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Ways to Increase Engine HorsepowerI have always been a bit of a "motorhead". If it had a fire breathing engine, then I was interested. It didn't matter if the engine was in a weed eater, a model airplane, a lawnmower, a motorcycle, or a car. If it burned fuel and produced horsepower, then I was interested in ways to try to get more power out of it! If the engine powered something that I could ride in, then I was interested all the more. Over the years as I've gained some hands on experience working on engines, I've also gained a better understanding of what works and what doesn't work. Unfortunately, many things that people do in the quest for more horsepower simply don't work very well. How do I know? I've tried many of them. Before we get too far along in this discussion about extracting more power from an engine, let's first look at the simple question, "What is horsepower?" The term horsepower was first coined by an inventor and engineer named James Watt. Mr. Watt developed steam engines and he wanted a way to compare his engines with one of the most common methods of producing power at that time - the horse. So, Watt calculated the amount of work that a typical horse could do within a standard period of time, and he came up with the definition of horsepower. For comparison purposes, 1 HP is equivalent to around 746 watts when looking at the term horsepower as it is used in the United States. With that little bit of background, now let's look at some ways to try to increase the horsepower of an engine.
Just go with the flow! First of all, you need to understand that an engine (whether it be a tiny nitro engine on a model airplane or a huge turbine engine on a jumbo jet) is basically just an air pump. An internal combustion engine takes in air and combines it with a fuel and burns it. This burning (combustion) is what generates the mechanical power to do work. Understanding that an engine is essentially an air pump can help you better understand ways to increase horsepower. Anything that you can do to increase the amount of air going into an engine can potentially increase the power output of that engine as long as you increase the amount of fuel accordingly to match the additional air. Naturally then, increasing the air flow through an engine is at the heart of any effort to boost power output. Let's take a look at some ways to increase the air flow through an engine with the potential of increasing horsepower.
1) HIGH FLOW INTAKE - If you can do things to try to reduce restrictions where the air enters an engine, then you can allow more air to be able to get into the engine. Let's take the human body as an example. Imagine trying to run a race with a sock stuffed in your mouth and your nose almost totally plugged up. You wouldn't make it very far very fast! In the same way, an engine that has a lot of restriction on the intake side will not be able to live up to it's true power producing potential. What are some of the things that cause restriction on the intake side? Something as simple as an old, plugged up air filter can create a huge amount of restriction. No sense in trying to hot rod an engine for more horsepower if you don't even take care of basic maintenance like regular air filter changes. Sometimes you will see high flow intakes that have a shiny chrome pipe with a cone filter on the end. They sure look nice, but do they really add power? They can; however, they can also reduce power output in some cases.
If a stock air intake system was well designed and it draws cool air from outside the engine compartment, then taking the stock intake out and clamping on a shiny "high flow' intake could actually reduce power in some cases. The reason for this is because cool air is denser and contains more oxygen for any given volume of air. Hot air is less dense and contains less oxygen. Since it's the oxygen that actually combines with the fuel to burn, you want to have as much oxygen as possible. True, a high flow intake that draws in hot air from under the hood might actually flow a higher volume of air, but if the air is too hot, then this additional volume of air flow is offset by the decrease in density (and resulting reduction in oxygen). If the air is hot enough, a so called high flow intake might actually result in less power. A well designed aftermarket intake will be designed to draw cooler air into the engine. In that case, there would be an increase in power. How can you know if a particular intake will be beneficial for your engine? One way is to see if the company has done actual dyno testing to verify a power increase. Look for verified test data and remember to look for an air intake that draws cool air. Sometimes these are referred to as cold air intakes.
WARNING: At this point, I'll share something I've run across more than once over the years. That is that some people have said they damaged their engines by running with a high flow air filter made of cotton gauze. Apparently, these cotton gauze filters which allow more air flow also can also allow more dirt to get through. Oddly, the dirtier these type filters get, then they usually filter more effectively. That is because the dirt that gets trapped on the oily surface of the cotton gauze will build up to the point that it will acts as a pre-filter of sorts. The oily dirt will trap new dirt particles; however, it is thought that a clean cotton gauze filter can allow very fine particles to pass through. If you are working with an off road vehicle that will see lots of dust, then I'd strong recommend being careful with cotton gauze filters. At the very least, you should consider an Outerwears type pre-filter. Actually, if it were me, I'd probably run with an Outerwears type pre-filter even on a street car to minimize the possibility that my expensive engine was going to ingest abrasive dirt particles. For off road vehicles or even street cars, an oiled foam filter element can also provide outstanding protection against wear. Just remember, you are NOT going to help your performance in the long run if you wear your rings prematurely and loose compression. In that case, any horsepower gains in the short term will be more than offset by the reduction in performance and engine life!
