Re-Propping 353 Fastech for higher HP
 

I am replacing the original HP500 carb motors in my 1999 353 with new naturally aspirated motors that we have dynoed at 700 hp / 700 torque. I had been running the original bravo 4 blade 15 1/4 x 30 props and was getting about 5100 rpm on the old motors. The boat is equipped with factory extention boxes and 1:50 drives and we plan on keeping the rpm to 5800 on the new motors. Since the hp and rpm is significantly higher now I doubt the original props will provide the best performance, however we plan on trying them for a benchmark. Any suggestions for stepping up to next size? Thanks

Go with Maximus 15 1/4 lab finished props

They worked best on our 353 with twin 700 HP

Since we had 1.35 gears 700 HP /800 pounds torque and 32 `pitch with rev limiter at 5450 you would probably look at 34 `pitch with your 1,50 gears

take care on the drives , I recommend to upgrade to Imco SCX

The Bravo Drives won´t live long

If a large percentage of the additional HP comes from the additional rpm then I would lean towards 32's. They can always be made into "33's" if needed. With similar HP my 382 ran 32's or 28 Max (fully 15 5/8 blades though). Cruise with the Max's was great but it started busting drives.

Were over 600 hp at 5k and have a nice flat torque curve so its not set up to be a screamer. I plan on running around 4k cruise, but well see... :) Drives are on Santas list for next year, hopefully mine will last one season. I know someone who picked up a used set of Imco Platinums a few years ago and he loves them - no issues whatsoever being turned by 800 hp motors on a much heavier boat than mine.

We just tested the boat with the new motors and the bow seems to be carrying way too low. My 353 was originally equipped with carb HP500's, 1.5 Bravos, extension boxes, K planes and Latham steering. I have always felt the boat ran with the bow low which aside from losing speed, gives the steering a bit of a darting behavior. This has been hard to understand since these boats all came configured like this and one would think they dialed in pretty good. Now after running the 700's this bow down behavior is exaggerated and potentially dangerous at speed. It seems like it's plowing when the motors crank up. I would like to see the tab angle a bit higher but they are level with the hull in full up position. My engine guys have a lot of race experience but have not done any of these hulls. They feel we should switch to props with less stern lift, perhaps 30P 3 blades (no pitch change since we are also looking to pick up another 500 rpm). We thought of spinning the props "in" but this is normally not recommended for this boat and supposedly can introduce other problems. Any thoughts and did you find the Maximus to raise the bow attitude any?

353
 

These stepped hulls do run bow down compared to non stepped. I do agree though that the 353's could use a little help. Usually adding more rake to the prop will add bow lift. You can try turning blades in, it's easy with bravos just swap props and put in reverse. My experience is it makes a ton of difference on a fully surfacing drive, but not that much with non surfacing.
My communications with Scott at Formula said a few of their race boats ran this way.

Call B Blades and ask what they suggest.
One other thing, my 353 with 500's came with labbed 31's from the factory. I hurt a prop and used a non labbed (30) on that side for a while. When trimming out for max speed the labbed prop held allot more trim before blowing out than the non labbed did.

I would think you lost about 300#s with new motors if they are alum headed. I would not think that would make much difference but when I pulled alot weight off my 292 engines it also needed more trim to lift bow or boat will run nose heavy and loose. If I have heavy cooler in bow makes it worse! If I have 3 big guys in back seat it helps. If I run tabs down past neutral also makes it worse. I had merc lab my 30 bravo1s with more cup and seemed to help. I have heard of some 33 outlaws that add weight to swim platforms to help settle boat at high speeds?

We're not running aluminum heads and doubt the other mods saved any weight. Do you remember if your tabs went any higher than neutral (level with hull)?

mine were slightly higher but I had my indicators marked at level and honestly don't think it made any difference when I ran level for bow lift.
You already have the advantage of the standoff boxes which offer more leverage on the transom to lift the bow when trimmed. I would call Brent at B Blades and ask him which prop offers more bow lift, but like I said these boats run flat, it is the nature of the beast!
I don't remember if you mentioned wheather or not your props are labbed? This does or at least can make a large difference in the amount of bow lift they can carry.
You may try to pm axapowell or one of the other 353 guys on here running 90 plus mph and ask them their thoughts.

Not running labbed props now but I am talking to Brett. Looks like they installed spacers at the factory and thats why the tabs only go level - I have no way of knowing if the ride attitude would change even if we got them to go higher.

I played with my tabs a bit, it really made no difference from parallel to slilghtly up as far as trimming. In fact I had to go a notch or two down to actually notice a response.

You can always take the spacers out, but don't think it will be worth the time.

Your biggest bang (in my experience) would be labbing for effect. B blades has a $40 trial I believe to test out different prop configurations. You may like a 5 blade with more rake but it will be harder on the drive especially with that hp.

Joe 308,

You might have some luck contacting Axapowell on here. Sounds like your engine combo / horsepower is right around the same as his. He runs boxes and Sportmaster shorties and claims to have run as much as 97 MPH. I can not tell you what props ran that top end number but I am sure he could. I do know he has worked with BBlades on both his 4 and 5 blade props.

The BBlades test program only involves stock props, I have three sets in transit right now, but testing will give you a base line to work from. $45 per prop, per test, plus UPS, gets you 15 days to test them, includes ship time. Not a bad deal if you are searching for the better mouse trap.

Joe, with the -2 Sportmasters and no spacers turning the props in, for more bow lift, was in fact my fastest set up. Labbed 32 Bravo 1's with the diffusers removed and a 1.5 gear ratio at 5700 RPM's. A perfect day, with perfect air and a tail wind! A little chine walk around 85, but went away as I approached 90. Boat felt a little loose, but not unsafe.

Around the dock was not good turning the props in. The boat would always seem to want to go to the port side while backing into my slip, no matter what input I would give it. I finally decided to turn them back out and stop searching for the top number. Pretty happy at a high 80 speed and all of the handling you could want. Brett is a good guy to work with. Accurate info will lead to an awesome finished product.

My 5 blades just about keep up with my 4's on top. A larger diameter (15 1/2") 28 pitch Maximus has a better cruise speed and are much more efficient. I've been playing a little with spacers over the past two years, but don't think they make enough difference in the bow lift. Remember not to over trim.

Dave

Thanks for the info Dave. Do you recall the rough cost per prop to lab the 4 blades? Merc will do this as well but not sure if they go as far as Bblades with the diffusers. Also are you running the factory merc racing 502 blower motors or custom built? Mine have a pretty flat torque curve 700tq/700hp @ 5200/5800 on the dyno. There was a rumor floating around that Formula raised the x-factor at some point in the 2000's but my hull is a 99. Feel free to pm me if you prefer.
Joe