PDA

View Full Version : Whant to raise the x on bh



craigdskilling
09-29-2011, 08:32 PM
I have a 18 383 400+hp running 80mlp.Want to raise the x what is involved in doing this.Is it very expensive to do.I now the magic spot is17.5 to center but what gains can i see.when i changed from the alpha it looks to be a inch low from the spot.My hatch is cut now to fit the carb from the high rise intake on it.The boat is running great i am very happy with it but i want it to be all that it can be.i am running 27 and getting 31 in a few days so hope to do some runs with that.not sure what i will see in gains.My rpm are at 5500with the 27.thanks Craig.

younger
09-30-2011, 12:49 PM
Craig I will be very interested to see what rpm you will pull with the 31's. If you can turn them 4900-5000rpm and reduce your prop slip you have now, you should pick-up a few mph. I'm guessing your gear ratio is 1.5:1 and at 5500rpm you have around 14 and change % slip. It would be nice to see it a little lower. To raise the x you will need to fill the transom assembly hole you have now and re-cut the hole to your desired height. Raising the engine and drive that desired amount. You already have the hatch cut so no big deal there. Test those props and let me know. Hope the motor will pull them. If you notice that you have to idle your carbed motor to high so that the motor does not stall when going into gear. You may want to think about changing the ignition curve. By running more initial timimg say 15 degrees at idle and bring in a total of 34-35 degrees by 3000 rpm the motor will not stall. If you are running a stock thunderbolt IV ign. 24 degree built in advance for the sbc your initial timing at idle is propable 8-9 degrees at proper idle. The BH will have stalling issues. What you can do is run a thunderbolt IV ign. module for a v6 which has 14 degrees built in run 20 degrees initial plus the 14 in the box will give you 34 total and the set-up will like it. The only problem is the starter has to work a little to sart the motor when hot. The best of luck! I hope you can run 85!!!!!!

glashole
09-30-2011, 01:05 PM
craig

as discussed i have a set of 31's you can try if you want to make the trip

craigdskilling
09-30-2011, 08:16 PM
Well Glashole you now when you see a good deal on these props you take them.You can always use a spare set.The drive is a 1:5:1 ratio and i am running everything msd6.so can i change the timing on that if i have too.
But what if i changed the x do you think that inch will make a big change in speed.and what kind of cost do think this will be.

younger
09-30-2011, 09:30 PM
The right x will give you some, but you are not far off. Test the props Craig, test the props. If you do the work youself just time. Pay someone get ready! When I saw your boat run it was stable and smooth at speed, You have no stern lift, it ran strait and you could stay in it. The additional x will reduce some drag and free up a small amount of prop suface area in the water. With that you will pick up some rpm and speed. Handling doesn't appear to be a consern from what I have seen.

Wazzy
09-30-2011, 11:29 PM
Good luck Craig with the new props. I hope the weather stays nice so you can post some numbers. But looking at Rons face after the ride this summer the boat is plenty fast all ready. :)



If you get a chance send me the fly by from this summer. Thanks and good luck. Jason

OFFSHORE GINGER
09-30-2011, 11:40 PM
Younger , i disagree when handling does not become a concern ......considering rasing the X has a host of many other factors involved , and for starters ..height , taps , ext , ext , or why not just flip the boat and add an X-tra set of strakes for more lift ?

MOP
10-01-2011, 06:54 AM
Everyone forgets that Steve's 18 with 100hp less hit 79, raising the X will give a lot more than is bantered in these late BH posts. Getting the gear case clear of the water flow is key to higher speed and better handling, without the stern lift created by the low X you will have less wetted surface. None of this is supposition it is proven fact, it is all in black and white in previous posts. IMO if you are not going to do it right why do it at all!

craigdskilling
10-01-2011, 09:05 AM
Those that have a real set up bh boat,Do you find that you have more stability at higher speeds or does it porpise a lot at all speed.If i raise the x will that come into play.my boat now can handle 80 in chop and power threw it well.With the x up can i see into the 90mlp or am I dreaming.:rolleyes: Glashole tell me more of your bh.did it do any of this.
I have some great vid but how do i put it upon the site.

