I was reading up on hyper eutectic pistons in Wikipedia and in the "Performance replacement alloys" section of Hypereutectic piston - Wikipedia, the free encyclopedia it mentions that using forced induction is bad in that it increases the temperature and may cause premature detonation and/or knocking.

I am currently in the middle of an engine rebuild of a 351W and I need to buy the pistons now so I can get the block balanced. I am not sure if I will be OK with using a supercharger with these types of pistons or what. Anyone have advice on this?

The compression ratio will be the same as stock (9:1). Not doing a stroker motor.

 

If you're planning on forced induction you really should invest in forged pistons.

 

dont believe everything u read on wikilieingmother****ingpedia.....

u can edit everything on there to say **** holster... its ****ed up as a football bat....

anyways....

 

The problem you run into with the hypers is heat expansion causing ring issues. I'm not saying anything bad about hypers, I run them myself right now in my 460 with 10:1 CR and ran them in my old race 429 at 11.8:1 CR with no issues, but they do have to be setup properly, as I have also seen 8.5-9:1 CR with munched hypers that were not setup with proper ring clearance.



Courtesy of KB-Silvolite:



Suggested Piston to Wall Clearance

KB Pistons can be installed tighter than other performance pistons. A close fitting piston rocks less, supports the rings better, and seals the engine for maximum power. When a loose fit engine is desired the rigid skirt design of the KB Piston allows the builder a choice without fear of piston damage. See the clearance chart below for minimum and realistic maximum loose fit clearance for KB Pistons.





Special Notice on Top Ring End Gap

The Keith Black pistons unique thermal conductivity, ring location and varied end use requires special attention be paid to top ring end gap. KB pistons make more HP by reflecting heat energy back into the combustion process and, as a result, the top ring runs hotter and requires additional end clearance. Increasing ring end gap does not affect performance or oil control because normal end gaps are realized at operating temperatures. Failure to provide sufficient top ring end gap will cause a portion of the top ring land to break as the ring ends butt and lock tight in the cylinder. The broken piece may cause further piston or engine damage. Safe top ring end gaps can be found by multiplying the bore diameter by the appropriate ring end gap factor from the clearance chart below.

Example: 4" bore "Street Normally Aspirated" = 4" bore x .0065 = .026 top ring end gap. NOTE: Second ring end gaps do not need extra clearance. Dyno and track testing has shown that 34 degrees or less total ignition timing makes the best HP and time. Excessive spark advance, lean fuel mixture or too much compression for the fuel and cam used will make heat sufficient to butt piston rings with as much as .060" ring end gap. The entire top land can expand enough to contact the cylinder walls, when close to melt down temperatures are reached.

<center>

<table border="1" width="90%"> <tbody><tr><td colspan="7"><center>AUTO APPLICATIONS</center></td></tr> <tr> <td rowspan="3" align="center" valign="bottom">APPLICATION</td> <td colspan="3" align="center">Hypereutectic</td> <td colspan="3" align="center">Forging</td> </tr> <tr> <td rowspan="2" align="center">Ring End Gap Factor</td> <td colspan="2" align="center">Suggested Piston To Wall Clearance</td> <td rowspan="2" align="center">Ring End Gap Factor</td> <td colspan="2" align="center">Suggested Piston To Wall Clearance</td> </tr> <tr> <td align="center">Bore To 4.100"</td> <td align="center">4.100" & up</td> <td align="center">Bore To 4.100"</td> <td align="center">4.100" & up</td> </tr> <tr> <td>Street - Normally Aspirated</td> <td align="center">.0065"</td> <td align="center">.0015" - .0020"</td> <td align="center">.0020" - .0025"</td> <td align="center">.0040"</td> <td align="center">.0035" - .0045"</td> <td align="center">.0045" - .0055"</td> </tr> <tr> <td>Street - Towing</td> <td align="center">.0080"</td> <td align="center">.0015" - .0020"</td> <td align="center">.0020" - .0025"</td> <td align="center">.0045"</td> <td align="center">.0040" - .0050"</td> <td align="center">.0050" - .0060"</td> </tr> <tr> <td>Street - Nitrous or Supercharged</td> <td align="center">.0080"</td> <td align="center">.0020" - .0025"</td> <td align="center">.0025" - .0035"</td> <td align="center">.0050"</td> <td align="center">.0045" - .0055"</td> <td align="center">.0055" - .0065"</td></tr></tbody></table></center>

 

Hypereautectic pistons work great for naturally aspirated builds. If you want to be serious with a blower, turbo, nitrous you run forged pistons. Not something to cheap out on. Especially since the motor is already apart. It's not like you have a built motor and you're gonna have to rip it apart to put in pistons that can handle a supercharger.

 

X -4 forced induction = forged...Lew

 

That is exactly why I added the reference, wanted to get the thoughts from the group about the accuracy of that article.

 

I would really like to use Keith Black pistons but, from the conversations here, it sounds like I might be better off going with forged pistons (someone correct me if I understood the wrong thing).

I have a rebuild kit in mind and it comes with aluminum forged pistons, I am not sure if I can get them (summit) to add the KB pistons and not sure if I should after this thread.

 

One of the things to keep in mind with forged pistons is the extra wear they will inflict on the cylinder bore. The hardness of the piston will cause the bore to wear out quicker, whereas the big thing with the hypers is the ring clearance. It is extremely important to get it dead on.

I have run both forged and hypers and for just about any rebuild I would get into today I would run hypers without a moments hesitation. The only exception would possibly be if I was doing something on the real extreme end of things, and then again, that would not be a motor that would be being put on the street. To give you an idea of what I consider streetable btw, my original motor that I built for my F250 was a 429CI Ford on a 71 Block with TrickFlow heads, roller rockers, aluminum highrise, I beam rods, a 880 Holley, 11.8 to 1 backed by a C6. Just under 12 to 1 and it ran on pump gas with hyper's. When jetting the carb, what stopped us was the tattle tale on the tach, each time we bumped the jets up, we gained 100-200rpm. When I came back and the tattle tale was showing almost 7500rpm, I said enough and we dropped the jets down. The motor was literally going to take fuel until it blew. That motor was used on the street, on the highway pulling a car trailer, and racing every other weekend at the speed pit. The only reason I detuned it was the motor was aimed too much towards top end power and I was starting to need the truck more as a work truck, so I changed out the cam, swapped in a 460 crank, dropped the CR to 10 to 1 with another set of hypers and jetted down. That was in 06 and the motor does anything I ask of it for a work truck, including hauling a N14 diesel in the bed (3500lbs) or a load of railroad ties (3000ish) in the bed, down the highway at 70mph with no problems. The stroker motor on my 79 Harley is 98", with a 4 3/4 stroke. When I originally built it, I used forged pistons with brand new cylinders. A year and a half later, I pulled the topend and had to bore the cylinders, as the forged pistons were already at the top of the wear range for the bore. This time I went with the hypers, bumped the CR up a half point to 10:5 to 1. This motor has now been together since 2001 and has been dynoed at the rear wheel at 100Hp/105Tq. Considering the motor left the factory with about 45Hp, thats a pretty good jump, and the last time I ran a compression check on it, the numbers were still right where they should be.

Just 2 motors for your consideration that are well beyond stock and running hypers with no problems.