All About Engine Coatings - Are They Worth It?
Once reserved for high-end aerospace and military applications, high-tech coatings have percolated down into racing and in recent years have even become available to mainstream hot rodders. Some professional race-engine builders swear coatings offer significant horsepower gains; others dismiss any alleged power benefits but do allow that some types of coatings may enhance engine reliability. With all the hype surrounding the subject, HOT ROD decided to take a look at just what's available in the world of coatings, and-in conjunction with Duttweiler Engineering-perform an exhaustive series of dyno tests to evaluate some of the more common coatings' effectiveness when applied to a typical 1.4 hp/ci hot rod engine.
So just what are engine coatings, anyway? Basically, they are an entire family of chemical surface treatments applied to various engine components. Depending on the particular coating and the desired end result, the object is to prevent the migration of heat, radiate heat, reduce friction, shed oil, retard corrosion, or simply make the part look better. Most coatings fall into one of five broad functional categories: antifriction lubricants (lubricity coatings), thermal-barrier coatings, thermal dispersants, oil shedders, and corrosion and chemical-resistant coatings. Some coatings may fall into more than one category. For example, you might have a corrosion inhibitor that is also a thermal dispersant. Detailed composition info is a closely held secret among various competitive coating outfits, so we'll concentrate on the claimed benefits in typical applications rather than get into detailed, high-end metallurgical metaphysics.
Lubricity Coatings
Lubricity or antifriction coatings consist primarily of dry-film or solid-film lubricants that reduce friction, galling, and seizing. In some instances, this category can also help disperse heat. These coatings typically contain molybdenum disulfide or tungsten disulfide. The application method and binder technology are critical in getting the coating to stick to the metal surface in long-term use.
In the engine's bottom end, dry-film lubricants are usually applied to piston skirts, engine bearings, and the main and rod journals. On the top side, dry-film lubricants are sometimes applied to valve stems, rocker arms, pushrods, lifters, valvesprings, and cam lobes. Under heavy loads, moly-based dry-film lubricants can actually hold oil on their surfaces, enhancing the integrity of the oil film between the metal parts. These same lubricants can delay metal-to-metal contact if oil pressure is lost. Although some claim that by reducing friction, lubricity coatings should offer some power gains, normally an engine's journals and bearing surfaces are separated by the oil film and never come into contact, so it's hard to see how coating the bearings would add any power under standard operating conditions. Therefore, the main advantage is really as an insurance policy, enhancing longevity and providing emergency protection if something goes wrong.
Lubricity coatings also lower a part's temperature. Applied to upper-end parts like valvesprings, they can greatly extend their fatigue lives. Some builders claim a 15- to 30-degree oil-temperature drop, which could permit using thinner oils without compromising parts longevity. Thinner oils offer less drag, which may translate into increased power.
Oil Shedders
Usually based on PTFE (Teflon) or similar fluoropolymers, oil shedders, as their name implies, help a part shed oil to improve crankshaft windage and oil return. They are usually applied to the undersides of pistons, connecting rods, crank counterweights, windage trays, and the insides of oil pans, timing covers, and valve covers-anyplace oil isn't needed. Shedders may improve overall high-rpm engine lubrication while reducing oil temperature and can also help reduce varnish, sludge buildup, and corrosion. To the extent shedding oil may cut drag on rotating parts, power benefits are also claimed.
Thermal Barriers
In theory, heat management offers great potential for improving an engine's power output. Often, ceramic-based thermal-barrier coatings (TBCs) are used to reduce heat migration, reflecting heat rather than absorbing it. They may be applied to piston-top surfaces and top ring grooves, combustion chambers, exhaust-valve heads and faces, exhaust manifolds and headers, and inside exhaust ports.
When applied to piston tops, TBCs reflect heat back into the combustion chamber. The additional heat translates into more energy to push the pistons down. To the extent coating the piston tops makes the top surface smoother and minimizes the development of local hot spots on the pistons' surfaces, TBCs may decrease detonation potential. On the other hand, TBCs may prevent heat from dissipating down into the pistons and rings, through the cylinder wall, and into the water jacket; this may actually increase detonation potential. The tilt point is related to whether the engine will be subjected to heat over a long period (as in an endurance motor) or in short bursts (like a drag-race car). Consult your piston manufacturer for specific application advice.
