New CMB .21

[Marty Davis]

Marty, I wouldn't want to be argumentative (as if) but that looks like a very long pipe length to be testing at. I don't understand why you are testing at such a low rpm for a .21. I have on water rpm of just over 34,000 rpm plus and Mauro from CMB runs higher rpm than me although I've not tacho'ed his motor. If I tried to race at 26 to 28,000 rpm I'd be going backwards compared to others. Your dyno graph shows the motor completely without power over 32,000 and only .75 bhp at 30,000. Thats not normal. Dave

Dave:

Good question.

Are you running a geared setup?

For our hydros, it seems that in order to run high pitched props with sufficient diameter to stay hooked up in rough water, it is necessary to run in the area presented.

I would like to be able to run 40K like the RC Car Guys are doing, but we must have requirements that make that unmanageable. I have never been able to get a HYDRO to work to my satisfaction in high rpm bands.

I would be very much interested in your thoughts on this.... By the way look at blow down time on this engine 29.5

Marty Davis

 

[Marty Davis]

I think it's marked, but I just want to be sure, which % of nitro did you use for the test? It's marked 65%, but it is the right value?It's quite amazing the ton of nitro you run in USA, here we are at maximum 30%... The price is not the same I also think!

Did you add some head shims for the test?

I try to keep all the info in that box current to the test that I am doing.

YES, that is the percentage that I run, except for the Internats.

Marty Davis

 

[steve wood]

i'm working on one right now. i feel the timing numbers are a little lower than we normally run, and a lot lower than what the newest nova and cmb were coming in at(190 exhaust!).head volume is better, but still too big, if you can compare it to the nova and latest rs cmb

 

[Terry Keeley]

i'm working on one right now. i feel the timing numbers are a little lower than we normally run, and a lot lower than what the newest nova and cmb were coming in at(190 exhaust!).head volume is better, but still too big, if you can compare it to the nova and latest rs cmb

Anything near the 21RS numbers I get?

https://www.intlwaters.com/gallery/displayimage...m=70&pos=61

188/129/220 is pretty stout for a 21 especially when there doesn't seem to be any lack of torque...

 

[Marty Davis]

i'm working on one right now. i feel the timing numbers are a little lower than we normally run, and a lot lower than what the newest nova and cmb were coming in at(190 exhaust!).head volume is better, but still too big, if you can compare it to the nova and latest rs cmb

Steve:

Suggest that you look at the numbers that are shown on the dyno sheet. The reason for the low intakes is to balance the time areas between intakes and exhaust. Also notice the blow down time of 29.5 degrees, what I consider to be the best for our use.

Marty Davis

 

[steve wood]

the one i have apart has 184 exhaust with a blowdown of 30.2 on the transfers and 28.6 on the boost. if i raise the liner.005 the exhaust will go up and the blowdown goes down a little. 185.5 ex,29.9 and28.4

 

[Stuart Barr]

Steve,

I would strongly recommend that you try the motor with stock timing.

Stu

 

[Marty Davis]

the one i have apart has 184 exhaust with a blowdown of 30.2 on the transfers and 28.6 on the boost. if i raise the liner.005 the exhaust will go up and the blowdown goes down a little. 185.5 ex,29.9 and28.4

I never measure the Boost since it is so difficult to get correct. Just use the side transfers. I sure wish that you would try the engine stock before you start modifying. I think that you will be amazed.

Marty Davis

 

[Roxyflash]

I dont think Steve likes that type of motor Looks like a MAC. LOL

 

[Marty Davis]

Marty, I wouldn't want to be argumentative (as if) but that looks like a very long pipe length to be testing at. I don't understand why you are testing at such a low rpm for a .21. I have on water rpm of just over 34,000 rpm plus and Mauro from CMB runs higher rpm than me although I've not tacho'ed his motor. If I tried to race at 26 to 28,000 rpm I'd be going backwards compared to others. Your dyno graph shows the motor completely without power over 32,000 and only .75 bhp at 30,000. Thats not normal. Dave

Dave:

I am curious about the head design. Do you know anything about that with the very narrow squish band? Your thoughts.....

Marty Davis

 

[Don Ferrette]

Marty (or anyone else who has an '08 RS-7 in their hands) could you give the i.d. and o.d. of the exhaust stub on this motor please?

 

[TERMINATOR]

Marty (or anyone else who has an '08 RS-7 in their hands) could you give the i.d. and o.d. of the exhaust stub on this motor please?

steve if you would like to play with another one i will bring mine to the meeting sunday. i would love to have it modded , and i have another one on the way also.. let me know . and don i will measure that for you tomorrow.

terry

 

[DaveMarles]

Marty (or anyone else who has an '08 RS-7 in their hands) could you give the i.d. and o.d. of the exhaust stub on this motor please?

Don, You want to get the tapered header. Exhaust stub is 16mm od, 12.4 id.

Dave

 

[carlnoki]

i realy hope that the '07 version of the motor is ok and does well, because the '06 version of the motor won't even swing a JG E-20T. ask Don Ferrette!!!!!!!!!!!!!!!

carl

 

[Don Ferrette]

Since I'm not at home to check, what is the thread size on the RS-7 crank? :unsure:

 

[dave roach]

Don

Should be 1/4 -28

Dave Roach

 

[Don Ferrette]

DonShould be 1/4 -28

Dave Roach

Thanks Dave.