philip clemmons

How much power and what mods have you guys done to get to upper 40s low 50s with the BJ 55?

hibby

philip check some of the previous posts in the last few weeks. I know myself and peerpsi have posted numerous things we have have done props, set-up, motor, pipe, etc. Hibby

philip clemmons

Exactly...................I was looking for a more streamlined version.

I have been reading for two days and a lot seems to be opinionated info from those who dont own one of these boats. I'm at 30 + pages now (and pulling my hair out) and was looking for a little direct advice if you dont mind.

I am mainly looking for engine/pipe/prop combos. I know tuning is another whole issue, but I need an engine and wanted to get some ideas of what level mods I should be looking at.

Do you have a link to these threads you reference?

Thanks again!

PEERPSI

CC racing Pro Mod Zenoah 26 CC using drop mounts rear mount hole extened a quater inch
CC racing 2" band powermaster pipe with 3" offset, set to 14" from cylinder
square collet no clutch, no water pump
Aeromarine rudders, long version, using the water pickups stock ones removed
Dasboata prepped stainless steel balanced and sharpened 7015/3
Warehouse hobbies solderless flex shat and prop shaft

Documented 54.19 MPH and runs in the 50's every time out know. RPM's at 17160. Less then 20% slippage on prop.

Good luck.

philip clemmons

Sounds like you know your stuff! I have Aeromarine rudders, but dont know how to tell long from short?

Whats it worth to remove the clutch? (is it just less hassle, or worth speed?)

How about the stock pick ups? Do they create drag?

Ever tried one rudder for less drag?

What is the rear mount hole extended 1/4" mean, and drop mounts? Is this to change shaft angle, or just to eliminate the clutch?

Thanks for your patience..............I know engines but am new to boats, terms, and the hardware used in them............[8D]

PEERPSI

I should also mention I had to make spacers for the engine mounts. The drop mount lowers the collet about 1/4 so that the collet and flex shaft line right up. The stringers Proboat uses aren't spaced the usual 5" so you need longer bolts and spacers. I turned some up on the lathe out of PVC rod. The slot in the drop mounts needed to be extended a quarter inch to get the mounts to fit the stock holes. No big deal just a little filing. You could probably get it to run with one rudder but not with the stock servos. Removing the stock pickups gained 3.8 MPH. I tested for top speed, pulled to shore and then switched over. Went straight back out in less then ten minutes so water and temperatures were the same. I've attached some pictures so that you can see my setup.

Dockman

The thread (New speed for BJ55 With m5) and (BJ55 Strut/Stuf Tube) both have a lot of good info and not 30 pages long.

danielplace

Toxic engine, 2" band pipe, MRD carb, 500ml gas bag down in right sponson next to engine, real tape on lid radio box lowered to bottom of hull instead of on top of rails, 1/4 scale steering servo, dual speedmaster rudders with dual pickups each, Octura X470/3 prop. 57-59 mph top speed. Sorry to say all the mods were a waste of time because the hull was never designed to be driven faster than
35-40mph and any more engine than stock no matter the setup it just won't handle it. Rollovers and blowovers are every run if you drive it like a boat should be able to be driven. These hulls were designed as playboat not performance machines. My honest recommendation to anyone is not to modify the engine for performance as a first move but rather take the same money and get a real hull first with the stock engine and you'll be so much happier and then modify from there. It will be a much faster and enjoyable experience trust me on that.

black talon

My Feedback: (5)

when lowering the stock rudder mounts,it means using the bottom rudder holes as your top ones and drilling two new ones for your bottom holes in the mounts. the problem with this is instead of sliding thru the corners it barrel rolls. as mentioned the hull is not meant to be a speed demon,but the next biggest bottle neck is the exhaust system.

Scott.b

Good info here.Thanks guys..

PEERPSI

Actually what Dockman and I discovered one night was that differnet BJ55's have there hardware mounted at different heights. As much as half an inch difference. This explains some of the very different setups people have reported.

Scott.b

My boat should be here wednesday Ill let you know what mine is to compare notes.

Dockman

Very true take all measurements from the bottom of the sponsons.

philip clemmons

What radio box is that?

What are you guys doing for strut and prop positions?

