12 psi in 4th and 5th on stock car
 

My car is stock other than a drop in K&N and an HKS downpipe. Recently I've been seeing 11.5-12 psi on the VDO mechanical boost gauge in 4th or 5th gear. Speed is between 70 and 90 MPH so no real high RPMs. I don't think there is enough time in 2nd or 3rd to build boost above 10 or there is not enough engine load at that point to push it above 10. I am just guessing though. I always run 93 octane and I have an AEM water injection system so I think I'm still safe from detonation, however I am still a bit concerned. I know the stock ECU is safe up to maybe 11 max, but better at 10psi to be safe. I have not made any changes to my car so it is almost as if it just started boosting higher by itself. The weather here in San Antonio, TX is still in the high 80s if that makes any difference. I don't drive the car when it's over 90 or below 50.

What is the best way to solve this? It there some sort of bypass that can be set to bleed boost once a set PSI is reached? I wish I knew why it has been boosting higher recently but not in the past.

not enough time in 2nd or 3rd to build 10psi boot?
i will get 10psi boost almost instantly from 2k rpm + all the way to redline in 2nd or 3rd gear..

Yes, I guess not enough time in 2nd or 3rd to build boost. I'm going to go for a spin Saturday morning so I'll check out the boost in 2nd and 3rd again but I was pretty sure it was only in 4th and 5th. Either way it's making too much and I don't understand why it's changed. I was rock solid 10-8-10 for months after installing the K&N and HKS DP. I felt like with the stock exhaust and cat (all stock besides DP) that the boost would not get that high. I certainly want to protect my good original engine and keep it safe.

It's not that you don't have enough time to build boost, it's that in the higher gear you are generating more engine load which spools the turbos differently, and your wastegate can not flow enough to compensate for the addition in load. What you are experiencing is wastegate creep.

But with your water/meth injection, I wouldn't worry too much. I've been boosting 12.5psi or so on the stock ECU with 350cc/min of progressive water/meth injection for a couple months now. Of course, your situation might be different, and I wouldn't recommend it.

To fix the creep you either port the wastegate (easy to do, but requires removal the twins), or buy a boost controller. A simply $30 ball & spring manual type will do the trick, but an electronic boost controller will allow for greater flexibility and tuning.

I doubt the wastegate is being overwhelmed mechanically with the stock cat and downpipe. The factory boost control system is mapped for the factory intake and downpipe. In colder weather more boost is being achieved at higher gears, but you haven't hit fuel cut or anything. I'd just keep driving it.

https://www.rx7club.com/attachment.p...1&d=1284482692

You can see the "boost zone" allows higher pressures from about 3000-5000 rpm, which is probably where you are experiencing it.

That chart was hard for me to understand but I see the "overboost" point from about 3k to 5k that you're referring to.

I just drove the car. All the runs I did in 4th and 5th were from 55 to 80. Temperature outside is 70° F
It will repeatedly boost to 12 in 4th or 5th but it basically hits 12 for 1 second max, and then drops to 11 or 11.5.

It will briefly boost to 12 in 3rd gear but only if I shift into 3rd from 2nd early and start pulling from 2500 or so. If I downshift into 3rd going 60 or 70 there is not enough load to push it to 12. So I only hit 12 in 3rd when I start at low rpm and only for a second.

It's running smooth and perfect, no noises that would indicate deto, but I have heard so many times that 10 psi is safe, 11 is possible trouble that I'm concerned.

Is there anything I need to do or should I just not worry about it?

Add an electronic boost controller and you'll be fine. It's just a boost spike due to the cooler weather. However, it could get a little higher as the weather gets cooler.

It'd be nice to have a wideband on there to make sure it isn't running lean, even though it's probably fine. You could drill out the restricter pill for the wastegate if you're really worried about the boost. Aftermarket controller would be one solution, but it's not like those don't vary with the weather still.

Get a proper electronic boost controler, or don't floor floor the car when in higher gears and low rpm.

Can any of you recommend a good simple elec. boost controller? I might end up getting a wideband too but i really wanted to keep my car stock and uncluttered.

The limitation for the stock ecu is volume, not boost. The stock ecu can supply "X" amount of fuel, regardless of boost. You could run 20 psi of boost at low rpm (read low volume) and be safe. I don't think there is anything wrong with your car, or anything that needs attention. It should boost higher with the mods you have done. If you never hit fuel cut, you should be fine.

Thanks to all of you for the advice. What a great resource.

I'm going to look into drilling out the restrictor pill. Are there any disadvantages or negative side effects? I'm assuming that would allow more boost to be vented by the wastegate. I just want to do it right the first time and protect my engine. I don't have any current plans to raise the boost or do any modifications that would raise the boost so maybe drilling the pill would be the best solution. A powerFC is about the only thing I've got my eye on.

