How to Read Torque on Dyno Test Cummins Engines

Inventor James Watt first coined the term horsepower in 1780. Accounts vary as to how he came upwards with it, just the generally accepted version involves trying to develop a method of computing the corporeality of work performed by a draft horse operating a pump to remove h2o from a coal mine. Watt had modified a steam engine to improve its performance and he sought a mode to quantify its power by relating it to that of a draft horse. Since horses were the primary ability source of that period, the term horsepower was applied to his work. Through observation and measurement, Watt determined the equus caballus'due south ability to generate a torque (twisting forcefulness) most a capstan that operated the mine pump. He calculated that the horse could move 33,000 pounds i foot in one minute. He called that 1 horsepower.

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An engine dyno is ofttimes called a brake because information technology brakes or resists engine output for the purpose of measurement. A very early dyno chosen a prony brake may take also lent its proper name to the dyno. It used a form of brake shoe to resist engine ability. Nearly modern dynos utilize a h2o brake absorber or an eddy current absorber, which uses electrical current to brake the engine.

An engine's VE curve mimics the torque bend particularly at the torque peak. Equally shown here by the shaded areas, information technology falls off at lower RPM due to poor mixture quality and insufficient inlet airspeed. On the upper end it is express by bereft time to make full the cylinder due to increasing RPM.

A load cell attached to the dyno absorber outputs an electrical signal consequent with the amount of torque being absorbed by the dyno. The dyno software converts this signal (voltage) to a torque reading and then calculates horsepower. (Courtesy SuperFlow Technologies Group)

i HP = 33,000 lb-ft/min
Or
1 HP = 550 lb-ft/sec

In applied science speak, piece of work is divers as a force times a distance and it is expressed in ft-lbs while torque is expressed in lbs-ft. Oddly plenty, information technology is unremarkably referred to as pes pounds and I will follow that convention from here. If you study Watt's calculation y'all'll run into that applying one horsepower for 1 minute produces 33,000 lbs-ft of work because a time element is introduced. If you divided 33,000 by 60 (seconds) you get 550 lbs-ft/sec. Watt's calculations were based on the horse generating a strength around the circumference of a circumvolve with a lever arm representing the radius much like the throw of a crankshaft. Working astern, yous can convert the rotational strength of a crankshaft into horsepower by multiplying 2π (two revolutions or half-dozen.2831853) x RPM x torque divided by 33,000. To simplify, divide 33,000 by 2π (6.2831853) to get 5,252, which is the constant applied to the following formulas:

HP = (torque x RPM) ÷ 5,252
Torque = (HP x v,252) ÷ RPM
RPM = (HP 10 five,252) ÷ torque

Notation that 5,252 is constant throughout these formulas while RPM, horsepower, and torque are the variables. That's important considering 5,252 represents the stock-still RPM where torque and horsepower are equal. It is abiding. If you're looking at a dyno sheet, the torque and horsepower numbers should match at 5,252 rpm. And if the dyno curve is presented graphically, the horsepower and torque curves always cross at 5,252 rpm.

At that signal, torque begins to fall off while horsepower continues to ascent. At any point forth the graph or chart, you tin can calculate ane value from the other past using the constant 5,252. This one fact makes sure you never become cheated by a fabricated dyno sheet.

All engines generate a particular torque signature based on displacement, engine speed, VE, and flow path dynamics.Not surprisingly, all engines are influenced by specific architecture (i.eastward., I4, I6, V-six, Five-8, 5-10, V-12, etc.), each of which applies unlike attributes to cylinder filling, mean internet torque, and overall engine smoothness. Every combination generates a torque acme or "sweet spot" where its detail tuning dynamics achieve maximum volumetric efficiency. In the case of competition engines, this oftentimes exceeds 100 percent VE, sometimes by a considerable margin.

