ok quick run down of my engine:
383, LE3 heads & cam, ported intake.
my pistons are currently SRP 16cc dish for a 5.7" rod. I am going to be taking my engine apart soon. I've been contemplating purchasing a new set of pistons, flat tops, to put the compression ratio closer to 12:1. my dynamic c/r with the dished pistons is pretty low, well under 8:1. I could theoretically run 12.5:1+ static compression and still get away with pump gas but I dont want to push it that far. a little under 12:1 would put me exactly where I want to be.
I bought my shortblock as a whole already assembled so I didn't have to go through choosing a rotating assembly.
sooo on to the questions:
what pistons should I buy. I am on a very tight budget. I don't need the best. there will ABSOLUTELY NEVER be a power adder on this engine. I just want it to hold up to my 6500ish rpm shift points.

What would be a good, reputable place to purchase them from?

how much trouble would i have selling my current pistons? Im not sure how uneasy one would get purchasing used pistons. If I found a set of used pistons that fit my criteria I would be all over them but I know im not always the majority.

 

Ya didn't give any spects on the engine or cam to tell about DCR with any other piston.

 

Has the deck of your block been cut? What headgasket do you run. I played around with the calculator for a little while to see what I piston I would go with. I would get a flat top piston for sure if I were you. Either way your SCR is way to low for your application. I don't know the specs of your cam, but i do know mine by Bret..and my compression ratio is 11.7 and i would rather have more based on my DCR. My cam is also a good bit smaller for sure. So IMO go with a flat-top piston with a 5cc relief. There are quite a few manufacturers that offer this type of piston for you. Mahle, SRP, Probe are a few that are forged, lightweight, and of high quality. You could probably get away with a hypereutectic piston by the sounds of it as well.

EDIT:
I saw in another thread that you say you run a Mr.Gasket 5716 gasket, and your pistons are .20 in the hole. If you are tearing your engine apart, and changing pistons you will need to get it re-balanced. I would consider getting you Deck height checked, as well as possibly 0 decked. You can run a better gasket like that, and get a better quench distance. This will raise your compression ratio, and increase you engines tolerance to detonation. Your SCR and DCR are WAY too low for your setup.

 

With flat tops make sure that the eyebrows are the right size for the big valves on those LE3 heads, otherwise you may run into some piston to valve clearance issues. Dont go with any cheapie crap, srp flat tips with good size reliefs would be good.

Steve

 

Probe makes a real good forged flat top(no dish) for your set up. The reliefs are set up for .800 lift with two or four eyebrow's.
If ya make the new pistons exactly the same weight as the old ones ya will not need a rebalance-- This weight also includes the pins and retainers. Ya need to get within a half a gram or so and your machine shop can do that.

Again give me your spect's and I will figure it up.

 

Yes, I guess I left some things out. ok, heres the run down of the current setup:
car: 1994 firebird formula, built 4L60E, 3.73s in stock 10 bolt, TCI super street fighter 3500 rpm stall converter
LT1 block
-bored .030" over
-decked (I do not know the deck height, I bought it used and I didnt check it. Stupid mistake, yes, but I was alot less knowledgeable then than I am now. I don't believe its zero decked.)
-clearanced
-2 bolt mains
forged eagle 3.75" crank
forged eagle 5.7" H-beam rods
forged SRP 16cc dish pistons
unknown rings
MrGasket .026" gaskets
LT1 casting heads with LE3 port job, ferrea 2.0/1.56 valves, comp 977 springs. 55cc combustion chambers. heads flow:
.100 65/57
.200 132/108
.300 195/142
.400 239/165
.500 268/179
.550 272/183
.600 272/188
Cant give out cam specs. It does have an IVC of 78* ABDC.
LT1 intake ported and port matched to heads. opened up for 58mm throttle body.
GM Performance Parts Pushrod Guideplates
Comp Cams Hi-Tech One-Piece Chromemoly pushrods, 7.200"
Comp Cams "High Energy" Rocker Arm Studs, 7/16"
Comp Cams Pro-Magnum Non-Self-Aligning Roller Rocker Arms, 7/16" stud, 1.6 Ratio
Comp Cams "R" Hydraulic Roller Lifters
LT4 extreme duty timing chain
Racetronix 38lb injectors
58mm BBK throttle body
MadZ28 mail order tune
1 5/8" MAC midlength headers
MAC 3" Y-pipe
carsound hi flow cat
SLP loudmouth
SLP cold air intake
taylor OTVC wires
NGK TR55 plugs

The engine makes power up to 6200-6300 rpm then slowly dies down. I have a dyno graph but there were other issues with the engine, so its really not worth much.
I get a 7.66 DCR based off of a calculated 10.72:1 SCR.
a flat top piston with 5cc valve reliefs using fel pro .039" thick gaskets (I dont care for the mr gaskets) yields a 11.83 SCR and 8.42:1 DCR.


would a hypereutectic piston be acceptable for my application? I could spend $500+ on a set of pistons. I could put it on my credit card and pay over time but I really dont like doing that. IF it needs to happen, I'll do it.
Like I said before this engine in this configuration will never see any power adder. My goal was 11s in a full weight vehicle.

 

For me to figure it I will have to have the ADVERTISED duration,LSA, and ICL.
Ya want more than 8.4DCR? No problem PM me the spects.
I have probably seen and had built a dozen cams just like your's in the past 40 years, so if its top secret(Heee Heee) I can't figure a way to go higher.

 

PMed you, 1racerdude.

if you release the specs nerve gas will be released at key dense population centers around the world killing many!

 

You can pick up a free calculator here http://members.uia.net/pkelley2/DynamicCR.html

Frees LR up so he can get his son's car put together quicker.

The KB hypers are good pistons for well tuned NA engines. I ran a set for two race seasons, 13.8:1 compression, 8100 rpm and never had a problem with them. The guys are right though... they will not hold up to detonation so it would be better to keep the tune & DCR on the safer side. I don't know that .3-.5 points loss in dynamic compression will cost you much. I mean... we're not talking about a class racing contender here are we?

My 2 cents.

-Mindgame

 

Mindgame,
Thank you for the DCR page. I've been using THIS DCR calculator for all of my calculations.

The car is not a class racing contender. No rules to abide by. I just want to go really fast in a straight line on a college student budget within my own personal set of rules

 

LR is waiting on parts.

 

I can certainly relate to that....... many many years ago. That was the days of the Ford Falcon and the little 289 that almost could.... good memories.

Best of luck.

-Mindgame

 

With 55CC heads,.020 piston in hole(stock). .039 gasket,flattop's with 4CC's valve relief==
11.94 static
8.49 DCR with your cam
With the 16CC dish ya got==
10.37 static
7.41 DCR
With a "0" deck and the 4CC pistons==
12.62 static
8.95 DCR
Cam numbers are safe I have a security clearance and an oath.

 

wow, thank you!
I had no idea my SCR right now was that low, I thought it was 10.7:1! Which head gasket did you use? the fel pro .039" or the mr gasket .026"?


maybe I'll get another job to pay for the pistons. I dont have anything else to spend money on for the time being lol.

 

I used the .039 here is with the .026=
10.70 static
7.64 DCR

Ya don't have to wonder "why" any more.