I have been reading threads and talking with a few people about getting a cold air box. From reading on the forum, I have seen that you can get sufficient air by doing the cold air box mod and having a K&N filter, (the K&N I have) but at which time a guy would have to do a fuel mod( I have DP and CB as well).

My question that I have is shouldn't the ECU compensate enough for colder air? I was thinking about driving my FD on a really cold day, even winter for extreme example, and picturing my car getting nice fresh cold air compared to a hot summers day. Wouldn't this be a huge change in relation to a stock box versus a cold air box? Some people drive there car in the winter(crazy if you ask me ) and surely they have no problems because of it

Could someone point out something I am missing?

 

you dont need to worry about the ECU response for colder air. Regardless of the plethera of people that are going to come on here and flame my post, the colder air is not going to cause the ECU to run the car lean.

 

So if I did this cold air box mod or bought a M2 box or whatever, I shouldn't have a prob? I want to do this mod but have some concern, but I agree that it should be capable with the stock ECU.

I read the thread about how you tested your car at the track with the ram air and such....interesting. Did you notice anything different when changing your system during the test, other than MPH outcomes?

 

I never changed out the system on the same day, but the results were done over a 9 month period running at sears pont every wed and sac raceway every saturday. I was able to take the many runs I ran without the ram air and the many with (with the stock box and the M2/rx-7fasion) and get an average.

What im trying to say is that even though I did not change the box on the same day, I also didn't do 1 or 2 runs, these were more than 60 or 70 runs.

Interms of feel its really hard to feel a different when you have a helmet on and two twin turbo's screaming. The trap speed was enough of a difference for me.

 

What i meant was anything different on any gauges( a/f, boost)?

Thanks for the info ZeroBanger

 

I dont have an a/f gauge, I didn't get more boost but It definately spooled faster.

 

Faster spooling? Really.... that is definitley a plus. Are you seq still?

 

I'm still sequential.

 

The ECU does compensate for temp changes. The thing it doesn't compensate for is changes in how well the system flows. Opening up a better flow path to get air into the air box will change the flow. Even so, it seems pretty clear that you should be fine with the stock ECU, DP, CB, and modified air box.

-Max

 

How about if you added RX7store hard pipes (to stock airbox w/K&N)? Still OK on the stock ECU?

 

Yeah; I think that would be fine, too.

-Max

 

...

 

on turbo charged cars the intercooler has more impact on a intake temps than the inital incoming air temp.

 

Wouldn't the engine get only as much air as needed, not caring how well it flowed into it? Even if a guy had an aftermarket air box? Being a turbocharged engine, by the time you were into the gas you will allready be into boost. Am I right or am I right? Or would you get an increase in boost because of the flow? ...then a guy just controls that with the wastegate control(Home Depot control)????

 

the more the air you get into the engine, and assuming you find a way to get the air out fast (flow) the car makes more power. The more power the car makes the more fuel you need. The stock ecu will work to a point then it will run out of fuel and engine goes bye-byes.

 

The fuel maps have "baked in" assumptions about how well the whole engine system flows air. These assumptions become invalid as you increase the flow capacity of the engine systems. The ECU samples the air temp and pressure, but does not directly measure flow. So, if you increase the amount of air flow, you will run leaner that you did before. In the case of a minor flow change and the stock ECU, you'll still be fine since the stock maps are reported to be very, very rich.

NOTE: Other cars' ECUs do measure flow with hot wires and flapper doors. Those systems are called "mass-air". The FD just uses a different kind of fuel injection control system known as "speed-density".

I have an incomplete but perhaps still usefully instructive web page that may explain why changing the amount of restriction in the intake will affect the flow of the system:
http://www.maxcooper.com/rx7/how-to/...ystem/why.html

-Max

 

Adding a DP, CB, and intake will most likely cause your car to boost over 12 psi. Possibly over 13 psi. I recommend installing a boost controller with those mods, and the stock ECU.

 

I have the home depot boost controller in my car.... that should suffice until I get my Power FC.


Thanks for the info Max. I'll check your page out...