2stroke
10-05-2007, 06:53 PM
#21
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dude you are sorely sorely misguided
i dont know how you think a waste spark system decreases emissions.... think of what would need to happen for that to even work.... lets say you inject way to much fuel (which isn't a problem with computer controlled cars anyway) by the time your done with the power stroke there ISN'T ANY OXYGEN LEFT! so it would be impossible to burn any more fuel. Toyota might say its for emissions to convince people that their vehicles are more green than the others guys but its pure propaganda...give yourself a pat on the back you fell for it
the reason a waste spark system even exists is because of simplicity. every manufacturer has been doing this for years. take for example the 3.8 in a buick grand national way back in the 80's 3 coil packs with two terminals on each coil, thats a waste spark setup. any 3800 since then has 3 double terminal coils. same with a lot of the 3.1 and 3100 motors and of course the same goes for the 3400 The northstar 4.6 litre engine uses 4 double terminal coils because its waste spark. This is not done for emission purposes its done because its cheaper and easier 3 coils instead of 6 or four coils instead of 8
i dont know how you think a waste spark system decreases emissions.... think of what would need to happen for that to even work.... lets say you inject way to much fuel (which isn't a problem with computer controlled cars anyway) by the time your done with the power stroke there ISN'T ANY OXYGEN LEFT! so it would be impossible to burn any more fuel. Toyota might say its for emissions to convince people that their vehicles are more green than the others guys but its pure propaganda...give yourself a pat on the back you fell for it
the reason a waste spark system even exists is because of simplicity. every manufacturer has been doing this for years. take for example the 3.8 in a buick grand national way back in the 80's 3 coil packs with two terminals on each coil, thats a waste spark setup. any 3800 since then has 3 double terminal coils. same with a lot of the 3.1 and 3100 motors and of course the same goes for the 3400 The northstar 4.6 litre engine uses 4 double terminal coils because its waste spark. This is not done for emission purposes its done because its cheaper and easier 3 coils instead of 6 or four coils instead of 8
waste spark ignition uses one coil for two spark plugs, both ends of the coils secondary side are directly connected to a spark plug with means that two plugs are ignited at the same time; one is fires on the compression stroke of one cylinder and the other is fired on the exhaust stroke of another. a four cylinder engine has two ignition coils a six cylinder has three, and an eight cylinder has four the computer ignition module, and various sensors combine to control spark timing. the computer collects and processes information to determine the ideal amount of spark advance for the operating conditions. the ignition module uses crank/cam sensor data to control the timing of the primary circuit in the coils. remember that there is more than one coil in distributor-less ignition systems. the ignition module synchronizes the coils' firing sequence in relation to crankshaft position and firing order of the engine. therefore the ignition module takes the place of the distributor. primary current is controlled by transistors in the control module. there is one switching transistor for each ignition coil in the system. the transistors complete the ground circuit for the primary, thereby allowing for a dwell period. when primary current flow is interrupted,secondary voltage is induced in the coil and the coils spark plug(s) fire. the timing and sewuencing of ignition soil action is determined by the control module and input from a triggering device. double ended coil systems are based on the waste spark method of spark distribution. each end of the coils secondary winding is attached to a spark plug. each coil is connected to a pair of spark plugs in cylinders whose pistons rise and fall together. when the field collapses in the coil, voltage is sent to both spark plugs attached to the coil. in all v6s the paired cylinders are 1 and 4, 2 and 5, 3 and 6. (or 4 and 1, and 3 and 2 on 4 cylinders.) with this arrangement one cylinder of each pair is on its compression stroke while the other is on the exhaust stroke. both cylinders get spark simultaneously. this burns any raw fuel left from the ignition of that cylinder. these systems have been shown to have reduced exhaust emissions due to the firing of one on the compression stroke and one on the exhaust stroke.
taken DIRECTLY from a text book, Copyright 2005 Daimler Chrysler Corp.
10-05-2007, 07:51 PM
#22
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Two strokes make a little over half the power on each cycle twice as often.The powerband is influenced by much more than just pipe characteristics.You must consider
port timing.port angle and placement,primary compression ratio,clyinder head design,intake system and length etc, ect.I raced and developed them for many years.
port timing.port angle and placement,primary compression ratio,clyinder head design,intake system and length etc, ect.I raced and developed them for many years.
