RCSPORT FLYER

My Feedback: (11)

Has anyone done anything with the Honda GX35 lately? I have the 31CC and would like to know if the 35 is much stronger, i.e. more rpm's etc.

tim220225

My Feedback: (4)

What kind of RPM did you get on the GX31? I put a 2 needle barrel carb 9.5mm on mine and made a header pipe for it and got it to turn 6400 with an 18/8 prop. I need to bore the intake a little bigger snd I want to try a 10.5mm carb I have. There is a guy that puts these and the 35 in boats. He makes cams for them too. I have heard the 25cc piston will fit the 35 bore but haven't looked into that. Be a nice stroker motor from what I hear.

Tim

subarubrat

My Feedback: (1)

OOOhhh, and where did this nugget of joy come from? I like the idea of that. I will have to look at the numbers and see if that is plausable. My GX31 and 35s are all runing strong. I was out flying the 31 on a Rascal today and a 35 on a DR1 the day before that.

tim220225

My Feedback: (4)

I heard there was a guy doing thew scooters who was trying this and I read his information on a web page my kids were looking at. Sounded interesting but I didn't have the time to look into it. Been too busy doing conversions on these Echo twin cylinder engines I discovered. [8D] I am still looking for a plane for my GX31. Sounds soooo good.

fouryaks

Do you guys know of a good source for the Honda Gx motors. I have been working on a Ryobi Four stroker. I have a CNC mill, and lathe so I have been lightening it up somewhat. But, it is still weak. I tig welded a header, and pipe for it.....Boy it sounds sweet... Now if I only had a plane!.....

Thanks!

tim220225

My Feedback: (4)

OK this got me looking. There is a correction I need to make on what I read before. Per the Honda web page the GX31 and the GX 35 have the same bore. The bore is 39mm. The stroke on the 31 is 26mm and it is 30mm on the 35. So the 31 piston fits the 35 bore wise. I then looked around and found pictures and diagrams of the pistons. The 31 piston has more height from the center line of the wrist pin to the top of the piston than the 35 piston has. The area above the top ring is thicker also. So if the 31 piston has more height it will have more travel or stroke. Issues could result if that extra travel is too much and the piston kisses the combustion chamber. So one would need to measure that to see. Also the extra stroke would produce more compression ratio and this could lead to issues like detonation because of our crappy gas. You could fly cut the top of the piston as that would reduce the final compression ratio and or eliminate the possibility of the piston hitting the top of the cylinder as well as lower the detonation issues. Don't know if there is any type of coating on the piston that would be removed by the fly cutting operation. If there is a coating would this cause the piston to peel or flake due to heat? I would think 10:1 or so would be very easy to get and that would make a huge difference in power without porting the engine, matching the intake to the carb, or installing a larger 2 needle carb. Now if I could find a GX35 engine and a GX31 piston my Bridgeport and I would be happy

davewallace

My Feedback: (29)

Hi Tim,
Those are some good thoughts on the GX-31. Don't forget that the valves may interfere with the taller piston. If the valves don't extend past the squish band, you would be in good shape. I would use a length of solder stuck through the plug hole to check the clearance. Just insert it until it touches the cylinder wall and turn her over. I know this is old news, but others may not know. The nice thing is that of performance doesn't improve, you just use the old piston. What does your GX31 weigh with EI?

Dave

tim220225

My Feedback: (4)

Hey Dave, I think if my memory is mostly there that it was about 5 pounds or so. Will work great in a WWI plane of some sort. Been tempted to just put it on the Eindecker 90 I have. But another plane would be nice too.

Tim

davewallace

My Feedback: (29)

Hi Tim,
That Eindecker should be able to handle the extra weight ok. The Echo probably need lead in the nose in the first place. It sure would sound great.

Dave

RCSPORT FLYER

My Feedback: (11)

Tim, I'm getting 6600 rpm's with an 18-8 APC prop,stock carb. I'm putting the engine on a 90 inch SE5a and i would like to have just a little more power on takeoffs. I'm using it on an Ace 4-120 that weighs about 16 lbs.It flys pretty good . You just have to be patient and gain altitude a little more slowly than you would with the more powerful engines.

tim220225

My Feedback: (4)

I want to do a Balsa USA 1/4 scale pup or the DVII. Both should be 12 to 14 pounds and should do well. So many ideas and too many engines and too little time. My 6400 was with a Zinger prop. What did you do to the carb and intake?

Tim

RCSPORT FLYER

My Feedback: (11)

I haven't modified anything yet. I have a carb with a larger throat that i'm going to put on it. I'll bore the intake port to 10.5 mm.to match the carb. Also the exhaust port at 10.5mm.Actually i'm just copying what "Jimer"posted on 11/24/05. He's getting 7100 rpms with an 18-8 wide APC.

GoeKeli

My Feedback: (18)

Can this engine be blown with a simple blower? Maybe mechanically belt driven? Sounds a bit over complicated but if it really helps it might be worth it. EFI? hahah!

joe

subarubrat

My Feedback: (1)

The engine is a great candidate for that. Low compression, rhobust construction, and no valve overlap that I can see. The problem is the precision machinework needed to make one dictates that it would be a one off project and far too expensive to produce.

NM2K

My Feedback: (14)

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Nitrous oxide injection would be far simpler, cheaper and would provide similar power gains.

