mkiv98

iTrader: (5)

So my mostly stock except a downpipe car shows a peak boost of 12.2 psi on my old school blitz dual turbo timer. Whenever I want to replicate the condition while watching the meter, I can't. (side note, does boost pressure change depending on external factors like the weather or how you are driving? it seems to be a different pattern every time I try to test it)

I have a power fc with a few other bolt ons ready to go on the car...I want to install the powerfc at least to supply to fuel needed for this extra psi.

Also, at what pressure should you worry about damaging the engine?

potatochobit

iTrader: (1)

the stock injectors and fuel pump should not be used for anything over 14psi safely, I believe
and running over 10-12 you want a nice intercooler anyway
if you have a PFC, it can control boost since you dont have a boost controller,
but I would leave it at 10 until you get a new intercooler and have it professionally tuned
dont mess with any injector adjustments until then
of course, I could be wrong since I have not messed with my boost controller in like 7 years

edit:
the temperature of the air is what affects the pressure most
but, if you are still running sequential, you could have all sorts of little issues that need to be addressed
that would explain an iradic boost pattern

arghx

iTrader: (3)

I'm not convinced that your engine is in danger from this. It's stock with a downpipe. There's plenty of fuel for that. It's not like you are running a 3 inch straight pipe here. If you were significantly overboosting you would have hit fuel cut, which on the stock ECU is past 12psi at most rpms:



There are also indications that the stock ECU runs safely at 12psi. This is from Tashima, "Sequential Twin Turbocharged Rotary Engine of the Latest Rx-7," 1994:



80 kpa boost pressure is roughly 1 atmosphere * .80 . So 14.5psi * .80 = 11.6psi . Who detonates their engine with just a downpipe? That's a bit of a rhetorical question but you see what I'm getting at here. One thing I find interesting is that the Power FC actually has the boost target set to .80 kg/cm^2.

On the stock ECU, the boost control system and sequential turbo transition are based on rpm, throttle position, and gear position. Weather is going to affect it some just like any boost controller.



On the Power FC it is based only on rpm and throttle position. See https://www.rx7club.com/showpost.php...8&postcount=65

I'm not sure what other bolt ons you had in mind, but I bet if you installed a wideband (before the cat) on your engine as it sits now you'd be surprised how rich it's running under full throttle. If you were planning to do a bunch of mods anyway then just go install everything but if you are wondering whether the car is safe as it sits, I strongly believe it's fine.

mkiv98

iTrader: (5)

wow thank you for the extremely informative post. and this is why RX7club is one of the best forums out there. thanks for taking the time to post the graphs. I will install the powerfc and keep monitoring what happens.

j9fd3s

iTrader: (3)

i didn't know this until it happened, but the boost cut line isn't flat, the stock ecu will happily run 17+psi up to about 4500rpms, and then it hits fuel cut.

my friends car has been doing this for probably close to 4 years, stock ecu, and its totally fine

Speed of light

iTrader: (8)

I agree with arghx's post and assert that there's plenty of empirical evidence to back up the conclusion that there's no problem here. I would not bother installing the PFC as an antidote or repair for the condition you've described. Just drive it as is.

mkiv98

iTrader: (5)

but I wanted to install a powerfc for more power =)

Sgtblue

iTrader: (16)

^Since you already have the PFC and apparently have plans to add anymore performance modifictions ("more power")...bigger IC, cat-back, intake... and especially higher boost levels, then adding a PFC at this point is appropriate IMO.
Yes. Colder air = Denser air = the possibility of boost spike increases at wide open throttle (WOT) and load.
If you haven't already, read through the stickys for more info on BOOST SPIKE and BOOST CREEP and make sure you understand the differences.

arghx

iTrader: (3)

What mods are you planning to add?

mkiv98

iTrader: (5)

right now it's a downpipe...have some parts sitting around: Apexi intake, PFC, RB dual catback. I have no idea if the cat is stock or not, but I doubt it since the previous owner was intelligent enough to eliminate the coolant expansion tank.

and will add intercooler later.

right now I only have a boost gauge/turbo timer, so I may need a water temp gauge as well, but I believe the pfc commander has a reading for that.

are injectors/fuel pump necessary at that point?

I see that you wrote most of the PFC articles in the FAQs. very informative. I will run the base map according to your guide.

I should be done with messing with the car after all this. Just want to keep it running reliably while maintaining a bit more power than stock.

mkiv98

iTrader: (5)

installed an apexi power intake and power fc. car actually runs even more rock solid and idles perfectly, does not buck, has much more power, and boost has a less erratic pattern that does not go past .80 kg/cm2.

a cop passing by stopped to take a look and tell me he had to stop and look at the fd. I believe he has similar toys on his STi

how are is the accuracy on the gauges on the PFC commander? I was planning to get water temp an analog boost gauge but this seems to have everything I need already.