Should I buy this car and rice it out? :D

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Oct 9, 1999
Originally posted by: Vic
Originally posted by: Zenmervolt
No, you don't understand. In my example when cylinder 1 is at TDC, cylinder 2 is at BDC. This is how almost every 4-cycle in-line two cylinder I have seen is set up.

As for boxer engines, you're blowing smoke. I have a boxer 4 in my car (1976 VW-Porsche 914). Cylinder arrangement is as follows:


1 3
2 4


Cylinders 1 and 4 are both at TDC when cylinders 2 and 3 are at BDC. Cylinders that are directly opposed (e.g. cylinders 1 and 3 in my example) are never both at TDC or BDC at the same time.

Actually, I do understand.

First, look at the drawing on this page here.
Note how the opposing pistons are always at TDC together at the same time, then BDC together at the same time. This is how all horizontally-opposed engines are made.
See the pictures here

Second, VW and Porsche numbered the pistons for their old flat engines different that most other manufacturers. They did number them the way you showed above and the firing order was 1-4-3-2. Now you calculate piston positions based on that.

OTOH, Subaru numbers their flat 4 pistons like this:


2 1
4 3


And the firing order is 1-3-2-4, which is just the opposite (because the VW's were rear-engine and the Subarus are front-engine).
Wow.... Bizzare....

I think I have the same concept in my head that ZV does... dispite the animation, I'm having trouble computing it.. lol


Sep 18, 2002
Originally posted by: Zenmervolt
Originally posted by: Vic
The pistons in ALL 2-cylinder 4-cycle engines move up and down together,
Sorry, no. The first and most obvious is horizontally opposed two cylinder engines.

However, even with an in-line 4-cycle 2-cylinder both pistons do not move up and down together.


First, we will name, in order the four cycles. Intake, compression, power, exaust. The piston in each cycle is moving down, up, down, and up respectively. Let us further assume that the cylinders are called cylinder 1 and cylinder 2. When cylinder 1 is in the intake cycle, cylinder 2 is in the compression cycle. When cylinder 1 is in the compression cycle, cylinder 2 is in the power cycle. When cylinder 1 is in the power cycle, cylinder 2 is in the exaust cycle. When cylinder 1 is in the exaust cycle, cylinder 2 is in the intake cycle. When cylinder 1 is in the intake cycle, cylinder 2 is in the compression cycle...

I think it's assumed that it doesn't apply to opposed cylinders.. How could they possibly move together if they are on opposite sides of the crank??


Oct 14, 1999
I think in I2 engines the pistons move together, in cycles shifted 360 degrees apart.