CMB .90 vs A90 vs k90

[guilderoy]

Ok guys. give a modeler some expert advice.

Which is the better motor.

Parts, output, reliability, etc.

The engine is going in a 42" aeromarine sprint cat.

 

[Ian Inverarity]

Guilderoy,

I have A-90's, A100's and K-90's. I have also extensively seen and raced against CMB 90's. I feel my mod A100 is the most powerful, the mod A-90 next, mod K-90 next. I feel that the mod A motors are more powerful the CMB's. The highest quality is the K-90, absolute jewel. Depending on pricing where you are the CMB is cheapest, and probably easiest to run. All are quite reliable if treated properly and are well backed up for parts.

Are you going to race it or just play?

Ian.

 

[guilderoy]

All out Racing! HEat racing the sprint cat.

 

[TimD]

Do you want torque or rev's?

If you want massive torque the CMB and A motors are the pick, however if you want BIG rev's then the K motor is the one due to it's crank design. All of the motors you mentioned are good items and competitive.

Never run 90 tunnels personally so I can't say for sure what is desirable, but on smaller tunnels revs are more useful as the torque makes tunnnels do wierd things with the appropriately pitched props.

 

[guilderoy]

i'm thinking, that since this is a 42" sprint cat. maybe it would be better to go with a torque specific engine, simply due to the weight of the boat and the prop (3blade) desired to push it. And probably in my twin 80 rigger, set it up with k90s, being that it is a lighter boat.

 

[Ian Inverarity]

If it's torque you want for the cat, you cant go past the A100. I used to run a mod A100 in a 46" mono which could do 65mph in heat racing trim on the circuit. It would run props from my gas boat, such as a 70mm 3 blade 7016/3 at 19000rpm. I stopped using it because it had more torque than the hull could handle at that speed!

Tim,

I'd argue that point about crank design, but there is no point going over old ground!

Nitrocrazed racing: Real engines have double sided cranks!

 

[TimD]

Tim,

I'd argue that point about crank design, but there is no point going over old ground!

Nitrocrazed racing: Real engines have double sided cranks!

MOST double sided cranks develop run-out when revved very hard Some double sided cranks run on needle rollers instead of bearings

P.S. I knew I'd get a bite out of you Ian, thats why I posted it!

 

[Ian Inverarity]

Tim,

Ah yes! And I took the bait!

Nitrocrazed racing: I like my cranks if four bearings! Tested to 27000 rpm.

 

[Anders_Martinelle]

If it`s torque you need i can recomend the Russian engines.

Both A and K engines pull big props and high rev.

Have been running my K90 with a AB1667 6,4" cup at 25k.

Have tested the A engine lately and both are good....

Anders

 

[TimD]

There is the answer you want to hear!

Especially if you consider Anders being the current world champ for 90 Hydro ;D ;D ;D

 

[Ian Inverarity]

Anders,

Which A-90 are you testing, the LS or the HP? I use the the HP and have not been able to get the K-90 to use the same size props when running the same pipe and length.

Ian.

 

[TimD]

Ian,

Perhaps another question should be what pipe, CR and nitro % did he use to pull that prop at that RPM?

 

[Ian Inverarity]

Tim,

That would be interesting. I have not tried other props in the rigger with the K-90 tho, I am basing my comparisons on what I could do in the mono. I also dont have a tacho in the rigger. 8)

Nitrocrazed racing: I feel the need....

 

[Anders_Martinelle]

I have tested the A-90LS Mk II it`s called i think.

At this time i can just say that i have tested it with a "older" Picco pipe.

With the same pipe and a K90 there is a differense in pipe length of 2cm!!

But that is including a differense in timing so the real differense is not that mutch but still.......

In that case the A engine should rev alot higher but i have not seen that yeat.

I have now also adjusted the timing in the A engine so it`s the same as my K motors,but more tests will follow in that case.

I have not tested the engine after the mod.

In normal race setup i run AB 1667 5,8"cup at 22-23k.

The pipes that i like for the K motors is the Picco and MAC 13 and 15cc pipes.

And the MAC pipes i modify with a extended muffler section,very simpel pipe to find the right setup with........

Anders

View attachment 146

 

[Ian Inverarity]

Anders,

Ah yes, the LS has the same bore and stroke as the K-90, 27 x 26. The HP has a larger bore and shorter stroke, 28 x 24. I have never seen an LS over here, all the A motors in Aus are HP's or A100's. My HP used to run 22-23k in the mono, but I have recently found i can run a shorter pipe and dont have rev readings at the shorter length.

What are the stock timings of the LS motor? I have raised the sleeve timings of my latest HP, but on my first I actually lowered the sleeve. The disc timings have all been way too short, if you have increased them to what you run in the K motor you will notice a large improvement!!

Is the 'old' Picco pipe still available? If not would it be possible to get measurements of yours? I know someone who can make pipes for me. 8)

Ian.

 

[Anders_Martinelle]

What pipe do you use Ian?

The stock timing of the MkII is 184 exhaust 130,132 boost and transfer.

The new discs have 40-60=200 intake.

The old Picco pipe is not available today.

But maybe soon 8) 8).

TimD: MUCK , 9:0 , 55%....

Anders

View attachment 154

 

[Ian Inverarity]

Anders,

I use the Bolly MP-92X carbon fibre pipe currently on both the A-90 and K-90, but have used the Macs 15cc muffled pipe on the K-90 and I also tried on of Hammer's Titanium pipes. The performance of all was about the same so I use the Bolly's because they are cheaper, quieter, lighter and pretty strong.

Those timings sound close to the A-90HP from memory, I will have to check. The disc timing is higher tho, the old ones were around 180-185 from memory!!

The AB67 pipe looks a bit like the 'old' Picco pipe, have you had the chance to compare them?

Ian.

View attachment 155

 

[Anders_Martinelle]

Nope,but i will soon.............

Anders

 

[Ian Inverarity]

Keep us posted! ;D

Nitrocrazed racing: Say, that's a nice pipe...

 

[Ian Inverarity]

Anders,

Found my data on my previous A-90HP. The stock timings were inlet 182, closing at 51. Trans 129, boost 126, exhaust 183. They have moved the timings around a bit tho, it seems every motor I measure (produced at different times) has been slightly different. I haven't measured my new one.

Nitrocrazed racing: Yet more motors...