First post looking for advice

[A5BLASTER]

Ok hello gents.

My first post here and not sure if this is the spot to post this but I need help with a idea of doing a experimental engine use.

I have a copperhead surface drive on my duckhunting boat and want to replace it with a Hirth f-33.

The motor is powered by a vanguard 23 right now but it's heavy and want to use the f-33 to lower the weight if the motor on my boat.

The vanguard produces more torque and produce'sit at a low rpm rate and dosnt make as high rpm rate as the f-33.

What I need to know is how can I go about increasing the am out of torque the f-33 makes and how can I go about getting it to make the torque at a lower rpm rate.

The reason for increasing the low end torque is so the engine will make enough power to the prop to push the boat out of the hole shot and plane it out.

The Vanguard makes 38#' s of torque and tops out around 4000 rpm's.

I know I can change out the belt pulley size and tooth count to help deal with this but I only have so much room in the drive systems case for changing to diffrent size belts and pulleys, so I want to rework the engine to make up the most of the diffrence and then change out belt pulley size and tooth count to make up the rest if need be.

I have contacted a few performance shops and didn't get anywhere's with them because none of the shop's i contacted knew anything about aircraft engine's.

So what all can be done to rework this engine to fit my needs?

[1600vw]

No expert here, but i would go or try this engine instead of the F33.. Go with the f23. It's 50 hp and a twin cylinder. It may weigh more but the power will be awesome.

http://www.recpower.com/F-23%202%20cycle%2050hp.htm

[A5BLASTER]

I have already looked at that engine and it isn't possible to use it do to its physical size and the whole scope of this project is to drop weight.

The F-33 is the perfect engine to try but I need to know if it's possible to rework it to produce the torque and hp curve in the rpm range i need to target for my application.

The engine will be used direct drive no clutch no electric start and it will have to have a custom built exhaust built that is tuned to a two stroke engine.

Also have a cooling fan attachment to add to the engine to help deal with heat in the block due to long periods of running at idle and periods of time running at half to full throttle with not much movement of air across the engine block.

Hopeing the guys on this fourm can point me in the right direction as to what all can be done to this engine to achieve my set goal's for it.

In the end run it just may not be possible with a 2 stroke engine but I'm still willing to research it and see if it could be done.

[Dana]

In general, 2-strokes make their power (and torque) at a much higher rpm than 4-strokes. You can move the power and torque curves around a bit with exhaust tuning, but not that much. Really, you need to play with the belt drive ratio to get it close and then fine tune it with with exhaust tuning, not the other way around.

[turtle]

In general, 2-strokes make their power (and torque) at a much higher rpm than 4-strokes. You can move the power and torque curves around a bit with exhaust tuning, but not that much. Really, you need to play with the belt drive ratio to get it close and then fine tune it with with exhaust tuning, not the other way around.

Exactly. Plus there is more noise with the associated higher rpm.

Considering that airplane props need to spin slow, and slower running engines last longer and make less noise, if it was possible to make a high-torque low-rpm 2-stroke, they'd already be manufacturing them.

[A5BLASTER]

Thanks for the reply's gents soild info so far.

I understand two strokes make their hp and torque at higher rpm level's.

Is it not possible to rework or install a aftermarket camshaft in this engine to adjust the torque and hp curve on this type of engine.

Then turn around and install aftermarket heads and do some piston work to increase the top end rpm's.

Basically that's what they do to the vanguard engines these style of boat motors run to increase hp and torque.

I'm asking because I don't have as much knowledge of this type of engine as I do the 4 stroke vanguard engines.

[A5BLASTER]

Exactly. Plus there is more noise with the associated higher rpm.

Considering that airplane props need to spin slow, and slower running engines last longer and make less noise, if it was possible to make a high-torque low-rpm 2-stroke, they'd already be manufacturing them.

Are maybe the reason no company makes a factory offered two stroke aircraft engine like what I'm trying to build up is because aircraft don't preform with a engine like that.

The useage I'm trying to do with this aircraft engine has never been tried before. And in the end run it just may not be possible to achieve it, but innovation never happens if people don't try.

[martymayes]

What I need to know is how can I go about increasing the am out of torque the f-33 makes and how can I go about getting it to make the torque at a lower rpm rate.

Increasing the amount of torque will be a challenge, lowering what torque it has to a lower RPM is not too difficult, however, "lower" is a relative term; it's still going to be turning faster than the Vanguard. I think you should be able to get performance close to the vanguard.

