twin 67

[Watercadet]

80-84 engines are a few grams lighter than 67's if that means anything.

For us (and by us I mean me) Andy, a few grams means nothing. But for you it is another few MPH!

Adam

 

[AWaddle322]

Andy,

Is the NAMBA course the same size as the IMPBA course?

I also feel that you are right about the 80 something motors being a little faster but how much consistancy do you give up. Have you seen more broken parts on 67 or 84's?

My experiences indicated that you will break much less with 67 over 80 something engines regardless of engine manufacture.

Allen

 

[Brian MAhoney]

Re RPM range for 90s,

I'm shure I have seen a multi boat with an CMB RS 91 running at 23,000 rpm. If this is OK in a half hour multi race then I cannot see any problems with a Hydro running 22,000 to 23,000.

Brian

 

[Preston_Hall]

22,000? I was thinking it was well over 25,000. :lol:

Seriously.

 

[AWaddle322]

Brian or Preston,

With what props are you all getting these RPMS with? Just curious.

Allen

 

[TimD]

The 91RS has a new crank. It might be able to sustain the rpm's. The 90 evo's will develop runout at those rev's. Seen it more than once. Don't get me wrong - I'm not bagging the CMB at all.

If you look at the lengths of the pipe that will give you an indication of the rpms the motor is running at. In the hydro's here a lot of CMB users are running Mac's pipes at 300mm appprox - that's less than 21,000rpm. Closer to 18,000 with that pipe.

 

[AndyBrown]

Andy,

Is the NAMBA course the same size as the IMPBA course?

I also feel that you are right about the 80 something motors being a little faster but how much consistancy do you give up. Have you seen more broken parts on 67 or 84's?

My experiences indicated that you will break much less with 67 over 80 something engines regardless of engine manufacture.

Allen

Allen,

The NAMBA course is the same size, but with 5 bouy turns instead of three.

OPS, Picco, O.S., K&B 80's, 81's, 82's we have all seen lots of broken parts over the years compared to the same brands of 67's.

For the MAC 67-84 comparing the difference is very small. However, the most bullet proof set-up would lean toward the MAC 67's but not buy much.

 

[John Knight]

Andy,

A MAC 67, AB Parabolic pipe and a CMD coarse remote needle. Yep all your stuff. What would be a good flowmeter number as a baseline to start with? Thanks.

John

PS: Any idea if you and/or John are coming to Charleston's race 9-10 Oct this year. Been a while for you!

 

[AndyBrown]

John, I think around 8 @ 40"H2O

Don't know about that race. John may go for sure.

 

[Brian MAhoney]

Allen

The 23000 rpm I was refering to is on a sub surface multi racing set-up.

Brian

 

[AWaddle322]

Andy,

This topic really has me thinking on a couple of things.

What is the equation to figure out rpm whan you know pitch, mph,etc?

How do you equate true pitch of a prop when cup is added?

what amount of slip is believed to happen with out riggers?

with real boats with twins they cut slip percent in half, is this true with model boats?

I was not trying to bad mouth MAC 84 earlier. They are by far the most reliable of the 80 somethings that I have ever run. We now know that the 67 would be the most bullet proof, what about consistancy. I had a set of CMB evo 80 one time that would run great for a couple of laps and then one would always shut down regardless of needle seeting. I always suspected that this was due to the sleeve being so thin did not allowing for propore expansion. Would this be a common trait among same stroke bigger bore 80 something motors?I have never tried to run a evo 67 motor so it may have been something with the older evo series motors to.

It has always seemed that 67 were easier to maintain propoer needle seeting over the 80 something motors. All of this could be in my head too as I have no proof of this.

Brian, I have no clue a sub surface multi racing set up is. Must have something to do with mono's overseas. The only mono I have is 29 feet long and has twin 502 cubic inch big blocks, but the only remote control it has is for the sound system. Does this count?

Thanks for the help in advance!!!!!!!!!!

Allen

 

[AndyBrown]

Allen,

You need to sell that twin 29 footer and buy a bunch of twin R/C boats.

 

[Preston_Hall]

Brian or Preston,With what props are you all getting these RPMS with? Just curious.

