Supercharger/Procharger related question
 

What would cause me to loose power as soon as I get under boost? Everything is perfect, until I start to get boost into the manifold. This happens right at 4700 – 4800 RPM. Here are some engine stats.

Engines: 502 carb(x2).
Exhaust: CMI 2-piece
Carbs: Holley 750, re-worked by Nickerson Performance
Ignition: Mercruiser with Accell Supercoil & Mallory Soft Touch Rev Limiter
Fuel Delivery: Mallory 140 GPH performance marine pumps

Any help would be greatly appreciated

Check your belt tension and also your ducting for leaks.
If the belt slips or the boost blows off, it feels like the power just falls off.
-The boost loads the pulley which will make it slip if it's not tight.
-If you have loose hose it may just blow off the boost when it loads up.

Just words of experience..
Dave

Are you using a flame arrestor?

What is your fuel pressure, at idle and 4700rpm?

Check for good voltage at the plugs and proper fuel flow filters ect!

Fever,

If you start to loose power as soon as boost kicks in, it sounds like your fuel pressure is incorrect and/or the regulator is not boost referenced to the carb box.

That Mallory pump is only good for 14# fuel pressure. That means you can only run 6-7 # of boost, max. Also that pump has an internal bypass. That lock nut and screw is located at the bottom of the pump. It should be set all the way in and locked, and you should use the 4309 regulator that returns to the tank.

Let us know how you make out
DAVE

You do not start going into boost until 4700? Procharger M4 with twin carb box? I also agree that fuel is the problem, or very loose belt.

If you want to talk, email/PM me you phone number & I will give you a call.

Thanks all for your input:

I’ve checked the belt tension and they are very tight. The hoses are also tight. The pulleys I’ve got are for 5 lbs of boost. The fuel pressure at idle is 7 lbs, and at 4700 rpm it is 14 lbs. Since it is boost referenced in the box, I know that I’m getting 7 lbs of boost in the box, and that the pumps can keep up with the demand. I was told that the fuel pump was set to 12 lbs of boost from the factory, and that I had to remove the spring, and stretch it out to get the 14 lbs of boost that I need, without having a return line to the tank. I have a boost referenced regulator between the carb and the fuel pump. I don’t have flame arrestors, I use the K&N filters that come with the Prochargers. The loss of power happens weather I nail the throttle, or roll into it. It seems relative to the position of the butterflies being open enough to allow boost into the intake.

Budah, you asked what has changed, it’s a long story.

I got the Prochargers with 3 ½ lb pulleys and a stock marine holley 750 carb (rejetted of course). I put it on and tweaked it, but never felt I was getting the gains out of it that I should. I purchased 5 lb pulleys, and sent the carbs to Nickerson performance. They said that I needed to upgrade my fuel delivery system and sold me the Mallory 140s. The only problem was that they did not modify the pumps to deliver any more than 12 lbs of psi, even though they told me that I should be getting 14 lbs of pressure. I was assuming that this was because I was not putting out enough boost to obtain more than 12 lbs of fuel pressure. It was not till recently that I learned to obtain the fuel pressure levels I needed, that I had to elongate the springs in the pumps. In the mean time, I’ve been trying to correct the problem by adjusting the jet size. I was still having WOT problems. After getting the fuel pressure correct, I went back to the original jet size that Nickersons had put into the carbs. When I told them of the problems I was having, they suggested I tighten up the belts. I really cranked on these things, but nothing changed. Now they are telling me to go down on jet sizes. I only make it out to the boat every other week or so, so each test takes a while. I was hoping that the expertise on this board could help expedite this process.

Thanks again

Rev limiter kicking in too early? Try removing it.
BTW, how do your plugs look? Wires & cap OK? What's your ignition timing? Initial & total.
Gary

We can give you guesses all day but need more info. Sounds like you have hit on the ovious.

Does the motor just stop climbing or does it slow down once up to 4700?
I still want to know about starting to go into boost at 4700, motor should be in boost before that rpm.
Type of boat?
Prop, outdrive, Outdrive gear, speed of boat at 4700
We know 502 but heads, cam, compression, timming, exhaust (kind & tail pipes) gas you are using?
Plug gap?
Ignition type/kind?
Procharger model number? M4?? The procharger dual carb box or something else?
Enclosed engine compartment getting enough air?

Just some of the questions.

Last year I could not get mine over 4K, motor would scream to 4K & stop. Changed out MSD box & first pass out motor turned 5600.

Did rpm go up when swaping pulleys? You say 3.5 pulley, what is the size of your crank & blower pulley?

When I have a loose belt everone in boat with me is telling me belt is loose because they can hear it.

I snaped to your name, Boat ia fountain Feaver?

I checked the rev limiter and ignition system including the timing. I’m at 32 degrees full advance. The 4700 rpm is the rpm where if I open up the throttle any further, I start seeing boost on the boost gauge. If I slam the throttles before this, I don’t event get to 4700 rpm. If I ease into the throttles, when I reach 4700 rmp, the boost quickly climbs up to 3 lbs, but my rpm starts to drop off by a 200-300 rpm.

The 502 is stock except for the items I listed in the earlier post. The Procharger is a M1. I think that I confused you with the 502 carb (X2). I meant 2 engines, not 2 carburetors. Both engines are experiencing the same exact problem

About your other questions: The boat is a 1993 32’ Fountain Fever. The prop is a Bravo-1 28” 4 blade. Drive gears are 1.5 to 1. Compression is stock, timing is 32 degrees full advance, exhaust is CMI 2 piece, and I always use 92 octane gas. The ignition is stock except an Accell Supercoil. Plug gaps are .035. The engine compartment is closed, but I have an automatic hatch opener that I sometimes use while underway to get fresh air into it. It does not make any difference. When I swapped the pulleys, I also had the carb worked on. I don’t know the diameters of the pulleys, but ProCharger ensures me that they should produce the 5 lbs of boost.

Thanks again for all the help.

Try backing your timming off to a max of 30. The problem has to be 1- fuel, 2- ignition (boost is keeping plugs from firing) 3- Detonation (what is your water temp gauges saying) 4- belt slipping (I don't think so) Interesting thing is both motors have exact same problem.

Have you put a bigger prop on since you procharged?

I can try adjusting the timing. I’m concentrating on it being a fuel problem, but don’t want to rule out ignition. I was under the impression that the Mercruiser ignition with a 50,000 volt super coil should be sufficient for an engine with 5 lbs of boost. I was thinking about upgrading to a MSD system, but with twin engines, you always have to buy 2 of everything, and they are not cheap. When I installed the Procharger, the instructions have you take out the thermostat. The temperature gauge never reads over 100 degrees. The oil temp stays around 200 – 210. I did go from a 27” Spenelli to a 28” Bravo I. The Bravo has a larger diameter. If I can ever get these engines running right, I might have to go to a 30”, or at least that is my hope.

run it without the flame arrestors,see what happens.

Grasping for straws. Cheap things to try.

First try to back timing to 30. If no change replace sparkplugs with new regaped plugs at 25. These changed will not make HP but maybe see where weak link is.

Look & mark throttle where the motor starts falling on face. Then after marked look at where throttle shafts are at that setting. I am wondering how much in secondarys you are into. If the secondarys are too rich it could cause the motor to start falliing. You say you think fuel but it sounds like the amount of fuel you have check out.

Another though is your valve springs are worn out. Once motor starts going in boost the valve springs are not strong enought to close at the high rpms. How may hrs are on the motors?

I would say your prop is too small. I feel that your motor should be in boost before 4700

Turbojack,
Thanks for all the input. I’ll try your suggestions. Unfortunately, the next time I’ll be at the lake won’t be until Labor Day weekend. I’ll let you know how it goes.

I hope I am wrong.
last boat had, 350 mag with a weiand supercharger 142. This thing was a rocket up to 55mph and then would loose power and die down to 30 mph plus making nose at those speeds, at idle, sounded perfect. spent tons of money fuel to electric. The bad word was detonation. Check your compression.

bsc - that is kind of what I was also looking at. that is reason to try less timing, & my asking about engine water temp.

