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Average engine longevity: 4032 vs. 2618 forged pistons?
Average engine longevity: 4032 vs. 2618 forged pistons?
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Old 11-30-12, 01:43 PM   #1
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Default Average engine longevity: 4032 vs. 2618 forged pistons?

Hi guys,

I've searched and read any forged piston thread I could find, but I'm trying to get a sense of how many miles can be expected out of a build with each of these pistons at say, stage 2 or stage 2+ numbers. Assuming everything being equal (properly built, proper tune, etc.), how long can one expect before needing to rebuild the engine due to piston-wall clearance and wear? I'm not factoring detonation into the equation - assuming a proper tune.

I've read that 2618 builds can be expected to last between 50K and 60K miles before losing enough compression to require a rebuild. What I haven't found is how long a 4032 build should last in comparison. From what I've read, 4032 forged pistons seem to offer the best compromise between being able to handle detonation better than stock cast pistons, while also being able to maintain a tighter piston-wall clearance due to less expansion and thus less piston slap and supposedly less wear than the 2618 alloy.

Also - does a rebuild necessitate a new block, or can the cylinders be honed and salvaged? Obviously this depends on how long it is left once compression is low, increasing blow-by and risking fuel dilution which means lower octane and det, etc. Would the labour/work on the block to salvage it be worth it vs. just getting a new short block?

Anyway, let's just say that I'm in the market for a new short-block (stock lean tune and 2 track days after 28K miles - brutal) and my tuner/engine builder (remaining nameless since I'm using some pricing of his below, but he is a VERY well-known engine builder and tuner in the North-East) has stated that for stage 1 and even stage 2 #'s, all I really need is cast pistons - as long as I promise not to track the car. He said that 2618 pistons would be a modest price increase to build the motor, but a 4032 would necessitate a LOT more labour and block work in order to get the piston-to-wall clearance necessary to take advantage of the 4032 pistons, increasing the cost of the build by quite a bit. I know you can't just "drop-in" a set of any pistons, but is the machine work/labour required that much less with a 2618 build vs. 4032? Rough estimates he gave me were;

1. 2618 build: $7200+tax in parts and labor for the upgraded shortblock we discussed, OEM engine gasket set and other required gaskets, air oil separator and install, fluids, oil filters, zip ties, adhesives, shop supplies, retuning for the new engine on the dyno and road, fresh spark plugs, ARP head studs and cam gear bolts, cylinder head rebuilding and resurfacing, and the shortblock replacement labor. The cam gear bolts are often seized and have to be damaged to extract them." ($2900 for the built short block).
2. Stock build: $1100 less than the built motor above (not sure if AOS is in this price though)
3. 4032 build: $8400+taxes. "We don't use 4032 pistons without performing additional tear-down, blueprinting, bore and honing, and assembly work to get the bores more round and get the piston to wall clearance just right to take advantage of them. That increases the cost to $4100 for the shortblock."

I'm more than convinced that at Stage 2, a proper tune would more than likely be fine with stock pistons, but I just can't help to want to upgrade the motor to add that extra reliability. I'll never go more than stage 2 (even if the stock turbo goes, I'll only upgrade it for reliability, not increased volume), but I bought the car so that I could drive it spiritedly and do a track day or two a year and maybe a HPDE to improve my skills. This is how Subaru portrays the car in their marketing campaigns, but I digress...

So, any info you guys can offer to help me make my decision would be great. Again, I've researched into the advantages and disadvantages of both alloys over the past few weeks on the differences between the two. I'm just looking to see how much longer a 4032 build will hold compression numbers for at conservative power levels. My tuner is a very busy guy and he's been more than fantastic at answering all of my numerous, lengthy e-mails full of build and tuning questions, so I don't want to harp on him too much. I've asked this question to him, but I've taken a lot of his time, so thought I'd ask the question in here before bothering him yet again with this question.

Also, I've searched first and read all the threads I could, but all of them discuss the differences in the two alloys with the advantages/disadvantages of each, but nowhere could I find a longevity comparison.

