I was interested in learning about what boost levels can a stock S4 13B TII handle safely. This question is assuming that everything is properly tuned and there are not fuel restrictions and such. I would just like to know what the stock internals in this engine can handle safely. Also assuming the engine the engine has a stock port job as well. I assume this question has been answered before, but I would just like a straight answer just to be sure. Thanks

 

I would say 14 or 15 psi, depending on your set up.

You don't find very many stock fds now days, even something like aftermarket IC effects your psi somewhat

 

^That is a very misleading and general statement. Different turbo's at the same psi will flow very different amounts of air.

The big questions are what turbo? What injectors? and what intercooler? 'Safe' really depends on the individual setup. With bigger injectors, turbo, fuel pump, intercooler, ecu, excellent tune, etc, the block itself can usually handle about 350hp.

 

For mines, I try to keep my boost between 5 and 10psi for stock.
I'm playing it really safe.

 

The block itself and internals (Rotors, apex seals, ect.) Excluding things such as turbo's, intercoolers, fuel, ecu, ect. I don't know how to be any clearer, is it making sense what I'm asking? haha sorry

 

10psi is a good safety number.

On a bone stock engine it's really going to boil down to the condition of the car. Moreover the fuel system. If you have a weak fuel pump, bad fuel filter, or a gummed up injector it will lean out long before 10psi.

My personal opinion is that you need a good wideband setup before you start tweaking the boost. It will allow you to monitor the AFR as you increase boost to make sure your not going overboard. Again, personal opinion is the Innovate LC1 system. I'v run several of them and love em for the price. I'm also kinda partial to the TurboXS manual boost controllers. They have made a good combo for me several times.

 

if you actually read the thread owners question instead of my comment, you wouldve noticed he said a stock car. that means stock turbo, stock injectors, stock intercooler.

 

The stock turbo is well outside its efficiency range by about 12 psi. Pushing it further is pointless, and will lead to higher IATs and risk of detonation.

If you're talking about what the engine itself can take, there are few modifications made to the actual block on high-HP builds. IIRC, an S4 rear iron can be broken around the 450-500 whp range. Certain S5 rear irons have reinforced castings, and can handle more. Engines can also be strengthened with additional dowels.

 

thank you for clearing that up, what if you have an ECU and then other items that improve performance? is 12 psi a solid number no matter what

 

Ive ran 14psi and had no troubles

 

The OP specified "stock internals", which means stock rotors, eccentric shaft, and associated gears, seals, etc., inside the engine. The turbo, injectors, and intercooler are external.

Excellent question. No, 12 psi is not a solid number. See below for more...

A boost gauge is not a very good limit indicator. There are two main factors that limit the amount of boost pressure: 1) The point at which the engine fails mechanically, and 2) The point at which the engine detonates. Since the engine will most likely detonate before it bursts from pressure or strain, let's look at some of the factors that affect the detonation threshold:
- Fuel octane rating
- Intercooler efficiency
- Compressor efficiency
- Air pressure (yes, altitude affects this)
- Air temperature
- Air humidity
- Engine temperature (affected by radiator, oil cooler, thermostat, etc.)
- Engine load (driving up a hill, rapid acceleration, pulling a lot of weight, etc.)
- Compression ratio of the rotors
- Fuel/Air ratio
- Ignition timing

For example, if your engine has 9.7:1 rotors, no intercooler, and a crummy Mexican Ebay turbocharger, and you live in Death Valley, use 87 octane fuel, and attempted to tune the engine yourself, then the engine will detonate at a low boost level. However, if your engine has 8.5:1 rotors, an efficient front-mounted Spearco intercooler, an efficient Garrett GTR turbo, you live in Aspen Colorado, use 115 octane race fuel, and paid for professional tuning, then the engine will be able to run much more boost before it detonates. This is why you need to take it with a grain of salt when forum members chime in about how "My engine runs ten million psi boost with no problem".

Given that, see this below website for some good general guidance. It is a bit out of date, so check with this forum before you buy anything that may have been superseded by a better product. For example, the FCD has been made obsolete by the Rtek ECU upgrade.
http://fc3spro.com/TECH/FM2W/power.htm

 

If you're looking for a good example, my motor's on 70,000KM's and still has 95psi on all faces, and it's been run with 10psi of boost on stock turbo since birth. I just keep my fuel filter fresh, and have an upgraded fuel pump (Walbro 255). I run 94 octane for peace of mind as well.

 

what mods do you have on your car? how often do you check the compression

 

My setup is:

- S4 13B
- S5 Turbo
- S6 Rotors
- FCD
- Blitz Boost Controller @ 10psi
- Walbro 255 Fuel Pump
- Stock Injectors
It's a very basic setup, but it's holding up fine. As for compression, I've had the car 5 months and only checked it last month. I'll probably check it every 6 months.

 

^ Props for the proper use of an FCD!

 

whats your estimated hp?

 

lambof.god, your setup really is the bare minimum to safely run that boost level on the stock turbo. The walbro fuel pump drives up fuel pressure by overwhelming the stock FPR, which is keeping you from detonating in the mid-range. With a stock fuel pump and injectors, there is a lean spot just before the 3800 RPM secondary transition when they hit max D/C under higher boost.

The same setup with a stock fuel pump or even an FD pump would be a recipe for disaster due to lack of fuel and the negative effects FCDs have on fuel and timing calculations.

 

Umm, because I've yet to be on a dyno, and due to the fact that I have the full Racing Beat system, I'd assume around 220. I can't get proper numbers until I fix my clutch, but that'll happen this summer.

I understand this, but I also bought the car this way, and plan on changing some things. Once Rtek comes in, I can remove the FCD as well as my fuel pump switch, to remove some potential fail-points. Keep in mind that I also got the car from a very questionable PO that managed to mess up everything but the fuel system and the main engine components. I also have a Apex Recirc. BOV for what it's worth. To be honest, I figured of everything on the car that the fuel system was the best part.

To validate my statement about the PO; I recently found out that the fuel filter hadn't been changed for 4 years.. Shocking.

 

I've been wanting to swap out my walbro for an FD pump because it was overpowering my stock FPR and running rich on an Rtek 1.7. I know the switchover is lowered to 3500rpm, but has it been verified that the 10psi of boost at stock fuel pressure doesn't have the lean spot?

 

So, does the walbro pump take out the lean spot?

 

I have my minimum injector transition point set at 3300 RPM, but they'll typically transition at about 3500 RPM. The other requirement is positive manifold pressure. While tracking down a staging problem with my Rtek 2.1, I logged the primaries maxing out at 3700 RPM and 6psi in 5th gear. 3600-3800 RPM seems to be the trouble spot, so the 1.7 chips take care of it by going down to 3500 or 3600. I wouldn't be concerned with it if you scale back to an FD pump. I ran that setup for 6 months before going 2.1.

Here's the thread discussing it: https://www.rx7club.com/rtek-forum-168/secondary-staging-issue-844350/

Higher fuel pressure due to FPR overrun means a richer mixture across the board. It's a crude way to compensate. The worst of it is under vacuum, where I measured fuel pressure as much as 10 psi higher than stock.

When I measured fuel pressure with my FD pump, it ended up being almost exactly the same as the FSM specs for the TII pump.

 

Reviving this to ask a question after doing all my research and searching. What EXACTLY is considered safe on a stock turbo with a high milage engine? Lets say the 160k mi mark. The main thing at this point would be to keep it running as sound as possible. Lets take into this consideration:

-rebuilt hitachi using a 360 thrust bearing and ported wastegate
-stock fuel injectors
-stock ecu
-stock fuel pump
-stock everything for the most part

 

Thanks for the info RR88! Good stuff!

@ 160k, I'd consider a turbo engine to be on borrowed time. The safest way to run it is how it was designed. With all stock parts, running at stock boost using the wastegate spring.

 

Best short answer I've seen for such a complicated question as the OP had in a long time. The learning curve for engine management and function is super steep to a point and then it plateaus and you realize you only need to ask yourself these two basic questions.

 

anyone know how to stop the squeak noise on the rear of the 3rd gen rx7