GameboyRMH
GameboyRMH PowerDork
10/30/12 9:36 a.m.

I can get a set of these for a decent bit less than retail:

http://www.maperformance.com/wiseco-piston-shelf-stock-toyota-4ag-1.188-c.h-3228xc-6506p82.html

Which is still a hefty brick of cash. A lot of the advice out there seems to suggest that cast hypereutectic pistons are the bang-for-buck sweetspot, but it seems they aren't on the market anymore. Anyone know how these measure up in terms of thermal expansion?

Calling oldskewltoy!

92CelicaHalfTrac
92CelicaHalfTrac MegaDork
10/30/12 9:39 a.m.

Are you going to have a way to tune the car to take full advantage of the compression bump? How much of a change is it?

SkinnyG
SkinnyG HalfDork
10/30/12 9:40 a.m.

I've heard that Miata pistons will work - but I have not found anything to substantiate this.

GameboyRMH
GameboyRMH PowerDork
10/30/12 9:44 a.m.
92CelicaHalfTrac wrote: Are you going to have a way to tune the car to take full advantage of the compression bump? How much of a change is it?

The rest of the engine will be mostly stock, but one of the mods high on the list is a Megasquirt.

They're available in a variety of compression ratios and overbores, the ones available to me are 0.5mm overbore and "high compression," I'll have to contact the guy to find out exactly what.

92CelicaHalfTrac
92CelicaHalfTrac MegaDork
10/30/12 9:46 a.m.
GameboyRMH wrote:
92CelicaHalfTrac wrote: Are you going to have a way to tune the car to take full advantage of the compression bump? How much of a change is it?

The rest of the engine will be mostly stock, but one of the mods high on the list is a Megasquirt.

They're available in a variety of compression ratios and overbores, the ones available to me are 0.5mm overbore and "high compression," I'll have to contact the guy to find out exactly what.

Then go for the moon!

GameboyRMH
GameboyRMH PowerDork
10/30/12 9:48 a.m.
SkinnyG wrote: I've heard that Miata pistons will work - but I have not found anything to substantiate this.

Some Googling says Miata pistons will fit but require a...perhaps unwise amount of overbore.

Keith Tanner
Keith Tanner MegaDork
10/30/12 10:43 a.m.

"Miata pistons" come in a range of sizes. What's your stock bore?

GameboyRMH
GameboyRMH PowerDork
10/30/12 10:46 a.m.

Stock bore is 81mm and the only Miata pistons bigger than that are the 83mm ones.

Teh E36 M3
Teh E36 M3 Dork
10/30/12 11:04 a.m.

The stock pistons are pretty good units by almost all accounts. Was there something you were hoping to gain? Otherwise, for comparison, paradise racing sells arias forged for $475/set at 11:1 c/r and 81.5mm. I'd go for cams before pistons though. Shave the head .5mm for a little boost in c/r and a lot less $$.

Keith Tanner
Keith Tanner MegaDork
10/30/12 11:07 a.m.
GameboyRMH wrote: Stock bore is 81mm and the only Miata pistons bigger than that are the 83mm ones.

The only STOCK Miata pistons bigger than that are 83mm, you mean Or 83.25. Or 83.5. Or 83.75. Or 84.0.

But yes, I see your point. I don't know how the block would deal with that much overbore. A Miata block can take +2mm.

Matt B
Matt B Dork
10/30/12 12:00 p.m.
Teh E36 M3 wrote: The stock pistons are pretty good units by almost all accounts. Was there something you were hoping to gain? Otherwise, for comparison, paradise racing sells arias forged for $475/set at 11:1 c/r and 81.5mm. I'd go for cams before pistons though. Shave the head .5mm for a little boost in c/r and a lot less $$.

I'm no expert by any means, but what Teh E36 wrote makes sense to me. Personally, I'd do MS first, cams & headwork, then bump compression if you still needed it.

Also, I remembered something oldskewltoy said about 4A headwork and raising compression from an MR2 forum.

"Not sure of what your budget is... but I would recommend some head work. Intake side needs very little, bowl and seat work mostly. The exhaust side could use some porting, but the real key for power for you should be inside the chambers... deshrouding the chambers will allow you to run more compression, or ignition timing without worrying about ping/pre-ignition."

Hope ya don't mind oldskewl!

GameboyRMH
GameboyRMH PowerDork
10/30/12 12:01 p.m.

Extra compression feels good but I'm more interested in reduced thermal expansion, the car makes short trips and that should reduce wear, seems like it could be a good investment.

Matt B
Matt B Dork
10/30/12 12:09 p.m.

Ah, somehow I missed that it was specifically the thermal expansion you were after.

Carry on!

oldeskewltoy
oldeskewltoy Dork
10/30/12 12:55 p.m.

Look carefully @ the DETAILS.........

1st important thing to verify is the chamber size Wiseco(piston manufacturer) uses to determine compression ratio....

As far as I've seen... ALL of them have the wrong numbers for a STOCK combustion chamber... from what I've seen... all use 39cc chamber, the stock chamber is only 36cc. Look @ the crowns... if they have a peak on them... walk away, flat piston crowns are better especially for mostly "stock" rebuilds

What that means(36cc to 39cc chamber) is their compression ratio numbers will be off significantly... higher then what they say......

The BEST bang for your buck is to use the piston from the 1990+ 4AGE, it has a compression ratio of 10.3 to one, it also will fit MOST of the 4AGE rods.

