98Fever27

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?

nailit

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.

98Fever27

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.

launchpad475

iTrader: (1)

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

nailit

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?

89notch

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

98Fever27

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.

12meter joe

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?

blue thunder

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.

hec2buck

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