hellya

Why do the motors we run push 5 hp but the same cc motor in the rc boats claim 7.5 hp..................... heres a zenoha PUM upgrade kit

esutek

My Feedback: (1)

Based on the pictures you posted it seems to me to be build quality and engine preparation. I know my 27 didn't look like that when I opened it up.

chevyman_de

Mostly 4 reasons.
- The technology allowed for car engines is very restrictive. No separate liners for example...
- Narrower powerband for a boat engine. They don't need low end torque.
- Unlimited cooling capabilities. There's usually plenty of cold water around the boat.
- More fuel available to boat engines. They don't need to finish a 30 minute run on a 700 cc tank without refueling.

OLD_SLOW and in the WAY

torque.... in the boats we need all that can be made. we use a flying start against a clock if you are a tad early and have to slow down then good low speed grunt will out drag race the others to the first turn. the quick draw pictured is a "kit" engine using all the parts from a zenoah 260 pum engine. i have recently built a couple of them ( and i race against them too) all i can say is there is no match either in quality or performance. fuel mileage will kill you in this in a typical race which is 2 1/2 minutes milling for the start and 6 laps ( 1 mile) its not uncommon to use 8 to 10 ounces of fuel. packing a radiator around is impractical but for a drag race set up where a boil off system is used you would never be beat. they also have a front intake rear exhaust that will spin 30,000 rpm..... can you say....boil the hides

Dr Honda

My Feedback: (4)

#1 reason....

Cooling.

You can't make 7.5hp if you can't get rid of the heat.

ibstar

anyone who says they get 7.5 hp out of a 25cc petrol engine is telling porkys
you might get upto 5 ish with a masive tuned pipe on the boats
but hp is not all thats needed. theres alot more to it
if you want a balls out race
get a cmb.90 nitro convert it to ait cooled nothing will ever touch you

hellya

BH Hanson will email a dyno test showing 7.5 hp @ 17000-20000 rpms with the 25.4 cc engine
http://www.bhhanson.com/Marine%20Eng...uct%20Line.htm

I can get 5 hp out of a 22.5 cc

Makes sense water cooled heads, plenty of coolant...... A radiator plus a waterpump for FGs is unlikely

ibstar

i can make a dyno and calibrate it to read 7.5 hp
what they use to calibrate it ?????????

hellya

ibstar.... BH hanson has been modifing the zenoha engine for the RC boats way before FG was even a company, its a very reputable company
I dont think that company would be able to stay in business for as long as they have if they made false claims

www.bhhanson.com

OLD_SLOW and in the WAY

i race with the current worrld gas boat speed record holder ( mike Bontoff/ Lohring Miller) and the Quickdraws they bring to race with are the finest engines made.... there is no comparison between a die cast weedy engine and the billet QD's. 7.5 hp is for the kit engine not there full race engines that will rev to, and maybe over 30,000 rpm. if they decided to make an aircooled engine there would be competition what so ever. BH Hanson was in on the development of the Zenoah 4 port design and if any body can get those numbers Hanson can.