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I've noticed a small flat spot when accelerating gently. It seems to appear in second gear, about half throttle, at 3000-3300 rom there is a slight drop in power that picks up again at 3500. I'm not sure I'd this is just a quirk of the car or normal. Under full throttle the Mx pulls cleanly. It's a nb8a. Has anyone else come across this ?

How many Kms?, does it do it when it's cold or warm?

Guessing other plug leads or cam angle sensor

Depending on how dramatic it is, what you're experiencing could be normal. NB8A has a slight flat spot in the torque curve as shown in the dyno chart below (between 2700 and 3500rpm in this example):



The solution is easy: don't let your revs drop below 3500rpm!

Guran wrote:The solution is easy: don't let your revs drop below 3500rpm!

No, no, no Bryan. The magic figure we want to always remain above is 5000rpm. 5000rpm!!

Guran wrote:Depending on how dramatic it is, what you're experiencing could be normal. NB8A has a slight flat spot in the torque curve as shown in the dyno chart below (between 2700 and 3500rpm in this example):

Not sure the dyno plot above is useful as a guide to NB8A torque curves, as at 98rwkw its definitely not a standard NB8A.....

Fair enough - though the owner of that car did state that it was standard except for a modified air filter.

Guran wrote:Fair enough - though the owner of that car did state that it was standard except for a modified air filter.

wow. In that case me wants one of them. 25+ kw from an air filter....

Thanks Guran, that dyno chart makes sense and lines up with what I'm feeling. It's possibly just a characteristic of the engine thats exaggerated but the cold running settings. It's a really small dip and I've only really noticed it driving up a gentle hill around the corner from my home so the engine is always cold at that point. Might let it warm up today then try it in the same spot.

I'll do some forum searches and try to work out how to test the cam sensor.

Thanks

Oh, and the cars done 130k

Sounds similar to mine, on cold mornings it has a big flatspot (Mine's a bit lower, about 2500rpm)

Once warmed up it goes away, and in warmer weather it doesn't happen much.

Zcootz wrote:It's a nb8a.

Any mods?

Nope, completely stock. It pulls well and no idle problems

Does the intake pipe from the MAF to the TB across the front of the motor have a Helmholtz resonator attached to it?

This one doesn't: viewtopic.php?f=54&t=49893&p=626317

But the NB8B one did like the NA8 one - you can't miss it - it's basically a pipe with a large chamber on the end. If you're keen to experiment, try swapping to an NB8B intake pipe as the Helmholtz resonator was supposed to remove the dip.

I was thinking perhaps the intake butterflies might have been "sticking" a bit but I think they open at a higher RPM.

It wouldn't hurt to do some maintenance on your intake manifold but it might not solve the problem.

http://www.miata.net/garage/manifold/index.html

With any surge of power issue on an NA / NB i'd be looking at your leads and plugs then the AFM.

I know my (stock) NB8A really comes on song at or around 3500rpm (feels a bit like Vtec kicking in... yo ). That might give the feeling of being a bit flat between 3000 and 3500rpm - but I think that's just the nature of the beast.