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Old 02-28-2012
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alkysbc alkysbc is offline
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Default Oil Pressure vs. HP and TQ

I know a lot of guys mess around with their total oil pressure to free up some extra power at the crank. Has anyone here messed with this on a dyno, and if so, approximately how much is there to gain? Does it take a lot of reduction in PSI to gain, or is it worth some power even with a modest drop?
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Old 03-01-2012
Roger Gates Roger Gates is offline
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Originally Posted by alkysbc View Post
I know a lot of guys mess around with their total oil pressure to free up some extra power at the crank. Has anyone here messed with this on a dyno, and if so, approximately how much is there to gain? Does it take a lot of reduction in PSI to gain, or is it worth some power even with a modest drop?
The first answer is yes to running different oil pressures - temps - viscosities for HP tests on the dyno as well as in competition. It is not really an easy question to answer, because there is more than just changing the pressure in a given build. It is hard to run a fuel engine on a dyno & test anything. We also usually run a multi stage dry sump system when possible on drag racing as well as circle track & road racing engines. I guess the application makes a difference. Small gripe {When I hear people slighting one form of racing over another ie NAZCAR vs NASCAR it is like waving a Red flag in front of a bull. All technology can in some way be used as a tool in the search for power and cross out the mistakes. There are very intelligent people in every form of racing. You don't have to slight someone else in order to make yourself feel better.} OK off the soap box.The "search for power" is the "search for power" weather it is in a Top Fuel engine or a lawnmower. In a normally asperated engine weather on alcohol or gasoline our best results seem to be higher flow lower pressures with a light - hot oil. The problem in a drag racing application is that the oil needs to be above 180/200 degrees when under a load. On our Nostalgia engines we heat the oil before running, but as soon as it starts it cools down going through the cold engine. On the dyno the oil tank holds 4 gallons of oil & is warmed to 300 degrees. There is also time after starting to bring up the temps in a controled setting. With the dry sumps we can change the pump speed anywhere from 35% to 70% of crankshaft speed which is more for the scavenging effect than supply side oil pressure which is controlled with a bypass at the point of entry & not inside the pump. By having lighter (less viscous) - hotter - faster flowing oil it is easier to maintain a higher vacuum in the crankcase up to about 7500 RPM using the scavenging which shows more power over a range because of the void the moving parts are in. Evacuating the "loose" oil is more important than controling the oil pressure to the crankshaft, camshaft & valve train shows the best results since the rotating parts have no outside resistance. With a supercharger it is beyound our capabilities to make a vacuum in the crankcase under power. On a Fuel engine if you do the Burnout with 175 lbs. oil pressure you will have maybe 60 to 80 lbs at the end of the run from heat - expansion & dilution if you are lucky. We ran a 4 cylinder Ford pushrod engine (originally designed for a tractor) with a multi stage oil pump. There was 000 wt. oil in it with every cylinder partitioned & sealed off having it's own suction section in the sump with vacuum gauges everywhere to check for air wash & ring seal. By changing the pump speed we could change the running oil pressure from the vacuum in the crankcase & top end. There is a juggling act here but with all the time spent we gained 8 HP over the whole band with 20/25 PSI oil pressure at the end point of the delivery passages. This is not a Drag engine (formula road racer) and has many restrictions, but 8 HP was significant for this little engine. In a NHRA Stock class or a bracket racer where there is basically an original oiling system higher flow - lower pressure would ultimately give the best results if everything was done right and care was taken from my experience. You just have to get it to operating temp the right way. It is very true that 90% of oiling problems originate on cold start up. I don't think it is possible to take an engine, bolt it on the dynomometer and find anything out by just changing the oil pressure. Setting up the oiling system for lower pressure is part of the engine build & not part of the tune up but could show benefits from less parasitic drag. I believe oil viscosity is at least as important as oil pressure. As an example instead of 50 to 60 wt. oil I run 0-20 off the shelf Mobile 1 oil in my blown alcohol motor with excellent results, but some people think I'm wrong. The pistons - pins - bearings - rockers - pushrods - rollers & geardrive look great so something must be OK with 35/40 PSI oil pressure. The 57 Chevy A/G nostalgia car that I drive sometimes has about 7 PSI oil pressure at idle & 30 to 35 under load at RPM but the oiling system is definately not like a normal SBC.
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