Choosing a Cam for More Power | Project LS-Powered 350Z

Tom
Update by Tom Suddard to the Nissan 350Z project car
May 10, 2021

The LS1 fitted into our Nissan 350Z now had new heads—Air Flow Research CNC-ported cylinder heads—but we still had to fill in the other half of the equation: our camshaft.

Pair them correctly, and your heads and camshaft can become more than the sum of their parts. Choose poorly, though, and the fancy part on one side of the equation can be hamstrung by the incorrect choice on the other.

Our goal here is a bit complicated: the fastest lap times possible while staying under 393 maximum average horsepower, a NASA calculation we dove into in our last installment.

Basically, we want a high-revving race engine that also has a broad, flat power curve. So does everybody else, right? We’ll get as close to ideal as we can while working within our current constraint: our “small” 5.7-liter displacement.

 

How to Read a Camshaft Spec Card

We’ll preface this explanation with a disclaimer: We’re not camshaft experts. Our last name isn’t Iskenderian. That’s how we ended up with a fairly mild street cam in our 350Z when we originally assembled it.

This time around, though, we leaned heavily on a few trusted sources to keep us on the right track: the AFR help desk, our friends at Comp Cams, and LS-building legends/$2000 Challenge winners Andrew and Calvin Nelson of PACC Performance LLC.

Okay, let’s talk camshafts.

Pushrod V8s, like our LS1, have one, while engines with a more modern architecture usually have two or four. Either way, the function of the camshaft is the same: to push their lobes against the valves, causing them to open.

In overhead-cam engines, the lobes push directly on the lifters or rockers, which push against the valves. In pushrod engines like our LS, the camshafts push against lifters, which push against pushrods, which push against rocker arms, which push against the valves. Same theory, different packaging.

The shape, size and location of these lobes all present tuning opportunities. Each valve gets its own lobe—picture a circle wearing a triangular party hat.

That circle is called the base circle, and it’s where the valve spends most of its time. The valve is closed when it’s against the base circle of the camshaft.

The party hat? Welcome to the lobe itself.

The height of the hat is called the lift, meaning taller hats open the valve further. The hat can have different profiles, too, with some keeping the valves lifted (thus open) longer.

The amount of time that the cam profile opens the valve is called duration. It’s expressed as the number of degrees of crankshaft rotation where the lobe is above a specific lift number (usually 0.050 inch).

While that’s the common metric to compare cams, there’s also “advertised duration,” which is the point on the base circle where the lobe starts. Advertised duration is usually measured at 0.006 inch of lift. This isn’t as important as duration at 0.050 inch, but can help you picture the party hat’s shape. Is it narrow and tall? Or does it feature gentle slopes on each side?

Can you picture the shape and size of the party hat? Perfect, now let’s discuss its location: Moving the lobe clockwise or counterclockwise on the circle can adjust the valve’s timing, meaning when the valve opens and closes in relation to the engine’s rotation.

The number of degrees of camshaft rotation between the high points of the intake and exhaust valve lobes is called the lobe separation angle. And by putting the intake and exhaust valve party hats right next to each other, you create a situation where they’re both open at the same time. This is called overlap, and it’s generally desirable in race engines.

Finally, there’s the intake centerline. This is the highest point on the intake lobe, described as the number of degrees of engine rotation after top dead center. Basically, it shows where the cam’s valve timing will be in relation to the engine’s piston timing. Modifying this angle can move the torque curve higher or lower in the rpm range. This measurement can also be changed during installation: It’s common to advance or retard your camshaft timing while degreeing in the cam.

All these variables bring us to the almighty camshaft spec card. These are typically printed on half-sheets of card stock, and one should come in the box of every cam you ever buy.

They list every variable we just discussed. Think of your cam card as your camshaft’s driver’s license, as you’ll be asked to show it constantly.

Lifters, pushrods, valve springs, rocker arms, heads: None of them can be decided without first consulting the cam card. Your tuner will want a copy of it, too, to choose the best base tune for your build.

If all this sounds like too many variables to handle, you’re right. Most cam companies make hundreds of different combinations of all of the above, and many offer the option for a custom grind if you can’t find an off-the-shelf option that works.

 

I’m in Over My Head; Now What?

Oh, thanks for the reminder: Your heads drastically affect your camshaft and vice versa. Hooray for more variables.

Why does your camshaft care what heads you have? Because when the valves are closed, the airflow of your heads is irrelevant.

It’s only when the valves open, and your camshaft gets involved, that the flow through your heads matters.

