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Old 06-30-2013, 02:24 PM
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104icl drawbacks

I see that most cams are to be installed at a 106icl. What are the drawbacks to running a 104icl? For instance a 110lsa cam ground with 6degrees advance.
Obviously this raises the dcr and decreases p2v clearance, just wondering if its a good idea to run a larger cam with a 104icl to keep dcr up..

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Old 06-30-2013, 04:25 PM
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lots of smaller engines use the tighter ICL,and short circle track.Large BBs use a wider ICL and LDA.
the lower icl and LDA has more overlap so can have a choppy idle
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Old 06-30-2013, 05:09 PM
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I'll run through the cam action for those fellows who don't yet understand a cam's functions and how they relate.....

Let's say we're installing a cam that has an advertised duration of 286 degrees and a 0.050" duration of 230 degrees. There is an intake valve lobe and an exhaust valve lobe for each cylinder. We will be interested in the way the lobes are ground in relation to each other and their relationship to the crankshaft (piston position). Let's say this cam is ground with an intake centerline of 106 degrees. What this means is that the highest lift point (max lift) of #1 intake lobe will be at 106 degrees after top dead center. With a little ciphering, we can determine that at 0.050" tappet lift, the intake valve will be opening at 9 degrees before top dead center and closing at 41 degrees after bottom dead center. (9 + 41 +180 =230)

Now, let's say that the exhaust valve lobe is ground on an exhaust centerline of 114 degrees. This means that the wide-open position of the #1 exhaust valve (max lift) will be at 114 degrees before top dead center. Again, with a little cyphering, we can determine that the exhaust valve will begin to open at 49 degrees before bottom dead center and will close at 1 degree after top dead center. (49 + 1 + 180 = 230).

This would be installing the camshaft "straight up", neither advanced nor retarded.

Lobe separation angle would be the number of degrees between the intake max lift point and the exhaust max lift point, so if we had a 106 degree intake centerline and a 114 degree exhaust centerline, we could add those together and divide by 2 to find the lobe separation angle, in this case 106 plus 114 divided by 2 would find a lobe separation angle of 110 degrees.

Sometimes, we may wish to alter the characteristics of the cam a little one way or the other. We may want to advance the cam in relation to the crankshaft position (piston position in the bore) in order to make a little more power (more cylinder pressure) down low in the rpm range if we need a little more power there, for towing or whatever. We all know that there is no free lunch, so if you gain some power down low, you must give up some power higher up in the rpm range. If we decided to advance the camshaft 4 degrees from the design number, then we might install the intake max lift point at 102 degrees after top dead center instead of 106. This would, of course, change the position of opening and closing of the intake valve in relation to the crankshaft (piston position). With the cam moved to a 4 degree advanced position, the intake valve would now open at 13 degrees before top dead center and would close at 37 degrees after bottom dead center. Now, you must realize that when you change the intake, you are also changing the exhaust (because the cam is one piece and when you change the intake lobe, you also change the exhaust lobe). So, with the new camshaft position, the exhaust valve would open at 53 degrees before bottom dead center and close at 3 degrees before top dead center.

On the other hand, we may want a little more power up top, trading off some power down low. In that event, we might retard the camshaft a little, installing the intake centerline at 110 degrees after top dead center instead of 106. You might do this in order to apply a little less low end torque to the tires to prevent spinning them excessively, for instance. This would move the intake opening to 5 degrees before top dead center, intake closing to 45 degrees after bottom dead center, exhaust opening to 45 degrees before bottom dead center and exhaust closing to 5 degrees after top dead center.

When changing intake and exhaust opening and closing points, you may improve the cylinder pressure or you may lessen the cylinder pressure. With every camshaft, there is a sweet spot. Advancing the cam and opening the intake valve sooner might allow some of the fresh mixture to flow out the exhaust valve because it is still open a little when the intake begins to open (the overlap period). Closing the intake valve is undoubtedly the most sensitive event in cam timing. Depending on charge velocity (choosing the proper intake manifold, heads and carb for the job), you can trap more mixture, making more power, or you can trap less mixture, making less power.

It is quite a juggling act to get the cam in the motor and degreed to the point that produces the effects that you are asking it to do. Choosing a cam and determining how to degree it in your motor should be the last or next to last thing you do for the motor, along with choosing the proper torque converter. Many of these young fellows run right out and buy the first cam that sounds exciting to them, with little or no regard to the static compression ratio of the motor or the operating range of the cam.

