Hi Ppl, i need professional help here. I have a RX7 RS Model 1997 with an APEXI N1 Titanium Exhaust Cat BACK, 3 inch downpipe. I just plugged in a mid pipe this weekend and obviously removed the CAT. Apart from the mega noise i am generating now, it seems that i have no back pressure and the boost in having sudden peaks. Im running the stock ECU.

The Question is this, am i doin any harm in my car with this mide pipe? Also, no back pressure isn't it bad for the FD? Please help as im in a dazzle!

Thanks Guys!

Matthew Sciberras

Malta

 

Wewt for double post?

Anyway, if it spikes too high you'll most likely blow an apex seal....

 

Thanks dude..so you think that the best thing is to put the Cat converter back? How much power would i loose? Also the noise is extremely high. Im back firing under high boost which is cool but somehow the engine doesn't seem to be enjoying it!

Do RX7s need back pressure? I think that im running too much of a lean non restricted system, am i correct in stating this? Please help! :-)

 

Most generally backpressure isnt good. On a turbo car, one that you can control boost on, you want the least amount of restriction possible. Do you have a boost gauge? If not get one ASAP because thats how youll really know whats going on. If its boosting higher than 10-12 PSI on the stock fuel system/ecu, then your motor is probably in danger. In which case youll want to get a rechip or a powerFC or its equivilent.

 

yes you are putting too much boost on your stock ECU. you will decrease your engine's life and turbo life.

and reason you have boost pike because stock wastegate will no longer slow down the tubo.

 

Yeah..that is the normal PSI gains im getting, but it spiked up for me to 15PSI once for sure. The worry is that some ppl tell me that it needs back pressure, and others say that i do not need it. Im not concerned about the noise really, as APEXI have this super silencer you can stick on the catback tip.

So...you think that i should leave this damn mid pipe right? I do not plan to change my ECU to REMAP in this present future.

Guys, you opinions are gold for me..please help!


Thanks

 

Sp what do you recommend mate? Shall i put the CAT converter back on?

 

I would put it back the way it was before it started spiking....unless you wanna rebuild soon. Just my opinion.

 

I suspect this is detonation. Put the cat back on before you run high boost again.

You don't really need backpressure. For instance, on a single turbo with a big wastegate, the ideal is to have no backpressure.

However, search for discussions of "boost creep" for some info on why you might actually need some backpressure with the stock turbos and wastegate.

Also, running a really open system makes the car run lean. So I guess you could think of that as "needing backpressure", but really you just need enough fuel for your flow. Having some backpressure around keeps you in a flow range that the stock ECU can handle.

So, I hate to say that you "need backpressure", but for boost control and proper air fuel ratios with stock equipment, you could consider that to be true in some sense.

-Max

 

Thanks guys...i'll put the CAT Converter back on then. Pity i bought it and spent $260 for nottin! :-)

 

Would it be sufficient to use an after-market BOV and Boost Guage?

 

Er.. that doesn't control your boost or boost creep. He would need to port the wastegate or he could try running a silencer in his aftermarket Catback.

 

Yeah...that is what my friend recommended infact. To stick a silencer instead of the mid pipe. What you guys think? :-)

 

It works, no doubt. With my midpipe, Apexi GT Spec and HKS Boost Controller, I was having spikes. Adding the silencer that came with the exhaust was restrictive enough to keep my boost in check, and I never had a spike again (eventually ported the wastegate). So, I can say first hand it's a doable solution.

 

ahh cool...sounds like a good plan then. The apexi exhaust cat abck comes with this super silencer which you could bolt on the tip and reduces the noise by 7 db. You think that this would actually serve a the same scope as the silencer instead of the mid pipe?

Thanks

Matthew

 

I would be weary of a mid pipe on stock ECU, just because it will allow too much volume airflow though the engine without the additional fuel. Everyone forgets about the flow of the motor, and instead just concentrates on the boost level. I would stick with the Intake, DP, and CB until you get injectors, and PFC. Then you can have it tuned for the Midpipe.
If your cat is clogged, or you want to remove the airpump I would get a restrictor plate/ restrictive silencer for the midpipe, but that's more of a guessing game.
Good luck.

