M.Piedlourde

The car I just purchased over the weekend is smelling faintly of rotten eggs at times, and I'm thinking it's time to replace the main cat. The pre-cat has already been replaced with a downpipe, and I'm assuming that the car is still running with the original main cat.

I'm not interested in upgrading the fuel system or ECU (all stock) right now, so can someone advise me on whether or not putting a hi-flow cat on the car will be dangerous with these mods?

Downpipe, aftermarket catback (a Greddy model of some sort), K&N filter (does that count as a mod?).

I've got no problem going with a stock cat, but for better performance I'd like a high-flow if possible. My main priority at the moment is keeping the car running right.

RedR1

iTrader: (5)

With the addition of a hiflow cat to your current setup (im not sure how detailed you'r K&N setup is...straight pipes or still on stock accordian tubes) you run the risk of running a little lean. General rule of thumb for the FD's is 3 minor mods per ecu tune. Others have gotten away with Catback, hiflow cat, downpipe, intercooler. . . . but not all of our cars are the same.

If you have money for a new motor. . . . . then get a power FC and the hiflo cat But if not, id say just get a stock main cat replacement.

rynberg

You won't run lean, but you'll need a boost controller to maintain boost at 10 psi. There's no problem doing that and it's still perfectly safe. Some of us have wideband a/f readings with multiple mods on the stock ecu and the car will still be pig rich.

Mahjik

iTrader: (1)

https://www.rx7club.com/3rd-gen-archives-73/stock-ecu-10-psi-myth-308996/

M.Piedlourde

I knew about the 3-mod rule, but I was curious to know if a K&N filter counted as a "mod". It's JUST the filter in the stock intake.

Thanks for your advice, it sounds like I should go with a stock cat to minimize any risk. The car doesn't have a boost gauge and it's still only running with the stock water temp. gauge, so I want to get those installed before I spend money on a boost controller.

RedR1

iTrader: (5)

No problem, but a good point that Rynberg mentioned that I forgot to (as well as numerous people in the thread Mahjik linked), is the boost controller. In most instances, any type of mod will generate some sort of boost creep when getting on the throttle. Like I always say, its better safe than sorry. Id play it safe with the stock cat like you mentioned, until a later point in time when you decide to spend more money (which.....we all do )

adam c

iTrader: (2)

Bad advice. Most mods won't generate boost creep. Generally, you only see boost creep with a mid pipe. In addition, the three mod rule is old, outdated, and unsafe. With 3 mods, you could easily overboost your car. The new rule is 10 psi on the stock ECU.

I would recommend a high flow cat. Replacing the stock cat could be very expensive. Buying a used one could be no better than what you have.

Rx-7Addict

iTrader: (2)

A high-flow cat coupled with your dowpipe and catback will really open up the exhaust. Along with the intake (or filter) you will be making a lot more power than stock. The stock ECU is setup for STOCK ONLY and can only handle slight increases in power/airflow. I would reccomend an aftermarket ECU to compensate for the increased power.

rynberg

Again, this is outdated knowledge. Wade did the FD community a huge favor by gathering wideband tests of different mods with the stock ecu. His research clearly shows that the stock ecu is rich enough to 10 psi to handle nearly any modification (short of large porting or single turbo). Subsequent testing by several of us have supported these findings. My A/F ratios with the stock ecu with SMIC, intake, downpipe, and catback were still well into the 10:1 range above the transition.

It is perfectly safe to run a full exhaust with a hi-flow cat and intake on the stock ecu, provided the boost is controlled to 10 psi. Any one who says different is relying on 6 to 7 year old "common wisdom" off of Robinette's site and not on actual wideband testing.

Rx-7Addict

iTrader: (2)

Yes, you are correct, it is safe at 10 psi. In his current situation, without a boost controller or ECU, he will likely be running 12-13 psi with his mods. He can either:

1) Get a boost controller, limit to 10 PSI and be fairly safe.

2) Get an ECU, run 12-13 PSI, get a tune, and also pick up a lot more power than you would with 10 psi on the stock ECU.

