Engine balance

[BusaNostra]

Straight 6 still the best ... but takes a lot of space.

No wonder why my Datsun body rot first before the engine die.

True with a straight 6 Jeep too

 

http://www.roadandtrack.com/columns/the-enginerdy-dept-straight-six-revival?src=soc_fcbks

[xcarguy]

Straight 6 still the best ... but takes a lot of space.

No wonder why my Datsun body rot first before the engine die.

True with a straight 6 Jeep too

 

http://www.roadandtrack.com/columns/the-enginerdy-dept-straight-six-revival?src=soc_fcbks

 

So, is the straight six is now mentally competing with the Busa V8? . . . . When's the install? :jester:

[NVP66S]

Straight 6 still the best ... but takes a lot of space.

No wonder why my Datsun body rot first before the engine die.

True with a straight 6 Jeep too

 

[url=http://www.roadandtrack.com/columns/the-enginerdy-dept-straight-six-revival?src=soc_fcbks][/url]http://www.roadandtrack.com/columns/the-enginerdy-dept-straight-six-revival?src=soc_fcbks

 

From the article: "The most effective way to reduce that vibration is to use the force of one piston to cancel out the force of another; in other words, as piston A moves in one direction (up), piston B moves in the exact opposite direction (down) at exactly the same time. But that's only possible for engines with an even number of pistons in a single plane, like an inline-four-cylinder."

 

No, no, no. I4 engines have terrible first order balance. It comes from the piston acceleration at top dead center being greater than at bottom dead center. Acceleration of the 2 outer pistons is not balanced by the 2 inner pistons. In a typical short-rod high performance engine, it's about a factor of 2 difference. This is why there are no large displacement I4s. The Pontiac 2.5 liter Iron Duke was about the biggest and it shook like crazy. Adding balance shafts helps, but with added weight and complexity.

 

The O4 engine (VW, Subaru) has no first order imbalance, but does have a 2nd order yaw moment. My airplane has a 360 cubic inch O4 and it shakes, but nowhere near as much as an I4.

 

I3 engines are better balanced the I4, but with a pitching moment, so when you take two I3 engines and glue them together to make an I6, that is cancelled and you get the famously smooth I6.

 

Mercedes-Benz and BMW both made marvelous I6 engines until M-B sold out and made a V6 because it's shorter and can be packaged transversely in a FWD vehicle.

 

OK, I'm cooled off now. End of rant. :jester:

[BusaNostra]

Typical 6 cyl inline firing order is 153624 and in a given time,

as far as the up and down motion, there is always a pair that goes up in down. To simplify it with my drawing below. Major reason a 6cyl inline has less vibration and well balance.

 

hey you are into plane too huh?

I built a Vans aircraft RV-6A from a kit. 360 cubic - Lycoming engine

[NVP66S]

hey you are into plane too huh?

I built a Vans aircraft RV-6A from a kit. 360 cubic - Lycoming engine

 

I have 4000 build hours on a Defiant that has been sitting for several years. I'm planning to use a pair of IO-320s with cold air induction. The 500 hours I put on the Westfield and refurbishing the donor car parts was a small blip in the airplane project.

 

For you non-airplane folks, Lycoming engines (they have most of the market) mount the updraft carburetor to the bottom of the oil sump and the intake runners pass through the hot oil!!! :puke: I put some thermocouples on my Grumman one day and measured a 28C temp rise of the charge air. The reason they do that is because that 1930s carburetor design needs all the help it can get vaporizing the gasoline. I plan a more modern fuel injection induction, which theoretically is a 10% increase in addition to better knock resistance.

 

As far as engine balance goes, many years ago I had a M-B 230SL with a marvelous 2.3 liter I6. Recently I had a M-B 230SLK with a 2.3 liter I4. Wow, what a difference in engine smoothness. That 1999 engine was rough compared to that 1964 built engine of the same displacement. I sold the 230SLK to partially pay for the Westfield. No regrets there.