I was driving around and of course I felt that urge to mess w/ the boost controller...so I did. I increased it 30% and it appeared to hold at about 9 psi. I took it down sum, and am now at 8 psi. I have stronger apex seals, so I'm not worried there, but I'm not familiar w/ the 8's fuel injectors. I've heard not to go past 10 lbs of boost unless you have bigger injectors installed. Is it ok to leave the boost controller set here and run 8 psi when I'm feeling naughty?? Or should I just kick it back to 5.5 lbs and have no worries? I've heard of other people on the forum running 8psi or more, but I'm not sure what their deal is w/ fuel pump, injectors and lines or whatever. The afr is still great though which makes me feel good to know the emanage is keeping the map in order.

 

It's never a good idea to start playing around with things that can make your engine blow, when its clear that you don't know what you're doing.

Boost doesn't kill 8's....bad tuners do.

 

If your afrs are fine i wouldnt worry about it. As long as you can get enough fuel to match the extra air flow you'll be ok.

I think the stock pump/injectors are good enough for around 12 lbs of boost, if your car is tuned correctly.

-hS

 

I think the main reason people get bigger injectors is so that it doesn't get too lean and get detonation, if you up the boost but the afr is still not lean enough to cause detonation, you'll be ok. Is that right BigOLundh?

 

Well, it's tuned pretty well. Like I said, my afr is between 10 and 12 under boost, rarely even hitting 12, so it's rich. Trust me, I wouldnt lean this thing out at all. Tuners 6 months ago did at their shop and that's what killed the engine then!! But, it's been rebuilt by much more qualified people, and my wideband gauge don't lie, it's rich .

 

I wouldn't turn the boost up past 8psi at higher revs without ignition control. You also should be monitoring your fuel injector duty cycles. You may be maintaining a good AFR, but you also may be running your injectors at 100% duty cycle, in which case you're on borrowed time.

 

Well, I can't monitor those right now, but I don't run it past 6000 rpm anyway, since the turbo drops boost after that, and b/c of the reasons u have mentioned.

 

Just so you know,3mm seals are not indestructible.

 

I can run 9psi safely and a spike up around 10 at low rpms doesnt worry me...

at 13psi you will be maxing your duty cycle

 

At the master mechanic school in KC, they had 13 PSI as the safe boost level for the Renesis.

 

am I missing something?

It's not good to think of fuel vs. boost, but fuel vs. CFM. Some of you are saying the engine is good for 'x'psi w/ stock injectors - but I'd argue that TWO psi a big enough turbo (read: CFM) could max out the injectors.

Am I jacked up in thinking this?

 

Acutally, the duty cycle would be maxed out well below 13psi. Depending on whether or not he's done my severed injector trick, he could be maxing out starting somewhere just below 8psi at 7000 RPM. But, the trick is that hardly anyone can hold that boost at that RPM with the Greddy turbo.

 

MadDog...seal all fixed and unit reinstalled? Back to 10psi?

 

You are absolutely correct.

There is no right answer to questions such as "how much boost?" or "how many psi?" because these questions in themselves lack the necessary information to answer them. You can not say that the injectors are maxed out after X psi. That is not correct and can totally vary based on the amount of flow that any particular turbo can provide at any set psi. A miniscule Greddy turbo at 10 psi may only be flowing what a T-04S can flow at 5 psi. This is also not taking efficiency into account. An a/f ratio vs boost is not a valid comparison. The only thing that matters is the amount of fuel vs the amount of air in the system. The pressure it is at is irrelevant. I have an air compressor in my garage right now that reads 120 psi because that's how much pressure is in the tank. It is at 0 flow right now. It's the flow that matters not the pressure. I could literally blow through a drinking straw and do more work than the compressor is doing at the moment.