2) HP EXHAUST - Another popular way to increase horsepower is to install a high performance exhaust system. Similar to how the person that is gagged will have trouble running a race, an engine will also have trouble operating at peak performance if it is gagged with a restrictive exhaust system. Allowing the engine to "exhale" easier will also allow it to "inhale" more efficiently. Keep in mind that more noise does not always equate to more horsepower. We've all seen (and heard) the noisy cars on the road with the big chromed coffee can mufflers hanging out back. Just because they are noisier doesn't mean that they are faster. When I was younger, I fell for that mistake. Because it is louder, it gives the illusion that you are going faster. I had an old motorcycle on which I gutted out the exhaust and made them into straight pipes. At high RPM, that motorcycle screamed like a funny car at the drag strip. It was very loud. The motorcycle itself wasn't particularly fast, but it sure sounded fast when I was blasting down the road. My ears still ring (tinnitus) from all my loud exhaust experiments earlier in life! Almost every vehicle I've ever owned, I've tried to increase power by uncorking the exhaust system. It has not always been successful. Like I said, it is easy to think something is faster because it has a more aggressive exhaust tone, but in fact you might actually be slower if the exhaust is not designed properly. I remember one time when I even took our Ford Aerostar family van to the exhaust shop to have a bigger exhaust made. I was looking for more power and better fuel economy. At that time, I was using a device known as the G-Tech meter which is a precision accelerometer that calculates horsepower based on vehicle weight and acceleration. On the Aerostar, I took some baseline measurements with the stock exhaust. Then I took it into the shop and had a bigger exhaust welded up for it with a free flowing muffler. It sounded better (louder), but I was greatly disappointed after testing with the G-Tech meter. NO GAIN IN HORSEPOWER! In fact, I think I actually lost a little power with the bigger exhaust. There are a couple things I think might have been going on here. First of all, the stock exhaust might not have been the biggest bottleneck on that vehicle. So, trying to uncork the exhaust did not make much difference. More likely, I think that another possibility about why the larger exhaust didn't help was because the bends made at the shop were the typical muffler shop compression bends that kink the pipe at every bend in the pipe. The stock exhaust, even though it was made of smaller diameter exhaust pipe, had mandrel bends where the pipe was not crushed where the pipe turned. Needless to say, that money was not well spent!
I remember a high flow exhaust I welded up for my Eagle Talon TSI. Turbocharged engines like to breathe and they respond much more dramatically to a good high flow exhaust than a typical normally aspirated engine. I bought a larger downpipe made for the DSMs, and I bought an assortment of pre-made mandrel bend sections. I then made a custom exhaust for my Talon by cutting sections of mandrel bends to the correct angles and welding them to exhaust pipe. It was like putting together a puzzle. I made a simple high flow exhaust that exited right in front of the driver's side rear wheel. That also reminds me of another turbo vehicle for which I tried some different exhausts. I had a Merkur XR4Ti with the same Ford 2.3L turbo engine that was found in the Mustang SVO and Ford Thunderbird Turbocoupes of that time period. Early on, I bought a nice stainless steel Borla CAT back exhaust. It was a dual exhaust that looked nice and it did improve performance some; however, since it was only a CAT back exhaust, it just didn't have the performance potential that I wanted. So, I bought a big 3" diameter downpipe that was made for the Mustang SVO. By the way, I should probably mention for those that don't know that a downpipe is the section of exhaust pipe that bolts directly to the turbocharger. A large diameter downpipe can help exhaust flow because the exhaust gases coming out of the turbine section of the turbocharger are swirling. This swirling effect actually results in restriction to exhaust flow. An oversized downpipe on a turbo engine results in an abrupt step up in size coming out of the turbine section into the large diameter exhaust pipe. This causes the swirling exhaust gases to break down into a more laminar flow. The interesting thing in all this is that the rest of the exhaust system doesn't have to be as large a diameter exhaust pipe as the downpipe. That first section of exhaust pipe right after the turbocharger is most critical. If you can transition down properly, you can run a smaller diameter exhaust pipe after the downpipe with no significant loss in performance. Anyway, back to my custom Merkur XR4Ti exhaust (seen in the small picture to the left). I took the large 3" diameter SVO downpipe to an experienced muffler shop. The SVO pipe was tweaked a little with the pipe bender to clear the different body of the XR4Ti. Since I still wanted to pass emissions testing, I also bought a high