Gas Mileage

I know another page with no pictures. Well I try to provide     some good useable info and pictures don’t always add to the page.

This is my page dedicated to gas mileage.  This has to be the most common question I am asked is how to improve gas mileage and will a performance chip hurt the mileage.

Well a lot of things contribute to lower gas mileage and some you have control over and     some things you do not.  I find most vehicles can be improved on but I will admit that big block chevy engines are the hardest.

The key number one change you can make that will yield you the most gas mileage     increase won’t cost you a dime.  Sounds to good to be true well your not going to like it.

SLOW DOWN.  Americans do way too much smacking the go pedal.   I am not talking about doing 10 miles per hour under the speed limit or any  craziness such as that but I will hit on that a bit in a minute.  Its the jack rabbit  starting every time you take off from a stop.  If you want to get better gas mileage, you need to make a conscious effort to limit the launches.  I can beat my wife every time at the gas mileage game. She has a relatively old 1999 Nissan Maxima  and the window sticker shows its gets a best of 28mpg on the     highway.  If she drives it, it gets 26 which doesn’t sound too bad but if I drive it and follow my rules on gas mileage.  I can get 30.  Best so far on that car is 31.5.   The key is when you take off from a stop use 25% or less throttle.  If your rpms go over 2000 rpms between gear changes your likely guzzling fuel.   It doesn’t hurt too bad to hit it once in a while just not like a teenager at every  stop light.  My black magic truck got 19city 24hwy pretty easily but if I play too much, I can drop it down in the 14mpg range too.

Things you can’t change is weight of the vehicle (other than don’t haul around the     kitchen sink unless its necessary).  Its going to take a certain amount of horsepower to make that truck/car or whatever run 60, 70 or 80mph down the highway.  We have very little control over that.  Tire Pressure does help. Check it at least monthly and keep it at the max level.  This reduces unnecessary drag and will reduce that hp level needed to push your heavy beast through the wind.  Large tires have more drag than small tires.  Now I am not saying put little 4″ wide tires on your truck but keep that in mind when you go slap on a 35″ tire and wonder why you get 10mpg.  Next is ride height.  I have lowered the black magic truck 3″ in the front and 4″ in the rear which reduces the overall frontal area of the truck by tucking the suspension into the chassis.  More wind you have to push the more horsepower its going to take.  Lifting your truck to put those big 35″ tires under it has the exact opposite affect by lowering that undercarriage where it can catch even more wind and help contribute to that 10mpg.  Which leads me to speed, I like to drive fast just as much as the next guy but on these trucks when you get to about 70mph it  takes a lot more hp to go faster due to the amount of wind your pushing and that horsepower is going to take a big hit on your gas mileage.  If you can try to stay  right at or just below the 70mph number.  You will be surprised at how that helps.

Increasing the fuel efficiency of the engine itself.  I know that is the one you were wanting all along but gas prices aren’t getting any cheaper so we all are going to have to start applying some of those above items to our daily routine whether we like it or not.  Chevy SBC engines are pretty fuel efficient compared to a lot of  others engines but the more power we can pull from that 350 cubic inch motor without significantly increasing the amount of fuel it requires will help bring those gas mileage numbers up.

1. We will start with the exhaust since its on the tail of the motors processes.   Problems here will back everything up and TBI trucks and cars have the worst exhaust design possible.   Just check out out the dyno numbers on the Black Magic truck from just changing the Y pipe.  I did not significantly change the fuel after that modification and 40hp at the rear wheels is a significant improvement.  So I recommend replacing just the section of Y pipe where the 2 pipes merge with the Flomaster Y250300 collector dramatically improves the oem exhaust design and combined with changing the large pancake cats used on most of the TBI trucks and cars is rather restrictive and heavy.  A nice high flow cat isn’t that expensive, I use a Thunderbolt 3″ catalytic converter $50 off ebay and will shed some weight that you don’t have to carry around and some more horsepower for the few times you do get to play.  those 2 changes alone will cure 90% of the issues with the factory exhaust and get you more power and gas mileage for typically under $200 installed.  You can add headers and a performance muffler which will add some more power but that Y pipe and cat are the 2 biggest issues with the oem exhaust design.

2. Next is going to be a set of underdrive pulleys. This can free up as much as 15hp     and that 15hp isn’t going to cost any fuel to make so it goes straight towards that hp  number that we have to have to move are vehicle down the road.  They are cheap. I  think it was $60 for the ASP crank pulley that I ordered for the plum crazy project.  While underdrive pulleys will hurt your AC operation at low rpms and the alternator doesn’t  charge well at idle.  the improved power and gas mileage is more than worth the trade off.  At over 1300 rpms all accessories are running just fine and I have never had one overheat from running underdrive pulleys.

3. Ignition system.  Pertronix flamethrower D3002 coil to throw a hotter spark down the wire, a nice brass terminal distributor cap and rotor button to have less corrosion than aluminum and some nice aftermarket low resistance plug wires so we don’t loose spark energy during the travel from the distributor to the plug and of course a nice set of plugs and with TBI vehicles I have had the best luck with factory AC Delco plugs.  But the more complete burn of the fuel the bigger the bang and thus more horsepower on the same amount of fuel which should add another 3-5hp to our free hp number.

