Hp 500 Carb Owners!
 

Ok guys, I need an honest opinion about service & maintainence for these engines. I have a single HP500 Carb in my 1998 Baja 25' Outlaw. I run the boat on a fresh water lake in Upstate NY. I do run the boat hard sometimes, but hardly abuse it. Just stretch it out from time to time.:cool: Anyway, I am by no means an "internal engine" mechanic. I understand the basics, but anything internal I would have to leave to the pro's. My question is how many hours (average) should I be able to run this engine with simple maintainence (25 hr oil changes, etc). A lot of people on this board talk about replacing valve springs at 200 hrs, tear downs, and other stuff. I find it hard to believe that I will have to do this so soon considering how and where I use the boat.
There is 180hrs on it now, and it runs like a top. I just want to do what I can to make this puppy run the long hull. I had great luck with my last boat (7.4 330hp). That motor still runs geat with over 800 hrs. Any past experiences or suggestions concerning an HP would greatly be appreciated.

I don't know what the manual says
 

I have no idea what the Merc Manual says. But I would stick with a 50hr. oil change. The reason I say to do the upper end work at 250hrs. is because you have a lot more lift and duration in the cam in the HP500 as compared to the 330's. The 330 could run for a long time and never have a problem.

The problems you will run across is that if you don't replace the springs they will fatigue and become weak, or even break. When this happens, you may get some back-firing thru the carb when you pump up the gas at idle, or a loss of power. And the biggest problem is the valves will float from less spring pressure, or better yet you risk dropping a valve. If that happens you will be spending a lot more money!!! Nothing like a little preventative maintenance!

Although, I do have a friend who has HP500 EFI's with over 400hrs on them with no service.

I change oil every 25 hours (cheap insurance). I have 165 hours on mine ('99s) and plan on doing the springs around 250 hours more as preventative maintenance than anything else.

Honest opinion:rolleyes:

Stop using the boat right now! Change the valve springs, Use the comp cams springs to replace them.
Sorry but myself and others have had costly repairs because of the bad design or matching of the springs that came with your motors. A few articles have been written on this subject including one by Teague in Powerboat. Crane has changed the part number for the old springs but they still seem to have excessive seat pressures. The comp cam springs seem to be the answer!

If you want to take it further send the heads out for some porting and exhaust relief. I changed cams over to the crane 168731 this combo seems to work well and I have seen mph gains across the whole rpm range! I'm guessing that I have increased HP by about 60 or so per motor. Remember that is a guess not fact. You will have guy's suggest the 168741 but after a lot of research it seemed a bit much for the work that I had done and might of hurt performance instead of helping it.

This is just my opinion and the results of many hours researching but there may be better choices maybe Dennis will jump in with some better ideas:)

BTW I had a lifter fall apart at 160 hours and bad inner springs causing the cam to wipe out and the motor to fill up with metal and a lot of roller bearings!

Good luck, Scott

"Although, I do have a friend who has HP500 EFI's with over 400hrs on them with no service."

They use the Comp Cam springs :D

Thanks Guys, that does make sense due to the cam. There is a high peformance marine engine builder in town that does wonders with marine engines. I think I will see if he can give me a figure. I assume that 5,200 r's is ok to run WOT at. That's where I am now after a good lab finishing job on a Bravo 1 24p. I guess there is a price to pay for owning a high performance engine, but I love that blue :D

MY 98 hp carb lunched at 220hrs...
 

I agree with the previous response, stop and have it fixed.
Advantage or dealer never sent warranty card so I wasnt
notified of problems with this motor, found out too late.JC

Do the newer 500efi have this spring problem????

"Do the newer 500efi have this spring problem????"

No they use the Comp Cam springs!

Thanks;)

the rollers too
 

While you're in there replace the roller lifers as well.

A FRIEND OF MINE HAS A 95 fORMULA 419 WITH TRIPLE 500H.P. CARBURATED. 550HRS NO PROBLEMS.

Panther,

That's a good point I forgot to mention that I could push the middle pin out of all my lifters but one with my finger!

Ditto on what Scott and Panther said.

Friend of mine with a 33 Outlaw broke 3 springs and just replaced those 3. Had around 200 hours at the time. Short time later he noticed a drop in rpm. Went back in and found 25 or the 32 springs trashed. OK. Replaced the whole set. Flushed the motors. Bought a couple of Dominator carbs to put on. Did that and on the shake down/jetting cruise, starboard motor shut down due to no oil pressure.

