New piston/ring design

BillUSN1BillUSN1 Posts: 271Member

With the new pistons not having the ring pin and the oil ring now being a 3 piece vs a 1 piece design, oil control won't really be an issue.

So, we come to the lower 4th ring.

I've read lots of discussions on it's advantages from oil control to piston slap (piston rocking in the bore), but is the 4th ring really needed?

I had this discussion with my machinist, who specializes in flathead fords, runs Bonneville with an open coupe flathead, and his input was they actually dyno'd one with and without the 4th ring and gained 8hp without it.

That may not sound like much but when a stock engine is about 125-130hp, 8hp is a good gain.

So, has anyone else with Hudson experience, experimented with these.

I would guess Randy Maas and Uncommon Engineering probably build the most Hudson 6s.

I'm just trying to lay out my build plan for the new 308.

Machine work is almost done.

Decked, New exhaust seats, guides, a couple thread repairs, 3 angle seats....Lot's more port and bowl work once I get it.


  • HughlyssesHughlysses Posts: 1Member
    edited September 2019
    Years ago, I discussed this with Jack Clifford. He claimed that 4-ring pistons would result in no measurable oil consumption, while 3-ring piston engines would use about 1 quart per thousand miles. My machinist thought the 3-ring pistons would have significantly less friction, but we went with 4 ring pistons.
  • Piston and ring technology have come a long way since these engines were last made.  What you should run is a function of your budget, desire for originality and application.  A street engine with average occasional use?  4 rings.  It's quiet and will use the least amount of oil.  

    Leaving off the 4th ring does indeed reduce parasitic losses, but the distance between the wrist pin centerline and piston top is significant, and the piston will rock in the bore. Engines built for optimal performance will omit rings - some drag racers have been known to leave off all but the top ring in the interest of speed.  They smoke like a freight train, but make power.  If you want to run stock pistons in a performance engine - yes, omit the 4th ring.  It will use more oil. Note that performance engines are noisier than stock; they do like to clatter as the pistons "slap" in the bore.  When I build a race engine, I go out to the maximum allowable piston to cylinder wall clearance to get the most HP.  Please note the engine doesn't last as long when you build one this way, as it will beat up the piston skirts, eventually breaking one off.  I have an engine in the shop now with a broken skirt from lots of high-revving operation.  No, it's not a Hudson, but the principles (and the outcome) are the same.  

    After that - I'd talk to a specialist at either Diamond or Ross Pistons.  There have been several Hudson engines on the Salt over the years, and I suspect one of these two companies have made custom Hudson pistons which will be lighter and have even less in the way of friction than even a stocker less the bottom ring.  In the last flathead I built, I used Ross pistons.  If you tell them what you're doing, they can build a piston for you.  

    The ultimate extension of the art is to install a piston with modern low tension metric rings.  The long stroke of a 308, coupled with the wide (compared to modern) rings results in something called "ring flutter".  Era rings will see increased oil consumption at elevated speeds.  I had a factory service manual which explained this in detail.  I have two long stroke sixes right now, and when they're on the highway, their oil consumption doubles.  

    There have been tests done with era rings vs modern rings in older engines.  In the case of the OHV Y block from Ford, a 312 gained 13 HP over the same setup with era rings.  This was a three ring, short stroke engine.  On a Hudson 308, I'd estimate metrics would free up around 20 HP on a race engine, as frictional losses increase as the ring speed increases. 

    When I build my "hot" Hudson engine, I'll be experimenting with rod length and short skirt metric pistons to improve the specific output.  It's not 'free' hp, as custom pistons aren't cheap, but a good portion of every HP freed up goes to the rear wheels!  

    Hope this helps.  
  • blondwookieblondwookie Posts: 239Member
    Bill, I'M asking did you oversize your valves and how much did you cut your deck? What head are you using and did you cut the head and by how much? I have a stock  55- 303 engine as well as a stock 308 numbered head
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