ImBatman

Ok this question has been batted around several times and every time I think that I have made up my mind I see something that changes it. Here are my motor specs one more time. .030 454, cast SCAT crank, 3/8 rods, GMPP aluminum 110 cc heads, cam undecided but solid and lumpy, 4spd, 3:70 gear.

Now here is the dilema. Everytime I think I am going to go with the forged L2399f pistons I go looking and see that I can get the same compression ratio for half the price with either the SP or KB hypereuetics. :eek: :smash: Being that I am not a drag racer and this car will never see nitrous What should I do? I don't want to cheap out but with 2 kids, 3 dogs, a wife and a mortgage I am not money bags either!! :cry So I guess my question is what do I do??? :confused: Forged or hypers? Pros\cons, +\-, do's\dont's? Any other cleche's? :D

Fevre

Go hypo.

ImBatman

:cool: Personnal experience?

Thanks
Wade

Fevre

I ran a set in a 383 but not for long, bad eng build. Piston's where fine but crank hit the pan rail. The hypo's are strong pistons that are used in the GM ZZ4, HT383 and other applicatons.

7T9Shark

I went with KB Hypereutectic because they are more stable than plain cast, and are very $$ reasonable. If you're not going to be drag racing or stump pulling you don't need forged pistons.

Gordonm

The hypos will work fine if you are not running 6500+ rpm for long periods of time. Also if no nitrous is being used. The hypos will also be quiter at startup as they can have a tighter fit in the bore of the engine due to expansion. The hypos expand less than forged ones. Just be sure when you have the block machined you tell them which pistons you are using.

gkull

I had very good luck with KB Hyper pistons. the close piston to wall clearance mkes more power. As long as you don't have heat problems or over rev them they should last for years.

I now only run forged and I have never even heard cold piston slap. That's probably caused by cheap loose fitting so called forged pistons.

wallyknoch

I`m a power freak, use the forged and you will not regret the choice. Just get everything ballanced. 94 will work very well with 11-1`s L 2465F-30 and the solid lifter cam. :thumbs: :D


[Modified by wallyknoch, 1:51 PM 7/2/2003]

ImBatman

Thanks guys. I am really starting to lean towards the Hyper's. With the money I save I can put that towards bearings and rings. :thumbs: Also GordonM I already have my block machined. Is there a risk that I need to be aware of?

Thanks
Wade :cheers:

wallyknoch

You should have waited and got the pistons first to be correctly fitted to the block. :cheers:

ImBatman

The past engines that I have built I had always done the machine work first then purchased the pistons. Those have all been small blocks in the past though. Is this something that with a BB I should have major concearns about? :confused: One thing I know of right off the bat would be roundness of the bore compared to the piston. This block was torque plated so I am pretty sure the bores are sufficiently rounded.

thanks
Wade

Fevre

I have heard of matching the ind piston to the bore to get an exact matching clearence for all but I would think that would be more for super high performance applications. I can assure you the Gen doesn't do it with the ZO6. Not saying that it isn't better, just not absolutely necessary. :thumbs:


[Modified by Fevre, 3:42 PM 7/2/2003]

BB wowbagger

I had hypos in my old engine and one of the pistons cracked and wrecked the block..So,from now on i`ll only use forged pistons..Maybe a little more $,but it gives me peace in mind :thumbs: :cheers:

wallyknoch

The clearances are important! And GM does fit the pistons when assembled. It will probably be ok, but it would have been better to fit the bore to the pistons. Thats why pistons are miked! :)

Fevre

Here is some more info on hypo pistons, parapharasing Norval:

Hypo pistons are stronger than cast and forged but the hypo's are more brittle. This means that the hypo's will retain their shape under a greater load than the other 2 but (yes another but) once it reaches its breaking point it will mostly likey shatter rather than bend. I think the cast will bend the most, but at a lower load than the forged, while the forged will bend some before breaking. The hypo's don't bend much they just break, kinda like the Lions defense. :jester


Hope I got that right Norval. :thumbs:


[Modified by Fevre, 3:56 PM 7/2/2003]

Fevre

Wally

Your not saying that GM bores each eng block to fit the pistons are you? Or is it that they check to make sure the piston and bore are within tolerence? If the former, no wonder cars cost so much.

Tom454

You should always provide the machine shop with at least one piston that you are going to use. Pistons do not all run at exactly the same OD. The bore also needs to be final-honed to match the rings you choose. As a professional engine builder, I would not consider boring & honing a block unless I had at least one piston in my hand. A full set would be better so I could mic them all and see what range they are running. This pertains to all engines... even lawn-mower engines.

Pistons are manufactured just like anything else.... within statistical tolerance ranges. 2 sets of "identical" pistons will not necessarily be exactly the same size due to production tolerance variance. This is true for all pistons... not just the cheap ones. I mic all pistons & bores that I use to assemble engines... it's truly amazing how much variance there is.

On daily drivers, I do not match the pistons/cylinders one-to-one. But on blueprinted assemblies, I hand match all holes. This requires measuring to a .0001 tolerance level, which in turn requires investing in good equipment. Extra time + good equipment = $$$. You get what you pay for.... or apparently less in some cases.

Also... I agree with the use of the hypers.... forged are sure cool.... but over-kill for most of us. The hypers are a nice compromise between plain old cast pistons & forged.... less thermal expansion than plain cast, tough durable alloy, more like forged. I use them in most engines I build. Any serious racing or forced induction... better to use forged although hypers will take quite a beating.

Hope this helps.

Tom

wallyknoch

As they build them, they have go and no go sizes and plug them in accordingly from boxes of pistons. GM even sells a fitted block that comes as a bare block and pistons to size. Numbered rods, remember. The tolerences are really close to cover any machining errors. You know, those built on Monday and Fridays. :lol: :lol: The guy will probably not have any trouble, but he asked the question and I should have kept my fingers off the keyboard. Hell, have a Corona, I just opened one. :lol: :cheers:


[Modified by wallyknoch, 6:13 PM 7/2/2003]

ImBatman

Thanks guys I appreciate all of your inputs and points of view. This is how you learn or at least how I do. Regardless of the best method it is a little late in the game for me now. :eek: I ahve gotten a lot of good information here and beleive that I can make a good educated decision on which way to go. If I were going to be twisting this thing to it's limit all the time and put a good deal of miles on it daily or weekly then I would probably be more concearned with the fit. That said I will still check the fit of each and every piston in the bores as I am putting it together. From the comments here as well as several other sources that I have tapped I think that a good hyper from either SP or KB is the way to go. Thanks again for all the help and if anyone else has more to add please do. I am always interested in other opinions and points of view.

Thanks
Wade

ImBatman

What about these? Any experience with this vendor? I am thinking that I should be OK compression wise with aluminum 110cc heads.

http://www.fastengineparts.com/products_view.php?id=135

Thanks
Wade