| Author | Message | ||
     Buell82 |
In the middle of my rebuild, and I am going to need to get some new pistons put in my bike. I was curious to find what you all thought between stock 97 S3 pistons v.s Wiseco pistons? Pro and cons? Change in performance? Anything you can tell me will be appreciated. All I know now is that I can get the same compression ratio with either or, but the Wiseco set are an extra $100. Thanks, Mike | ||
| Rocketman |
Wiseco pistons are forged as opposed to cast. You won't see any benefit performance wise, but the quality of a forged piston is superior to that of a cast piston. Such is of little use to you unless you go with better quality cylinders and build in extra performance to your engine. Rocket | ||
| Buellistic |
Buell82: Also have a 97 S3T, "BUT" have not desided how and when rebuild my Top-End ... As of my ride today it has 97,763.8 miles and still running very well considering the mileage ... Can tell you this, it will be rebuilt with Harley-Davidson/BUELL PISTONS ... In BUELLing LaFayette | ||
| Sloppy |
Warning on some aftermarket pistons. Not all of them carry the same dome angle for the heads that are on the bike. While Sporster and Buell pistons are the same diameter, they have different dome angles. Do extra research. Also look at the suppliers on this site. | ||
| Rick_a |
Cast pistons generally run quieter. Forged also run some very loose cold tolerances...which means that on really cold mornings, unless the bike sits in a heated garage, starting can be difficult, and warm up can take quite a bit longer. Like it's been said, they handle higher compression, higher power levels, hard use, and detonation better...but unless one intends to build such a motor cast pistons are the way to go IMO. | ||
| Rocketman |
I run the Wiseco pistons that came supplied with the original AAC cylinders back in 1999. It's Wiseco's direct replacement for the Thunder Storm piston, so goes straight in a TS motor. A word of warning though. Do not mix up Wiseco circlips for stock Buell circlips as the Wiseco circlips are a thicker wire gauge that sits in a corresponding size groove. Placing a Buell circlip in a Wiseco piston will end up in catastrophic failure. After my engine failure a few years ago, I found a brand new set of the same Wiseco pistons on eBay, brand new from a dealer in Canada for about $80 if memory serves. Rick, why is a forged piston set-up possibly harder to start from cold? Is this a compression issue? Rocket | ||
| Buellboiler |
Rocket, The coefficient of expansion on a forged piston is higher than a cast piston. As such the tolerance (piston-to-cylinder) of a cast piston can be tighter at assembly. This is the reason for the popularity of the newer cast pistons that have higher strength than typical cast and lower cost than forged. Forged can handle more stress (i.e. high revs, nitrous, etc.) than any cast counterpart. The cold start won't be as much of an issue as a cold battery. Boiler | ||
| Blake |
"The coefficient of expansion on a forged piston is higher than a cast piston." If it is, it ain't by much, probably not more than a 10% difference. The coefficient of expansion for aluminum alloys whether forged or cast are all right around the same 12.0E+06 IN/INoF. Grain direction due to forging and alloy composition can alter the thermal expansion coefficient of any material, just not that much. (Message edited by blake on June 12, 2007) | ||
| Rocketman |
Why is a forged piston set-up possibly harder to start from cold? Is this a compression issue? I'm curious about this point. And no, not to argue or debate it. I'm assuming an engineer might have a perspective on this I've not realised previously. Rocket | ||
| Sloppy |
From my recollection, forged pistons require greater clearances than cast pistons due to the greater density (less voids), thus expand slightly more than cast. I recall that they run at higher temperatures than cast, thus expand slightly more. It's been many beers since I took my Prop. of Mat. Class, so don't quote me. So as long as this clearance is accounted there should not be any reason why forged should be harder to start than cast. Also, forged pistons are heavier than cast pistons so it "may" reduce safe engine speeds. For a street bike cast pistons work great. For a supercharged, high comp. or race engines, forged are likely the way to go. Just stay away from hypereutectic pistons as they are brittle. In any case, you won't see any power difference. If you have the budget then get forged. If you can spend the money on something else, like ported heads, then do that instead. Any Buell specific perforamance shop should lead you in the right direction. | ||
| Blake |
"forged pistons require greater clearances than cast pistons due to the greater density (less voids), thus expand slightly more than cast." I don't see it. You can put holes and voids all through a metal part, but when it heats, it expands the exact same amount as when it didn't have the holes. I'm not seeing how a forged piston would necessarily be heavier either. Being that the forging alloy is likely significantly stronger than the cast alloy, it seems to me that a forged piston could be made lighter than its cast equivalent. Aluminum alloy castings have likely come a long way since I was sizing structure for the B2, so who knows. Maybe it's possible. | ||
