That wastegate actuator has an extra nipple for an external pressurized air source. Unless you want to run a Co2 bottle to keep the wastegate closed that is not for you.

 

When I setup the HKS actuator - I set it for about 8 psi on spring boost or there abouts - I also thought that if I wind the boost up by shortening it too much then I'd have less to play with on the electronic boost controller, and also less travel.

Setting it this way and setting the Hi and Lo boost up on the Profec B spec 2 gives you 3 different boost settings (off, Lo and Hi) which. I tend to only use Hi and off - switching the boost controller off if I suspect anything odd with the engine. It's easy enough to control the boost with the right foot for normal driving

 

I have been told on a dual port actuator you can run a pressure line to the bottom and top of the actuator. You put your boost controller on the bottom line and full boost pressure to the top. That way when your boost level is reached the boost controller starts bleeding air and the boost pressure in the top will overcome the spring and the lower port. Kinda like how an external works....

Yea I don't see the big advantage to having a threaded rod on the actuator apart from fine adjustment. Is there anything else that makes the HKS one a lot better than the standard one? And can you change the strength of spring in the HKS one? It just seems to be quite expensive, especially when I could just rip the flapper etc out and put an external on it...

 

The only reason I went for the HKS one was it was pretty much plug and play - swapped straight in.

It's spring is definitely stronger than the stock actuator - which was getting forced open by the exhaust gases before the boost I wanted. Using the same boost controller and solenoid, same hoses - the HKS one will hold 1 Bar all day long - the stock one could keep 12psi - it would hold 9 ok, but any more and it would just bleed off.

If you go for a dual port actuator - you can use a crossover 4 port solenoid - keeping it shut using boost pressure at the front until you reach your desired boost level, then firing the solenoid to switch the boost over to the other side of the diaphragm - the front side is then vented to atmosphere.

I'm still toying with the idea of that setup, but to be honest the 3 port solenoid and single port actuator work well enough.

 

Well..... I drew up the back of the turbo including wastegate flapper and the backplate in cad and designed a cutout to clear it. I then printed this and cut a profile out of cardboard to see how/if it would work. Below are some pics of it:







In this last pic you can see that it is at the max extension of the actuator. All the pics where taken with the actuator in this position.

In the first pic you can see that the flapper still doesn't open very wide. I dont think that the flow would be very good from out under the flapper into my wastegate tube.

So after all this I think that I may use that backplate shape I have drawn but pull the flapper out completely and port the crap out of the wastegate passages in the exhaust housing. Then I can run a nice big external much like BLUETII's setup at the bottom of this page
https://www.rx7club.com/showthread.p...light=external

What do you guys think about external size though? I have standard or near standard s4 engine exhaust ports and standard s5 exhaust manifold and turbo exhaust housing and wheel.

 

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/s5-stock-wastegate-j-spec-vs-spec-436262/

Scan through that thread. I think a divided pipe is not the way to go. Either do just a spacer like mine or do a bellmouth single pipe.

While some porting of the wastegate runners in the turbine housing may be beneficial since you have a hybrid, dont go crazy. The more material you take out the more likely you are to crack the housing.

My opinion is a stock S5 turbo or even like a BNR stage 2, the turbine housing runners are not the problem. It's the door and the way the gasses collide. Get the door to open further and make a larger volume where the wastegate and main exhaust gasses combine and you cure 95% of your boost creep.

 

Yea but with the spacer the gas still has to turn once it hits the backplate which creates a lot of turbulence. Having more space for the turbulence wont help much but the added flow into the turbine exhaust outlet would I guess.

And yea I thought about a bellmouth as well but the area to cover on the back of a S5 turbo is to big, I think that dividing them properly by using a block between the the turbine exhaust and wastegate passages the turbulence will be reduced as everything will be trying to move the same direction ie. down the pipe. Not sideways to get to the downpipe.

And lastly yes I agree with you comment about the door after seeing how much I can get it to open with the actuator. I don't think it will be enough to allow a smooth flow so this is why I think I am best to remove the flapper all together and add an external wastegate to the backplate like BLUE TII.

And have you seen any housings crack from overporting? If you have where did they crack etc? I am a little concerned about porting it and have been putting it off a little...

 

Bump... Anyone have a recommendation on external wastegate size? Leaning towards a Tial F46 at the moment.

 

35mm to 40mm area is good. be careful not to go to large...

 

Why do I have to be careful about going to large? What disadvantages are there? I thought the bigger they are the more they flow and the more chance they have to minimize boost creep that's why I was leaning towards a 46mm one.

 

This is i think 35.. and is a prime example of not being Big enough. if i was doing it again i would aim for 40-42. i get fuel cut at about 6200RPM in 2nd gear, and sooner in higher gears. My solution was to just use a FCD and when the waste gate sees about 9 psi it holds the flapper further open and is pretty good control.
Ive also used springs on the wastegate to help it open and was later able to hold 5 psi in 3rd gear til redline.
But i've already seen it creep to about 14 psi in 4th gear... pulling my motor out today, Cracked apex seal.

 

So then there is no such thing as too large? I mean as long as you have the right spring, how could it be?

 

Yea exactly I don't see any reason why it could be to big... I don't see a problem having a 46mm tial instead of my little internal

 

dont remember where i got this from. but i had it saved from a whiiiile back when i was researching wastegate sizing...

"Wouldn't the amount the gate has to open be a cruital factor as it will need to flow varying volumes to maintain a set boost level across a certain RPM range??


The wastegate responds to boost pressure. The more boost pressure on the diaphragm and it's spring, the further the valve opens. Ignoring early opening for a minute. If your target boost is 1.5 bar, when it the actual boost gets to 1.51 bar, the valve should open a little tiny bit. Now we all know that doesn't happen, the boost goes up so fast it flies past 1.5 and the valves opens vary fast. If the valve is too big, it lets too much exhaust gas bypass the turbine, boost drops fast and the valve closes. Then boost climbs rapidly again because the valve is closed. Valve opens and the cycle starts again.

With the correctly sized wastegate with the exactly same spring rate, the valve will open just as far but it is smaller and so will bypass less exhaust. Thus it may not completely shut again. If it is correctly sized it should not have bypassed way too much exhaust gas, maybe only a little too much. So the valve just moves a little more open and closed to control the boost. "


theres a formula you can use to size your WG correctly. but if your just building a car for fun, its probley not that big of a deal. if your trying to set records or compete at a higher level, WG size is actually very important...

 

Just like turbo and porting choices, bigger is not always better...

 

Nice info!

So...about that formula. I've got a book "Street Turbocharging" its got all kinds of formulas for turbo and IC sizing...perhaps theres some wastegage formulas too...

 

Wouldn't that be cured by running closed loop boost control? What that excerpt was basically saying is that a larger wastegate will 'overreact' to the spike in boost pressure and bleed to much exhuast off.

If your boost controller is set up to run an external wastegate I think it should be fine.