20 mpg hijack thread

[Jabes1]

Another thing I thought I would mention, torque converter. Get a low stall or towing converter and reduce slippage. I'm looking into getting the Hughes towing converter...
http://www.summitracing.com/parts/hu...make/chevrolet

Any more progress?

[bojak]

Yes, well a little more progress. I traded to a buddy of mine a YETI cooler. In exchange i got a set of headers, a set of turbo quite mufflers, and most importantly use of his welder, tubing bender and experience in helping me run out my new exhaust. So far i have sandblasted the headers and repainted them. This coming weekend is the install date so i am pretty pumped. I got a good deal on the cooler, so once the dust settles and i buy some pipe and misc. stuff i will have around 350-375 in headers and a true duel exhaust set up. Hoping to see some improvements on the MPG..... after i get over gooseing it becuase it sounds so good. I am going to do a milage comparison before and after and plan on posting the results. i think it will improve with each mod and it should get better and better but my money is on the gearing being the biggest difference maker. My realistic goal or hope is in the 17/18 mpg range. That would be pretty excellent for a really big brick.

[Chevrolet4x4s]

I got 17.75 around town the other day. 350 GM TBI replacement engine,electric fan,Edelbrock Performer TBI intake, mid length headers,daul exhaust, 32X11.50 15 BF Goodrich All Terrains, 3.42 gears, 5 speed.


I have gotten over 19 on the highway with half wore out mud terrains. I can see 20-22 on the highway fairly easily once I put on a new header gasket

Shane

[william-theglassman]

I am at 20mpg right now after rebuilding a holly 450 economaster .2000 rpm at 55mph .305 small chamber heads .270 jegs cam.2 in spacer .runs great .

[bojak]

i like the sound of 20 just not sure the big "Reba" can do it. whole lot of truck for 20.

[comegetsome2003]

OK so I read most of the post in this thread...I know it might not be in your budget right now but a Cummins swap is what your looking for.....my dually is a 91 model(square) CCLB....it has a 93 model 12 valve small pump motor in it with a 518 overdrive lockup trans in it....my truck has 29.3 Inch tires with 3.42 Gears(or so i was told by previous owner) and i got 20.7 Mpg last weekend on a 220 mile trip...my injection pump needs to be rebuilt cause i have a pretty good fuel leak that has developed lately....mpg would naturally go up without this leak...also gotta account that 4 22 inch semi wheels plus adaptors is extremely heavy on the rear axle...my motor is governed to 2200 rpm which is about 77-78mph....i run 70mph everywhere i go so im guessing 1950-2k rpm and its getting that kinda mpg id say prolly 24mpg if i slowed down to 55-60
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[Jabes1]

Awesome Bojak... I agree with the gearing. Im looking at 2.73's with that towing converter on mine to bump the mileage. I figure if its low stall its not going to be slipping like the stall converter I have in right now and I believe I have enough bottom end torque with my TPI that it wont lug the engine too bad. I also have a GearVendor which I can split gears with, basically I can be in second gear and turn on the GV and be in second over which is between 2nd and third gear keeping the engine happy if need be or any other gear for that matter. Headers should help, try adding a balance tube to the exhaust or an X pipe. Good luck, I'm still following this thread...

[BONUSCAB]

I skimmed over the thread and saw a lot of little BS type things that might get ya a 1-2mpg gain on a small, 2wd truck. If you want mileage, put a Cummins in that truck. 6BT, overdrive and some 3.55 gears. /thread.

[Skunksmash]

Originally Posted by BONUSCAB

I skimmed over the thread and saw a lot of little BS type things that might get ya a 1-2mpg gain on a small, 2wd truck. If you want mileage, put a Cummins in that truck. 6BT, overdrive and some 3.55 gears. /thread.

Oh yeah I didn't read how big his truck was. I was going to suggest the 5.3L that so many half ton single cab guys are doing. Over at LStruck.com they seem to be getting about 20-23 MPG with that motor. Maybe this guy could use the 6.0L LS?

[Jabes1]

Just popping in to see how this is going? Diesels are efficient, however it doesn't appear to bee what the OP has in mind right now. As far as BS little things... little things add up and with $4 a gallon, Id be happy at 17mpg in a big truck versus 15mpg LOL...

