Hydraulic Cam Selection Spreadsheet

I’ve been doing a bunch of camshaft research lately and wanted to share my AMC hydraulic cam selection spreadsheet with you guys. Basically I’ve got all of the “catalog” available cams listed in one spreadsheet, and then based on engine and usage it limits them down to just the ones that are acceptable. Then you can go through the list and pick one you like based on how choppy you want the idle, or what manufacturer you like the best, or what not.

So here’s the Excel file to download, and I believe that you do have to enable macros to run it. The forum won’t accept an .xlsm file so I had to put it into a zip file.

LINK REMOVED - look for the latest version in my replies to this thread

The rest of the spreadsheet details and descriptions of inputs are as follows:

Application:

The first set of criteria used to limit the cam selections is the seat-seat overlap, based on david Vizard’s application criteria list. There is no correction for engine size so keep in mind that you may want to aim to the low end for smaller engines. I’ve actually adapted DV’s recommendations to the overlap triangle data instead of relying solely on seat-seat overlap, because there are a number of “anomaly” cams that have slow ramp rates and hence long seat-seat overlap numbers, yet have very short (or negative) 0.050” overlap numbers.

·         Street Towing: Working trucks where low-end torque and mileage are important. Strong performance right off idle, excellent heavy load towing, good mileage, smooth idle. Use 1.7 rockers if possible.

·         Regular Street: Daily driven cars and trucks where a sstrong emphassis is on idle quality and low speed performance for good street manners and strong off-the-line response with a stock stall converter.

·         Street Performance: Hot street machines where performance is the pricmary conscern, but where reasonable street manners must still factor into the equation. Err on the short side, especially in a heavy vehicle.

·         Oval, Road, Heavy Drag: Oval track, all out road race, and heavier drag race cars.

·         Comp Drag Race: No compromise drag race engines.

Cylinder Heads:

The cylinder head selection impacts the flow area graph, and in the case of aluminum heads it adds 0.4 to the allowable DCR. The flow area graphing allows you to determine if a change in cam will truly result in a change in flow for your application. The “Dogleg 58cc” categories are intented to include all the big valve heads other than the small chamber 291C. If you have ported 291C heads, use the “Dogleg 58cc Ported” selection. Currently I don’t have a selection for square port heads as I don’t have recent flow data, but I could work it out based on the SAE papers.

Fuel Type:

The fuel type sets the Dynamic Compression Ratio (DCR) range for the application. Aluminum heads get a bonus of 0.4 DCR for any given fuel. Engines with zero deck get a 0.1 DCR bonus as well. Note that if you select a fuel type the cams will be limited by both a low and high criteria, under the assumption that you are trying to make a good performing engine and a low DCR isn’t acceptable.

Also note that if you pick an octane level there are maximum static CR limits imposed:

87 Octane

·         8.7:1, Iron Heads

·         9.1:1, Aluminum Heads

93 Octane

·         9.7:1, Iron Heads

·         10.1:1, Aluminum Heads

Rocker Arms:

Stock stamped steel rockers will be limited to 0.500” lift, and roller rockers have no limit. This doesn’t take into account the external “Rocker Ratio” field down lower on the screen, so keep that in mind. It’s all based on 1.6 ratio rockers.

Lobe Intensity:

We’re looking at opening ramp Hydraulic Intensity only, and lower numbers indicate higher intensity. Here typically it’s best to start with “All”, and then cycle through the selections to see how it effects the results. Keep in mind that the cams with higher intensity lobes are going to be more apt to have lobe wear related issues if your block has a slightly out of spec lifter or lifter bore, etc. But also keep in mind that cams with very low intensity (bigger H.I. numbers) are going to be produce less power.

Intake Phasing:

This is the additional amount of advance or retard used during cam degreeing BEYOND what is already ground into the cam by the manufacturer. Most people will intall cams at 0 degrees, but if you’re dealing with a low compression engine you may want to consider advancing the cam by 2-4 degrees by entering 2 or 4 into this field in order to get the DCR up into a reasonable range.

Rocker Ratio:

This gets passed through both the area calculations and the graphical results.

Exhaust Characteristics

Exhaust “Lope” at Idle:

Look at the Overlap Factor as a guide point to compare idle quality between cams. The crossover point between barely smooth and minor lope is about 1.5 for a 390/401 with dual plane intake with plenum notch and true dual exhaust (no crossover). If you have a fully divided dual plane (Edelbrock Air Gap) and / or exhaust crossover you’ll need to have a higher Overlap Factor in order to get a lope to the idle.

Exhaust Loudness:

Compare the EVO values at 0.050”. Bigger numbers indicate earlier exhaust opening, and that’ll make for a louder exhaust. If you’ll be running Trendsetters you’ll want to keep this under control.

Graphical Results

You can compare two cams graphically by manually selecting them in column A. Enter a “1” for the first cam you want graphed, and a “2” for the second. If you change criteria though your 1 and 2 may get removed if they were on cams that no longer fit the criteria.

The lobe lift curve is pretty straightforward. You can adjust the rocker ratio on the input area and see the resulting change in the lift curve.

The flow area comparison is really important. It plots the flow at each degree of opening, based on the cylinder heads you’ve selected. This will show you when you’ve got more life than the heads can support, and let you see the effect of changing heads on the flow capabilities of the cam/head system. It also calculates the difference in area under the curve between Cam 1 and Cam 2 so you can compare them.

