Mrmatt3465

iTrader: (10)

Hello,

I'm having an issue with my Primary turbo spiking to 13 psi on my stock Rx7. The ONLY mods I have are a Pettit 3" downpipe, new silicone vacuum hoses [Hose techniques] and Azeknightz turbo control solenoids. Everything else is bone stock.

When I do a pull in any gear, my boost pattern is 13-8-10 according to my DEFI boost gauge. I have replaced my precontrol and wastegate solenoids with BRAND NEW ones from Ray @ Malloy Mazda. I feel I MAY have discovered the issue but I would like feedback on the situation. According to the FSM page F-89 and F-90, testing the wastegate and precontrol actuators indicates that the actuators should "move between 10-14 psi". This is quite vague. Common sense says that if your target boost is 10 psi, shouldn't your actuator be open at 10 psi? Slowly applying pressure via my MITYVAC, I see that the PRECONTROL actuator begins to move at 10 PSI and is full open by 14. My wastegate actuator cracks open at around 8 psi and is full open by 13. I also leak checked the line from the primary compressor to the wastegate and it holds pressure all the way to the solenoid.

I realize that the downpipe is a FLOW mod and that I should expect a boost spike [most claim 1 psi]. I am definitely not comfortable with 13 as a spike. I have read that you can adjust the actuator rod length to help with boost. But most have done this for not getting ENOUGH boost. Is it possible for me to set this actuator to open the precontrol door sooner than 10 psi to help control my spike? How would I go about doing this? Has anyone else gotten a boost spike this great on a mostly stock set up? I do realize that an easier route would be to purchase a PowerFC and alter the duty cycle on the precontrol solenoid but I would like to see if I can solve the issue using the Stock ECU first.

Any feedback is appreciated.

Matt

arghx

iTrader: (3)

You're not the first person to report greater than 10psi completely stock or with minimal modifications. I made a thread on this topic here: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/perfect-10-8-10-boost-pattern-myth-934461/ . I essentially argue that

1) we have evidence that Mazda intended to run more than 10psi, at least under some conditions

2) the stock overboost fuel cut is there to protect the engine, as long as you don't make significant changes to the intake and exhaust system (like deleting the cat). The fuel cut allows for higher boost under primary turbo operation than at high rpm.

3) It seems like the stock tune provides a lot of fuel already, so there is a significant safety margin for a setup with only minor modifications

Mrmatt3465

iTrader: (10)

Arghx,

Thank you very much for that link. It has restored some faith in the reliability of my Rx7. Upon closer inspection of the design records you posted, it indicated a 100% stock Rx7 hitting as much as 80kpa [11.6psi] on the primary before transitioning to a lower pressure during both turbo's operation. The "roof" of the overboost cut is also as high as 26PSI but the "roof" of target boost cut is closer to 16 psi under primary operation.

This indicates to me that:

The 10-8-10 is 100% a myth and is closer to a "target" boost.

Primary operation may exceed 11.6 psi [13 in my case] due to minor flow mods by 1-2 psi. This is acceptable.

Now my next question is as follows. You state that the factory ECU fuel map is fairly rich to compensate for overboost situations as well as a reliability factor. Do we have a map of the factory fuel table to indicate injector duty cycle increasing as boost increases to maintain a proper AFR above "target" boost? I have read several times of rotaries shelling out due to both overboost and fuel cut. If I obtain a wideband o2 and monitor it under my stock map, what AFR should be targeted and what should be of major concern?

Thanks!
Matt

nismosilvia270r

iTrader: (5)

if youre not comfortable with it, you can open up the pill for precontrol.

in my case, I ran a larger orifice "pill" and it lowered my primary boost to a comfortable level.

sorry i didnt answer any of your last questions

arghx

iTrader: (3)

It's simple, it's oldschool, but it does work. The FD isn't unusual in its boost control system. If you remove the cat on an STi for example you get the same issues with overboosting and possible engine damage.

Those are graphs published by Mazda after the FD came out. Assuming they are "right" they do indicate that the FD was intended to run more than 10psi stock. Another interesting fact that corroborates the chart: if you purchase a Power FC, the target boost level during primary-only operation is .80 kg/cm^2, or 11.376psi. Of course that value is a little disconnected from what the engines actually ends up doing, but it points to the fact that the the 10psi thing is more of a murky idea that has been around since the 90s.

it's certainly tricky to read. The more important thing is to understand the overall trend.

People have observed 10-8-10. That doesn't necessarily mean that only a 10-8-10 pattern is "right" or "correct." If you do have a 10-8-10 pattern, I wouldn't then be worried. Nobody has really dug into the stock boost control maps in the stock ECU.

