I need a quick lesson on pistons. I am meeting with my engine builder in the morning to discuss my options with new pistons. So I need some recommendations and a quick lesson on what I want and what I want to ask for..

My engine was bored .030 over and he just honed it. I had hyper pistons there from an unknown manufacturer. Which is why he suggests new pistons..

So can anyone give me a quick lesson on what I want? I have read some issues people have had issues with Keith Black Hyper pistons cracking. I dont want to go broke with something expensive like Ross. Are there better "models" of Keith Black's to choose from?

I want to stay around 9.5:1 CR, but do not have my head purchased yet. Most likely a 64cc chamber.

Thanks

 

Did he just bore and hone this block? If the answer is yes you are in the wrong shop! You can bore a block first for sure but you DO NOT hone the block without the pistons as they are all slightly different in size so you hone each cylinder to the piston. Now as far as a good piston to use depends on the intended use. A street engine can use a good quality cast piston NP. Any engine making any kind of decent power should have a good forged piston in it. Truefully you can hear all kinds of opinions but just about all top line companies make a good product, just decide the power level you will be at and buy the correct piston for that.
Up to about 325HP cast is fine. anything above forge. Take the factory's lead on this. The 300HP 327's used cast, 350HP and above used forged. And yes people have stretched this but think about it.

 

He was going to hone it for the pistons I had, but he suggested I come back in and he can show me some options. He knows I am on a budget, but is really trying to get me to do it right.

 

However, wrong shop might be a harsh way of saying they have lower standards for less money. Truly a ring / piston / cylinder combination all needs to be done on a one to one basis. But you also pay for that extra time and labor and measuring and filing and honing. Budget shops cater successfully to guys with less money and they lump things together in cookie cutter builds. Bore to +.030, buy a kit of rings, ring the pistons, and install. Less service for less money. For most projects that's probably very acceptable. For a high quality precision blueprint build that isn't the best way. Just two different schools of thought and both work great for their respective application. As far as piston selection get yourself a goal based on power and budget. Start calculating your compression by using different components and then select that component from a manufacturer based on the power and budget you are trying to achieve.

 

Speed pro hypers. They use a standard ring gap and are comparably priced to Keith Black pistons. Keith Black pistons have a high upper ring and require a wider ring gap. They are notorious for breaking between the ring groove and top because of the thin layer between the top ring and piston top. A flat top 2 valve relief piston, zero decked block (9.000 deck), Standard .039 or .041 felpro head gasket and Dart SHP 72 CC heads get you right at 9.5 to 1. JMHO

 

Never really looked into Mahle pistons, actually never even considered them until I built the 427ci small block, there was only 2 that I know and at the time only Mahle fit the bill, these were off the shelf pistons that fit a new 4.125 bore with a 4 inch stroke.

I don't know but these motors are becoming more popular now but the Mahles came with the rings for them for about the same price as good forged pistons without rings which can run into a few hundred bucks themselves above the cost of the pistons.

The rings still need to be file fit but any good shop has a machine that makes the time a non issue.

 

I agree about the SpeedPro but I would get them without the coating it comes off after about 100 miles now you a have piston to wall problem, I realize it gets impregnated into the walls but a machine shop owner I know said he had to rebuild one on his dime because after the coating rubbed off the motor had some problems.

 

Yes, I am aware that walking into a shop where the sky is the limit and mentioning budget is not going result in a blue printed engine.. But it is far better than I could have done as a first build.. If had the extra cash, I would have built it on my own, blown it up and then learned from my mistakes..

 

Plenty of good pistons around, but when I rebuilt my 454 I settled on Probe street series forged. Haven't had any issues with them and pricing is very reasonable. Think I paid just over $300.

 

If you go forged, specify 4032 alloy over 2618. FWIW, I like JE, Diamond, Ross and Arias, among other good brands available.

 

Typically, Hyper alloy performs best w/ with very little piston-wall clearance ... when new, often equal to or just under 0.001"... See piston mfg specs & install notes.

On the other hand, forged clearance is always more than hyper ... some as little as 0.015" or as much as 0.007"... 4032 / VM75 alloy needs less than does 2618 alloy ... See piston mfg specs & install notes.

