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This post focuses on reducing emissivity of heat from exhaust manifolds through application of high performance ceramic coatings to increase available engine power, increase engine efficiency and to reduce emissions.
The proliferation of plastic engine bay components, as they age, become brittle over time and, moreover through heat cycling, thereby increasing opportunity for damaging something simply by touching or removing it.
Heat kills batteries:
Car battery (life) expectancy zone suggests heat significantly reduces battery life. This chart is consistent with a starting battery located in engine bay without thermal barrier. Considerable battery heat soak in LS400.
The radiator is always a source of heat to its environment, here returning a stream of heated airflow over the engine from which it was just removed....
Engine radiator cooling fans push exhaust manifold heat down and away from the engine compartment.
The LS400 thermal fan clutch incorporates a forward facing bi-metal thermostatic coil that measures downstream radiator heat to activate fan clutch, or not...thus it cannot sense heat at rear of engine compartment, including that emitted by exhaust manifolds
Reducing underhood temperatures increase engine power without decreasing engine efficiency or increasing emissions.
Raising the hood after operating or especially after running at highway speeds, suggests auto manufacturers left room for improvement in the thermal management department.
Upon shutdown, engine cooling systems stop circulating air and coolant, thus cannot dissipate accumulated heat from engine, resulting in increased thermal load into the engine compartment.
Heat is transferred from the hot components within the engine compartment by natural convection to the surrounding air and by radiation to the adjacent surfaces. The heat is then dissipated to the ambient mostly by convection from the exterior surfaces. This causes a temporary rise in air temperature of the engine compartment, which could damage thermally sensitive components by approaching their critical design temperature and causes more heat transfer to adjacent surfaces.
The exhaust manifolds contribute significantly to this phenomena in the tight confines of engine bay...like an oven. You could literally bake a potato.
Effective thermal coatings and barriers increase production costs, which explains why auto manufacturers have not done more.
Ceramic coatings can be applied to exhaust manifolds to reduce the amount of heat radiated into the engine bay. This heat reduction helps prevent intake manifold heat soak, which will decrease the temperature of the air entering the engine improving charging efficiency of your engine's air intake system:
Temperature Drop vs. Torque Increase chart courtesy of David Vizard.
One example: Toyota/Lexus sandwiched resin between metal intake manifold gaskets on the 1998 LS400 to ibetter nsulate the intake manifold from cylinder head heat.
Exhaust manifolds and catalytic converters employ heat shields, however shielding effectiveness is limited by barrier materials, coatings (if any) and coverage area.
Exhaust shields help, but do radiate heat into the engine compartment, so not the optimum solution.
As with NVH (noise vibration, harmonics) reduction, containment or isolation works best closest the source.
So too with exhaust manifold heat that it is never allowed into the engine compartment in the first place.
This can be accomplished through application of ceramic thermal barrier coatings from within and without the exhaust manifold tubes.
In addition to ceramic coating the exhaust manifolds, our exhaust manifold heat shields can also be ceramic coated to further contain exhaust manifold heat.
My 1999 LS400 exhaust manifolds were professionally sandblasting before dispatching to Jet Hot's coating facility in Oklahoma.
Jet-Hot is a recognized top tier supplier of engineered thermal management solutions:
https://www.youtube.com/watch?v=qC_LQa9a7yQ
OEM headers before cleaning and sandblasting. Very good condition for 175,000 miles and 20 years. After cleaning and sandblasting by Ace Sandblasting, Chicago.
There are numerous ceramic coating operations in Chicago....
None were proficient with ceramic thermal barrier coating application nor ceramic insulating properties.
We have enough collective manufacturing to build tanks in Illinois, but not apply thermal barrier coatings.
Research brought me to Jet-Hot's production facilities.
Jet-Hot reported reductions of underhood temperatures up to 50% through application of thermal coatings to exhaust manifolds.
The added benefit of containing heat within the exhaust manifold through coatings is faster warm-up of catalytic converters, improved exhaust scavenging...so the engine does not work as hard to eject exhaust, cooler engine operating temperatures means the cooling system does not work as hard...
Jet-Hot's ceramic coatings are commonly applied to premium exhaust headers.
Ceramic coatings reduce cooling of the exhaust gases in exhaust manifold.
There are multiple processes at work in transferring heat from a moving exhaust stream to the engine compartment air.
From inside to outside the header:
1.) exhaust gas to inner wall of header : forced convection and radiation paths in parallel.
2.) if ceramic coated inside header: conduction thru a relatively thin, but effective, insulator.
3). conduction through (stainless) steel header tube wall.
