Hey Guys,

Alright, so I've been slowly building my RX7 up over the past 5 years. Long story short is the car was bought with a blown motor and automatic and has since been switched over to a 99 spec engine/5 speed along with a host of other mods. Here's a quick list:

* Apexi PowerFC
* HKS downpipe
* Megan Racing catless midpipe
* Invidia catback
* Apexi intakes
* Greddy compression tube
* Stock 93 twins setup in rich man's non-sequential
* Aftermarket intercooler.

Currently have the PowerFC targeting .50 kg/cm2 and only 20% duty cycle (in other words, targeting 7 psi for safety). Took it for a quick test drive and MAN was this thing moving! I haven't actually felt what this car is capable of until today and I'm really impressed. Anyway, I noticed that even though I had the PFC set to .50 kg/mc the car hit .77 during one pull and hit what felt like fuel cut (knock was normal). So here are my questions:

1. I read that the PFC has a kind of haphazard overboost protection but that it can kick in as late as .25 kg/mc OVER what you have set. So for me, with .50 set, it makes sense I might not have felt the fuel cut until .77. Does this sound right, or am I nuts?

2. Any further suggestions to keep the boost in check with what I've set? I already ported the wastegates as part of the NS conversion.

3. Most importantly, how safe do you think the car is running at up to 10 psi currently on the stock fuel system? I do not plan to keep it this way at all, but do you all think I'm close enough with my mods to lean out too much?

On the run that hit .77, injector duty cycle was only 66% (I wasn't at redline, only around 5k or so I believe. I already have a wideband that came today and will be installing that next to monitor AFRs and will of course be getting this tuned (hopefully by Banzai) but what are everyone's thoughts? Should I not be driving the car at all currently until injectors and a new fuel pump are installed? I'll update the post with AFR readings after the install as well.

 

with the power fc you should have plenty of fuel headroom for 10 psi, but the base map might not be tuned correctly for those mods, u should check your air fuel ratios

 

If you can keep the boost to 10 psi you will be fine. If you can’t, you go boom. But why chance it? Just get the car tuned and be happy

 

That's the plan of course but I've still got a laundry list of things to get done before I get to that point (HKS Twin Power, interior work, new tires, some suspension bits, etc.). Seems like it'll never be done. Mostly just concerned with whether or not I'll be safe driving it every now and then for short periods of time before I get a chance to bring it to a tuner. Another problem is there doesn't appear to be any trusted or well known rotary tuners around the Atlanta area which means shipping the car to Banzai is most likely going to have to happen.

I plan to install the PLX wideband I purchased tomorrow (hopefully) for some more info on AFR and will report back.

 

10psi or even 7psi can be too much boost if the 25-year-old fuel system isn't working properly. I voted to install the wideband.

 

The problem is once you notice the wideband is reading lean it’s too late more often then not. Unless it is set up as a fail safe to the ecu to cut boost, but I don’t think the PFC allows for that. I could be mistaken on that however.

 

Fair point, realistically speaking though, if I have the PFC set to 7psi and it creeps to 10psi and then fuel cuts, I should still be safe. I mean 10psi with my mods should produce a healthy number but not outrun the stock (assuming it is healthy) fuel system from what I understand. Don't get me wrong, I'm not trying to justify running the car in this state, just that it would be nice to know I could drive it if needed. I think I've found a local tuner that's got a lot of experience with PFCs and 7s, waiting to hear back from them. Only other option is to ship it to Banzai or Pettit.

By the way, if I were to street tune the car, I wouldn't have anything other than the wideband, PFCs, etc. to tune with. I think I'm going to do a Supra pump with and larger secondaries just to be safe regardless. I've just read mixed things over the years on how far the stock fuel system can go. A lot of people have said the stock pump doesn't even really need to be replaced until you hit single or BNR territories.

 

I wouldn't worry about 10 psi if I were you. Just monitor your car as you make adjustments, take it slow, and be extra mindful when it's cooler outside. The PowerFC commander can tell you peak values as you make adjustments, like injector duty and psi. (So you can check after a run.)

If you haven't read the manual for the PowerFC, definitely give it a read. You can get the pdf off the Apexi website. I believe it clarifies the fuel cut protection threshold.

And excuse me if any of this is obvious to you! Good luck with your car.

 

Another quick update here... I've got hr HKS downpipe marked up for the wideband bung and in the trunk of the Miata for a quick weld tomorrow at the exhaust shop. Should have the PLX installed tomorrow night for AFR readings. 90% certain I'm going to grab a Supra pump from Banzai shortly. Considering modifying my spare fuel rail and throwing my spare 850s in for a 4x850 setup. I know it can be a PITA to tune with, but the whole car needs a proper tune anyway so why not. The 4x 850s with the Supra pump should be more than enough fuel for anything the stock twins can throw at it from what I've read. Thoughts?