The quondam adage that an engine is an air pump is convincingly truthful, but we might as well retrieve of information technology as an air processor. Ability is governed by the amount of air the engine can process over fourth dimension and the restriction specific fuel consumption (BSFC) generated by the efficiency of the specific component mix. It'south relatively easy to supply enough fuel, merely it is considerably more difficult to maximize airflow without the aid of a power adder. For whatsoever given collection of parts, an engine achieves a torque height influenced predominantly past intake and exhaust tuning relative to its size or deportation. Through circumspect manipulation of these and contributing component hardware, the torque curve can be shaped and positioned to adapt the engine's final awarding. This is a principal focus of all competent engine builders and information technology begins with the pursuit of VE relative to the engine'southward static air capacity.

The air mass component depends largely on available air density and the VE a specific component mix is capable of generating. It is primarily governed by inlet and exhaust catamenia path dynamics, combustion chamber efficiency, valve timing and elements of the bottom end and valvetrain that dictate final RPM capability. As shown in the illustration on page 50, the shape of the torque curve matches the VE curve at peak torque. This is the point of maximum engine efficiency and information technology typically reflects the lowest broad-open-throttle (WOT) brake specific fuel consumption numbers. Below the top torque trails the VE curve due to reduced combustion efficiency caused past inadequate intake menstruum velocity, air/fuel separation, issues and poor mixture quality. Above the torque peak, torque and VE pass up due to insufficient fourth dimension for cylinder filling caused by rising engine speed (RPM).

Fortunately in that location are methods to address inefficiency on either side of the torque peak and inflate the overall torque curve. This refers to the "area nether the curve" and seeks to expand the torque curve in all directions. Horsepower, being a office of torque, follows faithfully. More importantly, a broader torque curve frequently produces greater acceleration even with a slight reduction in peak torque considering information technology applies more than torque over a broader range. If the ideal mix of engine components targets an engine speed range nearly beneficial to the application, superior performance will accompany it. Complementing these performance gains with accordingly matched gearing and tire combinations ultimately leads to faster cars and meliorate racing all based on the effective production and utilization of torque. This works well even for engines operating well above the torque acme considering the upper finish of the torque curve expands, thus contributing more than horsepower to the car's performance.

Calculating Horsepower from Torque

Now let's calculate some bones torque and horsepower numbers. Once more we'll use our 2010 Camaro SS as a basis for our calculations. Its published numbers are equally follows:
HP = 426 bhp @ 5,900 rpm Torque = 420 ft-lbs @ 4,600 rpm

If the power peak is really 5,900 rpm, how much torque is the engine generating at that engine speed?
Torque = (HP x five,252) ÷ RPM Torque = (426 x 5,252) ÷ v,900 = 379.2 ft-lbs

Pretty darn good. Note that it is still making more than 1 ft-lb of torque per cubic inch fifty-fifty at the power pinnacle. That implies an engine that pulls very hard upstairs. Now, solve for horsepower at the torque peak:
HP = (torque x RPM) ÷ v,252 HP = (420 10 4,600) ÷ 5,252 = 367.8 hp

Even better. Since we're only at 4,600 rpm and the engine is approaching 1 horsepower per cubic inch, nosotros can infer that it volition exceed one horsepower per cubic inch by the fourth dimension information technology reaches the 5,252-rpm crossover point. We can't know exactly without a full dyno sheet, but lets assume that torque falls off to 400 ft-lbs by 5,200 rpm:
HP = (400 x v,200) ÷ 5,252 = 396 hp

Well in a higher place 1 horsepower per cube and still climbing. That's a convenient way of looking at the torque and horsepower relationship based on a gimmicky engine with published numbers.

How to Read a Dyno Sheet, Part ane

A properly equipped engine dyno can reveal a wealth of information about an engine besides torque and horsepower. It is really a high-terminate data-acquisition system that as well records all the various pressures, temperatures, vacuum, and about a hundred other things that are measured or calculated. I hash out many of them later in the volume so you may want to bookmark this page for future reference. Right at present nosotros're going to break down a sample dyno sheet and use it to encounter how torque and horsepower relate to each other in our calculations. (See dyno sail on folio 52.)

Note that the dyno sheet begins with entries to signal a test number, a date, time, and operator. Then it asks for a clarification of the engine being tested and the type of exam existence performed. There are 3 basic test modes: steady state at a selected RPM, a sweep test where the engine is accelerated (unloaded) through a selected RPM range at a fixed rate, and a step exam where the engine is held at predetermined RPM intervals until a stable reading is taken at each RPM level.

Step tests are usually run in 250- or 500-rpm increments through a selected RPM range, say, two,500 rpm through six,500 rpm for instance. The dyno canvas shown here tells the states that the test is a sweep or acceleration exam at a rate of 300 rpm per second, starting 2,600 rpm and ending at 6,400 rpm (in fact a controlled unloading of the power assimilation unit, not an actual dispatch test).

The side by side dyno printout from Cottrell Racing Engines provides all relevant information for one sweep test. See the text to learn how to evaluate and verify the information found in typical printouts such every bit this one.

This SuperFlow engine dyno plot illustrates how the torque and horsepower curves cross at 5,252 rpm as described in the text.

The exam takes about 13 seconds at that rate. Annotation that the test besides specifies the specific gravity of the fuel, the barometric and vapor pressures, engine displacement, and stroke. These are entered into the computer prior to the test. Take a look at the first three columns: RPM, corrected torque (CBTrq), and corrected power (CBPwr). For any given RPM, you tin use a variant of the horsepower formula to verify either the torque or the horsepower to see if they are correct. Let's attempt the torque at 4,000 rpm and run across if the horsepower computes properly.

HP = TQ x RPM ÷ five,252
HP = (435.viii 10 iv,000) ÷ five,252 = 331.91
At present attempt the horsepower at five,000 rpm and come across if the torque is correct.
TQ = HP x 5,252 ÷ RPM TQ = (444.ii ten v,252) ÷ v,000 = 466.587

Correct on the money with modest rounding. Now examine what's going on at the crossover point of 5,252 rpm. At 5,200 rpm nosotros meet 467.0 for torque and 462.4 for horsepower. Why aren't they equal? Considering the engine speed component is not exactly 5,252 rpm. Looking at the sheet we might infer that torque at 5,252 rpm is 468.9 ft-lbs by averaging the numbers we come across at 5,200 rpm and v,300 rpm.

HP = TQ x RPM ÷ 5,252
HP = 468.9 x 5,250 ÷ v,252 = 468.72 hp at 5,250 rpm

Note that we selected 5,250 rpm, not 5,252 rpm. Information technology seemed logical to split the divergence betwixt 5,200 and 5,300 rpm, just in fact the numbers are nevertheless slightly mismatched. If nosotros actually employ v,252 rpm for the calculation, the reply comes out exact.

HP = 468.9 x 5,252 ÷ five,252 = 468.ix hp at 5,252 rpm

The relationship is balanced based on the constant established by Watt in 1780. Later in the book, we'll encounter how you can relate these torque and horsepower numbers to other recorded data for tuning purposes.

Horsepower and Torque Ratings

Information technology's a skilful idea to keep dyno numbers in perspective. They are typically referred to every bit either gross or net figures. Gross ability numbers indicate the engine'southward operation potential nether ideal weather such every bit inside a dyno cell. This frequently ways headers with no restrictive exhaust arrangement and no parasitic losses from auxiliary components such as a fan, alternator, power steering pump, Ac compressor, mechanical fuel pump, and even the h2o pump in many cases. It is maximum observed power at the flywheel, which is typically corrected to SAE standard J607 or standard temperature and pressure (60-degree dry air and 29.92 Hg barometric pressure). This correction is used past most dyno shops and performance magazine testers.

