What's restricting my engine?
 

I've been on the dyno and got a healthy 200bhp at the fly from my supercharged 1.8 96 miata but on every run the car would start to slow down the build up of revs until about 6k where it took off again.
We bypassed the supercharger and had a run on the dyno and the car displayed the same behaviour.
The tuner things that the timing looks good throughout and the AFR's where stable and hitting the right marks for the amount of boost. I've also changed exhausts and it's still there.
It feels like something's opening up at 6k but i've no idea what. Any idea's on what could be moving?

You're looking at this the wrong way. It's not what's restricting, it's what's giving you extra torque at the lower RPMs. Your intake manifold has tuned runner lengths that give you "free" supercharging at certain RPMs. Unfortunately, ram tuning doesn't work across the whole RPM range. Do an internet search on ram tuned induction. I get a huge kick out of the early-60s Chrysler BB intakes. Wild stuff.

A true, passive restriction would show up as a torque and HP fall-off at high RPMs. It would be related to air flow and nothing else.

Maybe knock detection, either real or false.

Thanks guys.
Should've said you can see a definite drop off on the dyno graphs like the car's already peaked before it kicks in again.
Not got any knock detection on the car and the tuner couldn't hear anything whilst it was on the rollers.

you mean these? I bought a set a swap meet a few years ago for $500. They didnt look half as good as these. But I turned around and sold them for $750 later that day. I knew I would never use them. I dont have a BB Chryslers. Only small blocks ;)

intake manifold

oh - and supercharger

A good turbo setup would clear those restrictions right away! :)

We bypassed the charger and got the same drop off then sudden return in power so I don't think it's that but if anyone wants to send me a complete turbo setup to test with pm me :)

http://a3.sphotos.ak.fbcdn.net/hphot..._2287259_n.jpg

Here is them on the motor this is a pic from my friends house of the 300G they have been restoring.

If your car is building revs but slowing down, I would suspect a slipping clutch.

That's the trouble, it's not building revs. It revs freely up to this point and then kicks back in again after 6k but feels like it's pulling through treacle for a while.

dyno plot available?

I've attached the one run image i've got. This is one of the better runs. Normally it's more pronounced than this.

Whoa thats weird... What kind of fuel management? I can't really imagine much mechanically doing this...

That's definitely ECU. Way too high in RPM's and too peaky/pronounced to be related to tuned runner lengths.

I'm running a DIYPnp megasquirt v1.1
A few guys in the ms forum have looked at my map before but couldn't see anything up with it.