[rigon4]

I just made a almost 800 mile road trip from east Syracuse ny to hardyville ky and got 18.3 mpg in my 1987 short box half ton 305ci tbi 700r4. I hope to get better on my way home I did a tune up before I came down but the o2 censer was bad check engine light was popping on an off put a new one in down here and the trucks running like a dream so next week I hope to get 20 mpg on my way home

[bojak]

Sorry for no update for so long, had to take the family on vacation and that got into the budget. It did allow me to run several tanks of gas through my truck to get some before hand mileages. 12 is the number right now. Based on a 70% around town ratio and 30% highway use. It is getting the headers installed at a buddy's shop and it goes straight to muffler shop from there. I decided not to do it myself on these to items strictly due to time. I have a throttle body spacer and full tune-up supplies that will go in as soon as it gets back from muffler shop. I will then do some new mileages. Hopeing for 14/15. That would put me in a good spot until I do electric fans, re-jet tbi, and regear it. I might just get to 18 if I guess right on the gearing. Any advice on correct gearing?

[bojak]

Also I would love to do a diesel conversion, but that will never happen. With family, hobbies (other than REBA), and economy that's more money than I will ever throw at this truck in one shot. If I was mechanical on a level to do it all myself then maybe but i'm not and would get worn out at the shop on what that would cost. Even though my mechanic is a friend of mine he would still charge me enough to leave a mark.

[bojak]

I have some updates and questions. I have new headers on with tru duel exhaust run out. Installed new spark plugs, new wires, new cap and button, throttle body spacer, new fuel filter, and fresh oil change with some purple. I had to put new motor mounts as well as I was having some clearance issues with headers and transfer case from some worn out ones.
Today was my first day out on the road with it for any real time so it was my shake out run and also my first chance to get some new mileage data.
The drive was interesting. I'm new to headers so I am not sure about some of my observations. From a stop to getting moving it seems to bogg down just a little. This was under very light acceleration as was trying to see my best mileage. When you step on it it seems fine. At an idle it will be fine for a minute but then it will sputter after a minute or two. Never cut all the way out but sounded like it might. That was at idle under no accelerator input. Also under anything other than very gentle braking my collectors for the passenger side header is still contacting my drive shaft causing a very unpleasant sound. I thought / hoped the new motor mounts were the correction for that. I will complete my mileage data tomorrow but wanted to update my progress and get some feed back if possible from you guys who may know more about these kind of issues. Thanks for any advice.
On a possitive note the header exhaust set up sounds great for my taste. 2 1/2 straight back to turbo quiet mufflers turned out to the sides at rear bumper. Civil in parking lots and cruising but growls when I get down on it.
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[gchemist]

TPI or ram jet are ideal for trucks. Just started the debate all over.

[meatwagon83]

i think i would attribute the sputter and bog more to the throttle body spacer before the headers, and the only thing i can think of for the header hitting is either, a; put a lift kit on the truck or b:a block of wood and a floor jack to ever so slightly bend the header up a little

[bojak]

Thanks for the replies. After careful calculations the results are in. 11.78 mpg. My earlier pre improvement numbers must have been calculated wrong. Either that or by letting my motor breath I've actually hurt my mpg. Probably got some keystroke wrong on my calculator. Oh well, 3 more mpg and I'm in the teens.
Yes a lift will fix clearance issues but probably back the mpg back down.
Sputter, could I have fouled out a plug already ? How important is the O2 sensor? It is not reinstalled in the exhaust. I've had people say I don't need it but doesn't it effect fuel mix in the TBI?
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[INSIDIOUS '86]

If you don't have the o2 sensor you get a rich open loop mode on the tbi. That will kill mileage right there and can be causing the bog. Fix it and recalculate
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[INSIDIOUS '86]

If you don't have the o2 sensor you get a rich open loop mode on the tbi. That will kill mileage right there and can be causing the bog. Fix it and recalculate
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[Jabes1]

No O2 sensor in the collector is a huge problem for any fuel injection! Weld a bung on and you will probably notice a huge difference LOL. That sensor is there for fuel trims +/-10% You're running on a super safe rich map.

[CSGAS]

Free-flowing headers can be less efficient than cast manifolds if both are the same diameters and flow. This is because of how much heat that dissipates into the engine compartment.

Generally with tech up to the 90s, you can estimate 1/3 of the heat produced by combustion goes to turning the crank, 1/3 to pushing the exhaust out the tailpipes, and 1/3 as waste heat. When you improve the flow of the exhaust, it would make sense that the other two factors improve, right? Not quite.

If the power production hasn't changed, then the amount applied to the crank can only stay the same. This is because the power follows the path of least resistance, and your headers just became the weakest link instead of the restrictive exhaust. If it's not pushing the exhaust, then it simply becomes more waste heat. Again, this is comparing hypothetical cast iron vs tubular steel. The cast iron will slow the heat dissipation rate. As long as they don't melt you will have two of the three routes improved and the power going to the crank will be the easiest path for the power to apply itself.

For mileage your actual goal should be efficiency, meaning converting a higher percentage of the fuel you take in, to useable power. The more efficient your burn is, the closer you will get to the 17:1 ideal stochiometric ratio. 1980s tech needed about 14:1 or even 13:1 because of inefficient designs for heads, cams, etc.

