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Old 11-20-2006, 10:10 PM   #1
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Default Replacing Rods - Need more boost

My first post after searching:

I'm looking to turn up the wick some as I've gotten used to 240RWHP on my 02 FMII. Hydra is set for fuel cut at 13psi but I'd like to turn it up a little more...say 16psi or whatever my turbo can produce. I realize my stock rods are going to probably poke a hole in my block at that boost level so I better swap them out for something stronger.

My question is this:
  • Do y'all think I can just swap out the rods and keep the factory pistons?
  • If I do need to get pistons, will the block need to be bored or cleaned up if I get them the same bore as OEM?

I figure that I'd drop the oil pan and remove the rods and pistons from underneath rather than pulling the head or engine for that matter. I'm looking for ideas or suggestions on a simple way of increasing boost safely short of installing a new short block.

Dan
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Old 11-20-2006, 10:20 PM   #2
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i don't think you can push pistons in through the bottom, besides you can't drop your oil pan without pulling the motor. My feeling is you're going to yank your motor might as well do the pistons as well especially if more power is your goal.
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Old 11-20-2006, 10:26 PM   #3
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Thanks for your reply. A manual is on its way and I haven't been underneath the car to see that I couldn't pull the pan to get at the rod bolts. I'd have to pull the head any way to get the pistons out...I was just speaking out loud with out thinking too much. Sorry 'bout that.
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Old 11-21-2006, 12:39 AM   #4
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While your at it, you might as well get some valves, valve springs and some retainers too.
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Old 11-21-2006, 12:53 AM   #5
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And while the motor is out and apart and you're getting pistons, may as well bore it out. Same goes for the valves. And since you're taking parts to the machine shop, may as well pnp the head. And since you've spent so much money, may as well balance everything.

This is a very slippery slope. I'd come up with a power goal and a budget before doing anything. And keep in mind that your final invoices will be around twice your budget.

Ben
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Old 11-21-2006, 12:54 AM   #6
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do the rods or pistons go first assuming the tune is legit?
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Old 11-21-2006, 08:30 AM   #7
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Quote:
Originally Posted by mxv View Post
do the rods or pistons go first assuming the tune is legit?
Rods. When I blew mine, the pistons look surprisingly good. Except for the one that banged around on the snapped rod. It was from detonation, so the tops of the pistons had some marking, but weren't cracked.

I really think a budget build would be good rods and stock pistons.

Frank
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Old 11-21-2006, 05:32 PM   #8
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after market pistons are stronger, but also more brittle. they will handle more power but at the cost of reduced durability and resistance to knock. I am planning on using coated stock pistons in my DD rather than forged ones. hypereutectic pistons are excellent and forgiving. forged pistons also have more of a tendency to have/develop piston slap since they are affected more by thermal expansion than the hypereutectics. I haven't heard of this being a big problem in the miata community, however it is a known problem for some vehicles.

Now... 350bhp on the stock pistons is probably pushing your luck, but I don't intend to go that high after "attempting" to drive a 350 HP miata in GT4
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Old 11-22-2006, 10:56 PM   #9
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What is this coating you speak of? Are you re-using your current pistons or getting new ones coated?
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Old 11-22-2006, 11:42 PM   #10
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my current plan is to send a new set of stock pistons out to performance coatings for their tripple coating service.

1) ceramic coat: on the dish that helps keep combustion heat from entering the piston.

2) dry film lubrication: on the skirts to lower friction and wear

3) heat dissipation coating: on the underside of the piston to help dissipate the heat out of the piston and into the crankcase air, or in our case the oil splashing underneath the piston.

these 3 working together should (in theory) allow your engine to produce more net power and increase reliability.

The coatings will not make the pistons stronger... which is why they would only push the power ceiling up 20-30HP over non-coated. But they do increase the efficiency of the motor quite a bit.
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