Dyno Test Results

Dyno Buildups and Power Combinations

The following buildups are based on most people’s expectations for street and towing engines, and are intended as a reference point. This article and the dyno testing it is based on were originally from 2003. Since then, we have made improvement to many of the parts, and while some of the parts used have become obsolete, they have been replaced with better parts. Rest assured, we have done substantial testing since then, but have simply not had time to sit down and write up the results in an easy-to-follow article. During this round of testing, we tried numerous combinations, and chose these examples as representative of the most common type of buildups. Those of you looking for more serious Pro Street and race combinations should keep in mind that we have many dyno and track proven combos for you as well. A sound bottom end is important in any buildup, and for those wishing to build serious performance packages now (or in the future based on the bottom end you build now) should consider the 10:1 test engine with forged rods and balanced rotating assembly as the minimum short block specs. Remember that we are always happy to set you up with a custom tailored parts package, to suit your current and planned future needs, with your budget in mind. Package deals (if you are buying a lot of stuff at the same time) can be priced with a discount included, as well.

Let’s start with the advantages of using the 472/500 engine family as a basis for your next engine. This engine family has earned a reputation for longevity and power, partly due to the high initial build quality. You are starting with an engine with tighter specs than many new ‘high end’ cars, to include the square ness and uniformity (lack of casting shift) usually expected only in high dollar full race engines, from the bore centers, to the deck surface, to the rotating parts centerlines, to the exceedingly high nickel content of the castings (like a ‘Bow Tie’™ block that costs more bare than your complete core engine). These engines are also very light for their size, being within 60 Lbs of a small block Chevy, while still being tougher and more wear resistant due to the high quality materials and castings. They have numerous other advantages, including easy access to the distributor and oil pump, dry intake (no coolant passages), individual ports (not siamesed to lower production costs while hurting flow), conveniently angled spark plugs (easy access in the tightest of installations), and internally balanced, eliminating the need (and inefficiency) of external balancing.

’76 500 – 420+ HP – 550+ Ft-Lbs

For this exercise, we’ll go step by step and show you how to gain 120+ HP and 60+ Lb-Ft of torque with a stock short block, keeping things truly street able and running on pump gas. Here at Cad Company, we have dyno tested a large majority of the bolt on combinations for street applications of both the low and high compression 472/500 engines, simply following the clear, detailed installation instructions provided with the parts, and not spending time ‘dyno tuning’ or ‘dialing in’ each combination, to get a true representation of what you can expect by following these examples. Remember that most engine dyno facilities claim up to 10%, or more, gain is possible by spending a day dialing in your chosen combination. Remember to choose your dyno facility carefully, as race engine shop may tend to compromise part throttle drivability on you street car engine for maximum WOT power, and vice versa for a street performance tuner.

We will start with our low compression buildup, and move on to the high compression engine later on. Our low compression short block was based on a ’76 spec rebuild, and was built with 8:1 instead of 8.5:1 compression due to piston modification for later race combos not detailed here. The short block was bored 0.060″ over, with 0.002″ piston clearance, reconditioned stock rods with ARP fasteners on an OE crank turned .010/.010 (not balanced), and assembled following stock clearance specs using the following parts:

Initial Assembly Specs:
Standard off the shelf cast ’74-’76 replacement pistons True Roller timing set
Pistons had valve reliefs cut, dropping CR to 8:1, for testing purposes OE HEI distributor
Moly rings OE camshaft, new lifters 120cc heads (’74-’76) #493
Clevite rod and main bearings reconditioned OE pushrods Straight 45° valve job (OE valves)
Durabond cam bearings Stage 1 valve springs OE 76 manifolds and carb

And the dyno says: 493.5 Lb-Ft at 2600 RPM and 302.1 HP at 3600. While it had only dropped to 291.4 HP at 4200 RPM, keep in mind that that is where new (not 100k+ mile, 30 year old) stock spec springs begin to show valve float. At this point, the Edelbrock 2115 intake was installed, retaining the stock Q-jet carb. While the stock rubber end gaskets work fine with OE intakes, they tend to split with the installation of aluminum intakes. A bead of silicone does nicely here. Proper port sealing was assured by using our exclusive high grade composite intake gaskets. (Note: this combo likes more ignition advance than the stock combo). The results were +20 HP at peak, but our torque band was moved higher, and we lost 35 Lb-Ft at 2000 RPM and 7 Lb-Ft at the torque peak. Both with the 2115 and back to the stock intake for testing an experimental (now in our regular lineup as the CTA 120 TD) RV cam, we found around 15 Lb-Ft and 25 HP either way. This thing made 512 Lb-Ft and 323 HP (same peak HP as the 2115 with the stock cam, with the torque peak at 2700 RPM) by itself, still idling smoother than most stock 454s.

