Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Estimate of gains when converting to thinner piston rings

Estimate of gains when converting to thinner piston rings

Estimate of gains when converting to thinner piston rings

Greetings, eng-tipsters,

We build mainly obsolete engines, including Studebaker and Packard. The Studebaker Champion was designed in 1939, a 3" bore x 4" stroke flathead, using 3/32", 1/8" and 5/32" piston rings. It will require a substantial investment in new inventory to have pistons cut for today's thinner rings.

1. Any estimate of friction reduction which might be achieved and how it might affect horsepower and fuel economy?

2. Given the 3"/78mm bore range is shared with many engines, most all current ring widths are possible. Any suggestions as to which you'd choose and why?

3. Given an iron flathead is not as efficient at coolant regulation as an aluminum block with another seventy years of design science, is there any concern thin rings might not provide sufficient heat transfer from the piston to the cylinder walls?

Thanks in advance, as this is the one place to come for experience and not opinion.

jack vines

RE: Estimate of gains when converting to thinner piston rings

I can't answer your question. But many of us use modern-era "thin" rings in competition engines for only one reason- to [hopefully] avoid "flutter" at ultra-high piston speeds and accelerations (up to 8,600 g). In other words, we're only looking for better sealing of the combustion space under extreme conditions. So I've never researched the potential efficiency gains of thin rings.

RE: Estimate of gains when converting to thinner piston rings

Until the mid-80's nobody wanted to side grind rings thinner than .047" in the double disc grinders that took the castings, or split castings from the initial cast dimensions down to finished width. In this country they are usually old Besleys that more commonly grind coil spring ends.

The rings are guided between to rather large grinding wheels by thin steel strips that are held in tension between the wheels. These strips need to be thinner than the finished ring. The rings are pushed progressively through the space between the wheels. Pushing thin parts of any kind gets tough. Adding a total tolerance of .0005" to the job makes things tougher.

Making things even worst is the requirement to groove the face of the ring to accept a sprayed molybdenum coating. The grinding tolerance stack up gets huge if you want to groove a 2" stack of .040" wide rings for moly. The tolerance for that was .0002" total.

The adoption of roll formed steel wire as a ring material has pushed the technology forward and most have adopted some final grind that fixtures the ring in a plate between wheels that has a cavity for a single ring.

The computerized measurement of stack up has also helped to reduce machining error.

The development of narrower and narrower three piece oil rings (now down to 2mm) allows you the potential to make a ring pack that really helps reduce the compression height of the piston. New engines can be more compact and therefore lighter.

Now as to friction, The oil ring is the major contributor and all rings have relatively narrow lands in contact with the bore. The spacing of these lands has no effect. It is the spring load of the expander that has an influence.

It is much the same with the compression rings. you'll find that tapered face rings wear a band at the bottom edge and flat or convex faced rings generate a barrel shaped profile owing to the small amount of piston rock.

Reductions in static ring pressures have been made possible by improvements in cylinder bore concentricity. The unsung heroes here are the gasket makers that work to distribute the bolt load around the cores.
The gas pressure behind the rings generates the largest ring loads.

Your old flatheads with the giant hot spot near the exhaust are a bore distortion nightmare. A reduction in compression height won't do you any good. There really are no noticeable gains to be had with these engines with thinner rings. Kinda like putting hub caps on a farm tractor to improve the aerodynamics.

Heat transfer with thinner rings is not usually a problem with well fit pistons. Consider the huge increase in BMEP or h.p. per cubic inch with todays engines. Power went up while rings got thinner and moved closer to the top of the cylinder. Top lands went to 3mm and folks had to back away from that. Micro welding in the ring groove is treated by anodizing and coatings that don't weld as well as oil jets on the back of the piston.

As regards Studebacker six fuel economy, I suggest looking for a report detailing the 1949 Shell Economy Run, by a man named Greenshields at the Shell, Wood River, Illinois, refinery titled "One hundred miles per gallon is possible." He drove a Studebaker.

RE: Estimate of gains when converting to thinner piston rings

"Metric" 3-ringed pistons have been available for the Ford V8 flatheads for 15 years or more. Typically a 1.5, 1.5, 3.0mm ring package, vs. the stock 4-ring package (two oil rings). Lots of experience in the Ford world indicates few tangible benefits, small gains in terms of power or economy on street engines. Here is a recent discussion on the subject, lots of opinions both ways from both engine builders and owners (start reading around Post #16):

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close