Camshaft mystery

Camshaft mystery

Joined: December 11th, 2010, 3:10 pm

August 31st, 2011, 4:16 pm #1

I just built a 408C, 9.5:1 CR, iron closed camber 4V heads, Blue thunder intake, Holley 750HP carb. The engine dynoed well, standard correction 529 HP@ 6400 RPM and 496TQ @ 4900 RPM, torque is above 450 from 3000 to 6000. This is what puzzles me, the engine vacuum seems about 3-4 in./hg. low given the engine displacement and relatively tame overlap and LSA. Relatively clean idle is 1250-1300 with only 10.5 in./hg., timing (34 degrees) float levels and jet sizes were determined on the dyno and I have tried changing power vales, idle air bleeds, idle mixture volume screws, balanced primary and secondary idle screw settings. I still can not get clean idle speed to go down or vacuum to come up. I tried a 650 Hp, 950 HP, and even a friends Braswell. The results didn't vary 50 RPM or 1/2 inch of vacuum. Which leads me to believe there is something (maybe a lot) I do not understand about this cam. Lunati 41199LUN, same as 411A1LUN other than LSA, solid flat tappet, .558/.580, 238/248 @ .050, 272/282 Adv., 110 LSA installed at 106. Can anyone shed some light on this? All input is appreciated. Thanks, Chuck
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Joined: January 22nd, 2010, 3:07 am

August 31st, 2011, 5:16 pm #2

Mine would do fine until it got good and hot, then it would want to die in gear and idle high in park. I have only about 3.5 inches of vacuum at 1000RPM with my custom Lunati solid roller. She now will idle all the way down to 600 RPM and run like that all day long (though I still like it around 900-1000).

The first thing I did was check for vacuum leaks. I found a very minor one at the intake seal with some starting fluid. I changed that but was still having issues. What I ended up doing (after also buying a new custom built carb and it still did it), was adjust the idle scews out pretty rich. I adjusted according to the "book" and the engine wouldn't idle up anymore after half turn of each screw (I have 4 corner idle). I just ended up playing with it one day and found that if turned them out one full turn, my issues were gone. It runs pretty fat, but runs great now.

http://www.youtube.com/watch?v=_21iruIg9bI

Good luck. I can assure you that I know how frustrating it can be. It took me 8 moths and 400 miles to get the kinks worked out of mine.
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Joined: December 16th, 2003, 1:59 am

August 31st, 2011, 6:01 pm #3

if you ever have the carb apart maybe open the IFR's a thou or 2

there'll be phantoms, there'll be fires on the road... and the white man dancing
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Joined: October 1st, 2004, 1:55 pm

August 31st, 2011, 6:06 pm #4

I just built a 408C, 9.5:1 CR, iron closed camber 4V heads, Blue thunder intake, Holley 750HP carb. The engine dynoed well, standard correction 529 HP@ 6400 RPM and 496TQ @ 4900 RPM, torque is above 450 from 3000 to 6000. This is what puzzles me, the engine vacuum seems about 3-4 in./hg. low given the engine displacement and relatively tame overlap and LSA. Relatively clean idle is 1250-1300 with only 10.5 in./hg., timing (34 degrees) float levels and jet sizes were determined on the dyno and I have tried changing power vales, idle air bleeds, idle mixture volume screws, balanced primary and secondary idle screw settings. I still can not get clean idle speed to go down or vacuum to come up. I tried a 650 Hp, 950 HP, and even a friends Braswell. The results didn't vary 50 RPM or 1/2 inch of vacuum. Which leads me to believe there is something (maybe a lot) I do not understand about this cam. Lunati 41199LUN, same as 411A1LUN other than LSA, solid flat tappet, .558/.580, 238/248 @ .050, 272/282 Adv., 110 LSA installed at 106. Can anyone shed some light on this? All input is appreciated. Thanks, Chuck
That vacuum reading is very low for the overlap/duration of that cam, I would expect something in the 13-14" of vacuum range. Something is off so I would check for vacuum leaks to start with.
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Joined: December 11th, 2010, 3:10 pm

August 31st, 2011, 7:38 pm #5

I started checking for vacuum leaks. Capped plugged everything, spray carb cleaner at all sealing surfaces, no leaks.The vacuum is steady at 10.5. I also expected about 14 in./hg. That's why I think either I screwed up cam installation (although I degreed it 3 times from scratch to be sure) or there is something unusual about cam that is not evident from the specs. I emailed Lunati. Maybe I'll get an answer that makes sense......I know, not gonna happen. Chuck
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Joined: October 1st, 2004, 8:05 pm