OLD_SLOW and in the WAY

There is not chance of valve collision or piston hitting chambers with the GX31 piston mod. in a GX35 with stock cam or even up .136" lift

It does not increase stroke!

tim220225

My Feedback: (4)

I can see that the wording of my thoughts may be off. What I am getting at is that if the 31 piston has a taller "dome" area if you will, then the piston will stop at a higher point in the cylinder. Certainly this will increase compression. How much would need to be calculated. True the stroke would still be the same but the ultimate piston stopping point in the cylinder would be higher. It would be interesting to see how much this engine can take.

Terbough Bob

My Feedback: (10)

Too bad you can't modulate nitrous. It's either on or off, and I'm not sure I'd like to fly a plane with power delivery like that. Top that off with the weight of the solenoids, tank, pumps, lines, and I don't see it being viable on anything but a GoPed. The supercharger on the other hand... I'm deployed right now, but will be back at my home station in September, and when I get back, I'll finish working on a blower prototype for the GX-31.

av8tor1977

My Feedback: (6)

I want one!!

AV8TOR

tomservo

No reason you couldn't take the compressor wheel of a (very) small turbo, build a housing and run it on one of these with a sealed bearing and make it belt, chain or gear driven. I've seen some compressor wheels that are a mere 1.25" in diameter. Still overkill but at least do-able and could be done without adding a terrible amount of weight if combined with a mod flywheel, or if you were able to replace the flywheel with the compressor and build a housing around it. Doing it that way might require a slightly larger compressor due to the lower RPM but it could be an elegant solution. I don't know if it would move enough air at such low RPMs however.

If I had a 4 cycle I'd try making one up.

GoeKeli

My Feedback: (18)

Is there a soulution to this in an electronic injector? I guess the air volume would need to increase as well, hence a blower. Any way to make due with a simlpe ram air effect from the prop wash? What PSI would be beneficial?
Force feed this little goat!

joe

subarubrat

My Feedback: (1)

I am a huge fan of forced induction, huge. My daily driver is an STI that put down 300Hp stock and over 500 after the upgrades and this is a 2.5ltr 4cyl. There are similar gains possible with the lancer EVO, a worthy compeditor. Believe me from a novelty point of view nothing would be cooler, my two dream engines are a .10 4 stroke and a 100cc gasser radial, so practical is not my mantra. But in this respect I have to bow down and say that a better piston for a higher CR is our best hope for this engine. Now, a factory produced forced induction engine would be nice but unlikely because the cost of machining the extra components would be far greater than just putting a bigger engine in.

tomservo

That's not to say it can't be done - I recently saw a 7.2 CI supercharged V-8 someone built. It would be incredibly impractical from a retail standpoint - especially machining the blower. But repurposing stuff, could be feasable for one-offs. Look at what it costs to put a turbo on a car. It's ridiculous - but I'm working on getting a turbo compressor to play with, see what kind of RPM it takes to generate pressure. They're surprisingly cheap if you hunt around. It may take too many RPM to be feasible. Then again, we also don't need 400CFM.

hollbrow

Hey Guys- I have two 31's and a 35- I use them on scooters and in boats- stock, the 35 is only very slightly more powerful than the 31.
Learned of the piston swap a good while back- to end up with the compression around 10:1 you need to take approx. .024" off of the dome of the 31 piston- other than that it is a direct swap. I have not noticed a problem stemming from the coating being removed. A header pipe around 1/2" I.D. and 15" long is a worthwhile addition. A slightly larger carb can help, if you seriously know your way around the walbro carbs and can sort out the pulse and jetting requirements. The engines are limited by the carb bore size, and then the intake port size and intake ports
themselves- the 31 more so than the 35. Lift and duration changes to the cam helps somewhat. There is a fellow that can make the cams if you really need one. Do a dedicated search and you can find him. I have found that on a scooter, no matter what you do to them they just don't have what it takes- torque. They do a good job in a RC boat as long as you aren't trying to compete with a modded Zenoah. I have been hot rodding, modding, converting engines for 20 years and these hondas beat me down trying to get the power out of it I thought it was capable of- there is nothing short of a difficult billet head mod that will derive truly excellent power out of these engines, and even then, it is at a high rpm, and not suited for a plane. Those are my thoughts, based on my efforts with this engine.

subarubrat

My Feedback: (1)

Tomservo, some basic numbers that might help you are that the average turbocharger spins at 60,000 to 150,000 rpm. There are allot of factors that dictate the shaft RPM and "boost" at a given shaft RPM, the compressor's map is the chief thing. To generate maximum boost at a lower shaft RPM you want a compressor profiled for that. Now, an interesting cousin to the turbo charger is the vortech and other similar units. They use a gear driven impeller with a fairly high gear ratio and can spin around 50,000 rpm and make a great deal of boost, as you can see the RPM is much lower than the turbo. Don't just order any old compressor, look at the maps and search for one that meets your needs, the compressor could make the difference between success and failure if your able to get the kind of shaft RPMs you need. Just remember what you are up against is trying to spin this thing up fast at a high enough gear ratio, that is not going to be easy and you should definatly engineer in a 1 way bearing so that the compressor does not have to spin down with every throttle movement otherwise any throttle response will be horrific. Another point that comes to mind is how critical the blade to housing clearance is, you can't just put this in a can and go, you will need to cast, machine or mold something that fits. I would reccomend getting a junk compressor housing from a turbo and using it as a mold maker for making a composite housing.