UPDATED!!! Getting 500hp out of a 400 cid Pontiac combination (aside from supercharging!) can be simple if you at least consider a few things:
Induction - Minimize intake restriction
Compression - Build cylinder pressure
Ignition - Ignite the air and fuel effectively
Piston Rings - Harness the combustion pressure effectively
Exhaust system - Exhaust the combustion gases without restriction
Camshaft - Ensure the cam timing is appropriate for the rpm range
Valvetrain - Ensure any reciprocating component is sufficiently light and rigid for the operating rpm range
Friction reduction - Reduce friction throughout the engine (hint: piston rings)
EVERYTHING... comes down to time, effort, knowledge, and then... money.
From MY experience, stock components are good for about 400-425hp without much modification or a loss of low rpm throttle response and torque. Let's take look at the various subassemblies:
1.Induction - Minimizing intake restriction - The EASIEST way to accomplish that is with a good set of heads and matching intake manifold for the rpm in which you want your engine to run. Many estimate their horsepower by applying this simple "formula", HP=2(CFM). Two hundred fifty cfm is therefore "required" to make that hp. Now we know that one can attain that power with less cfm, but it then requires the use of more cam, compression, and/or rpm. Funny thing is; you end up building a "wilder" engine. UPDATE: Too big of an intake tract can cause a low vacuum situation, creating uneven droplet sizing and an uneven burn in the cylinder.
2. Compression - Build cylinder pressure - You do that by optimizing your static compression ratio (through pairing of the combustion chamber size and piston valve relief or dish volume), good cylinder head flow, and cam timing--- cutting to the chase, 10.5:1 for aluminum, 9.5:1 for cast iron are "safe" for running pump gas. UPDATE: More compression can be utilized if more camshaft (specifically a later closing intake valve), a lighter vehicle, more rear gear, and a higher stall convertor are used.
Static compression ratio is the comparison between the volume above the piston at top dead center, and the volume above the piston at bottom dead center. Since we are using aluminum cylinder heads, 10.5 is safe under all but the most mismatched combinations naturally aspirated with readily available mid-grade pump gas in most cases. Now this STATIC compression only goes so far, it will give us a little more PEAK power but what it really does is increase EFFICIENCY (thermal, fuel, and combustion--- it's a win/win situation!)and that boosts AVERAGE power and torque!
Good, efficient cylinder head flow will allow intake charge to fill the cylinder effectively allowing a higher volumetric efficiency--- which adds to the cylinder pressure since we have MORE air/fuel charge to ignite! I say "allowing" because everything needs to work together.
Cam timing can add to volumetric efficiency---- high lift will increase the AREA through which the air/fuel charge may travel into the cylinder, otherwise known as the valve "curtain area". A tighter lobe separation angle increases overlap which increases the breathing capability of the engine due to exhaust pulse scavenging (aiding intake flow into the cylinder by means of a low pressure pulse in the exhaust literally pulling more intake charge).
3. Ignition - Ignite the air and fuel effectively - First of all, use quality ignition components as more cylinder pressure and more air/fuel charge will tax a substandard system. Then, put enough static compression in the engine, optimize your deck clearance (have the deck of the block machined so the piston is VERY close to sitting flush), ensure that the carburetor to be used is in good working order.
4. Piston rings - Harness the combustion gases effectively - Top piston rings should be gapped to the minimum allowance or you are just giving away power! Adhere to the piston and ring manufacturer's recommendations. Gap the 2nd ring slightly wider and you are good to go. Why? Conventional rings will allow SOME charge to push through the ring end gaps down into the crank case. You do not want the 2nd ring to act as a "back up" to the first ring... it is there to scrape oil only. If the 2nd ring harnesses what the first ring let past, then any built up pressure WILL unseat the top ring. Also...
When thinking about harnessing cylinder pressure, cam timing should be thought of as a complement if you will, not a "power maker". We should hold onto the combussed gases as long as possible before we exhaust them so long as it does not effect top end power. If we open the exhaust valve too soon we have power going right out the tail pipe.... and a louder engine! Good thing is, if we are using good cylinder heads, the less we need to worry about the cam!
