CMB 91

nitro freak · Aug 12, 2011

WHAT R THE DIFFERENCES BESIDES CARB AND FLYWHEEL?

WHICH IS A BETTER ENGINE FOR A OUTRIGGER? AND WHY?

Joe Warren · Aug 12, 2011

nitro freak said:
WHAT R THE DIFFERENCES BESIDES CARB AND FLYWHEEL?

WHICH IS A BETTER ENGINE FOR A OUTRIGGER? AND WHY?

I Like the RS91 with a Mac`s 15cc pipe & the Current VAC 91 is much stronger running engine than the older version HR91. A New Improved 2010-2011 Roadrunner Twin kit compliments both of these engines well. if your thinking TWIN? Both require about 20 oz tanks ea .P.S. HR91 closed he intake window later than most about 70-72 ATDC........ You cannot correct the drum due to the material is Gone on the closing side.. However, the RS91 & VAC 91 are more around 62-64 ADTC. p.s. diff crankcase from HR/VAC91 too. the VAC91 has the flow windows to the sub ports. You will see the small ribbed area`s on the outside of the case.

dwilfong · Aug 13, 2011

In stock form the 91 VAC is a more powerful eng. the stroke is longer which you would think would make the power band lower in the RPM range but CMB installed a longer rod to bring it back up. also the transfer timing is supper high to balance the whole thing out. But with a RS with the right mods you can gain more in my opinion. the disk intake is easer to change timing and will flow more air. I also think that the rotating mass of the two piece crank will hold more energy when going thew the corners. I my self am not a fan of piston ports like the 91 VAC uses. I feel that proper cutting of the liner and piston on the bottom side work better.

If you are running stock. 91 VAC , with the proper mod 91RS.

David

Tom Foley · Aug 13, 2011

dwilfong said:
In stock form the 91 VAC is a more powerful eng. the stroke is longer which you would think would make the power band lower in the RPM range but CMB installed a longer rod to bring it back up. also the transfer timing is supper high to balance the whole thing out. But with a RS with the right mods you can gain more in my opinion. the disk intake is easer to change timing and will flow more air. I also think that the rotating mass of the two piece crank will hold more energy when going thew the corners. I my self am not a fan of piston ports like the 91 VAC uses. I feel that proper cutting of the liner and piston on the bottom side work better.

If you are running stock. 91 VAC , with the proper mod 91RS.

David

I wish CMB or someone would build a Mac 84 Clone , it would whip ass on these 91's . Never had anything run like a fresh set of Mac 84's !! B)

dwilfong · Aug 13, 2011

Tom Foley said:
dwilfong said:

In stock form the 91 VAC is a more powerful eng. the stroke is longer which you would think would make the power band lower in the RPM range but CMB installed a longer rod to bring it back up. also the transfer timing is supper high to balance the whole thing out. But with a RS with the right mods you can gain more in my opinion. the disk intake is easer to change timing and will flow more air. I also think that the rotating mass of the two piece crank will hold more energy when going thew the corners. I my self am not a fan of piston ports like the 91 VAC uses. I feel that proper cutting of the liner and piston on the bottom side work better.

If you are running stock. 91 VAC , with the proper mod 91RS.

David

Click to expand...

I wish CMB or someone would build a Mac 84 Clone , it would whip ass on these 91's . Never had anything run like a fresh set of Mac 84's !! B)

Tom I keep telling you the CMB 80HR P/L will fit right in the case. Have one I will be setting up next week. will let you know how it times out.

David

Joe Warren · Aug 13, 2011

Tom Foley said:
dwilfong said:

In stock form the 91 VAC is a more powerful eng. the stroke is longer which you would think would make the power band lower in the RPM range but CMB installed a longer rod to bring it back up. also the transfer timing is supper high to balance the whole thing out. But with a RS with the right mods you can gain more in my opinion. the disk intake is easer to change timing and will flow more air. I also think that the rotating mass of the two piece crank will hold more energy when going thew the corners. I my self am not a fan of piston ports like the 91 VAC uses. I feel that proper cutting of the liner and piston on the bottom side work better.

If you are running stock. 91 VAC , with the proper mod 91RS.

David

Click to expand...

I wish CMB or someone would build a Mac 84 Clone , it would whip ass on these 91's . Never had anything run like a fresh set of Mac 84's !! B)

Thats just cause you havent had a set of RS101`s yet......... 67mm Full cup HAULING ARS.......... I have had them both. Nothing Runs like a pair of RS101 with 60 nitro pumping there veins.........