Setting up a thermal barrier in the combustion chamber also helps the chamber retain heat for more power potential. Again, assuming detonation does not become a problem, this can increase combustion efficiency while lowering engine-coolant temperatures. Aluminum heads, which are said to reject heat quicker than traditional cast iron, may see particular benefits from TBCs. Barriers can also be applied to valve heads to keep them cooler.
Coating the inside and outside surfaces of exhaust parts with TBCs is said to increase exhaust-gas velocity, reducing backpressure and reversion. Coating the inside of a mild-steel header smoothes the surface by eliminating corrosion and scale, which should also enhance flow. Coating the outside should reduce ambient temperature, which may result in an overall temperature decline within the engine compartment.
Thermal Dispersants
These are the opposite of heat barriers: They radiate or disperse heat. As previously stated, keeping heat in the chamber is good provided you don't get into detonation. But if you do have a detonation problem, a dispersant could be in order. Many thermal dispersants are dual-category products. Besides their antifriction properties, dry-film lubricants often disperse heat (their use on valvesprings would be one example of dual-category use). Other, proprietary, thermal dispersants take the place of traditional black paint and are sometimes applied to brakes, intake manifolds, cylinder heads, oil pans, radiators, and intercoolers.
Corrosion Inhibitors
Corrosion is not just a cosmetic blemish. It weakens and destroys parts. Headers rust out. Aluminum intake water passages can corrode, especially on a salt-water boat. Exotic fuels like alcohol and nitromethane are also highly corrosive. A variety of coatings and electrochemical plating media exist for fighting corrosion while enhancing a part's appearance. Again, some of these coatings may have additional thermal-barrier or thermal-dispersant properties.
Building a Test Mule
With so many confusing options and coating varieties to choose from, which are most likely to provide the most benefits? The consensus is that if you want to increase engine output, putting thermal-barrier coatings on exhaust headers, piston tops, cylinder-head combustion chambers, and cylinder-head exhaust ports should offer real benefits. Placing oil shedders on the crank counterweights should reduce drag. Adding antifriction coatings to the piston skirts and main bearings provides the most engine protection, with some claiming additional power from them as well. But talk is cheap, so we got together with Ken Duttweiler and actually assembled a stroker GM LS-style engine to test the merits of these claims. The LS-style was chosen because its available sophisticated electronic engine management systems permit extremely fine control over air and spark, critical in localizing any changes in output.
The engine was built from a new bare GM Performance Parts LS2 engine block to take advantage of its larger 4.00-inch bore, but the rest of the external dress was standard Camaro LS1. With a Scat forged 4.00-inch-stroke crank, displacement came in at 402.1 ci. Scat 6.125-inch center-to-center rods swung Mahle forged pistons and moly rings. Duttweiler installed Dart's new LS1 cylinder heads, which flow up to 320 cfm out of the box, sealed to the block with Fel-Pro MLS gaskets and ARP bolts. Those two companies supplied all critical gaskets and fasteners, respectively, for the project. The final compression ratio came in at 10.2:1.
Coating the Parts
Dart Machinery applied thermal-barrier coatings to the exhaust ports, valve heads, combustion chambers, and tops of the Mahle custom-forged flat-top pistons. The remainder of the pistons plus the piston pins also got antifriction coatings. Federal-Mogul supplied two sets of engine bearings for evaluation-one set received antifriction coatings, the other didn't. Dart-applied oil shedders were used on the inside of the Moroso LS1 Camaro oil pan and windage tray, as well as on the Scat crank's counterweights.
How We Tested
Rockett Brand Fuel supplied its 100-octane racing unleaded gas for all tests. (Some stations even sell this street-legal gas right out of the pump.) Sweep tests were conducted at a 300-rpm-per-second rate on Duttweiler's sophisticated engine dyno that combines a Froude absorber with AVL control and data-logging, offering the capability for truly wide-rpm-band pulls and precise repeatability. For every test, the oil temperature was stabilized at 200 degrees F, while a GM thermostat ensured a constant 191-degree F coolant temperature. More than 188 dyno runs were made, yet ambient temperature variances were held to less than 10 degrees. Under these conditions, Duttweiler felt back-to-back runs on an otherwise identical test combo should generate no more than a 0.2 percent variance.
