1000 rpm from labbing?
 

I was running a 26p 4 blade bravo prop on my stock hp 500 carb. I put a B&M 250 blower on it and I am now pushing 625 hp. I am running a 30 p 4 blade bravo now. My only problem is I need another 1000 rpm so I can get my boost up to 5 psi then I think the 30 p will be the rite prop for speed. I am wondering if I can get it labbed by bblades and get the rpms back. I was running 5200 stock. Now I am at 4900 and should be pushing 6000. Any thoughts?

I would say its possible. Strictly by labbing, no, but like in my case I was too far down on the torque/hp curve that when i lost rpms during the heat, being to far down below wot range.... I lost even more when it go hot, so its possible. Which is exactly why dropping pitch by 2 inches netted me 900 rpm gain.

So if labbing raised you high( say 400-500) enough to get into your increased hp curve, the motor could possibly grab the remaining rpms..

As in my case, same issue.. I will prob need to lab my 25p's to get back near the top of my wot range.

Well I tried runningy 26 p And I only was running about 5100 but I am still only running 2 lbs of boost. I should be at 5. So that's why I need those extra rpm.

If you lab a prop for 1000 rpm, you will probably turn it into a potato chip. Did you re-cam the motor, where is the "should be spinning 6000" coming from?

I would suggest a different pulley or different prop. I would also look at a prop calculator app, and mess around with some numbers.

I've probably had 10 props on my boat in the last 9 months, they are all different. Even 2 of the same pitch props, they are all slightly different.

Good luck

I am not an expert by any means in forced induction, but shouldn't full boost (based on pulley) be coming in a lot sooner?

Boost is a byproduct of restriction. If its a 5 psi pulley it won't necessarily make 5psi on every engine. You might see 5 on one motor and 2 max on another. It all depends on how many cubic inches, cylinder heads and intake. I would suggest trying a pulley change first

I am thinking the same thing on a pulley change. It ran 6000 rpm and 5 lbs of boost on the Dyno. Which should have been under some load. I tried running my original 26p yesterday and got a few more rpms but it's still not enough. I figure running a smaller pulley will force more air in and will in turn probably give me more rpms.

Not sure if its the same but on my car changing to a smaller super charger pulley would produce more boost and hp but changing the crank pulley would produce more tq and hp with less heat. Not sure if this applies to boats being a whole different world?

If you were running 5200rpm w/ the hp 500 and 26p and now are getting 5100rpm with the same prop and 2psi you are down on power it seems. I would recommend a compression test and to validate the setup is right.

Hello Blue Thunder,

I take it you had your motor dyno tested and it made 625 hp at 6000 rpm w/5 psi boost? I ask this because most 500 hp motors that are super charged, make 600-700 hp at 5 psi and 52-5400 rpm. No labbing will increase prop rpm 1000. You will have to drop down in pitch to get the 6000 you require. However, I would agree that a pulley change is in order, as long as your cam profile does not require 6000 rpm. If this is a stock 502 cid, 500HP then the cam will not tolerate 6000 rpm. You will want to stay at 5400 rpm and change pulleys. As was mentioned earlier, you not making as much power now as you were with your prior set up.

Please call to review this in more detail.

Thanks,

Thom

I think this was meant for you 98fever.

On my 509 with a 741 cam and mild ported heads I only got 2-3 psi with a 5 psi b&m 250 setup no matter what rpm I pulled to. 5800 netted the same psi or less. I switched to a mega blower and super choler and I have 6.5 anytime I go WOT above 4200 rpms.

With 625 hp you should be able to spin a 26-28 pitch to 6000 rpms. I was able to spin a 30p bravo 1 to 5600 pretty easily. Maybe the different hulls come into play but I would think a fountain would be similar to my velocity.

Changing blower pulleys and crank pulleys to achieve the same blower rpm will yield the same hp, tq and heat. A larger diameter crank pulley is always perferred because it will let you run a larger blower pulley for less belt slip at any given boost level.

Well my Dyno sheet says 2 lbs at 3800 rpm. If I'm reading this rite. I'm gonna check for belt slip at kinks or leaks in my hose. Also sorry cp5899 for not getting back to you on the prop. I borrowed one a 30p and it didn't work anyway

Not a problem. I'm in no hurry to sell it as its a spare for me in case I need it. I would think with that kind of power you should be running a 30p though.

Yeah thought a 30 p was going to be the rite prop but I guess not. It put me down at 4800 rpm. That's too much lug on the motor for me

What RPM does your 26p Bravo net? You should baseline off that prop and go from there.

If all you did was bolt on the 250 to a stock HP500, then you don't want to spin it to 6000rpms.
Unless you changed the ignition, then the stock rev limiter will kick in at 5350rpms.
A 250 bolted onto a stock HP500 should make 625hp easily when set up correctly.
Was the blower refreshed ever??? It sounds like it is not making boost correctly, assuming you have the correct pulley combo to make 5# of boost on a 502 engine.

Pm me your phone number as I am only 15 miles from you and I may be able to help you with your questions and might have props I could let you try to see where you need to be, sounds like you need to get motor sorted out before worrying about propping from what you are saying, but either way get with me and I will try to help, a customer who has a 27 fountain that he just bought (Dean) was telling about you last week when I fixed his outdrive, Smitty

I met 98 fever 27 today after talking to him on phone earlier this week. He found 2 smaller pulleys to try to make more boost and I borrowed him a labbed 28 CE and merc/bblades labbed 30 to run along with his hopefully higher boost! I LOVE seeing a guy go faster and after this test he should know what prop his boat really needs and can have BBlades or CE lab his own 30 or build him the right prop, Smitty

You're a good guy Smitty, but the important thing is Will You Be Ready For HotBoat!?

VERY interesting results, 98 Fever found some smaller pulleys that gave him 5-6 psi of boost , in back to back testing he tried a CE labbed 28 that I have, a Merc labbed 30 that I had BBlades work on a few years back and his box stock 30 Merc .
He saw 78 mph with the CE turning around 5300/5400 (too small)
He saw 80-81 mph with the Merc labbed bblades tuned 30 at 5300
And DRUM roll- the box stock Merc 30 kicked BOTH there azzes with 83-84 mph at 5100
I am actually shocked, I was sure the 30 labbed would kick the stock 30's azz, especially since his motor made peak power on the dyno higher than any of these turned!!!
I also have a merc 30 labbed that was tuned up by CE last year that is typically 4+ mph faster than the other 30 he tested when run on my own boat, I had to keep this prop when he did his testing so I would have something to use on my own boat if I wanted to go out.
This brings up SEVERAL questions-does my tweaked 30 labbed suck so bad that a stock 30 can kick its ass?
Would my boat go any faster with a unlabbed 30?
Has my labbed 30 lost some pitch over time to where it slowed down??
I have a vast collection of props from 32's down, BUT in my collection I never bought a stock merc un-labbed 30 since my own boat has always went faster with labbed props.
This fall at hot boat weekend I am going to let 98 fever try my faster CE tweaked 30 and I am going to try his stock 30 and see what happens. I am also going to send my slower 30 out to BBlades or CE and have it checked/tweaked a little since it is slower than my other one and slower than a stock 30 (at least on a 27 fountain), I love this stuff and can't wait to do some more testing!! Smitty