AFR readings under light boost coming soon.

 

What wideband do you have? Most I’ve installed want to be 30-36” away from the turbos so that puts it in the midpipe in my experience.

I would definitely get a new fuel pump just to be safe. I would also rewire it before you tube since it’s very inexpensive insurance. Rewiring your fuel pump after the tube would require you to retune as it does add more fuel.

I don’t think I would add the extra 850’s into the primary rail. I would just do the fuel pump rewire and get all the injectors tester and cleaned professionally. More cheap insurance.

 

Anytime you put a mid pipe on you are at risk for boost creep. It's not as much "can my fuel system handle it", it's "can my boost control give me consistent boost".

Using the stock solenoids/pills can be a problem as-is. You may want to read up on using the PFC for boost control. You can also go with a manual or electronic boost controller.

Also possible that you could have to port the wastegate on the turbos, it's common to have boost creep with a free flowing exhaust and midpipe.

All that said, onto the fuel system. I would go with a Walbro pump from Banzai, they flow a lot of fuel, are bolt-in and are dead reliable. I don't see a good reason to run the Supra pump.

Do NOT do 850cc primaries. It's not a "these need to be tuned" it's "it's impossible or nearly impossible to have your car idle and drive worth a crap". That was an old-school band-aid for fuel before there were any other good options. If you stay pretty low on boost you probably don't need to upgrade injectors, just the fuel pump.

Dale

 

Dale, thanks for chiming in sir! So when I did the "rich man's" non-sequential setup I ported the heck out of the wastegate and cut/sealed all the flappers/holes. The idea was to do this conversion on the 93 twins as best as possible. Check the last page here for the pics of all that work: Build Thread. But, judging by the creep I experienced, it didn't seem to make a bit of difference since I had the PFC set to 7psi and it hit overboost protection right around 10.1psi or so. When you say, "You may want to read up on using the PFC for boost control" are you talking about reading up on the Apexi external boost controller that can be used as well or the PFC's internal boost controller in general? I've got it setup correctly from what I can see at this point (.50 target, 20% duty cycle for ALL options). Basically have it set as low as it will go for testing.

I honestly hadn't considered external boost controllers since I was always hoping to use the PFC to keep it nice and clean. If an external will hold the creep back better than the stock wastegate/PFC controller will though, I might have to look at doing that. I suppose I could always install a high-flow cat as well.

As for the Walbro 255, from the threads I've been reading, it seems most people preferred the Denso pump because they supposedly failed less compared to the Walbro. I installed a Walbro 255 in my old VR4 and liked it overall, it's also half the price of a Denso pump. Hmm...

Eventually, I'm shooting for 350RWHP with a proper tune on the 99 sequential twins. 4x 850s should cover that but I've read a lot of horror stories as you mentioned. I also read a lot of failure stories with bored our 850s (1300s), but I REALLY don't want to invest in a whole new rail setup just to run 350RWHP. Any suggestions?

 

If you want to see if you've got the baseline for boost control right, run straight hoses (no restrictors) from the compressor housing to the wastegate and cap off the nipple on the wastegate that goes up to the factory boost control. You should see about 7psi spring pressure and that's it. If that's the case all day long then a boost controller can bring the boost up - remember, boost controllers can only INCREASE boost, never lower.

The stock boost control solenoids rely on the pills in the wastegate lines, many times you have to play with the pill sizes to get it to work properly which I hate IMHO. But, some people have figured out other ways of getting the PFC's built-in boost control working well - you can also use the MAC solenoid to replace the stock solenoid. It's been a while since I read up on it, there's a lot out there on the topic.

I've had a Walbro 255 in my car for about 12 years no with ZERO problems. If you get a real Walbro you'll be fine, Banzai sells real ones they get straight from the manufacturer. Ones on Ebay are pot luck if you get a real one or a copy.

Banzai Racing also has a wonderful thread where they dyno-test a car as they add mods to it, you can see how much power each mod makes, when they increase fuel, etc. That can really help give you a roadmap.

For extra fuel, the 1300cc secondaries was a great option back in the day (I have them on my car) but I've heard horror stories lately of them locking up, having problems, etc. - even heard of people losing motors due to them. I think the best current solution is the Rotary Performance fuel rail with 2000cc injectors - it's a fair price, bolts right on, uses the stock fuel lines and stock FPR. They also have the settings for the PFC to set it up for the injectors. That will be LOTS of fuel for anything the stock twins (or BNRs) can do.