P.S. This is all assuming I won't be covered under warranty, as I've heard too many instances where they will try and deny claims even with stock motors. Even still, unless the short-block comes pre-assembled to the dealer, I don't want the Subaru "Master Techs" hacking up the job and would probably still go to an engine builder if choosing cast pistons.

Thanks guys!

Last edited by dantheman762; 12-10-12 at 05:08 PM. Reason: Fixed the actual quoted numbers for different builds.
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Old 11-30-12, 03:30 PM   #2
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Default Re: Average engine longevity: 4032 vs. 2618 forged pistons?

FWIW a friend of mine has been running an 06 STi with a Cosworth long block (read 4032 pistons)for ~130,000KM's in temps ranging from -45 to +35 for the last 5 years and last comp test showed 160-163 across the board.
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Old 11-30-12, 03:31 PM   #3
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Default Re: Average engine longevity: 4032 vs. 2618 forged pistons?

IMO only

DD Street car with a couple trackdays should have 4032 pistons.
Track only car running high boost 2618 pistons.

That said I have 2618 pistons in my street car, long story.
Long trips across town, at low speeds, at some RPMS and loads I can hear piston slap with the radio off. Does it matter? Who knows. A shift or load change noise is gone.
Cold always noisey.

Some 2618 pistons are coated and are not noisey. How long that lasts is debatable. Some builders seem to be having good results.

You can buy drop in pistons that will fit as well as a machine shop job. The drop ins are sized to fit the cylinder with the piston to wall clearance all figured in. Mahle manufactures 4032 drop in pistons. Takes the same amount of work as dropping in 2618s. (Stock size 99.5mm)

Alot of shops buy new short blocks from a Subaru dealer and drop in some forged pistons. $2700-$2900. Some shops do more work on the short block, and charge a few bucks more. Some coat their pistons some do not.

I would research short blocks and make a few calls. $9k for a stage 2ish shortblock seems off the deep end, but you did not include what exactly is done.

Myself I could not see installing a stock cast piston engine to replace my broken stock cast pistons. If you have to yank the engine and spend alot of money why not build it solid the first time?

To answer your question I do not know which would last longer. The 4032s would probably take the everyday cold starts better, but does it really matter that much? If the 4032s last 20,000 miles more do you really care. by the time the 2618s wear out you will probably need a valve job and a head gasket.

Good luck with your decision.
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Old 11-30-12, 05:06 PM   #4
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Default Re: Average engine longevity: 4032 vs. 2618 forged pistons?

Quote:
Originally Posted by Nigel View Post
FWIW a friend of mine has been running an 06 STi with a Cosworth long block (read 4032 pistons)for ~130,000KM's in temps ranging from -45 to +35 for the last 5 years and last comp test showed 160-163 across the board.
This is encouraging. This is what I'm looking for. Hoping an engine builder can chime in and give their $0.02. Thanks for this info.

Quote:
Originally Posted by VanishingPoint View Post
IMO only

DD Street car with a couple trackdays should have 4032 pistons.
Track only car running high boost 2618 pistons.

That said I have 2618 pistons in my street car, long story.
Long trips across town, at low speeds, at some RPMS and loads I can hear piston slap with the radio off. Does it matter? Who knows. A shift or load change noise is gone.
Cold always noisey.

Some 2618 pistons are coated and are not noisey. How long that lasts is debatable. Some builders seem to be having good results.

You can buy drop in pistons that will fit as well as a machine shop job. The drop ins are sized to fit the cylinder with the piston to wall clearance all figured in. Mahle manufactures 4032 drop in pistons. Takes the same amount of work as dropping in 2618s. (Stock size 99.5mm)

Alot of shops buy new short blocks from a Subaru dealer and drop in some forged pistons. $2700-$2900. Some shops do more work on the short block, and charge a few bucks more. Some coat their pistons some do not.

I would research short blocks and make a few calls. $9k for a stage 2ish shortblock seems off the deep end, but you did not include what exactly is done.

