Do I really need a fuel computer on my '93 RX7 with a downpipe,catback and drop-in K&N air filter only???

Some say you do and some say you don't.
So who is right?
And why?

 

3 mod rule is a safety net.
You may not NEED it, but when you blow your engine I'm gonna say "I told you so"


EDIT - I just realized that said drop-in. I take that back. If you go to an intake like a conical filter, yes you should get one.

 

as long as your boost is staying near stock levels, no.

 

The only way to be sure is to get a test with a wide-band O2 sensor.

I don't think you need one at your current mod level, but I don't want to be held responsible if you run lean and pop the motor. My unwarranted guess is that you will be fine, however.

-Max

 

You're safe with those mods.

 

With your mods, you'll be fine.

 

The car is so fast it's scary. Lots of wheel hop and spin. How can I stop it? And I don't want to tune the car. So is Petitte the best if I just want to plug in another unit?

 

Take your foot off the gas if you get wheel hop to prevent damage. You will get used to how fast it is.

The overwhelming consensus seems to be that you don't need an ECU. You are tuning the car if you change the ECU. You can get a "chipped" ECU from Pettit (pronounced "pet it" rather than "peteet"), but you can also get a PowerFC and use the base map that it comes with and have the option for adjustability in the future for more $$$. You generally need to re-tune when you change anything that the engine air flows through, but the car runs so rich in stock form that you can get away with a few changes before you need more fuel (which is what you get from tuning the ECU).

-Max

 

Ugh, YES! FD's use a map based system for engine management so when you do mods and increase airflow, the car doesn't realize it. The maps are fairly fixed so when more air is flowing in and out, the car will not adjust like MAF systems by adding more fuel automatically. That's a VERY rough explanation but in essence, that's why people's engines pop. With a ecu, you will not blow up your engine, BUT your car will also be faster because most turn the boost up to 12-13 psi. Also, you need the car to run richer because the excess fuel evaporates and helps cool the combustion chamber thus warding off detonation more. It's money well spent.

 

Ok, my question is this.

If you went nutso on your upgrades, say, intake, dp, IC, exhaust, and this that and the other but stayed at 11psi with a boost controler, would you need a new ECU?

 

Take a look at Wade's site. He's done some testing that shows the stock ECU is very capable with mods as long as the boost stays at the stock boost level:

http://www.newwave.net/~flanham/wlan.../3modrule.html

However, over stock levels, you are on your own...

 

At high rpms, the fuel cut kicks in at 10.7 psi, as long as you are not hitting that and you are not spiking, you can pretty much run any bolt-on with the stock ecu. I would still go to a dyno with a wideband to verify that your a/f ratios are ok. It doesn't cost very much and is good insurance.

That being said, I would never run a mid-pipe with the stock ecu. There is no way on a properly functioning car that you will be able to limit boost to 10 psi without porting the wastegate. You may also have spiking problems.

 

Right. Ok that was my basic thought. As long as i didnt go over stock boost levels I figured I would be Ok. thanks guys

and I figured that a mid pipe would cuase creap and so i figured i would leave that one out thanks again guys.

 

and heres a hypothesis of mine...
if you take the airpump out you are taking out air from the intake charge downstream of the MAP sensor and thus run extra rich. so if you take out the airpump you can run a few more mods to counter-effect this richening of the mixture.

 

I think the pump shuts off after about 2-3K rpm, so any change to the mixture wouldn't apply for practical purposes under WOT.

 

It cuts off at 3200 rpm I believe. Which makes the above suggestion a REALLY BAD idea. Don't cut corners modding an FD. It WILL bite you in the ***. Learn from those who have done it before us, they have paid the blood, sweat, and the tears to discover this good info.

 

If you plan on modding more then I would go with it, and trust me you'll get the itch for more speed soon enough. So you might as well upgrade it now.

Mike

 

Dothe ECU. You will get more power, and get a safety net at the same time. You probably spent a lot of money to get a nice car. Take care of it. It's money well spent.

 

I am listning and taking to heart all the above info. I just don't want to tune or learn to tune a PFC.
Is there a way to just plug in and go and be safe???
If so who do you recommend?
Thanks

 

Rob,
buy a PFS purple..it's fairly cheap and reliable and easy to tune although it comes pretuned. You can run 10,12 and 14 psi without worrying about popping the motor..

 

The FD doesn't care about how much air, it is just the pressure. Removing the air pump will have no significant effect on mixture.

-Max