velo

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..)

Dennis Moore

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

John B

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.

Dennis Moore

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

Madmax

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.!

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

Adivanman

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.

BadDog

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.

jpclear

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

Madmax

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?

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.!?

formula31

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.