Posts Tagged ‘RPM’

There are many great articles online on general piston design, piston ring design, and how the design of OEM and aftermarket pistons has changed over the last decade.

What we will focus on today is the choice of a proper aftermarket piston for your street engine running a significant amount of forced induction using supercharged, turbocharged, nitrous injected or a combination of these power adders.

So what we have in mind today is a daily driven motor, running in the rpm range up to about 8000 rpms with up to 18psi of boost pressure, and experience all the typical operating conditions of a daily driven motor including cold starts, short warm up durations, conventional oiling systems …etc

Before we start talking about piston design I want to first spend a minute talking about the different sections of the piston that are of interest:

The Crown: Is the top most surface of the piston which creates the moving bottom barrier in the combustion chamber. This part of the piston is in contact with incoming airflow, burnt exhaust gasses, and is part of the combustion chamber shape.

The Ring lands: Are the reliefs cut into the side profile of the piston where the piston rings sit. The ring lands are typically taller than the ring thickness which allows the rings to move and rotate in the bore. It also allows combustion pressure to contact the entire piston ring top face inside the ringland pressing it down (and out in some designs) improving ring seal.

The Skirt: The piston skirt is the extension of the side profile of piston which controls the piston movement in the bore preventing it from wobbling around and controlling the angular forces present on the piston walls from the angular rotation of the crankshaft.

The Underside: This part of the piston is exposed to the crank case and houses the wrist pin (connecting the piston to the rod) and exposed to the engine oil in 3 ways:

• Oil collected by the oil retention ring (the bottom most piston ring) is routed through holes in the side of the piston to the underside to drain back into the crank case.
• Oil sloshing around in the crankcase due to the crankshaft counterweights dipping in and out of the oil sump as well as oil forced up through the connecting rod up to lubricate the wrist pin (on forced oil pins).
• On engines equipped with oil squirters under the piston, where oil is squirted on the underside to help cool the piston mass for longevity or racing applications, which in some situations may also allow for an overall thinner crown without sacrificing the strength of the piston and while reducing the overall weight of the package.

When it comes to choosing the right pistons for your street car on boost there are five aspects to look into:

1- Construction
2- Design
3- Coatings
4- Other considerations

1- Piston Construction:

For a street driven application, you’re looking for primarily a forged piston with a high silicone content in the range of 12% to 16%. The high silicone content in the piston improves thermal management in the piston and reduces the overall expansion of the piston in the bore when heated due to boost and power.

This reduced expansion means that you will not need to use undersized pistons (that will grow to fill the bore as they heat up) and engine will not have large tolerances causing piston slap at cold starts and long warm ups in cold weather, which is ideal for street applications.

Furthermore, most modern engines come with high volumetric efficiency from the factory (for example the new mustang 5.0 engine in 2011 will come with 412hp stock compared to a much lower 165 to 205hp -depending on the actual model year for the older 1980s ford 5.0).

Having engines now producing roughly double the power that they were producing just 15 years ago, and having the potential of further doubling that power figure with nitrous injection or 15psi of supercharged boost, then care must be taken to making sure the piston ring lands are anodized for reduced micro-welding between the piston and its rings under the increased heat and pressures from forced induction.

2- Piston Design:

As mentioned earlier, the top of the piston (the crown) is both exposed to the incoming airflow, as well as constitutes the bottom of the combustion chamber.

