Miata intake manifold brace

I am putting my engine back together right now. I think I've read on here that a lot of folks leave the intake manifold brace off to ease oil filter access. I can go either way on the issue, but my question is, if there are zero downsides to leaving the thing off, why did Mazda put it there in the first place ? Anyone out there with an engineering big brain want to offer their opinion ?

I'm always skeptical about removing something that smart engineers deemed necessary and that Mazda went to the trouble to make and install on a whole bunch of cars. It's not like they waste money willingly.

I don't have a Miata so this is all just opinion but I would leave it or perhaps machine it out to lighten it. There are no downsides to having a rigid engine assembly.

I have had mine out for years on my rallycross Miata with no issues. 

I don't have a big engineering brain.

My guess, though, is that Mazda engineers are considering a decade or 200k miles of vibrations and fatigue. I would also guess that people who remove them are generally less concerned with longevity.

Keith said:

I've never seen a Miata intake manifold crack from the brace removal. I know that it's SOP to pull the intake manifold brace off a GTX and throw it as far away as possible.

I'll let you know, though. We're only about 15 years in testing the effects of intake manifold brace removal on Miatas I don't think there's a single car at FM that has one, except maybe Igor. And that's only because we haven't started doing anything on that car yet. Go ahead and remove it.

As for your little bolt and spring - it came out of the head? Doesn't look familiar to me. I don't know what's on the intake manifold and throttle body on a Protege BP, but I'd be looking at the various coolant lines or the idle speed control valve to start.

Stefan said:

Keith said:

As for your little bolt and spring - it came out of the head? Doesn't look familiar to me. I don't know what's on the intake manifold and throttle body on a Protege BP, but I'd be looking at the various coolant lines or the idle speed control valve to start.

Thank you, but I am not following you on this part of your answer ?

Does anyone have any data to show the relationship between throttle shaft breakage and intake brace removal?

Cousin_Eddie said:

Stefan said:

Keith said:

As for your little bolt and spring - it came out of the head? Doesn't look familiar to me. I don't know what's on the intake manifold and throttle body on a Protege BP, but I'd be looking at the various coolant lines or the idle speed control valve to start.

Thank you, but I am not following you on this part of your answer ?

Its from an old post about a Protege project here, I was in a hurry and didn't trim the quote. I searched Google for "Intake Manifold Brace site:grassrootsmotorsports.com" and grabbed Keith's quote.  You can ignore it.

Seriously, its been written about for decades and was held over from the days when the BP was used in FWD cars and I suspect it only happened in very certain circumstances like a car crash for example: where breaking the intake manifold off while the engine is running could cause the engine to run away (highly unlikely with relatively modern ECU's), but like many mods that we as enthusiasts do, the engineers have to design the products to work in a much wider range of conditions than we may actually use them in.

Update, we're now 28 years into the Intake Manifold Brace Removal Test and still no reported failures

I hucked the intake manifold brace on the BP I'm dropping in my Miata. 

I have never run one in any of my miatas. 

They're gone on all of mine.  I have yet to come across a verified report online of a manifold cracking.

The 90s Honda's have them too. The ones I had/have lost them - no problem.  It is quite a hunk of weight hanging off the head vibrating but the stud placement and material quality seem to handle it. But as mentioned above, we don't know what happens when application of sufficient force shortens the front end by a foot or two.  I do know it removed a pita factor when taking the intake off.

Is that the thing that get's in the way when you're trying to remove the alternator?

In reply to Woody :

Among other things, yes.