Comp Cams Variable Duration Mechanical Cam

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PackardV8
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Comp Cams Variable Duration Mechanical Cam

Post by PackardV8 » Mon Aug 20, 2018 12:43 pm

Back in the bad old days, when Rhoads lifters were the new trick, Comp advertised a Variable Duration Mechanical Cam. In simplest form, for street, set valve clearance at .030", for performance at .020" and for race at .010". Each changed the duration about ten advertised degrees.

Were the ramps specially engineered for this application, or did the marketing department just write copy to compete with Rhoads?
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Geoff2
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Re: Comp Cams Variable Duration Mechanical Cam

Post by Geoff2 » Tue Aug 21, 2018 5:50 am

Mech cams normally have longer ramps than hyd cams because they don't have the hyd 'cushion' that hyd cams have.
That said, Comp Cams MA [ Max Area ] Lift Rule lobes can be run with solid lifters or the Comp Pro Magnum hyd lifters.

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Re: Comp Cams Variable Duration Mechanical Cam

Post by pdq67 » Tue Aug 21, 2018 11:51 pm

Years ago, I came right out and asked CC about their max/min lash, for their good old 282S solid lifter cam and the Tech. said something like from .030" down to .015" or so hot lash. I think from normal lash, it's +/- .0075" or so...

And looking at the great old little-bitty -097 Duntov solid lifter cam at .012" and .018" hot lash. It's actually a tight-lash cam from way back then.

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Re: Comp Cams Variable Duration Mechanical Cam

Post by kirkwoodken » Mon Sep 24, 2018 11:45 pm

Paul,
I used to run my 097 cam at .006" and .009". Sounded like a hydraulic and I thought it ran slightly better. FWIW, the FI cams idled nicely with the Rochester FI. My observation is most of the loping came from poor mixture distribution of the 2 and 4 bbl intake manifolds, especially with low speed intake flow and ram horn headers. My 406 idles nicely with 255/263@.050 lift on 109 advanced 7 degrees. (Paul, you have a PM.)
"Life is too short to not run a solid roller cam."
"Anything is possible, if you don't know what you're talking about."
I am NOT an Expert, and DEFINITELY NOT a GURU.
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Re: Comp Cams Variable Duration Mechanical Cam

Post by F-BIRD'88 » Mon Oct 01, 2018 1:46 pm

Yes back in the day Comp cams used to say and promote playing with the valve lash setting of their Magnum mechanical flat tappet cams to adjust the actual running valve event duration +/- On those cams they gave a relative wide adjustment range. .030" down to .015" (or even tighter) to allow the end user to dial in the effective duration and overlap to find best performance... You can still do this with these Magnum cams and others like them. Don't know the exact limit you can open the lash setting till it is running on the flanks instead of the lash ramps. You'd have to ask Comp cams tech.. I suspect .032 to 034. A noticeable change in the sound of the valve train at idle is a clue.
This makes the valve events effectively shorter.
There is a practical limit. But can be effective and revealing as to car performance.

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Re: Comp Cams Variable Duration Mechanical Cam

Post by F-BIRD'88 » Mon Oct 01, 2018 1:55 pm

If you were to analyse a Magnum cam on a Cam DR.
You'd then see the lobe lift point where the lift profile changes from the lash ramp to the open/close side flanks on each side of the cam lobe. (It may not be the exact lift point on both sides of the lobe.)
Knowing what that transition point is on any mechanical cam is a good thing , allowing you to see the max practical lash point setting. Now you can set practical range limits of valve lash +/- adjustments for that cam.

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Re: Comp Cams Variable Duration Mechanical Cam

Post by F-BIRD'88 » Mon Oct 01, 2018 2:05 pm

The comp Magnum cams also respond to cam advance /retard changes adjustment to maximize the perf of your car. It tweeks the power curve. The popular Comp 294s-10 cam comes to mind. You can also custom order these cams in other LSA's. (Other than 110…) Eg 106 LSA or 108 lsa All you need to do is call and ask for that when placing a custom grind cam order.
You can do this with their mechanical Street roller cams too.

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Re: Comp Cams Variable Duration Mechanical Cam

Post by PackardV8 » Tue Oct 09, 2018 2:16 pm

Thanks for the confirmation.

It reminds me of way back in the day when the P&G Valve Gapper was hitting the market. They came around to Iskenderian and asked him to sell it in his catalog. They offered to do a demonstration. Ed had a SBC on the dyno with one of his cams with .018" recommended lash. Ed had Bones randomly set half at .016" and half at .020", taking no particular care to get them exactly that; then they did a pull. The P&G guys set them all with their dial indicator fixture, showing each to be exactly .018" and the pull showed zero improvement.
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Re: Comp Cams Variable Duration Mechanical Cam

Post by MadBill » Wed Oct 10, 2018 12:20 am

The reason I try to get the lash dead on is to help spot and accurately track any wear-induced changes.
Felix, qui potuit rerum cognscere causas.

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Re: Comp Cams Variable Duration Mechanical Cam

Post by In-Tech » Sun Oct 14, 2018 2:21 am

MadBill wrote:
Wed Oct 10, 2018 12:20 am
The reason I try to get the lash dead on is to help spot and accurately track any wear-induced changes.
That is very sound advice, I posted in another post topic...what's a couple thou between friends? :mrgreen: The engine couldn't care less, within reason.

I'm not talking about the world Warp lives in, the generalization is that the dyno won't repeat well enough to report a 2 degree change in cam phasing, again, within reason. Just sayin :wink:
Heat is energy, energy is horsepower...but you gotta control the heat.
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Re: Comp Cams Variable Duration Mechanical Cam

Post by 427dart » Mon Oct 15, 2018 4:50 pm

and then there was the Vari-Cam from the 60's that automatically advanced and retarded the cam timing.

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Re: Comp Cams Variable Duration Mechanical Cam

Post by blackford » Mon Oct 15, 2018 5:16 pm

That's interesting Magnum cam history especially since I use one in my SBF 331.

I use a 282S and an older experienced racer told me I could run that cam at .010 in a SBF with no problem so years ago I changed the lash from the recommended .022 to .015 cold (iron heads and block). Much quieter and has run great for years!

The Comp Cams lobe catalog states the lash range is .015 to .030 to "fine tune any high performance application". It also shows the rated duration to be at .015 tappet lift.
65 Mustang FB, 331 custom built with 289 H beam rods and 383W piston, 282S cam, AFR 185 Renegades, T5z, 9" 3.89 gears. 430HP@6500

2013 Corvette 427 Convertible daily driver

'65 Fastback

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Re: Comp Cams Variable Duration Mechanical Cam

Post by F-BIRD'88 » Thu Oct 18, 2018 2:07 pm

It would be interesting to see a dyno test comparo of say a sbc with a comp 294s magnum cam set at different lash settings. Another , say comparing a catalog 110 lsa version vs a custom 106 lsa version of that cam , in say a "typical" 10.5:1 383 sbc.
Other mechanical cams , (including rollers) also can use varing the lash as a tuning element too. May be to a more limited extent based on that cams lash ramp design.
You want to keep the running lash point on the cams lash ramp.

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