The piston crown during the intake stroke :To take swirl one step further, certain piston manufacturers have equipped their pistons with swirl enhancing crown faces either equipped with circular grooves or dimpled impressions on the piston crown. These groves and dimples are designed to promote increased swirl in street engines and have been shown to further improve torque delivery by another 4 to 5% over stock figures. Similarly, high compression pistons that gain compression through a very sharp protrusion in the center of the piston will reduce disrupt swirl in the chamber and lower combustion efficiency, although the increase in compression (at 3 to 4% per added point of compression) can negate this loss.	high swirl engines continue to tumble the air inside the bore Dimpled top pistons and groove top pistons improve airflow swirl and tumbling Custom machined dimpled top pistons for similar effect Not all cylinder heads are hemi(spherical) heads. In this application for example a piston with a kidney shaped dish and a raised outer edge will give better results than a flat or symmetrical hemi-style piston Asymmetrical piston for a hemi head, notice the lip that goes around the entire out rim of the piston to squish air towards the central spark plug Combustion profile showing the irregular distance between the spark plug and the edges of the boundaries combustion chamber on a typical flat top piston piston cutaway showing the distance between the valve relief and the first ring land which should be maintained at 0.2" If you’ve never seen a piston machined down before … watch this video: visible here: piston crown with thermal barrier coating, side skirt with friction reduction coating, forced side relief (FSR) piston with reduced side skirts for very high rpm operation (typical on race engines and motorcycles) visible here: bottom of the piston with oil shedding coating
The piston crown during the compression stroke : This brings us to a very important point which is engine ‘squish’. The use of asymmetcrical piston crown design not only continues the swirl process initiated in the intake system, but more importantly having an asymmetrical piston crown forces the air to rapildy move towards one side of the combustion chamber, especially as the piston approaches top dead center. This squish effect near top dead center can be used for several advantages: Getting a good air and fuel mix for more efficient combustion. Moving the air and fuel mixture closer to the spark plug for easier ignition. Reducing the distance between the tip of the spark plug, and the farthest pocket of air and fuel mixture that needs to be burnt. Reducing the flame front travel distance builds cylinder pressure faster in the chamber which reduces timing advance requirements at lower rpms, but also, maintains more torque delivery to the piston as rpms increase (and as the time that the piston spends between top dead center and 17* ATDC) starts to shrink rapidly compared to flame front travel speed past a certain rpm point, as well as for engines with a shorter rod to stroke ratio with faster piston acceleration away from Top Dead Center. Reducing the probability of detonation and uneven combustion from the better air and fuel mixture and better heat distribution.
Knowing these advantages during the compression stroke to shaping the piston top, then the typical flat top pistons of late become obviously obsolete. The best piston choice is actually a D shaped ‘reverse dome’ piston which combines an asymmetrical crown design with a thicker crown height that either mirrors the combustion chamber shape (as seen look into the bottom of the cylinder head) or with a thicker out ring on hemispherical head. The whole point here is that the air fuel charge is compressed in a tighter pocket area around the spark plug location, and moved away from the far cylinder walls. Then, to maintain the same compression ratio (even with this thicker crown height) the crown area around the spark plug is dished by the right amount to bring the total volume of the combustion chamber + the piston dish to be the correct volume for the proper engine compression ratio. Furthermore, on some applications we can take this one step further by milling down the cylinder head (or using a different cylinder head casting with shallower combustion chambers) which brings the spark plug down deeper into the bore, and offsetting the loss of combustion chamber volume with further dish in the piston crown. Bringing the air and fuel pocket closer to the spark plug, and bringing the spark plug closer to the center of the combustion chamber formed between the cylinder head contours and the piston crown contours boost engine efficiency, reduces detonation probability, reduces timing advance requirements, and promotes increased efficiencies at higher rpms as described earlier.
Finally, for a forced induced motor, care must be taken that the crown thickness after all modifications to the piston crown are complete (such as enlarging the valve reliefs for oversized valves, or increasing the piston dish for a shallower cylinder head and a lower spark plug position as described earlier) is still at least 0.175” thick with a good margin of safety being around the 0.200” mark for forged aftermarket pistons. Another thing to note is that typically enlarging valve reliefs not only reduces crown thickness as a vertical measurement, but also diagonally reduces the distance between the valve relief and the primary piston ring. This is even more evident on newer high efficinecy (low emissions) engines that come from the factory with a raised primary compression piston ring (or a reduced distance / lip between the piston top and the first ring land).To summarize: When choosing an aftermarket piston for your motor, look for a reverse dome piston top (rather than a flat top or typical dish type piston) with dimpled flat surfaces for better mixture, and still having at least 0.2” material thickness throughout the entire crown of the piston. If the piston I just described does not exist, a thick piston (high compression) piston can be machined down to make the piston I’m describing by someone who knows enough about this to do it properly (or by requesting a custom style piston from the piston manufacturer themselves).
