can't rev BBC

[red devil]

Just installed new BBC 454,bored 60,113cc large oval heads ,all new valves & springs,edelbrock torq 2 intake & torq 2 cam, holley 750 vac,stock GM hei,light springs on dist weights,log manifolds,berk jb with fresh berkley A imp,hyd place diverter,loader grate,top speed 61.7 gps 4720 rpm,can I find any more rpm with this setup without dumping any more $,wife is ready to commit murder,boat is a 71 glastron/carlson cv21,sure could use some advice,,thks.

[MellowYelloW]

i also have a 454bbc 30 over with torquer intake and holley 750 carb mild cam with a 12jg pump and "A" impeller and i am turning 5800 rpms. and i am running a pos points dist.

[Jetmugg]

Red Devil:
If you are running 62 mph in a 21 foot Glastron with what sounds like a fairly healthy but not radical 454, turning 4750, then you probably won't get a lot more speed without making a bunch more power. A 125 shot of nitrous might get you where you want to be, but it sounds like your setup is pretty good the way it is. That Glastron is a heavy rig, I personally don't think it's going to be practical to try and make it run 70 mph. I'm not trying to rain on your parade, but I've been there with daycruiser style jetboats, and they aren't easy to make fast. The other alternative would be to re-cut the impeller to A/B or B specs, in order to let the engine hit it's power peak. 4750 rpm sounds about right for an A impeller and roughly 400 HP.
If Mellow Yellow is spinning an A impeller at 5800 rpm, then he either has a VERY stout engine, or a pump that needs to be rebuilt. For comparison, I have a fairly mild (450-475 HP) 454 that turns an A/B impeller at 5200 rpm's, and I have hit 82 mph in my CP Gullwing.
If you really want to go fast, you should consider a different hull. If you can learn to live with 62 mph, then just relax and enjoy.
My 2 cents,
Steve M.

[johnnie jetboat]

I have a 18' Caribbean with a 454/berk JG 'A' and place diverter. I'm only turning 4500 rpm at 64 mph(gps confirmed)in good water. I sometimes shoot a 100 hp nitrous blast in her and only gain 100-200 rpm(hardly worth the risk).
Soon I hope to change those numbers with the 8-71 BDS blower set-up sitting on the bench.
Keep jettin...

[MellowYelloW]

hey jetmugg. my motor is a mild 454, that is new..only 19 hrs on it, the pump is also just been blueprinted to the motor. the builder said it was an "A" impeller. my boat is a 18' rogers custom and it moves really good. i was at lake shasta all last week and hit 5600-5800 several times.
you think maybe the builder may have put a different impeller in it.???
any input would be apperciated!
thanks
brian

[Jetmugg]

Mellow:
Something in the numbers just doesn't look right. Did a reputable and knowledgeable jet shop set up the pump? If it was a good shop, then you can pretty much count on them knowing what they are doing and telling the truth. I have heard of other guys getting pump "rebuilds" from other machine shops or speed shops, and they don't always know what they are doing with jet drives. I think if you talked to one of the professional jet shops (Walt's, MPD, GS Marine, Don's Pump Service, or one of the other well known shops), they would be able to give you an idea of what rpm's you could expect to turn with any given impeller. I'm not a 20 year veteran of jet drives, but I have picked up a decent amount of knowledge along the way. 5800 rpm just sounds too high for an A impeller, unless you are running 90 mph or more, and that takes a lot of HP. GPS readings are the easiest way to verify your speed.
Like I said, my basis for comparison is a well set up Dominator A/B and about 450-475 HP 454 that will turn it 5200 rpm at a tick over 80 mph. This is in a Gullwing hull.
Steve.

[MellowYelloW]

hey steve...jetboat performance built my motor and pump..the boat moves quick but i have not gps it...also i ran a guy that said he gps his boat at 70 and i spanked him but i dont think my boat does much more that 70. i guess the only way to tell is to gps it.
thanks
brian

[spectras only]

Mellow,as Jett says ,things don't add up!A mild 454 will NOT turn 5800RPM with an "A" impeller.A mild 454 starts at only 330 HP,and would only turn between 4700- 5300,depending of impeller selection and wear ring type.If you have an "A" in your pump now,I suspect too much clearence in your pump,or a "B" or "C" impeller, giving you 5800RPM.Otherwise a miscalibrated tach could be the culprit.