So my fd was pretty much bone stock with a down pipe only.

fixed a few issues (vacuum lines, sensors, water pump etc) and now the car runs good.


i just added a couple things And from what I understand the rule of thumb for the stock ecu is. It can handle up to 3 power mods? Than it might run lean and detonate?

so far I’ve added, Hks twin power. The 99 Ypipe. And the hks super dragger cat back exhaust. I have the racing beat mid pipe but didn’t put that on yet.

would it be wise to not put on the mid pipe at this point? Without getting a power fc and a wideband?

I was wanting to dyno it close to stock and was wondering if I should dyno it as is without the midpipe?

ps- since installing the exhaust I’ve been smelling a weird smell. I’m not sure if it’s some of the grease I got on the hangers and maybe piping.. not a pleasant smell lol Almost like wax or hot glue

 

Yes don't install the midpipe unless with a restrictor plate on the stock ECU.

 

You don't want to go catless on stock ECU, or any ECU, without porting the wastegate or having a restrictive exhaust. I question the benefit of adding a catless restriction when the stock main cat (not the US spec pre cat) is fine for a mildly modded car. I had good luck with catback and downpipe and stock airbox on my last FD, with stock ECU. It ran really well and I didn't have to worry about boost control issues.

If you keep the stock airbox and go with a high flow cat you should be ok. When you change the intake you increase boost and that can be a problem.

 

The 3 mod rule is a bit ridiculous and antiquated because "power" mods can have wildly different effects on the car.

The twin power isn't really a power/flow mod - it allows your ignition to support higher boost. The stock coils are fine for 300whp if they are low mileage and are driven properly (stock PFC map does not). I have always questioned the benefit of the 99 y-pipe with regards to flow.

The midpipe however is definitely not a good idea. You're going to put on a midpipe and haven't replaced the stock pre-cat with a downpipe? That's backwards.

Way way back I put a K&N drop in filter, port matched intake, and a downpipe on an otherwise 100% stock car and was hitting overboost fuel cut on the stock ECU.

 

Sorry let me clarify the car does have a downpipe replacement precat.

so right now it has a precat downpipe, stock cat, and now the hks super dragger.

has a stock air box and yes the hks twin power and 99 y pipe.

how about if I took off the stock cat and replaced it w a midpipe but put the stock cat back muffler back on?
I don’t know if I like the super dragger anyway...?

thanks guys. I should install a boost gauge too to see what boost I’m currently hitting. It feels it hits pretty hard 5k rpm and up! Is factory boost 10 psi?

 

The 3 mod rule doesn't apply to midpipes. Just drop the midpipe idea because that is way too much restriction to remove from the stock car. You literally can't control boost with a midpipe and stock turbos and can destroy your engine if you put it on.

You should have done a boost gauge before any of this was done but better late than never. The stock boost is around 10 psi, but it varies. Overboost fuel cut varies as well by rpm on the stock ECU.

 

I think the RB racing pipe is baffled, but still a risk. And if you think your car stinks now, wait till you remove the cat.

Efini ‘y’ pipe should flow marginally better, but mostly it’s benefit is the elimination of that soft coupler.

I don’t think the rule is antiquated but you made some different choices. I like the efini ‘Y’ pipe, but seems like most might have gone for an intercooler and intake with a BC. Instead you’ve got a Twin Power with stock boost and ECU and a baffled mid pipe?

 

The real rule of thumb is 10psi on stock ECU. If you go over that, you're going to have a blown engine.

Back in the day I had a downpipe/stock main cat/cat-back and I was boost spiking on the stock ECU. Getting up to 12psi or so. Take a guess at what happened when I passed a slow car in 3rd gear....

Dale

 

10psi works, as does keeping the main converter, although its really a HP/airflow thing

my friend had an FD, and it had a Tanabe muffler with the silencer in it, and something wrong with the primary boost control. it would hit ~20psi on the first turbo, and maybe 5-6 on the second. i should add that 20psi on pump gas and stock ecu was totally fine, don't try it at home.

 

So the problem w the midpipe exhaust and etc mod combo is that the boost going over 10 psi and blowing the motor on stock ecu? If I had a power fc then it’ll be ok? The motor is not the problem the tune and the ecu?

 

No.
A midpipe risks an over-boost condition called boost creep. Creep is caused by a lack of sufficient exhaust back pressure for the twin’s relatively small wastegate. It can’t be tuned for and is not controlled by a boost controller.
A BC is only good for controlling boost spike. Spike is also an over boost condition but is caused from opening the INTAKE side.

 

There's a whole mess of reasons.

First, the stock ECU has SUPER basic boost control. That's the 2 solenoids bolted to the front of the UIM. If you open things up and the turbos can spin up faster with less restriction, the ECU doesn't care, it runs the turbos up anyhow - this results in spiking, especially at transition.

You can actually run an aftermarket boost controller with a stock ECU and *lower* the boost since the stock ECU just goes ham.

The mid pipe is the "you must be THIS TALL to ride this ride" mod. That fully opens the car up, you will be WAY past what the stock ECU was engineered to work with. There are a WHOLE LOT of blown engines that can thank a mid pipe.

PowerFC has more headroom in its base map. It's better as-is than the stock ECU but no one can say "you are good to X" with either the stock ECU or the PFC. There's SO much that all ties in together. How much voltage does your fuel pump get? Intercooler heat soaked or is it a cool day? Secondary injectors have a crap spray pattern? Factory engine with 3-piece apex seals and 100,000 miles of wear? Every little bit contributes.