3- Piston Coatings Investing the money in getting your pistons coated has several benefits including: Increased power Reduced emissions Better response More resistance to catastrophic failure The best combination of coatings are as follows: A thermal barrier coating on the piston crown A friction reduction coating on the piston skirts An oil shedding coating on engines equipped with oil squirters in the crank case The thermal barrier coating gives a more consistent finish to the top of the piston crown. It helps reflect heat into the combustion chamber, rather than dissipating it through the piston materials and thus improves combustion speed and the completeness of the combustion process. However, this increase in combustion temps and trapping the power rather than dissipating it does require reduced timing advance, but will as stated earlier, pay back dividends on higher rpm motors or on engines with short rod/stroke ratios where piston acceleration away from TDC becomes a problem for power transfer into the pistons at higher rpms. One thing to note here is that since the thermal barrier coating improves torque delivery by accelerating the burn rate inside the engine, it can be used to boost torque output on cars with centrifugal superchargers or large turbos to give better response before the boost builds. Overall, it may seem like it’s disadvantageous to trap more heat in the chamber and that it possibly reduces the octane, boost, or timing limits of the motor but this is not true. The increased heat can be counteracted with timing reduction without power loss (since the burn rate is maintained) and the added advantages are that the thermal coating helps spread the heat out over the entire crown area of the piston, thus protecting any thin or weak spots from being pummeled to failure. Also in the rare event that you do have some minor detonation in the engine due to high load, a bad fill of gas, or some other factors, the thermal coating prevents piston pitting due to minor occurrences of detonation, and thus it prevents the creation of hot spots on the piston crown which could have become hot-beds for further detonation and a prevented runaway towards total piston failure! Seems like a fair trade off of some timing advance for increased longevity and increased high rpm efficiency. The low friction coating on the piston skirt reduces frictional losses between the piston sides and the cylinder walls. This protects the pistons from damage and scuffing on cold starts, if the engine is overheated or overboosted (and the piston expands due to heat), and during oil starvation conditions (high cornering G’s, coild oil, first crank after a rebuild). Reducing friction in the engine delivers more horsepower to the crank, improves the engine’s operation near redline, and gives the engine crisper response. One study showed that using lower profile skirts, with proper friction coating, as well as lower friction wrist pins can reduce the total engine internal friction by 40%… So, something as simple and non intrusive as coating your piston skirts is definitly worth the effort, especially on boosted street cars that need to run a full skirted piston (as opposed to naturally aspirated motorcycles that will more likely run a forced side relief piston which features a longer skirt in the primary axis of the piston motion as the connecting rod movement shoves and pulls the piston against the bore on the upwards and downwards strokes… and a short or no-skirt in the axis 90* with plane of the connecting rod’s movement). Finally, oil shedding coatings on the bottom surface of the piston help evacuate oil off of the piston faster. This helps keep the piston lighter and faster moving in its rotation, however since oil is used to cool the piston bottom and increase its longevity (especially in motors that will experience high cycles as we will explain later), then there is a debate as to weather this coating is beneficial or detrimental on different engines. Engines with oil squirters get plenty of oil volume delivered to the bottom of the piston at a constant stream of flow. These engines can do with a reduced duration for oil clinging to the bottom of the piston. On the other hand engines that rely on the crankshaft counterweights sloshing in the oil sump and indirectly sending oil up to the pistons to cool them (and up to the wrist pins to lubricate them on engines without a force-lubricated style connecting rod) could use with the oil clinging to the piston bottom for a longer duration. If you are doing a full rebuild, my recommendation would be to both coat your pistons AND install oil squirters. Otherwise, choose weather or not to use the oil shedding coating based on weather you have a dry sump, wet sump with squirters, or wet sump without squirters oiling system. 4- Other Piston Design Considerations As mentioned earlier there are other considerations to choosing your piston design which I have eluded to earlier. Even though most people judge engine life based on mileage, performance engines are more accurately judged on cycles. For example, an engine can run for 100 continuous miles at 7500 rpms in 1st gear, or at 1500 rpms in 5th gear…. the same engine could be tracked every weekend (spending a healthy portion of its life in the higher rpm ranges) or cruised on a highyway commute to and from work. Even though these two engines have the same mileage, they have lived through a different number of engine cycles. Engine cycles is what determines the amount of continuous (or accumulated) stress both on your pistons (for thermal management) as well as on your piston rings (for wear management). The advice given here is primarily for dual purpose vehicles that are both street cars but will see occasional or repeated track use. Vehicles that will be used primarily for racing, require a thicker crown for better thermal management, will probably use a lower silicone content piston (with much larger piston to bore clearances to allow for the thermal expansion of the piston after it stops slapping and warms up in the bore, and will definitely have lower ring height for the primary compression ring (which reduces the operating temperature of the ring from around 600*F to around 300*F) as well as using a thicker compression ring that is less likely to distort or fail under continuous sustained high rpm abuse (think about a car in Nascar racing that does the entire race over 5000 rpms…) These cars that are designed for ‘standing mile races’ as I like to call them or long term endurance racing will also have to be tune differently as I have a complete longevity tuning chapter in The Tuner Mastermind. However, for most street vehicles running up to around 18psi of boost, and having dual street / track duty… then follow exactly the piston recommendations detailed here and you will have a great combination of torque, efficiency, detonation resistance, and reliability.

