Things you learn, may be true

"Cé hé sin" (michael-m-mouse)
12/02/2019 at 16:32 • Filed to: Two stroke, Smoke

I asked the internet, as you do, for its opinions on the relative efficiency of the two stroke engine as compared to the four strok e variety and received answers, some of them true.

Here are a few answers, some or all of which are complete male cow droppings. Can you identify which, if any, are true?

1. Two strokes are less fuel efficient because they use fuel each time the piston goes down rather than every second time.

2. Two strokes have poorer durability because they need to run at much higher rpm

3. Two strokes are always less fuel efficient

4. Two strokes produce twice the power of a four stroke

Answers after the smokiness.

1 is rubbish

2 is more rubbish (they usually are less durable but that’s not why)

3 is sometimes wrong. Small two strokes like you have in a chainsaw or an old bike are inefficient but the huge diesel ones you find in large ships are the most fuel efficient engines available

4 is exaggerated. Two strokes produce more power than a normally aspirated four stroke but not twice as much

DISCUSSION (11)

Manwich - now Keto-Friendly > Cé hé sin
12/02/2019 at 17:05

#1 sounds especially stupid.

I think the problem with #3 is that in a lot of cases, people compare an old 2 stroke or a poorly tune 2 stroke with a much newer 4 stroke.

A modern 2 stroke can be very efficient and having half the strokes per cycle gives it a natural efficiency advantage.

As for people who say they have poorer durability, clearly they’re not familiar with one of the most popular heavy duty diesel engines ever... made from 1938 to 1995 :

https://en.wikipedia.org/wiki/Detroit_Diesel_Series_71

Cé hé sin > Manwich - now Keto-Friendly
12/02/2019 at 17:09

Sure is. The first two are here

I’m not sure if those DD engines were ever much used outside America though.

HammerheadFistpunch > Cé hé sin
12/02/2019 at 17:16

I was going to say...these are all wrong.

Modern 2 stroke outboards are usually slightly more efficient that comparable 4 strokes, if for no other reason than they are generally much lighter.

Manwich - now Keto-Friendly > Cé hé sin
12/02/2019 at 17:17

They were used in tanks in WW2 at the very least :

https://en.wikipedia.org/wiki/Detroit_Diesel_Series_71#WWII_General_Motors_6004/6046_engine

just-a-scratch > Manwich - now Keto-Friendly
12/02/2019 at 17:26

...and the 12 V- 71 is one of the best sounding engines ever made.

Future next gen S2000 owner > Cé hé sin
12/02/2019 at 17:35

Like most things in life, the answer of course is, it depends. State of tune, maintenance, design...all that. Although the 2 stroke in heavy ships is new to me. I didn’t realize they where 2 stroke diesels.

Case in point, the on-going 2 stroke vs 4 stroke outboard battle. The new Etec’s are amazing and arguably better than various 4 stroke competitors from Mercury, Yamaha, Suzuki, and Honda. Pro’s and con’s to both sides. Even emissions are way down on modern 2 strokes.

Manwich - now Keto-Friendly > just-a-scratch
12/02/2019 at 17:37

MultiplaOrgasms > Cé hé sin
12/02/2019 at 17:49

Not per se, but similar two stroke diesels were built by several manufacturers around the world in the 1950s and 1960s. The UK had Foden and the Commer Opposed Piston engines, Krupp in Germany had them, obviously the Soviets copied the Detroit , even Nissan built a line of uniflow two stroke diesels for their Nissan Diesel Trucks (that was also where the UD name originally comes from, Uniflow Diesel )

Cé hé sin > Future next gen S2000 owner
12/02/2019 at 18:15

Two stroke diesels are quite different to their petrol counterparts. Nothing happens below the pistons so they can use conventional lubrication and they also have exhaust valves. Marine ones are especially odd because they have an enormously long stroke and a kind of two part conrod.

Cé hé sin > MultiplaOrgasms
12/02/2019 at 18:17

Yes, there’s a video out there of a restored F oden two stroke which is horrendously noisy and had a tiny power band. Also, the Commer TS3 and the Deltic, both two strokes albeit very odd ones.

Cé hé sin > MultiplaOrgasms
12/02/2019 at 18:28

Here’s a Foden doing its noisy thing: