forged vs. stock 95 pistons

[BryanK]

Hey I've been doing some research into forged pistons vs. stock '95 pistons, and I was wondering what the general consensus was about each? I've heard that the forged pistons tend to slap... the forged metal doesn't expand as quickly as the stock hyperutechnic (sp?) ones and tend to slap around in the cylinders a bit. Anyone have any confirmations of the problems, or experiences to the contrary? Anyone forsee any other problems with the forged over the stockers? I'm really just aiming for ~400 hp, and I realize that forged pistons (on 1g rods in this case) may be a bit much, but I may be able to get a good deal. I'm not looking to raise compression any... sticking with the 8.5, just wondering if there are any other adverse effects of forged pistons. How common is the slapping phenomenon? Can't I eliminate this simply by adding a nice set of rings? Or maybe just let the car warm up for ~10 minutes before driving?
Thanks,
Bryan

 

[L2RTSiAWD]

My suggestion is if you are looking to only make ~400 HP and are not looking to raise compression you will be fine with a Big Rod/95 piston motor.

 

[Tevenor]

Piston slap from forged pistons is generally a screwed up machining of the block. A good machine shop that pays attention to detail generally will have very little problem with pistons slap. The only caveat is it depends to some extend on the make of piston. Different manufactures have different amounts of silicate which gives different expansion rates and hence different clearances needed.

 

[NosLaser]

Along the lines of what Tev mentioned, a lot of piston slap does indeed come from machining. A lot of people simply have their piston mic'd and the block bored .020" over, or whatever size neccessary for the piston, but the actual type of pistons and their piston to wall clearance requirements are a BIG factor. Cast pistons that are .020" over will have different expansion rates than forged; if the block is not bored with these differences taken into account, it can result in a plethora of pre-mature wear conditions, if not worse. If you are looking to make under 450HP, I would suggest that the 2G pistons will be more than adequate and it will save you money that can be spent elsewhere (like a REAL fuel management system other than an AFC, or a DSMDuhIThink.)

Regards,

 

[rdrkt]

Originally posted by Tevenor
A good machine shop that pays attention to detail generally will have very little problem with pistons slap.

I agree but most people do not have access to a “good” machine shop. Many times you almost have to know as much about what the machinist is doing as he does to make sure he will get everything right. However if the machinist isn’t very DSM knowledgeable or doesn’t have the greatest attention to detail you will have all the negative things associated with forged pistons. IMO most people have to deal with an average machine shop or less and they will not have more knowledge of what needs to happen then the machinist therefore a 95 piston would be a lot more forgiving, cheaper, and driveable.

 

[Tevenor]

If I wasn't sending my block to the best machinist I knew, it would have 95 pistons. Standard overbore, standard Mitsu clearances. So from that end I agree.

But if you going to pay for an engine rebuild anyways.....

 

[rdrkt]

Personally I would either do a 1g rod 2 g piston motor or a Ross\Crower combo. Which is in two very different price ranges.

 

[BatmanGSX]

I'm going to be running the 2G pistons on 1G rods. I did this because I didn't feel like boring the engine, I got standard bore and will just hone the cylinders and drop them in.

My concern is not the pistons, I believe these will hold as much power as I can make provided I don't get stupid. I am worried about the rods. We'll see.

 

[turbolover2]

I think for my next motor I am going to use EVO pistons with brand new big 1G rods. Turbotrix sells the pistons for under $300. They are slightly lighter (according to TT) than 2Gs, and they have a slightly higher comp. ratio (8.7:1) than 2Gs. Those 2 factors together should help spool time a bit. I was thinking of going with forged, but the slap factor (<-- ) changed my mind. On a daily driver that gets warmed up from ice cold 2-3 times a day, I don't think it's a good idea.

 

[Tevenor]

Originally posted by turbolover2
I think for my next motor I am going to use EVO pistons with brand new big 1G rods. Turbotrix sells the pistons for under $300. They are slightly lighter (according to TT) than 2Gs, and they have a slightly higher comp. ratio (8.7:1) than 2Gs. Those 2 factors together should help spool time a bit. I was thinking of going with forged, but the slap factor (<-- ) changed my mind. On a daily driver that gets warmed up from ice cold 2-3 times a day, I don't think it's a good idea.

So what you are saying is you have no faith in your machinist.

 

[turbolover2]

Originally posted by Tevenor


So what you are saying is you have no faith in your machinist.

Actually, I don't. I haven't yet found a machine shop that I trust to do a perfect job.

 

[rsk_wannabe]

Since some of you from NY are relatively nearby...

You may want to try http://merkelengines.com/

Several of the NJDSM guys have used his services and are very satisfied.

 

[90tsiguy]

I'm running the Wiseco 8.1:1's myself, with "big" rods, as soon as I get the motor in the car I'll let everyone know my opinions on slap etc. just as soon as I get it back from my machinist...I was going to go with the 2g pistons, but didn't like the notion of machining the rods to fit...I feel that it weekens the setup, so in my opinion, I went with the Wiseco's...

 

[GreenGVR4]

it is actully better to go with 2g pistons because they are a floating pin setup..

 

[NDgsx]

Um 2g pistons use a press fit pin. Aftermarket forged pistons use floating pins.

 

[UndergroundR32]

Can someone elaborate on what a press fit pin is/looks like, and how it works?

 

[GreenGVR4]

A press fit pin and a floating pin look almost the same depending on the manufacturer of the pin/piston. On a press fit the pin is slightly bigger than the rod in which case the rod gets heated up and the pin gets pressed in allowing it not to be able to move in the rod. Is their any partictular reason you ask?


[Mod Edit: I have corrected for spelling and punctuation. Although not required across DSMTuners, this is the Extreme Tuners forum and a certain level of grammar and punctuation is expected.]

 

[UndergroundR32]

No, none in particular. I'm using forged pistons in the setup I'm building and never knew what a free floating pin was. Or the difference between it, and any other design for that matter. :-\

 

[Slowboy]

Many of us have had the 1g rod, 2g piston motor at one time or another. I also did one where I did not even remove motor ( not real smart ) but I wanted those 2g pistons in there! This was about 4 years ago, and that motor still runs 12 sec. time slips, just in someone else's car. You should be careful of doing it this way however....

Now, with the machine shop, etc... I have a partner who has been building race motors for 20 years. It is still fun in the morning when the circle track guys come in with there "stroked and poked" motors and they see five 4g63 blocks on the floor.... They just have no idea. But that is besides the point.

If the machine shop does not use a torque plate to hone the motor, you should turn around and find someone else. When our motors are done without, the tolerances have to be a thousandth or so bigger, to compensate for the head being bolted down. This in turn leads to what a lot of people reffer to as "piston slap"

When a torque plate is properly used, it simulates the head being bolted down. The ARP studs can really distort the tops of the cylinder wall... and this can be proven very easily....

I have had the same 9:1 motor for two years, with hardly any piston noise even upon start up... My new FWD car is the same way.

Regards,

Mike Huml

 

[90tsiguy]

Mike-

You sure that you're saying that honing without a torque plate leads to piston slap? I have a hard time believing that, BORING without a torque plate I can believe would cause that... Just my $.02

 

[Big Woo]

Well you mst look at a couple of things

1: intended use of your car/motor street car, street/strip car, drag car, ect. Amount of boost you intend to run efficeintly, not 22psi on a 14b spooled with NOS. Level of engine preperation, what else have you done to your motor.

2: Budget Lets face it most of us work for a living and there's only so much love to spread around, so be realistic.

There is one thing that I don't agree with on this thread and thats people sugesting that they don't trust trier machinest. I think this one is very simple if you don't trust your machinest to get the clearences right for forged pistons then you should'nt trust him to do cast pistons either. Remember your budget, paying a quality machine shop is part of the cost of going to forged pistons.

There are many differnt types of alloys for pistons, as well as "cam and barrel" profiles roundness, and skirt shape. All of these come into play when setting the proper piston to wall clearence, differnt manufacturs use differnt alloys, and profiles, so they can't always be directly compared to one another. Most piston manufactures for forced induction engines use a varying piston to wall clearences depending on maximum intended boost pressure. With the clearence getting larger as the boost goes up. So if you have it clearenced for 30psi don't #@%#@%#@%#@%#@% when the pistons slap when you start it on a 40 degree morning. Just remember to be realistic ant think through your decisions, and weigh the pros &
cons of what you are trying to do.

 

[BryanK]

Sounds like a lot of you have a lot of experience with the '95 piston big rod motors. It also sounds like that is going to be my motor of choice. I just have a few questions. What would be the best route for swapping in a 6 bolt bottom end be? I'm going to keep my 2G head, and I'm just going to swap in the pistons that I already have, so what would be a good way to go for the bottom end. Should I buy an entire 1G engine that still runs, and simply pull the head/intake off and swap the pistons, that way I don't have to worry about finding oil pumps, oil coolers, blah blah blah, all the other stuff that I'd need for a 6 bolt swap... Or, should I just get a 6 bolt block with the crank and rods, and go from there? What is the best route for a 2G guy looking to swap in a 6 bolt? This may have been hit on before, but from all the research I've done I haven't been able to find a difinitive answer.
Thanks for all the help so far, definately enlightening.
BryanK

 

[Slowboy]

You sure that you're saying that honing without a torque plate leads to piston slap? I have a hard time believing that, BORING without a torque plate I can believe would cause that... Just my $.02

We "bore" the engine to within 5 thousandths, then do finish "hone" in three steps with different grit stones. We do not "bore" with the Sunnen equipment... Just finish hone. So, that is when we use the torque plate.

I am not saying this is the only cause of "piston slap", just something that can greatly contribute......

Does that help clarify at all?

Regards,

Mike Huml

 

[candela]

Not picking sides or anything , but I vouch for what Mike said. I bought a motor from a friend whom I know had everything rebuilt but here goes the story. I swapped motor in my car for this motor (big rod/2g pistons) in which everything ws brand new but was rebuilt by someone he didnt know.

Anyhow the motor was compression tested at about 120 psi across the board. I almost crapped myself after all this work to find this. I added oil immediately and it jumped up to about 150 psi across all in an even pattern. I soon did a leakdonw test and found an average of about 40% leakage past the rings (on the gauge not in total obviously). All past the rings....

I called the place where it was rebuilt at and spoke to the guy who rebuilt it. Long story short, he said he used a flex hone and tried his best... whatever that meant. The only thing that I assume is that it wasnt really doen with much detail or precision. EWverything is new and it runs like crap because the rings didnt seat properly. This is my case and Im sticking to it. I think a goo dmachinist is very very important

 

[BryanK]

Hey, I was just looking at Magnus's website, and apparently they won't use JE pistons. Anyone know why? I know Ross pistons are usually the standard for the wild drag engines, but whats wrong with JE's? Oh.... anyone got any advice for me about the best route for swapping in a 6 bolt? (see post above)
Thanks,
BryanK