Allen

You would have to ask Kentley about the prop. He hasn't told yet. I'm not sure he even remembers. But it was a stock ABC prop.

The prop was the same for the F Mono SAW and one of the Gas cat records.

That's for SAW. He would probably tell you the prop for heat racing. I think it is whatever Jerry reccomends on the F Mono. It twists that just as hard.

I could be very wrong about the RPM range as well. But I have heard a bunch of high strung record engines and this dude turns up just as good. The only thing to break was the carb.

 

[AWaddle322]

Andy,

I have atleat 4 twin rc boats? isnt that enough? I had to quit running them becuase I ran out of props (just picking on you)

And the 29' is not going anywere unless I find a Cat (Skater or HTM or Daytona) with a passion pit that will run over a 100 MPH in my price range.

No answere to any of the above questions?

Thanks,

Allen

 

[AWaddle322]

Preston,

My racing parner has a twin that has cmb 90 in it. I know that he uses 1667 with 6.8 of cup. I don't know how to equate the above but believe that these motors are turning between 15,640 to 17,210 acccording to my limited knoledge how to equate the above and prop-4-u calculator on there web page. It has my curious more than anything. If I am anywere close on how to factor in cup and use this calulator than these numbers are close. These motors are not really up there in that high rpm range liking you are talking about for most record motors, however every time we try to get more rpm we twist the 3 piece crank in them.

In playing with the calculator for Andy to have run 125 MPH (which he did and he actually at 130 at the end of the straightaway according to Stalker radar gun with Tommy Lee operating, say numbers with my own eyes). All he had to do was turn a stock x2170 to 25,000 rpms (we both now that it was not stock).

after more playing with this calcultor I am not sure that I have a 45 motor that will trun 25,000 rpms.

I hope that some one well tell us how to factor in cup or if you measure the prop at every 5 degree and take all numbers and average.

Sincerely,

Allen

 

[Preston_Hall]

If you look at the lengths of the pipe that will give you an indication of the rpms the motor is running at. In the hydro's here a lot of CMB users are running Mac's pipes at 300mm appprox - that's less than 21,000rpm. Closer to 18,000 with that pipe.

Hoe many RPM's would it be with a MAC pipe at 250mm (10")?

 

[TimD]

"How many RPM's would it be with a MAC pipe at 250mm (10")? "

more! :lol: :lol:

Seriously though - the MAC's 90 pipe isn't that good performance wise when run really short. Is that the length he ran? It can be worked out if you wish...

 

[Preston_Hall]

"How many RPM's would it be with a MAC pipe at 250mm (10")? "more! :lol: :lol:

Seriously though - the MAC's 90 pipe isn't that good performance wise when run really short. Is that the length he ran? It can be worked out if you wish...

Everybody always seems scared to shorten a pipe. If KP has taught me nothing else it is to see how short you can reliably run a pipe. And disregard any measurements. If it works, then it works.

But yes, I asked him how long the pipe was and he said 10" or LESS. So what would that RPM be?

In playing with the calculator for Andy to have run 125 MPH (which he did and he actually at 130 at the end of the straightaway according to Stalker radar gun with Tommy Lee operating, say numbers with my own eyes). All he had to do was turn a stock x2170 to 25,000 rpms (we both now that it was not stock).

Yeh, I saw him do 126 through the traps. Does this 25K RPM factor in any type of slippage factor?

At one time, if I remember correctly, a Picco 67 was metered at 28K.

At any rate, the point was that I don't personally think the larger engines are that limited. In the same thinking I don't believe any of this 40K stuff either.

 

[Don Ferrette]

"Everybody always seems scared to shorten a pipe. If KP has taught me nothing else it is to see how short you can reliably run a pipe. And disregard any measurements. If it works, then it works."

Well said Preston. When the whole package is right you'd be surprised where the pipe length can wind up. I remember KP's 90 mono at last SAW, sounded more like a 45 going thru the traps. That thing was awesome. B)

 

[Preston_Hall]

Tim D,

Are you going to calculate the RPM for the CMB 90 and 10" MAC pipe?

"How many RPM's would it be with a MAC pipe at 250mm (10")? "more!    :lol:   :lol:

They might have smiled that day but nobody was laughing.