One-hundred eighty-eight dyno runs? You bet! Everything was backed up, backed up again, analyzed, optimized, and verified. We started with everything coated and optimum spark and fuel curves. After the best, repeatable numbers were obtained, the engine was torn down, and all thermal-barrier coatings were removed. The engine was then reassembled and tested with just the antifriction coatings and oil shedders, re-optimized to obtain the best numbers, and torn down again to remove these remaining coatings for the final, plain-wrapper test runs.
All the preceding tests were with uncoated, stainless Kooks headers. After completing the internal-coatings evaluation, the headers were sent out to Xtreme Coatings to receive inside and outside thermal-barrier protection. The headers were evaluated in this standalone fashion because this popular coating is widely available directly from header manufacturers, and it is also one process the average enthusiast can get done quickly without hassle.
Internal Coating Test
Naturally, we did not want to intentionally test the engine to destruction, so the tests only evaluated the coatings' power potential. As shown in the tables, at least in this test series, the internal thermal barrier coatings were responsible for most of the power gains. With all coatings applied, the engine was up 8.1 hp and 6.0 lb-ft over its noncoated configuration. Coated, it made 559 hp and 547.6 lb-ft compared with 550.9 hp and 541.6 lb-ft uncoated. That's about a 1.1 percent gain in torque and a 1.5 percent power gain. Overall average output was up as well.
However, with only antifriction coatings and oil shedders applied and no thermal barriers, it turns out the engine was slightly down overall compared with its no-coating configuration. But if you look just at the extreme top-end numbers above 5,700 rpm, there is a trend of increasing gains for both the full-coated regimen and the oil shedder/antifriction regimen. This indicates that coatings become more effective as rpm increases, so a 7,500- or 8,500-rpm combo might show greater improvement.
Header Coating Test
Testing coated versus uncoated headers on an otherwise internally uncoated engine showed no statistically significant changes in overall torque and power output, although the engine was up a couple of numbers in the midrange. It could be that stainless steel headers are just less sensitive to thermal-barrier coatings than typical mild-steel headers. In any event, ambient temperatures with a heat gun in the vicinity of the headers did show a 200-degree-F temperature drop near the pipes at the pipe surface. Although the dyno numbers don't reflect this drop, in a tight engine compartment not using cold-air induction but rather ingesting inlet air from inside a hot engine compartment, a reduction in exhaust-radiated heat could translate into a big power gain: On a normally aspirated engine, every 10-degree-F inlet air temperature decrease increases engine power by about 1 percent. Even if the air were only 50 degrees cooler by the time it got into the inlet tract, that's a 5 percent improvement.
Chuck Jenckes, a leading engine development engineer, has a novel theory on the effects of header coatings on engine output. He says if you see a performance improvement from header coatings, it is not directly due to an exhaust-gas velocity change from temperature alterations. Instead, according to Jenckes, it's related to Mach number. "The speed of sound is dependent on temperature. As you change gas temperature, you change the effective tuning length of the header. Sure, velocity may increase, but it doesn't change the mass-flow rate." In other words, a change in the speed of sound changes the characteristics of the exhaust pulses. Under this theory, even greater gains might be realized by redesigning the headers (altering the pipes' tuned length) to take maximum advantage of any temperature change.
Are They Worth It?
The accompanying table shows how much Dart charges for the major internal coatings in our engine. Doing everything totals around $850 with Dart's package discount or nearly $110/hp gained. Coating the headers at Xtreme will lighten your wallet by another $150-$225, depending on the length of the headers. Based strictly on the raw generated dyno numbers, I would have to say that-at least at this performance level-the typical street car or dual-purpose drag racer not constrained by sanctioning-body rules limitations would achieve far more significant gains by spending the money on a better cam or cylinder heads. Jenckes added, "The average guy would be better off just spending extra time in engine assembly. Spend some time degreeing the cam, for example."
