supercharger and turbo cams

grumpyvette

Administrator
Staff member
read post #7 first, and if your buying a turbo cam you want limited overlap, early exhaust closing and try to select a turbo cam with a max lift in the range of 30%-35% of the intake valve diameter.

http://store.summitracing.com/egnsearch ... 115+307987

http://www.corvettefever.com/techarticl ... index.html

http://www.dougherbert.com/blowercamsch ... 0_633.html

http://www.peregrinesupercars.com/Camshafts.htm

https://www.hotrod.com/articles/ctrp-1106-turbo-camshaft-guide/

http://www.carcraft.com/techarticles/ct ... index.html

http://www.hotrod.com/pitstop/hrdp_1011 ... index.html

https://www.procharger.com/catalogs/ProCharger_Corvette_catalog.pdf

keep in mind limited overlap and extended duration cam timing on the exhaust timing on superchargers is fairly common , on turbos limited exhaust duration to limit back flow is more common, but turbos work best with higher exhaust pressure so the EVO is delayed and the wider LSA is used. but in both cases lower static compression and larger port cross sectional areas tend to help volumetric efficiency, compared to a N/A engine combo
When your using this style TURBO CAM the exhaust duration is usually some 5 to 10 degrees smaller in duration, but it holds the valve open a bit later. The reason is you don't want an early evo because you're blowing the cylinder down when you do this, so we gotta remove the duration so the exhaust valve starts to open later when there is more pressure in the exhaust gasses in the cylinder which results in increased pressure that tends to help spooling the turbo up faster due to that increased pulse pressure, Below is the type/style of hydraulic roller camshaft I would use with a super or turbo build with heads that flowed like the AFR 210cc on a SBC of about 406 displacement and about 8:1 static compression,obviously many parts would be similar but obviously some need to match each application
this style turbo cam,
240/232 @.050" tappet lift
.635"/.600" with 1.6/1.6 rocker arms
110 lobe center, installed at 110 intake center line

A crank driven supercharger on a similar engine would have a vaguely similar cam
centrifugal supercharger cam,
240/248 @.050" tappet lift
.635"/.630" with 1.6/1.6 rocker arms
113 lobe center, installed at 110 intake center line


comparecam.jpg


you could improve the engine efficiency with a super charger equipped engine combo,with a bit longer intake and extended exhaust duration increase lift and a wider LSA.
obviously you'll want to verify clearances
https://www.crower.com/camshafts/ch...orced-induction-noscam-small-base-circle.html

LiftCurveAread.gif


pistonposition2a.jpg

related useful info you should read

http://garage.grumpysperformance.co...lsa-effects-your-compression-torque-dcr.1070/

https://itstillruns.com/choose-cams-supercharger-7959078.html

https://www.enginelabs.com/engine-tech/inside-forced-induction-camshaft-designs-howards-cams/

http://www.kcams.co.nz/Menu/Selecting-A-Camshaft.php

http://garage.grumpysperformance.com/index.php?threads/supercharger-and-turbo-cams.1226/

https://www.hotrod.com/articles/hrdp-1011-cams-for-turbocharged-engines/

https://www.hotrod.com/articles/ctrp-1106-turbo-camshaft-guide/


Supercharged / Turbo Charged

Supercharged engines typically have a shorter intake, longer exhaust, and wider lobe center angle (LCA).
Supercharged engines can continue pushing charge into the cylinder longer than an NA (normally asperated) engine, and also the greater pressure differential between the manifold and the cylinder means the cylinder is filled quicker. This means they like a shorter intake duration on a later centerline, compared to thier NA counterparts.
Higher cylinder pressure after combustion means more gas to get rid of, so the exhaust valve is opened earlier than on an NA engine. This means longer exhaust duration, on an earlier centerline.
Early exhaust centerline and late intake centerline means a wider LCA. This means there is less overlap which also helps stop the pressurized intake charge being lost out the exhaust valve.