10-06-2007, 02:12 AM
#23
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waste spark ignition uses one coil for two spark plugs, both ends of the coils secondary side are directly connected to a spark plug with means that two plugs are ignited at the same time; one is fires on the compression stroke of one cylinder and the other is fired on the exhaust stroke of another. a four cylinder engine has two ignition coils a six cylinder has three, and an eight cylinder has four the computer ignition module, and various sensors combine to control spark timing. the computer collects and processes information to determine the ideal amount of spark advance for the operating conditions. the ignition module uses crank/cam sensor data to control the timing of the primary circuit in the coils. remember that there is more than one coil in distributor-less ignition systems. the ignition module synchronizes the coils' firing sequence in relation to crankshaft position and firing order of the engine. therefore the ignition module takes the place of the distributor. primary current is controlled by transistors in the control module. there is one switching transistor for each ignition coil in the system. the transistors complete the ground circuit for the primary, thereby allowing for a dwell period. when primary current flow is interrupted,secondary voltage is induced in the coil and the coils spark plug(s) fire. the timing and sewuencing of ignition soil action is determined by the control module and input from a triggering device. double ended coil systems are based on the waste spark method of spark distribution. each end of the coils secondary winding is attached to a spark plug. each coil is connected to a pair of spark plugs in cylinders whose pistons rise and fall together. when the field collapses in the coil, voltage is sent to both spark plugs attached to the coil. in all v6s the paired cylinders are 1 and 4, 2 and 5, 3 and 6. (or 4 and 1, and 3 and 2 on 4 cylinders.) with this arrangement one cylinder of each pair is on its compression stroke while the other is on the exhaust stroke. both cylinders get spark simultaneously. this burns any raw fuel left from the ignition of that cylinder. these systems have been shown to have reduced exhaust emissions due to the firing of one on the compression stroke and one on the exhaust stroke.
taken DIRECTLY from a text book, Copyright 2005 Daimler Chrysler Corp.
taken DIRECTLY from a text book, Copyright 2005 Daimler Chrysler Corp.
10-06-2007, 09:11 PM
#25
One reason the two strokes make so much power is because the fuel charge is similiar to a supercharged engine. It gets sucked into the crankcase which is larger in volume, then it's compressed, when the piston goes below the intake port the fuel charge is forced in rather than sucked in.
Does anyone remember back in the early 80's there was an article in a dirt bike mag where someone put the head and cylinder of a four stroke on a two stroke engine. They used a pipe going from the crankcase to the intake port. This way it would suck the fuel charge into the crankcase two times, when the intake valve opened there would be a pressurized fuel charge waiting to get forced into the chamber instead of sucking it in.
They called it something like NASC. Which was Normally Aspirated Super Charged.
Does anyone remember back in the early 80's there was an article in a dirt bike mag where someone put the head and cylinder of a four stroke on a two stroke engine. They used a pipe going from the crankcase to the intake port. This way it would suck the fuel charge into the crankcase two times, when the intake valve opened there would be a pressurized fuel charge waiting to get forced into the chamber instead of sucking it in.
They called it something like NASC. Which was Normally Aspirated Super Charged.
10-07-2007, 10:01 AM
#26
Direct injection on a 2 stroke allows fuel to be injected non related to piston movement. In other words fuel is not injected untill the piston closes the exhaust port....this is when a 2 stroke is dirty...when fresh air & fuel is pushed out the exhaust port. Current 2 stroke technolgy creates cleaner burning engines than 4 strokes...less fuel consumption....more power...less oi consumption...blah blah. 2 strokes do not make twice the power because the power stroke is limited to when the exhaust port opens.
10-07-2007, 03:00 PM
#27
Direct injection on a 2 stroke allows fuel to be injected non related to piston movement. In other words fuel is not injected untill the piston closes the exhaust port....this is when a 2 stroke is dirty...when fresh air & fuel is pushed out the exhaust port. Current 2 stroke technolgy creates cleaner burning engines than 4 strokes...less fuel consumption....more.
Thats an incomplete sentence--twice the power of what?
They do make twice (rough estimation) the power of a similiar sized four stroke.
10-07-2007, 10:20 PM
#28
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Subscribing... I gained respect for two strokes after riding two quads back to back, one a 700cc 4stroke, the other a modded Honda 250R... more "usable" poweband on the big 4 stroke for sure, but man when you hit that pipe watch out! They call it the lightswitch for a reason! Even with over twice the displacement I'm not so sure it could have caught that little 250... quite impressive.
10-08-2007, 12:10 AM
#29
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I have to agree that 2-strokes are becoming a thing of the past, I sure do miss watching moto x and not hearing the high pitched screaming sound of a 2-stroke. I've driven a 4-stroke snowmobile before (yamaha warrior) and I was not at all impressed. It was a smooth power but it felt like there was no torque at all, sure they get good gas mileage and last longer but it didn't seem as fun and it also weighed alot. Hopefully in time they will be better than a 2-stroke but it seems hard to believe. On a side note the rotax motors in ski-doos are very efficient, getting around 20mpg and making lots of power unlike my old '02 800 that gets about 10mpg and doesn't make anywhere near the power.
10-08-2007, 09:56 AM
#30
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Now by the sound of ctd's post it looks as if the two stroke might be up for another round with the advent of di and other technologies... anybody else heard this?
10-08-2007, 06:51 PM
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I had to sell my KX500 a couple years ago to purchase my 1998 Z28. A great trade in my opinion, but I find myself missing that 2-stroke 'punch' at about 5000RPM. I will again buy a 500cc 2-stroke, I am just hoping they won't completely ban 2-strokes from ever being run again.