Greg Guimond
10-01-2011, 09:22 AM
To MOP's point, any application that is designed for true surface running, benefits from a higher X. It is not uncommon for the really fast bass boat guys to run there Sportmaster gear case for example at 1.5" above the pad. On a 20' boat, the difference between even with the pad and 1.5" above was 7-8mph as an example with the exact same motor and boat weight. If you get better handling to boot from raising the X, then that is a strong second benefit.

younger
10-02-2011, 09:45 AM
When I staited handling is not a concern, this is with this particular boat. I have seen it run and it is rock solid at speed no chine walk or ill effects.

craigdskilling
10-02-2011, 11:14 AM
Younger you are right on the handling, Never have i felt out of control in higher speeds maby its do to the heaver teak swim platform on the back that keeps it down.Wazzy it's never fast enough.I'll take a vid of you and ron driving my boat and well see to big smiles going down the lake.But for worn it's addictive going fast.:hyper:

Greg Guimond
10-02-2011, 12:13 PM
Now I'm really confused. It sounds like both craig and younger have SBC powerplants, both have BH drives, and both have the same X dimension currently. If that is in fact accurate, why is craig rock solid steady at 85mph and yet younger is white knuckle? Seems like a substantial handling difference for just 16 versus 18 hull size difference.

craigdskilling
10-02-2011, 07:31 PM
Greg I'm not sure y.But younger does have more hp than i do.His boat will be lighter than mine and more out of the water,also he runs at 84 when he can hold on to it where mine can stay in 80 with no problem.Mine cant do 85 yet so that be a different game when i get there or faster.:boggled:

younger
10-02-2011, 09:19 PM
Greg you nailed it! You need hull to go fast and stay in control or a hull designed to go fast. Through my progression with 4 engines and as many different drives the bh is awsome but the boat has gone way beyond it's terminal velocity. The 18 has a higher teminal velocity then the 16. This is good resault's that the 18 is faster with less power then the 16. As MOP has mentioned many times before proper x he is right on. When Craig runs he has hull to ride on, in my case because of the nature of the short boat and power i'm riding on a spoon. At 80+ in the 16 it is like a dare devil spoon going through the water.

younger
10-02-2011, 09:28 PM
Greg you nailed it! You need hull to go fast and stay in control or a hull designed to go fast. Through my progression with 4 engines and as many different drives the bh is awsome but the boat has gone way beyond it's terminal velocity. The 18 has a higher teminal velocity then the 16. This is good resault's that the 18 is faster with less power then the 16. As MOP has mentioned many times before proper x he is right on. When Craig runs he has hull to ride on, in my case because of the nature of the short boat and power i'm riding on a spoon. At 80+ in the 16 it is like a dare devil spoon going through the water.

PMZONER
10-03-2011, 05:55 PM
Blackhawk Drive Unit, Though testing the X dimension can be increased in small increments until desired performance is achieved, in no case should it ever be increased by more than 1 and 1/2 inch (37mm) maximum. I don't know how many time you want to rebuild your transom? I'm thinking about diminishing returns here. The 90 degree X dimension, 16 1/16th (407mm) to crankshaft centerline. Depending on your transom angle, and I don't know on your boat. At 10 degrees 16 3/16th, at 16 degrees 16 9/16th. That's not much room for adjustment. You may be better off with prop swaps or trying to adjust your CG, Batteries, fuel etc.
Just some thoughts....so how fast is your boat now! :worthy:

craigdskilling
10-03-2011, 08:20 PM
Thanks for the measurments MOP say over and over that the magic spot on the 18 is 17.5in to center where the drive shaft well enter.I am running 80mlp at 5500rpm with bh 27 props.my motor is a 383 stroker balanced and blue printed pushing415hp for now.getting the bigger props to bring the rpm down and top speed up.everthing i have done is new this year.

PMZONER
10-04-2011, 10:33 AM
Those numbers are for a 454/502 MAG, just for reference, and not specific to any particular hull. I'm running the stock 31s on my Black Hawk...She moves right along!:outtahere:

Zoner

craigdskilling
10-04-2011, 05:02 PM
Zoner do tell please.what kind of speeds are you seeing and what motor.I cant wait to get my 31.just hope before it snows.:crossfing:

PMZONER
10-06-2011, 08:49 PM
502 MAG. EFI, 415 hp (never dyno-ed) stock except the quick & quiet has been removed, straight thru hull.
Last weekend temp low 80s, full tank of fuel(55gal), myself and first mate,(she is a brave... girl) 78.6 GPS. Flat no traffic river run....She has more to go. this girl is still new to me!!!! I'll look at the RPM when I'm not so focused on driving!!!! That's in a 22 Classic Black Hawk, your boat smaller, lighter....should go faster. :superman:

Good Luck, Zoner

craigdskilling
10-06-2011, 09:23 PM
That's fast eh.You have a good mate my mate will not let me over 50.so i do a lot of boating on my own.your boat is is what i always wanted so i i have worked on mine for the last 5 years.from stock 350 260hp and alpha drive to now.i would a little every winter to make it a little faster.I love my donzi like ever body on this site.Thanks for your info and enjoy that awesome boat.:wink: