Im not sure what chargers your running?? My M-3 will sit around the 2 PSI mark at about 3100 RPM, to me the boost should be coming in sooner then 4000 RPM (granted I dont know what pulleys/blowers your actually running) Whats the back of the boat look like? Soot?? What do your plugs look like?? Have you watch timing on a timing light to see how it reacts?

It has to be an ignition problem or a fuel problem, if the motor is sound inside.
Didn't read all posts, but did you do a compression test hot..
I had a problem with detonation and it broke the ring lands on the piston before. It wouldnt show up on a cold comp test.

New fuel in tanks this year and also ran two separate 5 gallon tanks just to see if anything changed - no difference. We checked the knock sensors while @ 4000 rpm all everything checks out

I'm running the M1-SC chargers. According to the dyno sheets I see 2.3 lbs @ 3000 and 2.8 @ 3500 and 3.6 @ 4000.Not sooty on the transom and I pulled all of the plugs on one motor and they look perfect Also checked timing and that was dead on as well

i think I've ruled out fuel running separate tanks to test. What would I look for as far as an ignition issue? Didn't do a compression test but did do a leakdown and all cylinders were 5% or less leakage.

Hmmm definitely very confusing for sure... the only time Ive seen a similar issue with my boat was when I was trying different props this year, Just simply wasnt putting out the boost or pulling the proper RPM... swap back the props everything was good. You havnt changed your props though at all correct?

i haven't changed props, been running the same ones for a few years.

How about full throttle travel at the TB?

Yes checked that too, fully open @ WOT. The thing that's just so strange is they both tan perfect on the dyno and now they're both not performing. Both run great up to 3500 rpm, you'd never know there's an issue until you push the throttles. I'm putting on two smaller props today to see what it does but I'm guessing it'll run right up to 5000 rpm but won't have any boost. I'm going to run it with the Prochargers connected and then disconnect the belts to see if there's any change.

Thanks everyone for all the suggestions - I've gotta get this figured out!

I can't wait to hear the solution! This is a head scratch-er for sure. Keep digging, the season is too short to be head down @$$ up in the bilge all summer!

friend of mine works @ Pro charger here in KC, have you called them ?

Definately is a dam interesting one thats for sure! I also cant wait to hear what ya find! Another thing you could try is dropping the pulley size down one, this will bring your boost in at a lower RPM, I downsized mine by 1 size recently because it wasnt building full boost at WOT. I know your having a different problem but would be interesting to see what procharger says about it.

i have. Spoke with two different guys there and they're baffled too. Had me check the obvious, belts, keyways, etc. but no other suggestions unfortunately.

Ive not read this complete thread but could it be a timing issue, are your ecm's locked or can you get into them and look at the timing and fuel tables ? have you verified 8* of timing in base timing mode and full advance ?

on the bottom of the hull,,is there anything in the water path to the motors prop that spins up?are there drive showers?is the trim indicator true to the drives position?

This is a long shot, but was anything done to boat that would restrict air coming into engine compartment? Reason I ask is on mine I found a couple of the bilge air inlets taped over inside the bilge when I removed the vents for waxing. Maybe try cracking open hatch an inch or so while running?

These are 540's with M1 Prochargers? I'm shocked that they make any boost.
Out of curiosity, what did they dyno?
I can't wait to hear the fix.
I leak tested an engine a bit ago and it leaked down good. When the heads were removed it was missing part of the pistons I believe on the exhaust side. Engine was down a little on power, but nothing that would have said tops of pistons melted.

L was going to say to check the air inlet , do you have an exhaust leak in the engine compartment that is polluting the intake air?

ECM's are not locked and we did go over timing and ran O2 sensors in headers. Everything looked good

I thought about that too but nothing was some to the air inlets a Dale I've even tried running with the hatch open 12 inches or so

Yes 540's with M1-SC chargers. Why wouldn't you think they made any boost? I've run this set up for years and always pushed out 5 psi at the plenom. They actually dynoed @ 930 @ 5500. I know Procharger doesn't rate them that high but never had an issue until now and all we did was a valve job.

So I ran smaller props over the weekend to get more rpm and spin the Prochargers faster. Got it up to around 4800 rpm and the boost gauges actually show about 5+ inches of vacuum! How's that even possible?

I guess not. I thought they were a 700HP supercharger. Good to know, that opens up options.
Have you borescoped a few cylinders?
Thanks

To me the only way thats possible at all (provided that the boost/vacuum gauges are both accurate) Is that theres something internally wrong with either charger, or theres a boost leak in both systems. If your building the engine RPM which your are you should most definitely be building boost. The weirdest thing about your problem is your having the issue with both motors. What did procharger say when you contacted them? How does your setup work on yours? As in airflow... charger, intercooler then into the plenum? Have you tried pulling one of the connections and verified positive airflow?

https://cimg8.ibsrv.net/gimg/www.off...a6150b5b6a.jpg

Pulled tubing off just before intake and there's definitely positive airflow there.

Have you pulled the pulleys off each charger and inspected the keyway? Long shot but maybe slipping under load/high rpm if keyway is wore/key broke?? Very odd and confusing problem for dam sure, Almost at a loss and makes zero sense as to why it would be pulling a vacuum at high rpm when theres positive airflow at idle

Damn !

https://cimg5.ibsrv.net/gimg/www.off...6544b27cf3.gif

If it we’re mine, I’d swap the chargers, inter coolers and ducting between the 2

See post 37!

5+" of vac at WOT?! Sounds like blower is getting in the way.

Could there be slippage at crank pulley?

checked the keyways there too and everything checks out. We're trying smaller blower pulleys next with the thought that the motor is eating up all the boost the blowers are producing. The fact that the boost went totally away and went to a vacuum as we increased engine rpm kinda points that way. Hoping to increase the boost at the same engine rpm with smaller pulleys is the answer. Fingers crossed!

I had to go down one size on the pulley on mine earlier this year. Wasnt producing as much boost. You should see a noticeable difference with the pulley change. I saw a 3 PSI jump with mine at WOT, also came into boost a little earlier which actually helped me plane out better. Curious to see if this fixes your issue!

Everything was fine in boat for a few years until onecengine’s boost faded away, so you just did top ends redone right ? Vslve jobs/springs probably. Anything else ? And you said they hit thedyno too. Issues only when in boat. So, if this ‘fixes’ them, I would not understand.

Could the blower belt/s be contaminated with oil, fuel, p/s fluid, cleaning/detailing products, etc?

Brand new belts.

Any update on this?

Crazy question, is the Drive pulley actually turning the impeller on the SC in question? or turning under load ( implying possible internal damage of the SC).

Thinking out loud, if it's not compressing, it's working as an air block as the engine is after more than it can draw through the system = no boost and drop in RPM's

So here's an update but still no fix. Decided to pull one of the motors and run it back on the dyno. Motor ran fine - 950 hp and 1000 ft lbs of torque. Put the motor back in the boat and its doing exactly the same thing - 4000 rpm max and showing no boost. This is really frustrating. Boat always ran great.

In what condition was the engine on the dyno, full marine trim?

What is different between dyno and in the boat, Fuel system? Ignition system? Exhaust?
Cooling water?

The problem lies in the differences somewhere?
Ryan

we actually ran it out of a bucket of fuel on the dyno to eliminate a fuel supply issue. Using boats ignition system and supply water pump. Only real difference is the exhaust system using the dynos headers.