Turbo Charged engines are more complicated.
Before the turbo charger reaches an efficient speed the engine behaves much like an NA engine, albeit a low compression one. This means to get the cylinder filled efficiently and producing good amounts of exhaust gas to 'spool up' the turbo the ideal would be a relatively tight LCA. However once the turbo has 'spooled up' and is efficient the engine behaves more like a conventional supercharged engine and wants a wider LCA.
Turbo engine camshaft selection, and the overall performance of the engine, is greatly effected by the turbo selection.
It is easier to get a turbo to spool up at lower rpm by choosing a smaller exhaust turbine housing than by manipulating cams. This means the cams can then be optimised for 'on boost' performance.
Typically higher boost levels, and higher rpm, require more cam duration. The main difference between supercharged and turbo charged engines, is that turbo engines do not flow from the intake out the exhaust, at overlap, as easily as a supercharged engine, and therefore tend to open the intake valve earlier. So turbo engines tend to have a longer duration intake than a supercharged engine, but still shorter than an NA engine.
The turbo charger should be selected before the camshaft, remembering that a turbo, much like a supercharger, can restrict power if it is not big enough.
 
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http://www.turborides.com/article3.html (I FOUND THIS ON LINE,SOME OF THE INFO USEFUL)

Pressure Differential

Unlike a supercharger that is driven directly form the crankshaft, a turbo is driven by exhaust gas velocity. Turbochargers are an exhaust restriction (which raises the exhaust gas pressure), but since they use energy that would otherwise be wasted, they are much more efficient than a belt driven supercharger. Normally when the exhaust valve opens, there is still useable pressure in the cylinder that needs to be dumped so it will not resist the piston trying to go back up the bore. That pressure makes high exhaust gas velocity. With a turbocharged engine, this is the energy that is used to spin the turbine.

With a well matched turbo / engine combo, boost pressure should be higher than exhaust gas pressure at the low side of the power band (near peak torque). As the engine nears peak hp, the pressure differential will get nearer 1:1. At some point the pressures in the intake and exhaust will be equal then crossover making the exhaust a higher pressure than the intake. At peak hp there will usually be more exhaust gas pressure than boost pressure. The ultimate goal is to have as little exhaust backpressure possible for the desired boost.

If the turbocharger is matched well to the engine combination, the camshaft selection will not need to be much different than that of a supercharged engine. The problem is that most factory turbo engines have turbo's that are sized too small and will usually have more back pressure than boost pressure over much of the useable power band. Car manufactures do this in an attempt to reduce turbo lag. When a turbocharger is too small, it will be a bigger restriction in the exhaust, causing more back pressure. A big mistake of turbo owners is to crank the boost up as high as they can thinking they are going faster, but in reality, chances are that they are just killing the efficiency of the turbo and most gains are lost. If you want to run higher boost levels and back pressure is a problem, cam timing can be altered to give respectable power increases for much cheaper than a new turbocharger. Before you go increasing boost and changing cams, remember that the oxygen content into the engine will increase power, not boost pressure. A good flowing head with a good intercooler can make a lot of power without high boost. You may not need more boost to get the power you want.

Valve Overlap

If you're one of many factory turbo car owners with a turbo sized too small, there will be higher exhaust pressure than intake. You should see that if both valves are open at the same time, the flow would reverse. Any valve overlap is a no-no if you're looking for higher boost with a restrictive turbine housing. The exhaust valve will usually close very close to TDC, but there is will still be more pressure on the cylinder than in the intake. You must allow the piston to travel down the bore until the pressure is equalized. If the cylinder pressure is lower than the intake manifold pressure, no reverse flow will take place. This means that the intake valve needs to open 20-35° ATDC, depending on the amount of boost you're using. Most street turbo's will work well when the valve opens close to 20° ATDC, only when boost gets near 30 psi will you need to delay it as much as 35° ATDC. In low boost applications (under 15 psi or so), opening the valve closer to TDC and maybe keeping the exhaust valve open a little after TDC is a compromise for better throttle response before the boost comes on. As you increase boost, you will need to delay the opening of the intake valve to avoid reversion. You want the intake valve to open as soon as possible, in an ideal situation, the intake valve should open when the pressure in the cylinder is equal to boost pressure. This can cause a little confusion with cam overlap. If the exhaust valve closes before the intake opens, the overlap will be considered negative. If the exhaust valve closed at TDC and the intake opened at 20° ATDC there would be -20° of overlap. In this type situation, pumping losses are quite large, although the turbo will still use less power than a crank driven supercharger.

