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Oil pressure as it relates to efficiency

  1. Oct 16, 2012 #1
    I know a guy that is really big into hot rods. He's got a late 80's model firebird with a custom engine in it. Dudes got probably got between $15-20k in the engine alone. It puts out somewhere just over 1000 hp, and he's done all the work on his own, so I feel inclined to believe the guy. But I really want to know how this makes sense as he didnt offer much explanation.

    He says a lower oil pressure is better as far as performance goes, because with the higher pressure, the higher youre putting it up in the block essentially. Which if I understand correctly, means you would be putting a lot of oil on the valves, springs, rockers, etc. whereas with lower pressure you would be keeping the oil lower on the cam, pushrods, etc.

    is this the case? and if so how does this positively or negatively effect the performance of the engine?
  2. jcsd
  3. Oct 17, 2012 #2

    Ranger Mike

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    you had best carry 10 psi oil pressure per RPM you are turning...if you plan on cranking the engine to 7000 RPM you better have at least 70 psi oil pressure. Proper oil managament is critical in a race prepared engine bacuse you are providing lubrication and cooling. You need to make sure oil squirts from the connecting rod bearings to tjhe bottom of the piston to oil the wrist pin and carry off heat from the piston. You need to oil the valve springs and this is done by proper pressure on the top side. You need to make sure the oil is not getting airated and turn to foam when passing through thelifter galleries. Normally an engine can be hot rodded to put out one horsepower per cubic inch and in some cases 2 HP per cube. So a home built small block chevy can be bored and stroked to maybe 400 plus cubic inch and put out maybe 800 HP but unless major $$$ are used in the engine case modifications it will not last. my opinion..
  4. Oct 17, 2012 #3
    Agreeing with Ranger Mike and continuing the discussion:

    Your friend has little understanding of the science behind what he has done with his engine. It is not hard to get 1000 hp out of an engine. You can buy everything you need out of a catalog, and your machinist will know what to do when you bring the parts in for rework.

    Every competent mechanic knows how to do this, but few have an understanding of the science behind it. They think they do, but they don't. It is actually quite amusing to ask them how something works and listen to what comes out of their mouth. It frequently violates fundamental laws of physics. The mechanics you meet on these forums are a delightful exception. They typically understand the science very well.

    You need good oil flow to the entire engine. More than just lubrication, the oil keep things cool and clean.

    One thing that is sometimes done is to increase clearances between moving parts, or at least to adjust them to minimum material conditions of the drawing tolerances. That reduces friction and heat. It may also reduce oil pressure by reducing flow resistance. If that happens, it would be good to install a higher capacity oil pump to maintain proper oil pressure.
    Last edited: Oct 17, 2012
  5. Oct 17, 2012 #4
    Awesome stuff, thanks for the great replies! That pretty well cleared up every question I had! You guys rock
  6. Oct 18, 2012 #5
    Ranger Mike's information on the small block Chevy caused me to think of a friend of mine who has a local reputation of building the hottest engines. Most go into racing airboats, but some into NASCAR races. It is common for him to spend 50K on parts and machine work. He is also an excellent example of how a mechanic can do awesome things with an engine with no understand whatsoever of the science.

    He will rework the Chevy engine to accept a Chrysler crank, which he has also reworked. He has a very elaborate explanation as to why that is such a good idea and will spout a plethora of pseudo science to explain why, all of which contradicts rational thought based on real science and engineering. None the less, I watched him test a small block Chevy on a dynamometer and it peaked at 1375 hp. His customer paid a huge amount of money for it and blew it up in his first race because he tried to push it beyond that.

    So how can anyone so ignorant of real science perform so well as a race engine builder? It is through 45 years of trial and error, with a heavy emphasis on the trial and testing. He knows what has worked, and what has not worked. With that empirical knowledge base, he does well. He stays in business because his customers win races.

    I’m a design engineer who does engine work. Mostly gas turbines and jet engines, with a great deal of diesel experience in the past. Once in a while when I was hungry enough I accepted work for spark ignition engines, but they don’t excite me much. One customer had a gas turbine used in military helicopters and other military applications that had been getting 4000 hp. The customer wanted 5000 hp. So they hired us to figure out how to do that, and we did it. It is pretty easy to “soup up” a disposable engine to incredible power levels. But to do it while maintaining the original engine life requires many thousands of engineering man-hours expended by a dozen different disciplines. Several brilliant men with PhD’s helped in the effort. We had to use a materials knowledge based gained at the expense of decades and hundreds of millions of dollars of testing and development. It is not ignorant back yard mechanics.
    Last edited: Oct 18, 2012
  7. Oct 19, 2012 #6

    Ranger Mike

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    i can tell you one thing..1375 HP from a stock small block chevy block based engine is insane and short term at best. The stock engine case ( block) will not hold up. The crankshaft mains wont take it. The cylinder deck is not thick enough and the cylinders them selves will have so much harmonics that they will blow out. You can spin the engine up on a dyno one time maybe but those kind of numbers will not hold up. The basic design of the crank main caps are such that the splayed four bolt main design just wont hack the big numbers. You may get a way with a crank web girdle but the caps will eventually start to " walk " once you pass 850 HP and that is half just over 50 % of the top end number ( 1375)r. Unless this is an after market block specialty cast to be stroked and poked to bug cube numbers and thus has special cross drilled main caps, thicker cylinders and thicker deck, no way wil it last...this original block was made to take 50 hp per cylinder max and you are dumping 170 hp per cylinder on it...ouch
  8. Mar 29, 2014 #7
    I'm not sure what a Naturally aspirated Chevy will take, but do the math on this Buick I used to own, 3750 pound car, 455+.040, best 7.003 ET 1/8 mile times, built on a picnic table in the backyard. My freind has a about a 5500 pound Buick Estate Wagon, it's kinda high tech for a street car, twin turbos, DPI EFI. It was runnning 8.03,1/8 mile a few years back, I think he's into the high to mid 7's now and its still streetale and looks like your grandmas car. The lubrication system on Buick 455 is about as bad as engineering as it get from a performance standpoint. There's a guy near here that does testing for several NASCAR teams. He's was working on some low pressure oiling systems that increase flow but at a lower parasitic HP loss. I've saw a few "test" SVO Ford engines "fly apart" a few years back during testing. Stock blocks can take a beating if prepped right. Rule of thumb for a 455 Buick, if you go over 6000 rpm and make over 600HP, go ahead and start saving to build another one, you riding on borrowed time, I know, been there, done that.
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