On the 350 mag at 5 lbs of boost, safe to run 28 to 32 on timing,, Found this out after I blew the motor. @ 32 on timing, high octane and low air temp.
Good luck on the compression check, Time to go play at the lake. Lake Powell, UT.

bsc,
The inside of the engine is stock. This means that I have at the most 8.75/1 compression ratio. I was told by numerous people that I should not have detonation problems, since the Procharger is intercooled. I even went out of my way to re-plumb the coolant system so that the intercooler gets its water from a location before the oil cooler. Was your Wieand intercooled? I’ll try less timing and see if it helps. I hope it’s not detonation. Would octane booster help? That will be a lot of octane booster for a 130 gallon tank. Nickerson feels that the secondary jets are too large and recommended that I go down 4 sizes. They re-worked the carbs, so I’ll try this as well.
Thanks
Dan

You should not have any problems firing the plugs at only 7-PSI. The stock ignition will be good to 16-PSI w/o a MSD box. However your timing does sound a little too advanced. I would back it off to 20-degrees total and test. A couple of things on your statement tripped an alarm in my head. You stated on 2 occasions then as soon as you nail the throttle it cuts out. You also stated that you have to ease it to 4700RPMs. That indicates to me that you may have an enrichment problem. Check the accelerator pumps on those Holley carbs. Make sure that you get a steady stream of fuel flow when someone moves the throttles. You should see a healthy stream of fuel come from the center squirters with even the slightest increase in throttle movement. Keep us posted.

Roby

Also I forgot to ask. You are running carburetors correct? Why is the fuel pressure set at 14-PSI? I don’t know how you have it set up but how are you getting 7-PSI at idle and 14-PSI at full throttle boost? Is this a special regulator setup from Procharger? Is the fuel pressure more than 10-PSI at the carburetors? If so you need to back off to 7-PSI. 14-PSI will push the float down and flood your engine.

Roby

GotTheFever, I am running a procharged 502 mag as well. I am at 6 lbs of boost. every 4 weeks or so I experience the same problem as you. It won't climb over 4400 rpm. it gets there like a bat out of hell, but then it just flattens out!!!!!I don't know if you tried this, but I was reluctant to believe it was that simple, and tried everything else!!!!! Then I finally gave in and checked the inside of my distributor cap!!! sure enough the contacts were covered with a greenish white corrosion, kinda like what you find on a battery.. It wasn't much, and didn't think for a sec that it could cause the power and rpm loss at high rpm's. I decided to clean the contacts anyway with a nail file the wife had in her purse, and sure enough....BANG!!! WOW~ she climbed to 5200 rpm and kept pulling:D:D I now keep a cleaned up spare cap on board, and swap them every time I notice the upper rpm power loss... Good luck, and sometimes it's the simple things that cause the biggest problems:)

Take a spark plug type Hei tester and put it on a spark plug wire and snap the throttle it needs to keep a good blue spark. At all times and never blink off the OTC too is a st125 spark tester. You can do this test at home to rich will make it very flat on top end.Look at the heat line in the spark plug electrode it should be in the area where it bends what do the plugs look like? Black white burned up ect. Good luck looks at this stuff before you take it to the lake.

robyw1,
I think that the accelerator pumps are ok. If I’m at WOT, I can re-gain my power by pulling back on the throttles to about ¾ throttle where I am out of boost. About the fuel psi. According to Nickerson, I should be getting 14 psi. This is how he explained it. In order to get 5 lbs of boost, there needs to be 7 lbs of boost in the carb box. There will be 2 lbs of boost different between the carb box (above the ventures) and the intake manifold. If I start with 7 lbs of fuel pressure at idle, then I add 7 lbs of boost in the carb box, the referenced fuel pressure should be 14 psi.

Kanoosktr,
I don’t want to rule anything out at this point, even the simple things. I’ll check over the entire ignition system. The weird thing is that it happens to both engines under exactly the same conditions. Thanks.

fstboater,
It has been a little bit since I’ve looked the plugs over. I was originally looking at the plugs to dial in the carbs, but they never really revealed anything. If I did a full throttle pass, then removed them, they looked brand new. They had no sign of heat damage, but they also had no sign that they had carbon on them. After a day of boating I would look at them and they appeared brown to black in appearance. My intent is that the next time I’m out I’ll change out the plugs again, and get some more readings. It’s just a ***** to replace all 16 of them.

Thanks again everybody for your input.
Dan

Just worked on a cruiser this weekend that would lose power over 3000 rpm. Anti-siphon valve in tank was almost completely clogged. Another easy/cheap thing to check.
Gary

If your anti-siphion valve is still in your tank you would be starving the engine for fuel @ wot. You must remove it if your running a procharger.


David

Absolutely!!!!

And if your using Aeromotive 1000 pumps. you should be running Minimum of 1/2'' lines feeding the pump. Brett at Aeromotive recomends 5/8". Anything less than 1/2" will result in certain pump failure.:eek: