Anyone done an A/B dyno test with flipped pistons?

Engine tech, for those engines, products, and technologies of yesteryear.

Moderator: Team

ELS
Pro
Pro
Posts: 292
Joined: Sun Apr 24, 2022 2:24 pm
Location:

Anyone done an A/B dyno test with flipped pistons?

Post by ELS »

Interested if anyone has actually compared actual dyno runs with the old 'flip the pistons around' trick
I'd think it maybe would effectively increase the R/S ratio and aid with filling the cylinders at higher rpm, but would that be enough to overcome the added dynamic load.
no way to really know unless someone dyno'd it
dannobee
Expert
Expert
Posts: 898
Joined: Mon Nov 04, 2019 9:01 pm
Location:

Re: Anyone done an A/B dyno test with flipped pistons?

Post by dannobee »

Tested it. It makes zero difference. Waste of time.

There's a Mahle white paper, "Pistons and engine testing," that goes over optimal piston offset in great detail. Suffice it to say that any modern piston has been optimized by the makers and is consistent with what we found first hand. Page 154.
Walter R. Malik
Guru
Guru
Posts: 6353
Joined: Tue Jul 24, 2012 11:15 am
Location: Roseville, Michigan (just north of Detroit)
Contact:

Re: Anyone done an A/B dyno test with flipped pistons?

Post by Walter R. Malik »

ELS wrote: Sun May 29, 2022 7:47 pm Interested if anyone has actually compared actual dyno runs with the old 'flip the pistons around' trick
I'd think it maybe would effectively increase the R/S ratio and aid with filling the cylinders at higher rpm, but would that be enough to overcome the added dynamic load.
no way to really know unless someone dyno'd it
Did that very test for Chrysler in the early 90's using a 360 Magnum engine. Centered, .030" offset, .060" offset and .090" offset.
Cylinder wall friction is slightly different in most cases so, the lower the rod ratio the more it will differentiate.

There is a power difference but, it is minimal ... certainly not enough to reverse the pin offset and listen to the pistons slap and hurt the skirt.
http://www.rmcompetition.com
Specialty engine building at its finest.
ELS
Pro
Pro
Posts: 292
Joined: Sun Apr 24, 2022 2:24 pm
Location:

Re: Anyone done an A/B dyno test with flipped pistons?

Post by ELS »

Walter R. Malik wrote: Sun May 29, 2022 9:15 pm
ELS wrote: Sun May 29, 2022 7:47 pm Interested if anyone has actually compared actual dyno runs with the old 'flip the pistons around' trick
I'd think it maybe would effectively increase the R/S ratio and aid with filling the cylinders at higher rpm, but would that be enough to overcome the added dynamic load.
no way to really know unless someone dyno'd it
Did that very test for Chrysler in the early 90's using a 360 Magnum engine. Centered, .030" offset, .060" offset and .090" offset.
Cylinder wall friction is slightly different in most cases so, the lower the rod ratio the more it will differentiate.

There is a power difference but, it is minimal ... certainly not enough to reverse the pin offset and listen to the pistons slap and hurt the skirt.
well I was most worried about the added friction.
and also something I read in a book called an oil wedge, basically when the piston rocks to one side, if there's a ton of oil on the cylinders it can form a wedge and stal the piston... sounds real bad, but the book didn't elaborate on what happens when that happens, just that it shouldnt
Walter R. Malik
Guru
Guru
Posts: 6353
Joined: Tue Jul 24, 2012 11:15 am
Location: Roseville, Michigan (just north of Detroit)
Contact:

Re: Anyone done an A/B dyno test with flipped pistons?

Post by Walter R. Malik »

ELS wrote: Sun May 29, 2022 10:21 pm
Walter R. Malik wrote: Sun May 29, 2022 9:15 pm
ELS wrote: Sun May 29, 2022 7:47 pm Interested if anyone has actually compared actual dyno runs with the old 'flip the pistons around' trick
I'd think it maybe would effectively increase the R/S ratio and aid with filling the cylinders at higher rpm, but would that be enough to overcome the added dynamic load.
no way to really know unless someone dyno'd it
Did that very test for Chrysler in the early 90's using a 360 Magnum engine. Centered, .030" offset, .060" offset and .090" offset.
Cylinder wall friction is slightly different in most cases so, the lower the rod ratio the more it will differentiate.

There is a power difference but, it is minimal ... certainly not enough to reverse the pin offset and listen to the pistons slap and hurt the skirt.
well I was most worried about the added friction.
and also something I read in a book called an oil wedge, basically when the piston rocks to one side, if there's a ton of oil on the cylinders it can form a wedge and stal the piston... sounds real bad, but the book didn't elaborate on what happens when that happens, just that it shouldnt
Reverse offset pins present less cylinder wall friction. Some inline engines actually offset the crankshaft instead.
http://www.rmcompetition.com
Specialty engine building at its finest.
hoffman900
HotPass
HotPass
Posts: 3445
Joined: Sat Feb 23, 2013 5:42 pm
Location:

Re: Anyone done an A/B dyno test with flipped pistons?

