Best Out-tha-Box ported Hi-Perf Motor?

[Loki]

This ole retread's been away from 2-strokes fer decades.
I need a primer on a state-of-the-art bicycle two stroke motor.

Searches revealed - lotsa hi-perf mods; carbs, pipes, DIY porting etc.
Not much yet on the current crop of Out-of-Tha-Box Hi-Performance bike motors.

I'm a bit rusty to get that deep into the DIY scene; can read a plug, do gearing, basic build-em work.

Gasbike, Flying Monkey; have their ported motors that avrg. $300.
Most vendors seem to quote figures of "4-5 hp"
Any one particular 'triple throw-down' Gorilla motor you guys recommend?
If so - why?

Please reply if you have personal experience racing or streeting such a package deal Hi-Perf motor.

Thanks in advance,
RJ

 

[LandSpeedRecord]

If interested I can build you a ported motor to your liking. P.M. me on here and I can provide pics, descriptions and references.
Lee

 

[bahramu]

Best 66cc "out-of-the-box" engines you'll find are completely rebuilt from the crank up by reputed builders. Check out http://www.shop.crmachine.com/category.sc?categoryId=18 and
http://www.arrowmotorizedcycles.com/shop-now---racing-engines.html

 

[Sam90lx]

Check out DAX, I just ordered one of his motors.

 

[bahramu]

Dax sells stock kits from China. A good kit, but all stock.

 

[Loki]

Dax sells stock kits from China. A good kit, but all stock.

Good info ....

I've ordered parts from Dax; was ok for price except I couldn't afford $$$ for the motors.
Shipping was slow compared to others: 2 yrs ago.
That situation has improved a tad since.
All sellers: Warehouse drop ship usually throws a delay in the order cycle.

Balanced motors, like my PK-80, seem to work out better; only now they're going for
more reasonable $ = search.
Hey one seller's offering a 2" big frame mount option!
Just like Prego; it's in there.

Thanks

 

[Loki]

bahramu

Arrow & CR seem to do a credible job on their hi-perf builds ... watched vids.
Since Fed bicycle law says "max 3 hp" one can see why vendors don't like to give out exact
h.p. production figures; e.g. disclaimers "for racing".

 

[bahramu]

Another reason there's no exact HP #'s is no one seems to Dyno their bikes, or if they do they don't publicize it.

 

[Loki]

An interesting approach to calculating theoretical horsepower potential for any engine;
based on it's achievable (survivable) rpm.
Bear in mind, none of the following is 100% certain.

First Rough Method:
The old 'seat of the pants' calc method factors hp using a multiplier of 1.40 for each successive modification.
I picked this up from desert bike racers back in the day.
A stock* two-stroke 49cc motor can maybe achieve peak 8.2 hp
- if it can rev to 9500 rpm and live.
This figure is based on a starting (realistic) rating of 2.5 hp for 49cc.
* this means non-exotic materials and tried & true tuning methods; porting, carb, pipe etc.

More Accurate Method:
Using an algebra formula we can get closer to the truth.
(Displacement*rpm) / 4234.95 = HP
* Assuming a BSFC of 0.45 (which is a great estimate for general NA purposes)
49cc = 2.99016 cu. inches
2.990 x 9,000 = 26911.44 / 4234.95 = 6.35 peak hp @ 9,000 rpm

The real question is; how long can any two-stroke engine survive at this rpm?
One of the possible answers, 'It depends' on the materials used in manufacturing, along
with type of fuel, cooling, ambient heat.

A China motor may rev to 10,000 rpm but it probably won't survive for very long.
That's another reason for manufacturers specifying 32:1 fuel mix.

Knowing what parts cost its no wonder package hi-perf offerings suggest "4-5 hp"
Realizing the above; Will these package motors develop a full 6.35 hp?
A maximum of '5 hp' suggests Out-the-box HT motors will rev to 8500 rpm before signing off.
Cost: Arrows' big block race motor is currently $699 -if ya have a racer number.
That motor comes with no warranty.

 

[sbest]

An interesting approach to calculating theoretical horsepower <SNIPPED>

Interesting but none of this is very... helpful.
HP numbers do not come out of clouds, or grow by 1.40 for everything you do.
They are a measure of work, tangible, measurable and real.
An assumable BSFC is not and certainly is not a backwards tool to measuring HP.
How does Brake Specific Fuel CONSUMPTION even fit into measuring HP?
This is all wrong. It is like using Miles/gallon to measure power.

How to calculate HP?
A practical tool for us is this wonderful site:
Bicycle power calculator
It works by measuring work done against load and is based on real physics and math.

A theoretic tool? PLAN = gross HP
gross HP - friction - other losses = net HP
Average cylinder PRESSURE x LENGTH of stroke x AREA of piston x NUMBER of firings/minute.
Raise any of the above and you will raise HP. Reduce the losses and you gain.

If you want to double the HP at the same rpm, you have to double the cylinder pressure.
No other factor has changed.
If you want to raise the rpm to do it, you have to double it.
Only problem the VE, Volumetric Efficiency drops off with RPM.
Especially with the meager port design of these engines.
Can you double the HP? I believe you can and have done it with other 2 strokes by raising both rpm and pressure while increasing the VE at rpm.

What does this have to do with a boxed HiPerf motor?

Steve

 

[LandSpeedRecord]

There is not a standard dyno that measures these easily accessible or agreed upon at this point so numbers are theoretical at best. The hardest facts you have to go on is reputation and customer experience with the various vendors on this site or recognized by many members.. The short list is Fred Chemilski of CR Machine builder of the actual Fred heads, The motors by Arrow racing, and for quality as a base more so than performance is thatsdax. I am working extremely hard to be on that list and have references from other builders and customers but I'm new trying to market on here but have been developing these motors a long time.

 

[2door]

Along with 'stickers' you'll always want to buy products with the words, "High Performance" "Race" or "Racing", "Speed" and let's not forget "Billet" attached to the advertising hype. Simply using those words will guaranty an immediate and noticeable increase in your power and top speed. There are a few others. "Professionally Designed",
"Nationally Recognized" "Race Track Proven" and "Approved by the National Hot Rod Assoc." you'll want to look for when buying horsepower.

Tom

 

[scotto-]

Bicycle power calculator [/URL]
It works by measuring work done against load and is based on real physics and math.

A theoretic tool? PLAN = gross HP
gross HP - friction - other losses = net HP
Average cylinder PRESSURE x LENGTH of stroke x AREA of piston x NUMBER of firings/minute.
Raise any of the above and you will raise HP. Reduce the losses and you gain.

If you want to double the HP at the same rpm, you have to double the cylinder pressure.
No other factor has changed.
If you want to raise the rpm to do it, you have to double it.
Only problem the VE, Volumetric Efficiency drops off with RPM.
Especially with the meager port design of these engines.
Can you double the HP? I believe you can and have done it with other 2 strokes by raising both rpm and pressure while increasing the VE at rpm.

What does this have to do with a boxed HiPerf motor?

Steve

Just using the PLAN method, how much HP does my 215cc Predator 4-stroke produce......it started out as 212cc @ 6.5HP turning 3,600rpm.

It is now 215cc with 70 mm x 60 mm (bore x stroke). The compression ratio is 15:1 and it turns 9,000rpm. Friction is minimal for this high horsepower application, I just want to see what you come up with these parameters (roughly).

Thanks and look forward to hearing from you!

scotto-

EDIT: forgot too mention I run VP 110 race fuel......110 octane.