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Old 07-27-2010, 08:04 PM   #1
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Default Forged rods and stock pistons: semi-reliable on track?

So I have my ABSURDflow parts, GT2860RS, TiAL EWG (0.5 bar spring; 7-8 psi), misc intercooler parts and the rest of the necessary stuff to install the turbo sitting in my basement ready to go on the car. I also have to change out the clutch if Iím to hold any power, drill & tap the pan for the oil return, and I figured Iíd install a new rear main seal too. The plan is to pull the motor & tranny together to do that stuff.

The NoVA crew suggested that I install forged rods, you know, ďwhile I have the motor out.Ē Not a bad idea but this is where the slope gets slippery. I mean, I can afford a set of rods, but Iím not looking to do a full motor build just yet. ****, even 200 whp is going to expose a lot of inadequacies on this car as soon as it sees the track again (brakes, various ducting, needs vented hood, etc) so Iím not shooting for 300+ hp just yet. I think Iíd be happy at 225-250 whp for a while, as I re-learn how to drive and accumulate parts to build a motor and turn up the boost. I realize I will be running below the peak efficiency of the disco potato, but I didnít want to have to buy another turbo for a while and also it was the smallest turbo that would work with V-bands.

It should be feasible to run that power on stock pistons I hope. So what exactly will I need to do? I was thinking M-tuned rods, (have a local machine shop check small end clearance and assemble onto pistons), new rod bearings, new rings, new HG, light hone of the cylinders with a bore brush. Will that about do it?

I also have enough $ in the wife-doesnít-know-about-it stash to pick up a 6-spd. That and forged rods ought to let me drive it home from the track after pwning noobs, right?

Basically Iím trying to decide between two choices:
1. Install the turbo parts, keep stock internals & 5-spd, run low boost, maybe **** wonít blow up.
2. Drop the money on rods & 6-speed, but will I be able to track it *reliably* at say 250 whp with a conservative tune?

Option 3 (fully built motor) is out because I will also need to drop coin elsewhere on the car and if I wait to save up enough to do everything at once, Iíll never get this turbo installed.
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Old 07-27-2010, 08:12 PM   #2
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Honestly it sounds like you have a pretty good plan. Stock pistons will work fine. Do a quick and dirty hone, make sure you get all the gunk out of the ringlands and put on new rings, new bearings (rod and main...might as well) and you should be set to pwn some newbs. Just be kind of conservative with your tune and dont detonate and you'll be fine.

Edit: My current engine has 323 GTX rods (beefier than miata) and stock pistons. All I did was swap the crank for a long nose, new bearings, used pistons and new rings. Hell, I didn't even hone the bores and there were a few light scratches on a couple of the cylinder walls. Runs real strong.
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Old 07-28-2010, 12:32 AM   #3
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two common failure modes you'll find in a stock piston are melting and breaks at the thin sections around the perimeter.

generally these are caused by detonation. the forged pistons will succumb to it as well but the strength helps resist it to some degree.

one thing you can do to help keep heat out of the piston is a thermal barrier coating on the tops. you can send them somewhere (swain, replika maschinen, etc) or you can buy the **** from tech line and DIY coat them.

and of course, a conservative tune helps.
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Old 07-28-2010, 09:54 AM   #4
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this place charges $30 a position for a tri-coat: http://www.performancecoatings.com/index2.html

Quote:
First by impregnation of the skirts, pin bores and ring area with a dry film coating, reducing the effects of piston scuffing, piston rock and other friction induced problems.

Next, the piston dome is coated with a Ceramic thermal barrier to distribute heat evenly across the piston dome and increase combustion temperatures.


Finally, the underside of the piston is coated with a thermal barrier. This process evenly distributes heat in the chamber, thereby greatly diminishing or eliminating the chance of detonation, while reducing oil cling.
IIRc, Levnubhin has used them.
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Old 07-28-2010, 10:00 AM   #5
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I have many customers use forged rods and stock pistons. Many are make 300+hp on this setup.
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Old 07-28-2010, 11:20 AM   #6
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this place charges $30 a position for a tri-coat: http://www.performancecoatings.com/index2.html
I wouldn't recommend them for anything.
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Old 07-28-2010, 11:43 AM   #7
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Quote:
Originally Posted by ScottFW View Post
It should be feasible to run that power on stock pistons I hope. So what exactly will I need to do? I was thinking M-tuned rods, (have a local machine shop check small end clearance and assemble onto pistons), new rod bearings, new rings, new HG, light hone of the cylinders with a bore brush. Will that about do it?

2. Drop the money on rods & 6-speed, but will I be able to track it *reliably* at say 250 whp with a conservative tune?
EXACTLY what I did.

Got a fresh set of 9.1:1 pistons from a 94-97+ m-tuned rods+new bearings/seals/gaskets+ hone+rings.

Been running like a champ at around 250whp for a while now, and shooting for 300+ pretty soon here.

As long as you keep the tune safe AND/OR use something to help keep temps down/detonation away (w/i or e85) and keep the car well cooled (re-route and possibly bigger aluminum rad) I don't see a reason why it wouldn't be solid at 250whp.

EVEN if tracked.
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Old 07-28-2010, 12:17 PM   #8
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I think you'll be fine. If you plan to build the motor, and really will stay at 200whp, then I probably would not open-up the motor.
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Old 07-28-2010, 02:00 PM   #9
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I'm with hustler.
If you stay below that 250 mark, I would just save the cash for a full build, down the road.
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Old 07-28-2010, 03:01 PM   #10
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Well the least amount of power I'll be running is [whatever a 2860 supports at 0.5 bar of boost]. Just a quick look at a compressor map has me guessing that's somewhere around 200 hp? I am capable of self-restraint and having to drive the car home from the track tends to impart a sense of mechanical empathy. I could simply refuse to allow myself to buy an MBC.

