BUILDING YOUR PONTIAC ENGINE FOR HIGH PERFORMANCE... WHAT'S IMPORTANT?
THAT is a tough one if you are new to building engines or frequent some of the internet forums where you will get a dozen recommendations just for a cam swap.
The first thing to remember is the Pontiac engine is an internal combustion engine and will respond to modifications just like any other. If higher rpm is the goal, then the oiling system, along with the bearing clearances, must be addressed. I can tell you, in street type performance engine, if you are going to be revving your engine above 6,000 rpm, keep the bearing clearances as listed in the Machinery Handbook... .001" of clearance per inch of journal diameter. I say that because our Pontiac engine blocks WILL flex. Also, if the crankshaft is not perfect--- I have seen a number of crankshafts with .001" total indicated runout and rod journals with .0005" of taper. If blocks can move around during operation, then the clearancess will DECREASE! A little too much clearance will ALWAYS beat too little! The downside there is less oil control and lower oil pressure at idle below 1,000 rpm. If one were to fill the block for rigidity, then tighter main and rod clearances may be used. Nascar engine builders are finding additional oil control and efficiency with tighter bearing clearances in the .002" range for mains and rods. But we are talking about typical street/strip type builds where that type of modification simply isn't necessary.
When planning an engine build there are so many decisions that must be made, very few are black-and-white. These are:
How much money can you afford to spend on this project?
What are your performance goals for the vehicle?
Will this vehicle see many, if any, highway miles?
How important is fuel efficiency?
Are you willing to modify the vehicle to suit the engine or would you like the engine to suit the vehicle?
To me, those are clear cut questions and you should be able to answer them pretty easily. On the other hand, there are questions that are VERY subjective and you will have to give them some thought. Such as:
How much horsepower would you like the engine to make?
What constitutes drivability for you?
Are you willing to compromise drivability for the sake of acceleration?
Do you want to have the fastest car in your circle of friends? This is an emotional one here!
I can break it down to the very essence of what we are trying to do with our high performance pontiac engines... BUILD AS MUCH CYLINDER PRESSURE AS NECESSARY SO THAT WE CAN MAKE OUR CARS MEET OUR PERFORMANCE GOAL. When it comes the vehicle; apply as much torque TO THE DRIVE WHEELS AS POSSIBLE USING A COMBINATION OF ENGINE TORQUE AND TRANSMISSION/REAR END GEARING. That's it. That's the bottom line. So how do we go about doing it while retaining its user-friendliness?
Get help from the right people.
A problem as I see it is misinformation or focusing on the wrong areas. Watch out for the buzzwords and ideologies such as: velocity; you need to consider dynamic compression when choosing a cam; LSA; low lift flow; you need to keep the compression ratio with an aluminum head at 10:1 on pump gas to stave off detonation; Pontiacs are low rpm engines--- you don't have to rev a Pontiac, etc. While some of those words or statements not only have merit, they are very important. But how does one know which parameter or rule-of-thumb to pay attention to? Too often, these statements are thrown out there and will only confuse a situation when we are speaking in terms of a typical high performance street/strip type engine. It is the K.I.S.S. principle. Keep it simple, stupid! At least that's what my wife tells me!
Let's look at velocity. Okay, we need good port velocity for good throttle response and low rpm performance. So what velocity are we looking for? At what rpm do we want to achieve this velocity? Where is this velocity measurement taken? What affects the velocity within the port? Is it the port velocity we should be looking at, or is it the velocity of the charge as it exits the valve seat and enters the chamber? Should we be actually looking at CHARGE MOMENTUM and how it affects cylinder filling?
Applying the K.I.S.S. principle; This is a HUGE topic and I cannot do it justice, but let me say this; On a 455 with a conventional port layout, there is enough port velocity to deliver outstanding street performance with fully ported aluminum Edelbrock cylinder heads. If cam selection and/or installation is botched, the cylinder head will often get the blame. I believe enthusiasts were used to dealing with the meager port sizing of the stock cast iron heads, where overcamming is difficult to do because the port velocity was through the roof, and therefore very forgiving. The stock cast iron ports are small. So small, in fact, they are barely bigger than small block Chevy heads that were used to feed 327's. Big block Chevy 396 oval ports are in the 265cc range, if I recall. Out of the box Performer RPM heads are 215, so while that may seem big for a small block, it is pretty small for a big block. With bigger head ports, it is now possible to overcam. If you don't know how to select a cam, you can;
talk to a professional at one of the cam companies and purchase their cam
talk to someone that is willing to guarantee the performance of their cam and purchase their offering
talk to someone that is using a combination you would like to emulate and purchase the same cam they run
THE BOTTOM LINE TO ME: When speaking of velocity, we need the air/fuel charge to have enough velocity so that the cylinder keeps filling after bottom dead center... that leads to higher VOLUMETRIC EFFICIENCY!
You need to consider dynamic compression when choosing a cam. The compression ratio of the engine as it is running. It takes cam timing and rod length into account. But I NEVER hear enthusiasts speak about volumetric efficiency and how it can affect dynamic compression. OBVIOUSLY, if you fill the cylinders better, then the dynamic compression will be higher for a given STATIC compression. So if your heads flow like poop, does that mean you can run more STATIC compression? Or are you simply looking at the length of the rod and when the intake valve closes? And just when does the intake valve close? Are you running a hydraulic cam? How are the lifters adjusted? Does that affect the ACTUAL valve timing? Is the proper length pushrod being used? Does the pushrod length affect valve lift and VALVE TIMING? Does it affect pushrod hole clearance?
