Camshaft Horsepower Calculator using cam duration at 0.050 in, displacement and head flow to estimate peak power. Compare two cams and see where the heads or intake sets the limit.
Enter displacement, build strength and cam duration.
Heads and Cam Card
Head flow comes from your head’s flow sheet. Your cam card’s top RPM beats the estimate.
Power by Cam Duration
| Duration | Peak RPM | Power |
|---|---|---|
| 206° at 0.050 in | 5,200 | 390 hp |
| 212° at 0.050 in | 5,400 | 405 hp |
| 218° at 0.050 in | 5,600 | 420 hp |
| 224° at 0.050 in | 5,800 | 435 hp |
| 230° at 0.050 in | 6,000 | 450 hp |
| 236° at 0.050 in | 6,200 | 465 hp |
| 240° at 0.050 in | 6,333 | 475 hp |
| 242° at 0.050 in | 6,400 | 480 hp |
| 248° at 0.050 in | 6,500 | 487 hp (intake) |
| 254° at 0.050 in | 6,500 | 487 hp (intake) |
Peak RPM follows COMP’s published small-block ranges, about 33 RPM per degree. Rows marked heads or intake are capped there, so extra duration adds no power.
Real Engines Lose Different Torque
| Torque Drop | Real Example | Power |
|---|---|---|
| 7% | Kaase 521 ci Boss 9 | 465 hp |
| 10% | Typical street engine | 450 hp |
| 18% | 468 ci big-block test | 410 hp |
How much torque an engine keeps up top depends on the intake, heads and exhaust. Engine Labs measured the 7% and 18% drops on engine dynos and gives 10% as the typical figure.
Camshaft Horsepower Calculator for Engine Build Planning
Cam duration decides how high an engine can pull before power falls off. The camshaft horsepower calculator turns that duration, plus displacement and build quality, into an estimated power peak. It then checks the result against what the heads and intake can support.
It suits anyone choosing between cams, sizing a cam to new heads, or checking whether a builder’s power claim adds up. The US setting works in cubic inches, lb-ft per cubic inch, hp and lb-ft. The metric setting uses liters, N·m per liter, kW and N·m, with 1 L = 61.0237 ci.
The Westech Equation Behind the Estimate
The method comes from Westech Performance dyno operator Steve Brulé, as Jeff Smith describes it in Engine Labs. It starts with peak torque, estimated from displacement and a torque-per-cubic-inch figure.
$$T_{peak} = \text{ci} \times \text{torque per ci}$$
Smith notes that naturally aspirated engines typically lose about 10% of peak torque by the power peak. So the power estimate uses 90% of peak torque at the RPM where power peaks.
$$\text{hp} = \frac{0.9 \times T_{peak} \times \text{RPM}_{peak}}{5252}$$
On the defaults, a 350 ci engine at 1.25 lb-ft per cubic inch makes about 438 lb-ft. With a 230° cam peaking near 6,000 RPM, the hero result lands at about 450 hp.
How Cam Duration Sets the Power Peak
The missing piece is the RPM of that power peak, and that is where the cam comes in. The tool anchors it on COMP’s Xtreme Energy hydraulic cams, whose published operating ranges step up in a steady pattern.
| COMP cam | Advertised | At 0.050 in | Rated RPM range |
|---|---|---|---|
| XE262H | 262° | 218° | 1,300–5,600 |
| XE268H | 268° | 224° | 1,600–5,800 |
| XE274H | 274° | 230° | 1,800–6,000 |
The top of each range climbs about 400 RPM for every 12° of duration at 0.050 in. That is roughly 33 RPM per degree, which the tool uses to place the peak for any duration.
$$\text{RPM}_{peak} \approx 5600 + 33.3 \times (D_{0.050} – 218)$$
Use the 0.050 in figure, not the number in the cam’s name. The XE274H is named for its 274° advertised duration, but the spec sheet lists 230° at 0.050 in. Entering 274 would move the estimated peak about 1,500 RPM higher before any intake limit applies.
Outside 218° to 230°, the line is an extrapolation past the published data, and the tool says so. If your cam card lists its own RPM range, switch Peak RPM From to My Cam Card Range and enter the top figure.