flow 3" catalytic converter. I then had a shop install a Magnaflow muffler that had a 3" inlet and dual 2.5" outlets. The Magnaflow muffler was a straight through design with a perforated core with stainless steel packing for sound absorption. Basically, the Magnaflow was a real nice stainless steel glass pack. The dual exhaust looked good on the Merkur, the Magnaflow had a nice sound to it, and this exhaust system provided a bigger increase in horsepower. This allowed the turbocharged 4 cylinder engine to breathe better, and it also gave the potential to generate higher horsepower levels later. Using my G-Tech meter, I took a peak horsepower baseline reading when the car had the Borla exhaust. Back then, it was registering around 170 HP at the rear wheels. Over time, I did much more than just a big exhaust system, I ported the cylinder head, installed a higher lift cam, bigger turbo, intercooler, and so forth. That last G-Tech readings I took on that car registered over 300 HP at the rear wheels. Not bad for an old technology cast iron 2.3L engine that was basically a Pinto engine designed in the 70's.
As I've already confessed, I've had a hard time leaving good enough along over the years, and this has been true even of family vehicles that are far from high performance in nature. Take for instance, a 15 passenger Ford E350 van. Hardly what anyone would call a performance vehicle! Even so, being bitten by the horsepower bug makes it hard to leave anything alone. The same was true with the van. I converted the van to custom dual rear wheels for greater stability. That was mostly a safety upgrade. In terms of performance, I bought a 4" diameter exhaust that included a 4" downpipe that bolted to the turbocharger. This exhaust really reduced the backpressure and allowed the turbodiesel engine to run cooler. My exhaust gas temps (which are critical on any turbocharged vehicle) dropped significantly and my fuel economy increased around 2 MPG.
High Flow Exhaust on a Custom Dually E-350 Powerstroke Turbodiesel Van
The only problem with that exhaust on my E350 was the exhaust noise. After driving the van like this for a couple years, I got tired of the constant droning at highway speeds. I tried to quiet it down by welding in an extra glass pack muffler, but the resonating drone at certain speeds was still too annoying. I finally yanked the high performance exhaust and installed the stock exhaust again. You know that you are turning into an old fart when you actually go "backwards" and put in a more restrictive, quieter exhaust! That's a big change from my younger years when louder was better! That's one thing I've learned over the years. It is still possible to increase performance without excessively increasing engine noise. Remember, louder is not always better. You can actually be slower if you just slap on a loud muffler without any other improvements to air flow through the engine.
3) PERFORMANCE ENGINE MANAGEMENT - Another area where additional horsepower can be unleashed is in the area of engine management. It is possible to buy a "chip" for many different vehicles which is supposed to recalibrate the electronic engine programming for greater power and performance. This is one area that I have to say that I think there is a lot of "snake oil" and misunderstanding out there. A lot of people think they are going to transform their gutless economy car into a tire shredding monster just by adding a miracle power chip. NO WAY! It ain't gonna happen (bad grammar intentional)! Unless you happen to have a turbodiesel powered vehicle. More on that later. For most cars on the road today, adding a chip is not likely to make a huge difference in performance. Simply adding more fuel in the engine management programming is not going to automatically add more horsepower. More fuel without additional air flow is worthless. Worse than worthless, it can be harmful in terms of reducing power and lowering fuel economy. It is true that a performance chip could boost ignition advance some and extract a little more power, but the modern vehicle is tuned very carefully from the factory and it's going to be hard to add much power by simply slapping on a chip. The exception to this might be in the case where you made significant modifications to the engine to the point that the factory tuning is not adequate any more. This was the case with the Merkur XR4Ti I mentioned earlier. I had modified the engine to the point of nearly doubling the horsepower over the stock power levels, and the stock engine management tuning was not ideal. I got a tuner system that piggybacked the stock computer and allowed me to reprogram many different engine parameters using a laptop. I spent countless hours fine tuning the fuel and ignition curves to better match my engine modifications. I had a big fuel pump and big fuel injectors and I needed a way of making everything work well together. It did make a big difference on my car because I had made some big modifications. Again, just don't expect to slap on a chip to an otherwise stock vehicle and expect massive horsepower gains. As alluded to earlier, there can be an exception to this with turbodiesel powered vehicles.
