So how long will my stock NC motor last - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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View Poll Results: When will it it blow?
Next time you drive it/any minute now! 5 20.00%
First track day 1 4.00%
In another 5,000 miles 5 20.00%
More than 20,000 miles 9 36.00%
Forever as long as you learn how to shift! 5 20.00%
Voters: 25. You may not vote on this poll

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Old 12-14-2009, 10:37 PM   #21
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Originally Posted by MartinezA92 View Post
This.
The walls have to be honed with a certain grit stone according to what type of rings you have. IMO, if whoever is honing your block doesn't ask for your rings or at least what material they're made out of, you need a new machinist.
I hope you guys can elaborate on this some. Last time I built a motor I went through boring and honing, and from what I did then the big issue was the ring to bore gap...where you want it a certain amount for boost/vs nitrous/vs NA; with forged pistons requiring a slightly larger one since they expand with heat more than cast. I was hoping to avoid a machine shop altogether since I can do all of the assembly here. Since its a sleeved block the goal was to leave the bores intact with whatever coating it came with from the factory. That and I don't know of any machine shops with a torque plate for this motor locally so I have to weigh the pros/cons of just going with a low mileage block and not machining vs spending an extra 500 bucks for the machine work that might be questionable...
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Old 12-14-2009, 10:53 PM   #22
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Originally Posted by mann View Post
I hope you guys can elaborate on this some. Last time I built a motor I went through boring and honing, and from what I did then the big issue was the ring to bore gap...where you want it a certain amount for boost/vs nitrous/vs NA; with forged pistons requiring a slightly larger one since they expand with heat more than cast. I was hoping to avoid a machine shop altogether since I can do all of the assembly here. Since its a sleeved block the goal was to leave the bores intact with whatever coating it came with from the factory. That and I don't know of any machine shops with a torque plate for this motor locally so I have to weigh the pros/cons of just going with a low mileage block and not machining vs spending an extra 500 bucks for the machine work that might be questionable...
...There shouldn't be a ring to bore gap. If you had a gap you'd have shitty if not complete absence of compression I'd think. I think you mean ring gap, which is the gap between the 2 ends of the ring when its installed in the cylinder.

Lets say you get forged pistons. Lets say your clearance now is something like .0015 between the cylinder and the piston. Forged pistons almost always require more clearance. So if you need .004" clearance, you have to hone/bore/whatever you want to do to enlarge that cylinder. Then it has to have a certain surface finish that will be ideal for the type of rings you have.
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Old 12-14-2009, 10:59 PM   #23
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He meant that most manufacturers have a bore size to ring gap ratio. I picked that out pretty easily from what he typed.
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Old 12-14-2009, 11:20 PM   #24
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Maybe we should do an official pool to see

as some of you saw in the dyno day thread it put out 283 whp on my "conservative" tune with peak timing of like 13 degrees at 7k.

Since then I dropped it down two more degrees and added a bit more fuel without any noticeable loss in power (11-11.5 AFR), and put in two baffles in the muffler to slow down the boost creep (jumped to 14 psi at 20 degrees last week!).

Currently running 8psi to 4k, 10 psi 4-7k rpm. Peak torque is ~230 or so vs 140 stock.

For those who don't know the 06-08 NC motor has 10.8:1 compression, all cast internals. Motor was overrevved at least twice at the track with a 4 to 2 money shift last year prior to boost. (hit the same damn bump at the etown straight right at the 3-4 shift point!) Compression numbers were 210 dead even on all 4 just prior to turbo.

It's my second car so I only drive it to beat the crap out of it...in other words, if it was human it would be tiger woods. It has a few auto-x events on it, some 'local' drifting, and will see a track day or two again next year, some official drift events, and maybe hill climbs. About 41k on the car, 4k with boost.

At this point I'm torn--do I build the motor before it blows or let it die a natural death? I know honda guys run their hi comp cast motors to 10+ psi with few issues when actually tuned, with the duratec focus/mz3 crowd usually blowing trannys first, but they supposedly only go to 260 hp or so.
I'm thinking to just ride it till it blows since they are so damn common and cheap. Then I can just pick up a low mileage block and get forged internals and not have to worry about boring and honing. Poll only goes to 20k because that would take two years for me to do if not more and by then I'll definitely be building it.

This is the car...

Awesome dyno #s! I may have to get a PHRT NC in the future.

I think it should last at least thirty miles more.

If I were you, and I have been in some regards (I ran 12 pounds on my '03 w/ 10:1 factory pistons), I would buy another motor, build it, and then swap out your stock motor while it's still alive. If your stocker has good compression still, you can sell it and pay off your build costs

Please show us 1.8'ers the potential of that engine and make even bigger numbers. I have not heard of anyone making big power on the NC yet!

Last edited by Faeflora; 12-15-2009 at 09:44 AM.
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Old 12-14-2009, 11:28 PM   #25
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Originally Posted by neogenesis2004 View Post
He meant that most manufacturers have a bore size to ring gap ratio. I picked that out pretty easily from what he typed.
You don't discuss expansion rates when you're talking about a bore size to ring gap ratio. He was talking about wall clearance.
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Old 12-14-2009, 11:30 PM   #26
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Either way Mann, take Savington's advice. There is no such thing as a built motor without a trip to a machine shop. No matter how much of a pain in the *** it may be, it is a necessity. If you do it right the first time, you will be very happy with the results.

