S5 Stock Wastegate (J-spec vs A-Spec)
 

I found a nice litte suprise tonight!!

This may be old news but take a look at the pics....

A while back I bought a S5 turbo from Japan, it is a brand new turbo (NOT a rebuild).

I finally got around to pulling the turbo from my 91 TII.

I found that the turbo I had shipped from Japan has a spacer plate between the turbine housing and the rear wastegate cover plate. The spacer is a 10mm thick piece of steel that allows the wastegate flapper to open MUCH more than the turbo of my USA market car.....
The exhaust studs and the two bolts for the cover plate are much longer too. ALSO the flapper door actuator arm on the turbine housing is not impeded by the turbine housing (as on the a-spec unit). It can fully actuate until the flapper door is limited by the cover plate. With all these differences the "j-spec" S5 turbo wastegate flapper can open MUCH more than the a-spec unit.

The two passages on the jap unit seem to be the same as the usa unit.

Now for an opinion: Lest I be flamed by the gooroos on this board let me preface this by saying I am a degreed mechanical engineer that specialized in both fluid flow and turbines. I also have over 10 years automotive experience.
I have always had a problem with the predominant opinions on this board about the S5 turbo. I believe that the stock s5 wastegate passages are of sufficient diameter to flow bypass enough to control boost on a stock port car with a stock turbine and compressor while running free flowing exhaust and intake. One post in particular sort of enforced my suspicion when someone milled out their backing plate to allow the flapper to open more. I feel that the only part of the turbo limiting wastegate performance is the limit of the flapper door by the compressor housing and backing plate design. I also have a problem with taking out material in the wastegate ports of the turbine housing. By simple math removing any material from the housings will reduce its robustness. Sure it may last for a very long time but a stock one will always resist damage better.

I think if someone were to come up with a kit that provided this spacer and the replacement studs and bolts. It would save people the hassle of all this porting nonsense. The end user would need to likely grind on the housing exterior enough to allow the actuator arm to move freely. This mod could likely be performed without pulling the turbo as opose to the porting methods most people try.

Some disclaimers: I have no idea if the actuator parts are any different. Or if any other part of the turbo is different. It is possible the A-spec turbo actuator cannot operate the arm to that extent None of it looks any different externally thus I would doubt it is any different. The spacer seems like Mazda’s way of addressing boost creep, from the factory, for j-spec cars.

I also have no idea if all S5 “j-spec” turbos have this feature over the USA turbos. It may be that I have an efini turbo or some odd part like that.

AGAIN before flaming this is strictly for the S5 turbo guy wanting to run a full race exhaust, and free flowing intake NOT a hybrid turbo of any kind. When you start to change the characteristics of the turbine or compressor my observations no longer apply.

I'll definetly follow up with my results as I plan to run full 3" RB race exhaust and a cone intake with a cold air box.

EDIT: in the first pic the turbo on the left is obviously the old unit out of my car.
Also the pink line on the backing plate for the new turbo is a line i drew while kicking around porting possibilites prior to pulling my turbo and finding the difference.

Where is Ted when you need him?
I am interested in this...

-Fanis

Interesting theory. As they say, ' the proof will be in the pudding". Keep us updated.

That's an interesting little mod. It's not a factory item (not Infini either), it's just a little custom work. J-spec and US-spec turbos are identical in every way. Your suggestion that Mazda might have this to combat boost creep would not be correct, as stock cars do not have any boost creep and no manufacturer would add bits like that to a car to make it easier to modify. That's the last thing they want you to do. ;)

It's actually very easy to do, as I did something very similar with my DP. I replaced the backplate with a custom flange for seperate turbine and wastegate pipes. The shape of the backplate was traced onto a piece of paper and given to an engineering company who machined a new flange complete with holes for the pipes and a matching copper gasket. A similar procedure would be used to make one of those, and new bolts or studs are easily sourced from an engineering supply shop.

As you mentioned, the amount the wastegate flap can swing open is limited by the wastegate actuator. Just because this spacer plate permits further movment, doesn't necessarily mean it can move much further than stock. The only was to know if this really makes that much difference (and if it makes porting unnecessary) is to try it. Let us know how it goes with your mods. :bigthumb:

Couldnt we just have someone with stock wg ports grind the crap out of their backplate and see if there is a difference? Seems like a much simpler thing to do than making that spacer and cheaper as well. I would have done it but I already ported the wg and the grinded the crap of my backplate about 1/8-1/4" on my hybrid.

If i didnt hate R&R of the turbo so much i might try it. But If this new one goes in and works with no boost creep I'm gonna leave it in, save any problems.

It is an interesting little mystery. The more I look at it the more it looks like an after market piece. It may have been a japanese tuner R&D piece of some kind. I am going to play with it some more and see if the acutator will allow the movement.

i doubt opening the flapper door much more than the stock position allows for much more flow anyways. the flow path is not hindered much by the flapper door or the 90 degree it has to go through the waste chamber but it is through the wastegate port itself, air does not much like to travel at sharp 90 degree angles such as that one...

larger porting and beveled wastegate ports help more than anything IMO.


here is another suggestion as well, set an air compressor regulator to 10PSI and apply the pressure to the wastegate actuator. now pump it up to 20psi and try again. let us know what you see. ;)

If you've seen how little the stock flapper can open with the turbo 100% stock you might think differently. (Though maybe you have). I feel it is by far the main restriction in the system.