And we’re not just talking about static flow bench numbers. Because a valve is only fully open in the middle of its journey up and down, a lot of your engine’s airflow happens with the valve halfway open (hence the hyper focus on valve seat angles by top builders. The speed and height of that valve opening affects how air flows through the head.

What’s this mean in practice? Generally, heads that flow better need lower valve lift numbers to achieve the same airflow. This is a good thing: Lower lift means less wear and tear, and less potential for valve float. And yes, there’s plenty more to say on this subject, but we know when our expertise has run out, and that time is now.

We know everything we just laid out was pretty scary—at least, it sure was for us as we sat next to a 350Z that we just wanted to make more competitive.

Fortunately, you don’t have to go through this process alone. There’s a bunch of ways to make sure you’ve picked the right camshaft for your car, with the difficulty ranging from “I should have gone back to college before attempting this” to “so easy a toddler could do it.”

 

How to Choose a Cam: Using Software

We’ll start with the method aimed at people with advanced engineering degrees: math.

Engines are just air pumps, and thanks to accurate machining, popular part combinations, and lots of groundwork laid by those who came before us, it’s possible to do the math and figure out your engine’s exact power curve on paper. It takes nothing more than a slide rule, scratch paper and some free time.

Math costs zero dollars, so you can pretend to dyno every cam in a company’s catalog if you have enough batteries for your calculator. Then you can choose what makes the best curve for your application on paper.

Okay, we’re being a tad disingenuous here: Accurately calculating the curve of an engine by hand is so time-consuming that it’s not really realistic.

Computers, though? They don’t even break a sweat when asked how much power an engine will make. A few different software packages are available to do this math, and we downloaded one from Performance Trends called Engine Analyzer.

For about $100, this Windows-only software lets you input literally every single variable in your engine, then virtually dyno-test it as much as you’d like. Its maker claims the software is accurate, and spoiler alert: Our dyno testing seemed to back that up. By using software tools, it’s possible to test multiple camshaft and cylinder head combinations against each other without leaving your desk.

But there’s a caveat: They can only do math, not measure your engine. And because there are so many variables involved, it’s easy to get off track if you make too many assumptions or use some bad measurements from the internet.

We were fortunate to be working with common parts in a common application, but be careful of compounding margins of error when doing this. After a few hours of learning the software and going on a scavenger hunt for data on our engine, we were dyno-testing camshafts we’d found online with a few minutes of work per cam.

 

How to Choose a Cam: Go to the Dyno (or Find Somebody Who Has)

This next method for choosing a cam is probably the most common, and for good reason: It just works.

Rather than measuring every input and mathing your way to the output, why not just measure the output on the dyno?

Well, there are drawbacks—time and money—but you can minimize these by following in others’ footsteps.

Thanks to the internet, odds are good that you can find somebody who’s built something similar for a similar application, then crib from their notes and data. It’s always a good idea to verify information as well as you can, but this method can work pretty well for common applications.

Building a junkyard turbo LS, for example? Don’t bother doing the math: Just use the Sloppy Mechanics camshaft recipe and enjoy your car.

 

How to Choose a Cam: Call for Help

We’re lucky: Thanks to the logo on our business cards, we tend to get more help than most when seeking parts for our builds. But we didn’t need that access to get help finding a camshaft for our 350Z.

Because every application is unique, most reputable camshaft makers have tech support at the ready to help answer all these questions. Comp Cams is one such company, and the staff there was more than happy to help us choose a camshaft that would bring our 350Z to the limit of NASA’s TT2 rule set.

After a week or so of email exchanges and at least one long phone call to discuss specifics, Comp came back with its recommendation, and it surprised us: “We think this camshaft best fits what you told us you wanted. But we thought it over, and we think you’ll actually like this other camshaft better on track.”

After running these recommendations past our other experts, including the folks at Air Flow Research and the LS gurus Andrew and Calvin Nelson, we had our answer: “We’ll take one of each, then test them back to back on the track and on the dyno.”

Just like that, we’d ordered two camshafts for our single-cam engine, part Nos. 54-777-11 and 54-460-11. Each cam retails for about $440.

Comp also included the short-travel lifters and shaft-mounted rockers we’d need, along with kits to change valve springs, check our pushrod length, degree the cams during installation, and even swap cams without removing the heads from the engine. We’ll cover all that in the next update, but our order from Comp totaled more than $2500. Assuming you only need one camshaft and can borrow some tools from a friend, this project should cost you about $1000 less.