He is now rebuilding both motors.

DO IT NOW! Regardless of price. Or...

Once I am around 200-225 hours, I plan to have Jack @ Boyd's motorsports go through the heads. I do think though, that all of the above really depends on application, and how the boat is run. An HP500 in a 25' 5,000lb boat run pretty easy on a fresh water lake is quite a bit different than twins in a 33' 7,500lb boat run probably a lot harder in bigger water ( I know I would run it WFO if I had a boat like that:D ). Point is, I don't think this motor will self distruct if I use it one more time. I really do appreciate all of the comments. I like OSO for a lot of info. and past experiences. I'll let the board know what Master Jack finds out.

if your not that engine savvy, take it to someone that can perform the proper diagnostics and just not guess to replace **** at your cost. most of the time these engines with the 'bad' springs in them had a pwr loss due to float prior to failure. if your not a gear head or have deeeep pockets...keep it stock!

why the hell would you put a dominator carb on this engine!!! WAY TOO BIG!!!!...i know he wanted poor fuel atomization so he could wash down the cylinders and then have to replace the engine in short period of time...

i have never had engine oil in one of my engines for more than 10 hours.

"I changed cams over to the crane 168731 this combo seems to work well and I have seen mph gains across the whole rpm range! "...now how the **** did changing your cam increase your efficiency??????if you changed your prop due to the cam???...then it's the prop....not the cam.

The biggest problem with these engines was with the Gils reverting water. If the idle was high enough, if there was enough fall to the tail (or even a dry tail), then there wouldn't be as severe of a problem with spring breakage. You need to check to see if the engine is reverting water and take steps to correct it. If there are no signs of reversion, then I suppose you could push the replacement off to 250 hours, but why risk damage? You don't have to pull the heads or block to replace the springs, so just do them and be safe.

Yes, the newer engines don't have the spring breakage problem. One of the service fixes is to use the HP500efi spring as the replacement. The newer engines also have the benifit of a computer controlled idle and the cmi headers-which alone will help prevent the breakage problem.

late hp's have a VERY different riser to correct this issue.

To each his own Joe. Someone he knows at Mercury sold him on this idea. But aren't you just a little wrong on this. An engine still only runs at the correct fuel/air mixture that it can get into the cylinders. That's still an equation involving all the intake and exhaust systems. Just like many 350's run a Rochester QuadraJet at 750-800 cfm, but if you do the math on a 350 at 5000 rpm the requirement is only for around 625 cfm give or take. IOW, Mercruiser did the same as he's doing. I all comes down to jetting and mixture ratio. I do think it's questionable on how much return he gets from his investment.

Scott

Cam Specs............
 

What are the full cam specs mentioned in this thread, lift full duration & @ .50, RPM range, etc ? I also assume that they are Hydraulic Roller units ?

I am planning to change my lifters, springs and rocker arms this winter. Its on 2000 model year carb HP500s with 170 hours. Who has the best price on replacement parts and what tool should I use to compress the springs? I do not plan on removing the heads. JEGS has a few different tools but I don't know which one is better or easier to use.

Thanks

Shawn

Keeping it relatively simple, the problem with overcarburation is that is an engine can't pull the volume of air through it necessary to pull equal amounts or air and fuel, you are going to have raw fuel entering the engine...problem being that gas in it's liquid state does not burn. If fuel went directly to the venturi from the float bowl,it would discharge as large droplets. Since a good air / fuel mixture is important to efficient combustion,large droplets would be a poor way to start things off. The air bleeds allow air to enter the circuits. Through emulsion tubes, the air is mixed with the fuel. So an air / fuel emulsion is what is discharged in the engine, not just fuel. Another function of an air bleed is to prevent a siphoning effect form draining the float bowl into the engine when it is shut off.

Ultimately, what screw's up how a particular carb functions on any given motor, is the ability or capability of the engine to pass air through it with no restriction, and the Emulsion Tubes that mix the fuel and air. The fuel that is discharged from a carburetor is premixed with some air to make an air fuel emulsion. This is done in the emulsion tubes and the air comes from the sir bleeds. The air bleeds connect to the emulsion tubes in the well. The tubes extend down into the fuel well and have small holes to allow air to get pushed in to the fuel as the fuel travels up fuel the well. The amount, size and location of the holes in the emulsion tubes all have an effect of how the air mixes with the fuel.