Well, that's an old thread. I would say now that it was tuned rich to meet certain targets for cat life. I have argued in other threads that the FD doesn't run particularly rich under full load; it's about average if you compare it to other cars.

We have anecdotal evidence from the few people who have installed widebands on mildly modified engines. The FD came out in the "prehistoric" era--that is, before car forums existed. This is important, because people have to look backwards and try to guess how the vehicle was designed from the factory. When a new car comes out now, people strap it down on a dyno and read the stock wideband to get an idea of the AFR curve. Then they post it on the internet.
I am very much against the idea that overboost fuel cut somehow damages engines. Now, I'm sure somebody somewhere on the internet has some evidence of it becoming a problem. The fact is, every modern turbo vehicle has some form of overboost fuel cut from the factory. The overboost fuel cut may be based on actual psi from a MAP sensor; it may be based on a calculated engine load/charging efficiency based on the MAF sensor.

It may be based on the torque control logic, whereby the calculated engine torque exceeds the maximum allowable and then triggers fuel cut. It depends on the architecture of the control system. For example, Bosch and Siemens based systems rely heavily on calculated torque values, and will use a torque reduction request to control an overboost situation. The target torque is compared to the calculated torque. Then a torque reduction request will be calculated. It is either a "fast" reduction request or a "slow" reduction request. A "fast" reduction request will retard ignition timing or cut fuel; a "slow" torque reduction request will close the electronic throttle, or change the valve lift on vehicles equipped with continuously variable valve timing.

I don't doubt that a lot of engines have bit the dust when they go from stock cat to a catless midpipe. That is a big change in the exhaust system.

It depends on the running characteristics. At lower loads, AFR should read very very lean due to the dilution effect of the secondary air injection (smog pump). Under heavy loads, for a stockish car expect AFR in the 10s or 11s as a means of protecting cat life. The richer AFR cools exhaust temperatures, but also causes higher CO emissions. The FD is too old to have any sophisticated control logic here. There is no hard and fast AFR that is "dangerous" on a nearly stock car. In fact, if you hook up a wideband don't be surprised if the engine [I]seems[0/I] "dangerously" lean at heavy throttle and low rpm. It's like that to keep CO emissions down.

Remember that the stock ECU does have a basic knock control system that retards timing up to 7 degrees according to page F-44 of the service highlights manual. A Power FC and in most cases every other standalone doesn't have that. The stock computer (well, the stock tune, not so much the computer) becomes a problem when you modify the engine far outside of its stock parameters.

Btw, I would be very interested to see any data (or rough values from looking at a gauge) you can acquire with a pre-catalyst wideband on a nearly stock engine.

adam c

iTrader: (2)

I wouldn't worry about 13 psi on the primary turbo. Fuel volume is low because rpm is low. The stock ecu can keep up. 13 psi on the secondary could be a problem at WOT and 7000 rpm.

As mentioned earlier, you can drill out your wastegate pill if you are concerned. This would likely lower your 10 psi on the secondary turbo. If it were my car, I would do nothing, and enjoy the ride.

Mrmatt3465

iTrader: (10)

Thank you very much for your very in depth and detailed answer arghx. Adam c, I will do just that, nothing .

I'm sure someone will find this thread with the same issues I did and be happy they read it. I searched several times over and was never able to find a thread with such detailed truth in it. This is a good read for anyone running a stock or mostly stock rx7.

If I do invest in a wideband I would happy to post my results in this thread for the trend on a 98% bone stock 13brew.

Thanks again everyone!
Matt

tangoshark

iTrader: (18)

Good thread!! Arghx is definitely our man for turbo related questions. I just installed hks DP, eifini y pipe, racing beats cat back and 3 piece greddy turbo pipings along with vaccum hose job. Primary spiked to 12 psi and that's when I let off the gas. But it was raining that day so I didn't push it pass transition but I ll see how it goes on the 2nd turbo after the holidays when we get a dry day here in Oregon.

tangoshark

iTrader: (18)

Hey Matt,

Please keep posting back on the health condition of your car with the 13 psi on primary. I just installed HKS dp and efini y pipe with racing beat Cat back and I am seeing 12 psi on primary at WOT, so I am interested in seeing if there is any problem from having a spike like that in the long run.

thanks,

David

Mrmatt3465

iTrader: (10)

Hey David,

Well I've been daily driving my Rx7 since I bought it in December last year and have finally picked up a DD. Now my Rx7 as of last week sits in the garage awaiting pretty days as it should. As for the purpose of this thread and to answer your question, I have since put 4k miles on my rx7 including a trip to Tail of the Dragon among several 3rd gear pulls from 3k. A redline a day keeps the carbon away is what I like to tell myself :P During the summer, my boost would only spike to 12 psi with my mods (still only a downpipe and azeknightz solenoids). During this winter I have seen it as high as 14 psi. I noticed it would spike to 14 psi and hold to transition and then I would hold 9-10 psi from then on and not a psi more. My motor still pulls 17-18in of vacuum just like the day I bought it. My research has led me to believe that running too much boost is MOSTLY applied to twin turbo operation at higher RPM ie 13-14psi @ 5000+rpm. The stock ecu is capable of running this boost spike at lower rpm.

