I want to make some more power in my newly bought TII, first turbo car I've owned and the 6th rx7 I've had.

The car has under 70k Miles, runs great and has great compression, I am wanting to add some power but keep myself from blowing the engine.

Anywhere around 300+/-20HP I would be more than happy. I seem to be overboosting as per my prosport gauge it hits about 12psi. The car is bone stock but I have a nice downpipe going in and am in the middle of building a hybrid turbo as well.

The car is driven 2 or 3 times a month and to special events.

I have searched but most threads seem to be old.

 

A hybrid turbo will get you easily to 300rwhp, but you need a fuel cut defender and some sort of aftermarket ecu, either something chipped, or get a actual stand alone ecu. This needs to be done asap, just a downpipe alone can go over what is acceptable to the stock computer, and it will lean your fuel out on overboost and can very easily kill your engine. I am also thinking you will be needing bigger fuel injectors/pump soon if you plan on boosting much more.

 

Thanks for your reply. I plan on keeping the boost reasonable, as of now my boost peaks at ~12psi according to my prosport gauge. When it overboosts every once in a while it will go in limp mode.

Now that being said am at 5400ft above sea level. I could probably go a bit higher boost safely.

Now, what about using water injection on a fairly stock hybrid?

 

Something about your boost guage sounds off. If your car is stock you should be hitting boost cut near ~9psi. What I would reccomend before upping the boost would be to buy an upgraded fuel pump (walbro 255 would be plenty sufficient), upgrade your secondary injectors (720cc should do the trick, 1000cc would provide a little room to grow) and a fuel pressure regulator. That should take car of the fuel. Exhaust wise sounds like you have a downpipe, just finish off the rest with the aftermarket exhaust of your choice. Now you just need some sort of tuning capable ecu (for the money and the power level a 2.1 rtek would work just fine). Slap on your hybrid, make sure you have a wideband and boost controller and do a little tuning and you should be able to reach your goals fairly easily.

 

lower iat's are never a bad idea on any engine, water injection really has no downside to it. It is a cheap way to make your engine a little more reliable as well as more consistent power, At 12 psi it most likely is not a necessity, but it can keep the engine in prime temperatures longer.

That limp mode is the ecu trying to stop the overboost on the engine, Your downpipe is most likely the cause of this, and this is leaning out the engine, get some sort of fuel controller asap(rtek or stand alone) If you are staying at lower power levels the rtek will be sufficient, and if you go with the rtek you will need a fuel cut defender, If left alone this can and will eventually break your engine prematurely. If the hybrid you have does not have a ported waste gate get this done, hybrids even with a ported WG will drop boost at high rpms due to the inefficient exhaust layout on the stock housing.

 

Since you are in CO, you know that we have lower atmospheric pressure. at 6,000 ft or so (I am in colorado springs) the atmospheric pressure is 11.7 PSI.

Now someone mentioned above that stock is 9PSI and you are boosting 12PSI or so.

Your boost is controlled by a wastegate spring/actuator, this spring/actuator has the same pressure activation point at sea level or at our atmosphere.

So when looking at "total pressure" (Boost + Atmosphere) we can do some math.

Sea level
14.7 + 9 = 23.7 PSI absolute pressure

higher elevation
11.7 + 12 = 23.7 PSI absolute pressure

hey look, they match. You should be boosting 12 PSI because that is what the wastegate is controlling on an absolute pressure criteria. Everything is working just like it should be.

 

Ah yeah that's my fault for failing to notice the location of the OP.

 

It appeared to me that 12psi seemed somewhat high for a stock S5, but looking at the bottom post it seems appropriate for the altitude.

You're suggesting doing the fuel mods before I think on going hybrid? That actually seems like the safest approach. I was actually thinking of doing the hybrid and the down pipe before anything else, but that was my Go fast first, be safe later mentality in full effect.

I truly appreciate your reply, it seems most people wont bother with a somewhat standard question.




The engine and car are completely stock, this gem has under 70,000 original miles, which is the reason the boost spikes and the limp are killing me, although rare.

That being said my plans are to safely add the hybrid and the downpipe since it is what I have in had alongside another TII swap.
Now, on the water injection setup I am wanting to go with a boost sensing activated switch to control the output of meth/water and maybe even water sprayers to wet and cool the intercooler.

Regarding, Rtek I just passed emissions and am god for two more years so it's a feasible option, but I am highly concerned of about the fuel cut defender, since the ECU will not be able to see the increase in PSI to adjust fuel and run lean.

That's good to know it was concerning that I was over boosting, I do know that the cars PO did adjust the gauge to our altitude.


You guys are truly great help, no flaming haha. This is my first turbo car and my 6th rx7. I am vastly familiar with our N/A counterparts but Turbo=Voodoo to me.

 

Yeah I'd do the fuel first because with a stock fuel pump and injectors you will actually meet your fuel limits before you even max out the stock turbo. Throwing on a bigger turbo is just asking for it.

 

The fuel cut defender stops your ecu from leaning the engine on higher boost levels, this will work together with the rtek to allow your tune to work correctly.

 

Doesn't the fuel cut completely stop fuel delivery to the rear rotor?
And if circumvented the ecu would't see the rise in psi and lean out?

 

the defender sends at max a 9 psi signal to the ecu so it does not shut off fuel, but since the rtek will be controlling your fuel, as long as it is tuned you will have no hiccups. It is a band aid IMO but better then nothing, the real solution is a stand alone.

 

The stock ecu cuts fuel to the rear rotor when you hit fuel cut. With a fuel cut defender, the ecu is tricked into thinking you are at a safe level of boost and allows boost beyond its programmed limit. The danger in this is that the ecu does not add more fuel beyond the fuel cut level (the car is getting the same amount of fuel at 9psi as it now will at 13), meaning you will run lean and blow up without proper tuning. The rtek ecu has a built in fuel cut defender. As I mentioned before it would be the ecu I would suggest given your power goals for the money.