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.

What is needed to stop the boost creep on an s4 turbo? I really can't afford a rtek 2.0 I'll probably be getting a stock ecu or a rtek 1.5 or 1.7

I may try finding an s5 turbo but I'll already have an s4 but I'll have to get it rebuilt or get one in good working condition, and I know s5 are harder to come by and more pricey.

Car will be running stock boost when I first get her going, but I do want to set it up so it can run higher boost later on without having to remove too much stuff (mainly the turbo: I'll port the waste gate if that will eliminate all my boost creep and allow me to maintain stock boost as well as bring it up without getting boost creep)

rotary>pistons

Restricting the intake/exhaust is a good way to prevent boost creep, besides porting the wastegate.

How do you go about doing that? I always thought reducing the restriction is what brings up the boost pressure so it'd be hard to reduce the restriction while still having some restriction on it. I thought all you needed was to port the wastegate

rotary>pistons

Porting the wastegate definitely helps, but doesn't always do the trick. A hi-flow cat helps as well, and keeps you legal as well. Anything to restrict flow.

Port the wastegate out to >1", weld a valve as the new 'flapper'. Plain washers will deteriorate and will end up looking like a snowflake.

It's easier to identify a component turbo/intercooler/injectors that you don't want to replace and do everthing needed to support that component. You can't do the bare minimum but be ready for more later.

I appreciate that you are doing things on a budget, but cutting the wrong corners is how rotaries get such a bad reputation outside this forum. And in the v8 section.

I'm only planning on running stock boost when its first running, I just figured it'd be a good idea to port my waste gate as well as have an idea of what else will need to be done in the future.

rotary>pistons

well first of all to run stock boost on an S4 turbo you literally need to keep the intake/exhaust stock. even a downpipe will have it hitting fuel cut on cold nights.

second on my car i had enough fuel so that boost spikes were fine, so i never did anything. everyone else tries to run the stock ecu/fuel system and port the wastegate so they can run less boost.

the S5 turbo controls boost way better

so you have choices

Well maybe I'll try to get an s5 turbo if its a direct bolt on, I just figured I'd use s4 since I already have one, I'll have to check the cars exhaust to see if its stock...I'd just rather use the s4 because it'll cost me less money.

From what I'm hearing there's really no reason to keep the s4 turbo if you have the oppurtunity to upgrade it (which I will since I'm rebuilding the engine)

rotary>pistons

s5 turbo is a direct bolt on, IF you have the s5 manifold as well. s5 turbo and s4 manifold do not match up.

tru but in all honesty i would personally run what u have and make sure that u keep the boost at a stock level until you have the resources to run what u want to run. i built my s4 conservative so that i can have fun but also have it as my daily driver. now if you already have a daily driver i would take the time to build it right so that way u can do what u want to do to it. just my 2 cents. my fc was a budget build some wheelin and dealin with the guys here on the forum. im pushin 14psi on rtek 2.1 550cc prim 820cc sec 3 inch exhaust stainless steel tubular mani. apexi avc-r boost cont garett t67. we guesstimate anywhere from 300 to 350ish also forgot aeromotive 340lph pump and a few other things.

Yea I want to keep it close to stock, I'm very paranoid so I always make sure about everything before I do it.

I'd bring it up 1 psi at a time, slowly bringing it up. I'm in no hurry but I do want to eventually get it close to 10 psi but that's a long term goal, short term would be 6.5-7.5 psi

rotary>pistons

its very possible to do that but from experience ur gonna want to boost her. they love it. also i run water injection aswell which i think helps alot with knock and so forth. u seem to have ur head on right and kno what u want. luckily this forum helps out a lot with questions anyone has.

isn't the comp. wheel the same on both turbos? They move the same air. Your only upgrading is the wastegate opening size. enlarging the S4doesn't sound that hard to do.

there are many write up on here on how to upgrade the opening to the wastegate. many have been successful with it.

Its really easy to port the wastegate on an s4 I did it inside an hour after I got the turbo apart.

One of the better ways to restrict boost creep I've found is to keep the stock airbox and intake piping. It won't eliminate it totally if you have a free flowing exhaust but it really helps.

You will need an FCD. I think I have one for an S4 somewhere.

What's the range of boost that can be run with a ported wastegate? At first I'm going to run it stock but I do want to run more boost eventually.

rotary>pistons

With a good boost controller you could run 10-12psi. I had a poor quality boost controller and it would not hold the boost up top all the time.

Okay, so I'll still be able to run the stock 5.5 psi though without it , and anything up to 12 psi with it ? I guess I'll just have to figure this all out when I get everything put together, I just want to be able to run stock until I do want to run more later, I do plan on porting the wastegate so it'll prevent it from overboosting, that's definitely not something i want to happen, one person said you can boost spike 6psi over, which scares me.

I wanted to bump this up with a related question.

Would a FD pump support a Rtek 1.8 (4x 720cc)?

Not if they're being maxed out. FD pump is rated for about 300hp. According to the Rotary Performance website's calculator, 4x 720's should be capable of 350.

720 secondaries is enough for a stock turbo at 12 psi.

Okay thanks.

Also I was thinking of a Bnr stage 1 at 10-12 pounds rather than the stock turbo.

Most im going to run 10 psi since I've read about intake temps with stock tmic get hotter than they should be at 12 psi.

I don't like the idea of hot intake temps, seems like a bad idea.

Rotary >Pistons

do you have a wideband a/f gauge? get that and a boost gauge as your first mods, then you will know whats going on in the engine

if the exhaust and or intake is not completely stock, then you will get boost creep, you definitely want to port the waste gate as big as u can, and if your exhaust is really free flowing you still may run into some creep.


I don't really see any point buying the rtek 1.5 if your going to run it at stock boost levels keep the stock ecu, that way if your boost does creep youll hit fuel cut and know to stop instead of keep going and risk running lean and blowing up. ( it can be argued hitting fuel cut in it self is pretty bad, but I think its a hey stop what your doing warning, vs wrapping it out on a cold day in 4th gear and blowing it up)

if you want to go over stock boost on a stock ported motor, and stock turbocharger at all id at least just get the 1.7, walbro, and the 720 injectors. it adds more headroom for if your boost does go somewhat higher than u planned.

also get all of your injectors cleaned/flow tested, and change your fuel filter.

one benefit to a s4 turbo, with a loud exhaust is If twin scroll is hooked up and working, with it closed below 2800 the exhaust is noticeably quieter.

The car doesn't have an s4 Turbo I'm upgrading to s5, car does have a full exhaust, stock intake/airbox, stock tmic, blitz bov, and I do have a fuel cut defender.

I will run stock 550cc primaries and 680cc 1st gen gsl-se secondaries (flow same as 720cc on 2nd gens from increased fuel pressure), fuel pump and ecu will be stock until I can afford to upgrade.

I do plan on porting the wastegate, do I have to take apart the turbo to do it?

I plan on getting a boost gauge for when I first get it running and possibly a manual boost controller (if peak boost is really low like 6 psi), I'll later get a wideband.

Rotary >Pistons