Swapping Vortec heads on would allow you to run leaner, because of their combustion chamber design. Swapping aluminum heads on can also help, but only if you increase the combustion ratio to take advantage of them. It will be the improved combustion that makes more efficient burning, not the material of the head.

Keep the velocity of all your airflow as high as you reasonably can. This will help on the intake side by keeping the fuel droplets in suspension instead of falling to form puddles on the port floor or even inside the chamber. For the same CFM a completely unrestricted exhaust has relatively no velocity, producing more waste heat. For a typical street 350, running well, I like using 2-1/4" dual pipes all the way back behind the tires. Cats and mufflers don't have to be restrictive. Some of the ones with valves in them look interesting but I'd pin my hopes on Cherry Bomb Vortex mufflers and any cat you can see through with a 2-1/4"ish diameter. The rare metals still do their converting, as long as the exhaust passing through them has heat.

Sanderson, Speedway, and a few other places have cast iron headers. A lot of people put faith in their Corvette ram's horns, but most of them are about 2" outlets just like 4x4 stock manifolds. The ones that are 2-1/2 are in the "if you have to ask..." price range. Wraps and coatings can slow heat dissipation too, as long as you're willing to accept the trade-offs.

There's no replacement for displacement. That goes for the size of the engine, or the size of the blower. Yup, blower. The Weiand 142 is one of my long-gone friend's favorites. I like the way belt-driven blow-through chargers can usually be installed without so many custom parts. These include the Procharger, Paxton, Vortech, etc. Since they will change the pressure of, well, everything between it and the tailpipe then all three factors will increase. This is more efficient than an unblown engine, but you will have to re-gear to a taller ratio to see an improvement in MPG from this. Find a spot where your charged engine makes the torque it needs to do the job you want, see what RPM the old combo made the same power at, and use those numbers to determine how much (in percent) you can change your ratio.

The same goes for turbochargers, but typically they don't do their work at low engine speeds. You'd have to go backwards (shorter/lower gears) to deal with the range they do their work in.

The large block engines are another way to get your mileage. My mentor had a 396w/.030 over, that got over 20 MPG in a station wagon using what was called a Mil-O-Mor cam that Isky had (no longer in production). 500 inch Cadillac engines make their power WAY down low, as in a power peak stock near 2000 RPM. If you gear your rearend to work in that range, you can still create a LOT more power than an 80s 350 can. We had a 472 in a Studebaker 1/2 ton that got 17ish and the only time it ever saw the highway was on the way to Bakersfield once.

In general a stick-shift is more efficient than an automatic at transferring power from the crank rearwards. A lower rated unit like a 350 or 4L60 will be more efficient than a 400 or 4L85, largely because of how much power goes to becoming torque converter heat.

Roller cams have the capability to be more efficient than flat tappets but only if they are ground with higher ramps and shorter duration (and with those two comes less overlap). The stock rollers from 1987 through the LT engines and up to the last Vortec in 2002, were very conservative. Aftermarket RV/tow cams will be more efficient. They are available for Caddy and BBCs.

Overdrive can be great, but having an extra gear down low and using direct drive in combination with a taller gear is more efficient. At 1:1 the internal configuration is passing the most power it can, all other gears and idlers soak up energy. This is the advantage that TCI 6x transmissions offer, even though they are automatic. The driveshaft will also rotate fewer times for the same mph, so harmonics don't get as bad and momentum is lower. Aluminum driveshafts have a greater part here than in wheels.

12-bolt rearends are more efficient than 9-inchers. This is due to the location of the pinion gears and the resulting pitch of the angled gear teeth.

Rotating mass should be lightened. Honda engineers (yes, no one wanted to give them credit for years afterward) determined in an annual MPG race with other manufacturers that a light flywheel with little mass is more efficient that the heavy flywheels with more stored momentum. Driving techniques also included accelerating up hills and coasting down them. Why use throttle to get to the top of a hill after coasting, and again to increase momentum down a hill? You can cut your time on the throttle in half by coasting down a hill and accelerating up. As always, roll into and out of the throttle instead of stomping on it. This is where the "imagine an egg between your foot and the gas pedal" comes in.

