Ok,,having like far to many old sets of pistons Jahns and Silvolite I was wondering. I had talked with someone before and they said that "those old clunky things are outdated" and that basically technology has advanced beyond what was then a Great idea . Would using old Jahns pistons and MT aluminum rods in a motor now a days be a waste? Would the parts not stand up? Is there something better that will preform and last better ? have these parts just become,,neat to have in a vintage motor?
if your gonna have al .rods it mite be wise to invest in some liteweight pistons like ross otherwise your defeating the purpose. those jahns are kinda heavy. and ones ive run across havent been matched very well for weight.
It really depends on what you're going to do with the motor, and if the pistons are cast or forged. Jahns made both, but as I remember, Silvolite pistons were all cast. Your info on being outdated technology is probably correct...IF...you are building a contemporary, every trick in the book, maximum HP drag engine. I just bet that's not your plan. Street Driver....either should work just fine. Competition Engine, unblown, for your new dragster....cast will be fine, forged better. Blown Engine for the digger.....only forged pistons
The old alum rods don't hold up well for prolonged street use. They tend to stretch and fatigue. The new alum alloys hold up much better for street use. The old pistons are heavy cast items, similar to stock pistons of the time. However the compression ratio is what made them so popular. I think for street use the pistons would do just fine, the rods might make you want something better
Another thing to consider is that, at least in my experience, Jahns forged pistons (or almost any of the older pistons) tend to require a lot of side clearance, due both to their skirt design, & possibly the alloys. Even on a 4.00 bore the specification is usually .008, or more. Depending on the application, though, that may not be a problem. I agree with MyEvilTwin about the rods....I wouldn't personally touch them for an enemies' engine, even if they were N.O.S. in the original boxes. There are people who feel differently, & it's their money to burn. Rods are kind of a critical component, ya know? The aluminum rods of today are light-years beyond the stuff made even into the '80s.
I think the biggest issues for Jahn's forged line and the other, can't remember names, big suppliers of forged hotrod pistons were the expansion needed, requiring huge clattering clearances when cold, and shape. Modern pistons are ground to complex shapes that allow them to be close to round when hot, old ones started life round. I think both design of shape and slots and new materials have greatly reduced the clearances needed on forged pistons.
They are still on the leading edge for paper weights, ash trays and trophy toppings. Seriously, they are the dinosaurs of the high performance industry as manufacturing technology, materiels, and design have left them in the dust. Frank
one more quick question,,if using Fuel injection like say Hilborn or such,,do you want high or low compression,,( think I have heard with blowers low compression but not sure )
You know, I have to Laugh at the remarks some guys make about how Shitty the Tech of Old Hot Rod parts like these Jahns Pistons. Sure, They Are OLD TECH ... But they sure did make alot of cars go FAST and set alot of Drag & Land Speed Records for many years. I also saw the statement that they were LIKE original Pistons in construction, How many of you are running OEM pistons in you Daily car & how many miles you got on them ? Again, I agree with you that they are OLD Tech ... But whats wrong with that ? Most of the cars that are on here consist of Old Tech, Except you Street Rodder guys with Deep Pockets that have all the State of the art Shit That 'Ol Boyd or Foose whittled out. I think these "" THATS SHIT CUS ITS OLD .. BUY NEW TECH STUFF"" statments are from All The Die Hard Small Block Chevy Guys that can run down to Pep Boys & pick up a set of ROSS Hi-Comp Super Slick Forged pistons for CHEAP ! Now if your a PoorBoy and say you had a set of 11.5-1 Jahns Pistons for a STUDEBAKER V8 or NASH Inline 6 and you just cant run over to NAPA to pick up a set of Pistons for it.... How many of you are gonna call ROSS and have a set of pistons built special for your Odd Ball Hot Rod engine ? These Old Tech Pistons been Building your Hot Rod History for MANY years, I say if ya got em or can getem... RUN THE FUCKERS ! Now on a side note .... I DO NOT feel the same about Aluminum Rods for street or Drag use. I run Jahns in my DeSoto on the street, Have 2 more sets for DeSoto that will be run, A set for Chrysler Hemi that i will run & a set of old JE for Chrysler, And a set for a 347 Pontiac that will be used. They Nay Sayers have Prolly never had to improvise as they Either have expendable $$$ to do whatever they want or have 350 Chevys that can get Pistons at the Local Piggly Wiggly. Fuck It .... You Guys out there with Jahns pistons on the shelf.... If you Think they are SHITY JUNK and ya got any for Hemi's, Y-Block Flathead, Pontiac, MoPaR 6 & 8s, Hell just about any engine built before 1962 send me a P/M with the application and ill give ya $50.00 for them Out Dated Paper weights
I used .125" over Jahn's 12 to 1 forged pistons on my hi-perf 348 with stock rods back in the 60's. When I got the crank assembly back from balancing at Holman-Moody's the counterweights had a large amount of weld added to compensate for all the additional weight. I guess that was before they came up with Mallory metal for balancing.
