What will break first

W

WorkingOnWise

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In planing my project, I reallllllly don't want to go past the 49cc limit, but I also really need at least 3hp, and closer to 4 to be realistic, to do what I want. My bike plans are discussed in the thread "Heavy Hauler Project".
I did some quick math and found that a 49cc engine is 3 cubic inches. I have build several high performance engines, and it has never been a problem to get a reliable 1hp per c. i. d. out of an automotive engine, and still be very ''streetable" 1.25hp per cid was in reach if I was willing to give streetability and gas milage, and 1.5hp per cid was doable if I as also willing to give up durability as well. That translates into a 350hp Chevy 350, a 430hp, and 525. A 350hp 350 is a very fun engine, good power, good gas mileage (for a V8) and very streetable.
Now, to bring those numbers to a bicycle engine, I know we are talking a 2 stroke and not a 4 stroke, but a 2 stroke will typically get you higher hp numbers that a comparable size 4 stroke.
So, what do I not know that explains why we don't see 49cc 4hp 2 strokes? That's what I need for my project. Is it just a matter higher compression and a stronger connecting rod? I assume the crank in a typical 2 stroke in not a weak link, and in my experience, cranks fail from vibrations and lack of lube, rods fail from rpm's and compression pressure.
If I build a super strong rod, say from titanium, and bumped the compression to 11 to 1, would I have a 49cc 4hp engine I could rely on? What would break then?

Thanks
Keith
 
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11to 1 wow thats alot of compression to turn over u migh rip the sprocket off the spokes lol it would be pretty tourgey tho and race fuelli think is 7 dollars a gallon i would get a dax 70 , they look the same as a 50 an are preety good engines with care.
 
Tanaka 47R is 2.8hp in stock trim. Add their expansion chamber along with their jetting recommendation and you will prolly see 4hp. Reliable horse power at 50 to 1 oil ratio.

Search the posts of Egor, he had something real to say about porting these Happy Time 2 strokes. If you can afford to blow one up you might end up with a real power house of an engine.
NOTE: Make sure the rod's small end has a roller bearing and not a weak bronze bushing.
 
Ratroder,
I looked at those engines. If I bought one of those, I'd never be able to ride the bike, cuz, well, my very understanding wife would Kill me! $138 per hp! If I coulda charged that building car engines, I'd be set! Lol

Gauge,
I didn't consider the fact that I'd have to start it somehow! At 11 to 1, pull starting is not practicle, huh? A kick starter st too much like a motorcycle. An electric starter will add to much weight, which is one reason for me not wanting to go above a 49cc. Maybe one of those wind-up spring loaded starters like what was on some briggs motors would work?
 
i have one of those spring loaded staters on my leafblower i hate it it sometimes gets stuck , but whats the real reason ure staing 50cc
 
Yeah, I spent a good bit of time beating on those wind-up starters myself! I think it was wind wind wind release, wind wind bang wind release, and it started =-)

Well, the reasons for staying under 50cc are :
1) Weight - I need to be able to carry the bike up and down stairs.
2) Physical size - I don't want to have to hack and grind on the bikes frame.
3) Efficiency - gas mileage
4) legality
5) The "wow" factor of being able haul the whole thing around at 30mph, getting 120+ mpg from a weed whip!
 
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One of the Honda/Clone 4 strokes should have the umph you are wanting. You need torque more then HP. You will be sacrificing speed for torque. Check out http://davesmotors.com they have some below 49 cc engines cranking our 4 plus HP.
 
(dahbigkahuna )he wants a light weight bike so 4 strokes are out of this discussion, but does anyone know the diffrence in weight betweeen the dax 50 and 70
 
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