Camshaft Degree Question for Pastry, Paul Carter, whoever..... Voodoo 704
 

Good morning, we are currently degreeing the camshaft in the 467 we are building, it is the Voodoo 704. Compression is right at 9.35-1. We installed it dot-dot with the Cloyes 9-keyway bullet set first to check it, and it came in at 107.625° Intake Centerline. We then moved the crankshaft gear to the "2A" keyway and rechecked, it came in at 105°. We haven't tried advancing anymore yet. If we move the crank gear to the "4A" keyway, and it moves the camshaft close to the same amount as it did with the "2A" keyway, in theory, it would move it down to 102.5-103° Intake Centerline. My question to you is, would you leave it at 105°, or would you advance it more, even if it came out down at 102.5-103°? I checked the lift at TDC on the Intake and Exhaust lobe, and if I measure it correctly, the Intake is open about .089", while the exhaust is only open about .067", so the Intake lift is only about .022" higher than the exhaust with it at 105° Intake Centerline.

Thanks!

http://forums.maxperformanceinc.com/...ght=Voodoo+704 Post number 4.

When you checked the lifter rise at TDC, make sure that is done on the exhaust stroke, not the compression stroke.

Usually, Paul tells me to shoot for .030" to .040" (intake lifter higher than exhaust lifter) But the tighter the LSA is, the harder it is to reach those numbers.

Personally, I'd leave it at 105 and the .022" lifter rise you have and run with it. That's close enough.

A tid bit for conversation....

"On Harold Brookshire cams (Ultradyne, Lunati VooDoo, etc.] Harold always wanted them advanced at least 4°, but really preferred 6°. I've advanced his cams as much as 7° with excellent results."
Paul Carter

Paul has extensive dyno experience with Voodoo lobes on various builds.

Not apples-to-apples but another tid bit to share, on all my previous solid roller UltraDyne cams from Harold had 6 degrees advance ground it. That said, all were ground with a 108 lobe separation.


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On paper .085 intake tappet lift is 106 intake centerline, so what you are seeing sounds correct.

Honestly I'd be happy with your 105 centerline.
104 centerline would push it further into Harold's ideal range.

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Paul still posts on PZ. He is a great source of information.

If you have the time and don't mind doing it, I'd go ahead for giggles and move the crank key way to 4A and check it again.

As we all know and I'm sure you're aware, moving the keyway another 2 degrees doesn't always equate to that. It might move it 1 degree or it might move it 3 or 4. Just never know as those tolerances aren't perfect.

If it only moves it forward 1 degree that would pretty much be perfect and put lifter rise closer to what you're looking for, but only one way to find out.

I have a cloyes Billet set in my T/A. It varied just like what Jones described, on my most recent one the further down the scale the more it tended to vary. IRC I used the +6 key and would have liked to go a little further yet but the +8 key moved it 4 more.

The more capable the exhaust is, the better it should respond to less advance, and vice versa. Example would be if this was a round port with open headers, it might like less advance, versus d port with RA manifolds and a full exhaust. I assume this is a d port, and if you picked this cam you have headers. If it is a timing chain engine the torque to rotate the cam adds some slack, generally add 2* from were you have it on the stand turning it by hand. Doesn’t apply if it is a belt drive or gear setup. But at 105 it is really 107, and your difference at tdc is close to .008-.010” less than what your reading. Difference between rolling the engine over on the stand with a bar, versus in to car at 5500 rpm. Advance 2* should change the intake .007”, and only .005 or so on the exhaust, or about 009” total. It will run fine where it is at, but would very likely respond to the extra 2. Tim at Bullet told me in the early days of Ultradyne Brookshire use +6 as there std advance. I would try the 4 and see were it lands, same thing Jones said. FWIW

Thanks guys, we will try the "4A" keyway tomorrow and see where it ends up. I myself would like to see the relation between the Intake and Exhaust at TDC a little better. I would rather the Intake be lifted atleast around. 030" higher than the exhaust, but I just don't want to get too greedy and over-advance it.

You guys talking lobe lift or valve lift at tdc

Tappet lift at TDC. We use the lifter bore fixture with the dial indicator attached to it.

Harold Brookshire said once .025” to .050” difference @TDC was what he like to see at the valve. Tappet lifts X the rocker ratio.

Maybe someone has an actual Cam Doctor file for the 704 intake lobe. Using a generated / spline curve file.

If the intake is in @ 106 moving to 105 ICL will increase intake lifter raise by about 0.0036" @ TDC

Going from 110 ICL to 106 ICL will increase intake lifter raise by about 0.0143" @ TDC

Stan

I was going to say engine only cares what happens at the valve so rocker ratio should play a big roll in this.

Very true, and different rockers will differ more than people may think.

Vizard rocker ratio testing, article suggests this is from ISBN-10 ‏ : ‎ 9781613251621

See the valve lift TDC ratios.

https://i.imgur.com/9jSnyj7.jpg

Harold Brookshire was the brilliant designer of Voodoo and Ultradyne lobes.

Jones method places huge emphasis on pressure differentials at valve lifts for a given crankshaft degree.
I do believe this is the root of what matters: the actual pressures of the intake port vs cylinder vs exhaust port the engine has during that phase of the cycle.
This is why I STRONGLY believe there is no one LSA, every engine combination will be different.

Maybe of interest.

David Vizard's PowerTec 10 EP 17 Big lift rocker shootout
https://www.youtube.com/watch?v=aOco86KPzEU

Stan

UPDATE: We have it at the "4A" keyway, and just now checked it, it comes in right at 103°. I checked the relation of the Intake and Exhaust tappet lift at TDC, and the Intake rise is at .093", the exhaust rise is at .0612", so that makes the Intake open .0318" more than the exhaust at TDC. I think we may leave it at 103, what do yall think? What would you do?

Run it and observe closely, take notes. I have hugely powerful tools but I cannot tell you.