What about going this route?

https://www.rx7club.com/3rd-gen-archives-73/my-boost-control-setup-perfect-10-8-10-pattern-178136/

There are no ill effects of drilling the w/g pill, it will just result in lower boost. The actuators are 7psi actuators, so the purpose of the pill to restrict the pressure signal sees and allow it run slightly more boost. You can remove the pill altogether and you should run between 7-9psi.

That would be a great way to control your boost. You need two manual boost controllers. He used higher-end Hallman Pro RX boost controllers, but you can use cheaper $30 ball & spring manual valves and you'll be fine.

Dual manual boost controllers are one option if you're ok with spending the time adjusting them.

the reason why I like the factory dual solenoid design is because it keeps the wastegate completely shut before transition, and it keeps the precontrol completely open after transition.

https://www.rx7club.com/attachment.p...1&d=1287243131

In the above diagram the 95% duty means the actuator is shut, while 5% means the actuator is fully open. Mazda designed the precontrol and wastegate solenoids to work together with the sequential turbo system. You can't really do that with aftermarket systems. The only boost control system that can do this properly is the Power FC itself, because it mimics the factory control system.

I don't see what the big deal is with swapping or modifying a restricter pill in this situation. You know Rx-7's aren't the only turbo cars with restricter pills right? The Evo X has one turbo, 3 restricter pills, and two solenoids from the factory and that car runs 23psi peak from the factory.

All I want to do is get back to 10-8-10. If drilling or replacing the restrictor pill is the best way I am all for it. I prefer to keep things as Mazda intended and use the stock turbo control system because I think it works pretty well. I don't drive my car much, usually less than 1000 miles a year. I'd like to keep it simple, OEM.

Do I have to remove the turbos to get to the restrictor pill? Is there a specific thread in the FAQ that I should be looking for? I am hoping to avoid having to try different combinations of pills. Just looking for the simplest solution, but I always want to do it right the first time.

since you dont want a cluttered interior my suggestion is to run a boost controller and ditch the boost gauge. Given that most controllers display boost in real time it doesnt make much sense to have both.

Spec 2 is a piece of garbage in my opinion. The spec S is simpler and works better in my experience. Don't mess witht he pills. That's opening a can of worms.

I wouldnt mess around with drilling the pills (pita trying to find a measurment that hits 10-8-10 on the money)... they are easy to get to though if you want to remove them and test what the boost is like.

I would just get an ebc unit. easy to setup and will be most reliable for holding at 10psi. porting the wastegate would be good too!

any cooling or fuel reliability mods? radiator? alum ast? vac lines? fuel filter? fpd? fc thermoswitch?

Beyond old internet forum rules of thumb, I'm not convinced there is a problem with him briefly hitting 12psi but only in his current mildly modified configuration. I'm sure the mixture is rich enough, but he can verify with a wideband. He's got AI on there already. The JDM cars had a precatless downpipe from the factory anyway. Clearly Mazda expected boost to climb a little bit right after transition, or why else would they have raised the fuel cut so high?

I know several "oldschool" owners who used to run downpipe and catback back in the day on stock ECU (which is riskier than the OP's setup) and never had any problems despite small boost spikes occasionally. One guy I know got 110k out of his original motor in that configuration. Remember, one mistake with an aftermarket manual or electronic boost controller and you can get crazy overboost.

If it were my car I'd just keep driving it and stay on top of the maintainence (fuel filter etc). There's no need to be a hypochondriac about it. Mods blow engines, and this car is basically stock.

I have an aluminum AST, new mazda fuel filter a few months ago, and a pettit fan switch. I think my car still as the fan recall fix. I also have an extra OEM foglight switch on the center console in between my fog lights and defroster switch that will turn the fans on whenever but the pettit fan switch seems to override the fan recall because the fans run for some time after shutdown regardless if I've switched the fan switch on for 2 minutes before shutdown or not. Fans come on low at 180 and it never gets above 190 for me. I have all the hose and dale clark check valves for a full vac job but I've been putting it off because the car runs so good.

I thought about getting the AEM Tureboost setup. It could replace my VDO poost gauge and it's the controller too. I tried real hard to find gauges that match the car though. I might just go to the trouble of porting the wastegate and see if that fixes it.

Is the general consensus that porting the wastegate will solve this boost creep?

After doing some reading I have come to the conclusion that I am overboosting and boost creep is not my problem. I did not understand the difference earlier when I started this thread. I am assuming that since I still have the stock main cat, stock cat-back, and stock airbox that my higher boost levels are not creep but due to cooler TX weather, K&N filter, and downpipe. Some kind of electronic boost controller should be installed and I can lose the boostgauge and put something else in it's place. It sounds like a Power FC would not solve the problem but it could be tuned for the higher boost.