On the other hand, an 8hp gain on a Nextel Cup 550hp restrictor-plate engine would be a really big deal.
Do it Yourself?
Most of the manufacturers sell do-it-yourself versions of their coatings that in theory can be applied by the average end user at home. For occupational safety and environmental reasons, however, the retail version of the product may not be the same as the professional version. There is also the problem of maintaining quality control under austere installation conditions. Professionals maintain that achieving optimum application spray pressures and dispersion patterns, controlling the critical thickness of the coating layer, and properly baking it for a precise amount of time at a carefully controlled temperature-as is required by many high-tech coatings-is difficult if not impossible for the average home user. Especially important is film thickness and bake temperature, both to ensure coating effectiveness and longevity. Usually a special industrial oven capable of heating parts to a regulated 500 degrees F is used. Still, some home users swear by their home-brewed results, and home-coating will save some bucks.
Supercharger Test
Thinking maybe the more power an engine puts out, the more benefits it could see from coatings, Duttweiler also made some runs with the new Magnuson Eaton 122 high-tech supercharger and manifold package bolted in place of the normally aspirated setup. The engine was tested with the supercharger, all internal coatings applied, and uncoated headers, then later with no internal coatings and coated headers (since the latter had proved basically a wash in terms of affecting the engine's peak dyno output). Without internal coatings, the supercharger itself was worth about 214 hp and 191 lb-ft at the peaks compared with the normally aspirated configuration. With internal coatings, the supercharger gained 7.3 hp and 11.5 lb-ft for a peak of 771.9 hp and 764.6 lb-ft output on 11.8-psi boost. More significantly, average numbers were up by more than 10 as well.
BLOWER DYNO RUNS COATED
HEADERS ONLY ANTIFRICTION,OILSHEDDERS
,THERMAL BARRIERS SPEED TORQUE POWER TORQUE POWER (RPM) (LB-FT) (HP) (LB-FT) (HP) 3,500 660.4 439.9 688.7 459.0 3,600 665.6 456.2 694.4 475.9 3,700 671.4 473.0 699.2 492.6 3,800 677.5 490.3 703.1 508.8 3,900 684.1 508.1 706.4 524.6 4,000 690.9 526.3 709.5 540.4 4,100 697.8 544.9 712.9 556.5 4,200 704.7 563.7 716.9 573.2 4,300 711.3 582.4 721.5 590.6 4,400 717.4 601.1 726.6 608.7 4,500 722.7 619.3 731.8 627.1 4,600 727.1 636.8 736.7 645.4 4,700 730.4 653.6 740.7 663.0 4,800 732.4 669.2 743.4 679.6 4,900 732.8 683.6 744.3 694.5 5,000 731.8 696.6 743.2 707.5 5,100 729.3 708.1 740.1 718.5 5,200 725.2 718.0 735.0 727.5 5,300 719.8 726.4 728.3 734.7 5,400 713.2 733.4 720.4 740.6 5,500 705.7 739.1 711.9 745.5 5,600 697.4 743.7 703.2 750.0 5,700 688.6 747.4 694.7 754.2 5,800 679.7 750.6 686.6 758.5 5,900 670.8 753.5 678.7 762.5 6,000 662.1 756.3 670.7 766.1 6,100 653.7 759.1 662.0 768.6 6,200 645.3 761.7 652.2 769.6 6,300 636.8 763.8 641.3 769.3 6,400 627.4 764.6 630.7 768.9 6,500 616.1 762.7 623.6 771.9