ANyone had any luck with a prather 275?

danielplace

That radio box is a Aeromarine #13 box dropped down to the bottom of boat instead of on top of the rails. It helps to get the weight lower just like the low gas bag instead of the fuel tank that was also mounted to high on top of rails. The drivline was completely changed out to full 1/4" shaft from engine to prop. The stock clutch setup rarely makes it thru a gallon of fuel with a stock engine it would self detruct on entry to the water with a full mod engine. Solid throttle linkage is a must so as to guarrantee the engine is completely shut down before ingesting water. The stock throttle cable leaves plenty to be desired. There is almost nothing left stock when your done if you want to go fast. Unfortunetely they don't do well fast. Blowovers and rollovers are bad enough stock when you go totally modified and use the power available there is nothing you can do to stop every run from ending with the boat upside down. Gets old quick. Take this for what it is worth and I really don't mean to offend anyone but this boat is best left stock except for drivline mods to remove the useless clutch. When you want to go faster invest in another hull. You won't believe how much happier you will be.

Dockman

I have a prather 275, x472, prather 270, and a 6717/3 from dasboata. The 6717/3 is the best prop I have found to date. My buddy has a 7016/3 that I have not had a chance to test yet. My buddy and I plan on running our boats this afternoon and I hope to test his 7016? My best speed has been 51.1 with a RCMK motor and 7/8" Torque master pipe/header from Gizmo. The pipe is a 2" band and to date it appears that 12 3/4" is the best place for me. I have posted lots of info on my testing here on the links below.

http://www.rcuniverse.com/forum/m_9223585/tm.htm

http://www.rcuniverse.com/forum/m_9156666/tm.htm

philip clemmons

How did the prather 275 work compared to the better ones? Was it a little slow, or a big difference? Mine is OK but takes a while to get on the pipe (3-4 secs).

I still have a lot of tuning with strut, rudders, and carb. First time out 46 on radar, still very rich, and very wet. Still have the clutch too...................

Dockman

The clutch makes it easier to operate. I will make a test run this afternoon with the prather for a comparison. I do believe it will be 5+ mph slower then my 6717/3. 46 is real good if your motor is stock. Was that coming straight at the radar gun or at an angle? If it was at a angle then you were most likely running alittle faster then 46?

philip clemmons

It was a direct run at the gun, as I have been using radar for years.............

The motor is not stock.

I know nothing about the strut/rudder setup, but know I have a lot to gain there.

When it was stock, it would not pull the 275. It picked up 5-6 mph with it yesterday, so I know its making more power. It just needs tuning.

The carb is still rich on h and L, and the prop is less than ideal. I also moved the tank forward, which could be making it run wetter. The water was also glass, so I need to find the right setup for that. All in all, I have lots of room to work!

Dockman

I tried the strut 8mm up this after noon. It did not like the strut there.

Prop 6717/3 = 45.3 @16062

Prop X472= 44.4 @16131

Prop Prather 275= 41.6 @16078

PEERPSI

What sort of RPM's?

philip clemmons

I cant get my strut to 8mm, as the slots in it dont go down far enough. 5mm is about flush with the bracket.

What is a good starting point?

Do the props all seem to like the same strut height, or does each one like something different?

Glad to hear the P-275 is slow...........looks like 50 should be easy with the right prop

showme

Hmm?PEERPSI you are runnin at 8mm,but you are spinnig more pitch.Correct?
Dockman,Is ithookin upor blowing out?Too much slipp?I wonder if you could run higher and pitch up?(without needing more power.)On one of myothers I was able to run more pitch and a smaller dia,.(It would blow out but made it up on top)
Sorry if this is beatin a dead horse I'm tryin to catch up and I'm Thinkin out loud again.LOL.

PEERPSI

Less pitch, Dockman has a 1.7 pitch and I have 1.5. his is 67 mm while mine is 70. Dockman's effeciency numbers are lower then mine, around 76% while I'm at 80%. My last two outings where 7.5 and 8 mm. Best speed was 54.375 at 17600 RPM. For me that means I'm about topped out on RPM. For Dockman his RPM's seem a little low. If you do the math the 6717 at the efficency Dockman is seeing will have just about the same speed as my 7015 at the efficency I'm seeing. That means it's a wash as long as the extra pitch is not what is causing his RPM's to be low. If it is then it's too much pitch for this boat and hardware. If he can get the RPM's up and improve the efficency it will be faster then my boat.

His test today showed that at 60% of the prop in the water he is seeing lower speeds. That means at the 70% + that he was at before was more effecient. If I were him though, I'd be trying 6mm space between the hull and ferrule to see what that yields. Don't forget RPM's because that's part of the story.

showme

GOTCHA! Now I'm on the rite page.Thanks. HMMM?Wow! So many things could play a part. I"m glad there are several people sharing their findings.