500HP Reliablity & Time Untill Re-Build...
09-23-2003, 10:02 AM
#11
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Bad Dog
At high speeds the valve has inertia and once it is opened by the camshaft it wants to hang open from this inertia. An aftermarket camshaft with its higher lift and faster opening and closing lobes will put more inertia into the valve. An aftermarket camshaft will require a stronger than stock valve spring to close the valve at high speeds (overcoming valve inertia).
If a spring is chosen that is stiff enough to overcome the valves inertia at high speed the valve won't hang open and the valve spring tension will be matched to the valves high speed inertia. Valve inertia and spring tension are balanced.
At low speeds the valve inertia is dramatically less, the stiff valve spring tension is not matched to the low valve inertia. Valve inertia and valve spring tension are not in balance.
Without the valve spring inertia offsetting the heavy valve springs the valves snap shut very hard and pound the valves and seats.
The same thing happens to the lifters and cam lobe but with even more dramatic results because the rocker ratio multiplies the valve spring tension. The lifter, without any upward inertia at low speeds, really pushes down on the cam lobe hard with the stiff valve springs.
Low speed running is hard on the valve train of any engine with stiff valve springs and a high lift, fast opening and closing aftermarket camshaft.
Dennis Moore
At high speeds the valve has inertia and once it is opened by the camshaft it wants to hang open from this inertia. An aftermarket camshaft with its higher lift and faster opening and closing lobes will put more inertia into the valve. An aftermarket camshaft will require a stronger than stock valve spring to close the valve at high speeds (overcoming valve inertia).
If a spring is chosen that is stiff enough to overcome the valves inertia at high speed the valve won't hang open and the valve spring tension will be matched to the valves high speed inertia. Valve inertia and spring tension are balanced.
At low speeds the valve inertia is dramatically less, the stiff valve spring tension is not matched to the low valve inertia. Valve inertia and valve spring tension are not in balance.
Without the valve spring inertia offsetting the heavy valve springs the valves snap shut very hard and pound the valves and seats.
The same thing happens to the lifters and cam lobe but with even more dramatic results because the rocker ratio multiplies the valve spring tension. The lifter, without any upward inertia at low speeds, really pushes down on the cam lobe hard with the stiff valve springs.
Low speed running is hard on the valve train of any engine with stiff valve springs and a high lift, fast opening and closing aftermarket camshaft.
Dennis Moore
09-23-2003, 10:14 AM
#12
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Velo,
You will like the performance of the HP500. Being a 2001 model, it must be one of the last carb versions made, but still may be plagued with the valve spring problem the earlier carb motors had.
Even though it appears to be running well, some of the springs could be broken, most likely the damper coil between the inner and outer springs. Take the valve covers off to inspect. Or, if that is not possible, run the motor until fully warmed up, then shut it off for 10 minutes and then re-start it. If a puff of blue smoke comes out upon start up, it is a good sign that the valve guides and/or valve seals are damaged. This would raise suspicion that the springs were broken and have chewed up the guides. If such is the case, there is likely a bunch of metal shavings that have passed through the rest of the motor and started to take their toll (bearings, camshaft and lifters). If you do discover pieces of broken springs laying in the troughs of the heads after taking the valve covers off, you can bet that there may be a bunch of other pieces laying in the oil pan. I just went through this with my twin 1999 HP 500's that I bought with 115 hours and ended doing total rebuilds on both. But now they run great and will hopefully last a long time. Will be checking the springs periodically however.
BTW, you can alter the timing and the volume of the pump shot on holley carbs by changing the plastic cam that actuates the pump. These cams come in a variety of sizes and shapes. My belief is that with a lighter load on the motor (less weight or smaller prop) which allows it to rev easier, you can reduce the volume of the pump shot. You could simply experiment with smaller pump cams until you reach the point where the motor hesitates when you advance the throttle, then increase until the hesitation is cured.
Rich
You will like the performance of the HP500. Being a 2001 model, it must be one of the last carb versions made, but still may be plagued with the valve spring problem the earlier carb motors had.