Am I wrong on anything I stated? Should I port the wastegate anyways?

Agreed.

You can adjust the boost control duty cycles of the factory solenoids using the Power FC. So yes, it could address the problem without needing anything else, as long as it's set up properly. But as I've been trying to explain, you are trading one set of hassles for another. The Power FC will run ok in your configuration but there are a number of idle and throttle response problems that can come up which are not normally an issue with the factory computer. And this is coming from a guy who wrote a Power FC guide. You can't beat the factory computer for overall driveability and reliability as long as you don't try to use it on a setup that has too many modifications.

Pull the turbos out and risk messing something else up in the process? Heck no. If it ain't broke, don't fix it. I personally think your car ain't broke. Have you ever pulled the turbos on an FD with all the plumbing still there??? Do you have any idea how many things can go wrong???

You've got a bigger chance of screwing something up by messing with the car than by leaving it alone, and I'll stand by that.

Good, I don't want to pull the turbos. I've been putting off a vac hose job because I don't want to open a can of worms with everything currently working so well. I have never removed the turbos and am not looking for a project so I'll stay away from porting the wastegate.

I think I will try and get an electronic boost controller just to keep things safe.

Great thread....I'm in a simliar situation with some occaisonal boost spikes...but, other than that the car runs great. I'll keep remembering the "if it ain't broke don't fix it" line when I want to tinker with my FD, too.

There really isn't anything wrong with the way your car is running, and you are perfectly safe where you are right now.

If you feel like you must do something, drilling the wastgate pill (if you have one**) would be the simplest most cost effective way to lower your boost. To do this, remove the airbox to get access to the wastegate hose. Remove the hose. Take a Phillips screwdriver of the proper length and diameter and insert it into the hose. Push the pill out the other end. The pill is made of a soft material, and will drill out very easily. Find a drill bit that is ever-so-slightly larger than the diameter of the existing hole. Drill, and replace the pill the same way you removed it. After replacing the pill, look thru the hose to make sure the hole in the pill is not blocked. THIS IS CRITICAL!!!!! If you can see the light ;), replace everything. Your boost should drop a little.

**If your turbos have restrictors in the nipples, you wont have any pills, and this won't work

If you don't ever plan on adjusting the boost, you only want to limit your current spikes; a manual boost controller will work well. EBC's are great if you want to have multiple boost settings like:

OFF - ~7 PSI (stock wastegate spring level)
LOW - 10 PSI
HIGH - 14 PSI

or something similar. If you are only trying to tune back to around 10 PSI, the manual controllers will work just fine (and save you a little money).

aftermarket boost control can still vary with the weather. If you really don't plan on modding the car further I just don't see a reason to get one. If you can get the right sized restricter pill in there the factory boost control system will be able to keep things pretty stable, as the factory system is fully closed loop.

While I agree on principle, I have not met anyone who was continually adjusting their EBC with the weather. And in my area, we see everything from 110F+ to 0F (or below).

It's hard to know what to do. I would really be tempted to do the restrictor pill but I just have not looked into it much. The manual controller sounds simple enough once you get it setup. Kind of wish I had a wideband a/f gauge so I knew if any of this were a concern to begin with. I think my VDO mechanical gauge is probably accurate but I question that as well.

Really glad to have all the pros giving me help.

Does drilling the restrictor pill just lower the boost all around or allow the oem system to manage it and keep it at 10? I'm sorry if that is an ignorant question. I am just wondering if it just generally lowers the boost would I be able to make 10 psi when it's hot outside.

I just read the FAQ post regarding restrictor pills. It didn't really make me want to dive into it. I have much to learn about the FD turbo system. I really just want to not worry about it like AdamC and Arghx are suggesting but my only concern is that it's 70 outside and I'm afraid when it's 50 I'll get into fuel cut territory. I'd rather be overly careful at this point than have to rebuild an engine.

http://www.autosportracetech.com/RX-7/faqs.htm#Pills

If I were you, I'd go to a hardware store and buy a few welding tips of various sizes to try, and not drill out the factory pill at all. Here's a welding tip chart: http://bikesmithdesign.com/Welding/Tips.html . It'd be faster and cheaper than installing and tuning an electronic boost controller on a car that is basically stock...


Well it depends. The more boost you are trying to run relative to the spring pressure, the less stable a boost control system tends to be as weather changes. It also depends what you are measuring boost with. It's a lot easier to notice variations in boost control when you are taking logs through something like a Power FC than when you look at slow responding digital displays or buffered mechanical gauges.

