That depends on the builder! Let's take a look at a few design characteristics, of which, some have never heard. DECK HEIGHT AND BORE SPACING If we look at the typical 10.230"+ deck height traditional Pontiac engine (326 - 455) and compare it to some of the other marques out there we notice pretty quickly that we do not have dedicated small- and big-block castings like the Big Three do. What we DO have is a tall deck engine with a small bore spacing of 4.62". Together, those two design parameters conspire to limit the factory cylinder heads' capability to fill the cylinder due to the required small cylinder bore diameter shrouding the intake valve and the tall deck height necessitating low angle-of-attack intake ports. The engineers addressed the breathing deficiency somewhat when they reduced the valve inclination to 14 degrees back in 1967, enabling them to utilize a 2.11" intake valve in a 4.12" bore. For a small block, those valve and bore sizes aren't too bad but for a big block, they are lacking. The "large" valve size presents a problem within the intake tract as it is too large for the size of the port, creating flow issues as the charge exits the valve seat area and enters the chamber--- the flat chamber floor and 30 degree seat exascerbate the problem. They promote intake charge dispersal into the combustion chamber and low lift flow, but not cylinder filling via mass flow after bottom dead center.... which is what we are actually after if we want to make torque AND horsepower . So the simple fix is to port the heads or, better yet, substitute a better head. INCREASE VOLUMETRIC EFFICIENCY What do you do if you are on a budget? Play up those low rpm qualities if you have one of the bigger displacement Pontiac engines by porting the cylinder heads and getting the valvetrain worked out so you can further exploit the low rpm benefits of the 455 by tailoring the valve events appropriately! Use a 1.65:1 rocker arm to get that valve up and out of the way QUICKLY! If you have a few extra dollars and want to go overboard--- and who doesn't want to go overboard--- purchase a custom ground roller cam to maximize your efforts. Something in the range of 236-244 degrees intake duration @ .050" lift on a 108 LSA and .600" lift with the 1.65 rocker arm. The better the port-work, the less duration you will need. Figure 500 horsepower and 550-600lb/ft of torque (depending on the builder)! Substitute a set of ported Edelbrock aluminum heads and port-matched intake manifold and now you are pushing 600 STREETABLE horsepower. Visit http://www.sandovalperformance.com/#!engine-components/vstc11=page-2. I didn't forget the 400; it will also benefit by putting out 550hp at 6,500 rpm and remain remarkably streetable. If porting or substituting a better head is out of the question; the search for more power turns to the shortblock. INCREASING DISPLACEMENT The easiest way to make a major increase in displacement is adding a "stroker" crankshaft. Considering the already-long stroke, meager intake port areas, and tall deck height (that dictates low angle of attack intake ports and therefore, a tight short turn radius that induces shearing and a reduction of flow at higher rpm), we ADD STROKE making things worse! Any flow issues you see with a 4" or 4.25" stroke will appear sooner with a 4.375" or 4.5" stroke crank due to the increased piston speed and therefore, airspeed for a given rpm. That is why hp/ci goes down as displacement goes up with a given cylinder head. A 400 with its 3.75" stroke crankshaft is actually a good match for the port sizing as it came from the factory... GO FIGURE! It is my opinion that a 4" stroke combination may end up being the best hp/ci drag racing combination using readily available aftermarket cylinder heads. We'll see. Just to be clear: If you have a 400 and you want to stroke it for increased displacement, go for it. The extra cubes you will get from a 4.5" stroke over a 4.25" is free. But I suggest going the extra step in preparation to MAXIMIZE the performance of your new combo so you get the most for your hard-earned money. ADDING DISPLACEMENT VS. INCREASING VOLUMETRIC EFFICIENCY Adding stroke will skew the output lower in the rpm range whereas improving the volumetric efficiency of the engine and optimizing the static compression will provide gains THROUGHOUT the rpm range! So, it is actually the DISPLACEMENT, VOLUMETRIC EFFICIENCY, AND COMPRESSION THAT DETERMINE THE TORQUE OUTPUT OF THE ENGINE--- NOT STROKE. The best bet, if a guy could afford it, is to go with additional cubic inches AND a good set of cylinder heads, then you get the best of both worlds! A large gain in low rpm torque and high rpm capability for high horsepower. So to answer the question: The Pontiac engine is a "Low RPM Torque Monster" only if you decide to ignore the characteristics that actually produce torque. Questions or comments? Feel free to E-mail us @ email@example.com
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