[lefty's pride]

I’m running a stock 12jc, I was wondering if or at what rpm the jet caveats? Is there a sufficient gain going with the inducer that Berkeley carries? Any body have a good chart for impeller cut on the berkeley site is says that the aluminum is good for 500 hp but if you look at the chart the max is much lower but the rpm is still correct. If any body has answers it would be nice. and if any has other good facts id like to hear them

thanks

 

[Luckie Stiff]

Not sure where you're located, if it's Langley VA, try Duane @ Hi Tech marine for help, if it's Langley B.C. there is a guy on here that has a boat shop somewhere in BC, maybe do a search for him

 

[lefty's pride]

im in lanlgey b.c. canada.

 

[jetboatperformance]

Lefty's Not certain I completely understand your question , there isnt a set rpm that will your jet will "caviate" The charts show the RPM vs the power absorbsion , If what your saying is the charts go beyond the HP for an aluminum Impeller (oem is typically 450hp) , they (the charts) are also refering to the "cut" of the impeller whether its aluminum , Bronze or stainless Here the A/T Dominator Chart to help you Tom



H.P. 9.5 9.25 AA A B C
150 2900 3050 3200 3600 3800 4050
200 3200 3350 3500 4000 4200 4450
250 3450 3600 3700 4300 4500 4800
300 3800 3950 4050 4550 4800 5100
350 4050 4200 4300 4750 5100 5350
400 4250 4400 4500 5050 5300 5600
450 4450 4600 4700 5250 5500 5850
500 4650 4800 4950 5400 5700 6050
550 4800 4950 5100 5550 5850 N/A
*THESE RPM VALUES MAY VARY ACCORDING TO HOW YOUR BOAT ALLOWS THE PUMP TO LOAD
HORSE POWER REQUIREMENTS ARE AT THE PUMP SHAFT

 

[lefty's pride]

That chart does help for the one question i had the chart that i was using was

If you look at this pic you see the max hp is less than there 500 and it also doesnt show the a3 and a4 cut impeller. is that what the 9.5 and the 9.25 is in your diagram? and this is showing when the engine maxes out (stalls) in rpm? also this berkley chart is very close to what i have for horse power i dont see any more than 3500 rpm now but im looking to re build my engine but im looking for what hp requirments i need and whee i neede to go to a stain less or brass im not looking to make huge power id like to see 454 or around that

 

[jetboatperformance]

First that chart is ancient (no offense please ) , suggest you use the AT chart or something more up to date , without know more about your actual boat (and engine) I'd say your way down on power or your tach is incorrect and need to look at possible engine issues with what looks like a BBC (in your pic) and only 3500 rpms ? and its not a cavitation problem . Happy to try to help, more info please Tom

here "Duanes" chart , maybe someones got a clearer copy ?)

 

[Canuc]

lefty, spell check on your hometown hand if your pump is cavating you could have a worn impeller or wearing . if the pump is getting good flow through the intake you shouldn't need a inducer unless you are runnin a small impeller cut . good time to have a look with winter here . California marine in Richmond sell's A/T parts . your right their comparable impellers to the Berkeley A3 and A4 is the 9.25 and 9.5 . they don't fit a Berkeley without machining them to 9'' OD . i also stock small parts , kits and impellers . let me know if i can help.

 

[lefty's pride]

Ok I'm running a 1979 454 casting #361959 stock, with the older heads on it cast #353049 again all stock. Also a 850 holly I know it is way to big. I got a 650 holly double pumper to replace it for next year help with that low-end power. I do believe I’m down on a little power with a bit of blow by. But looking on the net I don’t find many sites say I have more than 250hp. And to the last post. I rebuilt the jet two years ago I had leaky bowl seals and worn bushings but I replaced the impeller at that point due to some nicks in the impeller surface. But I don’t think that I am cavatating, I was just wounding when I go to build my new motor at what rpm if any would the pump cavatate? The biggest problem I had doing the re build is getting the rope packings to seal. Last thing California marine is overly expensive I found ordering parts from cpproformence is cheaper with great help

 

[jetboatperformance]

ok im running a 1979 454 casting #361959 stock, with the older heads on it cast #353049 again all stock. aslo a 850 holly i know it is way to big. i got a 650 holly double pumper to replace it for next year help with that low end power. i do beleave im down on a little power with a bit of blow by. but looking on the net i dont find many sites say i have more than 250hp and on that old cart the rpm with the a cut impeller it puts me rith in that area.

actually an 850 would be fine and Let me know if we can help as you go thru the diagnostics Tom

 

[lefty's pride]

Well and maybe im running a little higher in rpm but it cant be more than 4000 rpm I don’t think that an 850 is good for the application turning the motor at 4000 rpm using a 850 cfm carb I’m told I would need a volumetric efficiency of 135% because I’m not adding a blow nor am I going to turn over 6000 rpm I’m just not going to need that large of a car. Plus I have heard from many people and from Kershaw performance I was told to run a smaller carb it would help with low-end power and with fuel economy

 

[Canuc]

glad you got the parts thing figured out so what impeller do you have ? if you want to keep your motor lugged down for economy then the 650 dp would work good for you . the log manifolds you have would be better for low rpm aswell .