I would wager that if you need to log it to notice it, it's probably not really going to affect the average Joe all that much. ;)

Can anybody attest to the accuracy of a mechanical boost gauge, more specifically a VDO? AdamC I think you have or had a VDO mechanical guage. Does it jive with boost readings on your powerFC?

On an FD with sequential twins it is a little less of a concern. High boost 4 cylinder applications with internally wastegated single turbos tend to have the most problems with spiking and fluctuation with the weather.

That's a complicated question... every gauge has to be referenced to an instrument, and that instrument is referenced to ambient atmospheric pressure. So it all depends what you are measuring it against. The default calibration for the stock MAP sensor on the Power FC usually reads low.

Drilling the pill lowers boost. Simple as that. This assumes you have restrictor pills. Its easy to do, costs nothing, and won't clutter your stock interior with something you don't want (EBC). Drill the pill. If you are not satisfied, you can always get a boost controller later. Just don't drill the pill very much. Too much, and you may not even make 10 psi.

My VDO boost gauge shows exactly the same as my pfc.

I have the same 12psi boost. All I have is an HKS downpipe. I ported my wastegate so I'm not worried. Even my airbox is all stock.

Did porting your wastegate do anything for you? Pretty sure boost creep is not a problem for either of us since we're both using the stock airbox and stock muffler and main cat.

I added downpipe and ported my wastegate when I put in a new engine. Before things were all stock with a 10-8-10 boost pattern. While my engine was out, I asked the experts on this web page about preventive maintenance. bdfd_3s said that I should port my wastegate for peace of mind. So I did. Still don't know while my boost is around 12psi. Just makes me feel better knowing the wastegate is larger to keep the boost under control.

Why are you comfortable running 12 psi? According to many on this site you are right on the edge of engine trouble if your ecu is stock. That is what this whole thread is about.

Just want to make sure I got the right hoes & pill...

My 1/16" bit went through it and removed a tiny bit of material. I thought that was a little strange because the original hols is supposed to be .062" right? So the 1/16" bit should have slid in without any drilling necessary. I might drill it with a 5/64" but that comes out to .08" and I'm not sure if that is too big.


If this looks right please let me know. If I need to get a drill bit in between .06 and .08 I can do that. I don't think the 1/16" bit really did anything at all but it did make a few tiny dust shavings.

1/16th is .0625. Not much bigger than the original hole. The pill material is very soft. I would run the same bit a couple more times just to smooth it out, then reinstall it. You should see your boost drop slightly, which is what you wanted :)

A maximum of 11 psi should be ideal.

Thanks Adam. I would love to end up at 11 psi. Do you think a difference of .0005" will accomplish anything? It just seems like such a small amount. 5/64" is definitely way to big.

Here is a drill bit chart in case somebody else goes down this road.

1/16 .0625
52 ... .0635
51 ... .0670
50 ... .0700
49 ... .0730
48 ... .0760
5/64 .0781

http://www.thedirtforum.com/conversions.htm

I'd like to try a #52 or #51. I'll post my results.

Run it thru the hole several times until the bit doesn't fit so tightly. That should do it.

Drilled the restrictor pill with a #51 .067" drill bit. Took the car for a highway spin, here are the results. I was somewhat limited on how fast I could drive. I couldn't really check boost on the secondary turbo in 4th or 5th.

On primary turbo in 2nd and 3rd it boosts to 12. In 4th and 5th WOT at about 60-70 mph I still get 12 psi. I think that would still be on the primary in those gears at that speed.

I did a 3rd gear run from 40mph to 120mph. Boost was 12-8-10 but tapered off to 8.5 or 9 max at 6000-7000 rpm. Drilling the pill seems to have worked for secondary turbo boost that is too high. I think I may have drilled it out a little too big.

Does the restrictor pill not effect boost on the primary turbo? Bottom line at this point is that I'm still hitting 12 psi easy on the primary in 1st through 3rd. I don't know what primary boost would be in 4th or 5th since I can't drive that fast.

Agreed, and if you go with a simple ball & spring check valve with adjustable spring tension vs the simple adjustable valve that most manual boost controllers (MBC) consist of, it'll allow the turbos to spool up faster. And if you're too lazy to make your own, you can always get one already made.

12 psi on the primary won't hurt anything because the stock fuel system will plenty of fuel at low rpm. On a stock car, boost will tend to drop off a little at high rpm in higher gears. Sounds like your problem is solved.

BTW, you cant go 120 mph in 3rd gear ;)

The primary has its own actuator (precontrol actuator) with its own solenoid and pill. The secondary boost tapers off a little bit up top from the factory. Your secondary boost sounds fine to me. Just about every factory turbo car tapers boost a little bit near redline.