Duration @ .050

[toolmanmike]

I hope someone can explain. When I switch my Dyno 2000 software from "advertised duration" to "@.050" and change the specs, I loose HP and Torque. The cam in question is a Lunati Voodoo hydraulic roller #60710. Specs are: advertised duration 258/264, (@ .050 207/215), lift 485/485,Lsa/Icl 112/106, rpm range 1000/5000. When I switch to @.050 I loose 53 hp and 10 ft.lb. I tried it with the Isky E-4 (260/260 or 216/216 @ .050) and lost only 6 hp but gained a couple ft/lb of torque. I think either cam would work good in a 10.5/1 273
with some head work and put out around 325 hp. What causes the losses when I switch to @.050 specs?
I have read that advertised duration is accurate for small cams and @.050 is better for big cams over 300 degrees. Which specs are more correct?
The Isky would be a cheaper set-up because it is a solid lifter cam. Quite a few of you guys have ran the Isky with good results. I think the Voodoo is too new for any results. There was one guy on Moparts that put one in a 318 and liked it well. I sure like the high torque specs and flat curve of the roller throught the rpm range. toolmanmike

 

[SGBARRACUDA]

The reason is "advertised" duration by different manufacturers are figured by many different methods. Duration @.050 or .020 is a constant that can be used reguardless of the maker of the cam.

 

[ramcharger]

The .050 duration will be more accurate than the advertised because everyone has a different way of measuring their advertised specs and the program can give an educated guess as to how it was really measured.

Take notice that the advertised specs on the intake vary by only 2 degrees advertised but @ .050, the specs vary by 9 degrees. That's where the difference lies. The advertised specs are also hard to compare between different cams like Hyd flat, Hyd roller, solid flat and solid roller. Don't forget that that Isky solid won't have as much duration due to lash too. Same goes for solid rollers. Generally speaking, solids will need 8 to 10 more degrees of duration to match that of a hydraulic. More sophisticated dyno programs most likely take these differences into account.

 

[toolmanmike]

That being the case, the roller is less of a cam than the E4. Using @.050 specs for both cams, the E-4 puts out nearly the same torque and 43 more hp than the roller does. ( and at only .425" lift) that's what doesn't make since to me.

 

[pishta]

The roller is almost unlimited in the rate of opening the valve so you get a much faster opening, then a longer hold time and a faster seat, making a small roller make as much power as a large hydro. The hydro is limited to the ramp "opening" speed by the diameter of the lifter, Mopars have an advantage with their larger .904 diameter lifter. Chevy has to use a mushroom lifter to approach the ramp rates of a properly ground Mopar cam. Comp cams makes a series that is designed for the larger lifter. Most Cams are ground to a generic Chevy lifter diameter, I heard even MP did theirs like that for some reason.

 

[ramcharger]

That being the case, the roller is less of a cam than the E4.

No, it's not. The duration would be about the same as far as what the valve sees. Like I said before, the solid cam would need 8 to 10 degrees more duration to equal a hydraulic. The hydraulic roller most likely has a much higher rate of lift than the solid too. It's called the "Area under the curve".

Using @.050 specs for both cams, the E-4 puts out nearly the same torque and 43 more hp than the roller does. ( and at only .425" lift) that's what doesn't make since to me.

Like I said before, that's because your dyno software doesn't take into account the difference in duration caused by lash on the solid lifter cam.

Dyno software is fun and it's a tool. Think of it as a torque wrench:

You put a 3/8" drive crows foot on the torque wrench and you get the wrong reading due to the length from the centerline of the nut and axis of the drive on the torque wrench.

You are comparing apples and oranges (solid and hydraulic) and the software, regardless of what it "says", is not making the compensation between the two cams. There may also be a LSA/ICL difference between the cams that you haven't mentioned yet.

 

[toolmanmike]

The two cams were my top choices. I didn't want to compare the two because they are both so different by design. I was questioning the accuracy of my software because of the huge loss of HP when I switched from "advertised"
to "@ .050" duration on the roller cam. If the roller was superior to the solid lifter cam it might be worth the few hundred bucks for a few extra ponies and a good amount of extra torque. I wish I had the extra $'s just to experiment
toolmanmike

 

[ramcharger]

There are some really, really sophisticated new programs out there that I'm sure could give you a more realistic comparison. Maybe there's someone here who has one and can give you a hand on this decision?

 

[dodge freak]

On speedtalk there are a few custom cam designers (who do make custom cams for not much more cost than off the shelve cams) they claim .050 ratings are misleading cause after .050 the rate of of the valve opening can still vary much between cams.