What MOST means... the earliest 4AGE engines had a different crankshaft, and smaller(pin and journal diameters) rods. The early engines use a press-fit 18mm diameter pin, while the larger rod uses 20mm full floating pins

If you are building for performance... there are many pistons now "available" that are superior to the Wiseco.

custom piston for 4AGE

Wiseco I know of...

Toda

stock slugs...

first pair... 9.4 to 1, and RARE Singapore, and non cat areas in europe 10 to 1

10.3 to 1

Teh E36 M3
Teh E36 M3 Dork
10/30/12 1:10 p.m.
GameboyRMH wrote: Extra compression feels good but I'm more interested in reduced thermal expansion, the car makes short trips and that should reduce wear, seems like it could be a good investment.

I'd go with stock there too. Remember they gave pretty good warranties on these things when new, and nothing beats stock pistons for longevity under street driven circumstances in my opinion. Forgot about the '91 10.3:1 set... that's a pretty good deal.

fidelity101
fidelity101 Reader
10/30/12 1:11 p.m.

If you're on a budget you can try re-using stock pistons and decking the head a tad.

oldeskewltoy
oldeskewltoy Dork
10/30/12 1:22 p.m.

I just looked @ Wisecos offering - http://www.wiseco.com/Catalogs/SportCompact/SubaruToyota.pdf

piston volume is 5.9cc...

do the math......

3.189" - bore 3.031" - stroke .015" - deck .047" - stock head gasket 36cc - chamber volume

If you do the math... that piston will deliver a static CR of 11.38... WAAY too high.... Piston volume should not exceed 3-3.5cc, and that is a bit high, likely requiring chamber de-shrouding to avoid ping...

GameboyRMH
GameboyRMH PowerDork
10/30/12 1:37 p.m.

This is a '92 JDM motor so I have the 10.3:1 pistons.

Now that I have your attention oldskewltoy are there any parts of the rebuild kit where you recommend using genuine stuff or is the aftermarket stuff fine? Also for headwork I was thinking valve deshrouding/"joggle" removal, combustion chamber deburring, intake porting and a 3-angle valve job, sound good?

oldeskewltoy
oldeskewltoy Dork
10/30/12 2:31 p.m.
GameboyRMH wrote: This is a '92 JDM motor so I have the 10.3:1 pistons. Now that I have your attention oldskewltoy are there any parts of the rebuild kit where you recommend using genuine stuff or is the aftermarket stuff fine? Also for headwork I was thinking valve deshrouding/"joggle" removal, combustion chamber deburring, intake porting and a 3-angle valve job, sound good?

I prefer all the OEM stuff..... I know Aisin makes after market stuff.... I still prefer the Toyota stuff.

I rebuilt Grunts lump(4AFE) with Rock Auto parts... and once I looked @ the head gasket... I got OEM. The other Rock Auto gaskets I'm using.... So far... no leaks (about 20k miles so far)

OEM required(imho): oil pump, head gasket, timing belt tensioner bearing OEM preferred: all gaskets, belts, seals, and water pump.

For headwork... if you deshroud(remove joggles)... have the head cut .005" to .010" depending on how much you remove - to regain lost compression.

Hmmm, re-reading your desires.... ASSUMING the head hasn't been cut before (measure chamber volume... should equal 36cc) I'd cut the head .015" (3/4mm)-.020"(1mm). the above chamber work, along with an .015" cut should lower chamber volume to about 34cc. that along with your stock pistons will give you a static CR about 10.6. pretty good especially with deshrouded chambers.

3 angle is always good... BUT... not all 3 angles are =. Recommend you give your machine shop the TRD Bible showing the recommended 3 angle.

leave intake side alone for the most part... areas you want to work are the bowls and seats... and if you can the exhaust port retaper

Do you have a spare head? I STRONGLY recommend you work on that first...practicing removing material from the needed areas in a non NEEDED head. Operating the tool and getting the proper results requires practice... and experience.

btw... I'm currently free.........

GameboyRMH
GameboyRMH PowerDork
10/30/12 2:47 p.m.

I'd like to send my head to you but I'd hate to see what it costs to send a 50lb block of metal a quarter-way across the planet twice, and keep it duty free on the way back...I will look into it though.

dean1484
dean1484 UltraDork
10/30/12 2:58 p.m.

Getting back to the OP's original question of are they worth it? In my book not really. The stock pistons and rods are very good. I use to build 4age motors to IT spec and we never had a piston related failure. From what I have learned over the years with 4AGE's is that a really good port and polish of the heads and decking the head (you can remove allot of material from the stock head) can easily net you 10.5 - 11 / 1 compression

Spend the time to balance every piece of the rotating assembly. The pistons and rods should be separated from each other and put on scales and then all of them made to match the weight of the lightest component of the set. Don't forget to include the bearing caps and bearings with the rods and you also have to include the wrist pins as well. The next thing is to measure the volume of the heads or CC the heads and remove material from each combustion chambers so all the chambers are equal in volume the largest of the 4. Try to see where the differences are and remove material so that it matches the others. This is not always easy to do. Then have it balanced with the flywheel and clutch assembly. A Lot of this can be done by you and cost you only time and effort. The cost will be for the machine work on the head and the balancing of the rotating assembly. But that should be less than a cost of new pistons.

oldeskewltoy
oldeskewltoy Dork
10/30/12 3:48 p.m.
GameboyRMH wrote: I'd like to send my head to you but I'd hate to see what it costs to send a 50lb block of metal a quarter-way across the planet twice, and keep it duty free on the way back...I will look into it though.

30#-32#...

and I've sent heads 1/2 way around the world.... to Switzerland, and Africa...

the cost to ship the swiss head was $162

To save money, I might be able to supply a head, and that way it is only shipped one way....

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