NORMALLY ASPIRATED DYNO RUNS INTERNAL COATINGS, UNCOATED HEADERS NO COATINGS
(BASELINE) ANTIFRICTION,
OIL SHEDDERS ANTIFRICTION
OIL SHEDDERS,
THERMAL BARRIERS, COATED
HEADERS
ONLY SPEED TORQUE POWER TORQUE POWER TORQUE POWER TORQUE POWER RPM LB-FT HP LB-FT HP LB-FT HP LB-FT HP 2,000 418.4 161.2 414.7 159.8 421.8 162.1 409.4 157.3 2,100 410.9 163.0 405.7 160.9 414.5 164.7 407.7 162.1 2,200 410.6 169.9 404.6 167.3 414.1 171.8 410.1 170.2 2,300 415.2 180.2 408.9 177.4 418.6 182.0 415.3 180.5 2,400 422.9 192.5 416.6 189.7 426.1 194.2 422.4 192.4 2,500 432.1 206.0 425.8 203.1 435.0 207.3 430.6 205.1 2,600 441.6 219.7 435.3 216.7 444.3 220.8 439.0 218.1 2,700 450.5 233.1 444.2 229.9 453.1 234.1 447.2 231.0 2,800 458.2 245.8 451.9 242.4 460.8 246.9 454.7 243.6 2,900 464.4 257.7 458.1 254.0 467.1 258.9 461.2 255.7 3,000 469.1 268.7 462.7 264.9 472.0 270.2 466.7 267.3 3,100 472.3 278.9 465.9 274.9 475.6 280.8 471.1 278.3 3,200 474.3 288.5 467.9 284.5 478.0 290.8 474.4 288.8 3,300 475.3 297.7 469.1 293.7 479.5 300.6 477.0 299.0 3,400 475.9 306.8 469.8 302.9 480.6 310.2 478.9 309.1 3,500 476.3 316.1 470.5 312.3 481.5 319.9 480.5 319.2 3,600 477.0 325.7 471.5 322.1 482.5 329.9 482.1 329.4 3,700 478.2 336.0 473.0 332.6 484.1 340.4 483.7 340.0 3,800 480.2 347.0 475.3 343.7 486.3 351.5 485.8 351.0 3,900 483.1 358.9 478.5 355.6 489.3 363.4 488.4 362.6 4,000 487.1 371.6 482.6 368.2 493.3 376.1 491.7 374.9 4,100 492.1 385.1 487.6 381.6 498.1 389.5 495.7 387.7 4,200 498.0 399.4 493.3 395.7 503.7 403.6 500.5 401.2 4,300 504.5 414.3 499.6 410.2 509.8 418.3 505.8 415.2 4,400 511.4 429.6 506.2 425.0 516.4 433.5 511.5 429.6 4,500 518.3 445.0 512.8 440.0 523.1 448.8 517.5 444.2 4,600 525.0 460.2 519.1 454.8 529.5 464.1 523.4 458.9 4,700 531.0 475.0 524.8 469.4 535.4 479.1 528.9 473.4 4,800 535.9 489.2 529.6 483.3 540.5 493.6 533.8 487.4 4,900 539.5 502.3 533.3 496.5 544.4 507.2 537.6 500.8 5,000 541.4 514.2 535.5 508.7 546.8 519.7 540.1 513.1 5,100 541.6 524.7 536.3 519.7 547.6 530.9 541.0 524.2 5,200 539.9 533.5 535.4 529.3 546.6 540.4 540.1 533.7 5,300 536.3 540.6 532.8 537.3 543.6 548.1 537.4 541.6 5,400 530.9 545.9 528.5 543.6 538.8 553.8 532.7 547.6 5,500 523.9 549.3 522.6 548.0 532.1 557.5 526.2 551.5 5,600 515.6 550.9 515.3 550.5 523.7 559.0 518.1 553.4 5,700 506.2 550.8 506.6 551.0 513.9 558.5 508.5 553.2 5,800 496.2 549.2 496.9 549.6 502.9 556.2 497.9 551.0 5,900 485.6 546.1 486.3 546.5 491.1 552.3 486.5 547.1 6,000 474.6 541.7 475.1 542.2 479.2 547.5 474.6 541.9 6,100 463.2 536.4 463.7 537.3 467.6 542.5 462.4 535.7 6,200 450.8 530.4 452.7 533.0 457.0 538.4 449.8 529.3 6,300 436.6 523.9 442.4 531.0 448.2 536.7 436.3 523.4 6,400 442.3 539.4

Photo Gallery: A Look at High-Tech Engine Coatings and What They are Worth - Hot Rod Magazine



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