Subaru WRX Forum banner
1 - 20 of 39 Posts

·
Premium Member
Joined
·
6,750 Posts
Discussion Starter · #1 ·
I read on WRXtuners that boosting 15.5 psi on the stock turbo will cause your injectors to hit 98% duty cycle...eh? That doesn't sound right to me, but of course I'm no expert. Anyone here know for sure?
 

·
Registered
Joined
·
50 Posts
Well, from what I understand, anything above 80% causes the injectors to go "static" and effectively stay open continuously anyway...
 

·
Moderator
Joined
·
895 Posts
what about if you have other mods? say, an exhaust or whatnot - then im guessing your duty cycle would be lower at the same boost level?
 

·
Registered
Joined
·
1,895 Posts
I'm helping a friend do some tuning on the UTEC in his car. He has a stock turbo/stock fuel setup and when going over 15psi he reached 98% injector duty cycle.

I expressed surpise when he told me about it - but here's a log:



We're still trying to figure out if the reading is correct - and/or if the MAP sensor is calibrated properly.

Either way, the car is running rich - but the injectors are working HARD to keep it that way!

Thankfully there are no knock events, the UTEC is adding up to 22 degrees of advance along it's map...

We're starting to get confident in the readings we're seeing - we're going to try to pull some fuel out of the map to see if we can relax the injectors a bit at rpm...
 

·
Registered
Joined
·
1,895 Posts
Interesting to note on the log is the turbo's (or the UTEC's) inability to hold boost to redline.

What's also interesting (and perplexing) is that the injector duty cycle is past 98% even when the TPS is only reading in the upper 60's... :eek:
 

·
Registered
Joined
·
1,895 Posts
Here's a chart showing boost vs. injector duty cycle.

 

·
Premium Member
Joined
·
6,750 Posts
Discussion Starter · #9 ·
Wow that's crazy...what are the possible repercussions of this?
 

·
Registered
Joined
·
1,895 Posts
If everything I'm reading here is right (and remember - the jury is still out if the log is valid) then I think it's safe to say that the level of boost we're running on his stock turbo/stock fuel setup is too high for the safest "acceptable risk" category...

I'll keep you guys posted. I'm a little confused because of all the knowledgeable people that say that the stock turbo won't cause our cars to hit high IDC (90%+)... However from what our logs are telling us (and I hope that the sensors are miscalibrated, or the logs are off) the idc is WAY high.

I don't have any firsthand experience - but it's commonly accepted that you don't want fuel injector duty cycle over 90% on a regular basis...
 

·
Premium Member
Joined
·
6,750 Posts
Discussion Starter · #11 ·
Right, and it doesn't make any sense...there's tons of people running 15.5 psi for over a year now...wouldn't you think that running at that high of a duty cycle for a year would destroy the engine, or at least the injectors?
 

·
Registered
Joined
·
26 Posts
Stock turbo, injectors, up-pipe & UTEC here @ 15.5 psi dropping to ~12 psi at redline gives me a constant 98-99 injector duty cycle time above 5700 rpm. No knock, runs well.

Anyone know if it's really accurate?
 

·
Registered
Joined
·
1,629 Posts
OK, everyone laugh at me.

But here goes.

I have an FP turbo which is a hybrid of the anemic stock turbo.

I'm adding Sti injectors, Perrin fuel rails, and an S-AFC.

I don't trust the fuel system. Don't ask how much I have spent so far. But I dont want to fry my engine.

misterx

EDIT: Lately, the Prodrive ECU is learning the FP turbo.. Skinny Son says the car is getting stupidfast.

I agree. Especially in the top end.
 

·
Premium Member
Joined
·
6,750 Posts
Discussion Starter · #14 ·
Rick Hunter said:
Stock turbo, injectors, up-pipe & UTEC here @ 15.5 psi dropping to ~12 psi at redline gives me a constant 98-99 injector duty cycle time above 5700 rpm. No knock, runs well.

Anyone know if it's really accurate?
<! Thread Self-Hijack --

ROBOTECH RULES! :D

-->
 

·
Premium Member
Joined
·
6,750 Posts
Discussion Starter · #16 ·
MisterX said:
What's robotech?

Remember, I'm pretty old.

misterx
Robotech = anime from the late 70s early 80s that helped pioneer the "mecha" style of anime, whose main draw was young people piloting giant robots in the future. Good example is Gundam...
 

·
Moderator
Joined
·
895 Posts
Verdugo said:


Robotech = anime from the late 70s early 80s that helped pioneer the "mecha" style of anime, whose main draw was young people piloting giant robots in the future. Good example is Gundam...
*cough!* oooooookay, back on topic now ;)
 

·
Registered
Joined
·
103 Posts
I'm with MisterX here...

There are two things that all the engines that have lasted 30,000+ miles making over 400hp have in common: lots of fuel and relatively low boost (17psi or less). Does it make total sense? No, boost to some degree shouldn't matter (as God has pointed out numerous times) with proper tuning, and Cobb has been getting 250 whp out of their RT-spec kit without any fuel upgrades and doing so very reliably for quite some time. I don't know, all I can say is this:

I want a 100k mile motor, so even with a mild turbo upgrade (260-270 whp) I will be doing upgraded injectors, rails, and pump, and I won't push more than 17 psi peak. Conservative? Yes. Overkill? Certainly. Peace of mind? Yup, that too. Compared to a new motor, fuel upgrades and small sacrifices in boost are cheap insurance.
 

·
Registered
Joined
·
1,895 Posts
stilesg57 said:
...Compared to a new motor, fuel upgrades and small sacrifices in boost are cheap insurance.
Amen! :D
 

·
Registered
Joined
·
1,895 Posts
Rick Hunter said:
Stock turbo, injectors, up-pipe & UTEC here @ 15.5 psi dropping to ~12 psi at redline gives me a constant 98-99 injector duty cycle time above 5700 rpm. No knock, runs well.

Anyone know if it's really accurate?
Rick, what are you logging with? Your experience seems to closesly mimic my friend's UTEC logged scenario...
 
1 - 20 of 39 Posts
Top