4. Air intake, if the motor doesn’t breathe well its not going to make good efficient     power.  The stock air cleaner setup is pretty restrictive and I have a bunch of info the recommended pages to help you out there.

5. Next  the chip. I can gain a good 12+hp at the rear wheels even on 87 octane fuel as shown on the plum simple dyno base runs.  That chip did not add any fuel to the stock programming to achieve those power numbers so that extra power didn’t cost any fuel to make and while part throttle won’t have the full 12hp gain there is a gain there and that helps push the beasty down road consuming less fuel.

6. Electric radiator fan.  The mechanical fans driven by the water pump on these older vehicles is ancient technology.  Its heavy and robs power that can be used at the wheels.  Converting to an electric fan with a nice fan switch will reduce this parasitic load on your motor. I have created another page just for this electric fan conversion using newer modern production automotive fans.  I have converted all my stuff to run electric fans and have never had a heating issue with any of them, in fact over 40mph the fans nearly never come on and they shouldn’t.  There is enough wind blowing through that radiator to keep it cool.  this modification is a MUST if you want good fuel economy from your vehicle.

7. Gearing. Many trucks out there didn’t come with overdrive transmission  or someone has removed  them and that is really going to hurt fuel economy. More gears the better to keep the engine in its powerband and keep the rpms low.  All your modern trucks nd cars are running 6spd+ automatics and that currently isn’t an option for the older injection crowd but you need as many gears as you can get and gear the differential for the transmission your running as well as the size tire on the vehicle.  However, a  lot depends on the weight of the vehicle.  I run a mild gear in the black magic truck  with its manual 5spd transmission and it runs right at 1700 rpms at 70mph but I have a LOT of torque available and weights 3950lbs so it requires very little throttle to maintain 70mph and that part is the key.   if I tow, I can easily drop down to 4th gear.  the 4spd automatics like the 700r4, 4L60E and 4L80E transmissions don’t quite have that luxury.  If you gear for 1700 rpms on the highway your first gear ratio will be too high and your truck will struggle to get moving from a stop.  if you don’t tow or run on the highway 90% of the time then you need to gear for that 1700 number at 70mph.  But if you need to tow or do a lot of in town or mountainous driving then you need to gear more for around 2000-2300 rpms at 70mph. If your truck is constantly shifting out of overdrive on the slightest grade then you aren’t     running enough gear.  The heavier you are the more rpms you need to turn to get that     torque number up.  Typically between 2000-2400rpms at 70mph is a good range to stay     between.  The 2wd plum simple truck with 3.42 gears and 4L60E trans runs right at 2000 rpms at 70mph and I believe that is going to be a good number for it.  But if  you don’t have overdrive your quickly going to be pushing the 3000rpms mark at these higher speeds and while that isn’t going to hurt the engine gas mileage will definitely suffer.  non overdrive transmissions should only be used for racing or in applications where your putting less than 5000 miles per year on the vehicle or you only drive 55mph which was the speed limit when those transmissions were produced.

8. Oil, strangely enough using the 5w-30 light weight oil does help reduce the amount of resistance the engines rotating assembly experiences during normal operation.   Using synthetic oil is also a good idea.  Running synthetic oil for7k miles vs     standard oil  for 4k miles the cost isn’t that much for using the synthetic and your engine will be more efficient.

9.The engine itself.  While the TBI heads don’t flow very well the swirl ramp in     the intake runner does just that. Swirls the air entering the combustion chamber just like the Tornado device you have all seen advertised.  Well TBI and Vortec heads both do the same thing automatically just vortec heads do it without hurting air flow.  This swirling keeps the air and fuel mixed well and improves efficiency of the engine.  The key thing GM left out of the trucks is they should have put the roller cam in the trucks just like they did the TBI cars.  Roller cams have less friction so less potential power is being robbed and the open the valves faster and more efficiently to make more power at the same rpm than equivalent flat tappet cam.  These engines also utilize low tension rings which wear less on the cylinders due to less friction so if you rebuild your engine keep that in mind.  Is it worth converting to a roller cam?  Well it depends on the cost of the parts.  I think long term you will get enough benefit to justify the cost.

Now is all this going to turn your 12mpg suburban into a 30mpg Honda.  No, but you will be pleasantly surprised just as to how well it can do when the above is applied and that can be the difference between being able to keep you big beast or having to sell it off for something that does get better gas mileage.

Pretty much all the small block V8 Chevy engines are capable of getting at least 16cty     – 20mpg hwy with the correct modifications and driving skills.   Now you big  block 454 guys, those engines are pretty inefficient but strong and their strength is what makes them guzzle fuel.  Gearing is pretty much your only choice.  The fewer rpms that heavy 454 rotating assembly has to turn the less fuel its going to drink. I have seen these get as good as 17mpg but it takes overdrive, a mild gear and the right modifications and driving to pull it off.