mtgbiker

Cay,
I'm running 1.50 bravo's.
The boat comes out of the hole with less effort than with the 330's and acceleration is better but not huge.

I went by my engine builder's shop this afternoon. He says the motors are built to run at 5700 however he feels the hull and weight is a contributing factor. By all means, I'm not upset with him. He built great motors designed around the 990 GM heads and HP500 intakes. I was just ignorant to think this boat would be able to turn the rpms with 24-26p props.
He does not think that changing manifolds will yield lowering the peak HP down to 5100-5200. He really wants to change the cam and intake as a combination to get me 500hp at 5100-5200.

As a kicker, if I do this in the fall, I'm definitely going with Dart Pro-1 heads, then we are taking 525 -550hp at 5200. This could be a huge difference. Until then, I'm going to run different props and enjoy the rest of the Summer!

SB

iTrader: (1)

Dart Oval ports or rectangulars ?

Hp and Torque = same at 5252 rpm.

525-550ft/lbs at hp peak is a tall order for a marine friendly relatively low compression 454. Remember, tq peak is typically 1200rpm lower than hp peak rpm. This means your tq peak will be a bunch higher than 525-550ftlbs.

More torque will spin a larger prop to same rpm. More hp will spin smaller prop to higher rpm.

What if we take head $$$ and use it instead towards a 496cid stroker rotating assembly ? A suggestion to atleast think about.

==============
CayFormula knows these boats real well, he's proved that. By his experiences it really does seem that something is off in the tune or rigging - exhaust, fuel system, flame arrestor, heat, airflow, etc,etc. Concentrate on this before you drop more $$$ on engine parts.

CayFomula

mtgbiker,

Is this the same prop you were running before the mods? If so what pitch, model, rpms & speeds?
Have you tried any other props since the mods? If so what pitch, model, rpms & speeds?

I agree with SB you should sort out the tune or rigging before you put more money in to the project.

SB,

Thanks for the kind words, you obviously know your stuff also.

mopower

Myself and a friend both have 272s with 540s and have the same problem , only higher up. From reading here and other sights , it seems as though there can be a MAJOR difference between dry dyno tube headers and the wet exhaust in a boat . I mean upwards to 100 hp . Here's my dyno results with dry tube headers and I have a hard time turning 28 Bravos 5000 rpms. Tried some labbed 24 Bravos and turned the close to 6000. So at this point I iin the market for some 26s , although my 28s are at the prop shop getting trued up first

mtgbiker

You all have great suggestions!
I am going to do everything possible with rigging and trouble shooting before going back into the motors.
A little bit more info to share:

Exhaust=CMI etop's.

Ignition= MSD modules and Distributor's.

Flame Arrestors= K&N 11x5 tall.

Holley marine 4150/800 cfm's 80p & 90s jets/6.5 power valves.

Holley Blue electric fuel pumps with bypass regulators @8lbs
idle and 7.25 wot.

Timing dead set at 38* per dyno and builder. Checking this tomorrow!

Also going to turn the props "in" per Cay!

Thanks everyone. I need all the suggestions I can get!

mtgbiker

Mopower and Cay,

How much do you think the Silent thunder platform hinders the RPM's not letting these motor's breath?

I cut all the baffles out of the platform and took the external platform rubber flappers off. I do have new internal flappers until they burn out!

mopower

I don't know. Cay claims quite a bit on his. I've heard "nothing" on others , so I can't say. I have ext. flappers and baffles. Internal flappers went away years ago.
I can attest to the fact that mine got a lot richer in the boat as compared to the dyno.We both have Innovate WB O2 meters.Once in the boat I went down four jets in the primary and two in the secondary plus enlarged the intermediate air bleeds.
And I'm not done yet.

mtgbiker

SB,
I agree this could be a tall order, but going to superior flowing heads with the same dome pistons and smaller
chambers could yield 10:1 or more. She's at 9.3:1 now with 990 GM heads at 110cc chambers and slightly larger exhaust valves.

Also, these motor were punched out .030. SO that helps a bit. Stroking it to 496 would be awesome, but then again....budget and baby needs new shoe's per the wife!

CayFomula

I removed the Silent Thunder platform on mine and it made a huge difference 7mph however this was since my motors were modified and Whippled. I now turn 30p Bravos 5700-5800 rpm at 93+. It seems that most other people that have tried removing the platform didn't see much increase.

mopower

And your are 454s ? right???