Both options will work, but I'd reccomend the ECU. Especially considering you can get a PFC for $800.

rynberg

Well, I agree, I would certainly spend the money to pick up a used M2/Pettit for $400 if nothing else. Running 12 psi is a substantial power gain and having the chip does allow for a little bit more safety (presumably).

I was just countering the myth that the stock ecu is not safe with mods at 10 psi.

shaun.sheldrake

Agree completely with rynberg, I run a DP, MP, CB and Intake on stock ECU with a ball and spring boost controller (follow Damien's design) ... have tested with the wideband - still very rich ... plenty of extra power over stock set up and boost is rock solid.

CantGoStraight

I know that the boost pressure is something to consider......but I thought that even if you stayed at stock boost levels if you increase the air flow in and out of the motor you have to compensate with fuel. He's already got two mods with the K&N's and a DP....he mentions a cat back, and want's to do a high flow cat........seem's to me he's pushing it even at stock boost levels. It's his motor to pop and there are plenty of people on here with motors to sell so I guess it's his choice.

rynberg

You don't have all the facts and are basing your opinion on 6-7 year old info. The stock ecu runs below 10:1 A/F above the transition. Even with several bolt-ons, the car will still be below 11:1 A/F above the transition. This is perfectly safe, and very conservative for only 10 psi. Ask any tuner.

As good as Robinette's site is in general, the three mod rule is VERY wrong. People need to learn from the info generated in the last 5 years.

Gadd

Here's my car with a CB, DP, stock airbox mod, stock ECU and a boost controller. Still darn rich..........

KevinK2

no problem, as Rynberg 1st said and Gadd showed.

note that you should not track (driver-ed) the car with stock intake plumbing. search "air box mod" for mods that give a cold air intake without stealing air from the IC. without this type of mod, the drop in K&N does nothing, since the restriction is in the inlet elbo to the box.

adam c

iTrader: (2)

Here you go

https://www.rx7club.com/forum/showth...hreadid=121491

alberto_mg

air box mod is good to do if you do it properly, but come on don't track the car? that is getting way to ****.

KevinK2

No, although true I'm usually ****.

It's what mazda found out when they tracked the FD on a hot day and toasted an engine. Intake and IC ducting was redesigned in 99 as a result. Search intake in ciriani and/or robinette sites listed at FAQ for the article.

Montego

iTrader: (1)

Try this one on for size:

Mild street port
M2 CAI
PFS SMIC
DP
MP

EBC set at 9.5-10.0 psi on a stock ECU.

t-von

iTrader: (8)

Actually the 3 mod rule isn't very wrong. 3 mods and no boost control can easily cause an overboost situation which is very true. The only problem with the outdated site is the fact that he isn't taking the stock 10psi boost level into account with additional mods. I'm not trying to prove you wrong but I believe the info Robbinette provided is still right, it's just incomplete.

I added a downpipe and did the poor mans intake mod with the stock box and my boost shot up to 12psi after transition.

Mahjik

iTrader: (1)

So, with 2 mods, your boost changed; proving that the 3 Mod Rule really isn't valid. You are making the same points as rynberg, but rynberg is correct. The hard and fast rule of "3 mods and then you need an ECU upgrade" is like the old "the world is flat". It was correct at the time with the information that was available, but new information revealed a more accurate finding (as with what the stock ECU can or cannot handle).

adam c

iTrader: (2)

Incomplete is wrong. The three mod rule says its OK to do three mods without doing anything else. Thats wrong.

At what point did the world stop being flat? I missed that one

RevZempoe

had exact same problem. try checking your battery and alternator. I bet your alternator is overcharging your battery which in turn is causing the acid to boil/burn. worst smell ever.

t-von

iTrader: (8)

When you put it that way, your absolutely right. But remember, not everyone is going to visit the Rx7club forum to find out that you need to maintain the stock 10psi to allow safe engine operation with additional mods. If a person "ONLY" got their info from the Robinette site, then the info he provided is somewhat safe. Notice I did say "somewhat safe"! Thats what I was meaning when I said that his 3 mod rule isn't very wrong. It also depends on what particular 3 mods you do.