Or it is corrected to SAE standard J1349 (77-degree dry air and 29.93 Hg) as used by OEM automakers. The difference is about 4 percent; and then for comparison testing you should always compare numbers based on the same correction factor. Different correction factors can be mathematically converted, but it is always easier to compare apples to apples.

Net torque and horsepower represent the real world with all the ugly parasitic components in play, including the air cleaner, a full frazzle organisation, and all the items required to brand a vehicle fully functional. Few of these items are always in place on an engine dyno, but they are in that location for a chassis dyno examination and the numbers vary appropriately. The chassis dyno also accounts for all the friction and inertia losses in the drivetrain and the tires.

We pay closer attention to this today, but in the 1960s and 1970s, they looked at things a little differently. For racing and insurance purposes, the OEMs oft underrated restriction horsepower (bhp). Typically they published a brake horsepower figure at a specified RPM, but neglected to mention that power kept ascent to a higher place that point. Information technology was an arbitrary rating, and not necessarily the maximum output.

In 1971 General Motors switched to internet ratings, although they even so published both ratings for just that one year. All of the other automakers followed them shortly. Today we see only net ratings—isn't information technology interesting how high they have climbed as automakers improve efficiency? Still, muscle car enthusiasts often long for a style to compare net and gross ratings for their cars. In that location is no direct conversion factor, only nosotros might infer some educated guesses based on horsepower per cubic inch.

One horsepower per cubic inch used to exist the magic number. Among others, the fuel-injected 283-ci smallblock Chevy V-eight achieved it dorsum in 1957. Most cars had far less. At 128 gross horsepower, a 263-ci 1952 Buick directly-eight provided 0.48 hp/ci. A 375-hp 396-ci Chevelle offered 0.94 hp/cl in 1966 while the average vehicle was still mired somewhere betwixt 0.five and 0.8 hp/ci. The 1970–1971 Dodge Challenger R/T had a 390-hp 440 Six- Pack that delivered 0.88 hp/ci.

How virtually the 1969 Z28 Camaro? Its 290-hp 302-ci engine delivered 0.96 hp/ci; a gross rating that we know was meliorate. The engine made more horsepower above the published RPM and the cars were fast for their weight and displacement. Big-valve fe cylinder heads of the mean solar day barely flowed 200 cfm, yet Traco Engineering and GM dyno sheets show more than 400 hp from blueprinted Penske Trans Am engines. That'south more 1.3hp/ci in gross or race trim.

Of course these were race-prepped engines, only if nosotros presume 1.1 hp/ci (relatively easy to attain today) it is easy to encounter that the production 302 probably made 330 to 350 hp gross, which may have nettled about 275 in the car. An educated guess, but probably nonetheless enough to provide the ETs and speed those cars typically ran. 1 can only speculate.

Low-compression base engines suffered miserably. The base 1971 Chevy 350 was rated at 245 gross hp, but only 165 net hp. That'south 0.47 hp/ci, which is worse than the 1952 Buick straight-8. Go figure. It serves to illustrate how much engines are affected by lower compression ratios, unfavorable fuel and spark curves and excessive parasitic losses in the engine and in the driveline.

Indicated Horsepower

While the engine dyno is an constructive tool for measuring an engine's output, information technology can't direct measure losses within the cylinders due to the friction and inertia of the operating parts. Information technology just measures output at the flywheel, not what is left on the table due to physics. We know that the engine makes torque when combustion pressure forces the piston downwardly and turns the crankshaft. The force applied to the piston superlative is only the combustion force per unit area (cylinder pressure level) times the area of the piston pinnacle. Since gasoline engines operate on the expansion cycle, cylinder pressure varies greatly during a power stroke. It is greatest only afterwards ignition and falls off quickly equally the energy is transferred to the piston to turn the crankshaft.

