So I am going to talk about something completely outside of the ordinary. For this blog anyways. As some of my readers may or may not know I am a huge car guy. Automobiles have captured my imagination like nothing else ever has. I love to work on, tinker with, and build up old cars. I have an 86 Ford Ranger that I re-built in high school, a 78 Trans-am that me and my grandfather use to go get ice cream in on the weekends, and my most recent acquisition a 95 Ford Bronco. It is the Ford Bronco that I intend to talk to you about today.
I am like to go hunting, I like to go camping, I like to go skiing, and I am a Scout Master, all of these things are greatly added by having a four wheel drive vehicle. Due to my being a Scout Master I often have to tow a trailer filled with the boy’s gear. This necessitates having a truck. Then there is the fact that I am not only poor, but also rather cheap, which means that I have an old truck. Anyone who drives an old 4×4 truck knows that 4×4 truck and fuel economy do not go hand in hand. The old War Wagon, as my mother dubbed it, is not horrible on gas, by truck standards, but it leaves a lot to be desired. When I bought the truck it would do about 12-13 mpg city, and the best I ever pulled down was 15 freeway, but I averaged about 14. So not great, but then again for an old truck that’s not too bad.
Then there was the issue of performance. I really wished when I was shopping for the truck I had done my research a little better, I was a little naïve about the engine offerings in the Bronco. I had driven a 351 truck, and loved the power, but the mileage was terrible. Then I drove a newer 302 powered truck, and while it was a little down on power it got a lot better mileage. I figured it was due to the engine being smaller. What I didn’t know was because the 302 truck was equipped with an overdrive transmission. People with the 351 see similar real world mileage as I do.
The truck I bought is a very nice truck, it is an XLT, has every bell and whistle on it. It had hardly any rust, and only 80,000 miles. It was a heck of a deal. Shortly after purchasing the truck I quickly began to realize that I need more power. I didn’t want more power I needed more, that’s my story and I am sticking to it. I also set out to see what I could do to get better mileage. I set out to achieve the impossible, I wanted to have my cake and eat it too. How hard could it be?
So I started my research and found an article called Project Mile per Gallon. Basically in this article they took a 460 powered Bronco Centurion (an extended cab F-350 converted to be like a bronco, basically it was the original excursion), and took it from getting 4 mpg city, and 8 mpg freeway to getting 8 mpg city and over 13 mpg freeway. Not to mention it had over 600 foot pounds of torque. This was all achieved through simple bolt on modifications, this greatly intrigued me. So with Project MPG as my guide I started Operation MPG. I did not want to just re-create what they did in Project MPG, I wanted to take it a step further, see just how far I could take it.
Well very early on I found out that the world of trucks is filled with just as much bitter politics as the world that we constantly engage in. When I asked about tips and tricks for better fuel economy, I was told it was impossible. When I asked for how to build more power out of a 302, I was told that the short stroke of the 302 made it impossible to be a proper truck motor. If I wanted more power I should just swap in a 351 and be done with it. Well if you know me at all I do not do “it is impossible” or “can’t be done”. It can always be done. So I set out to rewrite the paradigm of the truck world.
So why is it that the 302 Ford is written off as a truck motor? Basically the answer is because it is a short stroke motor. What this means is that it likes to rev, which is a trait associated with top end horsepower, something sought after and prized by many hot rodders. However most hot rods are light weight vehicles, a heavy truck needs low end torque. A long stroke motor has several advantages at low RPM operation over a short stroke motor. The longer stroke means that the motor can draw more air in on the intake stroke, it applies the force of the combustion to the crankshaft for a longer period of time, it can push more of the spent exhaust gasses out on the exhaust stroke. These advantages disappear in the higher rpm range, where the length of the stroke becomes a hindrance. So does this mean that it is impossible for a 302 to build power down low? I do not believe that to be the case. The motor in my truck has 302 cubic inches, 5.0 liters of displacement to work with. This is nothing to laugh at, newer heavier vehicles are making due with smaller motors, making more power, and getting far better fuel economy. The answer comes down to maximum efficiency.
I know there are those out there who believe that it is impossible to increase the power of a car, and increase the fuel economy as well. Everyone knows the high output motors are gas hogs. That is simply not necessarily true. It depends on how it is that you build that power. Fuel economy and power are directly tied to volumetric efficiency of a motor. The power of an engine is generated when gas, air, and a spark meet up and cause an explosion in the combustion chamber. This explosion sends the piston down the cylinder, which spins the crankshaft, which turns the fly wheel, which turns the transmission, which turns the drive shaft which spins the differential, which spins the axles, which spins the wheels. The bigger the boom, the more power you have. How you get this bigger boom determines if your quest for horsepower is met by fuel economy gains, as well as power gains. One way to build more power is to make the engine bigger. More gasoline can equal a bigger boom. This is the easiest and cheapest way to build power. The other way to build power is to improve the volumetric efficiency of an engine. When the combustion takes place, not all of the fuel in the chamber is burnt, a lot of this unburnt fuel flows out the exhaust valve and is lost to the ages. By maximizing the volumetric efficiency of an engine, you burn more of the gas in the combustion chamber, and less gas is required to achieve the same amount of power.