| Aesquire |
The grain structure of a forging means it will expand a wee bit more than a casting. That grain is why the melting point is higher, again by a bit. The shapes involved, though....hmm. Pistons have to come out of the mold, I think the current state of the art involves a 3 pc. mold, 2 halves & an insert, to make the hollow underside. ( It's been over a decade since I worked in a mold making shop ) Forgings are pounded into the hollow shape in a series of dies. Checking the Wiseco site, they have some good info. State of the art there. Yes, they can & do make forged parts lighter than cast....that's the usual rule. New casting technology is more like plastic injection molding, & its possible to get pretty close to forging characteristics. Funny, though, Ruger makes very strong parts with traditional molding methods. Lost wax, ( investment casting ) about as old as metal working. ( they too, do it state of the art ) MMC, or Metal Matrix Composite, uses powdered metal & plastic, pressed into a shape, then heated until the metal "sinters" or partially melts & binds into a solid piece. Cheaper by the day, MMC is only getting bigger. Bottom line, Smith & Wesson, and you have to figure that by this century they know metal, uses MMC for parts on many items. BUT! if you order a revolver from the "custom shop" division, the Hammer & internal bits are forged. The regular guns use MMC. | ||
| Buellistic |
Blake: "i" worked on the B-58 ... It was GROUNDED so much "i" thought it was going to be painted YELLOW like the rest of the ground support equipment ... In BUELLing LaFayette | ||
| Aesquire |
Oooooohhh! B-58 Hustler, that's ahead of State of the art. One of the most impressive & shortest lived U.S. aircraft. Ever see the pics of the planned passenger pod? It was a pod on ground handling wheels, with seats & windows, to replace the monster fuel tank/H-Bomb pod. Supersonic VIP transport. Considering the plane was a stone %&^ch to fly, it's a good thing they never built it. ( holding pitch within 3 deg. on landing or you stall, or overshoot, makes landing a glider seem like childs play. ) | ||
| Blake |
Patrick (Aesquire), If I recall, the effect of the grain structure that is imparted during forging causes an increase in thermal expansion coefficient along the longitudinal direction of the grain, and a decrease transverse to it. Plastic in metal matrix composites? You meant carbon or graphite, yes? What was it the XB12R Pro-Thunder bikes were running, metal matrix composite connecting rods I think. Very interesting and promising stuff. Gets me all excited about doing some structural analysis again.  | ||
| Rick_a |
Facts are, the forged pistons I'm running require about double the cylinder to piston clearance of a cast piston. That clearance is set at the widest part of the skirt (pistons are oval and tapered when cold, they only become round at operating temperature...or at least are designed to). Not only that but when cold at the piston crown a cast piston has a fairly tight clearance with the bore, while these forged pistons have a huge gap from the cylinder walls in comparison. It is a noticeably greater taper which definitely suggests greater thermal expansion. They also must be denser as forged pistons almost universally adapt a cut-down slipper style shape to maintain near cast weight. Add to that a very cold engine that's been left out in near freezing temperatures all night and that's my theory on why my Buell has become one cold natured bitch on some mornings. It cranks over fine. The battery stays on a tender all night. The cranking pressure is 195psi so I don't think lack of compression is an issue. It just needs some throttle blipping for a minute or two before it idles on it's own. Anything over about 45 degrees F and it's fine. I've run it rich up to the point that the plugs have fouled and it hasn't helped one bit. I've tried all manner of initial ignition advance settings to no avail. The cold start is a theory, as a few others have had similar issues, but the higher density and thermal expansion of forged pistons over cast are regarded as textbook fact. On Ruger's investment casting process...I own several Ruger's, and every cast part is very substantial in mass. | ||
| Rick_a |
I forgot...a forging has a rougher internal shape due to limitations of the forging process and leave substantially more mass at the wrist pin boss that has to be lightened elsewhere. Keeping it stock or mild...go cast. Going crazy with high pistons speeds and compression ratios...forged pistons are good insurance. | ||
| Blake |
If cast pistons were good enough for Burt Munro... Be careful with your assumptions, many times even what might seem like the most common sense assumptions turn out to be incorrect. For instance, the larger gap between piston crown and cylinder wall may be to allow better communication between combustion chamber pressure and the rings. That may be more applicable to a higher performance application or it may just be a different approach used by the particular piston maker. Fun stuff. Where's all the BadWeB professional high performance motor-heads when we need them? | ||
| Steveshakeshaft |
MMC conrods? I'm very impressed. | ||
| Rick_a |
