impellor question

[W.O.T]

i have an aluminum A/B impellor machined and blueprinted by MPD. i was wondering if it would be worth it to switch to a B impellor to get more rpms. i dont know how close they are in size. i want to experiment a little to get the most out of my boat. i dont know to much about pumps so any good advice will be appreciated. the motor is a 468bbc apprx. 600hp. im not sure if it is a dominator or berk impellor either my pump has a few mixed parts. heres a pic im sure someone would know.
http://myspace-344.vo.llnwd.net/01260/44/37/1260637344_l.jpg

[DEL51]

MPD would be the first ones to say experiment.If they never did just that, they would not be the tallented group that they are.make sure you have the shims and gaskets. Do not be afraid to call them back with your ideas.I am a happy customer.DEL

[SmokinLowriderSS]

Cutting from an AB to a B should gain you about 150 RPM, perhaps a few mph. You should be spinning really close to 6,000 RPM with 600HP on it.

[Nucking futs]

That impellor doesnt look to be b/p. It looks like its in stock form to me.But like before mentioned, going from an "ab" to a "b" will only give you about 100/200rpm. Im running an aggressor b/c in my cruiser and its spinning 5900 with 600 HP.
Call Jack at mpd, he will set you in the right direction.

[W.O.T]

the previous owner had the pump built before i bought the boat. i have the receipt for the build. i think im having some other tuning issues that are keeping my rpms way down other than the impellor then. im kinda stumped. i now im not getting the most out of the motor and pump. i think i might have the motor dyno tuned sometime this winter. im only getting 5k rpms at wot. :rolleyes:

[Nucking futs]

Thats becuase your impellor is an "A" maybe?

[Oldsquirt]

Look at what is stamped on the rear of the impeller. If Jack cut it, it will be stamped with "MPD" and the cut size.
As far as the 5000 rpm peak....that just tells you that your pump, with that impeller, requires the same amount of power to turn 5000rpm as your engine is capable of producing at 5000 rpm. Doesn't matter if you have 600hp if it comes too high in the rpm range. A dyno run would be helpful in matching impeller to engine.

[W.O.T]

Look at what is stamped on the rear of the impeller. If Jack cut it, it will be stamped with "MPD" and the cut size.
As far as the 5000 rpm peak....that just tells you that your pump, with that impeller, requires the same amount of power to turn 5000rpm as your engine is capable of producing at 5000 rpm. Doesn't matter if you have 600hp if it comes too high in the rpm range. A dyno run would be helpful in matching impeller to engine.
thanks i will definitelypull the bowl and take a closer look. sounds like its could be an a impellor. the receipt from mpd says it was machined. the motor only has about 6-7 hours on it just built by tom papp. i asked him about the rpms and he said it is definitely in the hunt. he never did any pump work to the boat. im sure if i had the right pump setup to compliment the motor it would make a night and day difference. thanks for all the advice

[SmokinLowriderSS]

Look at what is stamped on the rear of the impeller. If Jack cut it, it will be stamped with "MPD" and the cut size.
As far as the 5000 rpm peak....that just tells you that your pump, with that impeller, requires the same amount of power to turn 5000rpm as your engine is capable of producing at 5000 rpm. Doesn't matter if you have 600hp if it comes too high in the rpm range. A dyno run would be helpful in matching impeller to engine.
Exactly. The ability of the engine to put out 600HP at 6,000 RPM isn't worth squat if it only puts out 363 HP at 5,000. The pump just won't let it spin any faster.
Saw a guy on here once with a 718 HP 502, that spun his pump, the same impeller I have, 4,000 RPM, that's it. I spun it 4800 with a 350 HP engine. At 4,000 RPM, he had 202 HP, period. At 4,000 RPM, I was turning 330HP. Engine build completely unsuitable to a jet drive.
If the 150RPM cut gets you ahead of the pump, so that you gain HP now faster than the pump demands it, it's a good idea. If not, you throw away a bit of holeshot and spent money getting nothing.
An engine dyno run would be helpful, tremendously.
If you post here or PM me every engine spec you have, I'll give ya the electronic dyno version from Desktop Dyno. Head flow data would help, manifold, all cam specs, exhaust, you know, the works. If you don't know actual CR, enough info and I can calculate it (head chamber volume cc, piston dome cc, bore, stroke, head gasket thickness, and closeness of piston surface to deck surface at TDC).
If I were a betting man, I'd wager there's a long overlap cam involved in this engine that's killing the torque production, up arround 300* or more. Rectangle port heads perhaps as well?
Good luck to you WOT.

[W.O.T]

thanks smokin lowrider. you helped me out a while back i sent you most of the info i had on the motor. i have merlin heads with the D shaped ports and a steve long racing roller cam. if im reading the chart correctly it the cam has 12 degrees of overlap. intake and exhaust lift is 599. yeah like you said if the B impeller will let the motor get the R's up it would help alot. heres a pic of the motor so you can get an idea
http://myspace-605.vo.llnwd.net/01265/50/69/1265239605_l.jpg

[W.O.T]

That impellor doesnt look to be b/p. It looks like its in stock form to me.But like before mentioned, going from an "ab" to a "b" will only give you about 100/200rpm. Im running an aggressor b/c in my cruiser and its spinning 5900 with 600 HP.
Call Jack at mpd, he will set you in the right direction.
yes the impellor looks stock i dont see anything special done to it. the receipt i have has blueprinting work on there to. i think someone may have swapped the impellor out with a stock A before the boat was sold. almost all the bolts on the pump were really loose and the gaskets on each side of the bowl blew out on me the first trip out. i know it didnt come from MPD like that. just an idea and like everyone says sounds like an A impeller

[bp]

as craig said, the impeller would be stamped mpd if mpd worked on it.
it is subjective to say that you will increase RPM by 150-250, going from an A to a B, because you have no idea what the hp curve looks like at the rpm you're running with the impeller you have, and you don't know what the hp numbers are 200 or 250 higher. if the hp curve is really flat around 5k to, say 5500, you won't see much of an increase at all.
if you're interested in performance, the FIRST THING you should do is dyno the engine, play with valve lash, play with timing, play with whatever else you got, but KNOW what your hp numbers are, and what the hp curve looks like.
provide the KNOWN hp and KNOWN curve to MPD, and you'll only have to do it once.

[Cs19]

That impellor doesnt look to be b/p. It looks like its in stock form to me.
If its a stage 1 blueprint job then only the front side of the impeller gets detailed.
CS

[Nucking futs]

If its a stage 1 blueprint job then only the front side of the impeller gets detailed.
CS
Gotcha, I don't know anything Chris, you know that.....

[W.O.T]

i will have the bowl off tomorrow and ill probably pull the impeller to get a better idea.

[SmokinLowriderSS]

thanks smokin lowrider. you helped me out a while back i sent you most of the info i had on the motor. i have merlin heads with the D shaped ports and a steve long racing roller cam. if im reading the chart correctly it the cam has 12 degrees of overlap. intake and exhaust lift is 599. yeah like you said if the B impeller will let the motor get the R's up it would help alot. heres a pic of the motor so you can get an idea
http://myspace-605.vo.llnwd.net/01265/50/69/1265239605_l.jpg
Not knowing WHICh Merlins you have, my Summit catologue shows 3, with 310, 320 or 345cc!!!! ports, none of which are going to be of any help at moderate RPM. The airflow capability is so high in those huge runners that it gets sluggish at modest RPM's and fuel separation happens, cylinder filling suffers, etc.
I'm searching for flow data, and think it's not gonna look good. Flow numbers curtesy of Car Craft Magazine archives.
Flow data at .600" lift, just to simplify my typing (exhaust with pipe):
Merlin 310VR ----------------- 310cc port -- 313/207
Jenkins Aluminum Merlin ------ 310cc port -- 296/214
Jenkins Aluminum 345 Merlin -- 345cc port -- 330/248
Compare my 353049 GM Iron - 253cc port -- 264/187
If that cam has arround 300* seat-to-seat of duration (let alone more), that's gonna hurt ya in the mid-range as well.

[W.O.T]

im not sure which heads i have. pretty sure i Merlin II rectangular port heads with 320cc intake runners/ 119cc chambers 2.300/1.880 valves. the duration on my camshaft is 292 intake/exhaust

[SmokinLowriderSS]

I'll try to put something together on DD tomorow AM. DD is busy right now running an iteration to find a good cam for a blower-motor on another thread. 4.18 million spec tests to run, been at it for about 12 hrs, 62% done (2.16million). Should be done about 5AM, while I snore. LOL
292* duration isn't too bad, but it shoves the RPM higher, all other things equal.
Guy with the 502 I alluded to earlier, was running 302* or 306* if I remember right, fully race ported rectangle port heads too, and those 2.3" valves.

[W.O.T]

thanks for the help. so from the way it sounds i have a motor that likes to run some high rpms? now im anxious to see what impeller i have. i know it will probably be a while before i get a dyno tune but does it sound like my mill would probably be best running a B assuming i have an A right now.

[SmokinLowriderSS]

Depends on your HP curve. A "B" could be too big to get the motor ahead of it. Just depends on your engine's power developmant curves.

[W.O.T]

thanks smokin lowrider. i think im going to make one more river trip next weekend then pull the motor for a dyno tune before i start messing around spending money on anything else. thanks

[SmokinLowriderSS]

Thx for the reminder of the PM from a while back. I had a build on your engine saved already. :) DD is only as good as the info I can feed it, and some of yours is pretty sketchy. You need to put her on a dyno and see exactly what's happening, and where. I bet with some time & knowledgable effort, you find the HP you're missing.
Also, beware, it's my understanding (others'll correct me if I'm off base here but it's what I've always heard) that the best HP mixtures on a dyno run will wind up too lean for regular driving, by a dangerous step or 2. That might be old-days before the O2 sensor mixture correctings came in to play, I do not know. If they are well set with genuine O2 readings, I'd think they'd be fine.