What should be taken into account here is ... OP's motor's already been bored AND already been run ... AND it's been honed again ... SO, the overall bore sizes should get close attention & several measurements before proceeding any further. It seems your builder may be on top of tis.

It may be there's too much meat honed out already; creating too much clearance for a thirty-over Hyper/cast alloy??? And, if so, may be a thirty-over forged piston is best choice. Or, bores may remain small enough for hypers' tighter clearance? Get busy measuring.

I like cast & hyper (including skirt-coated) from sealed power aka speed pro fka TRW ... but Not any cast or hyper from UEM aka KB.

At 355", a 64cc chamber & a 9.5:1 target ... flattop piston is likely.

But, if OP runs a large 76cc chamber, SP makes a few pistons with a very small dome that'll also get OP close to 9.5:1 target. such as hyper p/n H101CP & H618CP or forged p/n L2304F. G'Luck

 

It isn't rare to hone a block to size without the pistons in hand. Often the customer brings in a block and wants it bored and honed to the smallest size it will clean up to.
To have the pistons in hand at the bore and hone time the owner would have to know where his or her block will clean up. That is a WAG factor in most cases to put a bore gage in it and know for sure. Otherwise the block sets around bored waiting for the owner to determine what brand and what compression pistons he or she purchases.
Anymore with CNC machining pistons are accurate unless used pistons are used. The clearance is machined in the piston. If the pistons aren't the same then I'd buy a better piston. It's good to know the intended use of the engine. Raced and run hard the owner may want a few tenths extra in the hole. With good forged pistons especially. KBs and cast not so much.
If the hole is a small amount to small it can damage, kill or maybe sieze an engine. A couple tenths large won't. It takes good equipment to deal in tenths. I've seen shops who use cheaper measuring devices that won't gage in tenths and have been doing it for years.
I see more new start ups have problems with bearing issues and failure to clean issues than piston size issues. You won't need to spend a ton of cash to check those sizes. At a minimum pick up some plastigage and check for your own satisfaction.

 

The brands theskunkworks listed are all good brands. The companies he listed or most of them, will make a piston anyway you want them. A little pricey that way but great pistons. Personally I like JE for my persnal stuff, and have never been disappointed.

 

A couple of thoughts.

First, OP - you've been working with 63Mako on the engine design; don't go into free-form mode now Mixing and matching engine design points is a sure point of failure...63Mako knows what he's doing: stick with his advice. This is also a discussion with the machine shop - they've likely got their preferred brands...which I suspect they've already told you...and shops generally do best with what they're used to. Not disagreeing with all the good advice here - but too many engine cooks does spoil the build

I'm not opening up the "pistons in hand to bore/hone" debate - been there, done that - do what your shop asks for However, two questions/comments:

1. I think you had noted that the shop determined that the deck height issue was "cheap pistons and bad machine work" - cheap pistons I get, and a slightly lower compression height in "rebuilder" pistons isn't uncommon - but how is he addressing "bad machine work"?

2. At the very least the builder has made a ring type decision for you by doing a final hone - what are they telling you to buy?

I use a bunch of SpeedPro, and SRP/JE for everything else - but any good brand works. SpeedPro makes a line of pistons intended for the bobweight of stock vs. aftermarket cranks...I can't remember what the extra letter is on the P/N but it's worth asking the shop about if you go that direction to get in the ballpark.

You note the head is still "TBD"...wanted to ensure you realize that any discussion of CR is completely meaningless without knowing the chamber size - and the deck height.

Finally, if I read this right the shop tore down the engine solely to replace the pistons. Honestly...once the bearings are out just putting everything back together is a crapshoot. I can't recall when it was overhauled, but if it's been a while this shortcut may prove expen$ive...

 

You guys saying you need the pistons in hand need to join the 21st century.
With CNC machining and today's manufacturing capabilities, pistons rarely vary .0002 from one to the next, even cheap SpeedPro hypers.
Gone are the days when the old TRW bricks varied by several thousandths from one to the next.
KB pistons aren't really a problem as long as you set your ring gaps to their specs. I had a set for a 383 that were bricks, though. Went to SRP's and saved a ton of weight.

