no more rpm after .75 throttle

[shoboat]

Tony & Jeff,

Look at pipes, you both are needing a better set up if you want to go faster.

You will need to open your intakes more and get more fuel into your motor.

Pipe design and the correct stinger size. I think if you look at these things you will

find your answers to your questions. You need more RPM and you are stuck with your

current set up and your pipe length is only giving you so much RPM. So this is why you

are going the speed you are stuck at? More fuel more power to a point. Just go slowly

on intake openings. Shorter pipe more RPM, more RPM more Speed!

Have Fun Testing,

Mark Sholund

 

[Tim Kish]

Sorry for lack of detail,

JAE style rigger

NR Hybrid engine

H7 by mark, can't remember numbers right now

S pipe, at 8in

66% nitro

water flow at 0.050 diameter through head.

Boat will get to max speed real fast, about 68 .. and then go flat about 3/4 throttle. and then no more..

I think a few people have nailed it , richen it up to start , cut the water down to almost nothing and shorten the pipe slowly.

Absolutely nothing wrong with an S-pipe, one of the best 21 pipes ever made they just need to be short to work.

Also don't expect to see huge speed increases, most guys are racing around the 70 mph mark no matter what you read here.

Tim

 

[Duck899]

Sorry for lack of detail,

JAE style rigger

NR Hybrid engine

H7 by mark, can't remember numbers right now

S pipe, at 8in

66% nitro

water flow at 0.050 diameter through head.

Boat will get to max speed real fast, about 68 .. and then go flat about 3/4 throttle. and then no more..

I think a few people have nailed it , richen it up to start , cut the water down to almost nothing and shorten the pipe slowly.

Absolutely nothing wrong with an S-pipe, one of the best 21 pipes ever made they just need to be short to work.

Also don't expect to see huge speed increases, most guys are racing around the 70 mph mark no matter what you read here.

Tim

yep, agreed, 70 mph is plenty fast in heat racing trim.

 

[Joe Warren]

If this Boat has full throttle range on the bank? & the throttle servo works correctly? BUT it Does Not on the water under load?? Either the Pipe Volume is too Small or pipe is too short. 3 3/4 from the band to the center of the Plug would be a good starting point if it is a inboard engine.

 

[shoboat]

Greg,

Bingo!

You have just told Tony the secret to these boats.

Some are running too much propeller and the pipe is too long to work better.

With a shorter pipe length you will not be able to run all those big cup numbers.

RPM = SPEED

Shorter Pipe = More RPM

Have Fun Testing,

Mark Sholund

 

[ALLAN YUEN]

I was surprised that our club guy show me better A/A.21 pipe ( really good working ) for NR21 Wrap . Did you try it from Al Hobbs ?

 

[RodneyPierce]

I can tell you that I have struggled to get my boats over the 72-74 mph mark. Its not easy! I got to mid to upper 60's quick. But after that found it very hard to achieve more speed. It aint easy, but I would start with load and pipe length. Its a fine balancing act when your getting to those speeds. A few of these guys make it look easy to run high 70's but I have surely not found it easy to get there!

 

[dwilfong]

Remember when a .21 gets up there in the RPM it will have little toque.

eng with lots of little knife ports will restrict the flow at high RPMs.

Thy are made for cars that have little resistance and can rev to the moon.

A boat the resistance gets bigger exponentially with water resistance the faster you go.

Try a .21 with out all those knife ports and see what happens.

The toque will be at a higher RPM and will pull bigger props at more RPMs

You have to over come the resistance of the water to go fast.

Toque is the only way to do it.

Or run a very small prop and let it scream.

The CMB high nitro pipe is a very good pipe for a 3 or 5 port eng.

will get you 32000 and still pull a bigger prop.

It is harder to tune a screamer with a short pipe. choosing the right prop to load the eng gets very hard and by the time you get it the eng changes and you start all over.

I had a chance to check out the new CMB BETA.21 and it looks real good.

Huge case ports and a nice liner port setup.

O and the liner fits right in a MAC or CMB green and red head case.

 

[dwilfong]

Greg that is so true to each his own.

I always used the H7 as my bench mark on my .21 hydro.

If it could not pull that prop in stock form there was a problem.