Dale

 

https://www.rx7club.com/single-turbo...ontrol-900599/

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

10psi on the stock fuel system should be fine, however there are a bunch of things that need to be checked/working, especially with a midpipe.
all of them are making sure that the fuel is consistent all the time, even in a boost spike, and the ignition is up to snuff. if you give the engine enough fuel all the time, and the spark plugs aren't too hot, and you don't have inductive crossfire, or spark leakage, these engines are pretty tough

 

Dale, great info again as usual. I've read that thread by Banzai you are talking about and it is great. It's stuff like that which is why I've bought just about all my performance parts from them (PFC, exhaust, brake kit, etc.). They are my go to and I wish they were a bit closer to tune the car once it finally gets to that point (although I might just bite the bullet and ship it to them). I might heed your advice on the Walbro pump and save the money towards other mods.

As for the boost issue, just so that I understand you correctly, you are saying to remove the restrictor pill from the wastegate to turbo line, and then run a vacuum hose straight to the wastegate solenoid. That way it is basically just running off wastegate spring pressure (which should be roughly 7 psi) but will still show boost pressure from the wastegate solenoid. That's a damn good idea actually. Still quite possible it will creep though, right? Since it's been so long, I'm also not 100 percent sure that I didn't reinstall the precontrol pill as opposed to the wastegate pill (I know one of them was missing). I ordered a set of new jets that are 0.064 which should be the correct size. Even if the precontrol pill was in there right now, the difference (0.059 I believe) is so minimal I doubt it would account for 3 psi boost pressure difference, right?

I'll remove the pill as suggested, install the wideband, and see if it holds at around 7 like that. If it does, I'll have to do some research about using the MAC valve instead (I used one of those on my VR4 as well for EBC)

 

Thanks for posting these. I knew of the first thread but had not read the second. Thanks!

 

Banzai is about 700 miles from Atlanta, you could make a road trip out of it .

You're a little off on the boost pressure testing. You want NO solenoid involved - this is the part by the intake manifold that has an electrical connector. You want a straight vacuum line going from the nipple on the compressor housing to the nipple on the actuator down on the turbo. That actuator has 2 nipples - one normally goes to the compressor housing and has the pill in it, the other goes to the metal vacuum spider that is between the turbos and water pump housing - that hose eventually goes to the solenoid on the intake manifold. The solenoid vents to the primary turbo intake.

Anyhow, you JUST want the hose that normally has the pills in it and the other nipple capped off. That will demonstrate the lowest possible boost the car can run.

Dale

 

Got it, thanks for the clarification. I'll give it a shot.

 

Small update I thought you all would be interested in. I had the downpipe off the car and in the back of my Miata along with an 02 sensor bung ready to go for welding. Took it to a Midas and the guy wanted FOURTY dollars to weld it onto the HKS downpipe. It's like a 3 minute job and costs them nothing in materials so I thought that was complete BS. Called around a few other shops and the price ranged from 35 up to 50. The only muffler shop that would do it for a decent $20 was like a 45 minute drive away in rush hour traffic so I said the heck with it.

Took it home, drilled the hole with a step up drill bit, and then used my cheapo Harbor Freight mig welder to weld the thing up myself. Wasn't perfect, but it is definitely on there and I smoothed it out a bit afterwards. Overall looks really nice (I'll post a picture up later tonight). I would have paid up to $30 for a muffler shop to weld this on with a proper welder, but most the people I talked to were trying to rip me off so I just did it myself. What's everyone else think about that pricing, am I just a cheap ***? Anyway, should have the downpipe on tonight and with any luck the wideband wired in as well. AFRs coming soon.

 

Last time I had a downpipe bung welded on it was $20 and I did supply the bung. They did it while I waited.

It was a local muffler shop but that was also probably 12 years ago .

Dale

 

add a restriction plate between two flanges/pipes of the exhaust to raise the back pressure so that the boost doesn't creep.

 

our local shops are that expensive too....

 

Every car is different. Install a wideband and get a professional tune to be safe.

 

Voted incorrectly lol, with those mods, a good tune, and a good functioning fuel system you should be perfectly fine. It's similar to my setup i've put 10,000 hard miles on. I'm running HKS downpipe, RP straight midpipe, HKS catback, pettit intake, powerFC, and RP comp. fuel pump on stock turbos and stock injectors. I make 300 at the rear wheels on a mustang dyno at .7 bar. I would highly suggest getting a professional to tune the car.

 

Think I've found a line on a (hopefully) good tuner. The shops called DBW Motorsports and they are familiar with PFCs and RX7s, apparently they've tuned more than a few. I've had a hectic week so I wasn't able to install the downpipe or wideband just yet. Hopefully will have some time over the next few days. I want to for sure see what the AFRs are showing and test the turbos with just gate pressure as Dale outlined above. My current plan is to throw a Walbro 255 in it after that no matter what. I've got some interior stuff to straighten out and some tires to get after that but then I should be ready for the tune. I'll update with the AFRs for sure.

Who voted marclar!?