Technorati Tags: boost, centrifugal, Octane, piston, RPM

The other day I had a thought about DIY modifications, possible fuel savers and other performance tricks and tips to increase gas mileage. See, although this is a performance oriented blog, as the cost of oil per barrell crosses the 70 dollars per barrell threshold once again, and as the economic depression in the USA (and thus in many other parts of the world) seems to be very much a mainstay till around 2012 according to analysts, I can’t help but think about mileage and how so many people might want performance parts for their car, but they may also NEED better fuel mileage.

Ouch. My first gas tank in the USA I paid 75c per gallon @ 1998

This got me to thinking about how we as automtive enthusiasts modify our cars for increased volumetric effeciency and higher performance in a specific rpm range of around 4000 rpms and higher. This is mainly due to the fact, that when you are racing, you spend alot of your time on the eastern half of the tachometer in the higher end of the rev range and thus it makes sense that most performance products and tips are focused towards higher rpm effeciency. However, there are some (but not all) performance modifications (and racer’s secrets quite frankly) that we as enthusiasts may use to gain that power advantage, but can be utilized to effectively boost gas mileage.

This isn’t only a theoretical debate as I’ve done this ‘accidently’ on my first car, a 1991 Toyota Celica GT back in 1999. In typical 10 year old car fashion it ran horribly when I first bought it, as indicated by my first tank of gas that was over in about 180 miles. Over the next two years I modified it and tuned it, not only increasing its performance and acceleration, but also acheiving over 32mpg (which is about 4 mpg over the factory figures, when the car was brand new, and more importantly I was doing this on a 10 year old car that was definately not babied throughout its life).

My friends and I also went out and replicated these results on a 1988 Celica GT-S, a 1996 Jeep 4.0 I6, and my friend’s moms Nissan Quest V6. My uncle also bought a 1993 Cadillac Deville that was getting double the mileage on cruise control as it was during normal driving. I recommended he change one thing on his car, he did and he got his mileage back. Then I went ahead and did a similar electrical fix (different part though) on my dad’s 1994 Cadillac Fleetwood brougham.

Anyway, enough stories of the past, let’s look at the future… I’ve sat down and brainstormed every thing you can do to boost mileage on an older car and I have come up with a hand written rough draft of performance modifications that you can do to your car to gain back it’s factory mileage and to even go beyond that by another 4+ mpg.

I am thinking of turning this draft into a fully detailed guide, but first I’d like to know that there is serious interest in this guide before I go ahead and invest time in this product….

If you are seriously intersted in a mileage booster guide please show us your interest by subscribing to this topic below.

The beauty of these kinds of modifications is that they obviously pay you back with time, so if you start out with a horribly performing car, or if you put a lot of mileage on your vehicle, then this information will end up saving you money in the long run, which is really cool.

Technorati Tags: boost, cadillac, effeciency, Jeep, Mileage, RPM, Toyota

Building on the beautiful high revving v8 powerplant, MTM motorsports upgrades the performance, looks, styling, and handling of the 4.2 Audi RS4.

