s4 turbo, how much power can it make efficiently?
 

Just curious as to how much power a s4 turbo 13b can make with the stock turbo efficiently.

I was under the impression it can do 10-12psi making 225-250whp.

What would be required to make this kind of boost, would all the exhaust need to be upgraded to bring the boost this high?

Obviously fuel system and other things will need to be upgraded.

I believe a bone stock turbo 2 can get away with 10psi without upgrading the fuel system, but it is pushing it a little hard.

A free flowing exhaust is an obvious upgrade, but don't forget to port the waste gate if you are using the s4 turbo. If not you will outflow the stock waste gate and boost creep and possibly damage your engine.

Yea I'm planning on doing all that before the engine will be installed, how low of boost is the lowest you can run with your wastegate ported?

When I first get it running I want it to be as close to stock as possible, especially if I dont have a fuel cut defender or rtek to prevent fuel cut from bringing up the boost.

I'm doing the same thing as you then!
Im about to stack my engine this week and I'm swapping it into my s4 GXl and want to be as close to stock besides reliability mods. Stock 5 pounds, and full exhaust.


Except I'm using a s5 turbo instead of the s4. But I'm still porting the waste gate.
I believe 5 pounds is the lowest boost you can run because the waste gate spring is a 5 pound spring.

Here's some write ups for porting your waste gate:


http://www.aaroncake.net/rx-7/s4wastegate.htm


http://fc3spro.com/TECH/HOWTO/ZWG/zwg.html

This is all future planning for me, I've got a blown s4 turbo engine and I'm planning on getting a 87 turbo rx7 that has a blown motor and needs a few things, it'll be my first turbo car so I'm wanting to give it a foundation capable of 10-12 psi potentially, but starting as close to stock as possible.

There's no sense in trying to push tons on boost on a car before its ready to, always best to make small steps , especially on a turbo rotary. So many people are desperate to make a lot of power, over boost their engine and boom.

My last rx7 (my profile pic) was an na, I did every mod I could to make it faster and lighter, in the end it just made it less streetable as well as idle worse, it was a lot of fun to drive but I learned a lot from owning that car, definitely learned na is slow and gets no power for your money and time compared to what i could have from a turbo (my s4 na was roughly 160-170+ hp at flywheel with streetport and full exhaust).

I ported my wastegate as big as I could (probably 38 to 40mm) and It ran 6-7psi with a TID and 3inch exhaust. With no boost controller.

I used a turbosmart manual boost controller and I could never get the boost to hold. I would set it to 12 psi, then it would drop back to 7ish in the top end.

just a correction. the stock flapper is a little over 20mm, so those figures are grossly exaggerated even if it was modified with a new flapper it is difficult to fit even a 30mm+ passage. 38-40mm, not even close with the stock internal gate. not as if the stock turbo needs a 40mm gate anyways.

I can't remember if I used an 1 1/4 inch drill bit or 1 1/2 drill bit. I made it as big as I could. I could be thinking of the size of the flapper too, it was a few years ago.

I would do 10 to 12 psi for daily.

I have a friend running a reliable S5 turbo/engine at 12lbs with ~240 wheel hp/250 tq. I would say the S4 wouldn't be too far off that. His car is very well tuned with a standalone which makes a big difference.

Link: s5 TII vert stock block/turbo 242.6whp and 250ftlb tq

I wouldn't recommend running 10psi without at least upgrading the secondary injectors a bit. 680 or 720...

Yea I'd be happy with 225+ @ 10-12si, I won't have a standalone, maybe an rtek if anything, but I'm planning on running stock boost with 10-12psi as my goal.

Stock: nothing over 9 psi. Period. Anything more will blow the engine. I've seen it twice firsthand.

The very first modification to run more boost should be a better fuel pump. An FD fuel pump work well. Walbros work, but have increased fuel pressure side effects.

The simplest "safe" means of running a stock turbo up to its limit of ~12 psi would be an rtek 1.7, 720cc secondaries and an FD fuel pump. This can be done for $3-400.

I was looking at rtek 1.5 for when I first get the car going, I don't think one will be easy to find though.

The cars missing the ecu and maf sensor , its an 87 turbo2. I also will need all the intake and probably the underbody tray, it does have an electric fan.

This will be way in the future, engine was running with blown coolant seals and needs to be rebuilt/replaced.

It would only be as hard as going to Digitaltuning.com and buying one. But why go with a 1.5? That gives you nothing to go with your "boost goals"?

1.7 is only $10 more than 1.5 as well.
I guess a "downside" would be that you have to have 720cc secondaries rather than being able to run the 550cc.

