Yes, the Kyosho F-86 does benifit from better designed ducting. The stock Kyosho F-86 has been clocked at 54 mph. With ducting and .15 CV-R engine I'm getting 82mph. Here is what I have done with the Kyosho F-86
http://www.geocities.com/cnhilgers/F86mods.html . I have also changed out the stock engine for the O.S. .15 CV-R car engine pictured at bottom.
Updated: Videos are outstripping geocities bandwidth. I'll post the new links soon.
The 82 mph speed in the video is close to the 90 mph exhaust velocities on the test stand. The exhuast outlet is at 100% FSA in these videos. If I narrow the outlet to 75% fsa I should theoreticly get exhaust airspeeds of 135 mph which would translate into 120 mph flight speeds in theory.
Actually, the performance with the stock engine was very similar in my fully ducted setup. The Kyosho fan may be too much for the CV-R to really shine. Although, the thrust to weight of the CV-R is 9.5 to one in the setup pictured below (CV-R weighs 5.75 oz with head fins cut down as shown) which is the same as an O.S. .91 installed in a BVM Viofan (1.5lb O.S. .91 produces 14lb thrust in the Viofan).
The CV-R and home made tuned pipe puts out 3.4 lbs thrust at 27.1k rpms on the test stand. Installed thrust is 75% of that or 2.6 lbs. The tuned pipe is 2 oz lighter than the stock engine's pipe and the CV-R does not have a pullstart so that saves another 2oz for an empty weight of 3.25 lbs as opposed to the stock setup's 3.5 lb empty weight.
The lesson here... efficient ducting really pays off.