SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: bertus on April 25, 2009, 11:21:54 PM
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Just wanted to see what your guys' input is on this....When i flatfoot the boat i am only at about 42-4300 rpms. Its a 21ft with a 460, msd ignition/dizzy, a berk 12jc a pump. I hear most people running closer to 5k rpm's. Is there something that needs adjusting to get more out of it? or is that normal?
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Just wanted to see what your guys' input is on this....When i flatfoot the boat i am only at about 42-4300 rpms. Its a 21ft with a 460, msd ignition/dizzy, a berk 12jc a pump. I hear most people running closer to 5k rpm's. Is there something that needs adjusting to get more out of it? or is that normal?
How sure are you of your tach first of all?
Everything needs to be pretty dead nuts for it to make it's full potential of HP.
A stock automotive 460 will do exactly what you say yours does...how stock is your Ford?
You need to gather some info.; Max timing (above say 2500 RPM), vacuum reading at WOT, actual WOT RPM, and how much beer you have in the boat... ;D
I'm betting it's something simple, this combo should make about 4,500 RPM without too much effort IMO.
GT
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x2 with GT, you may be getting close to floating valves much over 4,500 w/ stock valve train components.
p-jet
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With every aa cut and stock(marine) 460 combo I've seen 4300 sounds about dead on. Same with a 454 as far as that goes. Of course we were never at sea level either.
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It has some mild work done to it. It has roller rockers, a mild cam, its bored .030 over with upgraded pistons and rings, full msd ignition & dizzy, harman marine tt headers, edelbrock performer intake w/ a holley 800 carb. There is usually at least a 30pk or two in the boat. I have checked the timing with a light and everything seems accurate. When i hose run it in the yard when you rev it the rpms runs all the way up to 5800-6000. Obviously being in the water will put a different type of strain on the motor so i dunno. I was just checking. It seems like there is more in her and I didnt know if maybe there was something i was missing
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Well here goes.. ;D On my old Hawiian with a big cheby with some work done and a new A impeller in the pump it would turn 5800 on top... Now on my Nordic I'm runnin' a big blue oval.. Not sure of the insides but it does have roller rockers and a tunnel ram witha Holley 850 DP and a mild cam... Don't know what's in the pump but it will turn 4600-4700 at approx. 4500 ft above sea level.. So just a little food for thought I think 4300 does sound a little low.. so after typing all this I forgot where I was headed..lol.. :screwy:oh well good luck
Andrew
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FWIW here is a little more rookie .02 from me. My new motor will pull an ab to 5400(so far, low 70's.) that's about 500 on the ricter scale. At first I felt a little :mad: :banghead: :mad:. Then I started thinking I'd have to make about 600 hp at sea level, to end up with 500 herel. Imo you need a gps # to go with the r's(especially if you don't know the imp. cut) Also if you have re-cammed and you are running a aa that might be part of the problem. You may benefit from an A cut'ish.
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I was told it was an A impeller. 12jc-A pump. now i have no idea if somewhere along the road that has been changed or not but that what i was told was in it. I am running low-mid 60's on gps. Im thinking maybe the rpm gauge is set to 6cyl. I will have to check that when i get it back
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I was told it was an A impeller. 12jc-A pump. now i have no idea if somewhere along the road that has been changed or not but that what i was told was in it. I am running low-mid 60's on gps. Im thinking maybe the rpm gauge is set to 6cyl. I will have to check that when i get it back
If the tach was set for a 6, the tach would have read like 5500 RPM if it were really running 4200...Just so you know ;D
GT
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oh okay. I dunno chit about tach's so doesnt surprise me. :banghead:
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I was told it was an A impeller. 12jc-A pump. now i have no idea if somewhere along the road that has been changed or not but that what i was told was in it. I am running low-mid 60's on gps. Im thinking maybe the rpm gauge is set to 6cyl. I will have to check that when i get it back
It sounds like you may have an AA, if there are no problems with the engine.
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the engine is off a fresh rebuild and has been thoroughly gone through. I may have an aa impeller however how would i be able to run low-mid 60's with a aa impeller? Is that possible?
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Is what possible? A aa cut will provide the most mph per rpm. 60+ out of a 21' boat at 4200 doesn't sound quite right to me but wtf do I know.
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Rob your mph is mid 60's right @ 4300rpms what are you worried about?
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im turning 4,300 rpms no gps number yet though....bbf but i just moved the gas pedal more closer so i can get the secondaries to open...i was messing with it today and realized just that...where my pedal was set at i couldnt push the pedal down far enough...but i guess to answer your question my bbf is turning around the same rpms...on a stock single point ignition no gps numbers....18ft boat
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I wonder why the pedal was so far up ;D
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the engine is off a fresh rebuild and has been thoroughly gone through. I may have an aa impeller however how would i be able to run low-mid 60's with a aa impeller? Is that possible?
I have a Kona, 18 ft, Berk 12JC, with an AA. Olds 455, 4800 rpm, 65 mph.
(however, this will probably change as I just had the boys at JBP bless the pump)
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Like everyone else is saying AA will do it. I had a stock 460 with tunnel ram and 750 DBP and 4500 was all it would go.
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if you have a A or AA could be about right depending on how strong it is. Check for the secondaries opening. Mine do so ~4200.