As for updates, I have been considering picking up a PowerFC. I need to find a good tuner in the SC/NC area for me to really seal the deal though. A PowerFC will really shine with a good tune. I had been considering this to help quell the 3k hesitation as well as add expandability and a proper boost controller for the twins.

Matt

SpooledFD3S

iTrader: (10)

I want to bump this thread since I too experience boost spikes in lower rpms on the primary turbo and wonder how safe it is for my motor.

The thing I want to bring up is how efficient is the stock SMIC would be when the primary turbo spikes to 13-14psi. It sounds crazy to think such a small intercooler should be able to handle these kinds of boost levels, but then again, the rate of airflow of 13 psi at lower rpm should be theoretically equivalent to 9-10psi at higher rpms..am I wrong?

Mrmatt3465

iTrader: (10)

The stock boost control pattern more closely resembles a 11-8-9 pattern with the precat in place. With a Pettit down pipe I have been seeing ~13-8-10 as my boost pattern. The factory intercooler is perfectly fine at low rpm as it is only seeing the boost of one turbo. I've been toying with the idea of playing with my precontrol pill and going slightly larger. I believe a Holley #60 or #62 jet in the precontrol would bring boost to a 11-9-10 pattern or so. The larger precontrol pill will slightly lower the primary boost while spooling the secondary slightly more. Playing with pills is a delicate balancing act from what I have read. When I eventually get the time to experiment with playing with my pills with my single mod I would be more than happy to post back.

Matt

tangoshark

iTrader: (18)

during the winter days last a couple months I have hit 13psi on primary on cold morning (33 degrees F), but after transition it never goes over 10psi and goes down to about 8 approaching redline. I think it will be pretty safe if you keep your stock airbox and stock main cat untouched.

The mods I have are HKS DP, stocking main cat, RB single CB, Efini Y pipe and cross over, Greddy 3 piece IC piping, and vacuum hose job. Nothing else.

oh and when it gets warmer outside like 50, 60 degrees, my primary stays at 10psi WOT on the primary so only goes to 12psi on cold days. But different cars will react differently so if you are hitting 13, 14 psi constantly you better get a boost controller or PFC.

tangoshark

iTrader: (18)

double post

tangoshark

iTrader: (18)

what's your mods?

energ3tic

...

SpooledFD3S

iTrader: (10)

sorry for the late reply but I have a 3" downpipe, RX7 store high flow cat w/ airpump and a racing beat catback. The airbox is stock and sealed.

I noticed that the boost spike is not very consistent in the higher gears. If I'm in 4th or 5th gear, the primary turbo at say 3000 rpms will spool 11 psi at times, and then 13-14 psi at other times. In the lower gears, the primary turbo is usually never higher than 12psi. After the transition at 4500 rpms however, boost is right around 10 psi.

I'm thinking I may have an issue with my precontrol system since it's the main valve that limits the primary turbo's boost by venting some of the exhaust to secondary turbo(which is off before 4500rpms). I'm kinda ruling out a bad solenoid since the ECU did limit the boost to 7 psi in limp mode one time..maybe the hose going to the precontrol actuator is leaking or clogged..

tangoshark

iTrader: (18)

Have you had a vacuum hose job done?

I used to have delayed and inconsistant transition issues, and that's when I did a vaccume hose job, replaced both turbo control solenoids (vacuum and pressure), and check all other solenoids and check valves and replaced the bad ones. So if you haven't dug into the vacuume hoses and rats nest, this should be a pretty good time to do that now. Once you dig in there, you will find out there are a lot things you are unsure if they are working properly.

SpooledFD3S

iTrader: (10)

There was one bad check valve that was split in half near the turbos that was replaced when I changed all the check valves with the daleclark's vitons. Since then the second turbo comes on fast and strong. The motor was rebuilt not too long ago so all the hoses look somewhat new.

I adjusted the turbo precontrol rod last night 2 full turns "out" so it's not pulling the valve shut so tightly and it seemed to have lowered the boost while making the transition a lot faster. (makes sense since it's bleeding exhaust to the 2nd turbo sooner) Weird thing was that it seemed to be adjusted properly with it preloaded about half a pin width..but maybe with the higher flowing exhaust it's necessary to adjust it down a bit to compensate. I only drove it once since the adjustment, but boost seems to be doing a 11-10-11 pattern now instead of the 13-10-11