500HP Reliablity & Time Untill Re-Build...
 

A few Questions on the HP 500.
I currently need to repower a 22 Velocity.
I have an oppertunity to purchase a
2001 HP 500 Carb.
140 Hours on the motor - No Maintance done to date. Excluding oil Changes...

The motor is currently running great, Leak Down is problem free...Though I assume the Valve springs are going to have to be done before i run it?

How long will this engine be Problem free befor it needs to be re-built... Any Average numbers out there I have herd everything from 300-700 hours... I will be running this on a small lake with little chop... its my only boat so its probably a 75% Cruise and 25% top end boat...

Any Help is appreciated.. thanks

Option#2 is a 500MPI (425HP EFI) zero hours for about 2000 cheaper.... (not including periferials like ram steering..)

Any engine that uses a Holley double pumper carburetor (500 HP) gets a big shot of raw fuel every time the throttle is moved (whether the engine needs it or not). The raw fuel washes the oil off of the cylinder walls and wears out the rings and bore prematurely.

This raw fuel problem is particularly severe with the 500 HP because the Dart Single plane intake manifold doesn't retain any heat to vaporize the raw fuel that puddles in the manifold runners. Most engines have an exhaust heat crossover passage that heats the raw fuel and reintroduces it into the air stream.

The raw fuel will also collect in the oil pan, diluting the oil, and its lubrication properties. This diluted oil is splashed onto the camshaft and pumped into the rocker arms accelerating valve train wear. It is really important that the oil and filter be changed every 25 hours of engine operation.

The stiff valve springs, needed for the high lift camshaft, will need replacing every few years because they will take a "set" during winter storage (unless you remove the rocker arms and relieve the valve spring tension during winterizing).

Stiff valve springs and high lift aftermarket camshafts (like the one on the 500 HP) close the valves very quickly and the exhaust valves and seats may need a valve job after about 300 hours. Especially with constant low speed running.

I would buy the 500 HP, it is a great performance engine, but it isn't as reliable as a stock engine.

Dennis Moore

I would agree with High-tide on this one, and maybe you get puddling in a dual plane not the Dart.

Looks like excess fuel again from somewhere can kill.

Holley carburetors have a positive displacement diaphragm style accelerator pump. Whenever the throttle is moved the pump shoots raw fuel into the engine. Opening the throttle slowly shoots the same amount of fuel into the engine as when the throttle is opened quickly. When slowly opening the throttle, an engine doesn't need a large pump shot.


The Quadrajet and Weber/AFB/Edelbrock Square Bore carburetors have a plunger accelerator pump. When opening the throttle slowly, the plunger bleeds off fuel, back into the float bowl, through a slot in the pump cavity. When the throttle is opened quickly, only a small amount of fuel bleeds off and a large fuel shot is pumped through the accelerator nozzles. The amount of fuel varies according to the speed of the throttle movement.

The Holley really floods an engine with excess fuel, especially when making slow throttle speed adjustments around a launch ramp or dock. This is why tuning the accelerator pump circuit is so critical on a Holley and not on other styles of carburetors. It is very easy to shoot too much raw gas through the positive displacing accelerator pumps with a Holley.

The double pumper Holley carbs also have mechanical secondaries. If the throttle is opened at low speeds, the secondary accelerator pumps will shoot raw fuel into the engine whether it is needed or not. With vacuum secondaries, the fuel will not start flowing into the engine until it builds up enough manifold vacuum to use the additional fuel. The 500HP has a bad combination because the Dart single plane intake manifold needs high rpm to build manifold vacuum and the double pumper carb is feeding it a lot of fuel at low rpm.

The positive displacement double accelerator pumps, mechanical secondaries and cold running intake manifold, allows raw fuel to enter the cylinders without being mixed with the air. The raw fuel won't burn and washes down the cylinders and rings.

Dennis Moore

I'm gonna hafta side with Dennis on this one. A boat doesn't have the advantage of a loose converter like a performance application in a car, and cannot burn all the fuel that a hard shot from a mechanical secondary Holley will deliver at low rpm. The fuel has to go somewhere, and that's down the cylinder walls and into the oil pan. A vacumn secondary 800 or 850 or whatever would have been a much wiser choice.

HP500 is still a kick @ss motor tho. Would definately go with that choice.!:p

Now please don't throw rocks at me forum stars....!:crazy:

Mr. Moore,

In the interest of brevity and politeness, all that I can say is that you obviously have little or no experience with the operation of Holley mechanical secondary carburetors.

As I have said in other posts, I think that the Technical Q&A forum is an important tool for people looking for answers, however it is annoying and or dissapointing when someone who has no idea what they are talking about posts "facts" that have no basis in reality.

Guys,
I have built an engine with a cam that required 140 seat pressure, I realize that this cam will require some valve-train maintenance but I am curious as to why low speed operation would exaggerate the wear on the valve seats as stated in post #2 P5 above. I thought I was doing my engine a favor by cruising at around 3000 RPM and taking it easy. Engine is a 502 with all the good stuff for a blower motor with 5psi max boost. At 3000 rpm it is still pulling 1 pound or 2 of vac. Cam has a lift of about 0.610 or so with the 1.7 arms.

Tim T.

Adivanman; I was wondering if you had anything constructive to contribute here cause I was kinda interested in this discussion and would hate to have this thread deteriorate into another wizzing contest. --- Jer

Agreed.!

Can we all just get back to the original subject for poor Mr. Velo.? The HP500 is a great motor. Do we all agree? Poor guy gets this kinda response after only 4 posts........he'll prob never post again..! How is that helping the board?:rolleyes:

I for one am appreciative of all reponses I get when I ask a question, but it seems that the negative attitudes expressed by some could be curbed a bit.

I think everbody is right here. Adivanman, in a 22 Velocity, an HP500 is gonna be a lightning bolt acceleration-wise, and the mechanical secondary carb shouldn't cause any problems, and in fact, will prob be VERY responsive. Put this motor in a heavier boat that can't achieve high acceleration rates to burn a heavy pump shot from the Holley, and you will have Dennis's explanation.


Can't we all just get along.!?
:D

The excess fuel goes out the exhaust. Never even has time to dilute the oil on the cyl walls. Go with the HP 500, have the heads rebuilt at 300 hrs as was said and replace most of the valve train and you will be fine.

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

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

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.

Adivanman is right on this one!
 

Excellent post. I worked for GM at Rochester Products a long time ago, and this is textbook.:D

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.

Definately........that was the kinda post that helps people..!
:)

Thanks.!

Do the HP 500 EFI's have the valve springs problems too or is it just the carb motors?
Mike

500 EFI's do as well.

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'm with Fever Mike. Have a pair of 99 500s in my Baja. 205 hours and no problems. They've been very reliable.