I have an 18ft light weight jet boat. The motor is a 454 bored .30 over,9.5-1 compression,torker2 intake,holley 750vac sec,large oval port heads(ported),full roller rockers,3 angle valve job,over the transom headers,hei ignition,msd 6al ignition box, and the motor is balanced and blueprinted.
I narrowed the cam down to 3 choices. Someone told me not to go over 235 duration @.50 on my cam because my motor will never see the rpm's to make the horsepower. Is this true. I am planning on purchasing cam,springs,lifters and pushrods to match my cam.
These are the specs for the 2 cams I narrowed it down to.
Choice #1- This cam says A/B impeller,9.5 compression and performance use.The rpm range is 2500-6500,duration @.50 244 intake/254 exhaust,(.570 intake/.575 exhaust valve lift), and 112 degree lobe seperation on intake/exhaust.
Choice #2- This cam says good pleasure use and good economy. The rpm range is 1700-5700,duration @.50 222 intake/226 exhaust,(.525intake/.525exhaust valve lift), and 110 degree lobe seperation on intake/exhaust.
Choice #3- This cam says A impeller,needs improved intake, and likes headers. The rpm range is 2000-6200,duration @.50 234 intake/237 exhaust, (.564 intake/.566 exhaust valve lift), and 112 degree lobe seperation on intake/exhaust.
Those are my choices. I got these cams from the comp cams list.I noticed that the lobe seperation is a lower degree(112,110,108 etc) as the cam gets bigger. Does this effect the sound and idle? Could someone please explain this to me? I am so lost as to whats good for my boat. I want the best out of those 3 cams. I want a real rough lopy idle. I am also looking for a cam that can give me a real beefy sound. I would appreciate any help on this guys. Thanks 396--out!
I have found that if u run tighter lobe centers that a jet tends to run a little harder i usually try to run 108 centers.Also i wouldnt be afraid to run a little bigger cam everybody tries to match the cam just right and not go to big but when they get the motor together they find out they actually went a little small for what they were looking for.I hope this helped.
396,
Going to throw in another twist to your search.
Ideally, you need to know how much air flow your heads are capable of flowing. If your heads will only flow...as an example...260cfm @ .560 lift vs. 265cfm @ .600 lift.
Since the lift @ .600 does not flow much more than the valve @ .560, There would be no reason to buy a cam w/ .600 lift if your heads cannot flow the amount of air that the cam is trying to provide. Good luck, Mike
Given the information you have posted, I would go for cam 3. 2500rpm is a long time to wait for power... It could make the hole shot a bit rough... And 6000 is a good "soft red" line. If you blast to 6500 all the time, you will have less engine life, than 6000. (With an occasional blast to 6300 to impress someone.) Cam 2 is not enough to impress you, and cam one might be a little tough to live with...
However, there is a lot that you did not tell us. What kind of heads and valves? What is the red line for your engine and accessories? (Remember that waterpumps have a red line too...) If your accessories red line at 600 rpm, your decision is made.
I have pretty much the same motor as you and have the 1st cam in my boat but with 108 lobe separation. This was recommended by George at Clay Smith cams. It sounds bitchen at idle = 1100 rpm and still a little lopey. Although I run a tunnel ram with 2 750's and have the bigger valves = 2.19 in and 1.88 ex. Good luck!
Just get an Isky 280 Mega.
Since you asked, the tighter the lobes (112,110,108, etc) the rougher the idle.
Cam 3 would be my choice, alternatively get cam 2 and install it retarded 6* to move the rpm range up a little higher.
By now, you should be totaly confused. So this should help confuse you a little more with my 2 cents. Torque is what you want so I would say 108 lobe seperation. A jet boat and not that high RPM is another vote for 108. Oval port heads don't breathe that well so .550 to .600 lift is plenty. And I would call Clay Smith and talk to him. Maybe my 2 cents worth was overpriced!
And one more thing. Consider a roller cam as flat tappets can and do go flat, especially when approaching 600 lift area. The roller will give you more power everywhere. It has nothing to do with the "roller" itself, rather in the camshaft can be designed to open the valve very quickly. That is why roller cams make more power throughout the rpm range.
[ August 23, 2002, 11:05 PM: Message edited by: Fiat48 ]
Fiat48:
Oval port heads don't breathe that wellOne commonly overlooked thing.... the 71-72 402 BBC heads out flow almost every other BBC head that came factory stock. They are the only castings that have the small open chambers and the largest oval runners of any BBC head.
With any head after 72 the above statement applies.
My two cents, spend a little extra$$$$$$ Ditch the ovals, buy a set of rect. go roller and be done..The ovals were put on truck motors and early pass. cars.. Not performance till lateron I beleive 454 vettes..Smog motors!!!!!Maybe i should pay ya the two cents lol wink
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