s4 turbo vs s5 turbo
 

Ok so i been reading around about the differences between the s4 and s5 turbo. It turns out my s4 13b had an s5 turbo on it, but it was blown and needed to be replaced. So today i picked up a s4 turbo that was professionally rebuilt for $175 It looks brand new! No shaft play!

So this is what i have noticed so far...

S4 Turbo: The intake housing and center housings are exactly the same as the s5. However the exhaust housing and wastegate are very different. The s4 Looks like it has a single wastegate with only one wastegate port in the exhaust inlet housing, but that wouldnt work right without an open exhaust manifold. Because there is only one wastegate port in the split exhaust housing therefor when the wastegate is open you would still be getting boost to the exhaust turbine. Im not quite sure how that would effect the turbo if you modified an s5 manifold to fit an s4 turbo... The wastegate has a smaller spring in it for 5.5psi i believe.

S5 Turbo: turbine, intake housing and center housings are the same as the s4. The exhaust housing, it seems to be quite bigger than the s4 On the wastegate part to be exact. The s5 turbo has dual wastegate ports inside the exhaust inlet housing. Also i believe there are two waste"gates". The manifold is more like a t4 manifold. 8-8.5psi stock wastegate.

This may not be accurate information, im just saying what i know so you can help me out. This is not learning information! or is it o.O?

So here is my theory... Yes the s5 turbo has more boost and it may be that it gets better airflow through the wastegate ports. And less lag for having individual exhaust manifold ports connected through the turbo. I can see how that would add faster boost build up but.... The s4 turbo when the wastegate is actuated im sure a big majority of the exhaust will go out the wastegate. But wouldnt having only one port in the exhaust housing keep the turbine spinning through the non ported side ? there for it would probably be the same as having the s5 turbo minus the wastegates.

So Can you change the wastegate springs from an s5 in a s4 and get the same performance? So same amount of boost build up speed? If not would it be worth it to swap my exhaust turbines as everything else in the turbo is the same? Along with my wastegate of course! Btw i have no catalytic converters 3" corksport downpipe to a 2.75" magnaflow muffler back to a fartcan.

Please correct me if im wrong about something and if my theory is just terrible.

The S5 turbo have a 5.5 psi spring in the wastegate, same as the 87-88. The S5 also have an electronic boost controller which raises the boost to 7.5-8psi. The controller is mounted on the driver side under the Intercooler. It's a small box with 2 vac lines and a wire connecter.

The s5 turbine housing and wastegate would be an improvement if you want to swap it. You will see no psi increase, you will see a possible drop in boost creep over the s4 wastegate though, as the s5 wategate is supposed to be better and it is for the most part. I will say you definitely want to port the wastegate on either turbo as they are lacking control once you open the exhaust up.

S5 turbo > S4 turbo. The wastegate actuators, compressor wheels, compressor housings and CHRAs are identical. The S5 turbine housing and manifold are better designs.

If your S5 turbo is blown, you can steal the turbine housing off of it, and then swap it onto the S4 you bought (as long as it is not an early S4). If you remove the housing and find a double heatshield on the S4 CHRA, it's early S4. In most cases, it's a direct swap. More info/pictures here: https://www.rx7club.com/2nd-generation-specific-1986-1992-17/how-rebuild-stock-ht-18-turbo-build-hybrid-959045/

How much quicker does an s5 turbo spool?

Great info thanks, i did notice the boost controller when i was pulling the engine for the rebuild. In order to change the boost on that would you have to program the ecu with a chip to change the boost? or get a manual boost controller? Can i swap the exhaust housings without having to re-balance the turbine? and is it even possible to do?

yes
yes
yes

and

yes

It's noticeable when accelerating from cruising rpm. If you keep the rev's up, you probably won't feel much of a difference.

Well my car is street ported on an s4 turbo with twin scroll delete and a fmic so she's pretty laggy. I start to build boost at around ~3200 rpm and see full (10 psi) at about 4500. I have a s5 manifold and t04 v trim hybrid that is gonna be my temp before I go aftermarket manifold + turbo. I'm interested to see her spool.

Some help
 

There is lots of turbo information regarding the differences and uses and potentials on This website. Owner of the website is Reted

http://www.fc3spro.com/main.html

http://www.fc3spro.com/TECH/MODS/TURBO/wgp.htm

http://www.fc3spro.com/TECH/TURBO/compmap.html

S5 Turbo Charger Swap
 

I'm planning on swapping out my stock S4 turbocharger for an S5 turbocharger and manifold. I already have an 1987-91 Racing Beat 2 1/2" downpipe installed.

Will an S5 turbocharger mount up to my current Racing Beat Downpipe?

Is there any differences when it comes to mounting an S4 and S5 turbochargers to aftermarket downpipes?

s4 and s5 turbo uses the same 3 bolt downpipe.same gasket..
The Manifold it sits on though is different,so when you get the turbo,get the manifold too.
An s5 turbo will not work on an s4 manifold,or vice versa.

;)

:pat: back at ya Barkz! (waits for Barkz to make a mistake now. then :pfanndina...heh,heh!)

:icon_tup: Great!

Now I can move forward. I was going to buy a rebuilt S4 unit, but after reading up on the benefits of an S5 turbocharger I decided to step up.

This is off topic, but how well does the stock s5 wastegate work with a full exhaust?

I don't feel comfortable porting my waste gate myself, at most I'd modify it so the flapper door opens more.

Rotary >Pistons

With my S5 setup, a good tune on both the ecu and ebc, I build boost around ~2000, and full boost by ~2800. i really enjoyed the response on the freeway in 5th.

It can still creep. Not as bad as the S4, but in 3rd-5th it'll be questionable.

I'll be running a fcd , gsl-se secondaries, stock primaries.

How high would it creep? I really dont want more than 9 psi on my setup.

Ideally I'd like the waste gate to hold it close to the stock boost level so I can increase it's peak with a boost controller.

I may have to pay someone to port the waste gate, I've never taken apart a Turbo and don't want to mess anything up.

Rotary >Pistons

pulling the snail off is rather easy, remove the 4 bolts that can be removed and use the remaining 2 to assist in pushing the snail off the CHRA evenly, against the oil feed and return castings (1/2 turn on each bolt at a time).

once apart also clean up the flange which sits inside the snail on both edges so it won't need to be cinched down with the bolts.

once the snail is off you can do whatever with it. sand blast it, powder coat it, grind it, whatever without worrying about metal getting inside the turbo.

How hard is it to put back together?

I just really don't want to mess with it and risk the chance of screwing something up.

I'll do a practice run on my old s4 turbo to get an idea of what I'm dealing with before I make my final decision on the s5.

I forgot to mention , I'll be be using the stock airbox. I hope that will aid in restricting the boost/boost creep.

Rotary >Pistons

BNR has an upgraded wastegate actutaor that's supposed to cure boost creep and drop.

bnrsupercars.com

Well I don't have a bnr turbo nor can I afford one so that doesn't help me

Rotary >Pistons

I was not suggesting you buy an BNR Turbocharger, I was informing you that they sell an upgrade wastegate acutator that remedies the problem you are having. I just figured that would help you with the issues you are having. I

f not Turbo Smart sells stock fitting wastegate acutators for boost spike and creep issues.

Didn't know that, thanks for the info.

No worries. You are welcome.