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iv been told by a VERY good mechanic that knows about boats as well as cars that the bigger the cam in a boat the better. is that true? i kind of believe him because he has this bad ass 24'eliminator that hits 120 on a single non blown engine that he built. would a bigger 5 something lift cam be better for my 1975 jet boat? it has a 454 that is basicly stock except for the intake and cam. it runs a good 60MPH. im wondering if i would pick up any speed with that cam and bigger carb?any help would be apreciated. thanx.
mach1 454
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Not neccesarily.How high do you plan on revving your motor?A bigger cam will raise your hp levels at higher rpms.do you want to be revving 8k to make power?
A cam that is to big in a jet boat can hurt you.If you are running an a impeller you will probably not see high rpm for that cam to work.you might need a smaller impeller.
If you have a high comp ratio,head combo carbueration,etc, and everything to match then you can go with a bigger cam.
How big a cam are talking about? This all depends on what your current set up is.If you want alot of reliability stay with a hydraulic type.If you are running a near stock motor with mild or no head work stay with something aroun 230-240@.50 duration with around a 550-560 lift on a 108 center.this should work well for an a -b impeller which should put your peak hp around 5-5500rpm.
A hydraulic roller type would even be a better choice if the funds allow the big advantage would be a motor that will make the same hp at higher rpm and more torque at lower rpm with the same or more hp.
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Bottom Line the parts have to match, and work together !!!
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The cam specs charger described is about the best for a natural aspirated BB engined jet boat with "A" or "B" impeller.
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230 -240 @ .050 will peak HP at 6,500 - 7,000 RPM. That is way too much for a mild BBC jet. If the boat does not turn that many RPM's now, the duration should be much less. Also lobe separation should be 110 or 112. Lift should be determined by flow numbers of the heads. Stock head flow numbers are available from most performance cyl head shops.
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I agree with Info on the lobe separation spec,However 550/60 lift isn't that much for even a standard chev BB 427/454's. Had boats with standard blocks running with cams like the above for long time before giving any trouble .Just my devalued CDN 0.02 worth http://free.***boat.net/ubb/wink.gif
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Infomaniac i run a 248@50 with a 580 lift cam ona 108 center its peak hp is reached at 481hp at 5600 rpm.motor is a bbf 429 with 11-1 comp ratio heads will be ported soon to boost the hp.Cam is a hydrualic type.A solid will probably pull higher peak numbers.I'am currently spinning an a-b impeller to 5100.with the bottle it goes to 5500.
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A cam in the low-mid .500 inch range with a duration of 225-240 deg@.050 will work great. Stock heads can't support the flow of anything bigger; most mildly ported heads can't either. Also, big cams need more compression because the longer duration tends to bleed off cylinder pressure. With a 225 deg dur you need to be running at least a 9 somthin comp ratio. About 10.5-1 with polished chambers and correct timing will net you more power and a broader torque curve. Solid lifters are more of an rpm thing and won't get you a whole lot of increase. Marginal at best. CompCams makes a few really good jet boat/marine cams. Check out their website. Hope this helps. Don't hesitate to ask any questions. Most of us are here to help!
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HERE MACH1, link to comp cams marine cams. http://www.compcams.com/catalog/106_107.jpg
I USE THE 11-244-4, I ran the 11-240-4 before and it ran alot better with the 244-4. 454BBC
merlin heads, elderbrock perf.rpm, 10:1, 850cfm DP holley,EMI thunder exh., AT with a A/B imp. runs 65mph at 5000 rpm.
DANO
[This message has been edited by DOHARA (edited April 05, 2002).]
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Just remember, you can NEVER go too big. First pick out the cam, then build the motor around it. If you use this train of thought, you will never go wrong!
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Since you said your engine is basically stock, does that mean you're still running the exhaust through logs? If so, bigger is NOT better, you don't a good way to get rid of the gases. Why put in a lot of gas if you can't get it out.
After reading what you said about yourself in another forum, believe me, you won't be happy using twice the gas for the same amount of power by using a bigger cam.
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You need to look at the whole setup. Without carburation, head and exhaust work the bigger cam will hinder rather than help. Are you running the oval port heads or the rectangular ports. That can be a big difference. Also do not forget to check the valve to piston clearance, it is amazing the damage a little piece of valve can do. Cliff