 

Thanks dude....in fact i decided to put the CAT BACK back on. Anyone wants to buy a midpipe? :-)

 

Just keep the midpipe and save up and buy an ECU like a power FC or something then you can reinstall it and get it tuned. If you install a boost controller there is a good chance that even with the full exhaust you can keep it from boost creeping and the upgraded ECU will give you the extra fuel and control you need. Some people have experienced boost creep with a boost controller and upgraded ECU so if that did happen you will need to install a restrictor plate or remove the midpipe until you could remove the turbos and port the internal wastegates.

 

I had similiar questions a while back, at some point we all do. Just wanted to further clarify, that no backpressure is good on force-induction cars, if you have the fuel to support the increased flow rate, this applies to any car. It's not the fact that just because you have an rx-7 its any different from the next turbo'd car. The point is freeing up backpressure allows the turbos to spin faster, and unless you restrict them from doing so by introducing an obstacle for it, you are pushing more cfm (air) into your intake, and without more fuel you are running too lean a mixture which would lead you to destroying your engine. What happens is the air gets so hot and pressurized it will actually ignite the fuel even before the spark plug hits it- this is called detonation. The fuel and octane is actually what keeps it from getting to that point, mind you have the proper mixture or are running on the rich side, or running higher octane.

 

Thanks guys for the help. Im running on poor octane..that is what we get in Malta! :-( I was actually thinking of getting a Power FC but the thing is this...in Malta there is nobody who knows how to tune RX7s well. So basically i would end up buying the Power FC and keeping it in my room, unless i take the car abroad to the UK or something.

I just went for a spin with my FD and my midpipe still stuck on. The back-fires im getting are out of this world!! Especially on second gear when hitting the limiter. All you see is this huge red light...like a flash light...from the corner of your eyes...amazing stuff! Pity im going to loose this scenario!!

Mind you...i need to take some aspirin though...the noise gives you such a bloody migrane...!!! :-)

Im open to much more ideas guys...so if you please....help me out!


Thanks

Matthew Sciberras
Mazda RS 1997

 

Yes, it's best if you have someone who knows how to tune it correctly preferrebly on a dyno machine, so that you can get the maximum gain out of it. But I know several people who have tuned their own power-fc, yes they run a little rich, but it's a lot better than running a little lean, hell they got maps and all the information for them on here.

Besides you don't have to just get a power-fc, you can send your ecu off and just let them program it to the mods you are running.

 

what octane, ron or aki?

low octane and water inj'n are a good power combo. search

silencer might help boost control. could try running low boost, as is, with MP to avoid spkes. Just plug the hose from the wg actuator to the solenoid valve ... should be 9-10 psi. check newbi links for boost control, and related hose pics.

 

If you stick with the stock twins and run just 10psi the base map on the power FC will work fine with intake and full exhaust, buy a datalogit and tech edge wideband and you can tune the power FC yourself on the street.

 

Thanks guys..thing is this...my car runs on 12 PSI as standard. It is a Japanese import and since it is a 1997 RS model, apparantly it runs at 12 PSI. That is what my boost gauge always read and what the info of standard RS 1997 models say that they should do.

As per power FC, do you guys know from where i could make a good deal and they program it for me and i just plug n' play?

 

Remember adjusting the exhaust not only spools the turbos more, but it also opens up the FLOW of the motor. Kind of like breathing through a large straw versus small straw. Even if your internal wastegate was ported to maintain an even boost level, you would still have to either pull the midpipe, or buy an aftermarket ECU to adjust out the map to compensate for the additional flow. Some turbo cars with a MAF sensor factory installed are more acceptable to performance mods because they can adjust the fuel based on the Mass Air Flow entering the engine. Therefore if you open up the straw so to speak with open exhaust, the MAF sensor will read the additional engine airflow and the ECU will add the additional fuel needed. However the RX7 is a speed density system where it does a lookup for Engine RPM, and Vac/Boost Level for the timing, and fuel pulse needed. If the engine flows more in a speed density system, it throws the factory calculations out of sink for an optimum A/F ratio. Hense the need for it to be RETUNED. The first three mods can be used because the factory has put a safe fuel map for the stock config and therefore you can lean it out alittle with the mods, and you will see a good difference in performance. More than likely the midpipe will lean the factory ECU out too much and POOF there goes your 13B apex seal. Prepare yourself for a rebuild if you want to continue the midpipe flow on your stock ECU at 10-12psi. good luck either way man, but the mid pipe isn't enough performance in my opinion to risk a 4K+ rebuild. You probably aren't even looking at more than 1 or 2 tenths in the 1/4.