Which is better?

It would probably be cheaper to get pistons of stock bore since one wouldn't have to pay for labor costs of boring out the engine...

What's the reasoning in getting 0.020 overbore JE pistons?

just wondering....

l e o n

Well since Im in the process of figuring that out Ill tell you what Ive been told and what I think. Basically boring out .020 (assuming its done right)guarantees that the cylinders aren't warped or have irregular wear, and assures a tight fit for minimal blow by. Its the best thing to do if you have the means of doing it, and more important if you have high mileage. I have found custom forged pistons (in stock) at stock bore for the 420A Chrysler with a compression of 8:5:1 for $379. Not quite exactly HRC/JE piston's ratio of 8:8:1. I've talked to my mechanic (owner of Diamond Star Automotive) and he said with my 30k mileage I shouldnt worry about stock bore pistons giving me problems. I guess Ill find out :-)
Here is where I found the stock bore pistons:
--http://www.raceeng.com/importengine-main.asp
Hope I helped, lataz.

heh so let's say everytime one needs to rebuild an engine, they'd need to get bigger and bigger pistons each time, because of the increasing mileage and the need to bore?? :O


Hmm, wouldn't the compression lower be better? Then you can run higher boost?




l e o n

I get what your saying, but most times an engine rebuild is just replacing the rings, not the pistons too...

>>>>Hmm, wouldn't the compression lower be better? Then you can run higher boost?<<<<

I'm not sure why you said that, I Was talking about lower compression pistons,.....yes there better because you can run higher boost and the forged pistons cand withstand detonations better.

I was referring to the compression ratio with JE pistons vs the compression ratio you get with the pistons you are going with.

Is there a minimal compression ratio we should be at?

l e o n

Ooohhh :-) To tell you the truth there is no definite answer, HRC prefered to go with 8:8:1, which isnt a big jump from 8:5:1

8:5:1 is the "normal/safe" turbo charged motor compression ratio, like the GS-T's 4G63 motor. I think HRC used a 8:8:1 for a little more low end power. I think both are fine, both will definitely work, its just preference.

Correct me if I'm wrong peoples :)

A little clarification to whether or not you can use factory bores (since I seem to be the only one with forged pistons and stock bores). Its really quite simple: Measure the bores just like you would after boring a block (you may find the stock bore just as straight as a bored block). If the stock bores are within spec in regards to taper (if bore size is out of spec you've really f*ck up beyond discussion) it can be reused. I had 65K and nitrous with not a thing wrong with my bores. As far as piston to bore clearances they are set by the piston maker, doesn't matter if you bore or not. JE recommends .003", Ross .004". Most high strength forged pistons run anywhere from .003-.009 (hence there is no such thing as a tight fitting high strength forged piston). I say high strengh because there are basically two types of forged pistons you'll want to deal with. 2816 low silicon aluminum described above and 4032 high silicon pistons (JE's SRP, Ross sportsman, Arias off the shelf ect). These pistons run tighter clearances due to the high silicon (and less expansion) but are more prone to cracking (although probably stronger than what you'll ever throw at them).
If your bore is straight and measures x. you give piston maker x and they make the pistons to whatever clearance your heart desires. I foolishly didn't listen as if I were building a 700hp monster (went with .005" instead of .004" although they said it would be okay too) and now have to put up with a noisy when cold engine but the likely hood of blowing your engine due to piston to bore clearance issues is mute to none. And if you listen to the manufacturer you probably wont deal with as much noise (I still cant see a piston with .003" clearance being perfectly quiet). If you buy off the shelf pistons you have to do whatever is required but if you order them custom you can get what you need. I paid $425 including pins, locks and shipping and have a print out of each pistons weight, bore diameter in three places on the piston, piston crown thickeness ect ect. Another $100 bucks for total seal rings (well I paid $150 but oh well). Its been running for a year now and with nitrous so until it blows (there's always tommorow) I cant not recommend using factory bores. One thing I dont understand though. If your gonna replace all your pistons, boring is only $100 if not less so where is the great money savings? Do you plan on not pulling the engine or something? I didn't bore cause people said you couldn't(So much for listening to everything you hear). If you have excessive blowby and an excessively noisy engine it will be from not setting proper clearance and confirming straight bores not from using the stock bores.


Stan2gnt
Stan2va@aol.com
95 Talon ES-I-NOS
http://members.nbci.com/FlyEsi/home.htm
You too can have a never updated site complete with old info and dated pics!

Well, I don't know how much it will cost me to get my engine rebuilt (labor) since I'm located in Vancouver, BC, Canada. And who knows what boring would cost! Does anyone know of any engine shop nearby?


I think if the engine needs to be pulled out, it would definitely raise the labour cost. Is it possible to replace the internals without having to yank the engine out?

As well, what does it mean to say piston to bore clearance? How tight fit the piston fits in the 'hole'? :)

l e o n

A piston to bore clearance of .003" means the piston is .003" smaller than the block bores. I'm almost sure that boring the block will be $100 or below US funds. I'm also sure that no one will attemt to rebuild your engine while its in the car. To remove and re install our engine is typically $500 plus whatever fluids cost.


Stan2gnt
Stan2va@aol.com
95 Talon ES-I-NOS
http://members.nbci.com/FlyEsi/home.htm
You too can have a never updated site complete with old info and dated pics!

Alright, thanks for the ballpark figures. Guess I'll be calling around my area to see what they charge so I can prepare an "engine" fund.

heh


l e o n