Burt's pistons never lasted very long... http://www.indianmotorbikes.com/features/munro/ind ex.htm His methods were trail and error...but the results speak for themselves. | ||
| Sloppy |
Blake: I did some research last night -- apparantly forged pistons transfer combustion heat faster than cast and thus run at higher mean temperatures. While the piston face temperatures are lower, the heat path travels into the piston skirt whereas with a cast, it remains on the face. I don't have my old text books with me, but can someone grab the thermal conductivity and specific heat numbers for cast and forged aluminum alloy? While the coeffient of expansion are the same, if they run at different temperatures, they will expand to a different size, hence the greater clearance requirements for forged. Note, I'm speaking anecdotally here, so if someone can grab the actual numbers we can get to the bottom of this... | ||
| Blake |
Sloppy, A great reference for material properties of metals is the old Mil Hdbk 5H or its successor the MMPDS (Metallic Materials Property Data Standardization) handbook. Here's one good online source for Mil Hdbk 5H. It shows properties for 200 series alloy which it states is good for high temperature applications. It reports a room temperature thermal conductivity (K) of 70 Btu/[(hr)(ft2)(oF)/ft] for A201.0 Aluminum Alloy Castings. For a forging Aluminum alloy like 2014 that is also recommended for extreme temperature duty, the thermal conductivity at room temp looks to be right at 89 Btu/[(hr)(ft2)(oF)/ft]. That is a 27% greater conductivity at room temperature. Looks like you solved the case! How cool is that! Fun stuff!  Rick is known to instigate this kind of informative and interesting discussion. We're lucky to have him. (Message edited by Blake on June 13, 2007) | ||
| Rick_a |
More known just to instigate, though  | ||
| Rocketman |
Room temp is a little ambiguos when talking forged pistons. Laboratory conditions more like, where the temp is controlled to a finite. Rocket | ||
| Aesquire |
Blake, yep, expansion along grain structure.... And yes, plastic. Well, some sort of polymer that acts like glue under mild pressure, then acts as flux does in welding during heat treat. Ruger story. When Ruger came out with their first semi auto pistol, the engineers at the fabrication plant took one off the line, cut the frame & slide mostly away, threaded the inside of the barrel at the muzzle, screwed in a solid steel plug, loaded the potential bomb & fired it remotely. When they called Bill Ruger to tell him the gun wasn't bothered by this idiocy, he said he'd designed that gun to be strong, now quit playing around & get back to work. I've heard Ruger's called bombproof, but never featherweight. Rockets right, room temp is STP. Not the slippery goo, Standard Temperature & Pressure. | ||
| Mmmi_grad |
Great thread. Buell boiler is right and in real life. Wiseco pistons often end up seizeing in bikes. Extra care must be taken fitting them to the cyl bore. They do expand more. Thats why alot of Harley shops do not like installing them. | ||
| Mmmi_grad |
Rick A thanks alot for the link. Im about to pick up the dvd, it has 7 gigs of stuff on it, how they made the movie and extras. It will be the first dvd movie i have ever bought lol. Loved that movie and watch it sometimes. Its so real you know. Awsome acting, outstanding perfect movie. Just an awsome tribute to a real racer. More should be made like this!! | ||
| Blake |
Patrick, If it is a polymer and acts as a flux, then its mixture with metal is something much different from what I understand to be a metal matrix composite, where much stronger and stiffer fibers are added to metals in order to strengthen and stiffen them. No polymer that I know is going to do that. Room temperature for material properties of metals is considered to be at 77oF, quite different from the 59oF of STP. | ||
| Blake |
If a cast piston face gets hotter due to its lower thermal conductivity, then it would seem that it would expand more than the cooler piston face of a forged piston; the forged piston's face being cooler due to its higher conductivity allowing more heat to flow from its face to the skirts and then into the cylinder wall. | ||
| Mmmi_grad |
i have done some more thinking about this, I dont have the specs in front of me. Its been along time since i have dealt with a wiseco. BUT I do recall now understanding that indeed the cast pistons for harleys anyway expands more!!! However, the reason why wiseco pistons were scoring and locking up is because of an assumption that they EXPAND LESS due to being forged and more dense. I reemed wiseco pistons inc many years ago about their pistons and setup procedure for old bikes like the panhead and they sent me some new pistons!!! Its all blurry history to me Id have to look up thier instructions again to recall what actually happened. I do know the replacements and what I did about the situation worked and was all good, after a reinstall. This reminds me of seeing some big harley explode in an evo. The guy wanted bigger pistons after a stage 1 or 2 install and the master Harley tech installed them only to blow up and shatter and ruining the the crank on the bike lift!!! Yes everything was checked. The huge pistons just couldnt handle everything else. A prime example to MATCH YOUR PARTS WELL. |
