Possible flat spot

Zcootz · Postby **Zcootz** » Wed Mar 28, 2012 8:56 pm

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 ?

Regie · Postby **Regie** » Wed Mar 28, 2012 10:24 pm

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

Guessing other plug leads or cam angle sensor

Guran · Postby **Guran** » Wed Mar 28, 2012 10:42 pm

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! :lol:

zossy1 · Postby **zossy1** » Thu Mar 29, 2012 11:42 am

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!!

rascal · Postby **rascal** » Thu Mar 29, 2012 12:45 pm

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.....

Guran · Postby **Guran** » Thu Mar 29, 2012 1:01 pm

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

rascal · Postby **rascal** » Thu Mar 29, 2012 4:33 pm

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.... :lol:

Zcootz · Postby **Zcootz** » Fri Mar 30, 2012 7:55 am

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

Zcootz · Postby **Zcootz** » Fri Mar 30, 2012 7:56 am

Oh, and the cars done 130k

hks_kansei · Postby **hks_kansei** » Fri Mar 30, 2012 8:38 am

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.

93_Clubman · Postby **93_Clubman** » Fri Mar 30, 2012 12:04 pm

Zcootz wrote:It's a nb8a.

Any mods?

Zcootz · Postby **Zcootz** » Sat Mar 31, 2012 2:00 pm

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

93_Clubman · Postby **93_Clubman** » Sat Mar 31, 2012 3:26 pm

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.

Postby **Okibi** » Sat Mar 31, 2012 6:53 pm

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.