will this cam have a choppy idle in a 355 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-27-2008, 02:11 PM
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will this cam have a choppy idle in a 355

its a crane energizer with 286 adv duration and .465 lift but with 1.6 rockers right around .500 lift it has a 106 lsa and engine analyzer says it has around 11 hg of vacuum at idle im just wondering if it will sound lumpy or smooth
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Old 09-27-2008, 02:26 PM
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Quote:
Originally Posted by jarrettandroski
its a crane energizer with 286 adv duration and .465 lift but with 1.6 rockers right around .500 lift it has a 106 lsa and engine analyzer says it has around 11 hg of vacuum at idle im just wondering if it will sound lumpy or smooth
Lumpy!

Bogie
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Old 09-27-2008, 02:44 PM
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With that 106 lsa it should have a fair amount of overlap, giving it a "choppy rumble", but it may have a tendency to "load-up" at lower cruising rpm's and idle. Plan on changing/cleaning plugs often if you drive it much on the street. Should be a monster at 2800+. Hang on!!!!-Jim
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Old 09-27-2008, 03:18 PM
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hey thanks for your answers guys its only coming out on weekends so changing plugs wont be that big of a deal to me? what does load up mean??
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Old 09-27-2008, 09:06 PM
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Yea, very lumpy!!

We put the Comp 286 in my son's 400 and it's nasty! Not much vacuum for the power breaks either.
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Old 09-27-2008, 09:50 PM
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Lumpy like a bad cook's gravy. Your tires might get smooth though.

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Old 09-27-2008, 09:59 PM
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You will have to have a dual plane intake to get that much vacuum at or below 900 rpm with that LSA.
If you put on a single plane intake it will really thump with all the overlap and reversion.
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Old 09-27-2008, 10:27 PM
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This post is in response to j.d.'s comment "....a fair amount of overlap, giving it a "choppy rumble". I'm not picking on j.d. as there are many people who think "lumpy" is created at overlap. Please read these paragraphs by Iskenderian and make your own decision....

"What Causes Intake Reversion? Once and for all, let us have the TRUTH!

With the proliferation of the Motorsports Industry over the years, many new faces have come on the scene. In the cam grinding business today, there are many younger, less experienced companies struggling for recognition of their talents and a few have turned to postulating new theories in order to attract attention. However, they are I believe unfortunately, too often guilty of shooting from the hip.

Two in particular are responsible for perpetuating the "myth" that an earlier opening of the intake valve (even by a mere 2 or 3 degrees) causes the phenomenon known as "reversion". Nothing could be further from the truth! This misconception not only defies common sense, it also establishes a false premise from which other, incorrect conclusions can be drawn. Simply put, those who focus on overlap are on the wrong end of the cam-timing diagram!

Reversion, carburetor/Injector "stand-off" or the general effect of the backing up of the intake Fuel/Air charge normally associated with longer duration high-performance camshafts is actually caused by a Later Intake Closing! How do we know this to be true? The answer lies in the basic principles of physics. For as with geometry and trigonometry, these sacred truths do not change simply because someone chooses to ignore them in an attempt to garner a reputation.

Specifically, when the intake valve opens some 40 or more degrees before T.D.C. at the end of the exhaust stroke, very little (virtually no) exhaust gases remain in the cylinder. The piston is in the vicinity of T.D.C. (only .425" down the hole @40o BTDC - on a typical 350" Chevy with 5.700" rods) and no appreciable threat is posed to the forthcoming intake charge. The "False Reversion Hypothesis" taken to an extreme would lead one to the equally false conclusion that any overlapping of the intake and exhaust valves is totally undesirable. Automotive engineers of the late 1800's and early 1900's used to think this way. They were deathly afraid of overlap, so much so they actually employed "Negative" overlap (minus 5 or 10 degrees) to be absolutely sure none would occur. What was the result? These engines were severely "throttled back" or limited to low speeds and mediocre output. [ Reference: Iskenderian's Tech Article "Cam Degreeing is Simple"] But, more progressive engineers of the early 1920's who performed "brazen experiments" with longer duration cams proved these overlap fears to be only so much "stuff and nonsense", as both power, rpm and performance were actually improved. These engineers demonstrated that overlap did not cause engines to quiver, backfire or lock-up on the spot! Although, the ignorance displayed by their predecessors is easily explained by their lack of experience, (internal combustion engine design being in it's infancy) it was none the less the result of an incorrect hypothesis.

Should you need further persuasion that reversion is not caused by earlier intake opening and the resulting extension of valve overlap, consider this: What happens when you advance any camshaft? The intake as well as the exhaust valves open earlier. Does this advancing of the cam cause more reversion? Of course not. Throttle response and torque are enhanced. Yet, if these theories were correct wouldn't the engine run more poorly, especially at lower RPM? The answer is obviously yes, and because so, these theories are invalid. A brief look at what's happening on the other end of the valve-timing diagram will tell you why.

For when a camshaft is advanced, not only do both valves open earlier but they of course also close earlier - and here in lies the key to reducing Intake Reversion. Close your intake valves earlier and any tendency for the occurrence of Reversion or the backing up of the intake charge as the piston rises on the compression stroke will be reduced. It's not complex, nor is it a mystery. And the circumstances surrounding it's occurrence have not changed. In fact any experienced mechanic could tell you as much, for, as Ed's good friend the legendary Smokey Yunick might say, "Only country smarts are required to solve the problem."
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Old 09-28-2008, 10:11 AM
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good i wanted it to be a little nasty thanks for the answers
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Old 09-28-2008, 10:35 AM
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Reversion and scavenging are one thing.

Overlap with a single plane intake is seen by the sucking cylinder as a giant vacuum leak, one that is sucking in exhaust gases from the adjacent cylinder.
More lope due to bad combustion and lower vacuum sucking on the carb, altering the fuel atomization. = more lope.
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Old 09-28-2008, 10:42 AM
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Tech; I probably should have said " with that lsa AND duration" but I think most everyone knew what I was attempting to say. (Same long-duration cam with 106 VS. 112 lsa will sound "choppier" or "lumpier") Anyways- that article is great reading, and so I suppose my "not being clear" brought forth more good reading material. I apologize if my statement was not clear enough, but also- Thanks for the ISKY read. -Jim
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Old 09-28-2008, 12:26 PM
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Here's one guy's car with that cam in a 355 with 10:1

http://www.youtube.com/watch?v=wGQWf5VX6Lg
and
http://www.youtube.com/watch?v=CtjXWeHMzpM
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