Your opinions on flipping pistons

[FishFry]

Smokey Yunick and a few others are quite in favor of flipping pistons.

That means - given you have an piston with a certain offset at the bolt, taking the pistons out, and put them in 180 degrees from the original "front mark". The idea behind this is better rod to crank geometry - better response.

When you look at it, it makes sense, but you may pay with some slapping/noise while cold, and extra wear.

Is it worth it? Any experience or opinions on this?

Frank

[Walter R. Malik]

Smokey Yunick and a few others are quite in favor of flipping pistons.

That means - given you have an piston with a certain offset at the bolt, taking the pistons out, and put them in 180 degrees from the original "front mark". The idea behind this is better rod to crank geometry - better response.

When you look at it, it makes sense, but you may pay with some slapping/noise while cold, and extra wear.

Is it worth it? Any experience or opinions on this?

Frank

Reversing the piston pin offset is worth some minimal horsepower gains but, cylinder and piston skirt wear is increased some.
Your choice.

[jred]

Did it with air cooled vw's in the 70's with dean lowery, gained 3 hp on his dyno and a lot of noise with quiet exhaust ,

Race pistons have centered pins and you get piston slap but you don't hear it with open headers with stock exhaust if you put more clearance on the bore then the piston manufacture recommends it will make noise,,

I chased that noise in 1 engine with 3 tear downs and finally found the the stock replacement forged TRW pistons were marked wrong and the piston was really installed backwards..

[dannobee]

I don't know why this topic comes up every few months, but with any modern piston (made in the last 50 years), it makes zero difference. We tested it. ZERO difference when we tried it in claimer class SBC's.

viewtopic.php?f=84&t=65201&p=918259&hilit=mahle#p918259

Mahle has researched practically anything you could think of, including piston pin offset.

https://fdocuments.in/document/pistons- ... tml?page=1

Page 154 goes over pin offset.

[Stan Weiss]

The bigger the offset the more things change from no offset. With offset the crank and the piston are no longer at TDC and BDC at the same time. These 2 graphs use 1.5" offset which you will never see but is great for illustrating the changes.1 shows the crank journal travel and the other shows the piston travel.

Stan

ab-offset-crank-tdc-302.gif

ab-offset-piston-tdc-302.gif

[BCjohnny]

While the search function isn't the greatest, it should bring up what you might be looking for

My take on the topic

I agree with Walter, on a low output restricted class engine you might find gains, maybe enough to make it worthwhile ...... it sure livened up the one I played with

[FishFry]

While the search function isn't the greatest, it should bring up what you might be looking for

My take on the topic

I agree with Walter, on a low output restricted class engine you might find gains, maybe enough to make it worthwhile ...... it sure livened up the one I played with

LOL, I just realized that I actually answered on that thread. I'm definitely on too many forums

So yeah, I did the flip on my 261 Stovebolt, and gained a bit here and there, but nothing "night and day" as you describe it.
That's why I was looking for more experiences. Maybe I have not enough offset to begin with, or my 261 is just too lame of an engine - it's a street engine - hopped up though, but nothing radical.

Frank

[lefty o]

its not 1962 anymore, ill just have the piston i want made how i spec it.

[rebelrouser]

For what it is worth engine masters did an episode on flipping pistons. Sometime those guys are not the most scientific, but this seems a pretty straight forward test.

https://www.bing.com/videos/search?&q=e ... ajaxhist=0

[In-Tech]

Garbage, as Stan posted, it's really more important to have the camshaft correct for the dwell of either side. If you are flipping pistons to aid the wrong cam, change the cam. Bernoulli's equation can be used in a lot of life. https://www.princeton.edu/~asmits/Bicyc ... oulli.html

[Krooser]

IMG_20230208_160528200.jpg

Didn't work for me...

[Stan Weiss]

Maybe this explains it a little better than my graphs.

https://motocrossactionmag.com/ask-the- ... nk-offset/

Stan

[Tom68]

Maybe this explains it a little better than my graphs.

https://motocrossactionmag.com/ask-the- ... nk-offset/

Stan

From the link.

"Just so you know, Suzuki does not offset its cranks. Honda has a 4.5mm offset. KTM and Husqvarna use 5mm of offset. Kawasaki has 8.5mm of offset, and the Yamaha YZ450F offset is 12mm."

Just another variable you can use or not use, they really should include any piston pin offset with that info, or confirm zero if so.

Henrys engineers thought it was worth incorporating in 1932, but they were simpler times, weren't they ?

Flattie.jpg

[Matt Compton]

We did this on a few 602 crates. Along with back cutting rings. Worth on avg about 10hp in our tests.

[Tom68]

Green C4 aircraft 1908.

Green C4 1908.jpg