August 31st, 2011, 11:54 pm #6

I just built a 408C, 9.5:1 CR, iron closed camber 4V heads, Blue thunder intake, Holley 750HP carb. The engine dynoed well, standard correction 529 HP@ 6400 RPM and 496TQ @ 4900 RPM, torque is above 450 from 3000 to 6000. This is what puzzles me, the engine vacuum seems about 3-4 in./hg. low given the engine displacement and relatively tame overlap and LSA. Relatively clean idle is 1250-1300 with only 10.5 in./hg., timing (34 degrees) float levels and jet sizes were determined on the dyno and I have tried changing power vales, idle air bleeds, idle mixture volume screws, balanced primary and secondary idle screw settings. I still can not get clean idle speed to go down or vacuum to come up. I tried a 650 Hp, 950 HP, and even a friends Braswell. The results didn't vary 50 RPM or 1/2 inch of vacuum. Which leads me to believe there is something (maybe a lot) I do not understand about this cam. Lunati 41199LUN, same as 411A1LUN other than LSA, solid flat tappet, .558/.580, 238/248 @ .050, 272/282 Adv., 110 LSA installed at 106. Can anyone shed some light on this? All input is appreciated. Thanks, Chuck
If you just twisted the distributor to limit the total timing to 34 degrees, the chances are you have insufficient initial/static timing. Initial timing is determined in the driveway, takes 10 minutes. Then the centrifugal advanced must be calibrated to make up the difference between the two.

If you are using vacuum advance use ported vacuum, not manifold vacuum.

-G
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Joined: June 12th, 2009, 1:31 pm

September 1st, 2011, 2:25 am #7

Mine would do fine until it got good and hot, then it would want to die in gear and idle high in park. I have only about 3.5 inches of vacuum at 1000RPM with my custom Lunati solid roller. She now will idle all the way down to 600 RPM and run like that all day long (though I still like it around 900-1000).

The first thing I did was check for vacuum leaks. I found a very minor one at the intake seal with some starting fluid. I changed that but was still having issues. What I ended up doing (after also buying a new custom built carb and it still did it), was adjust the idle scews out pretty rich. I adjusted according to the "book" and the engine wouldn't idle up anymore after half turn of each screw (I have 4 corner idle). I just ended up playing with it one day and found that if turned them out one full turn, my issues were gone. It runs pretty fat, but runs great now.

http://www.youtube.com/watch?v=_21iruIg9bI

Good luck. I can assure you that I know how frustrating it can be. It took me 8 moths and 400 miles to get the kinks worked out of mine.
that cam sounds nice, but it is awfully hard on them idling so low.
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Joined: January 22nd, 2010, 3:07 am

September 1st, 2011, 2:41 am #8

That was actually a cold start, it is just where she idles when first fired. Once she warms up it increases to around 1000.
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Joined: December 16th, 2003, 1:59 am

September 1st, 2011, 10:21 am #9

I just built a 408C, 9.5:1 CR, iron closed camber 4V heads, Blue thunder intake, Holley 750HP carb. The engine dynoed well, standard correction 529 HP@ 6400 RPM and 496TQ @ 4900 RPM, torque is above 450 from 3000 to 6000. This is what puzzles me, the engine vacuum seems about 3-4 in./hg. low given the engine displacement and relatively tame overlap and LSA. Relatively clean idle is 1250-1300 with only 10.5 in./hg., timing (34 degrees) float levels and jet sizes were determined on the dyno and I have tried changing power vales, idle air bleeds, idle mixture volume screws, balanced primary and secondary idle screw settings. I still can not get clean idle speed to go down or vacuum to come up. I tried a 650 Hp, 950 HP, and even a friends Braswell. The results didn't vary 50 RPM or 1/2 inch of vacuum. Which leads me to believe there is something (maybe a lot) I do not understand about this cam. Lunati 41199LUN, same as 411A1LUN other than LSA, solid flat tappet, .558/.580, 238/248 @ .050, 272/282 Adv., 110 LSA installed at 106. Can anyone shed some light on this? All input is appreciated. Thanks, Chuck
have you looked at how much of the transfer slots are showing?

you may need to drill the throttle blades to get the proper orientation. the rough & high idle is a symptom

there'll be phantoms, there'll be fires on the road... and the white man dancing
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Joined: July 12th, 2008, 1:55 pm

September 1st, 2011, 10:31 am #10

Like Tin said, set your idle transfer slots too a square from underneath approx 0.020". Don't touch them again, this is your baseline. There should be a little screw at the back of the carb (underneath) that adjusts the back blades too give you your extra idle air if needed.. Like George said, ported vacuum only and Dissy regraph too give you about 16 initial and 34 total. What heat range plugs have you got?
Cheers.
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