I think I might try the compressor. Deal and see how it behaves. That's a good idea.

how a about getting copies of that template made and start selling them.
i would like 1.
also get the length of the studs if possible.

Looks like a quick low cost way of imporving the performance of the turbo, is the swing arm of the actuator longer than the stock US version? If so it should open and close the wastegate quicker.


Hey RockLobster I'm trying ot put together a resource site for rotaries. Project Rotary and the posting you made about the J-Spec turbo is great. Could you post it on my site? idealy as a article. Above is a link, any questions just email me. thanks

The length of the wg arms should be exactly the same between USDM and JDM. You wouldnt necessarily want the wg to open quicker... that would mean more lag. People with BNR's actually have to put more tension on the wg arm to get rid of the lag and be able to get more boost because of the enormous wg ports. I have to do this on my non BNR hybrid after porting my wg.

Huh?
It's an interesting piece - I wonder why Mazda didn't offer them for all their turbos! :P

Go ask Phoenix in CZ about his S5 turbo hybrid. :)
He's having trouble making 10psi! :D


-Ted

I really don't think gringing the back out of the plate could make that much difference if you have a real boost creep problem. The part of the backplate that the flap hits isn't all that thick, so you're only going to get an extra 3-4mm more swing out of it safely .

If I was making another DP (and I'm seriously thinking about upgrading my 2.5" one to 3") I wouldn't even use a backplate or seperate pipes like I have done. I would make a "big mouth" DP like this one, which eliminates the problam of the flap hitting anything, plus presents the lowest possible restriction to the gases leaving the wastegate. ;)

Like I said before, there is no difference between stock J-spec and US-spec turbos.

I at first thtought maybe it was a factory item on a late model JDM or non-usa FC of some kind where they might have used a freer flowing exhaust and/or intake to extract more power and raise boost levels. The steel seems to be very close in compesition visually but the give away is looking closer the turbo housing and backing plate are cast pieces with some machining. The spacer is a fully cut piece.

This makes for maybe an opportunity for someone to possibly offer these pieces for sale for owners maybe??? :D

I wish I were back in Sac where I can pull this shit off for a reasonable price.
In Hawaii, there is no way I can do this without costing up the ass - like $200+. :P


-Ted

I'm going to find a machining place in here in the twin cities and see what they might charge get the template made and try to find a sorce for the studs. The bolts are easy enough.

What does that do to exhaust pipe alignment?

Gonna change things that much?

so yea...before everybody goes and starts making these....somebody find out if it actually works.

If it does however work...I will be looking into it.

piping alignment is a good thought. gone be harder to install and remove a fully welded exhaust likew myself :(

Yes, please don't take this as any kind of solution until I try to install everything and test it for spike and reliability.

I would guess that 10mm or less would not have much effect on the alignment (well 10mm) of the exhaust. The hangers should pick up the difference no problem.

As far as a fully welded exhaust. Thats a tough one. I run racing beat stuff so it is very easy to remove and reinstall a particular component. Be it downpipe, presilencer, y-pipe, or mufflers.

I got the car running last night, I have not boosted at all yet as most everything under the hood was basically rebuilt mechanically save the short block itself.

I did find that this little spacer plate didd not affect the alignment or the installation of the exhaust. I am running a RB full turboback and there is plenty of clearance between the firewall heat shields and the downpipe. It is not putting any extra load/stress on any of the exhaust hangers either.

I don't know if the stock precat would present any problems as that is a bigger piece than a straight downpipe.

More notes to come, when i start boosting.

yes...give info....

I'm thinkin this would be a good mod in conjunction with a custom big-mouth DP like NZConvertible said....

If you did that you wouldn't need the spacer, because there'd be no back-plate for the flap to hit.

I beg to ask the question

"where did you get your turbo from in japan, and how much was it?"

Mazda in the states wants 2g's for it. It would be nice to find an alternative place, selling the same turbo brand new, for rebuilder enthusiasts, etc.

I got it from a 3rd party selling jap parts. RHD japan or something like that. It was an e-bay buy, but proved to be a great deal.

After playing with it for the better part of fall. in 50-70° F temps. I have a remaped ECU that is suposed to be good for up to 12.8 PSI.

I have been running it with the wastegate actuator getting full boost pressure all the time (bypassed with no controller).

WOT, above 4k rpm my AFRs are solid at mid 11s.

The car holds under 12psi. But it takes some time to get there (probably due to the bypassed boost controller).

No matter what gear, RPM, throttle pos, or speed i cannot get it to boost over 12psi in this config.

It seems that there is enough pressure difference flowing the wastegate to maintain 12psi on the stock wastegate with this spacer.

This result is not as good as i was hoping for. But perfect for me, being I want to only boost as much as stock, clean injectors can flow fuel for on my stock port engine. My only final concern is when i introduce the boost controller into the equation (to get the boost up faster) it might creap a bit more in 3rd and 4th gear. We will see.

Those that want to run less than 12psi will need to port the pasages and cannot just rely on a spacer.