Hi-Techniques rotary encoder arrangement attached to the forepart of the crankshaft provides the crank position signal that helps decide cylinder pressure relative to piston position and related valve action. Sharp eyes will note that this particular setup is installed on a dry-sump-equipped small-block Chevy race engine mounted on a SuperFlow 901 engine dyno. (Courtesy Hi-Techniques)

Combustion sleeping accommodation pressure transducers work in union with the rotary encoder. They directly sample cylinder pressure continuously so the software can relate combustion pressure to creepo bending and piston position. This is the indicator that measures mean effective pressure. Several types are shown: 1. intake/exhaust pressure sensor, 2. water-cooled reference-form pressure sensor, three. Spark-plug-mounted force per unit area sensor and 4. an uncooled force per unit area sensor. (Courtesy Hi-Techniques and Kistler Corporation)

Spark advance gives the combustion process a caput showtime before the piston reaches TDC, but peak cylinder force per unit area generally occurs about 12 to fifteen degrees after TDC when the piston is just starting to travel downward the bore. If we know the cylinder force per unit area we can summate the indicated horsepower using a widely accustomed formula called Programme.

Horsepower = (P x Fifty x A ten N) ÷ 33,000

Where:
P = cylinder pressure (MEP) in pounds per square inch (psi)
50 = length of the stroke in anxiety (stroke ÷ 12)
A = piston area in square inches (bore2 x 0.7854)
North = number of power strokes per minute [(RPM ÷ two)
ten number of cylinders]

And, of course, 33,000 represents 1 hp. This yields the following equation:
Horsepower = (MEP 10 stroke ten bore2 ten 0.7854 10 number of cylinders) ÷ (12 10 ii 10 33,000)

On closer inspection we notice the displacement formula in the centre of our equation. If we already know the deportation we can substitute it to simplify the equation.

Horsepower = (MEP x displacement x RPM) ÷ 792,000

It'due south all about cylinder pressure, piston surface area and leverage applied over time. Non surprisingly, all of these things can be modified to better an engine'southward functioning. Note that most engine modifications affect cylinder pressure level, displacement, and/or engine speed:

• If you shorten the stoke to increment RPM, you increment N, which gives you more power strokes per minute.
• If yous overbore the engine, y'all increment A for more piston area to exist acted upon by cylinder force per unit area.
• If y'all enhance the compression ratio, y'all increment cylinder pressure (P).

Because MEP merely occurs within the cylinder, it is difficult to measure directly. Engine labs like Hi-Techniques insert a minor pressure transducer directly into the combustion bedroom to measure the mean constructive pressure of an engine running on the dyno. (SuperFlow Technologies calls this Engine Cycle Assay.) A rotary crankshaft encoder is teamed with the pressure level transducer to pinpoint mean effective pressure at every degree of crankshaft rotation. The pressure level transducer is chosen an "indicator"; hence, the term Indicated Hateful Effective Pressure level (IMEP). This mean effective pressure measured on the dyno is the pressure level (P) used in the Program formula.

For an example, lets take a 360-ci Dodge engine on which the dyno has measured an IMEP of 180 at 4,800 rpm:
HP = (180 ten 360 10 four,800) ÷ 792,000 = 392.7 hp

The operative discussion here is "mean." The pressures we are discussing are mean or "average" pressures that occur over the elapsing of the power stroke. This makes them sound too low, but cylinder pressure level varies profoundly throughout the power bike. Just after ignition, the pressure level in a high-functioning engine may exceed 1,200 psi, but it decays apace during the expansion procedure every bit it pushes the piston down the bore.

If you take a four.125-inch piston with 13.36 square inches of piston area, that 1,200 psi very briefly becomes more than xvi,000 pounds of force pushing on the piston. Midway down the bore, the pressure level may be less than half the initial pressure and information technology drops off to near atmospheric when the exhaust valve cracks open. Proceed in heed that IMEP is an average pressure level derived from very high pressure level at the ignition betoken and at that place is rapid decay from there on down the bore. This average pressure times the leverage of the stroke length and many repetitions (rpm) yield average torque and, thus, the average horsepower that makes your motorcar go fast.