Ensure you have ENOUGH valve spring pressure as a bouncing intake valve will allow fresh intake charge to revert back into the intake tract (limiting the cylinder pressure AFTER combustion). Same with the exhaust valve, we will then have exhaust gases re-entering the cylinder.
5. Exhaust system - Exhaust the cylinder efficiently without restriction - That comes down to a good set of Ram Air exhaust manifolds or headers with 1.75" primaries and dual exhaust pipes with 2.5" of diameter. UPDATE: if other items are barely adequate for making 500hp, then the exhaust will be more important. In that case, go straight to using a good 4 tube header.
6. Camshaft - Ensure the cam timing is appropriate for the rpm range - SIMPLE. Along these guidelines, you really don't need any more than 236 degrees @.050". If you are on top of your game with ported induction and enough compression, you can do it with 224 deg's @ .050". Get ENOUGH lift, I like to see at least .550". To get that lift or more with a shorter duration, don't be afraid to go to a hydraulic roller cam. Lobe separation can be wherever you want it depending on idle quality. UPDATE: If money is an issue, the use of a larger cam will be a necessity, as will additional rpm to make the use of that cam. For bowl ported heads, you may need something in the range of 246-250 deg's @ .050" lift on the intake. Our Stage 4 hydraulic roller is 244/248 on a 112 LSA while our Stage 5 solid roller will make very good power (252/258 @ .050" with .620" lift on a 108 LSA).
7. Valvetrain - Ensure any reciprocating component is sufficiently light and rigid for the rpm range -
Anything over 5,500 rpm, we like to use a lightweight retainer.
Chromemoly pushrods are utilized for roller cams... for operation above 5,500 rpm, we like thick wall (.116" Smith Bros.) pushrods.
ENOUGH valvespring pressure. I CANNOT STRESS THAT ENOUGH. I like 130 on the seat and over 360 open for a flat tappet. A roller cammed engine will need MORE valvespring pressure.... not less (like it has been shown in a popular magazine as of late).
Pistons- I like using a quality lightweight forging because it will help the connecting rod live as well as using a lighter, lower tension ring pack.
Don't even think about using a stock or roller tip rocker on a roller cam with radically increased spring pressure!
8. Reduce friction (and parasitic losses) throughout the engine - That speaks to using the proper rings for a given bore diameter. Try to get the rings AFTER the bore is finished so you will know the EXACT size and can order your rings so you will not be forced to file off an excessive amount to get the proper gap.
Open up your piston, main and rod bearing clearances slightly on a higher rpm combo.
On most street strip engines, I don't see any need for more than about 60-70psi oil pressure. Excessive oil pressure simply eats up power. UPDATE: I have seen 1st hand evidence that excessive oil pressure doesn't necessarily help main and rod bearings live (on a typical street/strip build). Attention needs to be paid to the OIL FLOW PATH.
Lightweight oils can decrease friction, but try not to go too thin! Rod and main clearances demand a certain viscosity. Going to thin can adversely affect film strength while a thicker viscosity doesn't flow as well... and we all want our oil to flow freely!
Displacement will somewhat dictate the peak horsepower rpm. To make 500hp with a 455+cid engine with Edelbrock heads and mild cam timing around 230 deg's @ .050 and .500-.550" lift, expect to turn it 5,500rpm. For 400/389's, expect to turn your smaller engine just above 6,200 rpm. Now, if you want to skew your power curve LOWER but still make excellent torque numbers, you can use a BIGGER CAM, yes, a bigger cam with .030-.050" more lift, 6-10 degrees more duration @ .050" and a tight LSA on the order of 108 and ADVANCE your cam to an intake centerline around 102 - 104 degrees. A higher stall convertor would also be a good idea at this point. Something along the lines of a 4,000 stall.
Like it has been said before, there is always more than one way to skin a cat, From my experience, it's the drivability and reliability that begin to add up!
We offer 500hp cast iron headed, premium pump gas 400's starting @ $7,995.