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To those of you considering aftermarket forged pistons...


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So I have been doing a fair amount of reading up on "Drop-in" forged pistons. More specifically about 4032 alloy pistons as they have tighter tolerances and they seem like a better, longer lasting piston for people who are looking to stay under 400 HP. I do have a few questions however....

 

1. With a new short block what is the bore exactly? I have seen this below, but it talks about the piston diameter (min and max), but not the bore size.

 

http://www.legacygt.com/forums/attachment.php?attachmentid=79983&stc=1&d=1265554127

 

So I guess my question is this. What is the stock "A" bore size range? and what is the stock "B" bore size range?

 

As a follow up question, when a piston manufacturer sells a piston that is stock size (99.5 mm) what is the true size? I ask because it seems like the manufacturer would under size the piston ever so slightly to fit the stock range "A" and "B" bore within their spec.

 

Those of you with experience in these things, what do you think of this? Am I correct in my thinking?

:icon_twis Slide It Sideways :icon_twis

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  • 4 months later...
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So I was the lucky second owner of the 08 LGT Limited time bomb which finally gave way. I'm swapping to a 2009 sti block 257, but I am stuck on this piston situation. I have read a lot on both positive and negative of going forged and still seem undecided.

 

My LGT is a DD as it is my only source of transportation for the foreseeable future. Granite State Tuning has already sent me a tune for my tiny little build list which thus far looks like:

 

365lph fuel pump

750cc grimspeed injectors

CNT Racing catless dp

STI catless up pipe

Zero miles VF52 brand new built (journal not bearing)

and of course the EJ257

 

While in the shop the other day a local subie guru mentioned the forged pistons because of ringland failures. He suggested forged pistons, but my issue with that is my 2 mile drive to work (7 or 8 now because I am taking a longer way to let the battery and recharge system do it's job as well as let the engine fully warm up). From what I've read the forged pistons expand to such a degree that they will need a lot of warm up time. I have an auto start (5EAT) so I typically let my car idle for 5-10 minutes anyway prior to driving, I check oil daily (rotella t6 synthetic every 3k miles) and make sure to keep up on maint. I don't #racecar every day, but I do get on it fairly often when on the high way, i mean who wouldn't?

 

 

So with all that said.. I don't plan on telling my tuner to push boost to the max (which seems to be a leading cause of ringland issues) .. should I bother with forged? This isn't ever going to be a track car and could likely be transporting me across the US at least one more time. I don't have my sights set any higher than 350whp.

 

 

 

1) Should I worry about forged (If I should than now is the time since a new motor is going in)

 

2) If I should stay OEM (which is where i'm currently leaning) what can be done other than managing moderate boost levels, to prevent ringland issues?

 

 

***UPDATE*** Now leaning towards forged 4032's after reading more into it.. the OP had a great write up, but the OP's quoted text seemed geared more towards the 2618's as it spoke to things like piston slap and eventual bore out of round issues after not many miles which I completely agree with.

Edited by proflashrtist
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i've heard that, and i really don't plan to have the tuner push it to its limits with the tune, so the OEM pistons should hold just fine, but i've read some disturbing stuff about them in the 09' engines which is what im dropping in.

 

I haven't really decided either way.

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  • 2 months later...

Well this is a bit older thread but ill update you guys later next week.

 

I have a misfire on my built motor and Cobb plano is doing a leak down/Compression test this week.

 

The motor has 95K on 2816 Forged JE Pistons, Cobb/Crower rods, STI crank, STI Crank and Rod bearings, ARP head studs, Killer B p/u tube.

 

If the motor comes out Ill report back with pictures hopefully on what a piston slap happy motor looks like with almost a 100K and 4 years on it. :lol:

 

I am thinking its an exhaust valve issue but it will be interesting to see what the SB looks like

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  • 1 month later...
Well this is a bit older thread but ill update you guys later next week.

 

I have a misfire on my built motor and Cobb plano is doing a leak down/Compression test this week.

 

The motor has 95K on 2816 Forged JE Pistons, Cobb/Crower rods, STI crank, STI Crank and Rod bearings, ARP head studs, Killer B p/u tube.

 

If the motor comes out Ill report back with pictures hopefully on what a piston slap happy motor looks like with almost a 100K and 4 years on it. :lol:

 

I am thinking its an exhaust valve issue but it will be interesting to see what the SB looks like

 

Any updates yet?

MTBwrench's Stage 3 5EAT #racewagon 266awhp/255awtq @17.5psi, Tuned By Graham of Boosted Performance

 

Everyone knows what I taste like.
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  • 3 weeks later...
Well this is a bit older thread but ill update you guys later next week.

 

I have a misfire on my built motor and Cobb plano is doing a leak down/Compression test this week.

 

The motor has 95K on 2816 Forged JE Pistons, Cobb/Crower rods, STI crank, STI Crank and Rod bearings, ARP head studs, Killer B p/u tube.

 

If the motor comes out Ill report back with pictures hopefully on what a piston slap happy motor looks like with almost a 100K and 4 years on it. :lol:

 

I am thinking its an exhaust valve issue but it will be interesting to see what the SB looks like

 

Any updates?

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Any updates?

 

From another thread

http://legacygt.com/forums/showpost.php?p=5214023&postcount=237

 

Well I had been fighting a misfire cylinder two on my ride. Finally took it down to Cobb in Plano TX for a brush up on the tune and leak down/compression test.

 

Had 60 psi cylinder 2. The others were 150, 144, 140 on a 100K built motor. JE 2618 forged pistons with Crower/Cobb "long" rods.

 

After pulling the motor found a bad exhaust valve causing the 60 PSI. The block was also out .25 so its getting bored to 99.75

 

Im installing Manley turbo tuff H beam rods and Manley 2618 Platinum pistons 99.75

 

Selling the Crower long rods and custom JE pistons stock bore pistons.

 

Should have it back around Aug 27th

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  • 3 weeks later...

My new motor is in and running great. The Manley 2618 Forged pistons in this motor are so much more quiet than the JE pistons I was running before.

 

You have a tiny bit of noise on cold starts but it goes away completely. If you let the motor warm up a bit before you put a load on it, you don't really hear them at all.

 

My JE pistons were noisy all the time.

 

I HIGHLY recommend these Manley Platinum Series pistons.

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My new motor is in and running great. The Manley 2618 Forged pistons in this motor are so much more quiet than the JE pistons I was running before.

 

You have a tiny bit of noise on cold starts but it goes away completely. If you let the motor warm up a bit before you put a load on it, you don't really hear them at all.

 

My JE pistons were noisy all the time.

 

I HIGHLY recommend these Manley Platinum Series pistons.

How many miles did you get out of your JE Pistons?

Edited by Rhitter
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  • 2 months later...

Hi Scooby2.5,

 

I am finalizing my motor build and trying to choose between JE and Manley pistons -

lower noise is a good idea as it pertains to longer oil rings lifetime...

I am very impressed that your motor lasted 100K - congrats!

 

I take it you were diligent in warming up the car before pushing it, and running good oil - what oil where you running?

 

Is there any difference in P-W clearance between your new Manley pistons and the

older JE pistons you were running?

 

Were both pistons had coatings on their skirts?

(and how did the JE skirts looked like after 100k?)

 

Manley states that their pistons' pins are slightly offset.

JE does not state that in their catalog but I called then and they too say that their

pistons got offset wrist pins...

 

Perhaps the older JE pistons you got did not (yet) have implemented offset wrist pins?

 

Thanks in advance for sharing!

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  • 6 months later...

KGB. Man you posted this a while ago. I have been off the forums for a while......

 

Yes I warmed it up pretty well before driving it. By the time it hit close to 100K it did pretty well only using about 1/2 quart of oil changed at 3K.

The cylinder walls were .025 out though when the motor was pulled.

 

I am not sure on the clearances difference. Id say the manley pistons are closer because of less noise.

 

The JE pistons were not coated. Here are some pics after pulled

http://legacygt.com/forums/showthread.php/mo-ks-cobb-crower-b93768b-4-rods-je-pistons-247113.html?t=247113&highlight=cobb+rods

 

If you call JE with the order number from my pistons they might be able to tell you if they were offset....

Edited by Scooby2.5
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  • 5 weeks later...
I just ordered some Wiseco K598M100AP in 100 mm I'm guessing I'm going to go with the manley H tuff rods I'm not looking to do more then 340 whp on a 16G turbo and right now Im still debating on the 16G.. I assume a 255L fuel pump will be enough.
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  • 2 weeks later...
I just ordered some Wiseco K598M100AP in 100 mm I'm guessing I'm going to go with the manley H tuff rods I'm not looking to do more then 340 whp on a 16G turbo and right now Im still debating on the 16G.. I assume a 255L fuel pump will be enough.

 

With a 16G you really don't need forged rods, stock OEM rods will do fine. If your plans later on to go with a bigger turbo, then you may consider it.

 

Haven't heard any negativity with forged pistons (any brand), it comes down to the person that installs them and measures them correctly.

My wife's balls are delicious.
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The stock rods are sensitive to two things. First, too high cylinder pressure at low rpm. Very high boost at very low rpm is fun but will bend stock rods.

Second, very high rpm. You want to run into the 7k range the bolts are prone to failure and a good bolt kit is close to the price of a budget rod kit.

 

There are lots of people doing 400whp on stock rods by avoiding those two extremes.

 

 

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Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs.
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