Because of the nature of the diesel engine, more fuel does equal more power! Inject additional diesel fuel and generate more horsepower and torque! On that E350 van I mentioned earlier, I added a tuner chip on it, and I can instantly add 120 HP with just the push of a button! On my vehicle, because there is not a factory intercooler installed, I can not run at this higher power level very long before exhaust gas temps start to rise too far. But the point is that it is possible to add insane amounts of power (especially torque) to a modern turbodiesel vehicle by simply adding a performance chip to retune the fuel delivery as long as you have a way to monitor exhaust gas temperature and make sure they don't get too high. Turbocharged gasoline powered vehicles will sometimes also respond better than normally aspirated engines to an aftermarket performance chip. This can be true if the chip allows the engine to run higher boost levels, and the stock fuel system is able to safely deliver the additional fuel to match the additional air flow created by the higher turbo boost levels.
4) FORCED INDUCTION - With all this talk about turbos, we might as well talk some more about forced induction. Now are are really moving on to the big power adders! A forced induction system consisting of a turbocharger or supercharger can dramatically increase the horsepower of any engine. So dramatically in fact that you can easily blow your engine if you push it too hard. Most factory normally aspirated (NA) engines are just not designed to handle high levels of boost safely. It is possible to take a NA engine and add a low boost turbo or supercharger system and make some significant horsepower increases without adversely affecting engine longevity too much. BUT, this has to be done carefully with a well designed and tested forced induction system that has all the pieces of the puzzle properly matched. As mentioned at the beginning of this article, an internal combustion engine is basically an air pump. By adding a turbo or supercharger, you are increasing the efficiency of this air pump by cramming more air into the cylinder. This pressurized air is denser and has more oxygen. Matched with additional fuel, this can result in big power gains. You just can't go too far with forced induction of a normally aspirated engine; otherwise, you could end up with bent rods, a "holey" piston, blown head gasket, or worse. Fortunately, reputable companies that offer forced induction kits will carefully design their systems to work within the limitations of the factory engine. If you want to go really big with forced induction, then you will most likely need to dig deep into the engine and upgrade internals to handle the additional abuse that high boost forced induction can dish out. Upgraded parts like forged pistons that are resistant to destructive detonation are probably going to be on your list. Heavy duty connecting rods are another likely upgrade needed for high boost applications. A heavy duty head gasket that can handle the additional combustion pressure. Depending on the engine, you might even need a beefed up crankshaft. Then there are the other systems in a vehicle that need to be beefed up like the transmission and other driveline parts. If you decide to go BIG with forced induction, then you will need to have a BIG wallet.
Having owned (and still own) different turbocharged vehicles over the years, my advice to anyone really wanting to go big with forced induction is just to go out and buy yourself a good factory turbocharged vehicle. Do some research and find out which models are well built. There are many that have gone before you and there is a wealth of information on the internet. There are some factory cars of the past that were not really designed well to take much more additional boost. On the other hand, there are other factory boosted vehicles that were very well designed and have a lot of room for further improvement. One such vehicle is the early DSM cars like the turbocharged Eagle Talon and Mitsubishi Eclipse. I did my homework and decided to search for DSM that had the best potential for further increasing horsepower. I found an early 1993 Eagle Talon TSi that had the updated and stronger driveline which included the stronger axles that were added in 1993. At the same time, my Talon had a late '92 spec 4G63 engine that still had the stronger connecting rods and crankshaft. In 1993, the 4G63 engine was revised and the result was that it was not quite as durable as the first generation engines. Not to say that any factory turbo 4G63 engine doesn't have a lot of great potential; however, the point in all this is that with all the information available, you can read in forums and from other owners which model years to target on particular models of cars for the greatest performance potential. By making a good choice up front, you will have a good foundation on which to build as you seek higher horsepower levels. A good factory turbocharged vehicle will have a beefed up engine designed to handle the additional horsepower more reliably. In addition, a stock turbocharged vehicle will also likely have a beefed up driveline better able to handle the additional power.