Next, we put on the PCIII intake, which is a ported Edelbrock, with the necessary mods to enhance low-RPM transition, high RPM flow, cylinder balance, and fit on the engine right out of the box, which will be used throughout the rest of this buildup. Not worth any HP at this point, but improved EGT consistency and got back a few of those missing Ft-Lbs at the bottom end. The next addition will be our CTA 205TD cam, installed ‘straight up’ and not degreed, though it is ground advanced (we recommend following the cam installation and degreeing instructions provided with out cam kits, as they work even better that way – all cams in this group of runs were installed straight up to save time and tool, as most guys doing their first cam swap don’t have the time or tools to fool with it anyway). This change brought a 25 HP gain, with the peak at 3800 RPM and a 30 Lb-Ft gain with a 3000 RPM peak. There is the rest of our missing torque.

Our next change was exhaust. We replaced the OE cast manifolds with Sanderson’s 1 7/8″ primary/ 3″ collector block hugger (shorty) headers. While this gave us a gain of 10 HP and 15 Ft-Lbs, smaller primaries (such as the headers we now carry provide) would have been more effective.

It’s common knowledge among Cad enthusiasts that the stock valve train wasn’t designed for high lift, high spring pressure (remember the OE springs floating at 4200?), or high RPM (when this engine family first went into production, the common diff. gear ratio was under 3:1. As new replacement parts are being obsoleted as the inventory from the last run of parts is depleted, not to mention expensive, and are still no stronger than the originals, excepting the lack of wear. At this point, we chose our Stage II Shaft Rocker Assembly. The 10 HP gain was mostly the result of the increased ratio (1.72:1 compared to the OE 1.65:1), though on higher lift cams the increasing friction and geometry losses would make a noticeable portion of the gain. We now have 368 HP and 522 Ft-Lbs, and the graphs show us that this baby still wants more cam. At this point, it is still a cream puff, with a nice cruiser idle, great vacuum, and very drivable part throttle response.

To take it to the next level, we bolted on a set of our Super Street heads (see specs on the head page. If you’re building your own heads, basic porting guidelines come with the valves, for those of you with the skills and time. The valves are supplied at the correct length to avoid valve train hassle. Pro Tip: All valve stems must be fairly close in height (±.010″ or so) the whole length of the head, to get consistent lifter preload, when using non-adjustable shaft rocker setups, such as the Stage II setup we chose for this example.

Oh BABY! We gained 34 HP (402) and 6 Ft-Lbs (528)! Note that we only moved the torque peak up by 200 RPM while making our 34 HP gains – these are not race heads, so don’t listen to your Chevy pals telling you that bigger valves will always kill off the bottom end.

Now we’ll switch to mid length headers, which are the style that is a bolt in for the cars most of you are swapping your 500’s in to. While 1 7/8″ primaries sound small to guys familiar with Chevies, remember that we don’t have to wind up the big cad like a tabby cat strung out on caffeine, to make power. Our new line of headers with 1 3/4″ primary tubes gave us a gain of 12 HP and 15 Ft-Lbs over and above the power we were making with the 1 7/8″ primary headers, indicating that we not only improved the torque peak, but widened the curve with the smaller primaries. The smaller primaries also allow our headers to tuck in closer to the block and offer a better fit and easier installation as compared to similar headers with the larger primary tubes.

Our next step was ignition. While the MSD Pro Billet distributor gained only 2 HP and no torque, keep in mind that we are still working with very low RPM combos at this point. Besides, the gorgeous MSD unit is a steal for a completely new unit, while the old HEI is a tad bulky looking and has 30 years of wear and tear on it. While playing with the ignition, we found that at this point, going one step colder on plugs (from Autolite 646 to #65), and running a .040″ gap instead of .060″, gave us another 4 HP and 5 Ft-Lbs, for a total of 420 HP and 547 Ft-Lbs.

When going over the charts the dyno was spitting out, we noticed that early on, we could carry over 4 PSI of fuel pressure through the entire run. By the time we broke 400 HP, fuel pressure was dropping down, nearly to 2 PSI, well before the end of an 8 second pull. That begs the question of how the engine will fare while pulling a long hill, which can surely take more than 8 seconds, and it leans out because the carb’s fuel bowls are dry and starts detonating… We cured it by swapping in our chrome high volume pump, but some of you will chose to use an electric pump. There is an even bigger mechanical pump available, for those who need it but want to avoid an electric pump. Experience tells us that most folks who use a high volume pump without a pressure regulator, regret it eventually. Get it, set it, and keep the headaches away.

