GM’s 572 Big Block Chevy Muscle Motor
Is it still the King of the Hill

Except for those older hot rodders among us, the big block Chevy has seemingly been around forever, and there is a reason for this now legendary engine’s long term success. The original basic platform looked to have so many of the right ingredients and time was to prove that to be very much the case. Forward the clock over 45 years and we find that Chevrolet’s big block is still the engine of choice when big inches for brute power and torque are the goal. Originally designed to be a replacement for the famed Chevy 409 it would seem that the engineers concerned had more than just a casual interest in the engines performance capability. From the mid 1960’s to about 1970 the performance images of such cars as the Chevelle, Monty Carlo, Corvette and the Camaro were defined by the use of Chevy’s big block. Back in the 60’s NASCAR ran cars with stock bodies and brand identification was a key factor toward generating a strong fan following. That little ditty ‘Win on Sunday – sell on Monday’ might just have been more of a driving force toward endowing Chevy’s big inch muscle motor with performance potential than corporate GM might admit too.

Introduced as the 396 ‘mystery motor’ back in 1963 and later released to the public in 1965, it immediately generated great appeal to a host of performance enthusiasts looking for performance levels well beyond the reach of a small block – and that is just what they got. Historically Chevy’s big block does more than just dot the landscape with significant competition achievements from 1963 until now. Indeed it was more like a series of closely set paving stones outlining a path from then all the way to today. I am from England and let me say it was almost impossible to buy a UK race weekly paper that did not have some big block Chevy exploit or success mentioned in it.

When the big block was chosen to power the McLaren CanAm cars the world wide interest in the engine took off to another level. And it pretty much took me with it. As a performance engine development engineer I have, like many others, been enamored with the potential this engine has to offer. As for the general car enthusiast populace at large we can see that this engine has a huge following even though it is near half a century since it was introduced. That, right there, is a measure of this engines success. But success did not come about just because a big block works well as under hood decor. It’s mean machine rep was earned the hard way – on race tracks the world over. Every week a legion of big block Chevy’s competing in classes ranging from exotica like ProStock and National Muscle Car Association’s ProStreet to Super Stock will go to the track and come home with trophies.

The continuing success of the big block has driven another aspect in that it has become a cult engine and seemingly, a whole new generation of younger hot rodders are more than ready to lay out the cash to get a big inch V8 Chevy. Talking to some of the leading aftermarket performance hardware companies revealed that the best year of big block Chevy component sales ever for many, have, surprisingly, been among the recent years.

If you are a big block owner looking to tap into Chevy’s big motor adrenalin pumping power potential then be aware that ‘go really fast’ parts are available by the ton. The first place you should start to look for performance parts is Chevrolet’s performance catalog. This has blocks, cranks, rods and pistons for big inches. It also features heads, cams, intakes and more. If you don’t find what you want there the aftermarket will surely have it. Whether it is 600 hp being sought or 3000, today the performance potential of the big block Chevy is limited only by the engine builder’s imagination.

Power Potential

The big blocks introductory 396 cubes and the power that went along with such a displacement made for race winning performance. As successful as the 396 was, Chevrolet, to this day, is not a company about to sit back on its heels and bathe in the glory of the moment. Instead, the big block Chevy, as offered by the factory, went on a steady diet of steroids and over the years grew in power and displacement from about 375 hp and 396 cubes all the way to over 720 hp and 572 cubes. The current and largest iteration of America’s favorite big block was introduced as a 572 CID unit in 1998. It produced a loud and positive reaction with the press and racers alike at that year’s SEMA show in Las Vegas and I was plumb center of that group.

Big Block on a Budget

Figure 2. Published by CarTech under the SA design imprint this big block Chevy book has proved a runaway best seller in its category. The author, David Vizard, a successful race engine development engineer, deals out pin point tech accuracy. An instance here is the unique cam charts that allow a total novice to select an optimal cam in under 30 seconds!

