Think you know two-stroke engines?

[rayjay257]

25/30. The wording of #8 is totally wrong. They are calling the transfer ports intake ports. If they are going to include small 2 stroke motorcycles, chainsaws, etc then reed valves are the most common intake control. The oil doesn't originate in the carb it originates in the gas tank. Now some Kawasakis did have the oil injection into the carb but the oil originated from the oil tank. I forget what the other 2 I missed were and I guessed correctly on at least 3.

Oh, yeah, compression ratio. Is that from BDC or from EX port closing ? From BDC most are 10 to 12:1 and from EX closing most would be 6 to 8:1.

 

[rayjay257]

"Small four-stroke engines commonly have compression ratios of 12-to-1"???

Really? My 1969 Pontiac 400 had a compression ratio of 10.75-to-1 and required high-test gas...I always thought that was fairly "high" compression, and that small 4-stroke engines would be less than that, not more...

Modern 4 valve car motors with fuel injection are 11 to 12:1 and some are higher. And these motors are meant to be run on 89 octane gas. It's far easier to control the combustion on a small cyl than on a large cyl. If you had you Pontiac today you would need race gas if you wanted the motor to run like it did in 1969.

 

[Canyon Angler]

Modern 4 valve car motors with fuel injection are 11 to 12:1 and some are higher. And these motors are meant to be run on 89 octane gas. It's far easier to control the combustion on a small cyl than on a large cyl. If you had you Pontiac today you would need race gas if you wanted the motor to run like it did in 1969.

Yeah, it's pretty amazing what they can do with computers and electronic ignition, etc. Freakin Camaros today apparently have way more power than my 69 GTO with a 400 did (I had 350 bhp), and you can run them on Jenkem and Old Milwaukee.

 

[grizz55chev]

Large 2 strokes are more fuel efficient, who knew?

 

[rayjay257]

Yeah, it's pretty amazing what they can do with computers and electronic ignition, etc. Freakin Camaros today apparently have way more power than my 69 GTO with a 400 did (I had 350 bhp), and you can run them on Jenkem and Old Milwaukee.

I had a 68 Goat so I know just what you had. I sold it when I couldn't buy real premium gas. Around 1979 or so. Those motors didn't ping they KNOCKED when the octane was too low. We just rented a Kia Sonata for a couple of days and I looked in the owners manual and the CR was 11 or 12:1. Pretty amazing. I have been told that if you actually CCed the heads on those old Pontiacs that the CR was really only about 10:1 or a bit less even.

 

[rayjay257]

I used to ride observed trials and the 2S motors used in those bikes had amazing lowend power. I mean real grunt right off idle. They also had very short strokes which is backwards from what you would expect. The short stroke was less likely to stall at super low rpm. Makes sense if you think about it.

 

[Canyon Angler]

I used to ride observed trials and the 2S motors used in those bikes had amazing lowend power.

Yeah, no joke. Back in the mid 70s, a friend of mine had a RM370 ... that thing was a freakin beast, and he was a big galoot. A few years later another friend bought an RM80. I jumped on it and thought I could wail on it because it was so small and I considered it a kid's bike, and because I had ridden my stepbrother's Yamaha 125 which was clapped out. I opened the throttle on the RM80 and it hit the powerband (I was somewhat of a n00b on bikes) and the thing SKRAMMED right out from under me...scared the crap outta me!

 

[Canyon Angler]

I have been told that if you actually CCed the heads on those old Pontiacs that the CR was really only about 10:1 or a bit less even.

Don't know about that one way or the other, but I do know mine was an "interference engine" ... when I lost the timing chain (wasn't beating on it, I was put-putting it, and thought it ran out of gas), the piston hit the valve(s) and bent one or more valves (long time ago, I forget), and the collar of the harmonic balancer broke off and hunks of it got thrashing in the pan and caught between a skirt and the cylinder wall, scoring a cylinder...it was a mess. Tried to fix/rebuild it on a shoestring, and got it "fixed" ... for a while...but then it got a rod knock and finally threw a rod...

