Impressed with my truck's mileage.
 

My 305/700r4 TBI with the mods listed in my sig, just got me 16 mpg with a mix of city/highway. This is with a sluggish 700r4 that will be rebuilt soon.

I clocked it at 18 mpg mainly highway before.

Is this the norm or can I get even more out of it? It has 3.08 gears. I find the engine really doesn't have to work hard. I have an old s10 blazer with the 4.3 and that POS gets the same mileage as my truck. Pretty impressed.

Engine has pretty recent plugs, wires, cap, rotor, stuff like that. Think long tube headers will help any? It currently has true duals but stock manifolds.

Also was thinking about a Harris Performance chip.

Also learned to drive easier.... which helped tremendously and I find driving less stressful now. One of the benefits to lowering the suspension is focusing more on the road and driving more slowly I guess.

What else can you suggest for simple ways to increase the mileage even more? Mods I already have are listed below.

Re: Impressed with my truck's mileage.
 

A bed cover, if you don't already have one.

Re: Impressed with my truck's mileage.
 

Swapping to a standard transmission might get you alittle lower, not really highway wise but in the city you can do a lot of coasting and other tricks to lower mileage.

If your never hauling anything you could go even higher into the 2.X range of gearing , won't pull a stump out but will keep the highway cruising where you want. The headers, ignition, etc..mods never seemed to make a difference for me.

Congrats on your mileage, I'm in an '84 c30 dually and debating a trip I want to make because the gas cost will be so high...if I was at 18 it'd be an no brainer but at 10 it's a sketchy proposition.

Re: Impressed with my truck's mileage.
 

A bed cover is something I will consider. Standard transmission, although it sounds like fun, is something I won't tackle. Overall I'm sure it's not a hard install, but my last truck was a stick, I'm liking putting the selector in D and forgetting it lol.

Re: Impressed with my truck's mileage.
 

I doubt you can find any more gas mileage in that combo. I would leave it be. You could switch all fluids to synthetic. As well as your wheel bearing grease.

Re: Impressed with my truck's mileage.
 

im getting right around 18 city highway. rebuilt motor new sensors plugs andwell theres to much to list. but i prob would get way better mileage if i didnt have the 456 gears.lol im in the process ofdoing a 5 speed swap from a camaro . i figure after the tranny swap i should get atleast a extra 1 or 2 mpg extra.

Re: Impressed with my truck's mileage.
 

Desiel ! my '84 1/2 ton 4X4 with a 6.2 and 4 speed get's 25mpg when it driven normaly. 4.3's are normaly not mpg friendly .
MithBuster's say the bed cover wont help.

dccarpenter, I recently took a trip in my C30 dually and got 13 /14 mpg highway. I was really proud of the ol' girl she's normaly at the 10 mark !

Re: Impressed with my truck's mileage.
 

i'd be cutting cartwheels if i could squeeze 16mpg out of my 305 :lol:

Re: Impressed with my truck's mileage.
 

I doubt you can do much better. For reference, my 2010 Sierra Ext. Cab with 4.8 and 3.23 got 15.5 mpg city and 18 mpg. highway. Considering that is the latest fuel saving technology, that is probably the max for a small block full size pickup. I had a 2000 Silverado V6 regular cab that got 20 mpg city, but I drove it very carefully. That one had a bed cover but I don't think it helped much since I drove it only in the city.

Re: Impressed with my truck's mileage.
 

I've posted my mileage quite a few times but I'll post it again and how I get it. Someone said something about Mythbusters and the bed cover thing. A bed cover does the same thing as leaving the gate off or open, it creates a suction at the back of the truck that costs MPG. Leave the gate on and shut and the suction is still there, BUT, it's right in the bed which fills the bed with a higher pressure and the air skips over it as you drive. It also seems that the gate replacement cargo nets help with MPG. Mythbusters also did a segment on drafting. I don't reccomend doing this though. I drove 18 wheelers for 10 years and NEVER liked anyone being real close to my back end. The ICC bumper on the back of the trailer ALWAYS wins!! (LOL) Anyway, if you can stay 100 feet behind a big rig your mileage goes up 20%. If you get within 50 feet it goes up to about 30 to 40%. In thier test they got down to 2 feet and mileage jumped almost 75%. Thats HUGE but extreamly dangerous, one "hickup" somewhere and your all done.
Now for my mileage. I have an 84 3/4 ton K20, 350 eng, 465 trans and 3.08 gears out back. I get 17MPG driving 55 to 60 on the flats. I set the eng up (timing) by ear & trial and error. Now timing is near 14 degrees. It will ping if I mash it or am pulling a grade loaded and I have to go 50% throttle or higher. I leaned the carb out (quad) with smaller jets and rods. I almost never engage the secondaries. I use the granny gear to get her moving just a bit. This does help and it saves strain and wear on the clutch. I changed it during the restoration, origional clutch over 400,000 miles. I don't use the clutch once I'm rolling. I coast long down grades and draft where ever possible. I also tow a 16 foot equipment trailer sometimes which drops mileage to about 15. For some reason, known only to God, the 15 MPG seems to hold wheather or not it's loaded, go figure. Cool weather helps as does rain. Drive your long hauls at night, sleep during the day. Less traffic, cooler temps & higher humidity. Use all synthetic lubes and keep tire pressure up to spec and be very soft on the throttle. Thats about it. Jim