Even though it appears to be running well, some of the springs could be broken, most likely the damper coil between the inner and outer springs. Take the valve covers off to inspect. Or, if that is not possible, run the motor until fully warmed up, then shut it off for 10 minutes and then re-start it. If a puff of blue smoke comes out upon start up, it is a good sign that the valve guides and/or valve seals are damaged. This would raise suspicion that the springs were broken and have chewed up the guides. If such is the case, there is likely a bunch of metal shavings that have passed through the rest of the motor and started to take their toll (bearings, camshaft and lifters). If you do discover pieces of broken springs laying in the troughs of the heads after taking the valve covers off, you can bet that there may be a bunch of other pieces laying in the oil pan. I just went through this with my twin 1999 HP 500's that I bought with 115 hours and ended doing total rebuilds on both. But now they run great and will hopefully last a long time. Will be checking the springs periodically however.
BTW, you can alter the timing and the volume of the pump shot on holley carbs by changing the plastic cam that actuates the pump. These cams come in a variety of sizes and shapes. My belief is that with a lighter load on the motor (less weight or smaller prop) which allows it to rev easier, you can reduce the volume of the pump shot. You could simply experiment with smaller pump cams until you reach the point where the motor hesitates when you advance the throttle, then increase until the hesitation is cured.
Rich
09-23-2003, 10:26 AM
#13
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After a lengthy discussion with High Tide this morning, we offer these points for your technical consideration….
Holley Mechanical Carburetors…A few Facts and Considerations
Holley Carburetors require Vacuum to draw fuel from the bowls. Because the signal ratio (of the carburetor) is slower than the engines ability to climb, a secondary (and non-vacuum) source of fuel is required to bridge the gap. This secondary source of fuel comes from the Accelerator Pumps – both on the Primary Side and the Secondary Side of the carburetor.
The Primary Accelerator Pump bridges the gap between idle and part throttle. The Secondary Accelerator Pump bridges the gap between part and full throttle. That is the sole function of the Accelerator Pumps.
Holley Carburetors offer an engine tuner a huge amount of variability to adjust both the Primary and Secondary Accelerator Pumps to optimize the air fuel mixture without creating a lean or rich condition, regardless of application.
One Size and One Tune Up does not fit all. No two applications are exactly the same, even if the engine is – weight, environment, etc. all require tuning. To accommodate these variations, Holley offers an almost staggering array of components or options to optimize engine performance in individual applications. In direct response to Mr. Moore’s comments, we will limit our discussion here to the Accelerator Pumps.
Holley offers Accelerator Pumps in different sizes (volumes) for different applications. Your choice of Pump will allow you to control the total volume of fuel available (30 or 50 cc).
Holley offers Accelerator Pump Cams in a wide variety of sizes and shapes. Your choice of Pump Cam will allow you to control the aggression and duration of the Accelerator Pump shot. This is true on both the Primary and Secondary side of the carburetor.
Holley offers Squirters in a wide variety of sizes (and a couple of shapes). Your choice of Squirter will allow you to control the flow, velocity, and density of the Accelerator Pump shot. This is true on both the Primary and Secondary sides of the carb as well).
Holley also allows for additional fine tuning of the Accelerator Pumps via the pump cam arm. One of the more overlooked options for fine tuning, this purely mechanical “tool” allows you to control when the Accelerator Pump begins to open.
Summary – a knowledgeable carburetor tuner can control every aspect of the Accelerator Pump and tune it for specific application.
On that basis, if is absurd to assume that a competent boat operator, with a properly tuned carburetor, would have an issue with excess fuel pooling in the intake or washing down the cylinders while maneuvering at a dock or ramp. Please bear in mind that with a Holley Mechanical Secondary carburetor, the Secondary Accelerator Pump does not even come into play until you are at more than 50% throttle (probably closer to 60%).
The variables of this discussion could go on for ever.
Keep in mind that the primary consideration when tuning a carburetor is vacuum, which is dictated by the intake manifold and the camshaft. Idle mixture, jetting, and power valves are all gross and necessary factors that, by and large, are understood by people who are tuning engines. All of those operate in response to vacuum, and can often be set on a dyno, with no consideration of final application. Accelerator Pumps, however, are the final tuning tool that is directly related to the specific application. The mechanical aspects of the carburetor allow the end user to maximize performance and efficiency.
I would have no hesitation going with the HP500. I think that you would be very satisfied with it.
