LET'S GET BACK TO BASICS
I feel this is a necessary topic because I have been reading some postings online that can make a guy just shake his head in amazement. Even when talking about high performance street engines like I am here, we need to pay attention to detail. Everybody loves talking about cylinder heads and camshafts, but if you have no oil pressure, rocker arms that roll of the edge of the valve, or piston rings with .030" ring gaps, those nice new expensive components won't do you much good.
Here's the first thing to remember as far as I'm concerned: On higher performance and very large displacement engines, the basics become even more important because we are dealing with greater cylinder pressures and in some cases, higher rpm. Both of which will push components to their limits and our mistakes can be very expensive--- or if we're lucky, just give us something to laugh about with our friends later!
Let's think about the oiling system for a moment; The hydrodynamic wedge developed by the oil pump and spinning crankshaft must be maintained AT ALL TIMES at a pressure that is useful! I say that because too much oil pressure causes a condition called bearing wash where the oil just blows through the bearings and doesn't support the journal effectively. Oil FLOW should be a priority! Clearances that are too loose paired with an oil viscosity that is too light can be a problem... as can too thick an oil with clearances that are on the tight side. On a typical naturally aspirated street/strip Pontiac that most are building, 60-80lbs is enough... if you could take that reading AFTER the mains are supplied that would be great, but the next best place we have readily available to us is next to the distributor pad vs the typical location on the oil filter mount. If you are building your own engine(s), take a common sense approach and LOOK at the oiling system from the pump to the bearings and beyond. I guarantee you will see some things that can use some attention. There are some VERY knowledgeable racing engine builders that do some creative things to make their engines last at higher rpm.
Another thing to consider when it comes to oiling is the type of lifter to be used. Hydraulic lifters meter the amount of oil delivered to the top end whereas most solid lifters do not... check with your manufacturer. That brings us to restricting the oil to the top end, some builders like restricting oil at the lifter bore oil feed hole by tapping the hole and inserting a drilled stainless steel setscrew for the proper sized orifice. I must say I personally have never tried it, but I have heard of too many guys having lifter problems and I wonder if a lack of oil could be a contributing factor--- it just makes me uncomfortable, and if I am going to warranty an engine, then I need to be comfortable! However, there are gentlemen that say they have done it for years and never had a problem. Well, I on the other hand, prefer to restrict the pushrod; Smith Bros. offers pushrods with .020" and .040" oil holes. I prefer to restrict oiling AFTER the lifter gets all of its oil because the lifter body depends on the pressurized oil delivered to the lifter bore and any splash lubrication that may luckily come in contact with it. Ultimately, do what makes YOU feel comfortable.
Piston rings - gap them according to the manufacturer's recommendation and you probably won't need that vacuum pump anymore. Hopefully you can sell it to a racer making around 2 horsepower per cubic inch. Regardless of the displacement when using a factory block, well over 600HP/TQ has been achieved without a vacuum pump. If you are pressurizing the crankcase, I would look at my piston ring end gaps.
I have a 467 in the shop now that was rebuilt by a another shop. The owner says it was pushing the dipstick out under load so he installed a vacuum pump.
It didn't have many miles on it at all.
When the lower end of an engine is subjected to a depression, the air is removed, taking away the "vehicle" in which oil can be entrained around a spinning crankshaft; leaks are minimized as there is no, or less, pressurize to push oil past the gaskets and seals, and there is a greater pressure differential above and below the compression ring.
To be fair, a race engine that is built to utilize a vacuum pump will have loose piston ring end gaps as they are trying to maximize pressure differential... at very high rpm (or more to the point, high piston speeds) where ring flutter can occur.
The application of vacuum pumps on street engines brings us back to the subject of 'how much displacement do you need'--- because I believe they are related; the AIRSPEED developed in the intake tract from a 4.5" stroke is tremendous. At 5,000 rpm, it is something along the lines of 3,750 feet per minute, whereas a 400 can rev to 6,000 rpm for that same piston speed. Of course, those are mean piston speeds and not instantaneous velocities that are subject to rod length. But anyway, as the piston reaches 73-75 degrees ATDC, peak piston velocity is realized and cylinder demand is at its highest. If the intake tract is restrictive, then the piston has to try to pull against that restriction as it descends down the cylinder and back up again as it tries to push out the exhaust. There is a term for that... it's called "pumping losses".
Some velocity is good, in fact, if you don't plan to rev your engine past 5,000, then you want all the velocity you can get. But if you are looking for some rpm, then you will be needing some port size.
Port sizing leads us back to the question, "how will the car be used?"
A dedicated drag car will have a different cam and induction requirement (among other things) than a stock- or circle track car. Some may think, "horsepower is horsepower--- Right?"
In my opinion, no.
It isn't so much peak power, but the entire power curve. If one is after a peak number, then very often, low end power is sacrificed. That may not be a big deal if you are using a very large engine, but for smaller displacement engine, that can be a deal breaker! I can't stress this one enough, on a street/strip type build, if you keep your midrange torque and shift recovery point in mind, and actually build your engine to exploit that, your car will be faster! Also consider making your "target" peak power 500 to 1,000 rpm BEFORE your redline so your engine can spend more time (in rpm) making peak power.
Now, here's the cool thing. If your valvetrain and induction are right, as far as I'm concerned, your power won't nose over, at least appreciably. Here's why, you're making torque, and you DON'T ALLOW THE TORQUE TO DROP OFF FASTER THAN RPM RISES. THAT'S IT!
How do you do that? It takes a complete combination. If we start at the point the air and fuel ends up--- the combustion chamber.
Run as much compression as your fuel allows that is easy to attain-- easy in the sense that you do not have to excessively mill the head, changing manifold/cylinder head alignment.
Realize that just because an engine simulation software program says a certain size port will "choke" at a given rpm, doesn't mean your engine will just shut down at that rpm--- ESPECIALLY IF YOU CAM IT ACCORDINGLY!!! E-mail us @ email@example.com if you need assistance.
Make sure your pushrods are the proper length. That can be as simple as taking a marker and coloring the top of the valve stem, installing an adjustable pushrod and rocker, setting the preload or lash, and cycling the engine a couple of times. Remove the rocker arm and check the witness mark. It helps to actually watch the motion of the rocker arm as you do this. Too short of a pushrod (in the closed position) will have the rocker tip offset significantly toward the intake manifold side... too long will have it toward the exhaust side. Make the appropriate adjustment by lengthening or shortening the pushrod and check it all over again. Ideally, at zero lift and full lift, the rocker will be in the same position on the valve stem or just SLIGHTLY biased toward the exhaust side at full lift.
Since we are talking about pushrods, get some good chromemoly pushrods--- even for a supposedly mild hydraulic roller--- if you are staying with 5/16" diameter, then move up to the .116" wall. If you need help finding them, contact us and we can get them for you.
If your engine won't see more than 6,000 rpm, consider a big dual plane manifold like the RPM. Port match it because you don't want an undersized manifold runner causing turbulence at the gasket surface. Airflow studies have shown that vortices develop when air exits a sharp edged orifice and enters a larger area.
When you start looking at the basics, you start appreciating what the NHRA Stock, the FAST (factory appearing stock) and Stock Appearing drag racing classes have to offer.
But that's just my opinion.