I have read a lot on the forum. But I still have something that i dont understand. To not blow the engine, you can change 3 parts maximum without changing the ecu. Generally the first mods to do will increase boost. The stock ecu can not support more than something like 13-14 psi. So you need to be sure that your boost is enough low to not exceed those 13-14 psi.

But if you set your boost at like 10 psi with your 3 mods, is the hp output will stay at like 225-230 rwhp like in stock form with better exhaust flow (if your mods are dp,cb,intake) ? or output would increase over the stock form ?

 

Output with the exhaust will still increase even if you get the stock twins to hold only 10PSI


The problem is when you do a full exhaust on a 3rd gen you have boost creep problems..

-Zach

 

Oh, and 2 mods is more like it.. 3 is a little dangerous.


Usually 1st 2 mods is downpipe and cat back.

 

3 mod rule my ***.... when i blow my engine you can tell me you told me so until then BLEHHHHHH!

 

it is not necessary to change the ecu after 3 mods. It is recommended so you don't blow your motor however I have heard of a bunch of people with full exhaust and intake on the stocker that has not blown their motor. Basically, as long as boost levels are kept below or at 10psi then you will not have a problem with most bolt ons. What happens is the turbos have what is called boost creep where the boost will creep over 10psi and if you are not careful this will blow the motor. The more mods you have the more likely boost creep is. Make sense?

 

i think i read from a repitulbe source that the stock ecu is richer then say a power fc!!

 

That may be true from the factory but you can reprogram a power fc for whatever richness level and mod level you want. Making that statement is a little misleading, IMO.

 

True, the stock ecu runs rich, but only if your car is running 10psi. Problem is when you add things like a dp, exhaust and intake your gonna run about 12psi. Stock ecu only recognizes up to 10 so you'll run lean. If you get a boost controler and limit it to 10-11, your fine.
But, don't be a rock head. Do yourself a favor and buy a chip, or ecu upgrade like the Power Fc or AEM.

 

i ran my car on a wideband with

intake
downpipe
exhaust
ypipe

a/f ratio's never got over 10.5 and during the transistion it was so rich it was off the scale.

stock ecu can handle the basic bolt ons.. including an intercooler. DONT mess with the boost with a controller AND DONT put on a midpipe and the stock ecu is more than adequate.

search for my dyno post under "FD3S dyno with basic mods" in the performance section

 

The MAJOR problem with stock ECU is the FUEL CUT.
When boost is bigger than 10.7 psi. The STOCK ECU, cuts the fuel. This in effect created a lean condition.
Thus chance for seal to break is bigger.
If you keep boost at 10psi top
(no spike more than 10psi, no creep more than 10psi), l think you can go with as many bolt ons possible.

Reza

 

Uninformed question coming - if there is fuel cut then would this show up in a wideband run? Why didn't Qball get it in his run?

 

i don't think fuel cut is at 10.7 psi

 

AGREED but..

the ECU wont cut fuel at the transition spike..it only cuts fuel if its above the threshold for a certain amount of time. which is longer than what the spike lasts.

if you notice on your boost gauge. after the spike (14psi if you have a dp, cd, and intake) it tapers off to 8psi (even in winter there was no creep with the stock cat) on the way to redline way below the 10.7 limit.

thats why i say all the bolt ons BUT NO BOOST CONTROLLER and NO MIDPIPE.

i ran my car with a midpipe on the stock ecu before my pfc ( for a curious experiment)

it didnt cut fuel at the transition spike (16psi spike ..ouch) but did cut fuel after 5000rpm and the boost was at 14psi and steady.

this is just my experience... other's might differ but i doubt i'm a unique case.

i think 3 mod is a confusing thumb rule. it really should consist of what NOT to put on a stock ECU.

1) midpipe.. even pfc has trouble with this mod

2) boost controller.. tempts people to play with the boost when the stock ecu keeps nice and low

3)street port (not really a "bolt on")

 

Yes, fuel cut is not always at 10.7 psi.
I think the lowest point of the range is 10.7 psi at sea level altitude.

1000 rpm 11.8 psi
2000 11.8
3000 12.4
4000 13.3
5000 11.3
6000 10.7
7000 10.7

Please follow this link, there is discussion about the stock ECU:
http://www.scuderiaciriani.com/rx7/computer.html#STO
and about fuel cut:
http://www.scuderiaciriani.com/rx7/fuel_cut_info.html

I am not sure actually whether boost spike can trigger ECU fuel cut. Just to be safe, I prefer nothing above 10 psi.
I think boost controller maybe required to keep it below 10psi, after all the bolt ons.

reza

 

fuel cut differs at different RPMS and only if its above the setpoint for a certain amount of time.

the 4500 transistion limit is actually HIGHER than 10.7 which is the redline fuel cut limit.

i forgot the exact number but there is a chart search for "boost fuel cut chart"

so at the transition it spikes to 14psi.. then very quickly settles at 10psi .. which tapers down to around 8psi near redline. all within the stock ecu limits.

 

well b4 i read this forum, i had no ECU, and the mods were SMIC,MP,DP,CB and intake, i kept the boost at 10 psi for a year and still fine
i have a pettit ECU now btw

 

Wade's wideband tests as well as several of our dyno plots have shown the 3-mod rule is worthless.

Like the others have said, keep your boost at 10 psi and you can pretty much run any bolt-on with the stock ecu. That said, I would still never run a mid-pipe or ported engine with the stock ecu.

 

I too have read that the PFC BASE MAP is leaner than the stock ecu. This is probably only under certain situations. But think about it, how else does it make more power? It either advances the timing or leans out the mixture, there's no such thing as magic. It can be done because the stock ECU runs disgustingly rich.

 

Wade is not alone, Jeff at Rotary Power also said that as long as you have the main cat on and limit the boost you can run whatever bolt on your heart desires. With that said...since I have a dp and a cb, would it be a wise investment to purchase a boost controller?

 

I have a DP and K&N's and want to put a mid-pipe in but keep the stock exhaust at 10psi will this work?

 

I should have been more clear...my point was that just cause you run a PFC out of the box doesnt mean you could go ahead and install more boltons then you could with the stock ECU.

I bought my power fc a couple of years back because I interpreted the three mod rule literally. I since have learned that it is fine to keep the stock ecu as long as you limit boost to 10psi. But, i am happy that i did in fact get the power fc as now i could benefit alot more from the boltons by raising the boost. There is a huge difference in 10 psi and 12 psi. Obviously the tuning capabilities are huge too.

matt

 

Well my mods are FMIC and an intake, which gives me a max. boost of 9lb. I am about to add a DP and CB. Shouldn't keep me just good enough where I don't need an ECU upgrade?

 

you'll be fine with DP and CB.. but dont do a midpipe.

 

Thank U. I really don't like smelling like exhaust so, a midpipe is not an option.

 

Why would you want a midpipe with the stock exhaust? I see absolutely no point to that whatsoever. I think people jump to the midpipe mod way too fast. This should be one of the last power mods after dp, cb, intake, IC, and should be done with fuel upgrades. It should never be done without an aftermarket ecu. Just my opinion.