The more complete the burn, the more power that is achieved for each combustion cycle. So how does one go about improving the volumetric efficiency of an engine? An engine is an air pump, the more efficiently it moves air through the system, the more efficiently it makes power. So when you start building power, the most logical place to start is by improving the engines breathing. This is critical for a 302 as its short stroke accents the flaws in its intake and exhaust system at low RPMS. So I set off to improve the breathing of my 302.
I started with exhaust and studied how the venture effect, and exhaust velocity could actually help evacuate more of the spent exhaust gasses from the combustion chamber. This effect is called scavenging. Basically with a poorly designed exhaust system can result in up to 9% of the spent exhaust gases to get caught in the combustion chamber. These gases further dilute the incoming intake charge, basically wasting 18% of your combustion chamber. Not good when you are trying to scrape every last ounce of power out of an engine. There is a very short period of time for the exhaust gasses to escape the combustion chamber. That exhaust valve opens, and the piston pushes the gasses out. In most stock set ups, the piston alone is what expels the spent gasses from the chamber. However, by creating an area of low pressure in the exhaust system, when that exhaust valve opens, the high pressure gasses in the combustion chamber rush to fill the area of low pressure. This effect further aids the volumetric efficiency thanks to a period called overlap. During the overlap period both the intake and exhaust valves are open. So by having an area of low pressure in the exhaust system it is possible for the exhaust to actually aid in pulling in the new intake charge.
Armed with this information, as well as information about the evils of back pressure, and the importance of exhaust velocity, I designed an exhaust system that actually helped improve my low end torque, fuel economy, and of course makes my truck sound like the god of Hell Fire. The exhaust system goes from two 2 ¼ inch pipe, into a y pipe/catalytic converter, then into a 2 ½ inch pipe, into a flow master muffler, then into two 2.5 inch pipes. These steps help to counter act the decrease in exhaust slug velocity as it cools, by creating areas of low pressure pulling the high pressure gasses towards the exhaust tip. Let me tell you what, this set up, despite what everyone told me, dual exhaust set ups lose low end torque, you won’t see any gains in fuel economy, just run a single three inch pipe you’ll be better off, has transformed the performance of this truck. It picks up off the line much quicker, and it feels stronger through the power band. The throttle response is greatly improved. The best part is that I now average about a half a mile per gallon better city, and over a mile per gallon better on the freeway. More power, more fuel economy, better driving experience, I am in love.
The other aspect of improving the air flow through an engine comes from improving the air intake system. The intake manifold is not a choke point for the 302, the truck intake is seen by most to be a work of art when it comes to an intake manifold designed to make low end torque. However, that does not mean that there are no improvements to be made in the intake system. Basically the factory air intake system, the tubing that brings the air to the intake manifold, is one part that can easily be improved.
I am sure that you all have heard of cold air intake systems, they are often times the first thing that teenager supping up their mom’s civic, tend to buy. But are they worth it, are there any real power gains to be had? Well an engine is an air pump, the more air you get into the engine the better the combustion. Cold air is denser as such it has more oxygen per volume. So the cooler the intake charge, the more power the engine will make, to the tune of for every ten degrees you cool the intake charge, you gain 1% in horsepower. So while the big cone filters of some of these aftermarket intakes, might flow more air, but because they draw hot air from the engine bay into the system they do not provide great low end power improvements. Project MPG put a drop in K&N air filter in the stock air box ,and insulated the intake. They saw great gains from this.
This is what I wanted to vent about today, I have been looking for ways to improve air flow into the engine. I will be insulating the air intake. I have a new tube to relocate where the intake system draws cold air in from outside the engine bay. But there has to be more power hidden in that intake system. I am trying to find ways to increase intake velocity. The faster the intake charge can get into the engine, the more oxygen that can get into the combustion chamber. So this involves me trying to find ways to reduce reversion in the intake tube, turbulence that slows down intake charge. This means smoothing out the intake tube.
What I want to try to find is a way to create an area of low pressure behind the air filter, to help draw air through the biggest restriction in the intake system, the air filter.
I am trying to study the effects of Helmholtz resonator:
And how these things affect low end torque.
The problem is that it is 100% impossible to research cold air intakes because the first 50000000000 responses are always just “come here to buy this intake, because it is better than yours, trust us”.
It drives me nuts, I try to search for the whys of cold air intakes and all I get is cold air intake bring in cold air. Some kindergarten explanation of what it is, and then a million ads to buy a big open element hot air intake.
Sooo, yeah, if you guys have any information on this topic, I would greatly appreciate it. Am I the only one who had these issues with search engines?