RAW 80cc 2 stroke performance upgrades

BostonBiker said:

Any of you guys watch the tour de france? those guys bomb hills at 60+ mph... and theyre bikes DONT have motors, or disc brakes lol. just saying, it is possible, but like most of you said, no way in **** i would want to do that lol....

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Keep in mind that those tour de france guys are riding the finest bikes (with the finest brakes) that $$$ can buy!, Unlike so many guys I've seen here who are slapping engines on $20 yardsale bikes & want to "hot rod" them to make them go as fast as possible.

Anyone know the "Death Race" top speeds? Custom builders & dealers trying to blow up their bikes?

I'm kinda curious myself now lol

These crazy bastids;

http://motorbicycling.com/f15/death-race-09-a-7506.html

I heard tell they might be lurkin' around here somewheres...

o.o

it was a short track with no long runs to pick up speed
last year I hit 40 on a long run through the saguaro nat'l park
happy (spunout) walked away from me like I was standing still !!!

So it seems that happy would be one to stalk for some feedback on this "50mph" thing, although ya gotta wonder how many chinagirls have disemboweled themselves under his "care"

TBH, I'm quite satisfied with the 30ish my bike does, she tries to do more but what with the stock sprocket and pretty much no level straightaways around these parts I doubt I'll ever see any faster.

Yet because of these twisty roads 30mph on a bicycle is quite exciting. There's a (very) winding two lane by my house that's pretty much unpopulated, as the speed limit is 25mph I needn't worry about traffic coming up behind me and I take my bike out there to try and rip the knobbies off from time to time.

That old road is gonna be the death of me

moosinatrix said:

well brakes isnt the issue these brakes are designed to lock up the wheel if necessary,

Ever hit the brakes on a bike at 50? Locking up a wheel at 50 is not your best bet if you want to live long. what im worried about is traction. Also bike can do 50+ bone stock, i used ot get towed behind a truck at 50MPH and launched into a lake all the time! granted such speeds require much much more routine maintenance to the bike itself I.E. tightening bearing and other such important nuts/bolts, as well as keeping all moving parts well lubricated. Yes, but a quick ride into the lake is not sustained speeds with 5 hp driving through the rear wheel, is it?


and whoever said bikes werent meant to do speeds in excess of 40.... tell that to the person who invented the motorcycle. the first motorcycle wasnt much more then a biike with less mechanically sound parts and a motor strapped to it. The first motorcycles also only went around 15-25 mph...better go back and do some research on this before you start throwing money and time at making a motorcycle out of a slow, crude motorized bicycle. Technology has vastly improved since then and i should think bike could withstandalot more then what they did back then.

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That's all I'm sayin'.

O.K., I'll ad a couple more things....

First off, I am not trying to harsh your buzz, squash your dream, or otherwise ruin your day. If getting a crudely manufactured bicycle engine to run well enough to push a (hopefully) quality bicycle down the road at 45-50 mph, be my distinguished guest.

That's not really what these in frame chinabuilt kits are about.

If you want to make a bicycle, especially our typical run of the mill cruiser or mountain bike go really fast, you will need either a lot of time, money, testing, and patients, or 9 lives.

Stopping is crucial unless you want permanent assisted living care or a funereal. The typical bicycle brake is made to stop a bike and rider from 10 mph, not 15 extra pounds from 25 or 30 mph much less 50 mph.

In frame chinabuild engines make about 1.2 hp, you will need to make about 4 to get near 50 mph, and then transmit that power through the bicycle wheel. (once again, not made for the task, especially the walmart type of cheapo hubs!) If you can cheaply and easily increase the hp output by 300% you should be a formula one engine designer, or working for one of the major motorcycle companies.

The frame is also not made to have 15 extra pounds mounted up to it, vibrating wildly as you turn the engine up to 10,000 rpm. Oh yeah, you are gonna have to turn some rpms to go 50 unless you can get that baby to make some gorrilla like torque figures down lower in the rpm range and use a shift kit or other form of gearing to go 50 mph.

O.K., now I'm done.

I have a 50cc with a 36tooth sprocket, stock exhaust and a dellorto 12mm carb. Ive gone 37 on flat ground and 40 on a slight downhill with my motor in gear. If you had a 27 tooth sprocket this same rpm would achieve 50mph exactly, so its not impossible. I just bought a 66cc engine and i'm breaking it in at the moment, i have a sbp tuned pipe but the engine still 4 strokes all day. i plan to install a 27 tooth sprocket some time after break in and i plan to cruise at around 35. I am confident i will be able to do 40+mph and il let you know how much that + comes into play. I think the carb will be maxed out soon so il have to look for a 14 or 16mm.

Also, a shift kit does not increase your top speed more than a single gear. It just gives you better acceleration.

For top speed, no air filter is best.