 

[lefty's pride]

Do you think Im loosing with the log style manifolds? I don’t really want to run a stack Im trying to keep people around me happy since there all family at the lake and Im running A cut impeller. Id like to turn more rpm if I could I figured I cold hold 3500 for a long time with out hurting the engine but if I could turn more I would I think I could turn up to 4500 but nothing more with the stock rotating assembly

 

[Canuc]

logs are fine for what your doing , and they will help to keep you in with the neighbors . Like Tom said check tach , your rpm's are low for 454 with a A impeller .

 

[GT Jets]

logs are fine for what your doing , and they will help to keep you in with the neighbors . Like Tom said check tach , your rpm's are low for 454 with a A impeller .

Just throwing this out there, these guys ar giving you sound advice..

If you're looking to get the boat to run well while still getting some economy and you're gonna stick with the logs, I would recommend a 750 CFM spread bore vacuum secondary carb, they take a little tweaking, but have better part throttle fuel economy and it is there when you want to "blow out the cobwebs"...

You need to shoot for 4500 RPM at WOT, really for a few reasons. The first reason would be to prevent overloading the engine, if you're running WOT and only getting 3500-4000 rpm the strain on everything is huge and unnecissary, the second is pump efficiency, an A impeller works super duper well at 4500 RPM, if power will be that low (250+/-) maybe cut you're stuff down to a B (not recommended on a big block).

650 CFM IMHO is pretty small and if you're going to go that route, why not switch to a small block? I would be willing to bet you could find a killer trade and the boat would lose 200# in the process. bulb

The older impeller designs were rated at 330 or so HP, but with the advances in alloys and machining practices, that number has improved greatly. With your setup, you really can't beat an aluminum wheel.

Lastly, you would have to have some extreme hull/intake problems to cavitate an A at 4000 RPM. you should be OK there.

GT hand

 

[lefty's pride]

ok another question, if looking of Duanes chart is it safe to say that at the specified hp asorbed say 450hp (what im shooting for) at 5000rpm, if i where to change impellers to change rpm how does that adversly affect the speed of the boat

 

[GT Jets]

ok another question, if looking of Duanes chart is it safe to say that at the specified hp asorbed say 450hp (what im shooting for) at 5000rpm, if i where to change impellers to change rpm how does that adversly affect the speed of the boat

That my friend is the million dollar question. Nobody really knows for sure what it will do for speed.

What makes a jet boat move is the velocity of the exiting water multiplied by flow. Larger hulls need more flow, whereas lighter hulls need the velocity.

Big crap shoot either way. Sorry I wasn't much help.

GT hand

 

[[email protected]]

ok another question, if looking of Duanes chart is it safe to say that at the specified hp asorbed say 450hp (what im shooting for) at 5000rpm, if i where to change impellers to change rpm how does that adversly affect the speed of the boat

If we're talking a specific engine that makes xxxHP at xxxxRpms, then in theory using a larger or smaller impeller than required should negatively effect the output.

If your 450hp engine turns an A impeller 5000-5200 rpms, your pretty much there, the question is why you would want to change the impeller at that point? If your concerend with cruisn RPMs you might go to a larger cut, you probably wont loose much on the top if you have a broad power curve. Going smaller....all you have to gain is RPMs unless 450+ hp is made later.

 

[lefty's pride]

well 450 hp is what im shoting for in my engine build in the fall. i was asking the question just you know, i dont know where im going to get that # i was hoping to get it around 5000 mark but if it is higher i was wondering what it does to speed, they way i was looking at it was
if it takes 100 psi, to make the boat go 70 mph, and your using 450 to build that psi should it matter where in the rpm band it is?
i dont know if that makes sence just wondering if any one has tested and found out what effect if any it has

 

[1975sleekcraft]

850 vs 650

i ran a 650 double pumper on my 455. i am pushin 450 horse. i tuliped my intake valves. you really need more cfm than a 650 can offer. it creates a lean condition at w.o.t. stick with the 850 and jet it to your needs. imo
i am runnin an 800 now.

 

[GT Jets]

i ran a 650 double pumper on my 455. i am pushin 450 horse. i tuliped my intake valves. you really need more cfm than a 650 can offer. it creates a lean condition at w.o.t. stick with the 850 and jet it to your needs. imo
i am runnin an 800 now.

FWIW, nothing personal, but a larger carb has a much better chance of leaning out a setup than a smaller one....I think your setup was lean to start..bulb

Just my opinion, that's all...

GT hand