4.) if ceramic coated on outside of header: conduction thru a relatively thin but effective insulator.
5.) outer wall of ceramic coated header to engine bay air: free convection and radiation in parallel paths
The total heat transfer path thermal resistance is the sum of 5-component thermal resistances listed above.
After combustion heat has performed its role in the combustion chamber, it exits the exhaust port and into the exhaust header or manifold. If exhaust gases cool they lose velocity and the scavenging effect is diminished. Through insulating the exhaust system, exhaust gases inside pipes are maintained at the highest possible temperature resulting in increased exhaust gas velocity and higher efficiency.
Hotter, therefore lighter exhaust pulses travel faster at higher pressures down the tube.
Ceramic coatings increase the speed and maintain the quality of exhaust gas flow.
Ceramic coating your exhaust headers promote smoother laminar flow of exhaust which increases horsepower.
Less back pressure is achieved by reducing the need for the exhaust gas to turn back onto itself .
This allows for more efficient release of exhaust in a performance improving manner.
Insulating the tubes as they come out of engine to the collector can result in performance increases ranging from 5% to 15%.
In an internal combustion engine, scavenging is the process of replacing the exhaust gas in a cylinder with the fresh air/fuel mixture (or fresh air, in the case of direct-injection engines) for the next cycle. If scavenging is incomplete, the remaining exhaust gases can cause improper combustion for the next cycle, resulting in reduced power output.
Remnant exhaust gasses are extinguishers...both crowding the combustion chamber so that the new intake charge can not occupy it, and contaminanting an equal portion of the fresh mixture, rendering it useless as well. In internal combustion engine parlance this is called a "residual fraction".
Naturally aspirated engines typically see 7% to 12% Residual exhaust gasses in the chamber, thus, this is why actual volumetric efficiency readings are seldom read over 88% uncorrected on engine dynos.
Will post "before" and "after" readings when manifolds are reinstalled.
New exhaust headers arriving for processing at Jet-Hot. Jet-Hot's oven to remove residual surface contaminants. To achieve selective coating, parts can be masked or plugged through various means. Bead blasting insures durable adhesion and uniformity of ceramic coating. Polishing media tank. After polishing Polished and unpolished headers. Ceramic coating color options
Application of ceramic coating Ceramic coating is baked at over 600 Fahrenheit to insure durable finish results... Baking at 125 Fahrenheit in a paint spray booth does not cut it. None of the ceramic coating vendors in Chicago offered 600 Fahrenheit curing.
1999 LS400 Exhaust manifold heat shields after bead blasting by Jet-Hot. Although exhaust manifolds were bead blasted before shipping to Jet-Hot, due to their high quality and finishing standards, elected to refine (blast).the finish further before next phase application of precoat finish, suggests pride in workmanship.. 1999 LS400 Exhaust manifolds after application of precoat finish
Am installing 3UZ-FE engine from LS430 in my 1999 LS400.
The Jet-Hot coated exhaust manifold/headers and exhust manifold shields are installed with the cylinder heads, and, or, engine block removed from engine compartment.
Images of 3UZ-FE (LS430) engine with Jet-Hot coated LS400 exhaust manifolds and shields installed:
Jet-Hot coated exhaust manifolds and shields will significantly reduce underhood temperatures Very durable coating. The valve covers and front cam pulley covers contrast drab by comparison. Polishing will resolve this.
Looks really good, your LS400 will be very unique and cool when this is completed. Its good that the coated ones fit onto the 3UZ. Good luck with everything.
Nice, I did the same to the long tubes in my other car and hand wrapped them on top of the coatings as well. I can hold the primary's for 2-3 seconds after a four runs and not get burned
Exhaust manifold shields-temperarure readings after Jet Hot coatings
The LS430 (3UZ-FE) engine is behaving well in the LS400 engine bay.
The LS400 exhaust manifolds and Exhaust Shields were ceramic coated by Jet Hot before mounting on 3UZ-FE engine.
The result is a remarkably cooler engine compartment...all with a larger displacement engine.
Temperature readings were taken atop the left and right side exhaust manifold shields using a laser thermal gun.
Thermal reading atop left side exhaust heat shield before application of Jet Hot coating.. 301 Fahrenheit. (1UZ-FE)
Thermal measurement atop left side exhaust manifold heat shield after 70.MPH highway driving is impressive 101 Fahrenheit. (3UZ-FE) Thermal measurement atop right side exhaust manifold heat shield after 70.MPH highway driving is 102.5 Fahrenheit. Cool !
11-06-19, 09:09 PM
Thermal management - exhaust manifold coatings
