DGblk93

Thanks again Howard. I'm sure ther will be others considering the mod now too.

RacerX - what advantage does the Haltech or the Microtech have over the Power FC in your opinion.(maybe I should post this ? to the Engine Management Forum...)

Just seems that more people go with the Power FC.

Larz

It won't influence my decsision. I was just curious if anyone had any hard facts about one twin system retaining less heat than another. That would be interesting. I'm too poor to go single.

ijneb

Get with tuners local to you, find out what EMS they use/prefer and know how to tune best, get with people in your area and find out who they think is the best bet.

THEN get the EMS that that tuner is familiar with.

If you get a Microtech, but you have to trailer the car ~200 miles to get it tuned, when you could go with a PFC and the guy down the road can do it, it becomes a little more of a pain in the ***.

I think that is overlooked when people are going with a standalone.
-Ben

ijneb

I think what retains so much heat with the stock twins in the manifold area. In order to get rid of that, you have to get rid of any "stock" twin set up and get a new manifold design.

RX 4 Speed

I have a followup question for all of you... I have mostly the same mods as DGBlk93... except for his hi-flow cat and Petit Cold Intake. I still have the stock airbox with a KN Filter and the regular stock main cat. So is this the only reason why he is seeing a boost spike of 16psi where I am not? I do not have a boost controller... I figured with my basic mods, I don't need one, nor do I plan on modding further to gain more hp. I just hope I am not really spiking even though my boost gauge tells me I am not...

Good luck with your car, welcome to the club.

sonix7

Howard gives so much to this forum. he really takes the time to answer with detail. now I am considering the pwr steering removal mod. I never heard anyone say it like that. Howard could probably start his own forum by himself. plus he has "real time" experience. makes you think even if you don't want to. I learn something everytime I come across a post by Howard Coleman. if you are smart just use a search with Howard's name and you will see what I am talking about.

DGblk93

Sonix - I agree. He took a lot of time to post the info. Very cool.

RX 4 Speed - In my limited experience I have learned a couple of things. The stock cat and intake should probably be enough to keep your boost levels in check. Spikes occur when there is very little restriction in the system. I drove the car for a month with the current setup minus the Catback. That offered enough restriction to prevent spikes. Just keep your eye on the boost gauge. I think there's a 3 mod rule someone created...
Something like after any mix of 3 mods to the intake/exhaust you should consider engine management.

Thanks.

importrx7

I think the 3 mod rule is 1.downpipe 2.AST 3. Radiator

DGblk93

I dunno.

scotty305

iTrader: (2)

Here is my understanding of the '3 Mod Rule:'

The "3 Mod Rule" is a consequence of the method that the factory 8-bit ECU uses for calculating the proper amount of fuel (it also controls the ignition advance as well as a few other things, but we're primarily concerned with fuel for this discussion).

Pressure vs Actual Airflow:
The factory ECU basically 'guesses' the amount of air going into the engine by measuring the pressure at the intake manifold. Flow is related to pressure, and the stock ECU assumes that the manifold is flowing a certain amount of air at a certain pressure.

When you modify the engine's flow characteristics, you are changing the amount of airflow vs pressure. A free-flowing exhaust and intake will allow more air into the engine, but the computer is still seeing the same amount of pressure, and using the same amount of fuel as it was originally programmed to do.

What you can end up with is a "lean" condition: not enough fuel. A motor that runs lean will be much more likely to overheat. Rotary engines run hot in the first place, so running lean is especially bad. The factory ECU is set up somewhat rich (purposefully adding too much fuel) as an extra safeguard to prevent lean conditions and the overheating and detonation that accompany them.

Why 3 mods? And which 3?
It's been said that you can only make 3 airflow mods to your car before you'll need to change to a programmable ECU and have the fuel settings retuned. For instance: intake, downpipe, and cat-back exhaust should be safe. However, this is by no means an end-all be-all solution. It's said that removing the cat converter should be enough additonal airflow to necessitate an upgraded ECU. Downpipe, high-flow cat converter, and aftermarket exhaust should be a recipe for trouble also.



The best time to buy an ECU is as soon as possible. You can see power gains on an otherwise stock car by having it professionally tuned, and engine control technology has improved a lot in the past 10 years. Has anyone used a Pentium 1 computer recently? They were introduced in 1993. Pentium 3 is circa 2001, for reference. Which technology would you like to use in your car?

-s-

adam c

iTrader: (2)

Here is a link to an in depth discussion about the "3 mod rule".

https://www.rx7club.com/forum/showthread.php?t=308996

DGblk93

Alright then. It seems pretty clear that the next step will be an ECU and fuel pump (maybe a radiator and 86 the power steering too...)

Am I in jeapordy of detonation if I keep the current mods for a little while and keep the boost under 11 psi? It will still be another month or two until I pick up the new ECU and get the car tuned.

BTW: I do have a way of seeing the A/F ratios. My ApexI turbo timer has an A/F and O2 meter built into it. What would a good A/F mix be vs. an bad one? Looking for numbers. Thanks.

Howard Coleman

iTrader: (6)

scotty,

an excellent post.

my experience with the 3 mod concept is quite similar. i would only like to add that it does depend on what 3 mods you pick... for instance nitrous, a T66 turbo and straight exhaust would not qualify as ok w the stock ecu.

also not qualifying would be downpipe, resonated midpipe and catback. it would be hello 15-16 psi boost and the next hello would be to your friendly engine builder. BTW, at 15 psi the turbos are spinning over 150,000 rpm, cavitating and superheating the air. that's along w the computer misreading the boost and setting the mixture too lean. the key to maintaining your engine w the stock computer is to run either a stock cat or a high flow cat to keep boost a bit in check.

howard coleman

DGblk93

Thanks Howard. So keeping the boost at 10 and under should prevent me from running into the "too lean" scenario?

novadan67

Be careful when reading A/F ratio from your turbo timer. Anything that uses the stock O2 sensor is not accurate. Typical O2 sensors are only "accurate" in the "stoich" range (~14.7). Useful if you want to know your A/F ratio while cruising, but under boost (when it really matters) you will be out of the O2 sensor's "accurate" range.

saxman47

and finally I fully understand the MAP sensor vs MAF sensor....does anyone know why Mazda decided to go with the pressure sensor rather than the mass air flow?

GoodfellaFD3S

iTrader: (213)

to piggyback on Howard's comments on removing the p/s, one other advantage is being able to swap spark plugs much more easily, and it is one less thing to worry about when pulling the motor. I yanked out my p/s and a/c back in 2002 and haven't looked back since. Not one regret here

DGblk93

Oh man - I did those plugs a couple of months ago. PS removal is sounding even better.

jayk

After searching it seems that removing p/s usually means removing a/c? Is this true? I like being able to defog my windows when its raining out... Its the only reason I have an ac at all.

Howard Coleman

iTrader: (6)

the MAF (mass air flow meter) is a hinged door in the middle of your intake. as you open the throttle, more air opens the door wider and the door position is sent to the computer which tells the injectors how much fuel etc...

do you really want a DOOR blocking your air intake?

the MAP setup is far superior but does need to be accurately adjusted... that's where tuning comes in... wide band o2 and datalogit.

david as to your boost levels.... anything around 13 or less should be fine as long as your fuel filter is clean etc etc... BTW, change fuel filters ofter.... an absolute must.

howard coleman

GoodfellaFD3S

iTrader: (213)

It is definitely easiest to remove both at once b/c they share the same belt. I have seen setups where the FD had one and not the other, but it requires some tinkering. Personally, I love having just my crank, alternator, and water pump.

scotty305

iTrader: (2)

Thanks, howard. To expand on that, MAF sensors are more accurate, which is why many cars use them in today's emissions-focused automotive scene. They enable you to run a very eco-friendly mixture. Unfortuneately they are not only restrictive but also bulky and expensive. I'm not sure how they compare to MAP sensors in terms of response times.

Back to ECU's , another significant difference between stock vs. aftermarket is the number of bits that they work with. The sensors in your engine output an analog signal, that is there is an infinite number or possible values within the range of the sensor (for instance, on a temp. sensor that can read from 0-5V, the sensor can output 3.957697457439245 V. The ECU must convert this to a digital number. It has to round it off somewhere. In an 8-bit system, there are 256 possible sensor readings in the given range. (2^8=256) That's not a lot of detail when you consider something like water temperatures ranging from 0-260 degrees F, or EGT's, or 360 degrees of rotation vs the precise moment that fuel and spark should take place.

A 16-bit system can break that same sensor signal into 65536 readings (2^16), offering a much more detailed look at what the engine is doing. The same comparison can be made for outputs such as injector and wastegate control. 16 bits also offers more resolution available for fuel maps. Modern sportbikes have 32-bit ECU's, as does the RX-8. (2^32= over 4 billion possibilities within the sensor's range)

And we haven't taken clock speeds into account, either. I can guarantee you that a modern Palm Pilot has more processing power than the factory ECU of our mid-90's sportscars. If you're running a stock ECU, a '99 Civic has a more sophisticated engine management system than you. For my car, an ECU will be among the first $1500 spent on mods.

-s-