Mac and CMB

[Mark]

What's the difference between a Mac engine and a CMB?

Are they made the same with the crankshaft and how long does the problem with the crank getting out of balance take on the CMB engine?

I want the best out of the CMB, Mac and Picco. Don't know which one to get. I'm looking at a 90 size engine. How much performance difference is there between an 80 and 90?

 

[Bart Drieghe]

Mark , whats the purpose of the 90 engine ? Hydro ? Offshore ? FSR V ??

Your choice will depend on what u are gonna race .

regards ,

Bart

 

[Don Ferrette]

I'm real pleased with my MAC 84 my hydro. Even though they are produced at the CMB factory they are very different. I also own a CMB 90 that's sitting in a cat hull. If you are going with a 90 my top pick is the CMB, it's dominated the 90 size engines for years.

 

[Mark]

Don,

In your opinion, do you think the Mac 84 would be competitive against the CMB 90 in a hydro.

 

[Don Ferrette]

Well let's just say the MAC 84 is sitting in my SGX where the CMB 90 did reside. Don't get me wrong, the CMB is an awesome motor & now is in a Aeromarine 42" cat which should a great combo. The weight of the CMB made the rigger dig a bit in the corners & I can twist the 84 up higher so no loss of speed. For a cat, mono or FSRV type racing I think the big CMB is the ticket. Kentley Porter smashed the F mono SAW record with his CMB 90 powered Seaducer. In the hydro I like the way the boat drives thru the corners with the MAC, doesn't seem to dig in like it did before.

 

[Mark]

Don,

I was hoping to put the Mac 84 in a Hummingbird 60/80 hydro, Nitrocrazed has a Hummingbird but he has a 90 in his and had his hull specially built to suit. Do you think it would matter if I put the 84 in the standard 60/80 size hydro?

 

[Don Ferrette]

It'll be VERY fast. However you will probably find yourself overpowering that hull. I tried running an 80 size engine in that exact hull & found the boat to be a real handful in traffic or on small courses where the water gets rougher. If you get out front & have clean water you will be tough to catch, but a bigger hull like Ian's would be better. Set the rear shoes up the same way I told him back in the Hummingbird hydro thread on the sport & scale forum..... B)

 

[jaso]

Don, in your experience, do you think there is a specific weight that a .90 rigger should come up as for oval racing or do you think it's more the hull and how it handles that matters? Also wtih the Mac Vs CMB thing, does the mac have much advantage as far as how hard it revs Vs torque of a CMB? What size props will your 84 run in ya rigger compared with what the CMB would?

 

[TimD]

Also wtih the Mac Vs CMB thing, does the mac have much advantage as far as how hard it revs Vs torque of a CMB? What size props will your 84 run in ya rigger compared with what the CMB would?

Good question.

Although I have to say that the size of the prop the motor pulls doesn't always relate to how fast the boat is If a MAC84 is "only" pulling a H48 or similar but doing 27000rpm, will it be slower than another engine pulling a H50 at 20,000rpm?

Food for thought B)

 

[Don Ferrette]

Jason- To me it's more the hull & how it handles, especially in the corners. Races are won & lost in the turns. How many times have you seen someone who can't stay in lane one lose it to another boat who could? I'll give up a couple mph for being able to shave a coat of paint off the bouys any day.

Tim- The other factor that needs to be considered is power to weight ratio. Now keep in mind I love both motors & was equally happy with the CMB's power & speed, but with the reduction in weight the boat seems happier in the corners (see above). While the CMB has the torque to pull the big blade, you gain weight. The MAC is lighter hence the boat is lighter & will pull the rev's quicker & should, in theory, accelerate faster. As for the difference in props & speeds it ain't much, I can tell you that first hand.

More food for thought.......... :blink: :blink: :blink:

 

[TimD]

Just what I wanted to hear Don! B)

 

[Lay26]

back to the CMB VS MAC I was at this site checking out the cmb line http://www.cmbengines.de/Motoren/cmb21ls.htm and I too was wondering what are the differences, the volvala 21 caught my eye cause it looks exactly as a mac 21. whats up with that!! if you look closer you'll notice that there is a purple remote adjustable needle. the only bad thing with the site is that it's a german site. and i don't understand a word. someone help me understand the differencees and is this motor new!!! :unsure:

 

[Bart Drieghe]

Lay , ( real name ? )

There is nothing really said in german so , don't know what u can't understand and mainly cause he writes lots in english too lol

but if u want to know something out of german , copy /paste it inhere and i'll ( or others ) will translate it for u .

Regards,

Bart

 

[DaveMarles]

back to the CMB VS MAC I was at this site checking out the cmb line http://www.cmbengines.de/Motoren/cmb21ls.htm and I too was wondering what are the differences, the volvala 21 caught my eye cause it looks exactly as a mac 21. whats up with that!! if you look closer you'll notice that there is a purple remote adjustable needle. the only bad thing with the site is that it's a german site. and i don't understand a word. someone help me understand the differencees and is this motor new!!! :unsure:

CMB Valvola 21 is almost identical to the MAC 21 but it rotates in the opposite direction for gear drive.

Dave

 

[nitrotoys]

I have run and owned both engines.

I would say the CMB has way more torgue, but the MAC likes the Rs and not as much torque. There is some weight difference between the two, but in a mono i didnt really notice. a rigger im sure you do notice. as Don said.

It would be a toss up as to which one i would buy if i was buying one.

There both awesome motors. Both have ran very well for me.

Tom

 

[Lay26]

you know, I was probable sleeping as I was looking at this site. it was 2 this morning.

my real name appers at the bottom

 

[Don Ferrette]

Now I also have to add my CMB 90 is NOT stock, my MAC 84 is.

Even more food for thought............ :blink: :blink: :blink: :blink: :blink:

 

[shoboat]

Tim D,

I used your figures in my prop calculator and came up with the following:

A boat with a engine spinning 27,000 RPM @ 4.527" of pitch would be 82 MPH

Same Boat, but the engine is at 20,000 RPM @5.00" of pitch only 67.1 MPH

So I would think that you would rather have the lighter boat with a higher RPM

engine like the MAC 84. I think the other engine would be the best bet on a

mono though. The MAC's are designed too spin RPM's, and as you can see above

the H-48 would be FASTER than the H-50.

Just A Thought Fellas,

Mark Sholund

PROPS-4-U

[email protected]

 

[EatMyShortsRacing]

Well in the 80 / 81 / 84 versus 90 debate I do have to say the 90 works better in a mono than the 84.

My A90 Seaducer came up against a lot of 84 Seaducers in the US and I cant remember one being faster than mine (stock A90 Engine). Mine won the US1 straight line at the Detroit IMPBA Nationals (propped down for rough water) at around 60MPH (circuit trim). The 84s were also a lot fussier getting on pipe. In a mono I think the added torque of a 90 makes it a lot more driveable and I think higher top speed.

The hydro debate, well I am not as sure there...

Mark,

I thought my Hummingbird (60/80) was a handful at the Adelaide Nats and that was with a MAC 67 that I really didnt get wound up. Once I make a proper cowl for it (such a nice boat with such a poor excuse for a cowl) and trim it out come see it run and ask yourself what an 84 would do to that boat. Ian's boat I can see an 84 in.

EMS Racing Yes I have raced twice in a row in Australia now

 

[Ian Inverarity]

Craig,

I have a mould available for my Hummingbird cowl. If you want to borrow it to mould your own, let me know! I checked your hull and it should fit okay when you trim it. You may need to shorten the venturi on the MAC tho.

I am considering a 67 for my larger Hummingbird. Already have a 90 boat and can only race one X hydro at a time.... B)

Ian.