Otrbo, I'm not sure I have answered your question, but camshaft science is tough for me. I think I have just enough knowledge to be dangerous.
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Old 06-30-2013, 05:20 PM
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what Richard said is good info.He did not explain if yet another cam with the same specs but ground differently;IE:
108 icl and 108 lda will perform differently than the cam he mentioned even if both were put in the same position. The math gets complicated fast as you can see.

some times a person will have a tight icl ground so he can use a bigger cam with lower CR,again its all about when the intake closes and the rpm range you want/need
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Old 06-30-2013, 07:51 PM
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.

some times a person will have a tight icl ground so he can use a bigger cam with lower CR[/QUOTE]

Does it work? Is it done to simply keep dcr up?



Thanks for the time
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Old 06-30-2013, 08:15 PM
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Its the intake closing time that determines DCR.you have a potential 16 plus degrees to play with in total duration. I've seen cams ground at 99 icl. and 112 icl just for the mouse motors.
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Old 06-30-2013, 08:18 PM
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lousey explanation,wheres fb?
think of where the intake closes (2 cams same duration) with a 100 icl Vs same specs but 112 icl.

now add duration to the 100 icl until both cams close the intake valve at the same time,,,
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Old 07-02-2013, 12:23 PM
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The 60121 voodoo closes the intake valve at 61 degrees with a 112 lsa and 6 ground in advance. It is a 270/278 advertised, 221/229@50, .515/.530 cam.

The voodoo that was specd for me is a 278/282 advertised, 227/231@ 50, .530/.535 cam and closes the intake at 65 degrees with a 110lsa and 4 ground in.

For instance what would happen if you were to take the second cam, install it 2degrees advanced for a total of 6 degrees and put it on a 108lsa.

Both now close the intake valve at 61 degrees and give a dcr of 7.7. How does this affect the power band of the second cam? I assume it would just make for a ****ty idle and peaky power? Im just thinking out loud here, thanks..
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Old 07-02-2013, 04:00 PM
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There is nothing wrong about installing a 110LSA cam on a 104deg intake C/L...which is 6 degrees advanced...
If you care to you can experiment with the cam installed from a 100deg in c/L to "straight up" 110in 110Ex centerlines... The engine will show you what it likes.

As a general rule the torque hits slghtly sooner in the power band, when the cam is advanced.
BUt it does not turn a big cam into a small cam.

110LSA in on a 104 intake C/L is good. Never assume where the cam is thou...degree it in first, then move it as required. Yes VTP clearance on the intake side decreases as the cam is advanced in the motor.

usually somewhere between 102 and 109 is best, and it depends on the specific engine and what you are after.
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Old 07-03-2013, 11:25 AM
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Well I might try to run a 108/102 camshaft but not 100% sure yet, still have some thinking to do. I already own the 60121 but I bought it when I was building a 350..now its 383ci.

The lunati tech is saying he would run the second cam, a 110/106, the 60121 is 112/106 and he said it would be fine too. I'm just a hair splitter and want the truck to pull to 6000.
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Old 07-03-2013, 03:08 PM
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I read that when calculating camshaft overlap, subtract 8 degrees from the advertised intake/exhaust durations to account for hydraulic lifter travel. Is this about right for a standard lifter?
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Old 07-03-2013, 06:31 PM
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first question,what type of camshaft do you want to use?
what is your static CR?
lets discuss a few grinds,,,
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Old 07-04-2013, 10:57 AM
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I was looking at running a Voodoo Roller,278/282 adv. 227-231@50 .530/.535 110lsa/106icl.

I have 9.5 compression.. This one would close the intake at 65 degrees and have 60 degrees of overlap. That's without subtracting the 8 degrees for hydraulic lifters.
65 degrees abdc nets me a 7.6 dcr..

The engine is a "880" 383, vortec heads, performer rpm, 750QF annular with vacuum secondaries, 1 5/8 long tubes, GM roller lifters, ultra pro mag 1.5's. .035 quench with pistons .007 in hole and GM .028 head gaskets.

DAILY DRIVER!

I really appreciate the shown interest from members of this website, the knowledge that is shared on the day to day through this forum is sometimes the only drifting wood nearby to keep guys like me from drowning. THANKS!
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Old 07-04-2013, 03:47 PM
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using those heads are more of a concern that the camshaft.the heads will be at max flow around 5200 rpm.It will rev higher,the power wont increase much.you need another 40 CFM to make big power over 6,000 RPM
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Old 07-05-2013, 12:08 PM
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Quote:
Originally Posted by vinniekq2 View Post
using those heads are more of a concern that the camshaft.the heads will be at max flow around 5200 rpm.It will rev higher,the power wont increase much.you need another 40 CFM to make big power over 6,000 RPM
I was hoping they would pull to 5800, thats where im wanting to shift anyways. I was thinking with just a little port work they would hold up to 6000..
I know they aren't ideal but they are the best I found for under 700.
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