If you have a well matched turbo for the engine and application, it is a different deal altogether. A well matched turbine housing on the turbo will usually work well with cams with a lobe separation in the 112-114° area. If there is more pressure in the intake than in the exhaust, a camshaft suited for superchargers or nitrous will usually works well. When the exhaust backpressure is lower than the intake, reversion is not a problem, actually just the opposite is a problem. More pressure in the intake can blow fresh intake charge right out the exhaust valve. This can be a serious problem with a turbo motor since the charge will burn in the exhaust raising temperatures of the exhaust valves and turbo. This is also a problem with superchargers, which is why supercharger cam profiles usually work well with turbo's. In this type situation, the power required to turn the turbine is nearly 100% recovered energy that would have normally been dumped out the tailpipe, basically free power. Many will argue that nothing is free and you need pressure to spin the turbine and this must make pumping losses. They are wrong because a turbo is not getting anything for free at all, it is just making the engine more efficient. It is true that there are pumping losses, but on the other hand there are pumping gains as well. If the exhaust back pressure is lower than the intake, the intake pressure makes more force on the intake stroke to help push the piston down. At the same time another piston is on it's exhaust stroke. So the intake pressure is more than canceling out the exhaust pressure. Not free, just more efficient.

Valve Lift

By delaying the opening of the intake, the duration of the cam will be much shorter. A short duration intake works well with a turbo, but the problem is that sufficient lift is hard to get from such a short duration. This is where high ratio rockers can really pay off. A cam for a turbo engine can delay the intake opening by over 40° compared to an cam for a normally aspirated engine. This makes for much less valve lift when the piston is at peak velocity (somewhere near 75° ATDC), any help to get the valve open faster will make large improvements.

Roller Camshafts

Turbo motors place a large flow demand at low valve lifts, and roller cams cannot accelerate the valve opening as fast as a flat tappet. They do catch up and pass a flat tappet after about 20° or so, but up until that point the favor goes toward the flat tappet cam. The area where rollers really help in turbo motors (and supercharged) is cutting frictional losses. Any forced induction engine will need more spring force on the intakes. If you run a lot of boost, you'll need quite a bit more spring force to control the valves. As spring forces gets higher, the life of the cam gets reduced. A roller tappet can withstand more than twice the spring pressure as a flat tappet with no problems. On the exhaust side, it's not the springs that put the loads on the cam lobes. The problem there is that there is still so much cylinder pressure trying to hold that valve closed. This puts tremendous pressure on the exhaust lobes. So when high boost levels are used, consider a roller cam. I would definitely consider a roller cam on engines making more than 20 lbs. of boost.
 
https://www.hotrod.com/articles/ctrp-1106-turbo-camshaft-guide/
The scene is the local cruise hangout. The hood is open on a young car crafter's black-primer Pro Street Mustang, and a small group eavesdrops on a deluge of overlapping technical discussions regarding turbos, boost, camshafts, and a dizzying array of other power-related topics. The Mustang driver innocently asks for feedback on his cam selection and is quickly barraged with several contradictory recommendations, each of which are vehemently defended as gospel. The young driver is soon overwhelmed and quickly closes the hood of his car and leaves while a pair of turbo true believers square off in a technical fencing match that looks as if it will devolve into a jihad-like religious riot complete with willing martyrs.



While this scenario might be fictional, the debate is real enough and rages across the Internet in forums and tech chat rooms dedicated to anything related to boost. The problem with opinions is that everybody has one, with few rooted in real-world experience or established combustion theory. So we decided to seek out those who talk less and race more. Our participants include Kenny Duttweiler, who began experimenting with and racing turbo Buick V6 engines virtually from the moment those black sedans hit the showroom. He now builds the maxi-turbo'd, mini displacement, 299ci small-block Chevy powering the George Poteet-driven Speed Liner Bonneville streamliner that blitzed the Salt with a 436-mph exit speed last year. We also talked to street and dragstrip turbo expert Kurt Urban, who lets his 100,000-mile turbocharged street truck speak for his knowledge of how to use boost to become an Urban guerrilla. Then we quizzed our favorite rocket scientist, Comp Cams' lobe designer Billy Godbold, who lent his insight into eloquently combining cam timing with boost pressure and not getting squeezed in the process.