I used a custom cam from Mike Jones, Camking he goes by on speedtalk. His 224 @ .050 gives my motor a smoother idle (but a bit less vacuum) and higher rpms than Comps cam 268HE I had before. The LBC are 111, comps is 110. Not that much difference.

This is how "cheater cams" can "cheat", lol.

There might be other tricks too. All claim their cams will outperform the other guys8)

One thing is for sure, no pro racers (the top teams) use off the shelve cams, all have cams design for THEIR engine. Head flow after porting, intake flow, exhaust flow, compression ratio, etc. Even track design--tight banks, dirt tracks, etc play in to picking the "right" cam design.

You want a "perfect" cam for your motor, get a custom cam for your engine. (and let the cam designer worry about that .050 rating.

 

[1967DartGT]

My DeskTop Dyno program states that using seat-to-seat timing specifications as the primary method for simulation will produce the most accurate results. I have not noticed much difference when changing between seat-to-seat or 0.0505 timing as the primary simulation method, as long as you make sure that the lifter acceleration rate tab is set to "automatic". This way the program uses both timing specs to calculate the ramp rate for the cam.

 

[moper]

If you look at a cam lobe on paper, you'll see the shape starts from a flat line, has a small ramp up, then a "step", then it begins the lift ramp. That ramp is not a straight line, but rather a curve. Like a bell upside down. Now, the way desktop dyno looks at a cam is if you drew a straight line from zero lift to max lift. It looks like a roof pitch rather than a swoopy bell curve. Any time you can fill in more info, the simulators will get a little more accurrate. But in most cases, they plain just round off so the math works. Also, hydraulic rollers are much closer to a hydraulic cam's profile than a solid roller's. Because no matter how fast the ramp speed, the combination of spring and hydraulic lash adjuster will limit the rate of lift to no more than a hydraulic profile. They have less friction... but that's it. Thye have worse pushrod angles, weigh more, and can't open any faster.

 

[fishy68]

Toolman was the lobe separation and installed centerline the same on both cams? If they weren't that could add up to some of the difference you saw. Plus like Moper said desktop dyno doesn't actually follow what the cam's profile really is. It just draws a straight line from 050 to full lift where-as the lobe may be more bell shaped producing different results. Only the high dollar programs are accurate but of course you need to know the actual specs of the cam to input the parameters in them. Anymore I have my cams custom ground. I like Jim at Racer Brown. Heck of a nice fellow to talk to and don't charge much more than an off the shelf cam but he grinds what you need. I even used one of his cams in a buddies 454 chevy and it worked great.

 

[toolmanmike]

The files are DYN files and I can't download them. Everything is the same. I'm sure the software is screwed. If any of you has better dyno software and want to run some numbers I can give you some specs. Thanks! Toolman

 

[Prine]

Good stuff. Thats why I like Hyd. Roller Cam SBM's, the roller cams are really efficient.

I noticed that when digging into info on cams the super high hp stuff (like Top Fuel) run, the duration was relatively mild at around 220* @ .050", and the lift was rediculously high like .880".

 

[fishy68]

The files are DYN files and I can't download them. Everything is the same. I'm sure the software is screwed. If any of you has better dyno software and want to run some numbers I can give you some specs. Thanks! Toolman

You should be able to go into any existing cam file and modify it's parameters (duration, lift, etc.) and rename it and save it. I've done that many times to add cams that aren't in the list.

 

[toolmanmike]

If all else fails................read the instructions! I searched the user manual
(114 pages) and found this (While you will always find 0.050-inch lifter rise timing points published on the cam card and in many manufacturers catalogs, the Dyno2000 must internally convert 0.050-timing to valve motion calculations.
So to emphasize a point: When ever possible, use seat-to-seat timing specifications: they produce the most accurate simulation results.) Because of this, lower performance roller cams have only a slight performance advantage over hydraulic or solid lifter cams but optimize reliability. Now I need to reformulate my test mules and review the results. Thanks all! toolmanmike

 

[1wild&crazyguy]

Good stuff. Thats why I like Hyd. Roller Cam SBM's, the roller cams are really efficient.

I noticed that when digging into info on cams the super high hp stuff (like Top Fuel) run, the duration was relatively mild at around 220* @ .050", and the lift was rediculously high like .880".

you won't see much duration when your only .050 into a .880 lift cam, know what I mean?

I'd look at .200 with that big of a cam