Many still think gas engines are the only true performance package out there and that diesel engines are simply work horses. By definition, all performance engines (diesels included) are dynamically self-driven air pumps who’s power and torque are regulated by volume of air, velocity, swirl and stable fuel that is non turbulent in the inlet track. The inlet track includes head(s), manifolds, any type of air cleaners and air box plumbing for the turbocharger and turbo itself. All engines running on gasoline, methanol, propane, nitro methane or any other alternative fuels rely on good, stable and plentiful airflow volumes, and homogenous fuel mixtures in the runners. Inline diesels like International, John Deere, Kabota, Massey Ferguson, Cat, Cummins, Fords, etc, bigger valves and/or smaller valve stem diameters really do not help that much in turbo engines and we have tried nearly all combinations. But for normally aspirated diesel engines, some power gains are achieved using larger valves and smaller diameter stems.
Unlike non-turbocharged engines, turbo diesels like big ports with lots of volume but they really like velocity. So, smaller valves enhance velocity of the intake runner. Excessive porting and polishing of the inlet track, heads and manifolds are very crucial and important on these older heads (Figure 1, above). Sonic testing of ports is very important to make sure port walls are not getting too thin. When port walls get too thin they can flex, crack and heat up causing rich and lean running conditions in the engine. If you are running short distances like truck or tractor pulling, drag, dirt or mud bogging I recommend you fill the cylinder head water jackets with hard block or a good cast iron high heat epoxy. Always let the hard block material set up and cure for 21 days before final porting and valve job is completed. The thinnest intake runners or valve bowls should be is .110”.
The most interesting thing we have found through both wet and dry flow testing is how important the valve job seat angles, undercut widths and top cut angles above the primary seat angle are. A 30 degree inlet seat angle is something I do not recommend and absolutely no radius intake valve seat machining. A radius on the intake seat shows really good dry flow numbers but in wet flow dynamics and testing, it is a disaster (Figure 2, page 28). You must have sharp distinct angles on the intake valve seat to shear incoming fuel to eliminate vortices that try and form in the quench area of the engine. On all heads that have a flat quench in the valve seat area, unlike the later John Deere engines with a small chamber, I recommend you grind one into the head (Figure 3, page 28). It wakes up all these in line diesel engines like you can’t believe. I do recommend a primary exhaust seat cut and a full radius below the primary seat cut (Figure 4, above). This helps to increase and maintain a higher velocity out of the exhaust port. We all know the higher velocity in an exhaust port, the easier it is to spool up your turbo(s). Valve seat angles and size of the throat dimension is very critical. Use of 89% to 90% of the valve diameters on the intake side and 91% to 92% on the exhaust side really seems to work well even though dry flow bench testing shows that you may lose some cfm and velocity of airflow on the exhaust side. But the engine really likes it better that way. We have tried this on and off the dyno in a double taste test and it always works.
There is a lot of talk and controversy about 45 degree, 50 degree and 55 degree valve seat angles in diesel engines plus a very steep top angle cut of 39 degree, 46 degree and 50 degree. Well, with years of dry and wet flow testing, the steeper valve seat angles on both intake and exhaust seem to make more power and torque plus a much cleaner burn in the engine (Fig 5, above). Wet flow dynamics has proven this hands down (Fig 6, above). Through proper cylinder head porting procedures, sonic testing, combustion chamber design and correct valve seats angles, widths, undercuts and top angles, you can increase airflow between 80 and 120 cfm on nearly all in-line 6 cylinder heads. Valve seat cutter tips take years to design and perfect. A lot of people still rely on what they think is a high performance valve job using three angles 30 degree, 45 degree and 60 degree. Compared to today’s standards, a three-angle valve job is like wearing high top shoes. A five to seven angle valve job on most high performance heads is worth 25 to 35 cfm and usually the same horsepower. Remember head porting is an art and not a science. Good porting and valve work will put you in the winner’s circle. All you V8 and V6 diesel engine owners; all things mentioned in this article apply to you especially the top cuts and combustion chamber shapes. Good chamber shapes, sharp edges in the quench areas help shear the vortices to create more power and torque.
Engine coatings have been a great performance gain and longevity especially in the upper end of the engine. Use of Cermet coating on piston tops, combustion chamber area and valves has eliminated a lot of piston burning, ring land damage and burnt valves. Piston skirt with a high lubricity disulfide surface coating has eliminated piston scuffing. Coating exhaust port runners, turbo, and turbo pipes plus related hardware has eliminated heat, exhaust carbon build up in the runners and leaves a cooler running valve train. Coating undersides of the piston helps oil shedding resulting in a cooler running piston. This coating also works on rods, cams, lifters, timing gears and cranks. You can pick up between 20 and 50 horsepower with engine coatings.
Oil additives properly made and tested are very beneficial to performance diesel engines as well. They allow up to 57-degree reduction in internal engine heat and a large reduction in friction. The bearing and piston scuffing is reduced dramatically. Many years of dyno and track testing has proved engine coatings and additives are basically free horsepower and torque when added to your already best built engine you can build.
Joe Mondello has been involved in quality head porting and R&D at a time when Ed Iskenderian, and a few others started a high performance industry. Joe has been so successful that his tech manual was given a GM part number. Joe is an innovator and educator of the highest order. When he could have sat on his laurels, Joe chose instead to start a Tech Center in Crossville, Tennessee holding classes for any who desire to learn air flow secrets that took Joe a lifetime to find out.
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