Here I go again: Get your caliper out and measure the diameter of those pistons just below the pin. Measure twice: once at a right angle to the pin and once parallel to the pin. You may find that, inspite of some of the commentary, that they are already cam ground. Meaning that ther is a difference in diameter in the two directions. Cam grinding is not "new tech"; they've been doing it since I was a kid and I knew J.C personally. If you can locate a precision scale or balance you might try weighing them to see how much variation ther REALLY is. A hell of a lot of engines were rebuilt with Silvolites and I'm sure they didn't all self destruct in 10000miles. Same with many HiPo motors built with Jahns-after all, how did they stay in business for 60 years or more.
Remember Jahns always took more work to balance, (I mean metal removal), but if you are going to balance any how ,it's just a little more time. Also have had sets of pistons where they used the same inner molds for different bores, so some the oversized pistons could get pretty heavy. My 2 cents.
NEVER use the phrase outdated technolgy. NEVER!!!!! What worked 50 years ago will work everybit as well today. Maybe Ross or JE are lighter, it really depends. i would want to weigh them before i ever said that. We forget or dont know in the first place that despite our modern advances the records set in the 30s for HP pere cubic inch normally aspirated have not yet been beat. Clearance is another subject. piston requiring larger clearances DO NOT run loose in the bore, they are the right size when when warmed up. They just have more when cold . Often this is due to skirt porfiles , slotting or some times piston struts. Please remember the motor doesnt know the difference. All it asks is am I sealed with my rings. Do I have enough room to move and how tight do you want me to squeeze? The rest is just gobblygook . Might be nice to have and may even be an inprovement but that doesnt make the old school stuff junk, just different. Don
The guru has spoken!. In 1998 running an engine I built ,using advice gleaned from Desoto's articles I ran 13-1 Jahns Full skirt pistons on stock rods in a 331 Hemi bored to 354. I don't know how many revs I reached (no tacho ,just oil pressure gauge) I was was clocked at 121mph on Lake Gairdner....in FIRST gear. The engine ran perfectly,pistons didn't break or burn and bored was still OK when i sold the engine almost 9 years later. A piston is a piston, But Jahns made some good products which were eventually superceded by companies using technology taken from OEM manufacturers . The combined weight of eqach rod,piston bearing and ring combo was 350gms,which compares with todays components don't you think? If the price is right and the pistons still have the machine marks on the skirts , ring lands and grooves are undamaged there is no reason not to use them .Just calculate your compression ratio so you don't go too high or Avgas will become your biggest purchase each week. Also,many old pop up type pistons don't flow very well ,the high crown actually robs horsepower by preventing proper squish propagation. ALSO,they don't match modern combustion chambers well when using 60's popup pistons on SBC's ,The crowns will hit the head. I concur with alloy rods on the street. I have seen those old style M/T's cuase head marks on pistons when street driven. When changing down to enter a corner you could hear it! they make great column drops...if you owned 8 cars.
I didn't hear anyone say that the old tech was shitty. Just that tech has brought better quality parts. I still run stock cast pistons, and have a set of old Jahns cast hi-comp pistons on the shelf. They are similar to old OE pistons in that they were usually cast and somewhat heavy-new Ross (or similar) pistons are forged and possibly a little lighter. The alum rods could become a liability. I am all for using what you have, but if you think it is gonna fail and cost more money to rebuild than a set of new rods-my choice is just run the orig rods with good bolts(like ARP) or save up for good/new alum rods. I don't run a SBC, and parts are not cheap for Nailheads. But trying to save a buck on old parts often costs more in the long run. The question was "Is there something better that will preform and last better ?". The answer is....yes. Are the old parts/pistons suitable for use? -absolutely. Will the old pistons 'slap' more when cold? -very likely. Is it worth the money for 'new parts' made with 'new' technology? this is up to the engine builder/owner. I have a buddy who had a Nailhead built a couple of years back, using alum SBC rods, offset ground crank, and custom pistons. Was not all that much more to do as the rods and piston prices are not too crazy. It just depends on what you want out of the engine I suppose.
Me to.......I have a set of Jahns for a 331 and was stoked when I got them, high compression without having to spend the Ross bucks.