5) NITROUS OXIDE - Another addition that is similar to forced induction in terms of the possibility of big horsepower gains is nitrous oxide. Adding a nitrous system is like adding chemical forced induction, because you are effectively cramming more oxygen into the cylinder much like a turbocharger or supercharger. Nitrous (aka laughing gas) is simply a gas that contains additional oxygen. A nitrous system is designed to inject this additional oxygen rich nitrous oxide gas along with additional fuel to increase power. A nitrous kit can add 50, 100, 150 HP and MORE. Really, the sky is the limit. Realistically, your engine's shortblock strength is the real limit. You can not add unlimited amounts of power without exceeding the limits of your pistons, rods, and head gasket. As mentioned, nitrous oxide is similar to forced induction in that it crams additional oxygen into the cylinder. One advantage of nitrous over conventional forced induction is the chemical intercooling effect of the nitrous. As the nitrous oxide is kept in the storage cylinder, it is kept under high pressure which helps to keep the nitrous in liquid form. When nitrous is injected into the air intake, the liquid changes to a gas. This phase change from a liquid to a gas absorbs a tremendous amount of heat, and this results in a chemical intercooling effect that further increases density and oxygen content of the air going into the cylinder. In addition to the denser, more oxygen rich air, this cooler air is also less prone to detonation. Destructive detonation can occur when cylinder pressures and temperatures get too high. Rather than a controlled burn in the combustion chamber initiated by the spark plug at the right time, unintended combustion can occur prematurely at the wrong time and result in a dangerous spike in cylinder pressures and a destructive force that can put holes in pistons, blow head gaskets, and generally make a mess of your engine!
I've also had a little experience with nitrous oxide. Earlier, I mentioned the turbocharged XR4Ti that I owned. As often happens when you increase horsepower and performance past a certain point, weak areas are brought to light. In the case of my XR4Ti, a weak link was brought to my attention one morning on my drive to work. That weak link was the stock 5 speed manual transmission. I already had an upgraded clutch in place, but the transmission was marginal in stock form and with nearly twice as much power on tap, and it was only a matter of time until it grenaded. It happened while I was driving to work one morning and merging with traffic on the freeway. I pegged the throttle and the car rocketed forward as the engine boost peaked. There was a loud bang and to make a long story a little shorter, all the teeth were ripped off 2nd gear. What does a blown transmission have to do with nitrous oxide? Well, it was because of my blown transmission that I inadvertently got into nitrous oxide. Up to that point, I did not have a nitrous system. The decision to install a nitrous system on my XR4Ti was related the decision to install an automatic transmission. When my factory 5 speed blew, I had the choice of either upgrading to a heavy duty T5 manual transmission or go with a heavy duty C4 automatic transmission. Both of these transmissions were designed for use with V8 engines. I chose the C4 auto trans route thinking that it would be a better choice for drag racing. In hind sight, I should have gone with the T5 manual transmission, but "live and learn" is what it's all about. In any case, I installed a beefed up C4 automatic transmission in my Merkur XR4Ti. It was not simply a bolt in upgrade. It required a special bellhousing to mate the C4 to the Ford 2.3 engine. In addition, it required a custom driveshaft and a transmission mount. It was a quite a bit of work to adapt the C4 to the XR4Ti. Well, after all that work, I took it out for a drive with eager expectation. I was in for a big disappointment, because the car was a dog with the C4 automatic transmission. I installed a heavy duty torque converter, but it was too tight for a small 4 cylinder engine. There wasn't enough engine torque at low RPM to flash the converter and allow the engine to rev up. On a V8 engine, there is a lot of torque available at low RPM. A small turbocharged engine can produce much more torque than a V8 engine, BUT it requires the engine to rev up high enough to allow boost to build to reach that big spike in torque an horsepower. When I had the 5 speed manual transmission, all I had to do was rev the engine up and slip the clutch a little to get the turbo boosting. In my case, the "tight" torque converter of the C4 trans would not allow the engine to rev up enough starting off from a standstill. It was a real dog until engine RPM built up and turbo boost spiked. It was totally unacceptable to me, so I was faced with the prospect of pulling the transmission and installing a "looser" (higher stall) torque converter better matched to my small turbocharged 4 cylinder engine. Being one that often does things a little different than the norm, I decided instead to just install a nitrous kit jetted for a small shot of nitrous around 30hp or so. I wired the nitrous system with a pressure switch so when boost level rose above a certain point, then the nitrous would shut off. In effect, I was using the nitrous to "light the fuse" on my big turbocharger and once the turbo woke up and started building boost, the nitrous would shut off as the turbo took over. It actually worked quite well. There was one problem though. I had a small leak somewhere in my nitrous system. Even though I calibrated my system for tiny shot of nitrous for a very short duration, I was shocked to find that my nitrous tank was empty very quickly. A full nitrous cylinder should have lasted for a very long time in my application. I didn't have the car too much longer after that. Life was about to change. I was laid off from my job, and I ended up selling the car when we moved. I did have enough experience with nitrous oxide to know that it works and can easily add horsepower to a car. The advantage of increasing horsepower with nitrous oxide is that you only add power when you need it. The rest of the time, the engine is not subjected to additional strain and fuel economy is unaffected. When more power is wanted, you can quickly flip a switch and activate the nitrous system with a big boost in horsepower and performance. It can be a economical way to add power as long as you don't run the nitrous too much ( and as long as you don't have a leak)! Of course, you need to live in an area where you can get nitrous refills in order for this option to work, but thankfully nitrous is readily available in many areas.
CONCLUSION - The fact is that we've only scratched the surface in terms of ways to add horsepower, but we have touched upon some of the big ways to add horsepower to an engine. For those that want to explore the upper limits of the horsepower stratosphere, you can also dig into the cylinder head. Higher lift cams, more aggressive cam profiles, bigger valves, ported heads. I've done this as well, and you can gain some big increases in power, but at the same time it can be very expensive and time consuming to go this route. That brings me to some advice based on my personal hot rodding experience... look for the best bang for the buck modifications. Don't go too far with it our else it can spoil the fun. I've been there and done that. If you push horsepower limits too far, then you start opening a can of worms that you might never have wanted to open. Unless you plan to go for the ultimate power for racing, it is well advised to make sure any modifications that you make don't adversely affect the streetability and reliability of your vehicle. In other words, once you surpass a certain level of horsepower, it's going to get really expensive and it can also make your vehicle less reliable. Not to mention the decrease in fuel economy can make your frequent stops at the gas station a painful (and expensive) experience. All this is important to consider if you still intend to use your vehicle as a daily driver. If you go too far pursuing HP, you'll need to upgrade so many other systems on the vehicle that there comes a point of diminishing returns. In other words, let's say you could have gained 50 HP by spending $1000 on some well thought out mods, but instead you want to go really big and you decide to go for much higher horsepower. You could end up spending MANY TIMES more money for incrementally smaller gains in horsepower. My advice for the really power hungry car enthusiast is to find yourself a good factory turbocharged car and take it from there. You'll probably be time and money ahead and in the end you'll probably have a faster car too. One last parting word of advice. Horsepower can be very addictive. Be careful not to get sucked into the pursuit of ultimate horsepower to the point that you don't enjoy the intermediate steps of performance increases along the way. Be prepared to get to the point where you can say it's good enough. Horsepower can be a very expensive drug. As soon as you reach the next power level, you quickly become accustomed to that new level of performance and that "kick in the pants" doesn't satisfy any more. Then you crave even more horsepower to get that same level of enjoyment. If you are not careful, pretty soon you can bankrupt yourself trying to chase the never ending pursuit of more power. Learn to enjoy the journey along the way as you seek to increase your horsepower and performance. You might not have the most powerful car around, but some well selected modifications can really increase the enjoyment of your vehicle without breaking the bank, and while not adversely affecting the overall reliability and drivability of your vehicle. HAVE FUN!