[Dana]

Is it not possible to rework or install a aftermarket camshaft in this engine to adjust the torque and hp curve on this type of engine.

Then turn around and install aftermarket heads and do some piston work to increase the top end rpm's.

2-strokes don't have camshafts.

No aftermarket parts either, because the production volumes just aren't there.

[A5BLASTER]

2-strokes don't have camshafts.

No aftermarket parts either, because the production volumes just aren't there.


Ok not trying to come off rude or anything like that but. What drives the piston and piston rod up if it doesn't have a camshaft like very other engine does.

I don't know much about these aircraft engines that's why I have come here to find some help

[A5BLASTER]

Increasing the amount of torque will be a challenge, lowering what torque it has to a lower RPM is not too difficult, however, "lower" is a relative term; it's still going to be turning faster than the Vanguard. I think you should be able to get performance close to the vanguard.

How would you go about moving the torque lower in the power band?

I can increase the torque out put to the prop by changing the ratio in the belt pulley's but as I stated above I can only change them so much do to limit on space in the drive system housing.

Thanks for all the replys gents good info from y'all so far.

[Sam Buchanan]

Ok not trying to come off rude or anything like that but. What drives the piston and piston rod up if it doesn't have a camshaft like very other engine does.


It seems you are referring to the crankshaft.

[A5BLASTER]

It seems you are referring to the crankshaft.

Yes I was sorry bout that, my mind is going ten diffrent ways at six diffrent times tonight.

[Bill Berson]

You can change the two stroke ports some for low end torque. But not much change, so not worth it. Best to run as is at medium rpm, say 5000.
I think I would find a different prop to match the higher rpm, if needed.
It takes horsepower to make something move. Not just torque.

But that's another endless debate.

[1600vw]

Ok not trying to come off rude or anything like that but. What drives the piston and piston rod up if it doesn't have a camshaft like very other engine does.

I don't know much about these aircraft engines that's why I have come here to find some help

You keep calling these aircraft engines. While this is true they are built to be used in an aircraft, these are nothing more then snowmobile engines.

Two stokes use porting and some use reed valves, no cam shaft in these engines. Two strokes are totally different engines then a four stroke. Meaning they only share a few common parts. Like crank, rods, pistons. Not even the bearing in a two stroke are like a four stroke. Four stroke engines use what is called a babbit bearing. Two strokes use roller bearings.

Look at a 1/2 vw engine. That would work much better and about as light weight as you will find. The parts are less expensive and can be purchased locally when needed.

The crank drives the piston and rods in any four stoke or two stroke engine. The cam is then geared to the crank. The crank then turns the camshaft by way of gears in a four stroke engine.

Tony

[martymayes]

How would you go about moving the torque lower in the power band?

The easy changes are compression ratio, induction and exhaust length/tuning. If you want to go further, changing the port shape/timing and beyond that, drilling new ports. Lot of people draw the line when I suggest we drill a new hole in a cylinder, lol.

[1600vw]

The problem comes when one does not understand the exhaust on a two stroke plays the roll as the valves in a four stroke. Two strokes have no valves like a four stroke. The OP my find some info here that will help him understand how a two stroke works.


http://eaavideo.org/video.aspx?v=626943072001

[A5BLASTER]

Thank you gents for all the reply's soild info so far.

Martymayes, soild reply Sir thank you. So if I was to do those changes you talked about what kind of gains would I be looking at? And how would that affect the life span of the engine?

Also due to the application of the engine the exhaust would have to be keep to a very short and light weight due to being used on a boat.

The reasoning for changing the torque curve is to better fit the application of the engine, the engine will never hit its designed output due to the constant forces of the water on the prop and as such the engine needs to produce more low end torque to beable to get the boat moving have a small hole shot and get it to plane out. A boat on plane is where it makes speed.

I know I can increase the amount of torque to the prop by way of changing the ratio and tooth count on the belt pulleys, but if I can increase the engines out put I can limit the amount of change to the ratio.

All this is being said, the main reason I want to try and use this engine is to cut down close to 30#'s of weight on the transom of my boat.

In the end run it just may not be possible to use this engine type to replace the heavy engine that is in use now.

[1600vw]

Two stroke engines do not produce gobs of torque. They must spin real fast to produce the power they do. Lower the spinning no matter what you do and you loose this power or torque. If you want a low spinning torque engine stick with a Four stroke. You will never get this out of any two stroke.
Tony