 

They tore the block down basically to look at the condition of all the bearings and give me thought on what should be done as per what they found.

And when I originally took it there, my thoughts were to use the pistons that were in it and have the deck shaved down as we found they were in very deep and were not producing very good numbers.

They have done all the bearing work at this point and have determined that one side of the block is 0.015 out and the other side is dead on to the crank. So they suggest cutting the high side so the block will be in spec.

So he could stop right there, re-ring that pistons that I have, scuff the cylinder walls to the new rings, put it back together and be on my way. But the pistons will still be in pretty deep. That extra depth can be taken up with smaller cc chambers and head gasket thickness. BUT, not knowing the history on the pistons themselves, he is hesitant to reuse them. If he knew who made them, he could track down the spec sheet and see if it is directly the piston causing the depth issue. But there are no numbers on there that relate to any current brand.

Yes, he did warn me that new pistons MAY NOT bring them up to where he would like. So that is a crap shoot. He said that prior machining to the rods may also be the cause.

He's suggested Keith Black or Speed Pro for my price range. He is going to let me buy them on my own as my Military discount was better then his pricing.

As for heads, I am going to go with the Dart SHP. Most likely the 72cc. So now the decision is to buy new pistons or not. Since my block came in with a 0.030 over bore he suggested stepping up to a 0.040 Hyper so he can match the cylinder to the pistons specs as they hypers need to be tighter than the forged. He said sticking with the 0.030 may not yield results he is happy with.. So they style and size (cc) is up to me.

Am I on the right track? This has become way to involved for me. I have watched video's and TV shows about how SBC are so easy to build. I know its TV, but they never seem to go this indepth..

 

It really does not matter which piston you choose as far as the bore is concerned. A 4.030 bore and hone dimension is typical. The pistons are manufactured to fit that bore and have the correct clearance made into them. The pistons will generally have a "bore range" example 4.030 to 4.031 and a "Minimum" clearance. A hyper piston might measure 4.0285 with a minimum clearance of .001. A forged piston might measure 4.025. There is also a tolerance as to maximum clearance allowable for a given piston. Racing engines are many times built with .002 or more overbore to allow for more expansion. Check bore size carefully. If wear and taper is oversize by the time you clean it up it could very well have over maximum allowed piston to wall clearance. Custom pistons are available. If the rebuild is recent you could be fine. Given you have already determined inferior quality in the original build measure everything carefully.
That said there are millions of SBC rebuild that have been done using the stock pistons, ridge reamed, ball honed and slapped back together with new rings.
Engine will need to be rebalanced if pistons are changed. I think the coating on Speed pro pistons add .001 to the dimension if that helps.

 

X, I know this is your first time working with a machine shop and you're translating what they're passing on - but there are some real red flags for me in what you're being told.

I'd really suggest getting 63Mako or someone else you trust on a conference call with the shop...

 

This is all great info... I can honestly say this is like drinking from a fire hose..

About the current bore, he said that at its current size, it is right at the upper limit of most pistons, but not having the new ones and new specs in hand, the 0.040 would be the safest bet a allow him to get it set up to "his tolerances".

And I know there are tons of shade tree mechanics that slap motors together and never have a problem. Me, I usually get the short end of the stick. So my luck, there will be problems no matter who does the engine.

These are the pistons I am looking at:
Sealed Power 8-KL2256F40
Sealed Power 8-KH618CP40

With shooting for a 9.5 to 9.75 to 1 CR, the 8-KH618CP40 seem like they will meet those goals..

 

I really hope I am not loosing things in translation. The "lingo" is new to me.

The one thing I thought he did was measure the rods. But when I got there today, they still had the pistons attached to them.

There have been a few moments where I just wanted to pick up my block and leave as I was not getting the warm and fuzzy feeling. The review I got from local mechanic friends is that you either love or hate the owner. He does best when you give him the engine and free reign. So I have seen and heard some great things about his products. And I could tell from our meeting today that these 101 questions I had for him was keeping him from his work.

What red flags are you getting??