Two versions of the 572 were offered. A street version with an electric choke vacuum secondary carb and a pump gas friendly 9.6/1 CR was rated at 620 hp and a race version with a bigger cam, 12.5/1 CR and a Dominator style carb at 720 horses could be had. Knowing how conservatively GM performance rates their engines in terms of output I wondered just how much these big motors really put out and more to the point what a few hop up changes might deliver. At the time of introduction I was up to my neck in the production of small block Chevy performance books and articles and could not see a window of opportunity to focus too much on big blocks. But slowly the road to big block work began to open up and when I was asked to do a big block Chevy performance book (actually a series of three) the way became clear. At this point I made it known to the powers that be at GM that if they could spare a development engine I would like to do an extended series of tests and product evaluations on it. It took a while before a surplus-to-requirement motor was available but the wait was well worth it. I got a call letting me know a street 620 horse 572 with minimal use was available – where did I want it delivered. I told them and a couple of weeks later there, on the workshop floor, was a shiny 572 ready to go other than the carb. GM had done their part now it was down to me to show just how much potential this 572 big block had.

David Vizard

Figure 3. David Vizard, the author of this feature, is known as a prolific automotive tech writer with nearly 4000 main feature articles and 34 books (35th on its way) to his credit By profession, he is a research and development engineer. He came out of the aero-space industry in the late 1960’s and has worked in the race car business as a professional ever since. He has his name on over 40 patents ranging from cylinder heads to fuels. He is also a university lecturer and an experienced race car driver with many track records and championships to his credit.

Dyno Facility

As you can imagine a project of this stature requires the efforts of more than one person. Here I was fortunate enough to have the aid for the initial foray into advancing big block tech, of Terry Walters of Terry Walters Precision Engines (TWPE) in Roanoke VA. Terry is a now retired ProStock racer and engine builder. He is by no means new to big blocks. He piloted a Chevy powered IHRA ProStock car for the best part of 20 years. Also assisting here was Terry’s right hand man Jack Sain – a guy who has some 35 plus years of dyno test experience on high performance and race engines. The first step in our quest for greater output was to establish just how much power this motor put out as-received.

First Rounds – What to Do

When GM specs out a motor reliability ranks as the #1 criterion. With a strong emphasis on reliability everything about this engine has to be conservative so as to deliver the reliability and durability we have come to expect from GM. Also when they advertise a motor as making a certain amount of hp it had better do that otherwise they are not delivering on the advertised output. What this means to us as hot rodders is that we can tap into the big blocks potential for more power while still keeping viable mechanical safety margin in hand so as minimally impact reliability. Fortunately for us Chevy’s big block is one of, if not the toughest, production big block engines made. As for as-received output our first tests would reveal just how much power was produced compared to the 620 advertised hp. Our first series of pulls then were to dial in the timing and carburetor. The result, with an electric instead of mechanical water pump, was 682 lbs-ft and 634 hp on a dyno that tends to read lower than most so GM really does under promise and over deliver!

With a baseline established the first job was to decide what moves should initially be made. After a little discussion between Terry, Jack and I it was unanimously agreed that the best plan of attack was to look at what basic upgrades in single and multiple forms could be done to our street spec 572. The goal here was to see if we could find more output with zero impact to the street drivability of the engine. Since the introduction of this motor back in 1998 there have been significant advances in cam and valve train design, carburetors and exhaust systems. All of these design developments are practical to apply to our 572 so are promising avenues to pursue for our initial investigations.

As good a place as any to start here is the cam and valve train. Traditionally cam specs are developed via the experience of the engineer responsible and possibly a lot of dyno testing to establish the results fit the requirement. During the last few years I have managed to get the latest iteration of my ‘Torque Master’ program up and working after over a decade of developing it. Since then it has been improved upon and can predict what is needed in the way of valve events when given the data to model the engine. This one-of-a-kind program has proved extremely accurate at predicting the cam events required for an engine. A detailed spec of the engine is fed into this program along with the application and in seconds the program responds with a cam spec that is about optimal for the job in hand. What this means is that instead of days testing a dozen or more cams the Torque Master program nails down what is required for the specific engine and application concerned in a matter of 90 seconds. Since this is a street motor all the current street attributes this engine has must be either retained or improved upon.

Cam Shaft

Figure 4. If the heads are the engine’s lungs then the cam is the heart of the engine. Unless the valves are opened and closed at the right moments to suit the cylinder heads breathing characteristics in relation to the cubes that have to be fed power will not be made as effectively. This new cam drew heavily on computer modelling to optimize it’s valve events. The results show this obviously worked well.