Holley Mechanical Carburetors…A few Facts and Considerations
Holley Carburetors require Vacuum to draw fuel from the bowls. Because the signal ratio (of the carburetor) is slower than the engines ability to climb, a secondary (and non-vacuum) source of fuel is required to bridge the gap. This secondary source of fuel comes from the Accelerator Pumps – both on the Primary Side and the Secondary Side of the carburetor.
The Primary Accelerator Pump bridges the gap between idle and part throttle. The Secondary Accelerator Pump bridges the gap between part and full throttle. That is the sole function of the Accelerator Pumps.
Holley Carburetors offer an engine tuner a huge amount of variability to adjust both the Primary and Secondary Accelerator Pumps to optimize the air fuel mixture without creating a lean or rich condition, regardless of application.
One Size and One Tune Up does not fit all. No two applications are exactly the same, even if the engine is – weight, environment, etc. all require tuning. To accommodate these variations, Holley offers an almost staggering array of components or options to optimize engine performance in individual applications. In direct response to Mr. Moore’s comments, we will limit our discussion here to the Accelerator Pumps.
Holley offers Accelerator Pumps in different sizes (volumes) for different applications. Your choice of Pump will allow you to control the total volume of fuel available (30 or 50 cc).
Holley offers Accelerator Pump Cams in a wide variety of sizes and shapes. Your choice of Pump Cam will allow you to control the aggression and duration of the Accelerator Pump shot. This is true on both the Primary and Secondary side of the carburetor.
Holley offers Squirters in a wide variety of sizes (and a couple of shapes). Your choice of Squirter will allow you to control the flow, velocity, and density of the Accelerator Pump shot. This is true on both the Primary and Secondary sides of the carb as well).
Holley also allows for additional fine tuning of the Accelerator Pumps via the pump cam arm. One of the more overlooked options for fine tuning, this purely mechanical “tool” allows you to control when the Accelerator Pump begins to open.
Summary – a knowledgeable carburetor tuner can control every aspect of the Accelerator Pump and tune it for specific application.
On that basis, if is absurd to assume that a competent boat operator, with a properly tuned carburetor, would have an issue with excess fuel pooling in the intake or washing down the cylinders while maneuvering at a dock or ramp. Please bear in mind that with a Holley Mechanical Secondary carburetor, the Secondary Accelerator Pump does not even come into play until you are at more than 50% throttle (probably closer to 60%).
The variables of this discussion could go on for ever.
Keep in mind that the primary consideration when tuning a carburetor is vacuum, which is dictated by the intake manifold and the camshaft. Idle mixture, jetting, and power valves are all gross and necessary factors that, by and large, are understood by people who are tuning engines. All of those operate in response to vacuum, and can often be set on a dyno, with no consideration of final application. Accelerator Pumps, however, are the final tuning tool that is directly related to the specific application. The mechanical aspects of the carburetor allow the end user to maximize performance and efficiency.
I would have no hesitation going with the HP500. I think that you would be very satisfied with it.
09-23-2003, 12:58 PM
#14
Adivanman is right on this one!
Excellent post. I worked for GM at Rochester Products a long time ago, and this is textbook.
You would have to pump the the throttle a ton (which you don't in a boat) to get any measurable quantity of fuel.
Original question: I think an hp 500 (year for year) is worth twice what a stock 502 would bring. I just sold a 1999 for $9000 dressed.
You would have to pump the the throttle a ton (which you don't in a boat) to get any measurable quantity of fuel.
Original question: I think an hp 500 (year for year) is worth twice what a stock 502 would bring. I just sold a 1999 for $9000 dressed.
Last edited by John B; 09-23-2003 at 01:05 PM.
09-23-2003, 03:25 PM
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Thank You Everyone!!! Great Advice... and nice to see the entire group going the same direction with regards to the hp500 VS 502 (even when the boxing gloves are on) 
I think ill take a closer look @ the Springs... Probably just change em up now as preventative move and Buy the engine... Rich,Adivanman,HiTide,MrMoore,MadMax & everyone else thanks allot for your valuable insights and help in making my decision allot easier!!! Ill be sure and keep you posted as to how it goes! Mark
I think ill take a closer look @ the Springs... Probably just change em up now as preventative move and Buy the engine... Rich,Adivanman,HiTide,MrMoore,MadMax & everyone else thanks allot for your valuable insights and help in making my decision allot easier!!! Ill be sure and keep you posted as to how it goes! Mark
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