Fuel injection, even electronic, is not the big aid that one would think it should be. It reduces warm-up time and smog emissions. Introducing the fuel closer to the combustion chamber improves the chances of the droplets staying in suspension. Flatheads could get better than 20 mpg with a carburetor though. I could hit over 35 mpg in my first car, a slant-6 Duster. Carbureted Hondas hit higher ratings than the bulk of today's hybrids. A custom tune can help an electronic fuel injection system follow a curve closer to the ones the carbs produced, with some other advantages (like changing the tune depending on if your loaded or not--the purpose of VVT and other technologies). If you decide the expense won't be recovered in a reasonable time then stick with spreadbore carbs like Quadrajets and Thermoquads. The Holley spreadbores "just aren't right" but that has more to do with quality control and tolerances than any conceptual problem. The spreadbores can act like 2-barrels sipping fuel when you don't need power and opening up to 750-900 cfm if you need it. Squarebore carbs are meant for situations that don't often involve cruising--like making good numbers for advertising (or racing )

Correct or at least appropriate steering and suspension settings with components in good condition (right down to the bearings and races) will reduce rolling resistance. Wheels with flat hubcaps or a flat outer surface that's flush with the body lines (like high-offset wheels) will give less air resistance. Pulling in the window frames on pickups and sedans helps get the odd shapes out of the wind and also seals the alternative paths for the airflow. Mirrors, raingutters, side trim, bumperettes, door handles, wipers and side windows rolled down all impact airflow. Open wind wings to a certain angle (different for each vehicle) or shut all the windows--even if you have to turn the AC on!

The best speed for mileage varies with each vehicle, but it is not 55. It is the point where the sum of all mechanical resistances, becomes less than the effect of air resistance. I've found on most of my vehicles that it seems to be 62 MPH, but improvements have been made in both factors over the last couple decades.

If you are mind-boggled by all the tips and factors involved, then you are close to ready to tackle the mileage issue. The last brain-frying tip I will throw at you is--"You have to think of ALL those things at the same time!" Every element in your package or recipe has to complement every other element in it. Plan your choices ahead of time, and stick to the plan instead of throwing one or two items at something that had poor mileage to begin with.

I don't expect to go better than 17 on my truck, because I won't get the returns on my investment for adding more to my package. Let's see who can get there before I do (out of the people who don't already get it ahead of time).

ps (I've noticed I get about 10% better mileage if I pay about 10% more for the 100% gas available around here, instead of 10% alky--MY TRUCK IS SOBER!--but the mileage issue is essentially a wash as a factor. I didn't have ANY grainy crap in my float bowl when I opened it up after 6 months today.)

[kevinr1970]

Obviously there are some smarter people than me posting to this thread with good and valuable info.

My $0.02, although apples and oranges.
'98 Chev crew 4x4 short bed, Vortec 5.7, auto, 285/75-16 AT tires. Best I ever did was just over 15mpg, but never did anything extreme to get better mileage, just tried to not do anything too stupid while paying attention on a road trip or two.
'00 Chev crew 4x4 short bed ('88-98 body style), Vortec 7.4, auto, 285/75-16 AT tires. Best I ever did was around 13.5mpg, but never did anything extreme to get better mileage, just tried to not do anything too stupid while paying attention on a road trip or two.

Yes the 5.7 did marginaly better MPG wise, but the 7.4 was just better to drive.
YMMV... literally!

[bojak]

Question for the TBI experts, if i have deleted the cats on my new exhaust system have i messed up? My truck originally came with an up stream and after cat oxygen sensor according to what I have researched so far. I did have a bung installed on my new collector but no provisions for the one that would have been post cats. Whats the right set up? i got a hot rod buddy that keeps telling me to ditch the TBI and go carburetor and get a simpler set up. I am considering this but would love a 20 buck fix of an o2 sensor to be all I need. Yes I think 15 mpg is going to be ambitious. I am starting to temper my expectations. I will sort out the small issues I have now but that may be as far as I go with this small block. Starting to think about 13 mpg from a 454 rather than 15 mpg from a 350. That may be frustration talking but however far up the mpg hill I climb, a inevitable lift and the 35 inch tires will knock me back.
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[Jabes1]

Your precat 02 reads AFR while your post cat checks cat efficiency... at least on most newer cars. You can go on eBay... heres what you need to install the secondary 02 it in a sense tricks the ecu. You can turn the secondary off with a tune, but that's more than $20.

How's this for less than $20 A few links...

http://www.ebay.com/itm/Oxygen-senso...72e7b2&vxp=mtr

http://www.ebay.com/itm/02-OXYGEN-SE...cb06a3&vxp=mtr

[bojak]

Jabes1 that is much appreciated. I will let you know how it works out.

so weld in another bung and plug my secondary into one of those jobbys?

Also I think my mileage numbers are wrong still. I didn't put 2 and 2 together at the time but my speedometer is off......a lot. On my shake out run I took my garmin with me and at a GPS speed of 68 mph my speedo read 60 mph. I will ask for some help regarding that issue later. This is while running 285/75 r16 tires so I am a little surprised. I knew it wouldn't be dead on but was surprised at the actual difference. Glad I checked as it was just a matter of time before I earned a good driving award. Hate to think I was going 65 and find out the hard way it was 72.