Yet he needs bigger secondaries anyway so it works out!

I'm going to be running the car on stock boost and injectors, why have bigger injectors and 1.7 if Im not planning on increasing the boost right away? This is a long term goal.

As long as you're aware. Enjoy the boost!!

Well I'm aware of course, I've just never had a turbo rx7 or turbo car for that matter, so I want to start out at stock and work my way up.

My last rx7 was na , I never had it "stock", streetported and rebuilt by rotary resurrection, I personally removed all the accessories, bac (bad idea),emissions, black charcoal canisters, ported my throttle body, did throttle body mod , removed my 5/6 ports rods and actuators, had a racing beat streetable header, straight pipe in place of cat, borla catback, corksport intake and cnced maf adapter, lightweight rb steel flywheel, center force dual friction clutch, front and rear strut bars, dtss eliminators, 5 lug conversion, and a Jacobs rotary master ignition.

All in all it was a fun car, but the car hated startup (removing bac valve I'm sure is why), and the car idle was very erratic, low end power wasnt very good(street driving: i never drove it with working 5/6 ports, car never ran until i had engine rebuilt),I also bypassed my heater core on my coolant hoses,(because of a leak on the ends of the heater core) so the car had no heat , which really sucked.

The conclusion to me was after all my time and effort, my car really wasn't the super fast car I wanted, but it was quick don't get me wrong, (160-175hp on s4 na), now I know from that experience I should of just bought a Turbo rx7.

I first bought a turbo off my best friend when he moved out of the country. I had no idea what I was doing, had never worked on a car for anything other than changing a belt... Looking back there was so much I did wrong, that the P.O. did wrong, that could have been easily avoided. My second rx7 was an NA and I really wish I had an NA first. I learned so much more on that car and it was so much more forgiving. I'd say be glad you got to learn these vehicles on a much more forgiving platform, now that you know a bit about them you can jump into a turbo with a little more confidence.

Just be careful, boost is like crack.

Yea that's why I want to keep it stock when its first running, reliability is my main concern, I'll slowly bring up the boost as I have the right supporting modifications.

From the looks of it 5.5-6 psi will be my starting (stock) boost, then bring it up to 7-8 psi once I get what I needs for that, slowly going up, too many people are hungry for huge power numbers and without the proper supporting mods and tune, it'll be a grenade waiting to go off.

rotary>pistons

I don't understand why you need to run your fuel system at 100% capacity which is what 10 psi would do. Never mind the stock timing map wasn't made to go that high since fuel cut is ~8 psi. Leave yourself some headroom in case the boost controller sticks a little, the air gets a little colder, dirty gas, wastegate line leak... Things happen. Better to be prepared.

Yes, buying parts is expensive. But buying them twice is much more so.

720 secondaries and rtek 1.7 will be good to efficiently run the stock turbo.

He could probably get away with an fcd, fd pump and a fpr to up the fuel pressure a bit (which will increase injection could he not?

there are a few ways to run 10psi on a T2....

i think the #1 thing is an FD fuel pump. if you do the maths, the stock T2 pump will only move 550ccx4 of fuel, its exactly the same size as the injectors, and that is if its in 100% perfect condition. so the best thing to do is upgrade to the FD pump which flows more. its also a great idea to replace both fuel filters, there is one in tank.

second on the list is making sure the car runs right in the first place. i've tried to do this other ways, but on a T2 its just easier to pull the intake and check everything, literally. vacuum leaks are bad, the vacuum hoses need to be hooked to the right place. i find the vacuum diagram isn't good enough, so i actually pull each end of a hose and make sure it is right. etc etc.

third you need some kind of exhaust, the precat should be replaced with a downpipe at least. i like the Rb turbo back system/revII, although in CA we buy two more flanges and put a cat in the middle, it will pass smog like this.

4th, i like the S5 turbo better than the S4, response is better, and boost creep is basically 1-2psi which is fine. i've found the S4 turbo can creep like 6-7psi, and this means you either need to have the car setup for it, or restrict it somehow.

5th, electronics. this is an important step, as you need to get rid of the overboost fuel cut, and then either add more duty cycle OR larger injectors. i have found that if you can increase the injector duty, with an FD fuel pump, there is enough fuel for 12psi with the stock injectors. if you cannot increase injector duty, then larger injectors are needed.

these days the Rtek 2.xx is probably the best way, you get the FCD, you can adjust fuel and timing, and there is no add on boxes, or wiring splices, plus you are tweaking the stock maps, instead of starting from scratch like a haltech

i always ran F-cons, they work great as long as you don't go nuts.