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Old 05-07-2014, 12:11 AM   #1
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Default Mad props to whoever can explain this to me...



Notice the kpa drop right around 6300 rpm? At first I thought it was my VICS not opening up (which turns out they weren't) but once I got them to open up at 5800 rpm I am still having this 3-4 kpa drop in the same area.

Now this is a stock 99 engine in a 94 tub without any emissions and using the 94 factory header (instead of the 99's cast junk). I'm kinda thinking I am hitting the limits of what the stock exhaust can flow - from the manifold to the muffler. Or that the factory MAF is now a restriction - it will soon be gone though once I get around to getting a piece of pipe that fits.


Anyone ever seen this before or have any other ideas of what it could be?
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Old 05-07-2014, 12:19 AM   #2
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EDIT: NVM I just realized you're N/A. I would say elevation. I don't think you'd see exactly 100kpa unless at sea level.

Could you pm me or reply to this on how you're making the vics work on your 94. I'm working on the same thing.
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Old 05-07-2014, 01:02 AM   #3
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Toss a filter right on the throttle body. You'll probably pick up 2kpa.

This is normal since the stock intake does restrict some. Why are u running MAF if you got MS?
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Old 05-07-2014, 09:10 AM   #4
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Quote:
Originally Posted by buffon01 View Post
EDIT: NVM I just realized you're N/A. I would say elevation. I don't think you'd see exactly 100kpa unless at sea level.

Could you pm me or reply to this on how you're making the vics work on your 94. I'm working on the same thing.


VICS in from whatever spare port you decide, VICS out to whatever pin you decide (25, 27, 29 or 31 etc.) the strip at the bottom that is all connected is ground.
Don't pay any mind to the chip on the right or the large transistor on the left.


Oh and I still have the MAF because I haven't gotten a pipe of the correct size to replace the MAF. Hopefully I can get that fixed this week and test again
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Old 05-07-2014, 10:43 PM   #5
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Ok, we'll I ditched the stock intake tube and replaced it with a 2" diameter intake tube and also removed the MAF.

The flow loss is still there at the same RPM so I don't think the intake made a difference (may have made the drop worse but ill have to run some more data logs, although the math says that 2" tube should be sufficient for a 1.8 @ 7000 rpm and 100% VE so IDK)

I'm wondering if it is the exhaust but I'm not sure how to test that other than replacing it.

Anything else you guys think it could be?
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Old 05-07-2014, 10:51 PM   #6
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2" is too small for NA.

The exhaust wont change your intake pressure.
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Old 05-08-2014, 10:12 AM   #7
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if the exhaust was a restriction the MAP would increase or something like that.


you dont have anything triggering at 6400RPM that would open the IM? like the charcoal canister venting or something?


considering how much your PW drops to fuel the same AFR, I'm assuming there's a pretty significant power loss...can you feel it on the butt dyno?
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Old 05-08-2014, 07:26 PM   #8
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No canister anymore and I've tried playing with the VICS but it doesn't seem to shift around at all - it's at ~6300 rpm every time.

I didn't notice it in the butt dyno and the car doesn't burn oil or anything and runs fine. Only way I even noticed it was I happened to see it on a datalog.

I'm thinking it could be the 94 throttle body on the 99 engine ir something else causing the flow to go from laminar to turbulent
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Old 05-08-2014, 07:41 PM   #9
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Sub'd out of curiosity.

I wonder if it has anything to do with the tuned RPM for the runner lengths.

Next week I should have my red car going. I've got almost the same setup ('95 car, '99 head with VICS, MS, normally aspirated). I'll do some pulls and see if mine does the same thing.

You're always turbulent BTW.
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Old 05-08-2014, 08:07 PM   #10
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Well I went back through some of my old datalogs and it seems that this has been there since last November
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Old 05-08-2014, 10:16 PM   #11
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I'm actually thinking now that this could be a natural occurrence in the VICS manifold

See post #10

https://www.miataturbo.net/engine-pe...anifold-30223/
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