Indicated Torque

Dyno operators tell you that peak MEP occurs at the same RPM as acme torque. That'southward the point of maximum efficiency, but nosotros can summate the indicated torque at whatsoever RPM provided that we know the IMEP at that betoken. To summate indicated torque, multiply the MEP times the verbal calculated displacement and divide by 150.8.

Torque = (MEP x deportation) ÷ 150.8

Revisiting our 360 Dodge engine one time again, we simply plug in the variables. The 150.8 is a abiding.

Torque = (180 x 360) ÷ 150.8 = 429.7 ft-lbs
Now recall that horsepower equals torque times RPM divided by 5,252 and see what yous go.
HP = 429.7 x 4800) ÷ five,252 = 392.seven hp

The same answer we get from the MEP adding.

Brake Mean Effective Pressure

If yous already know the measured brake horsepower or restriction torque, yous can calculate the MEP required to produce it. But rearrange the formula equally follows:
MEP = (horsepower 10 792,000) ÷ (displacement 10 RPM)

Suppose you have an engine making 500 hp at half-dozen,800 rpm. If the displacement is 383 ci, what is the MEP?
MEP = (500 x 792,000) ÷ (383 x 6,800) = 152.05 psi

We know from the torque formula that the same 383 makes 386.17 ft-lbs of torque at the same RPM. And so we can as well calculate the MEP from torque using that effigy.

MEP = (torque 10 150.8) ÷ displacement
MEP = (386.17 ten 150.8) ÷ 383 = 152.05 psi

One of the results of precision in-cylinder pressure measurement is this output graph from Hi-Techniques Win600e analysis software. The graph displays the horsepower output of eight private cylinders from 4,870 rpm to 7000 rpm. Of particular note is the yellow trace (bottom), indicating that cylinder number-8 is not participating equally in the power process.

This screen illustrates an bodily pressure volume trace of a four cylinder engine that exhibits a acme pressure level anomaly on cylinder number-4, while confirming that net mean effective pressure was not seriously impacted. Yet, abrupt engine builders volition try to pinpoint the crusade of the top pressure drop in that cylinder. (Courtesy Hi- Techniques)

Mean Constructive Pressures

To review briefly, the Indicated Hateful Effective Pressure (IMEP) is the strength acting against the piston pinnacle. Information technology is a measured number. Friction Hateful Effective Pressure (FMEP) represents the frictional losses between the pistons and cylinders walls and the crankshaft bearings. The difference is the actual output at the flywheel. It is calculated from observed torque on the dyno. It tin can too exist calculated from observed horsepower which is derived from torque.

Combustion pressure level times piston area and the leverage imparted to the crankshaft makes our cars go fast. Dyno operators always tune for max torque because horsepower is a role of torque. Y'all might say that torque is the force that gets a machine moving and horsepower is what keeps it accelerating. That's pretty close to right, but the existent key to maximum performance is the area under the horsepower bend.

The motorcar with the greatest average horsepower beyond its entire RPM range will exist the faster car even if its opponent has higher acme numbers. The modifications we brand are all aimed at increasing the mean constructive pressure on the piston. MEPs range from 170 to 185 in most high-performance applications and most racing engines operate at slightly above 200 psi.

Mechanical Efficiency

An engine'south mechanical efficiency (ME) is its ability to overcome the frictional losses generated past its moving parts. The question is frequently asked; why does an engine idle? Well, considering at minimum throttle angle information technology makes simply enough torque to overcome its frictional and pumping losses. If we're lucky plenty to have both brake and indicated output figures, we can calculate an engine'south mechanical efficiency using the following formula.

