CMB help:whats the difference between 80HR and 91RS

[loverboy]

Hi there guys

we are building a friends 1/8 scale hydroplane and while we are looking for an engine we came up with a 91rs CMB.

No 1/8 racing in Greece so no point talking if its legal or not.We build it for fun.

So whats the difference between HR and RS engines?

I know HR stands for Hydro…any deferences in performance that should much the HR version a hydroplane use better and why?

I see the 91RS has removable frond part ..but the the 91HR or 80HR is one piece block...

….i see outriggers running on HR and FSR on RS….

Where we will find the best performance and fun time or more boating instead of swimming ?

….by the way i hate the "low" intake/carb of the HR versions…when not planning you get water in the engine easier

Also can anyone intently the year of this CMB on the photos?

We been told its a 2010

Thanx in advance for your help guys!

 

[steve wood]

only difference in the rs in the pics and current version is carb(they are now bar stock instead of cast and now have a low speed needle) and the piston now is flat with no dish. hr and rs motors are totally different from each other.either one will do what you want to do,if not worn out.the hr motors are easier to repair for the novice,due to the way they have to come apart(removing the wrist pin clip and pin through the exhaust stub and breaking down the crank,if needed). btw the 2013/2014 91/1.01 rs motors have a larger liner,and won't fit the previous ones.

 

[loverboy]

Hi there Steve

thank you for your input…the one in the photos also look to have a low end speed needle (screw on the throttle arm).

But i still don't get whats the deference between an HR and an RS version… Why the HR design is more suitable for hydros?

comparing the photos of the 91 hr and rs here http://www.seaducerboats.com/motor.htm i would say rs has less mass rotation due to the smaller fly wheel?

im really confused lol

 

[steve wood]

the rs crank is a 3 piece unit,with 2 counter weights,1 on each half,plus the pin.it is heavier than the hr style,hence the smaller flywheel. plus the rs uses a disc rotor,the hr a drum rotor.totally different builds