OTOH, I will eventually need forged rods. When I do a full motor build sometime down the road I should be able to reuse the rods, so the only money I will be losing if I do just the rods now would be the cost of one round of bearings, rings and some gaskets. I can live with that if it will mean the motor is reliable for 12-18 months while letting me run closer to ~250 hp.

If I buy a set of Beck-Arnley or Sealed Power rings for the stock bore size, will I have to mess with sizing the rings or will they be fine to just drop in? Likewise, should I expect a set of stock 1.8 bearings to just drop in? Plastigauging the bearings to check clearances is probably within my realm of capability, not sure about sizing piston rings though. I'm trying to minimize how much $ I have to pay a shop to do, or at least know what to expect.
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Old 07-28-2010, 03:43 PM   #11
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In my experience (albeit limited) gapping rings is easier than plastigauge, but that's just my preference. You really should check the ring clearances. It's just good practice at the very least. I second the 'just wait' idea though. Tearing apart a motor isn't exactly an easy or quick task. Might as well just wait until you can afford a set of pistons and do it all at once.
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Old 07-28-2010, 04:25 PM   #12
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to get 250hp you will be around 0.7bar.

my old setup (1.6) was making 225whp at 12psi with 2860 0.86
completely stock 1.6 with mods below (with 2860)

im also down for the just wait. that is my plan as i hope to hit 1.8bar next year on my built engine and unleash the power.
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Old 07-28-2010, 04:32 PM   #13
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and were you tracking it every other weekend? I'm running 1 bar daily on my 1.6L doesnt mean squat...
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Old 07-28-2010, 05:02 PM   #14
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I would do it, i've gone through to many motors not to install rods in a boosted miata motor.

If i were to do it all over again i would have spend the extra time on a quality motor right off the bat and just kept the boost low until i wanted more power. Which wont take long on the 2860.

If i were to do it ALL over again, i would have gone v8 right from the beginning though.
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Old 07-28-2010, 05:29 PM   #15
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I vote for stock block and 6 speed for now. Drive like mad at 200whp and be happy, and build your "power" block over the next year+.
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Old 07-28-2010, 05:39 PM   #16
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Quote:
Originally Posted by thesnowboarder View Post
If i were to do it ALL over again, i would have gone v8 right from the beginning though.
This is no more simple than what you're dealing with now.


Oh, and I made 254whp on a dynojet at 10psi 8* back from MBT; at 13psi I'm making 260whp on a DynoDynamics.. You're going to be way under the prime with that turbo and might want to consider a smaller AR to help wake-up the turbo a bit.
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Old 07-28-2010, 06:12 PM   #17
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The reason we suggested rod to Scott was because he's going to pull the motor and trans to do his turbo kit since he's doing the clutch at the same time.

We figure rods are cheap and easy to do while the motor is out...no urgency for pistons if his tune is good.
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Old 07-28-2010, 06:46 PM   #18
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and were you tracking it every other weekend? I'm running 1 bar daily on my 1.6L doesnt mean squat...
yes, i was.

and then i changed to my 2871 and have done the same.
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Old 07-28-2010, 07:40 PM   #19
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Quote:
Originally Posted by hustler View Post
Oh, and I made 254whp on a dynojet at 10psi 8* back from MBT; at 13psi I'm making 260whp on a DynoDynamics.. You're going to be way under the prime with that turbo and might want to consider a smaller AR to help wake-up the turbo a bit.
Living below prime efficiency >>> spending $3xx on another turbine housing.
So even at low boost the 2860 is making decent power with conservative timing. Stock pistons ought to hold up to that, so as long as I have the 6-spd and rods that won't bend I can at least avoid totally cutting off the turbo at its knees.
BTW, 8* back from MBT was how much back from detonating?
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We figure rods are cheap and easy to do while the motor is out...no urgency for pistons if his tune is good.
I've been reading today on bearing & ring sizing and it doesn't look that difficult really. ACL Race bearings for the rods are like $42. The motor runs like a top and I have no oil pressure issues so I'm not inclined to touch the main bearings or spend the extra $90 on them considering they don't seem to be a common failure point at this power level. Fresh piston rings in standard size are $100 for Sealed Power, half that for Rock brand and Beck-Arnley is priced in between. Plastigauge is cheap and I'm pretty sure somebody local will let me borrow a honing brush. Add $50 for a HG, a few bucks to buy some tools I don't already own and doing "just the rods" will probably cost $500-600. That's not too bad considering the big bump in reliability.
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Old 07-28-2010, 07:47 PM   #20
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Quote:
Originally Posted by ScottFW View Post
Living below prime efficiency >>> spending $3xx on another turbine housing.
So even at low boost the 2860 is making decent power with conservative timing. Stock pistons ought to hold up to that, so as long as I have the 6-spd and rods that won't bend I can at least avoid totally cutting off the turbo at its knees.
BTW, 8* back from MBT was how much back from detonating?

I've been reading today on bearing & ring sizing and it doesn't look that difficult really. ACL Race bearings for the rods are like $42. The motor runs like a top and I have no oil pressure issues so I'm not inclined to touch the main bearings or spend the extra $90 on them considering they don't seem to be a common failure point at this power level. Fresh piston rings in standard size are $100 for Sealed Power, half that for Rock brand and Beck-Arnley is priced in between. Plastigauge is cheap and I'm pretty sure somebody local will let me borrow a honing brush. Add $50 for a HG, a few bucks to buy some tools I don't already own and doing "just the rods" will probably cost $500-600. That's not too bad considering the big bump in reliability.
I have plenty of spare plastiguage that you can have, just remind me when you come to pick up the engine hoist.
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