One more thing, i wouldn't worry about brakes. Assuming you aren't going to be cruising all day at 50mph on a bicycle, you should slow down fairly quickly from that speed just from drag alone. I only had a front brake for most of the 1500 miles i put on my bike. Don't get me wrong, i replaced brake pads all the time, but you should have the common sense to avoid going to your top speed in busy areas, and in an emergency situation, standard rim brakes work fine(though the rim can get pretty warm).

You can always go faster

Here we go again with the theoretical armchair racing... "a 20T rear sprocket @ such n such RPM should make my bike go 60 MPH.... yadda yadda..."

The higher the gear, the more torque the engine needs to get back up to those RPMs... these engines just don't have any torque!!! this has all been argued here before.

& when clocking for top speed, DOWN HILL DOESN'T COUNT!

The day when someone ACTUALLY BUILDS a bike that can go 50MPH on flat ground; bring it out & prove it! stop talking about it, because so-far no one has been able to prove it yet!

I don't want to discurage anyone from tinkering & trying... but so-far, the "best of the best" MB builders haven't been able to do it!

VENICE BOY said:

Here we go again with the theoretical armchair racing... "a 20T rear sprocket @ such n such RPM should make my bike go 60 MPH.... yadda yadda..."

The higher the gear, the more torque the engine needs to get back up to those RPMs... these engines just don't have any torque!!! this has all been argued here before.

& when clocking for top speed, DOWN HILL DOESN'T COUNT!

The day when someone ACTUALLY BUILDS a bike that can go 50MPH on flat ground; bring it out & prove it! stop talking about it, because so-far no one has been able to prove it yet!

I don't want to discurage anyone from tinkering & trying... but so-far, the "best of the best" MB builders haven't been able to do it!

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Ahhhh... another voice of reason. Very rare around these parts.

IL keep you updated Venice boy

I must apologize; I saw this earlier today and failed to note the website.... A builder of a bicycle with a 80/66 cc engine welded together a "Y" shaped intake manifold and placed TWO standard carburators on the manifold. He stated his low-end torque was much better. There was no frame clearance problem.

The "Y" manifold was welded stainless steel, judging by the heat colorations. The slide cables were simply lifted by the single throttle cable. The carbs slid on just like on a single input manifold.

It looked simple enough. A "T" shaped input would probably work almost as well and avoids welding between the two arms.

I don't have a welder, but if anyone tries this, I'd be interested in knowing if the engine performs any better.

MikeJ

MikeJ said:

I must apologize; I saw this earlier today and failed to note the website.... A builder of a bicycle with a 80/66 cc engine welded together a "Y" shaped intake manifold and placed TWO standard carburators on the manifold. He stated his low-end torque was much better. There was no frame clearance problem.

The "Y" manifold was welded stainless steel, judging by the heat colorations. The slide cables were simply lifted by the single throttle cable. The carbs slid on just like on a single input manifold.

It looked simple enough. A "T" shaped input would probably work almost as well and avoids welding between the two arms.

I don't have a welder, but if anyone tries this, I'd be interested in knowing if the engine performs any better.

MikeJ

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I'd be interested in knowing how that could work myself....one would think it would simply drown the motor ?......insights anyone ?

Laters,
Salty

probably talking about mine. i would normally use a 16mm dellorto, but at the moment i didn't have one but needed way more airflow than i had with the one stocker. the obvious solution was two. it does not work as well in the mid range as a 16 mm single, but they get me to 40 in the end. you definetely have to be gradual with the throttle but the perfomance is there for a modified motor. on a stock motor i don't think it would run too bad, but it probably wouldnt give you more than a few mph.

sweet looking set up there .......I reckon if you just dial them in there right they work well once you learn how to work the throttle......what kind of bike is that set up in ?

Laters,
Salty

A. That's Real cool

B. To improve the mid range I would think you could attach the throttle cable to a lever arm with 3 holes in it. The two carb slides would be attached to either end of the arm while the middle hole connected to the throttle cable would be slightly off-center. This way the carbs would open one after the other rather than in parallel. You should have far better progression through the throttle ranges this way.

just a thought

Yeah actually, good point Prasinos! I had a dual carb/single cyl Honda XL250R, the second carb was on a "cam" so it wouldn't open until the throttle was about 1/3rd twisted. In this fashion the second carb acted a lot like the secondaries in a 4 barrel carburetor.

As it was a four stroke competing with two strokes, I assumed it made up for the lack of a pronounced powerband - it was quite effective in this too.

BarelyAWake said:

Yeah actually, good point Prasinos! I had a dual carb/single cyl Honda XL250R, the second carb was on a "cam" so it wouldn't open until the throttle was about 1/3rd twisted. In this fashion the second carb acted a lot like the secondaries in a 4 barrel carburetor.

As it was a four stroke competing with two strokes, I assumed it made up for the lack of a pronounced powerband - it was quite effective in this too.

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excellent ideas y'all....am wondering if when the second carb opens up if it would open entirely at full throttle......since the cable can only go so far ?.....thoughts anyone?

Laters,
Salty