If you have a carb that can flow 500 CFM in the same application and still properly atomize the fuel, it should make more power than a 400 CFM carb. From this perspective, larger is better. Ideally,a carb would present zero restriction to the intake stroke. Such a carb would have an infinite flow rating. Unfortunately, carbs require a pressure differential to properly mix fuel with air, which is why carb sizing is important. Keep increasing the size of a carb and, at some point, the booster venturis will not properly atomize the fuel/air mixture and droplets of liquid fuel will be pulled into the cylinders. Not only is this bad for performance, it's also hard on the engine. The liquid fuel tends to wash oil off the cylinder walls, increasing ring and bore wear. This is a particular problem with engines using large
overlap cams, since they provide lower vacuum levels. When using a larger carb and cam, proper tuning (carb and ignition) becomes more important.

It's important to understand that the basic sizing formula is just a guideline. It ignores a number of important factors such as manifold design, cam timing, weight,intended usage, load, etc.
Furthermore, it ignores important differences in carb design like venturi efficiency, bore layout, and secondary style and method of actuation. In practice, I have found that the basic formula for carb sizing applies mainly to square bore carbs with non-air valve secondaries (Holleys), and even then it can be conservative for a performance application. It typically yields a compromise of fuel efficiency and power.

Using a dual plane, divided plenum, intake usually allows the use of a carb with a larger CFM rating than with a single plane, open plenum, intake. This is because the divider cuts the effective plenum volume in half, increasing the signal to the boosters. Because of this fact, Edelbrock suggests multiplying the CFM predicted by the basic sizing formula by 1.1 to 1.3 for single plane manifolds and by 1.2 to 1.5 for dual planes.

Also, once you have a carb installed, you can determine how restrictive it is by using a vacuum gauge to measure the difference between atmospheric pressure and the pressure under the carb. With the air cleaner removed, the air above the carb will be essentially atmospheric. If there's any difference between it and the pressure sensed under the carb, it's due to the carb. The higher the difference, the greater the restriction. Measurements should be made at wide open throttle and 0.7 inches of mercury is considered non-restrictive.

This may be a bit confusing, but the jist of my point is, if you bolt a 1100 CFM carb on a motor that is designed to run a 850 CFM to match the mechanics of your motor, such as camshaft selection, intake configuration, exhaust flow and design, volumetric efficiency, max RPM, load, and venturi design, you are going to be passing raw fuel through the motor at some point, killing the power curve, and rinsing down the cyl walls, which not only removes the protective oil film from the cylinder walls promoting premature wear and failure, but you are also diluting the oil with gas, and in turn ruining the bearings and any other chance of longevity your motor needs to live past a couple hundred hours under the demands an Offshore boat operates under (or we put them under) .... and that's a fact!

when doing the math you have to factor in volumetric efficiency.

it's hard to cheat physics! the low pressure created by the downward stroke of the piston and it's volume is X.....at 100% VE it can only be X!...now you can actually bring in more only when inertia is still ramming home the IC when the piston is moving upward....thus VE is>100%....and you can never do this when over carbed!...plus fuel atomization goes to ****..

FindMe:
Nice oratory on carb theory! Pretty deep, but good stuff. And I stand corrected somewhat. The atomization is the key here. If you can get good signal from the boost venturies it could work but makes setup a much more critical with a large carb.

Joe:
Yup, gotcha man. Still, see below.

The thing I wonder about is whether these new dominators have annular boost venturies which are supposed to help increase the signal. I know folks have used these carbs quite successfully but I believe the power level was closer to 600 hp rather than the HP's 470. Like you said, X is X and VE=100% and no more (if all works well), but at the higher volume that can be fed by this size venturi to a 600 hp motor, they work.

Also got into Dennis Moore's Big Block Marine book and checked his info. Carbs over 850 cfm are not recommended on engines under 550 hp.

When we were running it was quite rich but there was no bog and actually the seat-o-the-pants dyno indicated more punch even down at 2000 rpm. However, top end was rather flat. Hmmm, just opposite of what you would expect. Well we'll find out in a couple of weeks when the motors are back up and then the guy working on them gets the fun job of dialing in these beasts. The heads are to get some massaging while they're down for freshening. I still question the returns he'll get without changing cams to get more into the cylinders.

Appreciate the comments. Education never stops. Made me get the books out again. :rolleyes:

Thanks, Scott