Dale

 

This x1000

The 3 mod rule is soo outdated and it goes back to when people had no idea why they were blowing their engines. Turns out out they were going lean because the mods were causing elevated boost conditions (boost spikes, boost creep, or simply elevated boost due to less restrictive components). So a MP, IC, Intake, CB, ect... It doesn't matter. It is all about the AFR's and the boost level directly correlates with how your AFRs are being affected. Boosting higher equates to a leaner conditions on the stock ECU. Boom.

The assumption is that an aftermarket ECU has been tuned for higher boost levels. Hence not an issue.

 

I'm curious, what down pipe did you have, and what catback, and did you have cone filters for intake or stock airbox?

 

My understanding is that boost creep when you open everything up is related more to the physical wastegate size, right? As in even the PFC can't prevent it at some point?

Is the PFC considered having more headroom because you can add fuel to compensate for the higher boost beyond what the stock ECU would do? It seems like the mid-pipe would still cause the boost to creep.

 

So I hooked up a boost controller real quick and it read 50 kpa. Which I think translates to 7.5 psi

weird! It feels pretty fast! I’ll do a few more pulls but maybe I’m safe for the down pipe? Lol

ill take it to the dyno w a wideband as well. If I do a few more pulls and it reads below 10 psi I’ll put the midpipe on and go dyno w a wideband

 

To add my .02, I am running a stock 1995 MT ECU with JDM downpipe, 99-spec Y-pipe and 99-spec air intake to stock airbox (with stock paper filter), OEM main cat, RB dual catback. With this setup, my car boosts to about 12psi on primary and 10.5-ish on secondary and my AFR's measured using an ECM AFRecorder-1200 are in the mid to 10's to 11.1-ish under any boost condition that I can try (partial throttle to redline, wide open throttle, etc).

I ran the same tests when I had a modified airbox with the adam-c duct, and the AFR's only changed about 0.1-0.2 points and primary/secondary boost was about 13/11psi. So not so sure about the 10psi limit, however I have also gone through my OEM fuel system with a new OE pump, relays, ignition switch, etc. and have good voltage at the pump.

 

see here how different parts dyno

https://www.rx7club.com/3rd-generati...added-1104322/

 

Okay... so on the freeway tonight it hit 12-12.8 psi I let off as I saw it spike so I didn’t stay in it. This was in. Third and fourth gear it’s cold at night and on the freeway w load..

but on the street it only hits 7.5 psi or so even through all of third gear.. it pulls nicely on the street even at that boost level..

so I probably will take the hks cat back off and put the stock muffler back on and keep the stock cat on.. for now at least. Putting these two on doesn’t seem to make a big add except more risk to the health of the motor!

Dale how do you know your motor let go on that 12 psi third gear pull? I only did a few pulls to verify boost but always let off quick and didn’t stay in it.

I’ll probably get another compression test after this again. 😬

just when I was starting to love this car lol

 

And what is your ambient temp, intake temp, and injector duty? At 13psi I have gone over 95% duty on the stock injectors on cool days. On a COLD day you might well be over 100%.

This is where the 10 psi rule works even if it is antiquated. It has to do with keeping injector duty reasonable at the lower range of intake temps. It's especially important if you have an intercooler that actually works.

Regardless - if you're using the 3 mod rule, the 10 psi rule, whatever... you're just feeling your way around in the dark. If you want to modify a turbo 13b and be sure it will last, then you need to log the relevant data and tune the ECU with a margin of safety.

OP - I think you're right to back off on the mods. If your boost is low in certain situations it has more to do with the boost control system than the engine. You might have a bad check valve, sticking solenoid, or leak that causes low boost. Need to nail down exactly when it happens.

 

One of the questions no one has an answer to is why Mazda designed the stock ECU to go lean at higher boost. There is a fuel cut that's supposed to kick in if you boost too much, but that seems to rarely if ever kick in. Funny thing is the FC's fuel cut worked great, ran into that myself more than once on my FC's. Regardless, it would have saved SO many engines if they just designed the stock ECU to go rich and pull back timing at high boost. Go figure.

Arghx, when I blew my motor back in the day I had an ANCIENT Greddy cat-back (before the SP!) and some sort of US-made stainless downpipes. It came with the car when I bought it. I don't THINK I had an intake at that point but that was over 15 years and MANY mods ago.

I bought the car with 68,000 miles with the downpipe and cat-back and the car just had a fresh Mazda reman installed. I can't remember the mileage when I blew it, but probably only had 20,000 or so on the engine. Rebuilt it myself and it's been in the car since then, 138,000 on the clock now.

ModBugs, as far as how I knew I blew it, the car lost power when passing the slow car in 3rd gear. Pulled over and had a rough, lumpy idle. I was only 5 minutes from home so I limped it home and later did a compression test - blown apex seal in the rear rotor. Also it helped that I blew about 2-3 engines on my FC's so I've been there, done that .

Dale

 

Did Mazda ever change the ECU by Series 8? You'd think they'd add more fuel if they were hitting higher stock power numbers by 2002.

 

They went from 8bit to 16bit, redesigned the whole rats nest and increased boost and exhaust diameter. I'm sure the ecu calibration changed.

 

Yeah and we just don't have good evidence if the later ECU is better or safer when doing mods. Long term we may see some of that as they come up on the 25 year rule, but right now not so much.

Also now people are going to get an ECU and get it tuned, where back in the day the tuning options were so limited. Not to mention that widebands were THOUSANDS of dollars - how do you tune a car without a Wideband?

Dale

 

the newer ECU is faster, and depending on which one you have, it is set up to run higher boost (11psi for the 280ps. 9.5 for the 265ps spec).

more fuel? same pump, same injectors, same fuel pressure regulator. actually if anything the 99+ ecu is leaner, the 92-95 ecu runs 10:1, stupid rich