Engine Essentials
Internal engine modifications are difficult to justify with a fuel economy ROI — they’re expensive! Few people have the tools and skills to do engine work themselves, and find they are paying a professional top dollar to do the work for them. However, there are times when internal engine work needs to be done, either to freshen up an older tired engine, or to repair a mechanical failure. If money is already being spent, then upgrades can be justified cost effectively.
The Chrysler 5.7 Hemi is notorious for failed lifters that destroy the camshaft. If you own one, chances are you may be paying a mechanic to replace your cam & lifters. He will probably tell you they are on back order, and it may be several months before the parts come in. The difference between a stock replacement cam and a fuel economy upgrade may not be that much, and in fact, may even cost less. Furthermore, if a fuel economy grind is available now, you are back on the road sooner. GM used the 3800 series engine in both Pontiacs and Buicks in the 1990’s. For the Pontiac performance they used an aggressive cam. Pontiacs typically sold to younger folks that appreciated a spirited power plant. For the Buick line (and Cadillac), they used what has been dubbed the “Peanut Cam”, with less duration and overlap than the Pontiac cousin. This delivered crisper off-idle throttle response and better fuel economy, desirable for the older demographic driving Buicks. Swapping the Buick cam into the Pontiac engine will give you better tip-in throttle response, as well as fuel economy. As a rule of thumb, higher lift is not your enemy; but longer duration and valve overlap is. Compare camshaft profiles to what the factory used as a guide. (There are over a million documents covering camshaft selection online. Do your research.)
If you’re mechanically inclined, head porting may be something you can do to boost performance & economy.
“Head Porting for Performance & Economy” will show you many “tricks” that aren’t standard, but deliver remarkable results. The techniques outlined have consistently delivered upwards of 40%+ increases in fuel economy with respectable gains in performance; both street and race. Fuel economy improves because you are utilizing more of the chemical energy in the fuel. Performance increases because you are using more of the chemical energy in the fuel. Basically, the HP Book shows how to massage the top end (cylinder head, intake, and exhaust manifolds) to improve combustion efficiency through mechanical means.
It is universally accepted that diesel engines are more efficient than gasoline versions when it comes to converting chemical energy in the fuel to power at the wheels. One of the biggest reasons is the difference in compression ratios. Gas engines are typically engineered at ~9:1 CR, while diesels may see 22:1. In math, the inverse of addition is subtraction; multiplication is the inverse of division. The inverse of the compression ratio is the expansion ratio. On the compression stroke, 9 volumes of air and fuel are compressed to 1 volume — a 9:1 CR. However, on the power stroke, the expansion ratio determines how much time the engine has to harness the pressures created by the burning fuel. When the exhaust valve opens, the fuel is still burning. It’s still generating heat. Everything is still expanding and building pressure. Unfortunately, the exhaust valve just opened, dumping all that energy into the exhaust! It’s wasted!! Higher expansion ratios allow more time for the engine to harness this energy before the exhaust valve opens. This equates to better fuel economy and better normal-driving performance.
To explain the influence of the expansion ratio, picture this: As an experiment, we’ll take a 3 meter long pipe (8’ to 10’ will work) and a piston sized for the inner diameter (ID) of the pipe. We’ll cap the pipe at one end with a “cylinder head” which includes a spark plug, and leave the other end open. The space between the piston and head is filled with a 14.7:1 AFR of gasoline and air. The piston is placed about 4 inches from the cylinder head, then rapidly pushed to about 0.44” from the head. This will give us a ~9:1 compression ratio. The spark plug is fired and the piston is released to move freely inside the pipe.
Let’s connect a bunch of data acquisition sensors to monitor what happens. The air-fuel charge is drawn into the pipe as the piston moves from TDC (closest to the cylinder head) to about 4” away. This is the Intake Stroke. It is then pushed toward the cylinder head to compress the air-fuel charge; the Compression Stroke. The spark plug is fired and the piston is released from the mechanism used to push it towards the cylinder head. The data acquisition system would see a rapid rise in temperature and pressure as the fuel burns. Meanwhile, the piston starts shooting down the pipe. As it does, the volume increases, reducing both temperature and pressure. Eventually the fuel is as burnt as it can get, releasing no more energy. The piston has mass and continues to move down the pipe. The temperature will reach ambient at some point, and then start exhibiting a chilling effect. The pressure will drop, eventually moving into the vacuum range. However, the piston is near the other end of the pipe when this happens!! The piston started at around 4” away from the cylinder head (BDC) and was moving under force to at least the 6 foot mark! If the expansion ratio allowed for that much piston travel in an engine, you could still be harnessing the energy from the fuel as the piston was scraping the ground.