Spreadsheet Results

Overlap Factor is the most accurate indicator of idle characteristic that I can find. It takes into account the seat-seat overlap, overlap at 0.050”, valve sizes, and engine size. If you can find a cam in the list from a similar build and you know how it idles, you can be very confident that cams with comparatively increasing or decreasing Overlap Factors will directly increase or decrease the idle aggressiveness.

Dynamic Compression Ratio (DCR) is critical in predicting low RPM detonation and performance. Set it too low and the engine will be sluggish off idle on have reduced torque at low RPM, set it too high and the engine will knock.

Intake Area / Exhaust Area are the area under the flow curve, including the effect of the installed cylinder heads. This will help you visualize the performance change from changing heads, or changing cams with the same heads.

The spreadsheet results are sorted in order of increasing Overlap Factor.

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General Notes:

Seat-Seat Duration

For the purposes of this spreadsheet, I’ve assumed 0.006” tappet lift to be the point at which seat timing is measured. That lines up with what Comp and Lunati cams use for advertised duration, but Crane, Isky, and Crower all use a different lift for rating advertised durations. Crane publishes theirs in their lobe master catalog, and most are rated at 0.004” tappet lift, but some lobes are different. Richard at Isky advised that they use 0.007” lifter rise for the AMC hydraulics, and also that their ICL is always 2 crank degrees advanced. Peter Harris at Crower advised that their advertised duration for AMC hydraulic flat tappet cams is measured at 0.005” tappet lift. For every cam listed, I’ve converted the advertised durations into seat timing durations at 0.006” tappet lift so they can be directly compared.

Dynamic Compression Ratio

In order to make accurate DCR calculations, I decided to use seat timing instead of 0.050” timing. Any DCR calc using 0.050” timing figures has to make assumptions as to the closing ramp rate in order to determine the actual intake seat closing point, and I wanted to eliminate that assumption. Finding the actual seat-seat duration for each cam as outlined above is the first step. If the lobe was symmetrical it would be easy from there to determine the IVC point, but most lobes aren’t. For example the Crane HMV lobe H-216/3027 has 56 total crank degrees of opening and closing ramp from 0.006”-0.050” during opening and again from 0.050”-0.006” when the lobe is closing (272 - 216 = 56 ). If the ramps were symmetrical that 56 degrees would be split evenly on both sides of the lobe, but in order to set the valve down gently there is actually more duration on the closing side ramp, with the split being 24 degrees on the opening side and 32 degrees on the closing side (instead of 28 and 28). So the true IVC closing point is actually 4 crank degrees later than would be predicted if we assumed symmetrical ramps.

Single Pattern vs Dual Pattern

Many catalog cams use a dual pattern design where the exhaust lobe has more lift and duration than the intake. This is helpful for heads with a E/I flow ratio of less than 0.75 (Chevy), and with more restrictive exhaust systems. If you are running cast iron heads with stock valves and open headers or a high flowing exhaust system, then a single pattern cam or dual pattern with only a few degrees of increase on the exhaust lobe is preferred.

Manufacturer Specific

Edelbrock

The Edelbrock cams use Crane’s HP series lobe profiles. These are old design slow ramp lobes, intended for conservative street use.

Summit

These cams also use Crane’s HP series lobe profiles. These are old design slow ramp lobes, intended for conservative street use.

Crane

The catalog offerings use the HMV lobes, which have reasonably fast opening ramps and slower closing ramps. The biggest problem with the Crane catalog selections is the split duration design, which isn’t needed with our iron heads, assuming a good exhaust system (or open headers). Avoid them as well if you have Trendsetters, as the large duration split results in early exhaust opening and extremely loud exhaust.

CompCams

All of Comp Cams ramps are very short compared to other manufacturer, and just barely assymetrical.

None of the XE cams for AMC are designed for 0.904 lifters.

The Extreme Energy (XE) series use the similar exhaust lobes to the Magnum series cams. Only the intake lobe is the newer Xtreme design.

The 280H has slightly slower ramps than the 270H and the 292H, so if you are on the fence in that range of cams know that the 280H will be less likely to fail during break in and will have less valvetrain noise.

Lunati

The Lunati VooDoo cams are designed for the 0.904 lifter. They were supposedly designed by Harold Brookshire, and should have a reasonably fast opening ramp and gentle closing ramp. The downside to the VooDoo series is that the larger ones are dual pattern design.

Engle

Most Engle catalog cams for AMC are designed for the 0.904 lifter. Their Hydraulic Intensity numbers are all over the place, but in general they run gentler ramps than Comp and Crane.

Schneider

This company doesn’t list the included intake centerline for their cams, nor do they have a published lobe list, so they were not included.

Here is my cam

Master          Adv              0.050              0.200               Lobe                  

Number     Duration       Duration         Duration              Lift                104             106             108             110              1.6             1.7              1.75

R24      311      278       197     0.4544   0.174   0.164   0.156   0.148   0.727   0.772   0.794

R6       322      286       200     0.4267   0.184   0.176   0.168   0.160   0.683   0.725   0.747

My cam - Ultradyne hydraulic flat on 111 LSA

#	Adv	.050	   .200	  lobe lift  104    106	    108     110     1.5	     1.6     1.7

H1       296      239       147     0.3280   0.097   0.090   0.084   0.077   0.492   0.525   0.558

H2       306      249       158     0.3412   0.114   0.107   0.101   0.094   0.512   0.546   0.580