Picking a Torque-per-Cubic-Inch Figure
This input carries the most weight, because it stands in for heads, compression, intake and exhaust all at once. A builder on Team Chevelle rates 1.2 as pretty good for a pump-gas engine, 1.25 as very good and 1.3 as outstanding. The presets come from real engines Engine Labs tested or reported.
| Engine | Peak torque | Torque per ci |
|---|---|---|
| Chevrolet Performance LT1 crate, 376 ci | 465 lb-ft | 1.23 |
| 468 ci big-block, oval port heads | 581 lb-ft | 1.24 |
| Iron 6.0L LS, TFS heads, COMP roller | 501 lb-ft | 1.37 |
| Kaase Boss 9 stroker, 521 ci, pump gas | 730 lb-ft | 1.40 |
| Engine Masters competition engines | Varies | About 1.50 |
Engine builders on Speed-Talk put the pump-gas ceiling around 1.40, with race gas and methanol going higher. For a first build with decent aftermarket heads, 1.25 to 1.30 is the honest starting range.
When the Heads or Intake Set the Limit
A bigger cam only helps if the heads can feed it. The third card applies the flow rule from the SuperFlow bench manual, which a Speed-Talk member notes was originally 0.43 for flow at 10 in of water and becomes about 0.2575 at 28 in.
$$\text{hp}_{max} = 0.2575 \times \text{CFM}_{28} \times \text{cylinders}$$
The default 250 CFM heads on eight cylinders support about 515 hp, leaving room over the 450 hp estimate. Street Muscle showed the other side of this rule, where ported LS3 heads added only 10 hp because the stock 306 CFM heads already supported far more than the engine made.
The intake gets the same kind of cap. Edelbrock rates its Performer dual-plane from idle to 5,500 RPM and the Performer RPM for 1,500 to 6,500 RPM. When the cam wants to peak above the manifold’s range, the tool holds the peak at the manifold limit and flags it.
Where the Camshaft Horsepower Calculator Misses
The 10% torque drop is an average, and real engines spread well around it. Engine Labs’s own examples run from a 7% drop on the Kaase Boss 9 to 18% on the 468 big-block, which is why the second card gives a range instead of one number.
That 468 shows the method’s weak spot. The equation predicted about 591 hp at 5,900 RPM, but the engine made 527 hp at 5,800, so the estimate ran about 12% high. The iron 6.0L LS came much closer, at 575 hp predicted against 557 hp measured.
Big-blocks tend to peak lower than the small-block cam data suggests. One owner on the Classic Corvette Club UK forum posted dyno results for a 489 ci engine with a 236° cam and 318 CFM heads, which made 571 hp at 5,850 RPM with 606 lb-ft of torque.
With torque per cubic inch set to match its 606 lb-ft, the calculator places that engine’s peak near 6,200 RPM from duration alone and estimates about 644 hp. Entering 5,850 RPM as the cam card top brings it to about 607 hp, with the dyno range card spanning 553 to 628 hp around the real figure.
Inputs are held to 30 to 1,000 ci, 0.80 to 1.80 lb-ft per cubic inch and 180° to 300° of duration. Head flow must be 50 to 700 CFM, cylinders a whole number from 1 to 16, and a cam card top speed 2,000 to 12,000 RPM.
Picking a Cam That Fits the Engine
How much power will a bigger cam add?
Usually some peak power, paid for with low-speed torque. In a Team Camaro Tech thread, one member notes the XE274H makes about 20 hp more than the XE262H, but only at 5,900 RPM. The smaller XE262H makes 5 lb-ft more torque and reaches its torque peak lower, at 3,700 RPM instead of 3,900.
The fourth card shows the same trade for your inputs. On the defaults, 10° more duration adds about 25 hp and moves the peak to about 6,330 RPM, while the usable range starts near 2,220 RPM instead of 1,800.
Does engine size change which cam works?
Yes, and a bigger engine can carry more cam with the same manners. The same Team Camaro Tech thread offers a rule of thumb of about 5° less duration for every 25 cubic inches smaller, which is why the XE274H suits a 408 better than a 350.
That ties back to the big-block results above. More displacement per cylinder makes the same duration act smaller, so a big-block tends to peak lower on a given cam than a small-block does.
Should head flow be measured with the intake bolted on?
The 0.2575 rule was built on bare-head flow at 28 in of water. Test the same port at a higher bench pressure and the CFM figure rises, which TorqStorm warns will corrupt the result.
An intake on the head changes the number too. One Speed-Talk member measured 300 CFM on a bare AFR 210 head and 270 CFM with a Victor Jr., spacer and nitrous plate bolted on. Enter the bare-head figure, since that is what the rule assumes.