Increasing an engine’s compression ratio can be accomplished by milling the block, milling the head, or with replacement pistons. Over-boring an engine will also increase CR slightly. The engineers responsible for modern OEM engines already take the CR to the ragged edge in pursuit of performance, fuel economy, and emissions. The Honda 3.5 liter V-6 used in the Odyssey minivan has a static CR of 10:1. The fact that it runs on 87 octane fuel is a tribute to the genius of the Honda engineers. You shouldn’t just crank up the CR and expect massive gains. It needs to be part of a well thought-out package. High compression ratios can cause detonation that destroys pistons and rings — but only at higher throttle and RPM ranges. You could run a 20:1 CR on 87 octane fuel if you never went beyond 10% throttle angle!
Camshaft selection can synergistically work with higher CRs to keep your engine safe on cheap pump gas. Toyota’s Prius uses a camshaft profile that creates what is called an “Atkins Cycle” engine. To elaborate: Back in the 1920’s George Arlington Moore developed an engine that used an extremely high static compression ratio of 16:1, but modified the camshaft with extended intake lobe duration. The piston descends the bore on the intake stroke drawing in the air and fuel. Normally, at the bottom, the cam closes the intake valve. Moore extended the intake valve opening to allow some of the intake charge to push back into the intake manifold. The dynamic compression ratio yielded a tolerable 8:1 CR, but the expansion ratio was still 16:1. Mike Brown created a package in the 1980’s for popular Ford 302, Chrysler 318, and Chevy 350 engines that included the pistons and camshaft. I met someone in South Dakota that had a Ford F-150 4X4 with the 302 sporting Mike Brown’s package. He got 23 MPG on mostly back roads, and he claimed the torque could easily pull a mobile home.
Looking at the economics of overall energy usage within an engine, much fuel is burned to overcome parasitic losses. It takes energy to drive the oil pump, for example. A popular “performance upgrade” is to install a high-pressure high-volume oil pump. Unless you’re going drag racing, the additional parasitic losses generated by the higher pumping load will not keep your engine alive for even 1 second longer. In other words, a stock pump is adequate. High performance valve springs force the valves closed at higher RPM ranges, improving horsepower. The higher spring pressures take more crankshaft energy to overcome the cam forces (overcoming the spring pressures). Again, unless you are shooting for the Daytona 500, stock springs will not float under normal street conditions, and will waste less HP to drive. Inside the engine the oil pump sends lubrication to the valves, rocker gear, camshaft, and so forth. After it does its job, it drains back into the oil pan. There is a special paint (available under a couple brand names) that repels oil like a fresh wax job on the hood repels water. It is applied in the valley, cylinder head under the valve covers, and other places to help the oil get back to the pan quickly. A windage tray in the oil pan keeps the crankshaft from battering the oil like a blender (which of course wastes energy). With a complete engine build, oil and coolant passages are probably plagued with casting flash and other obstructions. If you’re porting your top end, go through the drain-back, coolant, and oil passages in the head and block with your die grinder to remove restrictions. This reduces the energy required to drive your oil and water pumps, and helps oil get back to the pan quicker.
Thermal barrier and high lubricity coatings made their mark in the 1980’s. I used coatings extensively when I had my speed shop. What I discovered is that even under extreme usage cases, these extra-cost coatings didn’t contribute much. The greatest benefit I saw was coating exhaust manifolds and turbos with a thermal barrier coating. This kept exhaust velocities high and reduced under-hood temperatures. Even the companies that sell these chemicals tout rather dismal gains from their products. The guidepost of whether they work or not boils down to did the engine blow up? If you’re pushing the ragged edge with high compression, coatings may keep your engine together. Otherwise, don’t waste your money. If you are contemplating building an extreme engine, www.CaswellPlating.com is where I bought my coatings.
Again, “Head Porting for Performance & Economy; Save Gas and Kick... Butt” not only covers head porting, but also manifolds, pistons, and many other aspects of engine building.
FE3
MPGenie Basics 051 Training - Engine Essentials Part 1
MPGenie Basics 051 Training - Engine Essentials Part 2
