Is The Standard 1.8 Crossover Tube Restrictive? - Mechanical & Electrical - MX5Nutz Forum

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Is The Standard 1.8 Crossover Tube Restrictive?


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#1 carl s

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Posted 07 June 2020 - 07:51 PM

I've been looking at the standard mk1 1.8 crossover tube and where it attaches to the throttle body the design looks very restrictive with various indents etc. to clear things. Has anyone seen proof that this actually is a restriction?


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mk1 1991 Eunos with RS NB drivetrain: https://www.mx5nutz....howtopic=322586

ex - mk3 2006 2.0 sport

ex - mk2 1999 1.8is JRSC


#2 MR Wallace

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Posted 08 June 2020 - 08:47 AM

Apparently the standard one helps with torque but is slightly restrictive to top end power - https://supermiata.c...ata-intake.aspx


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#3 carl s

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Posted 08 June 2020 - 09:39 AM

Apparently the standard one helps with torque but is slightly restrictive to top end power - https://supermiata.c...ata-intake.aspx

 

Interesting article thanks, but unfortunately it references the NB, not the NA tube I've got.  But it does have some good info


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mk1 1991 Eunos with RS NB drivetrain: https://www.mx5nutz....howtopic=322586

ex - mk3 2006 2.0 sport

ex - mk2 1999 1.8is JRSC


#4 carl s

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Posted 10 June 2020 - 11:00 PM

This is the area that looks like it restricts the airflow, this big dent on the bottom of the pipe just where it goes into the throttle body. Anyone else thought this is strange?
 
49993422027_cabe217f15_c.jpg

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mk1 1991 Eunos with RS NB drivetrain: https://www.mx5nutz....howtopic=322586

ex - mk3 2006 2.0 sport

ex - mk2 1999 1.8is JRSC


#5 noobie

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Posted 11 June 2020 - 07:50 AM

You can use a magnehelic gauge or cheap digital pressure gauge to measure the pressure drop over that section. My guess is that its negligible compared to other losses in the system.


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#6 MR Wallace

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Posted 11 June 2020 - 08:41 AM

 

This is the area that looks like it restricts the airflow, this big dent on the bottom of the pipe just where it goes into the throttle body. Anyone else thought this is strange?
 
49993422027_cabe217f15_c.jpg

 

 

I'm still running the tube too, never noticed that though!

 

I think the article I referenced above relates to any BP/1.8 engine but I think the later intake pipes are round rather than squashed like above so maybe they're an improvement too (despite still having the resonance chamber)?

 

I keep thinking about making an intake just with a couple of 2.5" silicone bends and straight pipe, easy and cheaper than the likes of a K&N typhoon. For what I do a little more top end power is worth losing a little torque and having seen that stock intake pipe it must be a little restrictive.


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#7 carl s

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Posted 11 June 2020 - 08:58 PM

I still have the crossover pipe from the RS doner for my engine conversion, a bit of research and it looks like engines with VICS didn't have the resonance chamber in the crossover (apparently the VICS did the job of covering the 'dip') I'm going to see if I can adapt it to fit a mk1 as the tubing is a lot bigger bore than the one above.


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mk1 1991 Eunos with RS NB drivetrain: https://www.mx5nutz....howtopic=322586

ex - mk3 2006 2.0 sport

ex - mk2 1999 1.8is JRSC


#8 MR Wallace

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Posted 12 June 2020 - 08:43 AM

That's interesting, i assumed they all had that chamber. I'm sure it can be made to fit easily.

 

Let us know if it makes any difference.


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#9 carl s

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Posted 12 June 2020 - 10:34 PM

I will report back  :thumb-up: at the moment the car is off the road as the steering rack has been sent away for rebuild.  It's just struck me that when I had the car setup on the rolling road it had the K&N typhoon which was very unrestrictive at the time.


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mk1 1991 Eunos with RS NB drivetrain: https://www.mx5nutz....howtopic=322586

ex - mk3 2006 2.0 sport

ex - mk2 1999 1.8is JRSC


#10 carl s

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Posted 02 July 2020 - 01:17 PM

interesting post from the same thread on Miata.net:

 

Back when I was prepping for STS2 class...I tested 7 intakes. 2 were stock and modded stock. The others were the kings of that era. Best was modded stock. The resonator (97 1.8) helped in the midrange. And the mods were at the intake accordion to fit a cone to MAF and drink air behind the nearby headlight. And at that flat spot...I cut that out and fiberglassed in a round cross section and accomodations for the turn coming up into the TB. It was the clear winner, mostly due to the midrange gain. Testing was done scientifically with weather corrections, same level road averaged in both directions, high end datalogger and so forth.

 

Sounds like it does make a difference!


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mk1 1991 Eunos with RS NB drivetrain: https://www.mx5nutz....howtopic=322586

ex - mk3 2006 2.0 sport

ex - mk2 1999 1.8is JRSC


#11 Quinvy

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Posted 02 July 2020 - 06:12 PM

I was just reading that a hour ago. Lol
I can't really understand what the guy is saying. A picture would have been very useful.
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