Post by hoffman900 »

I think the advantages here are not a power difference in a single A-B dyno test, but how the pistons / rings / bore hold up over thousands of miles. Test an engine with them flipped after 3000 racing miles, and you may see a difference.
-Bob
dannobee
Expert
Expert
Posts: 898
Joined: Mon Nov 04, 2019 9:01 pm
Location:

Re: Anyone done an A/B dyno test with flipped pistons?

Post by dannobee »

Here's the Mahle pdf. They've tested it all. Page 154 is the info on pin offset, along with graphs of various pin offsets with the frictional differences.

https://fdocuments.in/document/pistons- ... tml?page=1
ELS
Pro
Pro
Posts: 292
Joined: Sun Apr 24, 2022 2:24 pm
Location:

Re: Anyone done an A/B dyno test with flipped pistons?

Post by ELS »

dannobee wrote: Mon May 30, 2022 6:47 pm Here's the Mahle pdf. They've tested it all. Page 154 is the info on pin offset, along with graphs of various pin offsets with the frictional differences.

https://fdocuments.in/document/pistons- ... tml?page=1
thanks! I was looking for that and couldn't find it.
malibuguy79
Member
Member
Posts: 57
Joined: Mon Dec 20, 2021 9:03 am
Location: Maryland

Re: Anyone done an A/B dyno test with flipped pistons?

Post by malibuguy79 »

If I am not mistaken, Engine Masters also tested this and found no real substantial difference
hoffman900
HotPass
HotPass
Posts: 3445
Joined: Sat Feb 23, 2013 5:42 pm
Location:

Re: Anyone done an A/B dyno test with flipped pistons?

Post by hoffman900 »

malibuguy79 wrote: Tue May 31, 2022 11:20 pm If I am not mistaken, Engine Masters also tested this and found no real substantial difference
This would he an A-B test, looking at the Mahle data and other sources, I suspect the difference as I said above would be after running. I heard Ilmor tests the NASCAR LS engine out to 20k miles. I bet you start seeing differences when you start carrying mileage out like that, or in. LeMans engine or even NASCAR engines with the mileage they need.
-Bob
NewbVetteGuy
Expert
Expert
Posts: 779
Joined: Sun Aug 07, 2016 4:11 pm
Location:

Re: Anyone done an A/B dyno test with flipped pistons?

Post by NewbVetteGuy »

dannobee wrote: Mon May 30, 2022 6:47 pm Here's the Mahle pdf. They've tested it all. Page 154 is the info on pin offset, along with graphs of various pin offsets with the frictional differences.

https://fdocuments.in/document/pistons- ... tml?page=1
That thing is INCREDIBLE... Answered my question on how much piston oil squirters reduce piston temps in about 20x more detail than I was asking.

Saving THAT one for later...


Adam
User avatar
af2
Guru
Guru
Posts: 7014
Joined: Sun Jan 28, 2007 4:42 pm
Location: Grass Valley, CA :Northern Foothills

Re: Anyone done an A/B dyno test with flipped pistons?

Post by af2 »

hoffman900 wrote: Wed Jun 01, 2022 10:51 am
malibuguy79 wrote: Tue May 31, 2022 11:20 pm If I am not mistaken, Engine Masters also tested this and found no real substantial difference
This would he an A-B test, looking at the Mahle data and other sources, I suspect the difference as I said above would be after running. I heard Ilmor tests the NASCAR LS engine out to 20k miles. I bet you start seeing differences when you start carrying mileage out like that, or in. LeMans engine or even NASCAR engines with the mileage they need.
Same as long rod v/s whatever.
GURU is only a name.
Adam
User avatar
Stan Weiss
Vendor
Posts: 4801
Joined: Tue Feb 20, 2007 1:31 pm
Location: Philadelphia, PA
Contact:

Re: Anyone done an A/B dyno test with flipped pistons?

Post by Stan Weiss »

Looks like some people have good results

https://www.rideapart.com/news/256853/f ... explained/

Stan
Stan Weiss/World Wide Enterprises
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
User avatar
Tom68
HotPass
HotPass
Posts: 2541
Joined: Mon Feb 07, 2022 3:43 am
Location: VIC OZ

Re: Anyone done an A/B dyno test with flipped pistons?

Post by Tom68 »

Off set crank to cylinder centerline has been used for a long time. Can't be all that great, not everybody adopted it, I'd imagine preignition and detonation damage would be more significant with the crank offset. Also rising combustion pressure would have a hard time chasing the faster cylinder enlargement with the piston accelerating so quickly from min volume.
.
Flattie.jpg
You do not have the required permissions to view the files attached to this post.
Ignorance leads to confidence more often than knowledge does.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
fabr
Expert
Expert
Posts: 584
Joined: Sun Jul 21, 2019 8:35 pm
Location:

Re: Anyone done an A/B dyno test with flipped pistons?

Post by fabr »

NewbVetteGuy wrote: Wed Jun 01, 2022 7:01 pm
dannobee wrote: Mon May 30, 2022 6:47 pm Here's the Mahle pdf. They've tested it all. Page 154 is the info on pin offset, along with graphs of various pin offsets with the frictional differences.

https://fdocuments.in/document/pistons- ... tml?page=1
That thing is INCREDIBLE... Answered my question on how much piston oil squirters reduce piston temps in about 20x more detail than I was asking.

Saving THAT one for later...


Adam
It was very informative.
Post Reply