Re: Impressed with my truck's mileage.
 

I am guessing that a 3.08 rear axle makes a big difference in highway mpg. I know my 4.11 ratio is an mpg killer.

Re: Impressed with my truck's mileage.
 

ChevyMoto... I got the same in my 87 GMC with the same setup. As you mentioned my wife's s10 with 4.3 also got 16mpg. I was quite impressed.

Re: Impressed with my truck's mileage.
 

I get about the same with my 86 swb. It has a stock, 140,000 mile 305 with a q-jet with a cat back exhaust backed by a 700r4 and 2.73 rear. I get 16-17mpg mix of city highway and 18-19 all highway. Even better is my 1978 Caprice with a GMPP 350 H.O. backed by a th350 and 2.41 gears gets about 26mpg all highway. This makes me think with a fresh motor my truck could get better!

Re: Impressed with my truck's mileage.
 

I get a solid 15 MPG with my 383 stroker engine and a 700 R4 tranny W/O the lockup converter and a set of 3.73 gears. That number that you gave is good for a square body.

Re: Impressed with my truck's mileage.
 

That is amazing. Seems GM cars from that era got decent highway mileage. Is the main reason because of the gearing because if you put a 2.41 in a C10 and did all highway, I doubt it would get 26. Maybe the bed has the biggest affect?

Re: Impressed with my truck's mileage.
 

I noticed the mileage with the new motor, the original motor was tired and I got about 10mpg highway. Put in the new motor and a 2200RPM converter and went cruising. Like I said she gets 26 on the highway, about 18 mix of city/highway on 93 octane(she likes some extra timing)

Re: Impressed with my truck's mileage.
 

You aint lying!!!!! I get around 5-6 mpg with my 305/350 and 2.73's. Im acutally ready to throw this POS 305/350 in the Atlantic!!!!

Re: Impressed with my truck's mileage.
 

Something not right there Slim. What is giving you problems causing the truck to get such poor mileage. With that combo, although not overdrive, should get you atleast 12.

Re: Impressed with my truck's mileage.
 

chevy, either my long time mechanic is lying, or is completely missing something cause he went over my truck with a fine tooth comb and there is nothing wrong. im getting about 9mpg. i dont bark the tires or anything crazy like that. i do a lot of short driving to and from work but i can't seem to get more then 9-10. granted that still lasts me 2 weeks, its still sucks!

Re: Impressed with my truck's mileage.
 

slimneverdies - If I were you, I would pay a local shop $50 to put your truck on an engine analyzer to see what might be wrong. At the current price of gas it would be a good investment. I have found that anything less than 10 mpg city means something is wrong.

Re: Impressed with my truck's mileage.
 

My 79 C20 scottsdale with 4.10 gears and 350/350 got 10 no matter how i drove it. somethings up with yours.

Re: Impressed with my truck's mileage.
 

maybe some HP ignition components will help
have you tried msd 6a , blaster coil
i have them on my stingray and i noticed a huge difference

Re: Impressed with my truck's mileage.
 

Something is very wrong but Im at a stand still cause I dont know if I want to dive into my 5.3 ls swap. This is my daily driver and I cant have it down trying to figure out all the wiring and extra accessories that's needed.

Where do I start??? My edlebrock carb needs a rebuild, for some reason my rockers keep untightening and I can hear them ticky,ticky,tick. I think the biggest problem I have is whoever had this truck before me put a crazy and choppy cam in it for no reason at all so I never seem to get the timing right.

So I just dont know

Re: Impressed with my truck's mileage.
 

When I was running the orignal 305 in my '87 Stepside 4x4 (4 spd, 3.42 gears) I averaged 14 mpg mixed driving and managed 16-17 hwy. Now Im barely squeezing 10 with a slightly built 350, regardless of what Im doing lol.

Re: Impressed with my truck's mileage.
 

If it were me, I would take a week vacation, call a buddy ( mechanical one) and dive knee deep into that 5.3 swap! if you have your motor, your trans, your harness ( custom) and your PCM, you wont need much more, oh and an 87 FI tank. you should be easily done in a week. youll be glad you did!

Re: Impressed with my truck's mileage.
 

I think this is why I haven't move forward yet..... I only have the engine and trans. All the wiring and computer stuff is what's making me second guess this. Then there's getting the dashboard to work.
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Re: Impressed with my truck's mileage.
 

I just averaged actually recoreded 15000+ miles on my ZZ4. I've documented the miles since breaking in the ZZ4 on a 1000 mile trip. Average total with city, highway and lead foot = 16.5 MPG. Lowest at 11 MPG, yea really lead foot. Highest 25 MPG, wow great back wind lower speed! Average now is 13.5-15 if I keep my foot out of in the city. 18.5 MPG on straight highway speeds of 70 MPH. Not bad for a square body. The difference is torque. The sweet spot for a 305 is ~2000-2200 RPMs at highway speeds. Keep it there and you'll do great. Keep city RPMs below 2300.

Re: Impressed with my truck's mileage.
 

I've gotten 15 mpg city with my bone stock "84 sliverado. 305 engine with th350 lockup convertor and 3.08 gears. I guess I'll find out what it gets on highway during cruising the coast

Re: Impressed with my truck's mileage.
 

is my q-jet the reason im getting 9-10? or is there anything else i need to be looking for?

Re: Impressed with my truck's mileage.
 

hey you guys with bad fuel mileage with a q-jet and a 305.

my 84 had the same problem for a while getting bad gas mileage. It ended up being the vacuum lines were dry rotted and they just disappeared. The truck still ran great but just got bad fuel mileage. We ended up replaceing a few lines and pluged the rest.
It solved the bad fuel mileage problem.

Just an idea, you guys may have the same problem.

Re: Impressed with my truck's mileage.
 

I dumped the q-jet on my 305/700r4 for an edelbrock and now im getting low to mid 20's. I have changed my driving style alot. Easy swap except the egr gets in the way. you just have to take the spacer and fill it with jb weld bake at 400 then install with gasket sealent.

Re: Impressed with my truck's mileage.
 

ncd and gold, thanks for the advice. i'll have my mechanic check it out tomorrow when he has the truck anyway!

Re: Impressed with my truck's mileage.
 

I still run the Q jet and get good mileage

Re: Impressed with my truck's mileage.
 

Well mine had seen better days and after 25 years and 4 rebuilds it was toast.

Re: Impressed with my truck's mileage.
 

Nice video and explanation of this guy's hydrogen setup on his 87' GMC. Never heard of this conversion, don't know how much it costs, but I will definitely be researching. His initial mileage numbers before the hydrogen install are low, so I'm not sure if he has a 700r4, and what gears, but his new mileage numbers are impressive for highway.

Anyone have any info on this system? Seems like with that much water coming out of the exhaust pipes, I might need to invest in stainless. Also, not sure if turbo style mufflers with packing would be ruined with that much water.

Re: Impressed with my truck's mileage.
 

Just watched the video and shot it full of holes. First off, he started it cold, there will always be water on cold start. Any combustion process has some water as a byproduct. Next he is using a simple process whereby you break water down into oxygen and hydrogen by electrolosis. The amount of hydrogen & oxygen produced is small and the speed of production is very slow. You would need 50,000 or 60,000 cubic feet a minute to make any difference. A cubic foot of gas is 288 cubic inches. 1 revolution of the eng is 350 cubic inches. With that info in hand, at an idle of 650RPM you would be processing 187,200 cubic feet of a gas for every minute of operation. Think about it for a minute. In this day and age when the car companies are looking for every advantage to boost fuel economy and in turn sales, don't you think they would be all over this like white on rice? Hydrogen production is expensive because it uses lots of electricity. In a vehicle, where does that come from? The alternator. What runs that, the engine. Which in turn gets it's energy from it's fuel. What the writer in the article is suggesting is a perpetual motion machine which defies all the laws of physics. Don't waste your money. Tune the eng, go thru the carb and lean it out, drive with a soft right foot. jim