ATTEMPTING to keep it simple: There is a relationship between valve timing, compression ratio, and volumetric efficiency that dictate the DYNAMIC COMPRESSION, or RUNNING COMPRESSION of the engine. Do you KNOW, FOR A FACT, YOUR ENGINE'S VOLUMETRIC EFFICIENCY? If not, you do not have all the information you need to make an informed decision because piston position and valve closure point do not tell the entire story. For example: A typical street car with a mild performance engine will exhibit an 85% volumetric efficiency, whereas, a Pro-Stocker with its 2.75hp/ci, 500cid engine will show a 115% V/E. Doesn't it make sense that will have SOME affect on dynamic compression? You can spend days, if not weeks looking at calculators on the internet or you can simply go to the camshaft grinder of your choice and look at the specs of camshaft for the required static compression ratio for a certain camshaft and they will get you in the ballpark. SIMPLE.
THE BOTTOM LINE TO ME: Dynamic compression is something to consider but nothing to get hung up on.
LSA, or LOBE SEPARATION ANGLE, is the measurement in camshaft degrees between the intake lobe centerline and the exhaust lobe centerline for a given cylinder. ALMOST EVERYONE has read somewhere, and will repeat, that a tight LSA will have a narrow power band and a wide LSA will have a broad power band.
Keeping it simple: LSA MEANS NOTHING. It's OVERLAP that is the real parameter. LSA is merely the displacement between the lobes and is a figure used for manufacture.
THE BOTTOM LINE TO ME: It is the actual events themselves (intake opening, intake closing, exhaust opening, exhaust closing) and how they relate to the four strokes (intake, compression, power, and exhaust) that matter. Cylinder head flow comes into play where a better flowing head actually needs LESS camshaft duration than a lesser flowing head.
Pontiacs are low rpm engines.
MANY Pontiacs are relegated to "low rpm torque monster" status when in fact, there are some VERY fast Pontiacs out there turning over 8,000 rpm. How does that relate to a street car? Simple. Rpm capability is there for the taking... IF YOU WANT IT. If you don't.... STOP READING NOW. If you have an engine that you want to make over 550hp with and you decide to make that power at a very low rpm, let's say 5,252 rpm (to keep the math VERY simple), you will need to make 550 lb/ft of torque at that rpm. That torque curve is on the downward slope so you will have made peak torque somewhere between 575-600 lb/ft . That's not a bad thing, or particularly hard to do. But we choose to trade a few lb/ft of torque for our Street Performance and Street/Strip engines since there is usually an overabundance of torque with Pontiacs, and gain 100hp and 1,000 rpm.... IF YOU WANT MORE RPM. All we are doing is making sure the engine is CAPABLE.
We like using ported Edelbrock heads even if the combo is a mild one. It allows the engine to make MORE POWER WITH LESS CAM! If the combination is efficient, then you can make over 550hp with only 230/236 degrees @ .050" and .530" lift.... PRETTY MILD. A combo like that will idle at 750 rpm and produce over 16" of vacuum. The best part? Horsepower will still be on the upswing when you reach the redline.... the engine is constantly accelerating!
THE BOTTOM LINE TO ME: The Pontiac is a low rpm engine... Only if you want yours to be.
You need to keep the compression ratio at 10:1 with aluminum heads to stave off detonation.
If one wants to run the same cams, heads, and intakes as the majority of enthusiasts out there... I agree with that.
Just about anything you want to do, if we are considering a street vehicle, can be accomplished with the engine and torque convertor and a streetable rear gear up to about 600hp... IF you choose to build your engine with a broad torque curve.
Big horsepower CAN BE very streetable. For example, we offer:
500hp 400 with ported Edelbrock D-port aluminum heads and a Sandoval Performance Stage 2 hydraulic roller and lifters. This combination is compatible with a 3.23 gear and a Coan 11" Pro Street convertor.
600hp for a 461 with Edelbrock Performer RPM round exhaust port cylinder heads and the same gearing.
630hp for a 488 with Edelbrock Performer round exhaust port cylinder heads and the same gearing.
More horsepower is available with any of the above combinations by installing a longer cam, but there will be a decrease in idle vacuum and idle characteristics may be affected. I cannot guarantee those numbers for other builds out there, but for what we do... those are realistic numbers. For the guys out there that are thinking, "no way", I ask you consider some of the 5.3 liter LS builds... 500 streetable horsepower! Some fuel injected, some carbureted... approximately 320 cid!
If we are looking to achieve good 1/4 mile times, the chassis and suspension are just as important as the horsepower the engine makes. If highway travel is important, the addition of an overdrive transmission may be of benefit if very low 1/4 mile times (requiring a low numerical gear) are desired.
Okay, at this point you are probably thinking: So how do build the most cylinder pressure to make my car perform the way I want?
Purchase a cam that does not contribute to intake reversion yet raises the valve high enough to fill the cylinders well. Our Stage 2 cams will support 500hp in a 400... 550hp in a 461. Stage 4 will support 560hp in a 400 and 600hp in a 461.
Raise the compression ratio - To AT LEAST 10.5:1 for aluminum when using one of our cams. Keep it at 10:1 for aluminum with other grinds.
Use cylinder heads that have enough PORT AREA to feed the cylinders.
Use a modern intake manifold design that is capable of filling the cylinders ABOVE PEAK TORQUE.
Good luck with your build!