I have a stock 93 rx7. I'm putting a apexi intake and a 3inch downpipe on with no cat. Just want to know if the car will run right with the stock ecu?

 

Yes it should run fine. But I hope you saying no cat means you are replacing your DP with precat for an unrestricted DP... Not smart to run NO cats on a stock ECU so be sure you leave your main cat. Are these your first mods?

 

i was planning on puting 3 inch all the way back with just a reasonator. the downpipe i have is straight 3 inch no restrictions

 

Are you going to put an exhaust on?

Either way, get a computer, IMHO. Why chance it?

 

Don't replace your main cat without first upgrading your ECU.

 

Wrong. The ECU doesn't matter if your boost stays put at 10psi. Usually you only need a manual or electronic boost controller to stop boost spiking. The bigger problem is that putting a 'full exhaust' usually causes your boost to creep and exceed 10psi.

So you'll need a boost gauge first, to see if the boost is creeping, and a boost controller since the full exhaust will usually produce spikes. Especially on cold nights. Then you'll need to port the wastegate if you observe the boost creeping.

Of course, simply leaving in the main cat is much simpler and cheaper. Usually you won't get boost spikes or creep, and in fact the boost may even stay at 10psi with the stock boost control.