Turbo Cam Basics
The one thing that all three of our noted sources emphasized is that the knowledge base established from turbochargers designed 10 or 15 years ago is antiquated when applied to the current crop of high-efficiency turbochargers—unless you're trying to get by on old, cheap turbos. "In the old days it was typical to see 1.5 to 2:1 backpressure ratios," Duttweiler says. "Today the backpressure is actually less than the boost pressure." The ratio Duttweiler is talking about is the relationship of exhaust backpressure to inlet boost pressure. Exhaust gas backpressure is naturally created when the hot gas exiting the exhaust ports arrives at the turbocharger's turbine wheel. The exhaust gas "stacks up" between the exhaust port and the turbine wheel, creating pressure as it would with any restriction. All internal combustion engines perform best when tuned with a certain amount of camshaft overlap in which both the intake and exhaust valves are open at the same time. If the exhaust backpressure is greater than the inlet pressure, the exhaust will push back into the cylinder and (given enough time) up into the inlet manifold. Exhaust gas doesn't burn a second time, so it works just like an emissions-era exhaust gas recirculation (EGR) system, reducing power, except it's happening at wide-open throttle (WOT). Because of the high backpressure ratio, older turbos required an earlier-closing exhaust valve, which was most easily achieved with a wider lobe-separation angle (LSA). This could be where the now-common wide-lobe-separation-angle theory propagated. According to Duttweiler, today's more efficient, larger turbos reduce that backpressure, which minimizes the power-robbing effect of exhaust dilution. That means the LSA can be tightened, which is contrary to the contention that all turbo cams must have wider 112- to 114-degree LSAs. With newer turbos, the reduced backpressure also means the exhaust valve can be opened sooner and held open longer, which is generally accepted as beneficial to high-rpm power production, just like on a normally aspirated engine. According to Duttweiler, to make good power, turbo engine efficiency depends more on low exhaust backpressure than tricks with the cam.


Duttweiler also mentioned that attempting to build a turbocharged engine with a set LSA (such as 112 or 114 degrees) can lead you astray. He mentioned some work he did way back in the early Buick Turbo V6 days while racing these engines in NHRA Stock Eliminator. Stock class rules required the intake and exhaust lift and duration specs to remain stock, so to improve power, he tightened the LSA on these engines to 109 degrees to help the Buick's really small cam improve power. The engine responded by building boost much quicker. "When you spread the lobe-separation angle way out, the engine gets lazy," Duttweiler says. As an example of a good V6 engine, Duttweiler says he built a V6 turbo Buick with a 215-degree-at-0.050 intake lobe camshaft that made 900 lb-ft of torque and 580 hp and idled at 16 inches of manifold vacuum. The concept of lobe-separation angle and duration is addressed more fully in the accompanying sidebar "Overlap Chronicles."
Duttweiler says this idea reinforces the concept that it's not necessary to use radical lobe designs with turbo engines. "A turbo allows you to run a milder lobe and valvespring package that's much easier on the engine." An example of this is a slew of very reliable turbocharged Bonneville engines built by several turbo engine builders, notably Duttweiler and turbo engine guru Mike Lefevers. Often these engines will make multiple 5-mile-long sustained WOT passes and require little more than pulling a spark plug for maintenance. A properly designed valvetrain and a less aggressive lobe design can virtually eliminate valvetrain problems such as broken springs, bent pushrods, and mangled rockers. There are caveats however. Duttweiler and Urban both emphasize that attempting to open the exhaust valve too early can cause bent pushrods. This is mainly due to the surface area of the exhaust valve attempting to open against high cylinder pressures. "You will need bigger pushrods," Duttweiler warns. "I see more bad things happen on the exhaust side trying to open against cylinder pressure."
Cylinder head selection also comes into play when selecting a camshaft. Just like with a normally aspirated engine, Duttweiler says a well-flowing cylinder head will allow shorter duration figures to carry the power to higher engine speeds. Less efficient heads do the exact opposite, requiring more duration to compensate for the weak flow. This is reinforced by what we've noticed here at Car Craft on our dyno testing of normally aspirated engines. With a given cam timing, adding better heads extends the peak power rpm point, while weaker heads will do just the opposite. But typically there are limitations when dealing with a turbo. Duttweiler warns that a properly designed turbo "will run the engine well past its ability to control the valvetrain and will go right into valve float!" That means valvesprings are just as critical as with normally aspirated engines. This tends to emphasize mechanical roller cams rather than hydraulic rollers, although hydraulic rollers seem to have an edge on durability for street engines.
If all this sounds just like what normally aspirated engines want (and it is), then go to the head of the class. Duttweiler says you can and probably should treat a properly sized, high-efficiency turbo motor like a normally aspirated engine. An early-opening exhaust valve can be beneficial for top-end power because even high-efficiency turbos still have to work against some exhaust backpressure. The earlier-opening exhaust helps to reduce residual pressure in the cylinder before the intake valve opens.
Advanced Classes
There's much more to cam timing selection, however, than simply tightening the LSA when using a more efficient turbocharger. The difficulty in choosing camshaft specs is that much of the advice that comes from professional engine builders is usually aimed at ultimate power applications such as Bonneville or 6-second, 2,400hp drag cars. Expanding on our comparison to normally aspirated engines, you wouldn't choose the same camshaft for a 500ci NHRA Pro Stocker as you would for a 350ci, 400hp street engine. Given this, there are many factors that go into choosing a camshaft for a street-driven turbocharged engine. Kurt Urban has tons of experience in such things, and he's used a variety of different cam designs based on how the engine will be used and the car it will power. When it comes to cams Urban says, "For me, it's what works in the car."