But at the end of the day it’s mostly the overlap used that determines the idle quality, not the Lobe Centerline Angle (LCA).

With a predetermined limit of 0.400 lobe lift the data for the engine was entered into Torque Master and the cam spec it produced differed somewhat from our 620 horse 572’s current cam. First it was shorter as measured at the 0.050 tappet lift point. The existing 620/572 cam profiles are 254 degrees on the intake and 264 on the exhaust on a 112-degree lobe centerline angle. With 1.7 rockers this cam delivers 0.632 lift for both valves. The Torque Master generated spec was 250/258 at 0.050 on a 107-degree lobe centerline angle with a valve lift of 0.680 on both valves. What we have here then is a cam that is 4 degrees shorter at the 0.050 mark on the intake and 6 degrees shorter on the exhaust. At the lash point (0.006 for a hydraulic) the situation is even more pronounced. Here the duration figures are more like 10 and 12 degrees shorter for the Cam Master spec’d cam. But the real big difference here is in the cams Lobe Centerline Angle (also known as the Lobe Separation Angle).

Cam testing

Figure 5. No serious cam testing can be done on a single cam engine without the aid of an adjustable cam drive as per this Jesel unit. This allows the speedy adjustment of the cam advance/retard within the engine so as to find the valve event sweet spot.

The 112 for the original cam is tightened to 107 for the new cam. This tightening of the LCA in conjunction with the duration used, if done without due caution, can compromise the idle quality of an engine. But at the end of the day it’s mostly the overlap used that determines the idle quality, not the Lobe Centerline Angle (LCA). Here we find that the original Chevrolet Performance cam (#88961557) has 105 degrees of overlap as measured at the lash point and 48 degrees as measured at the 0.050 tappet lift point. The Torque Master spec’d cam has the same 105 degrees at lash but, at 44 degrees, slightly less at the 0.050 point. So what does this mean in terms of idle quality? As Jack Sain pointed out “if practice follows theory we should find that at the same RPM the new cam will idle smoother and with slightly more vacuum”. Terry Walters also put his ten cents worth in here and noted, “As far as output goes we should find that the added lift of the new cam more than compensates for the shorter In/Ex durations involved. Also closing the intake valve some 10 degrees sooner (84 after BDC instead of 94) should all add up to much more low speed torque.

Cam Test Dyno Numbers

Doing a cam test is a lot more complex than is often supposed. It is not enough to just swap one cam for another. Before putting the test 572 on the dyno to test the stock cam it was necessary to replace the stock timing gears with a Jesel fully adjustable belt drive system. This allows the cam to be advanced or retarded as necessary until best output is seen. Terry Walters commented that he fully expected the stock GM cam to be timed in optimally as it left the factory. A batch of tests were done with the cam as factory installed and at 2 and 4 degrees either side of this. We won’t show the 10 curves involved here as it just looks like a grossly over filled piece of graph paper. Suffice to say that the best setting was, as expected, right where the factory put it and this was used as the baseline curves representing the best the stock cam can deliver.

So did the new, shorter duration, high lift, tighter LCA cam produce as predicted? To see how theory turned out in practice refer to the nearby graph. As you can see it bumped up the torque everywhere. Just as expected by most of us in the dyno cell torque went up. In this instance it was by some 60 lbs-ft at the lower end (3300 rpm) and this all came with 12 more horses at the top end. However there was more to this new cam than shown on the graph. Because the cam made so much more low-end torque the dyno was not able to pull the rpm down quite as far as we would have liked. The chances are that, at say 3000 rpm, it could be up by way more than at the first point shown (3300 rpm) on the graph. Another factor here is because the overall increase in torque, peak power was made at some 200 rpm less with the new cam. As dyno cell technician and head porter Sam Boase commented “you can’t beat a big block Chevy for pure Richter scale value” With that new cam those thundering big block exhaust pulses hit like a .44 Magnum and made standing by the engine feel like a minor earthquake.

