jahns pistons

[hotrodstude]

while cleaning up my storage shed i found a set of jahns pistons new in the box.the part number is 8-972,+.060 over for 3-9/16 bore. i have a1956 289 which has never been apart,sat of 30 years,are these pistons for a 289. my stude info is limited at his time.plus wat is the lightest stude body made from 1950-1966?

[Bud]

Your pistons could be for a 289, but the 224 and the 259 also have the same bore diameter as a 289. The difference between pistons for the different displacements is the location of the wrist pin in the piston skirt which means that the pistons cannot be interchanged for the different V8 engine displacements. Bud

[StudeRich]

The lightest Studes. are always the 2 Dr. Sedans, because of the short overall length, the '59-'60 Lark would have to be the winner. Unfortunately all 2 dr. Sedans have very thin 13 or 14 Ga. frames requiring a lot of stiffening for any amount of H.P. under the hood.

The top of your Jahns Pistons should tell part of the story, most were 289 with slight pop-up or flat top for at least 10.0 or more Compression. Unfortunately that will make it hard to tell from a 259 Piston because in normal 8.5 to 1 Comp. they are also flat topped, where as stock 289 are fairly deep dished.

The only way to know for sure is to get the pin location distance from the top, spec. for 289 and check to that.

I have a set of Jahns 289 Avanti pistons here that measure roughly 1 9/16" from the pin centerline to the outer edge of the piston top, the centers are higher because of the pop-up, making these between 11 and 12 to 1 Pistons, they have to be used with radically ported heads to run on less than 140 Octane.

If you have "pop-ups", HOW HIGH ARE THEY?

Also Jahns made "Street" Pistons" with stock type "T" slots for expansion on the upper skirt and are "Cam ground" and "Racing Pistons", that are solid skirt and round, these also have press fit in the Rod, wrist pins, making it impossible to install the wrist pin lock bolts like a stock piston. These also have way loose running clearance for high heat performance use. Both types have extremely thick walls and are quite heavy making balancing the engine a must.


StudeRich at Studebakers Northwest -Ferndale,WA

[Alan]

hot, Measure from the pin hole to the top and add half of .812" that should get us in the ballpark of what they fit. Jahns made some heavy, clunky pistons and if you are going to use the ones with a orange slice shaped glob of metal on the top you will need to mill a fire groove in the dome or it will run like s**t.

[PackardV8]

Piston Compression Height:
224 piston: 1.9531"
259 piston: 1.7232"
289 piston: 1.59375"

quote:Measure from the pin hole to the top and add half of .812"

Alan has been building Stude V8s for forty years and knows well the Stude piston pin bore is .8750" and half of that is .4375" - we all have senior Stude moments

Agree, whichever Jahns pistons you have, they are very old technology and wouldn't be the best choice for serious performance build today. Flog 'em on eBay and buy the good stuff would by a recommendation.

thnx, jack vines

PackardV8

[Alan]

Thinking of the rocker shaft diameter and it's been 51 years.