pawraith

has anyone tried replacing say a Zenoah 23cc with a Honda GX25-S3 4stroke? is this even possible? i would like to get into gas powered cars but i also think it would be pretty cool to have a Honda engine in a scale Civic or Prelude.

SAVAGEJIM

Sounds interesting, You most likely would have to do a fair bit of fabrication work to mount that to an existing production 5th scale RC.

Looking at the stats, it looks like you would have to get custom gears as well. 4-strokes generally turn much slower than non-valved 2-strokes, and considering our model gassers can hit 15000RPM and more, if teh stats read correctly on this engine, I dont think this one can break more than 10000 RPM. So custom gearing is a must for a given RC to mount this engine to keep up with an exact same RC that is powered by a 2stroke instead.

Another thing to consider: is the torque output of this 4-stroke engine comparable to that of our model gas valveless 2-strokes?
In general, 4-strokes will poduce more torque because they have a the larger geometric compression ratio.
Our model 2-strokes have to rely only on trapped compression ratio, which is much shorter, less than half in virtually every case, than a 4-stroke's combustion duration.
2-stokes fortunately make up for this some by firing every time the piston goes up where as the 4-stroke only fires half as often.

Now for the HP and torque differences in the specs.
This Honda 4-stroke is rated at 1HP and .92125ft-lbf
A 26cc Zen or CY is boasted to make considerably more with a pipe and maybe head mod: like 4+ HP and maybe 2ft-lbf?
But bear in mind the RC advertisers have a horrible habit of spewing out absolute lies and massive exagerations especially when it comes to RC engine HP and torque outputs. The 6+HP claims of a modded 30.5cc CY is absolutely false. I can gauranty if you put that engine on a properly calibrated and SAE adjusted dyno, that engine will never come to actual 6HP. Maybe 3 or BHP? and like 2ft-lbf?

I know that in nitro engines, many RC advertisers have told bold lies and cliam some nitro engines can produce 5HP! I have done some calculations, and the engines would have to turn 100,000 RPM and hold a torque of no less than .25ft-lbf, impossible for ANY nitro engine to do.

Maybe the Honda engine is underrated and it in reality makes much more HP and torque. Or maybe we have been fooling ourselves for so long into beliving out gas engines can produce 6+ HP.

Bottom line that I am trying to arrive at is this: If the Honda 4stroke cannot produce more torque than our model 2stroke gas engines, that Honda will not be able to turn the higher gear ratios required JUST to keep up with or model 2-stroke gassers.

OLD_SLOW and in the WAY

this is a stripped down Honda 35cc 4 stroke sitting next to the Marder frame... it appears that a new floor pan would have to be made to accomodate its slightly larger foot print.... but its do able

scarletboa

My Feedback: (1)

i would like to see a 1/5 mt with a 4-stroke.

wan6176

try built ur own wir that engine,if not do sell me that engine hehehe

pawraith

i think the 35cc might be a lil too large for what im wanting. the 25cc would possibly work though from what you've shown. unfortunatly i cant find any reliable specs on Zenoah engines or any other 2 stroke gassers so, i would also more than likely put a nitrous kit on it to accomodate the loss of power, or just to make it look cool, lol. anyhow, i also think that the additional torque would be helpfull if you were using it in a rock climber or another MT.

Edit: just talked to a friend who is an Efco dealer. he said that most 2 stroke gassers produce around 1 HP for a 26cc engine. so, my idea would deffinitly work.

Lars from Norway

Ok,most of them,but not the CY and Zenoah,these produces 2,9 hp.

pawraith

where can these specs be found from a "RELIABLE" source? even if they do produce that much more power, all i'd have to do is maybe put on a larger carb or port and pollish the manifold. my main concern was wether or not the 26cc 4 stroke would even fit onto the chassiss. as far as the power, there are plenty of ways to squeeze more out.

Lars from Norway

If you do a bit of tiny research you will find info and even maybe dynotests of these engines with differents combinations of tune pipes,carbs,porting and so on.In almost every shop i have seen that sell these engines/cars with these engines,it says 2,9 hp.

I like your thinking,it would have been an exiting project to put in the 4 stroke engine!A little bit of work,but far from impossible!

Leeber

http://corporate.honda.com/press/art...=2002060160469

Heres some info on a small honda 4 stroke. (GX25)
Says that performance is on par with a 2 stroke engine.

Specs are at bottom of page, maybe someone with 2 stroke
engine knowledge can compare them?

4 stroke GX25: 192 x 221 x 230mm
2 stroke Zenoah: 167 x 204 x 195mm

Another brand of 4 stroke:
http://www.fuji-imvac.com/engines/fjig0225.html