Sudden boost in power?

Technical Area Engine, Transmission, Exhaust etc
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  1. My model of MX-5 is: __Mk3 2009 1800cc
  2. I’m based near: __Stafford
  3. I’m looking for technical help or recommendations on: __sudden boost in power.This is most noticeable when the engine is cold. The engine performance is ok and smooth but come approximately 2500 - 3500rpm depending on how cold the engine is, it’s like a turbo boost?
    Is this impending doom? The car is high mileage @ 98k but drive very well
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It’s normal, it seems to be something that’s mapped in,

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Thanks for the reply Robbie. It’s good to know it’s normal especially as the car drives beautifully.

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I know exactly what it is you speak of as my '07 NC1 behaves the same. Obviously, when the car is cold (and I’m driving it to warm it up) there is a very noticeable shove around 3k revs, as you say.
I don’t push much past that at all until I’m maybe 10 mins into a particular journey so as I know it’s proper warmed up.
The post above mine suggests it’s mapped in…I get that but WHY would this action stop when the car’s warmed up and it does completely disappear ?

Can you shed any light on that Roadster Robbie ??

Seems a backward step for this “boost” not be available when engine is warmed up…

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Now that its been explained to me that its normal, it makes sense! It’s the start of the fun zone.
The MX5 is a drivers car, if you’re just pottering about rpm doesn’t need to go much above 3500rpm. If on the other hand and the conditions allow driving at and above 3500 is, as I say in the fun zone.
That’s my explanation. I don’t know if it’s right. Maybe someone here knows?

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I’m guessing the mixture is enriched when the car’s cold, like the old choke set up. It doesn’t stay like that for very long for good reason.

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Always thought that was the VVT kicking in.

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Hitting the power band might be more noticeable in the current misty weather. Cold, dense air with minute water droplets is supposed to be optimum conditions for combustion and resultant power output.
Water injection was a fad back in the day but has been resurrected of late as a potential means of reducing emissions.

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It’s the IMRC (inlet manifold runner control). The operation is a bit jerky when cold for some reason so you’re feeling it change quickly, rather than gradually when it’s warmed up.
Don’t get too excited, you aren’t gaining or losing anything at any time.

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Thank you all for your prompt and knowledgeable replies.

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I think it is probably the VVT as from cold the oil that controls the VVT is cold and viscous. When it warms up and thins, the VVT would jump in rather than the usual progressive action on an engine with warm, thinned oil.
If you start the engine and leave it to idle until the oil is hot, you may find this does not happen or at least is shorter in duration.

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Hi Rob, I was always of the understanding the the MK3 1.8 did not have vvt just the 2.0.

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Looks like I’ve opened a can of worms!!
The sudden boost in power I’ve been experiencing was never a problem to me. I just wanted to know whether it was normal with the car. My previous MX5 was a Mk1 and didn’t do this. Yes, it does get less noticeable as the car warms up

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You’re correct which is why it isn’t that, but is the IMRC.

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Oh dear, should have kept out of this one:-)
I thought all the duratecs, 1.8 and 2.0 were VVT but it seems just the 2 litre.
Never heard of IMRC, will read up on it; sounds like it may be some sort of purge system on the intake.

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There were far more variants of MZR/Duratec than you think across the Ford/Volvo and Mazda range.
Plenty were 2.0 with no VVT, no IMRC, poorer flowing cylinder heads etc That’s why there are multiple power outputs across (even the 2.0) the range.

Mazdas inlet manifolds have 8 runners, 4 long, 4 short. Everyone thinks it alternates solely between one set of 4 and the other, but it doesn’t. It does however change configuration twice throughout the full rev range when at operating temperature.

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I hate Acronyms

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Yes, acronyms are a PITA, lol

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Any in particular you are struggling with?

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MZR: Many Zoroastrians are Revolting
VVT: Very Very Tuneful
IMRC: I Married a Right Cuthbert.

I may have got the last one slightly wrong.