Also, one aspect that hasn't been brought up yet is how quickly the 2-stroke engine changes RPM. I once read that (for motorcycle applications) the 4-stroke was great for long term steady state cruising, while the 2-stoke was more for quick throttle changes.
I know new 4-strokes are getting better, but no 4-stroke will ever have the same unique and now extinct powerband and sound of the all-mighty 2-stroke!!
10-09-2007, 08:06 PM
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Aprilia, Piaggio (Vespa), Peugeot Motocycles, Kymco (Kwang Yang Motor Co Ltd),Mercury, Bombardier (Sea-Doo),Tohatsu,
http://www.orbeng.com.au/orbital/dir.../technical.htm
10-11-2007, 11:35 PM
#36
IMO, the main purpose of 2 strokes is a good HP/$ ratio. They are much simpler because of fewer parts. As a side benefit, with the notable exception of 2 stroke diesels, they can run and be adequately lubricated in any 360* orientation. Trying to "upsize" these motors or "modernize" them with expensive new technologies seems to me a misapplication of their core benefits.
10-12-2007, 12:30 PM
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I was also thinking about that the other day gametech.
They don't have engine lubrication other than the fuel/oil mixture.
How much HP alone is gained in lack of windage? I know it is not too significant, but that is one other advantage(as well as less weight) of the 2-stroke.
I do think, though if a DI could be placed on a 2-stroke, keeping most other parts the same, they could still be relatively simple, yet be able to catch up the the 4-stroke in the cleanliness department.
It's not likely, but I can dream right
They don't have engine lubrication other than the fuel/oil mixture.
How much HP alone is gained in lack of windage? I know it is not too significant, but that is one other advantage(as well as less weight) of the 2-stroke.
I do think, though if a DI could be placed on a 2-stroke, keeping most other parts the same, they could still be relatively simple, yet be able to catch up the the 4-stroke in the cleanliness department.
It's not likely, but I can dream right
10-13-2007, 06:04 AM
#38
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hmm you could put in a miller-cycle cam with a 1:1 timingchain and a positive displacement blower.. that way it would be 2-stroke (miller-cycle.. whick is an overhead valve 2 stroke.. and to you people about to flame me about differences between 2 and 4 stroke engines, google miller-cycle.. and read BEFORE you post)
10-13-2007, 10:07 AM
#39
I was also thinking about that the other day gametech.
They don't have engine lubrication other than the fuel/oil mixture.
How much HP alone is gained in lack of windage? I know it is not too significant, but that is one other advantage(as well as less weight) of the 2-stroke.
I do think, though if a DI could be placed on a 2-stroke, keeping most other parts the same, they could still be relatively simple, yet be able to catch up the the 4-stroke in the cleanliness department.
It's not likely, but I can dream right
They don't have engine lubrication other than the fuel/oil mixture.
How much HP alone is gained in lack of windage? I know it is not too significant, but that is one other advantage(as well as less weight) of the 2-stroke.
I do think, though if a DI could be placed on a 2-stroke, keeping most other parts the same, they could still be relatively simple, yet be able to catch up the the 4-stroke in the cleanliness department.
It's not likely, but I can dream right
Too late, its been done. Evinrude outboards are DI 2 strokes, with much less weight, lower emisions, better fuel economy, and nearly twice the low end torque of 4 strokes, with fewer than half the moving parts, and no engine oil, or filter to change ever.
Dirt bikes have gone 4 stroke because of emsisions regulations before the technology was present to build a clean 2 stroke. To please the manufactures (who cant sell 2 stroke bikes in CA no matter how clean running they are), AMA allowed 4 stroke bikes nearly twice the displacement, of the 2 strokes. even then it took years of r&d for them to compete.
The argument for 4 strokes in snowmobiles, is pushed by Yamaha, who have lots of 4 stroke engines they have developed for other applications, and are slapping into sleds because its cheaper than developing new engines specifically for snowmoble use. The rest of the manufactures are staying 2 stroke because of the the power to weight, and the fact that snowmobile drive trains are 100% CVT, unlike dirt bikes. With a CVT the engine is always in the "powerband".
Here is some ricer math for you. A company "BMP" has developed a $1,700 dollar bolt on package for the arctic cat 1000 cc, 2 cylinder 2 stroke engine, that raises it to 250 hp, and 160 ft/lb TQ, on pump 92. or a 1000 hp, 640 lb/ft 4.0 L V8, weighing less than 500 lb
10-13-2007, 10:16 AM
#40
Back on topic. To convert an ls1 to 2 stroke you would need a camshaft and 1:1 drive system, a large supercharger (able to move at least 5.7 l of air per crank revolution), and computer remap. A properly tuned exhaust system is critical to making big HP from a 2 stroke, so you would need to develope 8 individual expansion chambers, the outlets of which can run into a normal exhaust system.