Urban went on to say, "I try to design a cam around what I think the driver needs. Everybody wants big power, but what you really need is a cam that races well." As an example, Urban says, "With a Powerglide, a big camshaft and a big turbo don't work well together. The car would be lazy off the line, and the power would only come on hard at the top end." So in that case, he says a shorter-duration camshaft would probably work better to launch the car because so much of elapsed time is based on starting line acceleration. "In drag racing you want the car to leave, so I take into account what the car weighs, the displacement, how good the driver is, and probably a dozen other details to fit the cam. Sometimes I'll cam the motor smaller to make the car easier to drive and add duration later as the driver improves."
As an example, Urban says, "I built an engine for a drag radial car with a 427 LS. The camshaft had the normal split at 260/272 degrees (at 0.050) with a 115 separation angle. The motor used 1,400 pounds of fuel at max power, and the car runs 7.20s at more than 200 mph. At 1,400 pounds per hour—that's well over 2,000 hp. I tried a 272/280 cam to make more peak power, but the car ran slower because it wouldn't leave even though it made 5 more pounds of boost at the top." As both Duttweiler and Urban have emphasized, this is much like a normally aspirated engine in which too much duration killed the bottom-end power and the car ran slower.
To emphasize that taking into consideration how the car will be used is critical to camshaft selection, Urban built an engine for a heavy street car that appears to fly in the face of conventional turbo cam wisdom. "I built an LS engine with a 227/223 cam with 0.614/0.610 lift with a 72mm turbo—it makes 900 lb-ft of torque at 3,500 rpm in my all-wheel-drive Chevy truck. It runs 11.40s at 120 mph and I've got over 100,000 miles on it!" Here the application demands lots of torque because the engine builder is faced with a very heavy vehicle with a tight torque converter and not much gear ratio to help it get moving. The combination of a short-duration intake lobe with an even shorter-duration exhaust lobe than the intake (sometimes called a reverse split cam) means the cam timing emphasizes low-speed torque as evidenced by the incredible torque at a relatively low engine speed.
Urban went on to say "Turbo engines run faster (at the track) when you open the exhaust valve sooner. With short intake duration, the engine responds with speed at the track. By opening the exhaust valve sooner with either a tighter lobe-separation angle or long exhaust duration, the engine generally responds better. You will lose scavenge if you open the exhaust valve too late."
Overlap Chronicles
Overlap is defined as the number of crankshaft degrees of rotation established between when the exhaust valve closes (EC) and the intake valve opens (IO). This is established by several factors. We discussed this idea with Comp Cams' lobe designer Billy Godbold. Godbold says the popular belief is that the lobe-separation angle is responsible for the amount of overlap, but that is only partly true. The important other half of the equation is the length of both intake and exhaust lobe durations. If either intake or exhaust duration increases, it will affect overlap. The accompanying Comp Cams illustration makes this easier to understand. If we move the intake and exhaust centerlines closer together, the angle gets smaller—as from 114 degrees to 110 degrees. When this happens, that small triangle that indicates overlap increases in size.
With a given lobe-separation angle, overlap will increase with added duration. We've included a short explanation of how to calculate overlap from the opening and closing points given on the cam card. In our case, the specs for these three Comp cams are offered at 0.006-inch tappet lift. As you can see, increasing the duration from the smallest to the largest cam increases the overlap by an amazing 12 degrees, even though the lobe-separation angle remains at 110 degrees.
How to Calculate Overlap
Comp Cams XR276 HR hydraulic roller cam PN 12-423-8
Duration: 224/230 degrees at 0.050 at 0.006-inch tappet lift
Cam installed at 106-degree intake centerline
Overlap = Exhaust Closing (EC) + Intake Opening (IO)
Intake events: IO = 32 BTDC; IC = 64 ABDC
Exhaust events: EO = 75 BBDC; EC = 27 ATDC
Overlap = 27 + 32 = 59 degrees

Now let's look at three hydraulic roller camshafts with three different intake and exhaust durations yet with the same lobe-separation angle of 110 degrees. All overlap figures are given at 0.006-inch tappet lift.
Comp XR 270: 218/224 degrees duration at 0.050
Overlap = 24 + 29 = 53 degrees overlap
Comp XR 282: 230/236 degrees of duration at 0.050
Overlap = 30 + 35 = 65 degrees overlap
Comp XR294: 242/248 degrees of duration at 0.050
Overlap = 36 + 41 = 77 degrees overlap
Even though the lobe-separation angle of 110 degrees did not change with these three cams, the overlap increased a total of 24 degrees because both the intake and exhaust durations increased by 12 degrees with each larger cam.
More modern Tech info I found.
Its 8 years old now the article but it the basis of modern Turbo Boost platforms I have worked on & seen.

High Boost engines are another story...21-28 psi / 32-60 psi.
 
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https://www.enginelabs.com/engine-t...cam-test-set-the-stage-to-higher-performance/

Turbo LS Cam Test — Set The Stage To Higher Performance


By RICHARD HOLDENER AUGUST 30, 2019


Is it really possible to add more than 100hp to your LS motor with a cam swap? The answer is obviously yes, or this would be one very short and disappointing tech story. Before we get to the test, we first need to understand why it might be possible to get such big gains for a simple cam swap.


How much is a cam really worth on a streetable turbo LS application?

Naturally, the presence of forced induction plays a major part, but LS engines have a lot more going for them than just their propensity to swallow copious amounts of positive pressure. In terms of responsiveness to changes in cam timing, the GM engineers set the stage with the LS platform. What do we mean by this? Well, any LS motor has basically everything else it needs to provide premium performance, except the cam.


Our test motor is one of the most common LS engines found in junkyards. The junkyard 5.3L retained all of its factory components for our test, including the short block and factory 706 heads. Prior to testing, the motor received increased ring gap, new head gaskets, and ARP head studs. Although, none of this was mandatory at this power and boost level. We were prepping it for future testing.

No single component can make a motor, but almost any single component can break one. All it takes to ruin an otherwise perfectly good performance motor is one wrong part. Install the wrong intake, cylinder heads, or (in our case) camshaft, and you’ll have less than ideal results. When you cure the one missing component, the results can be amazing. The LS has plenty of displacement, head flow, and a more than adequate intake manifold. The only thing missing in the otherwise-perfect combination is adequate cam timing!


Knowing we had a cam swap coming up, we replaced the factory truck springs with a set of 26918 springs from COMP Cams.

So, just how much power did GM leave on the table when designing the cams for the various LS applications? In all honesty, the design criteria for the engineers was never to maximize power, but believe me, they certainly could. The factory offerings were (by design) mild compared to what was ultimately possible.

But, even the factory cams differed in their performance ability. Low-man on the power totem pole was obviously the cam used in our 5.3L LM7 (shared with the 4.8L LR4 and early 6.0L LQ4). Designed for low-rpm truck applications, the LM7 cam offered a .466/.457 lift split, a 190/191-degree duration split and 116-degree lobe separation angle (LSA).


We selected a set of FAST 89-pound injectors and FAST fuel rail for the TBSS intake to supply the necessary fuel for our turbo motor .

