I had an 80 El Tigre 440, stock dual carbs and stock exhaust with a Comet clutch. I don't remember when the clutch engaged, but I think it was something like 3000, and from there it pulled really hard all the way to whatever full throttle, 95mph was. Taking off in deep powder, or whatever, it didn't lag, then 'hit hard' like the quads that I rode. It certainly made the most power when it was up in the high end of the revs, but it wasn't all or nothing.

 

Was it a 5000 or 6000 series? Mines got a distinct pull. I've never drove a fully moded 2 cycle atv, so maybe I don't know.

 

k i guess ya that since their is a complete stroke that pushes exhuast gasses out it would be easier to push them out with less back preassure. this would save more inertia of the crank for the new set of strokes. but ya i forgot about valve overlap. so the performance exhuast would do a better job of ridding of all exhaust gasses. valve overlap is done for emisions it keeps some exhaust in the chamber for the new cycle. this gets rid of some sort of acid that is produced or something like that. and that is why 2 strokes respond better two pipes. its because the perf pipe sucks more gasses out of the chamber since there is no valves that define the cycles. isnt that what i said? thats what i meant anyway

 

6000 Water cooled
Not sure how the 5000 was different, but with my Panther 5000, it was a 500cc single carb, and the Panther 4000 was a 340 or something like that.
I contemplated putting the dual carb setup on my Panther from an El Tigre, that would have been cool, but ended up parting it out for cash. *sigh* my young foolish days.

 

Is there not an event during the cycle where the exhaust valve begins to open towards the bottom of the power stroke, and there is still gas expanding from the burning air/fuel mixture? If your exhaust is less restrictive in that case would the initial pulse moving past the exhaust valve result in a more complete emptying of the exhaust from the cylinder, thus allowing more fresh air to be drawn in for the compression stroke? Then more fuel would be needed hence fatter jetting. Just a thought.

These things are a lot different than a car engine with headers that created a negative wave and suck the turds out, like them guys holding the horses head in the water trough and trying to make him drink...........

 

I dont know about you guys but that turd story was not needed. And i think that the guy who made up the story about the TURDS is a little KOO Koo!

 

Yes, that's normally the case. Take these cam specs for instance. From a Ford v6 but what the hey, it's common 4 stroke theory.http://www.msnusers.com/RangerBill/3...fications.msnw
See where the exhaust valve begins to open at 32 degrees before bottom dead center. The gasses are still expanding alright and they still are the whole time, but you have to start getting rid of them. If you could make the valve snap fully open instantly it might be effective to wait until the piston is right at BDC before whacking the valve open in order to get all the energy possible out of the burning, but among all the other things a cam designer has to consider is designing an opening ramp that the tappet or lifter will follow without so much accelleration that it flies off the top of the lobe at the RPM the motor is to run at or that requires such spring pressure that excessive wear and early failure is to happen. Even in the case of roller rockers the lifter wheel must be a certain diameter to have a strong enough axle and to have roller bearings and so this diameter roller will not follow a cam profile that opens too sharply. The lifting force would be exceeded by the lateral force and you'd break the lifter off sideways unless your cam was a great size.
Mercedes Benz and Ducati are the only manufacturers to successfully have built desmodromic four strokes with a cam to open the valve and another reverse ground cam to close the valve by means of a forked assembly acting on the valve stem. This does away with valve springs and the consequent need for the engineer to need to consider the reciprocating mass when designing his profile. These motors are however quite complicated and need a good bit of setup. Great power and torque though, and never have to worry about putting a valve through a piston!

Scavanging is the word. Yup, it's all the same technology. The carb throat of a given diameter is jetted from the factory to provide the optimum mix (at the altitude considered) for the airflow that motor will draw at its intended full throttle RPM range. When you do whatever it is to cause a faster flow of air than this, be it displacement increase, cam change, higher operating RPM, or opening the exhaust up, whatever, you need to up the main jet size. The venturi effect that draws the fuel through the main jet can only pull so much fuel through that hole. When you draw more air, ya gotta mix more gas.
For the cam profiler it's all about compromises. Sacrifice a bit of this for some more of that. It carries on with the hop up. What you're doing is setting your own standard of compromises. More power output at the expense of a narrower powerband. Better breathing at the expense of a louder exhaust. Higher lift cam, possibly needing stronger springs at the expense of faster wear and shorter life. More power because fuel is being burned faster= poorer milage. And all this time you'll hope that the designer of the casings and transmission has engineered in enough margin of safety to permit you to get a given percentage more power from the machinery and not experience failure of the castings, bearings or gear train. That's why bigger displacement motors have bigger everything.

Anyway that's for the first guy's question.
" i just dont understand why you need to rejet a 4banger if you put an exhaust on" ..."so whats it all about???"
When you hop it up, that means your getting more air through. You need more gas to go along with it. That's what it's all about.

 

Great post Glenlivet. Very well said!!!!

 

well i got the scoop from my mechanics teacher who has been right for all the questions ive asked him so far. anyways he says that on the exhaust stroke with the piston moving 6 to 8 times a second at that speed when the exhaust valve opens it can a and will in lots of cases compress the exhaust gasses and not allow all of the to flow out. this also takes more inertia from the flywheel. these gasses will be left for the new intake stroke.