Torque and Horse Power Stock Cam

Figure 6. The blue lines in this graph represent the torque and hp output given by the stock 572/620 horse cam and the red ones those of the new cam. Note the huge increase in torque at the lower rpm shown on the graph. Also the torque seen was better throughout the rpm range and resulted in an increase of some 12 hp at peak output but at 200 rpm less than the stock cam. Average torque and hp were up by 22.2 lbs-ft and 18.6 hp over the range tested. This increase makes for a great street cam with more of everything needed for a street performer.

Now how about that idle. There are plenty of souls among us that like a lopey idle as it forewarns of things to come when the gas pedal is crunched to the floor. As it happens, at the same stock cam idle speed the new cams tendency to lope was noticeably less. However, the new cam was capable of supporting an idle speed about 100 rpm less and at that point the lope was back in full swing. The new cam also had a much different exhaust note in as much as it sounded a whole lot meaner from idle all the way to 6200 rpm.

All the initial cam testing was done at the beginning of our development. Since then we have had the opportunity to revisit the cam situation and fine tune it. The current sec is 250/254 at 0.050. that’s 4 degrees less on the exhaust. This was found to make the same top end but added about 5 lbs-ft at the low end. Also, to extens spring life the lobe life on the cam was reduce some. Overall the new spec cam produces virtually the same output but with spring life significantly increased. The part number for this cam is TBCW13087/3020-07. Just for the record this cam will work as intended in engines from 540 to 585 inches with intake valves of 2.25 to 2.3 inches diameter, CR of 9.4-10.5/1 and intake port volumes from about 300 to 345 cc. The cam shown here was used with the existing 572 valve train. If you want a cam like this for a 540 to 585 inch big block then, at present, Terry Walters Precision Engines (TWPE) is your only source.

Induction Investigation

Our cam tests then mean we have made a successful start down the road to both a greater and more streetable output from our 572. Next on the list to look at is the induction. This needs to be of concern because we are dealing with a very large engine, which, as delivered, has a relatively small carb. Now at first sight that may look somewhat out of step but this engine was originally intended to have good road manners while being able to produce streetable crate motor power second to none. The 620 plus hp it produces in stock factory form was well within the capability of a carb such as Holley’s vacuum secondary 850 we baselined on. The fact a vacuum secondary carb was used tells us that street driving and even mileage were much more than just a minor priority by the engineers who originally worked on the 572.

850 Vacuum Secondary Holley Carburetor

Figure 7. Seen here is the trusty 850 vacuum secondary Holley carb we baselined on. On a big inch street motor in the 550 to 650 hp range this carb is a good, cost effective, choice.

The baseline carb used then was a time proven Holley 850. However, Holley’s carburetor engineers are continually under the gun to refine the carbs they produce in an effort to keep pace with the outputs delivered by literally dozens of fuel injection systems striving to take their market.

This competition is good for the end customer and in this context Holley has produced, in the last 10 years, some really outstanding refinements that offer significantly improved performance potential. The new range of high performance street and race carbs are just such cases in question. The plan here is to test the practicality of replacing the trusty vacuum secondary 850 with a 950 HP mechanical secondary carb and to do so with no significant penalty? As you might expected we hardly went into this test with closed eyes. Previous experience with the current range of 950 HP Holleys on big blocks ranging from 454 to well over 500 inches at TWPE had shown premium results every time with nothing more than simple jetting to get the results. This round of tests with the 950 Ultra race carb on the test 572 was no exception. Good results were expected and, as can be seen nearby graph, after Jack Sain’s calibration skills had been put to work, is just what was delivered. The average torque went up by 15.7 lbs-ft and the average hp by 14.6. We were now seeing a peak torque of 710 lbs-ft and a peak output of 660 hp. These numbers are good and a point not to overlook here is that these increases came together with a more streetable power curve.

The Holley HP Ultra Series Carburetors

Figure 8. The HP Ultra series carbs from Holley are endowed with many new features too numerous to list here. One however which will appeal to racers who track calibrate the carb for the prevailing weather conditions is the fuel drain plug conveniently situated where the exiting fuel can be easily caught in a small container.

