Reply With Quotebring the horsepower up on that 454, or check your pump, i believe going to an A will bring the R's up, that pump should spin the same in a low feeboard 16' jet as well as in 26' daycruiser. if i am wrong , someone let me know.
I posted some info before on this, but I found the 454 I have is rated at 390hp vs. 330hp. Anyhow, at WOT I'm ~4100 rpm, and I'm guessing I have an "AA" sized impeller on a Dominator pump. Question one: How do I determine my existing impeller size? Second, the peak HP is rated from 4600-5000 rpm. So it seems that I'm not utilizing my available power. I guess the question would be, should I drop a size (or more) on my impeller, does an "A" sound right? I have a BHB (big heavy boat), so I don't want to go too small, but I am willing to sacrafice some acceleration to gain top cruising speeds. Currently at 4100rpm and a semi full load I'm in the low 40's, any idea on the gains I may expect? Thanks for all your help -this forum is a great source of info!
bring the horsepower up on that 454, or check your pump, i believe going to an A will bring the R's up, that pump should spin the same in a low feeboard 16' jet as well as in 26' daycruiser. if i am wrong , someone let me know.
You arecorrect that the pump has no idea what size boat it is in and will spin the same regardless.
I would not go smaller than an "A" in a large boat, but for that much boat, I'd go for upping the HP on that 454.
A Dominator AA demands 318 HP at 4100 RPM. Your 390 is likely rated at about 5K.
For about 2-grand you can put a set of Thru-transom headers on and pick up about 40 HP, perhaps gaining a few from the engine RPM along the way, and get near 4,300 RPM (about 100 RPM per 25HP).
For about a grand to $1500, IF you already have a set of good open-chambered heads, you can have a race machine shop stage 1 port them. The shop I plan to use will cost me about $1,000, plus about $350 for bigger valves, and they say they get very good results from mine, 80 HP or more is comon. Pick up a few HP from the revs, 440 HP gets you 4600RPM or so WFO.
Top that with a "A" cut, pick up to almost 4,900 RPM, gain a few ponies on the way with the RPM and push it right near 5000 RPM. This COULD top you over 60 MPH.
We'd need to know a lot more details about the motor to be more specific. I'm working here mostly from my Mk-IV experience and the impeller chart program JPCalc.
the engine is a 1996 Marine Power 454 Sportpac Premium non-EFI, I believe Gen V. So a smaller impeller will not raise the WOT rpm? I thought the smaller impeller would raise top rpm and with the rise in rpm's I would essentially be increasing my hp b/c I'm running too low right now (4100 vs 4800-5k)? If an AA is rated at 318 at 4100 rpm, I should have 60+hp on tap that isn't being utilized? I was thinking if an AA uses 318hp at 4100 rpm, an "A" would bring me to ~4600 rpm, but now I'm nearing the engines peak power range and utilizing the power curve? After this last weekend I know there are some maintenence issues, so I'm going to have the carb re-built (also new starter, fuel lines, pump, etc.) I'd rather do this all at once with a clear concious. Will the drop in impeller size increase WOT rpm and or top speed? If so, any guesses?
Reducing the impeller size will raise your wot rpms. What doesn't sound right to me is that your only turning 4100rpm with aa impeller. Sounds like you have motor or tach issues. 390 hp with a impeller should turn 4800-5000 rpm, going to aa impeller, maybe 300-400 rpms less at wot.
Look at the pump suction housing, above the drive shaft for a tag identifing model and impeller size.
I run a 390 horse marine power motor in my cruiser. I am spinning 4950-5000 on an "A" with a tight fresh dominator pump. Only have a few trips on it. Running about 65 mph. You should be seeing about 4600 on an "AA". RPM'S are RPM's boat size doesn't matter. Start with Tune up. Check compression and leakdown, ignition, carb, plug wires.
Worn out pumps spin higger RPM's due to cavitation. A pump under load is in a way a dyno, your motor will spin what it will spin.
thanks all, your advise re-affirms my thoughts... I'll dig in and find out what info is on the pump -that should help answer some impellers ?'s. I figured I wasn't spinning enough. I'm going to go through a full tune-up to make certain everything in on the same maintenence schedule and in top condition, perhaps I'll find some of the cause there.
Worse case scenario, to find out what impeller you have, you pull the bowl off the pump. The impeller has a stamping (or a casting letter) on the AFT side near the shaft. Unfortunately, the only way to see it, is open her up. It's as simple as it looks, once you unhook the cables (or unbolt the nozzle), remove the transom adapter ring (if you have one), and take the bolts out from arround the bowl, it opens up there, just slides off the shaft (once you break the gasket open).
the only model infomation I found on the Dominator pump was "S". Is that right? Manufactured 05/96. I still need to remove the pump to get to the impeller... maybe this weekend.
Finally! My boat goes in tomorrow... there was some fuel delivery issues last time I was out and the pump was bleeding (bad bearings?). With any luck I'll have some feedback on Thursday -I'm sure I'll consult the boards to assist my decision making. It may just be some worn out parts needing replacement. Finally save enough to get the new ride -and back to the shop she goes.... B.O.A.T. we all know what that stands for. Thanks
-j
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