WHat hydraulic roller cam to use ?
05-29-2003, 11:36 PM
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WHat hydraulic roller cam to use ?
Need help fast ! Friend is haveing cam problems and wants to switch to hydraulic rollers while they are out .
Motors are 510" with merlin heads (2.25" intakes) ,250 B&M blowers , single 1050 carbs . Want to get enough from the cams to make it worth while but needs a good idle . WHat cam exactly , can you guys say to use ? Thanks , JOE
Motors are 510" with merlin heads (2.25" intakes) ,250 B&M blowers , single 1050 carbs . Want to get enough from the cams to make it worth while but needs a good idle . WHat cam exactly , can you guys say to use ? Thanks , JOE
05-30-2003, 05:53 AM
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I am using the crane 139741 with 540 & procharger. Motor idle at 600rpm in gear & 800 out & pulls strong. I did not get engine dynoed since I did not to wait over 2 weeks for the engine shop to get it in.
05-30-2003, 06:06 AM
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Call Dean Nickerson, he has a cam that he uses for the B&M 250. He has done a lot of these so his cam will be right. I used his cam and had him set my 1050 Dominator up for my 250. Plugs look perfect at all RPM ranges. He jetted it and made all adjustments etc. All I did was bolt it on and check plugs. Perfect right out of the box. If you give him all your specs your results should be the same. He needs boat weight, dead-rise, speed, C/R exhaust info etc.
05-30-2003, 08:24 AM
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The 741 would be a good blower cam, but it may be too much for a 502. With my na 540 I have a pretty lumpy idle and it doesn't like to go into gear below 800rpm. Definetly does not meet my definition of a good idle.
05-30-2003, 08:43 AM
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Cord- if the 741 cam is not idling for you & you have 540. then I would say you either have a timing problem or carb problem. Mine is loppy but it goes in & out of gear with now problem. I have 1.36 gears with 30" prop & it puts a good load on engine.
05-31-2003, 09:25 AM
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A blower will smooth out some of the lumpy idle. A NA motor running a substantial cam will always be lumpier. That's mainly cause the vacuum signal is crap at idle. Big valves, big ports, big intake, and a significant amount of cam overlap will make it hard for the motor to get a consistent flow across the carb for fuel metering. Also the intake gets a "puff" of reversion from the combustion chamber when the overlap occurs. This stalls the intake airflow, aggravating the situation.
A roots blower app does 2 "good" things to reduce (or eliminate) this. #1: the positive displacement blower provides "fill" pressure to the intake even when the gauge reads in vacuum. There is no way to "stall" the airflow into the intake cause the blower is pumping it in. The vacuum signal does not manage the airflow anymore. #2: The carb is mounted on TOP of the blower, and it feels a CONSTANT and even draw across it and fuel is metered much more nicely at idle.
A NA motor can actually oscillate the airflow back and forth across the carb, which "double" loads the air with sloppy fuel at choppy idle. The blower completely prevents this.
That being said, a 731 is a good cam with a superior idle to a 741. Can be as much as 20 hp difference in them at 5400 rpm, though (usually more like 10-15 though).
A roots blower app does 2 "good" things to reduce (or eliminate) this. #1: the positive displacement blower provides "fill" pressure to the intake even when the gauge reads in vacuum. There is no way to "stall" the airflow into the intake cause the blower is pumping it in. The vacuum signal does not manage the airflow anymore. #2: The carb is mounted on TOP of the blower, and it feels a CONSTANT and even draw across it and fuel is metered much more nicely at idle.
A NA motor can actually oscillate the airflow back and forth across the carb, which "double" loads the air with sloppy fuel at choppy idle. The blower completely prevents this.
That being said, a 731 is a good cam with a superior idle to a 741. Can be as much as 20 hp difference in them at 5400 rpm, though (usually more like 10-15 though).
