that would be true only if fuel cut weren't working correctly, if it were still dripping/leaking some fuel in & combustion were happening...then there would be detonation.

But fuel CUT is not fuel "leak" or fuel "dribble". The fuel is CUT. ZERO fuel.
Air + fuel + fire = combustion
Air + fire - fuel = no combustion


and honestly, do you REALLY think Mazda spent thousands of dollars (maybe tens or hundreds of thousands?) engineering a safety measure that would be absolutely detrimental to the reliability of their engines, warranty costs, profits, reputation, etc?
That's like designing seatbelts that don't work if you're out of a certain weight range

 

...interesting arguement...but why do all modern cars go with ignition cut instead of fuel cut to limit boost or rpm's?

 

...sounds like Chris....guess he has a reason to do this...call Dave at www.Speedmachineperformance.com and ask him what he thinks and then call Chris back and say what Dave said..but be nice and be a pro about it...don't start **** between the two...both are great guys and have helped me a lot....wonder why RB dos not advocate porting the waste gate?? Aks him why and post here on the forum...we always need food for thought

 

Yes, if someone does find out more on this, I would like to hear

 

...automakers have been know to make many mistakes...recalls and so on...look at the SAFETY MODS for an FD-the stuff that gets replaced was all ENGENEERED by Mazda...your argument does not really hold...the original idea behing the fuel cut is so that the motor would last longer because we are forced to drive at lower boost levels....why do you think they came out with 6 psi and a 9-10psi limit? How long would a motor last if this were to go uncontrolled? Mazda would have been broke after the first year replacing all the motors under warranty...yes the FCD can be a bad thing...I ran all my turbos(S5's) at first with a RB full exhaust and a FCD with a HKS Air filter system and never blew anything....and I did not drive them for just for a month or two with these mods...the S4's are really bad with FCD and wide open exhaust because of the boost creep( i know that I replaced 3 motors in a black s4 before I could get him to listen to me-he removed the FMIC because he thought that was the problem-that was good for me because now I own a FMIC!!)...there I can see why no one would advocate the FCD WITHOUT more fuel
the S5 wastegate is better and boost creep with the RB exhaust and an aftermarket air filter have been minimal to 0 in my case but thtat can vary from car to car
RB exhaust, FCD, maybe an air filter kit on a S5 is safe with out an SAFC or other fuel mods for daily driving...this has been my case for every s5TII I have ever owned..but you will find other stories out there and it will be up to you (thread starter) what you will pick(mostly because folks throw in an aftermarket boost controller(with no fuel mods) and then the creep gets really bad and then POP)

 

Great link, RETed.

How about some S4 feedback? It sounds like all of the best advice applies only to S5 turbos.

Is it possible to install an S5 turbo in an S4 RX-7? I'm not real comfortable with porting things, I was hoping I could do this with just bolt-ons. How much can used stock turbos be had for and what kinds of costs are involved in rebuilding one? I don't mind all of the extra work, it would make a good learning experience, and if I do end up porting, I would like to have some practice on a spare.

 

"But fuel CUT is not fuel "leak" or fuel "dribble". The fuel is CUT. ZERO fuel.
Air + fuel + fire = combustion
Air + fire - fuel = no combustion"

you know, i woke up today thinking this same thing...honestly! it was weird. If you dream about what you have posted in rx7club.com then you know you have some issues. Anyways, yes this is a good arguement. I want know what everyone thinks =) As of right now, i think you are correct.

 

You haven't blown your car up hitting overboost fuel-cut.
I have.

Remember, overboost fuel-cut only cuts fuel to the REAR rotor only.
Factor in...

When you hit overboost fuel-cut, boost pressure drops.
When boost pressure drops, fuel-cut stops.
When fuel-cut stops, turbo starts making boost again.
Repeat step 1.

This causes a lean condition that blow the rear rotor.

I've killed a prefectly running 1987 Turbo II with only 61,000 miles on the OD, so you can't tell me the motor was tired.
Car was bone stock.
Exhaust was stock with the exception of punched out cats.

I hit the overboost fuel-cut twice within a 15 second period.
I felt a hesitation, so I had to boost it again just to confirm it was overboost fuel-cut.
On the second time, the rear rotor ate an apex seal.
Confirmed by lumpy idle, lower vacuum on boost gauge, and subsequent compression check - HIGH-LOW-LOW.

There is a REASON why FCD's are being sold.
It prevents ENGINE DAMAGE from hitting the overboost fuel-cut.


-Ted

 

Funny, I wrote all of that specifically for Zenki S4 primarily.


-Ted

 

nuff said about FCD'S

 

RETed..what do you say about the WG porting and why Chris @RB would say not to(if it was him-coudl have been someone else-poor guy-using his name and he does'nt even know it

..well I know what you say about it since you wrote this

http://fc3spro.com/TECH/HOWTO/KWG/kwg.html

but why would anyone say not to?

 

In my experience, it's not necessary.
That particular car that has that WG porting done to it is now having a very hard time MAKING boost.
With no stock boost control solenoid, it registers 2.5psi MAX.
With the A'PEXi AVC-R jacked up to 90% duty cycle (MAX), we could only muster 12psi of boost.
That particular turbo is a compressor upgrade with an H-trim wheel.
It's running a Haltech E6K and a ported motor done by me.
It's fricken fast for 12psi, but we were hoping to tune it up to 14psi max boost.

Exhaust is a 3" downpipe to 2.5" mid-pipe to 2.5" ID straight-through muffler.
The 2.5" rear exhaust pipe ID might be restricting it a little, but not down to the point of 2.5psi???
The owner is trying to get the whole exhaust build up to 3", so we'll see if the boost will come up a little.


-Ted

 

thanks for the reply..maybe I will wait to see what the rest of the COMING SOON mods will do as far as boost creep before I port the waste gate...I am willing to bet that most of the folks having major boost creep issues are using a too high boost level when seeting the boost in 3rd gear..or are using the wrong GAIN in models like the SBC series...they want to see 10psi with the stock turbo all the way to redline (in the 1st three gears)and crank up the boost to attain this level and then creep up to 18psi+ in 4th and 5th...

 

just wanted to clear up that I dont know what the guys name was, just in case someone gets mad at me.

I will call racingbeat at lunch today, and try to get to the bottom of this.

 

Oh, that second part wasn't directed at you. It seemed like most everyone else was telling me why porting the S5 wastegate wasnt needed and how much better it is, but weren't giving any solutions to people with an S4.

 

Ok I just got off the phone with JimTanner at racingbeat.
He said that if you are just going to add the exhaust you dont need to port the wastegate. If you start adding other stuff like intakes and things, then you have to start thinking about the fuel issues.

 

So does Racing Beat recomend just their FCD if you're just adding the exhuast?

 

they recommend the use of a FCD..theirs will do..you will HAVE to use it or you wil have fuel cut

 

sorry to hijack but just a quick question
what should be used to port the wastegate?
Normal bits and sanders dont work on the metal.

 

banzaitoyota used 1/4" carbide burr bits
I know they make bits for a dremmel that work on metal.

 

sorry to butt in on the conversation but im going to get a full 3" rb exhaust soon also (for a s4 tII) and wanted to know if a hks pfc fcon would be sufficient to not blow the motor considering i have a 3" hks intake setup with an hks fcd. I could buy injectors and a fuel pump with a safc but would rather not since i already have a fcon. any advice or comments would help. thanks and sorry again.

 

That's a bad way of thinking.

I'll apologize in advance for your dead engine.


-Ted