Anyone wanna give it a shot?

[clownpuncher]

I've got a friend ....
Lets say he's got a heavy 21 foot v-hull jet. Damn near 4,500 pounds worth of boat and "stuff"
Pump is a Berk 12jg with a Mag Bronze Legend a/b ( I believe this is equal to a Berk A)
Set-back, inducer, droop, yada yada yada
The old motor dyno'd 613hp on a Super Flow and spun the pump at 6400 rpm
The new motor makes 700 hp at 7000 rpm
670 ft lbs at 5200
These numbers came off of a DTS dyno at 98 degrees room temp and shitty barometrics.
Any pump gurus wanna give an opinion on what impeller would best suit a boat like this? For my friend
Intersted in hearing all aspects.
Thanks in advance:D
ROC

[ck7684]

I'm no guru by any means, but what more important, hole shot or top end? Have a graph of engine output throughout the RPM range? How was the performance with the previous engine? An "A" (berk size) sounds good to me, but like I said, I'm no guru...

[clownpuncher]

I do have a graph. Lemme see if I can scan it.
Boat ran well on the old motor, till it broke after 60 hours.
A boatload of people, gas and cooler would get me to mid 70's. Holeshot was nice, but, not a drag boat launch by any means. Great mid range punch.
Old motor peaked on torque at 3400 rpm.
New motor is way better, parts, build etc. Love my new builder, great guys. They actually drag race in Pro Street, build, R and D all their stuff. Very impressive shop.
I'm gonna run the boat with the current impeller tomorrow at the river and see what she does.

[VAMI]

I would think a B minus. are you sure the old engine made peak tq at 3400??????? and made 617 hp.That engine would have 950 ft lbs at 3400 to make 617 ( peak tq times that rpm) divided by 5252 = hp

[clownpuncher]

. are you sure the old engine made peak tq at 3400??????? and made 617 hp.That engine would have 950 ft lbs at 3400 to make 617 ( peak tq times that rpm) divided by 5252 = hp
Good catch. Make that a peak of 614 ft lbs at 3900 and supposedly 613 hp at 6400, per the dyno sheet.
I'm not too confident in the old dyno sheet. It shows too much fluctuation at the top. Whatever, live and learn who to trust.
Thanks for the reply.

[clownpuncher]

BTW, all the info I gather here is for my own info/knowledge/learning as I boat around and take mental notes of what peoples opinions were. I figure any day you learn something new, it's a good day.
Rather than make my own changes, I'm gonna leave that to the pros in the off season, which is right around the corner

[Squirtcha?]

I figure any day you learn something new, it's a good day.
Words to live by! I couldn't agree more.

[502 JET]

I'm no expert but I'll add my .02.
The engine is built for a drag car not a jet boat. The cam is wrong. 7000 rpms is too high. That's why a B- impeller was suggested above. It may let you hit 7k rpms but it wouldn't move that big boat too efficiently.
How many rpms could turn with the old motor?

[revndave]

My.02 You need a AA impeller for those big boats

[MikeF]

The old motor dyno'd 613hp on a Super Flow and spun the pump at 6400 rpm
The new motor makes 700 hp at 7000 rpm
670 ft lbs at 5200
Should have fixed the pump.:devil:
You'd need at least 860+ hp to turn that impeller at 6400rpm. The boat and or pump has issues.
New motor ok w/ same impeller and a tighter pump (but no advantage over original engine.)......Doh!

[Outlaw]

I have to agree big heavy boats love AA impellers.
Might have to re cam. or just advance the cam 4 degrees.
I had a large boat with a B, holeshot sucked, could not pull
a skier, and it loved the fuel.
changed to an AA lost 2mph but gained a useable boat.

[djdtpr]

These numbers came off of a DTS dyno at 98 degrees room temp and shitty barometrics.
ROC
Whos Dyno did you use im only asking cause my buddy has aDTS here in the valley Indio area.

[Sleeper CP]

Clownpuncher,
What are the numbers between 6,400 - 6,600. That would seem to be the better operating range. And do you know how high your friend wants to rev the engine?
For that big of a boat that is a bunch of rpm's. See the extended impeller rpm chart that I just bumped to page 1. As others mentioned a A, A+ or AA would be a good choice for that big of a boat. Just my .02
p.s. Since it's a 4,000 lbs day cruiser I wouldn't quess he is going to put nitrous on it is he?
He can put an impeller in it so it turns 6,200- 6,400 off the bottle and rev to 6,800- 7,000 on the bottle kind of like my brother and I do with our boat. See what it's doing at 6-6,200 on the dyno.
Sleeper CP
Big Inch Ford Lover

[Sleeper CP]

I just looked at the Extended RPM chart and compaired it to the numbers that you posted of 670 lbs ft. at 5200 and 700 HP at 7,000.
The engine is then making 675-680 HP at 5300 and probably 680-685 at 6,000. It only gained 30 hp over the last 1,800 rpms and most of that was probably gained between 5,200 & 6,000. So that last 30 hp is not really "usable" power because the impeller will "suck up" 50-100 hp over 200 rpms/ above 5,400 rpm's. An A or A+ impeller would probably be a good choice to spin the engine between 5,800- 5,900 rpm's. It will get up and running faster and save a lot of fuel while cruising:) Just my .02
What intake maniflod is he running on that thing?
Sleeper CP
Big Inch Ford Lover

[clownpuncher]

Man, been out of town for a few days. Thanks for all the replies. Good info.
Before I asked this question on the boards, I did get an opinion from someone whom I have huge respect, and their same response was basically "AA impeller might do it good". Not to say that any other opinions don't have any merit, but, we're gonna run it with the Legend A/B and go from there. Don't have the dyno sheet in front of me so I can't give those answers at this time.
The motor is a punched out Merlin 509. Total disp is now 523 cu. The manifold is a single plane, I think Dart? 2 stage 1000 cfm Holley, msd 6m2, heavily massaged Grumpy Jenkins heads flowing 385'ish? and a pretty large LSM cam, damn near 700 lift. Some high end valve train with rocker studs instead of a girdle and some polished springs. Comp is 10.5:1. Total timing is now set at 37 degrees, pump gas.
Anyhow, should be a fun trip next day or two. Hit the water on Thursday and Friday, drink beer on Saturday and Sunday, back on the H2O on Monday when the crowd goes home.
I appreciate all the comments/suggestions and I'll let y'all know the outcome when we get back from the river (next week or two:D )
Guess I have to confess a lil too. The boats actually mine, I was just flying under I guess. For those of you who've been around a while, my boat is Froggystyles old boat. Some know it well.
Thanks again for all the responses
ROC

[clownpuncher]

BTW, I'm under the impression that a Legend A/B is equal to a Berk A. Anyone have any decisive info on that?