2 stroke thread (with occasional F1 relevance!)

[flynfrog]

A-125..
How can you possibly make the call - on what anyone else but yourself - finds boring?

As I noted, my last dirt bike was a KTM 380 2T, & so no, aint no 4T 450 gonna impress me much, power-wise..

Here's an example of the kind of fun a bigger cc 2T provides.. https://www.youtube.com/watch?v=DxqPMR9MCx4

I did take the opportunity to have a ride on a 250 4T yesterday though, & it was - IMO - most def' "boring"..

JAW. Unless your KTM 380 2t is highly tuned, it has less peak power than any of the full face 450s, as current MX 450s make close to 60hp at the rear wheel. A KTM 380 2t is an off-road bike with a much less aggressive engine than an MX bike.

[J.A.W.]

At all the run what you brung meetings I have attended, the cars always lapped faster.
Perhaps one day we will find a way to make bikes corner as fast as cars.
Aero?

Well, A-G - what I can add is - that either those bike riders were bunnies or it was an F1 test session..

It is the aero-down force of formula race cars that makes the difference, road-type cars are not quicker..

At the Phillip Island GP circuit the quickest lap by a modified production AWD turbo Mitsubishi Evo is
'bout the same as the best lap done by a 250cc ( 2T of course) production Aprilia ( Suzuki engine) bike.


& there are cheap dirt bikes for play & dirt bikes purpose for competition - the latter are - say in the case
of KTM's 2Ts - available in MX or enduro set-up, but are based on a common design.

It is fairly standard procedure to mix 'n' match the engine parts to detune an MXer for off track/enduro
use, & to use MX parts to boost the power of the enduro models..

I have a moderately tuned ( ~100hp) 750cc Kawasaki 2T triple in a light Yamaha chassis as a fun roadbike,
- it can put more strain on your arms under acceleration than any 450 4T single - I can assure you..

[J.A.W.]

The scale is not proportional I´m afraid, or 500 2t should be around 100hp when they around 60 as much

What I mean is from 250 category bigger engines do not increase peak power at same scale, their power band is wider, flatter and more powerfull at low revs, but peak power does not increase that much

Well, here is some education for you guys on what power is obtainable from a basic 500cc 2T cylinder..

Anyone want to build a chopper? L.O.L... http://www.4x4tuff.com/ctsme8.html

[J.A.W.]

JAW. Unless your KTM 380 2t is highly tuned, it has less peak power than any of the full face 450s, as current MX 450s make close to 60hp at the rear wheel. A KTM 380 2t is an off-road bike with a much less aggressive engine than an MX bike.

Actually f-f, do please provide the dyno comparison to back your claim..
& it is neither difficult nor 4T expensive to get a KTM 380 to make more power - if you want it..

http://www.rpmmfg.com/BigBoreStrokerKTM410.aspx

[uniflow]

Am I back in yet? I think I've been locked out, too much M/C talk maybe?

[FW17]

Why does the power fall drastically in a 2 stroke? Is it because the expanding gases leave through the exhaust port

Can this not be controlled with a longer stroke or blower?

[uniflow]

Why does the power fall drastically in a 2 stroke? Is it because the expanding gases leave through the exhaust port

Can this not be controlled with a longer stroke?

They run out of blow down time, time for the gas pressure to drop below the trasnsfer pressure. At this point transfer gasses get pushed back down into the crank case for a time before transfer can occur. Run out of time to do stuff.
That is why this new concept FOS type cylinder offers hope for higher rpm as it has loads more blow down time / area And more transfer time area by way of extra transfer ports where the lower part of the exhaust port used to be.

Also it's a function of pipe length, you start moving past it's resonance range But this also can be changed by on the fly pipe length changes or tricks to modify wave speed ( retard ignition and heat the exhaust gases more ).

[J.A.W.]

Am I back in yet? I think I've been locked out, too much M/C talk maybe?

Don't - U - worry about that..

The car world still has some way to go to match that showroom road-legal output of..
.. 2T Suzuki/Aprilia N/aspirated.. ..280hp/litre..
.. from years ( decades) ago..

[FW17]

Why does the power fall drastically in a 2 stroke? Is it because the expanding gases leave through the exhaust port

Can this not be controlled with a longer stroke?

They run out of blow down time, time for the gas pressure to drop below the trasnsfer pressure. At this point transfer gasses get pushed back down into the crank case for a time before transfer can occur. Run out of time to do stuff.
That is why this new concept FOS type cylinder offers hope for higher rpm as it has loads more blow down time / area And more transfer time area by way of extra transfer ports where the lower part of the exhaust port used to be.

Also it's a function of pipe length, you start moving past it's resonance range But this also can be changed by on the fly pipe length changes or tricks to modify wave speed ( retard ignition and heat the exhaust gases more ).

In a 4 stroke the volume of cylinder is the complete cylinder say a 250 cc cylinder

A 2 stoke of 250 cc should actually have a cylinder capacity of 500 cc considering the bottom 250 cc as the area with the ports.

So if the same volume of air is in a 250 cc 4 stroke and 500 cc 2 stoke the work done in both the engines in its power stoke has too be the same right?

So if the 4 stroke is at 10000 rpm and 2 stoke is at 5000 rpm both will have same piston speed and same power and efficiency?

[wuzak]

So if the 4 stroke is at 10000 rpm and 2 stoke is at 5000 rpm both will have same piston speed and same power and efficiency?

No, the $T's piston speed will be double (assuming teh same crank throw).

The 2T will have slightly less air throughput. Power and efficiency depend on a lot of things, but I wouldn't expect them to be wildly different.

[J.A.W.]

No, as W correctly points out ( & this very point was discussed a few pages back)..

Suffice to say, the cylinder ported 2T could fairly be measured - swept volume-wise - from TDC to exhaust port..

So rather less - in fact - than the apparent hot gas/working volume of the 4T..

( & hilariously accurate Freudian slip/typo there W, 4T = $T.. indeed)

[FW17]

So if the 4 stroke is at 10000 rpm and 2 stoke is at 5000 rpm both will have same piston speed and same power and efficiency?

No, the $T's piston speed will be double (assuming teh same crank throw).

The 2T will have slightly less air throughput. Power and efficiency depend on a lot of things, but I wouldn't expect them to be wildly different.

I assumed a case were

4t = B x S
2t = B x 2S

[FW17]

Why does the power fall drastically in a 2 stroke? Is it because the expanding gases leave through the exhaust port

Can this not be controlled with a longer stroke?

They run out of blow down time, time for the gas pressure to drop below the trasnsfer pressure. At this point transfer gasses get pushed back down into the crank case for a time before transfer can occur. Run out of time to do stuff.
That is why this new concept FOS type cylinder offers hope for higher rpm as it has loads more blow down time / area And more transfer time area by way of extra transfer ports where the lower part of the exhaust port used to be.

Also if the exhaust and inlet ports are powered, remain closed during the entire down stroke and opens only during the up stoke and a high pressure blower is used to charge the cylinder; theoretically does this problem go away?

[J.A.W.]

W-F1.. ..check the ideal Carnot cycle.. the 4T just buggerises around.. ..for 1/2 the time..

[FW17]

W-F1.. ..check the ideal Carnot cycle.. the 4T just buggerises around.. ..for 1/2 the time..

Yes it does but so is the 2 stoke for about half the stroke