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Old 09-23-2014, 10:07 AM   #21
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You can cc the combustion chambers and clean up the bowls and reuse the head IMO
Pistons I'd replace for sure, IMO. Looks like you need to either bore or hone at the very least anyway
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Old 09-23-2014, 10:23 AM   #22
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Agreed. That scuffing probably looks a lot worse than it really is.
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Old 09-23-2014, 12:45 PM   #23
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Any photos of this magic epoxy placement?
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Old 09-23-2014, 01:01 PM   #24
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Quote:
Originally Posted by Savington View Post
Debunked long ago...
I realize engine harmonics (vibration at high rpm) cause TB hardware failures, thus all the focus on isolation/bracing the TB in high revving race cars. But this was on a new TB with <5 track hours on it before the failure in 100whp SSC Miata, stock rev limit. Shaft was cracked/split at the screw hole.
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Old 09-23-2014, 01:23 PM   #25
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Back when I was researching the throttle shaft problem, I was under the impression that everyone was doing this to their TBs unless they had upgraded to the Skunk2 TB - kind of like using Inconel turbo hardware to prevent exhaust leaks. The epoxy not only prevents breakage by strengthening the throttle shaft assembly, it changes the mass of the throttle shaft which changes it's resonant frequency and prevents future cracking.

Here's where my throttle shaft broke, both times:



My epoxy job:

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Old 09-24-2014, 02:02 PM   #26
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How hard is that particular epoxy feel with the thumbnail test? (Some feel more rock-hard than others)

Nobody's seen the magic epoxy break a piece off and get ingested?
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Old 09-24-2014, 02:05 PM   #27
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Quote:
Originally Posted by Savington View Post
Debunked long ago, this failure has nothing to do with an improperly adjusted throttle.
What was the data that debunked this?
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Old 09-24-2014, 02:24 PM   #28
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I have heard from more than one engine/racecar builder that this was an issue for high revving four cylinder engines. Both builders made said isolating the TB from vibrations was done with compressible gaskets between the TB/manifold and manifold/head, along with bracing the intake manifold. Perhaps that's why Mazda put a brace on the manifold - not for weight/load. In my particular failure I suspect it was overloading of the shaft due the fact that the cable was properly adjusted before the race. After the race the throttle pedal was bent when fully mashed to the floor (aka stomper in the SM world) which of course altered the throttle cable tension. Unfortunately I neither have data to prove or disprove what caused my failure. But I can say that in the following 15 years of racing Miatas after that incident it never happened again on that car, nor five others.
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Old 09-24-2014, 06:14 PM   #29
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Quote:
Originally Posted by JasonC SBB View Post
What was the data that debunked this?
A few properly adjusted throttle bodies with broken shafts. Search if you want more info than that
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Old 09-24-2014, 07:44 PM   #30
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Quote:
Originally Posted by JasonC SBB View Post
How hard is that particular epoxy feel with the thumbnail test?
It doesn't feel quite as hard as JB Weld, but it's hard enough that my fingernail doesn't leave a mark on it.

Quote:
Originally Posted by JasonC SBB View Post
Nobody's seen the magic epoxy break a piece off and get ingested?
With the scuffing and cleaning I did to prep the surfaces before applying the epoxy, I'm far less worried about ingesting the epoxy than I was about ingesting a throttle plate screw.
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Old 09-24-2014, 09:23 PM   #31
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Did you consider brazing?
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Old 09-25-2014, 12:49 PM   #32
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Old 09-25-2014, 03:15 PM   #33
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Quote:
Originally Posted by EErockMiata View Post
very enlightening- thx
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Old 09-25-2014, 05:05 PM   #34
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Quote:
Originally Posted by m2cupcar View Post
very enlightening- thx
FWIW, in my case, the throttle body shaft is fine, the screw broke all on its own.

--Ian
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Old 09-25-2014, 05:49 PM   #35
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Quote:
Originally Posted by EErockMiata View Post
Can someone source the JDM-yo mass dampers?

And I wonder if they need the OE manifold brace to be present to work properly.

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Last edited by JasonC SBB; 09-25-2014 at 06:04 PM.
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Old 09-25-2014, 08:09 PM   #36
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Emilio,

I propose using an accelerometer board to be able to log the G's that the throttle body is being subjected to. This little guy is $37:

EVAL-ADXL326Z Analog Devices | Mouser

It's a 3-axis unit which will measure up to 16 gees. I can build you a little interface circuit to output a 0-5 V DC voltage proportional to peak G's, all 3 axes if you like that you can then datalog. Then we can look at g's vs. RPMs (and MAP or TPS).

This way we can look and see if there is a particular RPM where the IM resonates at, and see if the manifold brace changes the peak value or the resonance RPM, etc.
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Old 09-26-2014, 02:16 AM   #37
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Jason,
I was thinking the exact same thing, but trying to decide what range sensor to get. Thought 16 might be a little low? Perhaps it's alright... any reason you like that one in particular?
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Old 09-26-2014, 02:25 AM   #38
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Next step up I could find is 100 G's. Too much?

I also like the analog outputs. You could go and capture a data stream, but it'll be around 3 kHz x 3 axes, and then you'd have to process the data, filter it, and extract the amplitudes and frequency (RPM). And log MAP too. With an analog output and a simple AM circuit, you get a simple 0-5V signal you connect to an aux input of an ECU.
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Old 09-26-2014, 08:43 AM   #39
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Was the failure that started this thread on a car with the intake manifold brace to the lower part of the engine block removed?
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Old 09-26-2014, 01:31 PM   #40
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Quote:
Originally Posted by sixshooter View Post
Was the failure that started this thread on a car with the intake manifold brace to the lower part of the engine block removed?
The intake manifold brace was removed, yes. IIRC, there are a number of people who've seen this failure even with that brace installed, however.

--Ian
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