The heart of the upgrade package is a Lysholm twin screw compressor elevating intake pressures to a modest 6 psi. This fairly low boost pressure means that the engine’s static compression ration can be left untouched and that the supercharger package can be a true ‘bolt on’ affair. Following through with this ‘bolt on’ strategy, MTM have coupled the supercharger with an integrated top mount intake manifold with integrated air to water intercooler courtesy of Laminova intercoolers. Also in the mix is an MTM bolt-on cat-back exhaust system exiting in an exotic dual dual (that’s four outlets) 3″ tips.

The car is further enhanced with suspension modifications, lowering, lightweight body parts rounding off the performance package.  The result of all of this work is shifting power up from 420 hp @ 7800 rpms to 540 hp @ 8220 rpms. Torque is amplified from an original 317 ft lb , 430 Nm @ 6000 rpm to a new 412 ft lbs, 560 Nm @ 3700 rpms.

The attention to sound engineering design in this kit (using a twin screw supercharger, coupled with an integrated manifold and integrated intercooler) resulting in short intake path lengths, means that the whole package is both still highly throttle responsive as well as having more power delivery on the top end. Not only is it impressive that the car gains over 120 hp with this modification, but more impressive is that the power band growns from 1800 rpms on the stock high-revving V8 to a very meaty 4500 rpms between peak torque and peak power. This not only makes the car faster in a straight line, but makes it much more versatile on exiting corners and carrying its hefty weight and the weight of the AWD Quattro system in the lower rev range.

See the car in action

Find out more directly from MTM motorsports

Technorati Tags: Audi, exhaust, Intercooler, Lysholm, MTM, PSI, RPM, v8, VAG

Supercharger performance is proud to present the newly updated power calculator. The only calculator built for enthusiasts by enthusiasts…

Get your copy today !

Technorati Tags: boost, CFM, compressor map, header, Intercooler, N2O, Power Calculator, RPM, water injection

There’s an abundance of bolt on and custom application engine performance parts available for any vehicle, and the internet is full of advice, trials, and feedback from enthusiasts, brand promoters, magazine editors, and even racers about which performance parts are best for your car. This is the triple distilled guide on engine performance parts to help you make the most power with the least effort…..

Engine performance hinges on one of THREE general factors:

1-      raw power factors

2-      Efficiency factors

3-      Power boosters

2-      Efficiency factors:

Most of the bolt on performance parts available in the market are actually geared towards efficiency, to name a few : intakes, headers, exhausts, cams, cam gears, ignition systems, spacer plates and phenolic resin gaskets, PCV systems, catch cans, lightweight flywheels, clutches and pressure plates …etc

The focus of these parts is never really to INCREASE the performance of the engine above it’s possible potential. Rather, the focus of these parts is to be able to optimize the existing engine’s performance so that no power is wasted and every possible ounce of horsepower that can be made, is in fact made. Furthermore, we want every possible ounce of horsepower that is made, to reach the wheels rather than being ‘lost’ in friction, mistimed combustion or other problem areas.

My point is that although a lot of money is typically spent on this part of engine modifications because these parts are accessible and easy to install, it is usually the least effective modification for the money because as stated earlier the maximum potential gain of these systems is whatever efficiency the manufacturer decided to overlook when packaging the car. This typically leaves a good range of 10-20% to work with on older cars, but increasingly, and with better designed newer cars we find that an efficiency gap of 5-10% at most is not uncommon.

The reason for this trend of rising motor efficiency is that efficiency brings with it advantages of better mileage and lower displacement requirements to produce the same acceleration and user experience.

There are only 2 exceptions to what I’ve stated above in which it is worthwhile to invest money in improving the efficiency of your motor:

1-      If you have a vehicle where the car produces peak power at 5000 RPMs but the actual engine redline is at 7500 for example then the addition of 3 modifications: 

a.       A new intake manifold with the correct runner design

b.      A new camshaft with the correct duration

c.       A new exhaust manifold with the correct runner design

These three modifications can shift peak power from 5000 rpm’s to 75000 RPMs and this as we stated in Part 1 ( Raw Power) of this article can potentially boost power figures by the ratio of those two RPMs or 50% to be exact!

