N/A 7000rpm Bogging.....
 

I just test drove a 91 FC N/A today with a brand new( less than 1000miles) streetported 4-port engine. He put in bigger injectors without any electronic upgrades. What do you think the problem is?

Jay Kim

For one, what the hell are you doing revving the engine that high before its broken in? 1000 miles is about the minimum for a good break-in.

As for the bogging, 4 port motors, even street ported, still have less port area than the 6 port housings on a n/a. It is simply out of the powerband by 7K. It could also be in the tuning, since he is using an ECU that was tuned for the 6 port engine. And with bigger injectors, hes drowning that engine. I think the injectors are the biggest part, tell him to put the stock injectors back on and see how it does. Since its n/a, the engine wont blow from running lean.

well....when I get the car, the car will be properly driven for another 3000 miles as a part of break-in period.
Does anybody have stock injectors for 89-91 N/A for sale?

Out of power band by 7000, huh? Well...that's not good. I was planning to rev this thing pass 8.5k rpm so I can be cool. :)

Does anybody in LA wanna trade header back exhaust system with magnaflow mufflers for their stock exhaust system? u just pay for the labor for the swap to be done.

Jay Kim

So wut you're saying is, the car with the 4port streetported engine will slower than the 6 port stock engine?

jay kim

Im probably going to get flamed for this, but yes. it woul dhave to be bridgeported to make good power n/a.

mazdaspeed7, you're mistaken :)

The stock 4-port engine has a smaller intake port area than a 6-port, but larger exhaust ports. 6-port motors also preclude exhaust porting. If the motor's streetported, chances are VERY good that both the intake and exhaust port duration have increased considerably... IMO, the engine's bogging because of the bigger injectors without proper control. Put stock injectors back in, and the car should run great to 8k, provided it has a free-flowing intake and exhaust.

...AFTER ~1500 miles!!! *grumble*

Brandon