Myself I could not see installing a stock cast piston engine to replace my broken stock cast pistons. If you have to yank the engine and spend alot of money why not build it solid the first time?

To answer your question I do not know which would last longer. The 4032s would probably take the everyday cold starts better, but does it really matter that much? If the 4032s last 20,000 miles more do you really care. by the time the 2618s wear out you will probably need a valve job and a head gasket.

Good luck with your decision.
Very good point. If it's only 20K miles more, then it's not worth it. Yes, I agree 100% about building it right the first time, which is why I'll probably pony-up for 4032's, as 50K mile engine rebuild is just not in the cards for me. Too short-sighted. However, if 4032's are only 20K more, then 2618's may be the most cost-effective option. Regarding the price quote, this was for absolutely everything (fluids, zip-ties, etc.) and worst-case scenario (not likely that I'll need timing belt, etc. replaced at 28K miles, but he's under-promising in hopes of over-delivering, which I like). Hmmm... I should look up when a valve job is recommended on a stock motor.

Any comments on what more needs to be done to the block for 4032s vs. 2618s? This is really what I'm looking for (after determining the longevity differences between the two) to justify my quote. Not that I don't trust him (the shop has an EXCELLENT reputation within the community), but just want input from others, along with not hounding him and making it sound like I'm asking him to double-justify his workmanship.

Thanks for your input - very much appreciated!
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Old 11-30-12, 05:50 PM   #5
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Default Re: Average engine longevity: 4032 vs. 2618 forged pistons?

I personally have not heard that 4032 would take more time/cost to build with than 2618. You should be able to get closer to stock like longevity out of the 4032 pistons vs having to rebuild the 2618 engine every 50k or so. 4032 you can run closer piston to wall clearances.

I have debated this for my future build as well. I think I came down to it being if you are a track only car and are going to run a big turbo with high boost go with the 2618. For a daily driver the 4032 is probably the better choice. Keep in mind that yes a 4032 is not as strong as a 2618 but can still hold up to much more detonation than our cast pistons. With a properly build 4032 block you should be able to go 100k+ without issue.

I think if you google the topic 4032 vs 2618 you will probably find a lot of good conversation on numerous forums. I have read over a lot
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Old 11-30-12, 10:31 PM   #6
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Default Re: Average engine longevity: 4032 vs. 2618 forged pistons?

Quote:
Originally Posted by LaW View Post
I personally have not heard that 4032 would take more time/cost to build with than 2618. You should be able to get closer to stock like longevity out of the 4032 pistons vs having to rebuild the 2618 engine every 50k or so. 4032 you can run closer piston to wall clearances.

I have debated this for my future build as well. I think I came down to it being if you are a track only car and are going to run a big turbo with high boost go with the 2618. For a daily driver the 4032 is probably the better choice. Keep in mind that yes a 4032 is not as strong as a 2618 but can still hold up to much more detonation than our cast pistons. With a properly build 4032 block you should be able to go 100k+ without issue.

I think if you google the topic 4032 vs 2618 you will probably find a lot of good conversation on numerous forums. I have read over a lot
Thanks Law. I guess I'll have to push my tuner/builder for a little more justification as to why the increased labour costs for a 4032 build. He gave me generics, but nothing concrete. Yes, I think I want 4032, but not at that price discrepancy... at least not without justification and what cut corners other builders are assumed to be making if they don't charge the increased labour.

Last edited by dantheman762; 12-07-12 at 10:07 PM.
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Old 12-06-12, 06:39 AM   #7
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Default Re: Average engine longevity: 4032 vs. 2618 forged pistons?

The $7200 and $9k sound like insane #s for a stock rebuild with pistons. I see that you are in Canada so that could be why the price is so high (not sure of Canada's pricing). For a refrence point, I paid $3,700 to have my motor rebuilt. This included a stock rebuild with bearings new timing belt kit and cp pistons as well as a full refresh of the heads including stock valves and other replacement parts. All gaskets were also factored into this price.