’70 500 – 525+ HP – 590+ Ft-Lbs

The base engine for test mule #2, essentially built to ’70 Eldorado specs, at 10:1 compression, and similar assembly to the 8:1 test mule. The short block features Cad Company’s direct replacement forged rods with ARP fasteners, and a balanced rotating assembly due to higher RPM testing to be done later, and was built using:

Initial Assembly Specs:
cast 10:1 replacement pistons True Roller timing set OE HEI distributor
Moly rings OE camshaft, new lifters 76cc heads (’68-’73) #250/902
Clevite rod and main bearings reconditioned OE pushrods Straight 45° valve job (OE valves)
Durabond cam bearings Our light duty street springs OE 70 manifolds and OE carb

Bone stock, it pulled 323 HP and 504 Ft-Lb of torque, about the same as the stock 8:1 with the CTA 120 cam, thoroughly dispelling the myth of the 200+ HP difference between the ’70 Eldo engine and the later smogger engines. Keep in mind that the factory rating system is not generally dependent on the actual power output of production engines. The peak peak rated HP of the ’70 engine at 4400 RPM (200 RPM above stock valve float?) is a good illustration of that.

As the milder combos follow a pattern, we will skip the repetition and get to the meat and potatoes of this test. The step-by-step changes made to Mule 1 were repeated, with predictably similar results, resulting in a pull of 449 HP and 565 Ft-Lb. That shows what compression does for the milder combos, but from here on out the 10:1 engine with the 76cc heads and bigger valves has a clear advantage. Stepping up to the SS 300 T cam, which can still be tuned to idle relatively smooth , and is not a monster lift spring or piston killer, gave us boosts of 28 HP and 10 Ft-Lbs, for a reading of 477 HP and 575 Ft-Lbs.

At this point, the Holley finally de-throned the Q-jet, with a gain of 3 HP and 6 Ft-Lbs, for a final power output of 480.1 HP at 5200 RPM and 581 Ft-Lbs at 3900, though it was still pulling strong with 473.4 HP and 452.4 Ft-Lbs when we quit pulling at 5500 RPM.

Other Tidbits Before retiring mule#2 from the dyno, we slipped in our new P/C 625 cam, reaching 508 HP at 5500, and then swapped in the PCIV intake and a 1050 Dominator for a best pull out of 3 weeks at 527 HP at 5600 RPM and 591 Ft-Lbs at 4000 RPM. This would make a great Pro-Street combo, though it is too hairy for many folks taste, to be driving on the street. It likes a torque converter with around 2200-2400 RPM stall, or a manual trans, and most likely wouldn’t run your stock vacuum power brakes (9″ at 1000 RPM idle at 5000 Ft Altitude) without a vacuum canister. Update: Having run this engine (the actual one, with the 850 Holley) in a 92 Chevy street / strip truck, we know it can be made to pass the tailpipe emissions test to ’92 light truck standards (using high flow cats, mufflers, and a full exhaust, that does not affect power to the wheels). The stock power brakes worked, but had less power assist than it originally did. The required torque converter can be annoying in traffic, and we eventually stepped down to a bit smaller cam for the sake of drivability (this truck tows our golf cart trailer to the track in Friday rush hour traffic). I have also driven a manual trans muscle car (’69 Firebird that belongs to a friend) with this cam, stock heads, and higher compression, and it is a blast, with no apparent compromise in traffic. It also breaks something in the stock 9″, every time the owner forgets to lift on the throttle, and engages the planetary overdrive at WOT, at the track.

Windage: The Caddy has a big arm, and with it comes windage. Installation of our exclusive PC7 oil pan brought a gain of 12 HP and 20 Ft-Lbs at 3000 RPM and 10HP/ 14 Ft-Lbs at 4000 RPM. The new aluminum pan has similar windage characteristics as well. This is not to be confused as a statement that the aftermarekt pan adds power – simply that the stock pan robs you of that power, and the aftermarket pan does not. Regardless, the effect is the same – more power a the flywheel. Also note that the higher oil capacity of the aftermarket pans will benefit you in lower oil temperature, and can mitigate the damage caused bu going a little too long between oil changes.

The carb thing: Throughout our testing, we tried a number of aftermarket carbs in the 650-850 CFM range, as well as several Q-jets. All were tried as shipped, and with 2 jet changes (2 really big jet changes in some cases – like 8 sizes worth, just to get it close enough to run). Throughout the testing, the Q-jet prevailed, though in the larger combos, the 850 CFM Holley stayed close to the Q-jet. Once we were almost at the limit of the ‘tame’ street motor, with the 300T cam, etc, the Holley came into it’s own and beat the Q-jet for peak power (but not average power under the curve), and in a daily driver you would be paying for your 3 HP with decreased part throttle response and greatly decreased fuel economy. All of the new aftermarket carbs tested need leaning out considerably, just to get in the ballpark. Keep in mind that carb manufacturers are catering to the masses, and the 500 gives the carb a much stronger vacuum signal than most engines, therefore needing smaller jets.

We did try large tube headers (2+”, using BB Chevy headers with the header flange kit once we were in the 500 HP range, and lost 3 Ft-Lbs without gaining HP. Even at this level, bigger is not better by definition – the design has to be right.

On the first runs with the 8:1 combo, we were running regular unleaded. With a switch to premium and retuned, we were within 1 HP for most of the power curve. The 10:1 was only tested with premium.

Cad Company