 

[Mustang71]

Yeah, no joke. Back in the mid 70s, a friend of mine had a RM370 ... that thing was a freakin beast, and he was a big galoot. A few years later another friend bought an RM80. I jumped on it and thought I could wail on it because it was so small and I considered it a kid's bike, and because I had ridden my stepbrother's Yamaha 125 which was clapped out. I opened the throttle on the RM80 and it hit the powerband (I was somewhat of a n00b on bikes) and the thing SKRAMMED right out from under me...scared the crap outta me!

I remember back in the day when I was riding my Honda 400 ex around and those 250r's were real fast machines. Same deal with the Yamaha banshee those old 2 stroke quads had some serious power.

 

[Little Al]

Much to my amazement I got all but question 6 correct although the wording of some of the questions were more leaning towards guesses some of the correct answers would be incorrect as the questions were asked incorrectly I think the picture at the beginning is a 3pot DKW I had one in a F jnr race car in 1960

 

[rayjay257]

Much to my amazement I got all but question 6 correct although the wording of some of the questions were more leaning towards guesses some of the correct answers would be incorrect as the questions were asked incorrectly I think the picture at the beginning is a 3pot DKW I had one in a F jnr race car in 1960

I would have said Saab but I'm not familiar with the Deeks [ although there is a pic of my DKW with Betor forks just above my desk ].

 

[Ted Jenkins]

The compression ones are odd. I don't think the push mower is running at 12:1 and I don't think the stihl is running at 6:1. The push mower gets 87 octane and the saws get 91 I must be doing it wrong.

You are missing some of the basic 2 smoke principles. As a engine is running changes take place to the compression dramatically. The basic design is supercharging. Thanks

 

[Overkill338]

"Small four-stroke engines commonly have compression ratios of 12-to-1"???

Really? My 1969 Pontiac 400 had a compression ratio of 10.75-to-1 and required high-test gas...I always thought that was fairly "high" compression, and that small 4-stroke engines would be less than that, not more...

Briggs engines are something like 7.5-8.0:1. Anything over 10:1 is high for street engines. The new Ford Coyote engines and Chevy LS engines are close to 11:1 but they are very efficient at heat dissipation.

 

[Ted Jenkins]

Is there any kind of boobie prize for 100%? I had to guess at several questions, but lucked out. As with many ideas there are some points of view that I do not agree with so had to put myself into what do they want not what is my opinion. Right now most ignitions are not magneto or points, but CDI boxes or electronic ignitions. It will not be too long before two smoke motors are banned because they keep mule deer from procreating. Thanks

 

[Mustang71]

You are missing some of the basic 2 smoke principles. As a engine is running changes take place to the compression dramatically. The basic design is supercharging. Thanks

I was talking more about the 4 stroke compression I just didn't say that. When I was a teen we used to do a lot of work to simple carburetor 4 stroke engines and we would work on basic small blocks and such. 10:1 was a lot of compression. 12:1 and you better have race gas. I know modern engines are computer controlled and all that but the question did not say anything about a 2018 fuel injected engine. So thinking simple 2 stroke I was thinking simple 4 stroke.

I'm going to say that those old flat head Briggs motors probably were about 6:1.

 

[Canyon Angler]

Briggs engines are something like 7.5-8.0:1. Anything over 10:1 is high for street engines. The new Ford Coyote engines and Chevy LS engines are close to 11:1 but they are very efficient at heat dissipation.

...and then there's my PowerStroke 7.3 liter diesel, with a compression ratio of 17.5-to-1

 

[Overkill338]

...and then there's my PowerStroke 7.3 liter diesel, with a compression ratio of 17.5-to-1

Non-turbo diesels are 18 to 20:1

 

[Overkill338]

I'm going to say that those old flat head Briggs motors probably were about 6:1.

They are around 7.5:1

 

[Canyon Angler]

Non-turbo diesels are 18 to 20:1

So if you counted the overpressure created by the turbo, would the overall compression in psi be roughly the same...?
In other words, do those non-turbo diesels have higher compression ratios to make up for the lack of a turbo? (Don't know much about diesels...)

 

[rayjay257]

its all about BMEP