I also had my choice of 4032 or 2618 pistons. Im not sure why that really matters, as the pistons should not just be dropped in.
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Old 12-06-12, 07:47 AM   #8
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Default Re: Average engine longevity: 4032 vs. 2618 forged pistons?

At stage 2 you're wasting your money building the motor to begin with. Just get a stock shortblock. Unless you're making significantly more power, you're just creating a large headache and monetary drain than you have to.
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Old 12-06-12, 08:01 AM   #9
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Default Re: Average engine longevity: 4032 vs. 2618 forged pistons?

If the motor is already apart why not upgrade with forged pistons. At the end of the day your putting in another short block that could have the same ringland issues. Just pistons is no headache at all. Just warm it up a little and go.
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Old 12-07-12, 02:54 PM   #10
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Default Re: Average engine longevity: 4032 vs. 2618 forged pistons?

Quote:
Originally Posted by subarudunk View Post
The $7200 and $9k sound like insane #s for a stock rebuild with pistons. I see that you are in Canada so that could be why the price is so high (not sure of Canada's pricing). For a refrence point, I paid $3,700 to have my motor rebuilt. This included a stock rebuild with bearings new timing belt kit and cp pistons as well as a full refresh of the heads including stock valves and other replacement parts. All gaskets were also factored into this price.

I also had my choice of 4032 or 2618 pistons. Im not sure why that really matters, as the pistons should not just be dropped in.
Wow! Did that include labour, tune, misc. items too? I tried to see if you had a build journal, but you don't. Would you mind telling me which shop you got this work done at? PM me if you'd prefer. The shop who quoted me is in the US, so these were USD prices, but we've had a par dollar for almost 2 years now, so I get angry whenever any Canadian retailer still tries to use the USD+ pricing to gouge us. I now know that I should maybe shop around, but this shop is VERY well known as an extremely reputable engine builder and tuner and they've treated me fantastic so far. However, if there's that much $ to gain by speaking to a couple of others, then I guess I owe it to myself to do that. Problem is, you can never tell if you're comparing apples to apples and this shop seems to have that extra attention to detail that an anal guy like me is looking for. Still, not looking to over-spend either. I've edited the post to better reflect what his pricing included (dyno and street tune for break-in and final, AOS+install, oil cooler+install, etc.) Thank you Subarudunk for making me think about shopping around.

Quote:
Originally Posted by brfatal View Post
At stage 2 you're wasting your money building the motor to begin with. Just get a stock shortblock. Unless you're making significantly more power, you're just creating a large headache and monetary drain than you have to.
This is what the shop is trying to steer me towards, but right or wrong, I'm currently (this can change) in the mindset that the only way I'd have cast pistons in my new engine was if Subaru was covering it - because it would be free. If I'm paying, I want added reliability from knock. My shop also did stress that if using stock pistons, to definitely NOT track the car. This is a no-go for me, as I want to be able to do at least 1 or 2 track days a year, even if they're for 3-4 hours with a max of 30-40 laps. I do appreciate this advice though Brfatal, as it does kinda make sense from a cost and longevity perspective. I just want to be able to track the damn car, that's why I bought a performance car.

Quote:
Originally Posted by subarudunk View Post
If the motor is already apart why not upgrade with forged pistons. At the end of the day your putting in another short block that could have the same ringland issues. Just pistons is no headache at all. Just warm it up a little and go.
Yes, this is my thinking as explained above to Brfatal's post. Thank you for re-enforcing my initial thoughts, but I'm open to any suggestion that has merit - even cast pistons if it can be said that they would be able to handle the odd track day. When a reknowned engine builder says probably not though, I wonder. Just knowing that forged slugs are that much more det resistant would be great, even with a proper tune. Especially if the 4032 alloy pistons seem to offer the best of both worlds in terms of det resistance and longevity. Still looking for more input as to how much longer a 4032 build should last vs. the 2618 build.

Last edited by dantheman762; 12-07-12 at 10:10 PM.
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