Jesus-Ninja
New Member
Hello all,
Engine has been in the car for a while now, and I've done a couple of track-days. Everything is going very well - sounds fantastic, still handles well, and goes like stink.... sort of....
Up to 4krpm it pulls like a train, but then by 4.5k it hits a wall and won't punch any higher. The engine will definitely rev freely out of gear, but under load it hits a point where it won't rev past. The problem is more pronounced in higher gears, as if it speed is a key component. This would make sense as aerodynamic drag cubes with speed, and the air becomes increasingly difficult to punch through.
So, it's like it's got no guts above about 4.5krpm.
Engine is a 1998 VVTi in an MX5 (Miata). Manual conversion is from an S14 (200sx / 240sx).
Techstream shows no problems aside from O2 sensors, which shouldn't affect open loop.
My initial thought was around fuelling - pump is a Walbro 255lph, although I wonder maybe if the stock Mazda pipework isn't up to the flow required. It's about 6mm internal bore.
Alternatively could this be an issue with the VVTi?
This is the last piece of what's been an immense jigsaw, so any help is greatly appreciated.
Engine has been in the car for a while now, and I've done a couple of track-days. Everything is going very well - sounds fantastic, still handles well, and goes like stink.... sort of....
Up to 4krpm it pulls like a train, but then by 4.5k it hits a wall and won't punch any higher. The engine will definitely rev freely out of gear, but under load it hits a point where it won't rev past. The problem is more pronounced in higher gears, as if it speed is a key component. This would make sense as aerodynamic drag cubes with speed, and the air becomes increasingly difficult to punch through.
So, it's like it's got no guts above about 4.5krpm.
Engine is a 1998 VVTi in an MX5 (Miata). Manual conversion is from an S14 (200sx / 240sx).
Techstream shows no problems aside from O2 sensors, which shouldn't affect open loop.
My initial thought was around fuelling - pump is a Walbro 255lph, although I wonder maybe if the stock Mazda pipework isn't up to the flow required. It's about 6mm internal bore.
Alternatively could this be an issue with the VVTi?
- Is there any way to force it to kick in to at least prove it one way or another?
- Am I right in saying that the VVTi on the 1UZ is more complex than a simple on/off, and it is able to progressively adjust the advance depending on TPS and load?
- How does the ECU read load? I assume it reads the vacuum from somewhere?
This is the last piece of what's been an immense jigsaw, so any help is greatly appreciated.
I have used the stock MAF and housing though, in the most elegant way I could. As an aside, I've also included some shots of the breather paperwork. The catch tank is filling up very quickly on track, and what is in there is just oil (no emulsion etc) Finally, there's a shot of a plug with nothing attached. If memory serves me, this went to some kind of pressure sender which was plumbed into the vac line with the stock carbon canister - any possibility that I need this for VVTi?
