What will break first

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WorkingOnWise

Guest
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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gauge

Guest
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.
 
O

OldPete

Guest
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.
 
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WorkingOnWise

Guest
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?
 
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gauge

Guest
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
 
W

WorkingOnWise

Guest
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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dbigkahunna

Guest
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.
 
G

gauge

Guest
(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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