Here's my problem at WOT with a 800 cfm Q-jet Stock intake headers, 500 lift crowler, 1.65 roller rockers mild port and bowl massage 71 heads, 9.8 to 1 compression aprox. The engine will not rev higher then 3700 rpm This motor is in my jet boat and it's under very heavy load pushing so much water throught the pump. Do I need to upgrade to a bigger carb? Or intake or both I want to get about 4200 rpm?
A couple of questions. Have you spent time tuning (i.e. mixture and timing)? Do you have exhaust manifolds or headers? Stage 1 valves? What intake manifold do you have? I don't think you need a bigger carb for only 4200 RPM. You only need about 550 CFM (just a guess- not a calculation). -Bob Cunningham
Landshark have you checked the pump bearings any grass in it a had jet boats with berkley pumps.That motor should go 5000-5200 easy. I had 427 L-88 in a 20 ft tahiti it spun at 5600.If you went over motor i would check pump.
It has headers and tuned fairly well thottle respond is great out of the hole the carb is opening all the way. Everything is new on the motor. It's a panther pump I think the load from the pump is holding the motor back. Bearing are greased and turns free.
Dry until you get to the collectors dump the excess water there so the rubber doesn't melt through the transum.
Boat Don't Rev - Need more info What are the cam specs? You'd want a fairly mild torque type cam for the rpm range you're running. A "Hemi-killer" type cam would never get into it's power band. Where is the cam installed? Did you degree it? What is your DCR? How much ignition advance do you have and when does it come in? I think you just have to do some basic tuning given the application you are running.
The cam has 114 center aprox 280 290 advertised duration more exhaust lift than intake aprox 500. The timing is about 38 degree all in aprox 2200 rpm if I bump up the timing any more my knock sensor starts to flicker!!! Rhoads lifters.
Sounds like too much timing to me, Buick's don't like a lot, try 30-32 deg. I would think in a high load application you would want less timing. Sounds like everything else is in order. Good luck
Cam choice What's your cam duration at .050"? Did you degree the cam in? You can't trust the timing marks on commercially available aftermarket timing sets. It's important for power to get the cam centerline set properly. You might have too much cam for the torque load you're putting on at low RPM. Or, if you have one of the "Popular Mechanics" 230-245 @ .050 "fast ramp" cams you might not have enough compression to make it work. Also, sounds like too much ignition timing. Big block Buicks have very efficient wedge combustion chambers and 32 degrees total is normally plenty of advance with pump gas. Have you made sure that the secondary air valve is opening under load? The preload on the air valve spring might be set too high or the choke interlock may be holding the secondary air valve closed. maybe we should all come out to the lake with you and get this thing sorted out :laugh:
I actually played with the timing alot less advance equals even lower rpm. I have to be careful because I can't here it if it pings and running the motor WOT for 10 to 15 min across the lake and back while it's pinging will surely destoy the motor. This summer I will put a SP1 on top but I will lose some torque but gain some HP I think that is the real issue a motor under huge load will it spin faster with hp or torque?
I really don't understand the huge load that you keep talking about. You are only running a 19' boat. How fast are you trying to run? Also say it is responsive and good out of the hole. If set up for top end it should be a dog taking off.
I would check the pump. I have never heard anything good performance wise with a Panther Pump. You may want to ask this question on the Banderlog forum as well.
I believe the "huge load" in question is the pitch of the pump impeller. If I remember correctly from my jet boat days, the pump "absorbs" a certain amount of torque/HP as determined by impeller design, internal clearances, etc. If I'm going in the right direction with my thoughts, it's possible that the pitch of the pump is such that it's going to require a lot more power to drive than the engine is producing. (Kind of like what happens if a car's rear-end ratio is too low.) Is the engine/pump combination new? If you just purchased the pump, did you make sure that is was designed for the power level produced by your engine? Has the pump been modified to become more efficient? Or to achieve higher speed? I hope this helps. Good luck.
Can you run uncorked? If that cam has some overlap you may suffer from reversion which would increase positive pressure pulses in the intake. If you have the stock rockers give them a try. If you pick up rpms then your on the right track. Advance the cam 4 deg will help with the intake reversion pulse. A smaller carb would equal more low end torque by increasing velocity. Once you get to a certain critical rpm the reversion pulse should go away and the motor rev on up making power.
The pump is used in good shape it had a 454 in it before marine block he said the pump was set up for jumping out of the hole fast and it does that great my top speed is about 55 mph. What do you mean about uncorked ? running the headers dry? I'm also new to boating but what I know about revision is that the cam overlap will suck water in threw the exhaust if there is too much water in the pipes this will cause the oil to get milky. Would the 1 inch spacer cause revision in the intake. Right now the water doesn't go into the exhaust until it reaches the collectors on the way down out of the boat. Here's a pic of the hose going into the bottom of the collector.