Let’s put this mild cam timing into perspective. The LS9 – the most powerful of the factory LS cams – offered a .558/.562 lift split, a 211/230-degree lsa, and 122.5-degree lsa. Though it was designed for a supercharged application, the LS9 cam was all but identical to the 427-inch LS7 cam. The difference being the LS7 cam offered more lift due to the 1.8:1 ratio factory LS7 rockers. The rest of the production cams (LS1-LS6) fell somewhere between these two extremes. Given the mild factory cam timing, it should actually come as no surprise that cam swaps on a naturally aspirated 5.3L can yield 40, 50, or even 60-extra horsepower.

The gains offered by cam swaps on the LS have been well documented. But, what allows a gain of 40-60hp on a naturally aspirated LS to exceed 100hp on a boosted one? The answer is in the multiplier effect. A naturally aspirated engine is already running under an atmospheric pressure of 14.7 psi. So, all we have to do to double the power output of say, a 300hp engine, is double the pressure, right? If we apply 14.7 psi of boost to the same 300hp naturally aspirated engine, we can see 600hp.


Dialing in the air/fuel and timing values was a Holley HP engine management system. The A/F and timing curves were kept constant for the two cams.

Why we don’t always see that much power is often a function of things like the tune, charge cooling, and turbo efficiency, but rest assured, it is possible. In fact, it is possible to exceed this simple formula with sufficient charge cooling (by using things like ice water). The real exciting part is when we increase the power output of our naturally aspirated motor.

Suppose we add a cam to our 300hp test motor and increase the power output to 350hp. If we apply the same 14.7 psi of boost to the 350hp, we can now reach 700hp. The extra 50hp offered by the cam swap increased to 100hp under boost! The key here is to do everything you can to improve the power output of the naturally aspirated motor prior to adding boost, which includes cam timing.




To get things started, we ran the 5.3L motor naturally aspirated with a set of Hooker 1 7/8-inch headers. Not ideal for the mild 5.3L, but it’s what we had laying around.

For our test, we performed the cam swap on the turbo motor. We also included a naturally aspirated baseline run with the stock cam prior to the installation of the turbo kit. We did so mostly for our own benefit – making sure our DIY-turbo system was performing as it should before performing the cam swap. The test motor was your basic bread-n-butter beater – a junkyard 5.3L snatched from a local LKQ Pic-a-Part.


Run on the dyno in naturally-aspirated trim with the TBSS intake manifold and stock LM7 cam, the 5.3L produced 359hp at 5,300 rpm and 384 lb-ft of torque at 4,200 rpm.

The 5.3L LM7 is a favorite among turbo LS enthusiasts. Prior to our test, the 5.3L received increased ring gap, new Fel Pro head gaskets, and ARP head studs. With the cam swap in mind, we also upgraded the stock truck valve springs to a set of 26918 springs from COMP Cams. We replaced the stock (early) truck intake with a Trailblazer SS (TBSS) manifold equipped with FAST 89-pound injectors. The TBSS intake was fed by a FAST 92mm throttle body. Run with a set of 1 7/8-inch, Hooker Headers, the naturally aspirated 5.3L produced 357hp at 5,600 rpm and 383 lb-ft of torque at 4,200 rpm.


After the NA baseline runs, we installed the Hooker turbo manifolds.

To run our turbo cam test, we configured the 5.3L with a homemade, DIY-turbo system. The basics of our turbo kit included Hooker cast manifolds, a custom 2.5-inch cross-under merge pipe, and 7675 PTE turbo. The Precision turbo was capable of supporting over 1,200hp, or more than enough for our little 5.3L. The PTE 7675 fed boost through a sizable air-to-water intercooler from Procharger. Like the turbo, the intercooler was oversized for our application and was fed a steady diet of 85-degree dyno water.


The manifolds featured a cross-under tube to channel the exhaust from the driver’s side to the passenger’s side merge manifold.

We fabricated a single 90-degree bend that connected the T4 turbo-flange on one end to the 3.0-inch V-band on the exit of the Hooker turbo manifold. This custom adapter also featured a provision for a single 45mm Hypergate wastegate from TurboSmart. In addition to the wastegate, TurboSmart also supplied a Race Port blow-off valve and manual wastegate controller. However, we relied on a 10-psi spring for this test.

Exhaust from the turbo exited through a single 4.0-inch V-band exhaust equipped with an oxygen sensor bung. Run with the stock cam at a peak boost of 11.0 psi, the turbocharged 5.3L produced 603hp at 5,600 rpm and 612 lb-ft of torque at 4,600 rpm. Now it was time for the stage 2.