We have to be clear about what we are trying to achieve from our bolt on power parts. Are we trying to increase the efficiency of the motor using a more efficient intake and exhaust (and other parts) to gain a 5-10% power boost… or are we actually trying to shift our peak power rpm upwards to gain a significant increase in RAW POWER production… Most people don’t think about this and end up buying a mish mash of low rpm and high rpm optimized parts ending up with something that doesn’t perform to its best potential and becoming a big waste of money.

2-      Sometimes people spend a lot of money on bolt on parts but still end up with a poorly performing car, in this case it usually best to invest in the following:

a.       An air fuel ratio tuner

b.      An ignition timing controller

c.       A set of adjustable cam gears

When the car has been extensively modified but is still poorly performing it either has:

1-      A mix of parts that aren’t working together (ie are designed for different flow capacities and different rpm ranges… such as installing a stump pulling designed header that’s optimized for peak torque at the lowest possible rpm and a short straight runner intake manifold that’s designed for the highest rpm horsepower peak… in using those together we find that the when the engine is able to exhaust air efficiently it is unable to breathe air in efficiently to create exhaust gasses… so that exhaust manifold’s potential is wasted, at the same time, when we get up higher in the rpm ranges and the engine can breathe air in efficiently, that air is trapped from exiting through a poorly or miss-designed exhaust manifold which chokes the engine negating any effects the intake manifold could have created)….

2-      A bad tune that is incompatible with the car’s fuel, ignition, and cam timing requirements. Getting a performance tune can unlock the hidden potential of the performance parts already installed, and this tune becomes more and more important the more power you are trying to make …. It’s not uncommon for a turbocharged import to go into the dyno room with a 300 hp engine and come out making an extra 200 hp at the hands of a capable tuner.

So if I had to summarize part 2: efficiency factors:

                Before purchasing any efficiency modifications for your vehicle look and see if there is a big disparity between your current peak power RPM and your Redline, If so then know that you have the potential to gain a significant amount of power, if not, the know that no matter how much money you invest on bolt on engine auxiliary parts then the most you’re typically looking at is a gain of some 10-15%, which is fine, however people expect that every part they install is worth 3-7hp and that by installing 10 bolt ons they will have 30 to 70 more hp when in fact all they are doing is going from 85 to 90 to 99 to 99.99% efficiency of power potential limited by their displacement , RPM, stroke and last but not least forced induction which I will explain in part 3… stay tuned !

Technorati Tags: engine efficiency, header, RPM, Stroke, Tuners

There’s an abundance of bolt on and custom application engine performance parts available for any vehicle, and the internet is full of advice, trials, and feedback from enthusiasts, brand promoters, magazine editors, and even racers about which performance parts are best for your car. This is the triple distilled guide on engine performance parts to help you make the most power with the least effort…..

Engine performance hinges on one of THREE general factors:

1-      Raw power factors

2-      efficiency factors

3-      Power boosters

1-      Raw power factors:

There are three raw power factors that decided whether you have a good ‘platform’ to build power on or not: Displacement, RPM, Stroke. Confused? I will explain:

                A: Displacement:  The old adage: “There is no replacement for displacement”.

Displacement is the size of your engine and thus the size of your cylinders, as your engine and cylinders get larger (by swapping to a larger engine, using overbore pistons, and increasing the stroke of your cylinder) or by any other engine design (wedge or rotary or other) that gives you a larger volume engine. As you increase the volume of your engine, you have more room to fill with nice combustible air / fuel mixture, and the bigger the volume, the bigger the potential bang, the bigger your potential horsepower.

It goes without saying that if I take a 6.0 liter V8 and a 3.0 litre boxster 4 with similar design from the same manufacturer that the 6.0 liter V8 probably makes about double the horsepower of the 3.0 liter boxster 4, and so one of the oldest and most effective tricks in hotrodding (and in Reliable OEM performance packaged cars) is to stuff a BIGGER motor , in a smaller chassis.

