David and Goliath Part 2.... Building the 400 vs. a Stroker

Okay, part two.

We know a given cylinder head will perform up to a given piston speed (airspeed) before they choke and putting that cylinder head on a SMALLER DISPLACEMENT shortblock will increase the useable rpm range over the bigger engine by delaying the rpm at which that choke occurs. We also know to feed a larger engine, the camshaft will need to be larger, something along the order of 6-8 degrees for every 50 cubic inches.... all things being equal.

So what gives? Why do people believe the 400 needs substantially more cam than a 455 to make the same power?


For a 455 that will make peak power at 5,200 (let's assume 100% v/e, a 400 will need to turn somewhere around 5,900 rpm to flow the same amount of air/fuel. It stands to reason then the 400 will need to turn 5,900 to make the same power, right? It's all about compressing enough air and fuel to turn the crank; the energy released converts to torque; and that converts to horsepower. Burn more intake charge or compress it more and you get more torque; turn more rpm and due to the formula for horsepower, HP = TORQUE X RPM / 5,252, you get more horsepower. So, according to what we have read above, concerning a given induction and camshaft sizing between large and small engines, if the 400 cannot approach its peak equivalent rpm, given the same componentry, we MUST have a mechanical problem limiting us somewhere. How many 400 engine builds have you seen where the horsepower peaks around 5,200 rpm. In fact, how many Pontiac builds in general have you seen where power peaks at 5,200? If you look around AT ALL, then you have seen many. The first step is ensuring the engine runs properly considering the components selected and, I suppose, some experience KNOWING when those components SHOULD be performing... but aren't. It has become obvious to me that many people out there think EACH AND EVERY PONTIAC ENGINE IS ALIKE, EVEN THOUGH THE STROKES MAY DIFFER. That is a mistake. The 400 and the 455's share a common deck height, nearly the same bore size, and cylinder heads. The differences in stroke, and therefore, rod ratio (let alone displacement) TOTALLY change the characteristics between the engines when it comes to airspeed in the ports (peak torque rpm), cylinder head, and camshaft requirements, so I believe it is nonsensical to think the 400 should peak at 5,200 just because a 455 may.

More than once I have pointed to a build we did here at Sandoval Performance where a customer wanted us to use a specific camshaft and he wanted AT LEAST 500 hp from a 461 we were building for him. Well, we made the X/E 274 Comp Cams camshaft work and it kept making power until we ran into valve float at 6,000 rpm! Well, you may say that cam is too small to be making power at that rpm.... apparently not. He had a REAL, USEABLE, 500 HORSEPOWER! Not 500 at the redline, and then shift.... but a good 500 rpm past peak hp to play around with.

Remember, that is with a small cam. EVERYTHING can be tuned! If a given engine does not perform up to expectations, an engine builder at that point takes the time to figure out what is going on with his combination, or, if you are simply putting an engine together in your garage and you don't have the resources to do any testing, you may be tempted to put a bigger cam in it (with its bigger valve springs--- hmmm), or perhaps resort to substituting solid roller lifters on a hydraulic roller cam in an attempt to gain some rpm by by-passing all the hydraulic mechanism's inherent high rpm problems. Not bad ideas at all, very understandable in fact. I guess the bottom line is; it ends up working--- at the cost of idle vacuum.

I JUST HAVE TO KNOW WHY the first component isn't working. Just swapping out components won't tell you what is happening. It may be the cam with a 110 degree LSA with only 6 degrees difference between the intake and exhaust lobe durations isn't "happy" in a 1.77 rod ratio, barely 10:1 compression, 3.75" stroke application. Perhaps mixture motion is weak; perhaps the intake valve needs to close later to take advantage of the long rods and their higher rpm characteristics.... perhaps a 112 or a 114 LSA and MORE COMPRESSION? Or is it simply weak valve springs not allowing the engine to reach its potential?

My bet's on the valve springs and/or compression!

If you want YOUR 400 to STOMP some of the strokers out there, you can't build it like a low compression, low rpm 4.21", 4.25", or 4.5" stroker!

For our 400's, we like:

  • a real 9.5:1 compression for our cast iron headed combinations and 10.5:1 for aluminum.

  • The Performer RPM intake for most 400 builds... runners ported for the higher hp and rpm combos. Torker 2 for hood clearance considerations even though they have less available material for porting.

  • We like our own hydraulic roller camshafts. They fall into a "custom" category as they are different than any others out there. For a 450hp cast iron headed combination, we go with a Stage 2 (276/288 adv. - 224/236 @ .050" .567"/.585" lift on a 112 LSA). Same cam for our 500hp Edelbrock headed combinations but with 1.65 rocker arms. We also designed (that Comp grinds for us) a number of LOW COMPRESSION compatible camshafts for you 400 cid/ 6x head guys out there with 8-8.5:1 compression. Specs for our "LC-3" Low Compression cam is 266/276 deg. adv., 214/224 deg's @ .050", .580" lift on a 108 LSA for a GREAT SOUNDING IDLE yet it provides enough vacuum for power brakes.

  • We like SRP, PROBE, and ICON pistons.

  • We use Eagle and Ohio Crankshaft connecting rods.

  • We like Edelbrock D-port aluminum cylinder heads for 400 builds between 500-600hp.

  • For milder builds, we like the Edelbrock AFB and AVS style carburetors. For Original LOOKING builds, where you want to make some good power, we like Sean Murphy Induction's line of Quadrajets.

  • For the more radical builds, we like Sean Murphy's prepped Holley carbs.

  • A 3.42 gear and a 2,500 stall convertor will get you by, but if you want to do some damage, I like a 3.73-4.10 gear and a 10" convertor... specifically a Coan Pro-Street unit. VERY EFFICIENT and drives like a stocker yet flashes to approximately 3,000-3,500 rpm depending on engine weight, driveline variables and vehicle weight. For the best of both worlds, get an overdrive transmission.

A 500hp 400 is not a difficult build. Just remember, volumetric efficiency and compression are instrumental at building TORQUE. Don't shortchange either of them because you have a "Pontiac 400" that is known for being a "torquey" engine. Build that torque and allow it to rpm. Do that and you have a winner! Add a little gear and some convertor and blow away A LOT of those "torque-monster" strokers out there that give up at 5,200 rpm!

GOOD LUCK ON YOUR BUILDS! If you need any assistance, feel free to call (765)432-3554 or E-mail us @psperformance@comcast.net

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