At this point then we have seen the benefit of the increased flow capacity of a 950 HP Ultra versus the 850 cfm of the original carb. The problem here if we are talking true street usage is that the 950, being a race carb, comes without a cold start system and does not have a vacuum secondary setup. Because our test 572 really liked that extra cfm it was decided that we would see if we could instigate the development of a bigger carb just for street use on high output big block Chevy’s. This carb would, in essence, be an 850 vacuum secondary carb on steroids. The target is to produce a 960 street carb. As I write this the first prototype, with a cfm rating of 930 cfm has been tested and produced promising results. Prototype #2 is coming along and so far has delivered 955 cfm. That should go on the dyno soon.

Black finish 950 HP Ultra Holley carburetor.

Figure 9. Here is the black finish 950 HP Ultra Holley carb ready for action. The calibration as received from Holley was close for our application. On this 572 the only calibration changes were made were the main jets.

850 vs 950 Holley Carburetor

Figure 10. As this graph shows our 572 really liked the change to the Holley 950 HP Ultra carb. It should be noted that low speed gains are not brought about by an increase in CFM. The fact that the low speed torque went up by some 20 lbs-ft meant that some other factor, such as fuel atomization characteristics, was likely more suited to the 572’s requirements.

More Induction?

The success of the 950 Holley over an 850 on our 572-inch big block prompted another question. Since more induction airflow proved beneficial to this obviously air-hungry big block via the use of the 950 HP Ultra how would the induction system react to a higher flowing and more race orientated intake manifold? We had an intake which was a proven race piece for engines in the 675-900 hp range. Swapping over to this manifold would allow us to evaluate the performance capability of the stock GM manifold at this engines current near 700 hp output. When an engine, such as our

Sniper Jnr

Figure 11. Here is the Sniper Jnr on an 808 hp 496 big block. Notice how tall it is compared to the 572’s stock GM intake. The fact that the stock intake can almost keep up with this intake within the 700 to 800 hp range is a true testament to it’s worth on a street motor.

572, is demanding a great deal of air for high output the intake manifold’s flow efficiency needs to be high. If it is, the engine’s air demand will be communicated more directly to the carb with minimal manifold losses. This means that if the engine needs more air installing a higher cfm intake manifold should pay off much the same as the step up to a 950 did. To establish the stock GM manifolds capability here Jack Sain prepped a Profiler Performance Sniper Jnr intake with a port match job and a 4500 to 4150 carb pad adaptor for use with the 950 Holley. The Sniper Jnr’s runner size was of the same order as the stock GM intake but the manifold was much taller with a steeper port downdraft. Numerous previous tests on heavy breathing race engines tells us this Darin Morgan designed manifold was very effective and has more than proven its worth on 496 to 540 inch engines in the 700 to 950 hp range which is close to where our 572 is at present.

The Sniper Jnr versus stock intake test proved very interesting. After a very careful tune-up with the Sniper intake the engine only produced a 6 hp increase right at the top end. At the lower and mid-range rpms our test engines stock intake matched or even marginally beat the output given by the Sniper Jnr. What this shows us is that even though it is a lower profile intake the stock Chevrolet Performance casting is, at this stage and probably up to about 800 hp, more than up to the job of effectively feeding our 572. This indicates, in no uncertain terms, that even in street form, our 572 wants more carb cfm and that the stock intake manifold is, at the present power levels, more than up to the job of meeting the engines needs. Unlike the race bred Sniper Jnr the stock GM intake fit’s under many hoods without the need of a hood scoop and does so with only a minimal sacrifice in output. For those two reasons we are going to do much of our initial testing with the stock GM intake as its capability has been well demonstrated at this and similar power levels.

Exhaust System on Performance Engine

Figure 12. To a large extent any modern high performance engine is only as good as the exhaust system it is equipped with. In this illustration you get a panoramic view of the Hooker headers used for most of our dyno testing. They were very much an integral part of the success of the project to date.

So where do we go with our 572 for the next batch of tests? Obviously there is more to be learned on the subject of carb cfm so this will be one of the area’s I will explore down the road. In the next round of tests we will look at possible cylinder head upgrades as the ability to produce more accurate ports for a given cost has opened up some interesting possibilities since the original GM head saw the light of day back in the late 1990’s.

David Vizard.

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