If you’re familiar with bottom end kits including overbore pistons, stroker cranks, stroker kits, and cylinder sleeves, then all these kits work on increasing performance essencially by increasing displacement and giving you more bang (quite literally) for your block.

B: RPM (revolutions per minute):

Every time an engine fires and ignites the air fuel mixture in the cylinders, the expanding gasses of the combustion process create a force pushing back down on the piston, exerting torque on the crankshaft, and rotating the crank, the transmission and eventually the wheels giving us acceleration. Depending on weather you have a 2 stroke, or a 4 stroke (or other) the engine will fire once every 2 or 4 revolutions. So say you have a 4 stroke motor at 1000 revolutions per minute, that means that within one minute you have 250 combustion events in your motor, which delivers torque to your crank (and eventually to your wheels for acceleration) 250 times in that minute. If we go up to 2000 RPMS, the revolutions double, and so also the rate of engine firing doubles to 500 combustion events, giving you essentially double the horsepower.

So, in terms of RAW power potential, the maximum RPM that your engine can operate at, is linearly related t how much raw power you can produce.

Formula one cars (and motor cycle engines as well) have in their quest to produce the lightest yet most powerful engines they can, used engines that are smaller in size (less volume/displacement) but more than made up for the loss of displacement by revving those engines up to 18000 revolutions.

So if you’re looking at an engine swap, and you have two engines to work with of the same volume, always take the engine that has a higher safe redline, as with that car, you have more revolutions to work with and ultimately more opportunity to make power.

cams, headwork, and other such modifications work on this principal of power production by trying to shift your peak power rpm up as high as possible giving you a higher peak horsepower figure.

C- Stroke:

What I mean by stroke is not the distance travel of the piston inside the cylinder, but rather, I mean weather we are talking two stroke, or 4 stroke, or other stroke.

A 2 stroke engine fires once every 2 revolutions. A 4 stroke engine fires once every 4 revolutions. If I had two engines of similar efficiency, the same peak rpm, and the same displacement, where one was a 2 stroke, and one was a 4 stroke, the two stroke motor would produce double the horsepower of the 4 stroke motor at every rpm point, because quite literally the 2 stroke engine has double the combustion events and delivers torque to the crank (and eventually to the wheels) twice as often as a 4 stroke motor.

Now in most situations we will not be able to convert our 4 stroke engine to a 2 stroke… but If for example I had the option to use a 2.0 liter 4 stroke in my race car vs. using a 2.0 liter twin rotor rotary engine which essentially fires one time for every revolution, then using the rotary engine of the same displacement will produce FOUR times the power output (holding all else constant : displacement, peak rpm, stroke, efficiency…etc).

To summarize section 1 of this series:

If I had to choose a motor for my race car, I would open up the rule book for my racing series and look for what is allowable in terms of maximum displacement, rpm, and stroke. And I would then choose the engine where the following calculation produces the largest result:

Raw power potential = DISPLACEMENT * MAX RPM / STROKE

This simplifies comparing for example two engines that are cheaply available at a junkyard if I wanted for example to build a low buck racer:

A)     4.6 Liter ford crown Victoria V8, 4 stroke, with 6000 RPM redline.

Raw Power potential = 4.6 * 6000 / 4  = 6,900

B) 2.3 Liter Honda CRV Inline 4, 4 stroke, with 8000 RPM redline.

Raw Power potential = 2.2 * 8000 / 4  = 4,400

C) 1.3 Liter Mazda dual roter, 1 stroke , 9500 RPM redline

Raw Power potential = 1.3 * 9500 / 1 = 12,300

D ) 1.3 Liter Hyabusa Boxster 4, 2 stroke , with 13000 RPM redline.

Raw Power potential = 1.3 * 13000 / 2 = 8,450

As you can see it’s very easy to see that if allowable in the rule books, and so ranking these engines according to my preference (from highest to lowest):

Mazda Rotary >> Hayabusa Boxster >> Ford V8 >> Honda I4

Of course the gearing, gear ratios, and final drive ratios for each engine would be different to make it work for my application… but when focusing on raw power potential this is how you pick them…

Technorati Tags: Displacement, Rotary, RPM, Stroke