What makes these two camshafts different? They look identical to the naked eye, but fortunately we learned how to read a cam card as part of this project. So let’s dive in.

In the first corner, we have Comp’s recommendation for a track car, which they describe like this:

The NSR (No Springs Required) Drift Cam for GM 4.8-5.7 LS is a drop in camshaft upgrade designed to wake up smaller displacement LS's and provide a wide, usable power increase for the grassroots enthusiast.

At first glance, this cam may seem too mild for our application. After all, we have fancy short-travel lifters and stiffer valve springs and shaft-mounted rockers and….

Yes, that’s all true, but we’re looking for something appropriate for a race engine. Comp’s expert suggested that this cam might provide the perfect powerband for fast lap times on track. Plus, its lobe shape is so kind that the cam can run with stock valve springs, meaning we should be able to rev our LS1 to the moon every single lap without throwing parts through the hood.

At 0.050 inch of lift, this cam has 233 degrees of intake duration and 243 degrees of exhaust duration. Lift for both intake and exhaust is 0.541 inch, while the lobe separation is 114 degrees with a 109 degree intake centerline.

In the opposite corner, we have Comp’s recommendation for our wishlist, which they describe like this:

HYDRAULIC ROLLER-Very strong from mid-range to high end torque and horsepower for LS engines with cathedral port cylinder heads.

This camshaft is from Comp’s LSR Cathedral Port All Out Power series and, at least according to the marketing materials, seems perfect for our application. It features more lift, slightly more duration and slightly less lobe separation.

At 0.050 inch of lift, this cam has 235 degrees of intake duration and 243 degrees of exhaust duration. Intake valve lift is 0.621 inch, while exhaust valve lift is 0.624 inch. Lobe separation is 113 degrees with a 109 degree intake centerline.

Oh, and did we mention the twist? See, to be gentle on the valvetrain—hence the “No Springs Required” part of the name—the first camshaft actually has more advertised intake and exhaust duration than the high-lift, high-duration camshaft. This means that the lobes of the NSR cam have less aggressive slopes, so the valves take longer to open and close. 

On the surface, it’s a simple question to answer: Does a more aggressive camshaft make more power? Based on our conversations with experts and our time with Engine Analyzer, we think we know the answer. But we’re not really worried about peak horsepower: We want fast laps with a favorable NASA dyno sheet.

Which one of these camshafts will get us there? That’s a question for the stopwatch and the dyno, which we’ll visit next.

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Comments
View comments on the GRM forums
Opti
Opti Dork
4/27/21 8:44 a.m.

With the specs supplied, the cams seem very similar with the exception of lift, so I doubt you see drastic differences between the two.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) GRM+ Memberand MegaDork
4/27/21 8:59 a.m.

I'm glad you touched on the potential pitfalls of dyno sim software.  You really (I mean really) have to read the user manual from start to finish.  Sometimes people just forge ahead and make assumptions, like cam lifter architecture.  Many dyno sim software suites make broad brush strokes when it comes to cam ramp rates, and simply assume a ramp speed based on the lifter you choose.  It assigns generic ramp rates for hyd flat, solid flat, hyd roller, and solid roller.  I've learned it's best to physically enter the actual valve lift for certain resolutions of crank degrees so the software knows your actual ramp rate.

Same goes for head flow.  If you just put an assumption of 0-300 cfm, it has to fill in the blanks and doesn't know that you have really good (or really bad) mid-lift flow in the actual heads you're using.

Dyno sims can be as much artwork as the parts selection and engine assembly itself.

DirtyBird222
DirtyBird222 PowerDork
4/27/21 9:16 a.m.

Choose the one with the most "chop" brother

rustomatic
rustomatic Reader
4/27/21 11:32 a.m.

The LS9 cam still works good, and it's cheap.  It really needs to be in a light-ish car, though, like a Z (as opposed to a pickup).  With a turbo, the powerband is quite satisfying, but it's also quite nice N/A (people complain because it likes RPM, instead of breaking axles from a dig).  Staying under 400 HP might be a bit difficult, though . . .

stonebreaker
stonebreaker New Reader
5/11/21 10:09 a.m.

In reply to Opti :

True, they're very similar, but two things:  the AFR heads are designed for higher lift flow, so the 15% higher lift cam is going to provide a higher average flow with these heads.  Also, the higher lift cam has 4 degrees of advance ground in, whereas the lower lift cam has 5 degrees of advance.  The 4 degrees of advance means a broader torque curve, higher in the rpm band, which is what they're looking for.

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