I know what it is like to cheap out on something, and regret like hell that I did not take the step that deep down I knew was the right step. Or worse, when I did not take the advice of someone who had much more experience than me.
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Old 12-14-2009, 11:42 PM   #27
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Originally Posted by Savington View Post
You don't discuss expansion rates when you're talking about a bore size to ring gap ratio. He was talking about wall clearance.
Rings have a gap because they expand as well.
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Old 12-14-2009, 11:52 PM   #28
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Guys. You buy rings for a bore size. There is nothing wrong with using the standard bore to fit new pistons/rings into. ASSUMING it is still within tolerances. You then simply hone it and gap the rings and you are done.

And to the Martinez guy... it isn't about the right honing stones. It is typically about hone angles for different rings/ring materials. Typically set by the ring supplier.

There is so much cross talk and people misunderstanding each other here its silly.
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Old 12-15-2009, 12:08 AM   #29
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Quote:
Originally Posted by neogenesis2004 View Post
Rings have a gap because they expand as well.
And the sky is blue. Doesn't change the fact that he was talking about wall clearance.

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where you want it a certain amount for boost/vs nitrous/vs NA; with forged pistons requiring a slightly larger one since they expand with heat more than cast.
Yeah, you can hone a cylinder to take new rings and drop a set of forged pistons in, but good luck finding aftermarket forged pistons that are sized exactly correctly to your OEM bores.
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Old 12-15-2009, 12:15 AM   #30
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crap I can't remember what the hell I was talking about, I just remember choosing some damn number to suit the forged pistons and turbo, it might very well have been ring gap as they would expand with the piston and ultimately dictate the ring to wall clearance....whatever

in any case I still think I can just do a rough hone job at home on a low mileage block, and as long as the ring gap is fine it should work and they ought to seal just fine.
I just can't see the point in spending cash on a half assed machine job as long as the numbers all check out. And hell if a 10k mile block has numbers out of spec then I think I'm probably screwed on the deal anyway.
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Old 12-15-2009, 12:23 AM   #31
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Is it really that bad if you do not have a torque plate? Torque plates have not been around that long, and many a high performance engine has been built without one.

Correct me if I am wrong on this guys, but I think that having a fresh bore is the way to go if you are taking the time to do a whole new engine, even without the luxury of a torque plate.
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Old 12-15-2009, 12:27 AM   #32
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Originally Posted by Savington View Post
Yeah, you can hone a cylinder to take new rings and drop a set of forged pistons in, but good luck finding aftermarket forged pistons that are sized exactly correctly to your OEM bores.
Just get the stock block honed and mic'd. Then give that number to wiseco and tell them to make you a piston with the clearance you want built in. Problem solved. Move on.
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Old 12-15-2009, 12:52 AM   #33
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Just pony up and buy a Cosworth longblock with cams and valvetrain. Then you don't have to worry about machine work etc. Of course, you are going to be working a lot of overtime to buy back your soul but who cares right?
My subaru cossie longblock is so awesome I barely miss my soul.
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Old 12-15-2009, 04:29 PM   #34
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Originally Posted by Savington View Post
This is terrible, terrible, awful logic. Built motors are bored to match the set of pistons you supply the machinist, and then they are honed to match the rings. (something about the material or design, not exactly sure what, but my machine shop wanted a set of rings both times.) Do not think for a single second that you can buy forged internals and shove them in a low-mileage block without machine work.
Actually, according to Wiseco, boring the motor is not necessary. The NC pistons are direct replacement, no machining necessary. Wiseco explained it to me as: they intentionally off size the pistons for older motors so that the block can be "refreshed". This is a fairly new motor, so refreshing is not needed.
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Old 12-15-2009, 04:39 PM   #35
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So they are building the additional clearance into the forged piston. How clever of them.
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Old 12-15-2009, 07:07 PM   #36
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that's interesting Stephanie that's probably the same thing I read at some point on the mz3/focus boards when researching this as I have no idea where else I could have heard it.

So then the question then comes down to honing, can I just use my drill mounted hone at home to lay down a crosshatch or will that screw up the bore size, or do I even need to do it all if the block is less than 20k miles old...
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Old 12-15-2009, 07:14 PM   #37
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So they are building the additional clearance into the forged piston. How clever of them.
I'll admit that is pretty slick. My only question would be the consistency between bore to bore, motor to motor, on Mazda's part. If a batch of motors came out .002-.003 large, that's all it takes to wreak havoc.

You still need to hone, though. If you know what you're doing, it's a garage job, but you still need to tear the motor down to get the pistons in.
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Old 12-15-2009, 08:23 PM   #38
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So then the question then comes down to honing, can I just use my drill mounted hone at home to lay down a crosshatch or will that screw up the bore size, or do I even need to do it all if the block is less than 20k miles old...
Just make sure you use a ball hone, not one of those shitty hones with the 3 bars on it. You just need to do it enough to make a nice crosshatch for the rings to break into. You just go low speed and up and down fast enough to get the correct crosshatch angle.

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Originally Posted by Savington View Post
I'll admit that is pretty slick. My only question would be the consistency between bore to bore, motor to motor, on Mazda's part. If a batch of motors came out .002-.003 large, that's all it takes to wreak havoc.

You still need to hone, though. If you know what you're doing, it's a garage job, but you still need to tear the motor down to get the pistons in.
True, but with today's manufacturing processes I think a motor being off by that much is nearly impossible. My tc uses 0w20 oil because it has a p-w clearance of like 0.0005". Its nuts what the OEMs can do. And now they have "vision" computer systems that can tell minute discrepancies less than 0.002-0.003". So it really is nearly impossible for a bad motor to leave the factory unless it was just poorly engineered to begin with.

I think we will both agree though that even with the clearance built into the piston, it would be dumb not to mic all bores and pistons to verify the clearance you will actually net.
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