The crankshaft, rods and pistons, rings and bearings, flywheel and harmonic damper all contribute to friction and inertia losses within the engine. (Courtesy Eagle Specialty Products)

ME = (restriction output ÷ indicated output) x 100

Presume an engine that has 488 indicated horsepower at 5,900 rpm and 460 ft-lbs of torque at 4,600 rpm. Its measured brake output is 426 hp at 5,900 rpm and 420 ft-lbs of torque at four,600 rpm. Calculate its mechanical efficiency from horsepower and then from torque.

ME = (426 ÷ 488) ten 100 = 87.29% ME = (420 ÷ 460) x 100 = 91.30% The deviation in mechanical efficiency represents the friction losses inside the engine. In this example friction withholds 62 hp and xl ft-lbs of torque. Note the higher efficiency at elevation torque. The engine achieves its best volumetric efficiency at that point and is amend able to overcome its parasitic losses.

And so why does this matter? Do y'all suppose those numbers carry a stiff resemblance to our 2010 Camaro SS restriction output figures? If they do, it means the Camaro engine really has the potential to make 1.3 hp/ci in street trim. Y'all have to have more than potential than what the restriction shows you in club to overcome frictional losses.

Are these numbers a approximate? Certain they are, but think about it. Who is better at finding engine efficiency than the OEM automakers? They want all the ability and efficiency they tin become and then they do everything possible to reduce friction and pumping losses. Racers do the same thing. They use thinner piston rings, narrower bearings, piston and bearing coatings and a whole bag of tricks to increasing MEP And then is the Camaro engine really a tamed downwardly racing engine? If y'all thought that, you might be close to correct.

Brainstorming with MEP Since mean effective pressure level is the master component of torque and horsepower, nosotros can use projected MEP in the torque and horsepower formulas to model deportation and RPM combinations that might adjust our particular needs. We too know that most race engines operate at or in a higher place 200-psi MEP and that number is influenced past piston area, stroke length and RPM. It is also dependent on how well the cylinder heads and camshaft fill the cylinders. Here's an example:

Say you're trying to break an existing speed record at Bonneville. Y'all've already got elevate and frontal area numbers for your car and y'all have calculated that you need 800 hp to get the job washed. Farther assume that you are class limited to 372 ci. Of course, traction, aerodynamics, and weather will influence your efforts, but 800 hp seems capable of producing the desired result. Well, that'south two.15 hp/ci, which is right upwardly there with some of the best normally aspirated engines. If you run 14:1 or more compression ratio with good cylinder heads and camshaft timing, you should exist able to generate an MEP of 200 psi and perhaps even 210 psi. Conservatively assuming that you achieve an MEP of 200 psi, what RPM will produce the desired horsepower given your stated displacement limit?

HP = (MEP 10 displacement ten RPM) ÷ 792,000
HP = (200 x 372 x seven,500) ÷ 792,000 = 705 hp

That'due south non going to cut it. Yous're going to have to spin the engine a good fleck faster or modify your package to raise the MEP. Let'southward try more RPM start since it might be easier to accomplish. Plug in viii,000 rpm and you but reach 752 hp, so you still need more engine speed. Try 8,500 rpm.

HP = (200 ten 372 x 8,500) ÷ 792,000 = 798 hp

Now that certainly seems possible. If you've built a big-bore small-block with a relatively short stroke information technology will probably handle upwards to 8,500 rpm without distress on the dragstrip or even Bonneville's five-mile dyno. So the respond is a definitive yeah. Y'all can get at that place within achievable RPM limits if you concentrate on building maximum MEP. That ways higher compression, cylinder heads with superior breathing, a calorie-free, stable ring bundle for optimum cylinder sealing, and all possible efforts to minimize parasitic losses in the short block. All things that nosotros strive for in a competition engine.

You can run into how the horsepower formula can help yous predict engine performance based on projected hateful constructive force per unit area. There's more than to information technology of form, but if you sweat the details and generate the required MEP inside your displacement and RPM limits, you're well on your way to making large power.

Written by John Baechtel and Posted with Permission of CarTechBooks

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