The exhaust energy was supplied to a single Precision 7675 turbo. The GT42 PTE turbo featured a 76mm billet wheel, 88mm turbine, and 1.28 AR, divided T4 turbine housing.

After allowing for a cool down, we tore into the 5.3L to perform the cam swap. Off came the damper, front cover, and cam gear, followed by the cam retaining plate, rockers, and pushrods. Using custom tools (no longer available), we made sure to keep the lifters in place during the cam swap. Out came the stock stick and in went the LJMS Stage 2 turbo cam supplied by Brian Tooley Racing.



The Stage 2 cam offered a sizable increase in specs, jumping to a .605/.598 lift split, a 226/231-degree duration split and 113-degree lsa. The lift increased by roughly .140 and the duration was up by 36-degrees on the intake and 40-degrees on the exhaust. The lsa shifted down by 3-degrees, but the important point is that the opening and closing events were designed specifically for a turbo LS application.


Boost was controlled by a single Hyper-Gate45 wastegate from Turbo Smart. The wastegate was equipped with a 10-psi spring.


After installation of the DIY-turbo system, the turbo 5.3L produced 603hp at 5,600 rpm and 612 lb-ft of torque at 4,600 rpm. Now, it was time for a cam change.


To provide access to the cam, off came the factory truck damper, followed by the front cover.


Removal of the front cover provided access to the factory timing gear. After lining up the marks for TDC, we removed the cam gear, followed by the cam retaining plate.


Out came the wimpy stock LM7 cam to allow installation of something considerably more powerful.


Designed by LJMS and supplied by Brian Tooley Racing, the Stage 2 turbo cam was made specifically for a turbo application. The Stage 2 cam offered a .605/.598 lift split, a 226/231-degree duration split, and 113-degree lsa.


In went the LJMS/BTR stage-2 turbo cam.


Run with the new turbo cam, the boosted 5.3L produced 730hp (actually 729.8hp) at 6,600 rpm and 649 lb-ft of torque at 4,900 rpm. The peak was almost identical (11.0 vs 11.3 psi), so the cam offered peak-to-peak gains of nearly 130hp. The gains out past 6,000 rpm exceeded 150hp (at the same boost!), which obviously sets the stage for even more power.

Obviously, they did their homework over at LJMS, as the turbo cam improved the power output of the boosted 5.3L to 730hp (729.8) at a higher 6,600 rpm and 649 lb-ft of torque at 4,900 rpm. The wilder cam timing traded off a few lb-ft of torque below 4,300 rpm, but offered peak-to-peak gains of 127hp and 37 lb-ft of torque.

The gains exceeded 150hp higher in the rev range and all the extra power is right where it can be taken full advantage of at the drag strip (or for any run through the gears).Since we ran this test at just 11 psi, the stage is set for even more power from this LJMS-cammed 5.3L with higher boost!


5.3L-NA vs Turbo (11.0 psi)

Adding boost to any LS motor improves the power output greatly, even one with a stock bottom end, stock cam, and stock heads. This 5.3L featured all stock (original) internals with extra ring gap (on the original stock rings), stock 706 heads with a spring upgrade, and a stock TBSS intake manifold. Run with the stock LM7 cam, headers, and the Holley HP management system, the naturally aspirated 5.3L produced 357hp at 5,300 rpm and 383 lb-ft of torque at 4,200 rpm.

After adding 11.0 psi of boost from the Holley turbo system, Precision 7675 turbo, and Procharger intercooler, the power output jumped to 603hp at 6,500 rpm and 612 lb-ft of torque at 4,600 rpm. Though this was a solid gain, we couldn’t help but wonder how much the stock cam was holding us back.


Turbo 5.3L Cam Test-Stock LM7 vs BTR/LJMS Stage 2 Turbo

It seems obvious from the looks of the graph that the stock LM7 cam was indeed holding us back. After installation of the BTR/LJMS Stage 2 turbo cam, the power output of the turbo 5.3L jumped from a hair above 600hp to 730hp at 6,600 rpm and 649 lb-ft of torque at 4,900 rpm.

The cam improved the power output by nearly 130hp, with gains exceeding 150hp higher in the rev range. Not only did the motor make considerably more power at the same boost level, but it allowed us to rev the motor past 6,500 rpm. The extra RPM would certainly come in handy at the drag strip.
 
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