The stock injectors can provide enough fuel to support ANY power level that the Greddy turbo could ever hit on an RX-8. Just raising the boost does more than just require more fuel. It also needs a different total timing advance. The added boost also produces more heat so the timing and fuel requirements need to take this into account as well. That small little turbo gets really hot really fast up there and you'll eventually come to a point where you can't give it enough fuel or pull timing out enough to make it work very well. It is safe to turn the boost up assuming the ecu program that it has can account for it. If there were extra map points above the stock boost level that were tuned to account for someone raising the boost pressure then you should be fine. If you already hit that boost level and didn't blow anything up then it probably did take this into account.

Another thing to consider is that with such a small turbo, the exhaust restriction is fairly large which means it is robbing the engine of more and more horsepower in the exhaust when at higher boost levels. What most people don't realize is that this can greatly affect how easily and engine will detonate! A larger turbo at the same a/f ratio with the same amount of total airflow into the engine (notice I didn't specify at what pressure) may not be as close to detonation at any time as the smaller setup is. With a turbo like the Greddy, you really start to push the safety of the engine when you go for higher power levels. It is safe to say that turbo kit was never intended to be pushed to the 300 hp level even though it can actually do it. Be careful.

 

...but the cfm at a given PSI will be close enough considering we're all using the same turbo with the same motor. 13psi may be safe with a t618z, but it's not with a t66.

also i (and i think most everyone else) is referring to peak boost, which as we all know doesn't hold with the greddy. X psi peak will begin to fall at X rpm every time.

..if you want, i can show you my injector duty cycle logs at a 9psi run...they're circa 85-90% at 11.5 afr. the guy in canada who got 313whp did it at 13psi, and the injectors were completely maxed, and he did so at a slightly leaner mixture.

 

All this talk is very interesting. Input from RotaryGod always makes me sit back and scratch my head, but in the way that I need to whenever I don't fully understand things . As for your splicing Maddog, I have not done so b/c I was scared to do it w/o bigger injectors and achieve the (76%?) or sumthing control that u have w/ larger injectors. I am running my car at the stock boost level now, at 5.5, but I was curious to know other people's input that had also taken the boost up temporarily as well. I know their is no real set "saftey" limit or standard, but having at least a reference point makes me feel a little more confident. Before I do anything too stupidly dangerous, I need to get this thing on a dyno b/c it has only been street tuned. Smooth as silk so far, but knock on wood it stays that way untill I can dyno it!

 

:D

See? The deal with me is, I know that I know a lot, but I don't always know WHY waht I know is 'correct'.

Thanks for the knowledge.

:D

 

Of course.

But since we ARE talking about a particular turbo, we are free to talk about specifics. He has the GReddy T618Z - with which we have much experience to answer his questions.

 

But did you not read the rest of the replies? Those who said things like "I thought so-and-so said x-psi was 'safe' on stock injectors?" I brought up the point because nobody had prior, that fuel vs. psi isn't the right way to talk about injector ability.

 

Believe me, I trust u and now that u have said it it makes perfect sense. But, since I can't monitor my duty cycles, and other people have this same turbo, If I know their duty cycles at "X psi", then I can have a ball park estimate, if not even better of what my injector duty cycles are. They should be working as hard or not as hard as everyone else's at the same psi, give or take a little.

 

that's what i was trying to say here...given the lack of variations in our turbo set ups, someone could say X psi is safe on the greddy with the emanage, and they would be alright. take everything you see on the internet with a grain of salt, particularly when it involves the longevity of your $30K sports car.

If someone was putting a different turbo on the car, then I could see why it'd be necessary to bring up the CFM x fuel topic..but then again if you have to ask that question, maybe you should reconsider using a custom turbo setup.

 

Yea man, I totally agree w/ u.

 

ok i'm not sure if this is right a stock rx8 motor with stock fule sys what's the max boost it can take??? also the greddy turbo what's the max boost it can put out????

 

I wouldn't bother going over 9 psi on greddy.

 

/\ yep 9 is good - feels very quick at that boost and IATs dont go too crazy so long as you dont try and hold 9 psi past about 6000 rpm
I went to blue injectors on the P2s but think you can get away with stock at this boost level