors, roof racks, bug shields etc. and ADD a front air dam.

Install a vacuum gauge on your dash and keep that needle as high as you can while driving.

All this with your new final drive gears should get you some very decent milage.

 

Thanks for the tips. I only drive the truck 2-3000 miles a year, so i dont want to spend thousands. THe CJ intake was the only one i could find for a qjet. I should check teh edelbrock performer line.
I have the narrower tires on it, but there are 6 whcih doesnt help. The mirrors are pretty big, but the box is too, so i dont know how much gain there would be, and i like being able to backup.
Monster baby - the trans seems to be pretty low in first. I am sure it will have plenty of power to pull the 3.54 gear.
If i keep the original exhaust manifolds and y pipe (both are in excellent condition) what muffler should i run? The one on there looks pretty cheap and probably doesnt help.
Brakes and all that stuff are good.
When i do the timing chain, should i put it straight up or advance 4*?

 

Some/a lot of, factory car 4bbl intakes are spread bore, all trucks, that I have seen, are square.

 

A trick with Q-Jets is to epoxy the plugs on the underside of the main body, ALWAYS. also never rebuild one without replacing the float. I have run Q-Jets on a Chevy for 370,000 miles with 2 rebuilds. I also was sent to Q-jet school in the 70s by a GM Dealer I worked for, I worked all tune-up work on the line because I had a Class A California Smog Installers License.

 

As a marine mechanic I have rebuilt many hundreds (more like several thousand) of Q-jets and 2-jets, most of the GM marine motors have one ot the other. I still don't like them, just more complicated than necessary. I always felt the float bowl was too small also.