SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: el mojado on May 08, 2013, 01:37:37 PM
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Found this roller cam used. Its going in a 20.5 ft mini day cruiser. 454 flat top pistons. HEI. 049 Stock rebuilt heads. Jacuzzi WJ-B pump. Dual plane intake.Cam is a chet herbert p/n BR252-OG. any opinions?
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If that cam card is correct that is way to much lift....if you do not notch your pistons your valves will end up knocking some some holes in there for you...I would look for a roller cam with under 560 lift your and keep your duration under 280 degrees your boat will be more enjoyable
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Cam info found on Doug Herbert's web site.
Cam Grind Type:MECHANICAL ROLLER CAMS
Application: CHEVROLET V8 67-93 396-402-427-454
Block Size: BB
Engine Make: Chevrolet (Chevy)
# Of Cylinders: 8
Manufactured In Year: 67 - 93
Cubic Inch Size / Volume: 396-402-427-454
Additional Qualifier:
Brand Code: Herbert Performance Cams
Cam Only Part #: CBR252
Cam Only Price : 229.99
Cam And Lifter Part Number:
Cam And Lifters Price :
Dur Int-Exh: 290/290
Dur @ .050 Int-Exh: 250/260
Lift 1.5 - 1.5 Int/Exh:
Lift 1.6 -1.6 Int/Exh:
Lift 1.7 -1.7 Int/Exh: 685/685
Lobe Center: 108
Valve Lash: .018-.020
RPM Range: 2500-6500
Description: Bestcam for396-402 c.i. Strong torque,easy on parts
You will want to have the heads cut so you don't crush the valve stem seals, and set up with the proper springs to match the cam. With flat top pistons you might not have an interference problem but, you'll want to double check everything during the build, not at start up.
If you decide it's too big, I'll give you the standard SCJB offer ;)
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Holy cam man... Way too big for that combo
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Woh there buddy, that's a bit much. If I was you I'd shoot for something with lift in low to mid 500's. it's a day cruiser not a tunnel hull
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If you are going to run we headers, buy can with a wider lobe center, that cam has the valves open together for a long time.
Worst case do a 110 degree, but better yet, look for 112 degree.
Look up the cam card for an actual marine camshaft and get a feel for what is close.
104 lobe centers would be fine for open, dry exhaust, but she will be lumpy, probably idle at about 1500rpm or so. It really needs more compression to work right.
Good luck.
GT
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Ok! Ok! Too big! I get it! Thanks guys! :D
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Max lift occurs when the piston is more than halfway down the cylinder. It does NOT cause piston/valve interference. Duration causes P/V interference during the overlap period when both valves are open. In a BBC the exhaust will clear near anything since its so far away from the piston crown. A tight lobe SEPARATION is just what a jet needs, it gives a narrow, peakier power band, but causes more interference problems. A jet only needs max power at max RPM of the pump capability (what the engine can actually turn it to). A BBC with the typical flat top piston with no intake notch, un milled heads, un milled deck will sometimes (50/50 chance, but will sometimes self clearance with a small crescent where the intake valve touches) clear the piston with a Comp Cams 292 hydraulic (great for Bassett exhaust, but too big for logs). A safer alternative and one that will always work is the Comp 288 or XE284 for Bassetts, and the XE 268 for log exhausts. Comp cams have typically faster ramp rates than other cams, this makes more power, but will cause a light valvetrain noise(ticking that you can't seem to get rid of, so don't try.) The best jet boat Comp solid roller is the 288AR, or for 496 builds if you want a bit more, the Comp XR286R. Any cam that says"easy on parts", or comes from a small or older "traditional" cam company usually means its ramp rate is slow, and may not make much more, or any more power than a fast ramp rate hydraulic cam(I.E. Comp Magnum or especially the Extreme energy series cams.) I have a cam analyzer and have analyzed thousands of cams in the last 25+ years. We charge $18.50 for this service, and can save you much cash and time. Ramp rate is extremely important to power production, and all cam companies don't have the latest computer design or manufacturing equipment. You can't tell ramp rate, or quality by looking at a cam. It is a safe bet that buying the same cam from the same company that your dad/uncle/neighbor used "back in the day" will be a disappointment, BUT if you never compare it to something modern, you'll probably be satisfied. At least until you race somebody with a newer setup..... Class dismissed. TIMINATOR