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Ive heard this before: a larger engine or more cubic inches will "need" OR "take" a larger cam (mostly regarding duration) than a smaller displacement engine of similar design. In addition to being able to utilize the larger cam, the engine's attitude and smoothness will likewise be affected. How true is this?
For example:
-289 engine and a 347 based on our basic pushrod N.A SBF:
-E303 camshaft, 110 lsa, 512", 280 adv duration in:
1)289
2)347
Will this cam "seem" smoother in the 347?
If yes does the principal sill hold
1)E303 289
2)E303 302
Will this cam "seem" rougher, "sound" rowdier when running in the 289 when compared to 302 all else being equal? Thanks, Ive wondered about this for some time.
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RE: Cam size Versus Engine size: large CI = smoother?
Generally speaking, yes.
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RE: Cam size Versus Engine size: large CI = smoother?
It goes a little beyond that.... take a 302 with GT40 heads and the E-303, change the heads for "bigger" heads (Edelbrock, Canfield, AFR, TFS).... and the cam will run "smoother"...... increase engine CID's, and the same thing happens.
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1986 GT-X303-289 heads-1.72 rockers-RG 4+1 Trans.
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RE: Cam size Versus Engine size: large CI = smoother?
Thanks, I suppose then that I can expect my (used $70) E303 cam to act a bit rough (in comparision) in my fuel injected 289 I am building ... I am wondering then, if it is a good thing that I got a heavier flywheel than expected (found out today its 29 pounds) it was only $78.99 though perhaps its weight will help me to more easily drive in stop and go traffic with that cam.
I got my hands on one of those early systemax 1 lower only intakes, and was trying to duplicate the entire 50 state exempt kit, the lunati cam was close to the E-303 cam but with less lift:
512 lift 220 dur@050 281 adv dur 110 lsa = systemax/lunati
498 lift 220 dur@050 282 adv dur 110 lsa = e303
Im guessing that its a good thing that I went for the e303 for cost and drivability... the cheapest I could find the lunati cam was for $280 not inculding tax and shipping & handling...
When looking around for a used e303 cam I saw that many people complain that It doesn't give the rumpity-rump hot-rod cam sound that they bought it for, perhaps they need smaller CI or restrictive heads then? haaa ha well the reason I got it was
1) 50 state legal (but maybe not with other mods?)
2)similar to the lunati cam (closest in specs I could find anyway)
3)really cheap and plentiful.... [#1 reason here]
RE: Cam size Versus Engine size: large CI = smoother?
Best source for cam info is a cam company catalog.
Comp cams has a great one.
Overlap ( the amount of time both valves are open together in degrees)is the critical dimension, as far as a choppy idle goes. The more overlap, therougher the idle.
As far as the E303 goes, the reason its not so choppy an idle is because its really not that radical.
Remember the E stood for (Emissions).
But if you had one of the old B303 cams, now they sounded good!
My personal feelings are you won't notice much of a difference between a 289 and a 302.
Only 13 cubes different, that's barely 4 %.
For performance, better heads is the biggest gain( other than forced induction) you can achieve.
RE: Cam size Versus Engine size: large CI = smoother?
I forgot to add.
More overlap equals more emissions,(Raw fuel is being drawn out the exhaust port)which is the difference between the non compliant B303 and the emissions legal E303.
An example of a car with extreme amounts of overlap, would be a Top Fueler or Funnycar.
Raw fuel is blown out the pipes by the combination of high intake manifold pressure and tons of overlap.
Overlap increases with increases in duration(generally).
Too much duration/ overlap can be countered with an increase in static compression ratio.(or boost)
On the larger engine question.
Increasing cubic inches 351 vs 289/ 302 for instance.
All other things being the same, lowers the powerband of the larger motor.
Same amount of airflow feeding a larger mill. Makes sense doesn't it? And calms the idle too!
RE: Cam size Versus Engine size: large CI = smoother?
When you say 289...... are you using an early block?......
__________________ ACRONYMS:
LUK=Let Us Know, GL=Good Luck, LMK=Let Me Know, JIC=Just In Case, BTSTDTRT=Been There Seen That Done That Repaired That, YCYDYP=Your Car Your Dough Your Prerogative and the classic... DILLIGAS=Do I Look Like I Give A S***
1986 GT-X303-289 heads-1.72 rockers-RG 4+1 Trans.
Quote:
Originally Posted by Joel5.0
Great thoughts will overwhelm a feeble mind.
There is never money to do it right, but there's always money to do it over.
The proof of understanding is the ability to explain it. (H. Torruella)
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Cam size Versus Engine size: large CI = smoother?
perhaps its weight will help me to more easily drive in stop and go traffic with that cam.
haaa ha well the reason I got it was 
