calculon

iTrader: (29)

Does anyone see anything wrong with doing this?

Have my 44mm TiAl wastegate on the exhaust manifold with a spring set to 25psi (just for discussion sake that is) which is the MAX boost i EVER want to run.

Then, on the charge pipes, likely near the compressor outlet, before the intercooler, have a larger, say 60mm TiAl with a very low spring, like 7psi, which is the minimum boost I'll want to run when boosting. Hook up my EBC to the 60mm to control everywhere in between.

Anything wrong with my idea that I'm failing to see? Anyone ever done something like this that's willing to offer some details. In looking for pop-off valves, I can't specifically find any, googling that is. And by my understanding, they're simply wastegates on the cold side. I don't see any reason this wouldn't work for crisp boost response and complete control of boost through a broad range.

thanks
ryan

RETed

The turbo will overspin and eat bearings.


-Ted

DelSlow

iTrader: (2)

calculon

iTrader: (29)

Are you saying that that problem will occur with my setup and not with an actual pop-off valve, or are you saying that that will happen with a pop-off valve as well?

Got any other solutions with the same end results but without the overspin?

Have you done this before Ted? Not trying to knock your credibility, just interested if you're speaking from experience or from EXPERIENCE.

Thanks though, I hadn't considered that downside.
ryan

calculon

iTrader: (29)

Is that your car Del? If so, please describe your experience with the setup, specificaly with regards to the results, and the possible downside Ted mentioned.

Thanks guys
ryan

NissanConvert

iTrader: (1)

I think FD_Newbie got an HKS pop-off valve for another forum member for like $150. Probably cheaper than your dual wg system.

I would set your intended boost at least a pound lower than the wg pop-off to avoid the wastegate & boost controller interfering with each other. I don't know how you would over spin the turbo so long as your real wg is working properly, but maybe Ted could help me out?

BLUE TII

iTrader: (9)

From what I understand you want to run two wastegates.

One at your normally desired max boost pressure (funtioning as normal wastegate) and one wastegate set at a higher boost so if the first wastegate fails, it will limit maximum boost.

The problem I see with this is the main cause of wastegates not opening I have experienced is that when they aren't often used they tend to weld/stick themselves shut over time.

This is of course much more likely with your second "safety" wastegate that will never open under normal circumstances.

The other wastegate failure modes are easy to eliminate.

To avoid diaphram failure use a high quality wastegate, put the WG "head" away from heat sources or even in airstream, or use a liquid cooled wastegate.

To avoid loss of pressure in hoses use hard lines and -AN fittings or braided hose and fittings and again be careful to route them away from heat sources.

I used the $100 Greddy pop off valve and more than payed for itself the first time I boosted and found major boost creep issues.

calculon

iTrader: (29)

Where'd you get your pop-off valve? How do you adjust the pressure at which they'll pop? Springs like wastegates?

Thanks
ryan

NissanConvert

iTrader: (1)

It looks like the twin chamber units function as BOV's and pop-off valves.

HKS

DelSlow

iTrader: (2)

No, but it is a car that was using a wastegate to regulate boost.

SPOautos

From your description it sounds like your asking if you can regulate your boost on the intake side instead of the exhaust side. Is that what you are trying to do? When you get to a desired boost level a 60mm Tial on the intake side opens up to bleed all of the excess air so that it will maintain at a specific pressure?

if that is what you are saying then Ted is right, you will over spool your turbo because it will always be trying to overcompensate for the "hole" in your intake system.

Typically a pop off valve is mechanical and when you reach a certain spring pressure it opens to vent off but you dont want to do that all the time and actually regulate boost that way. You just want to set it up so that in the event that you go way over your desired boost it saves you. That way it doesnt kill your turbo.

Actually not only will it kill your turbo but it will also kill your power and probably engine....a turbo overspooling generates massive heat. Enought to blow a engine. I had a blow off valve go bad once which caused my turbo to overspool and the ait's went from 20C to 60C instantly and I let off. To be honest for the stock fd temp gauge to jump that fast instantly it was most likly MUCH hotter than 60C. It blew my engine.

The picture above is most likely used as a standard pop off valve should be.

Stephen

calculon

iTrader: (29)

SPO, you got what I was trying to say, and I agree that that configuration would overspin the turbo, or at least spin it as hard as my motor could possibly make it spin.

So, what if I Teed the pressure signal from my EBC's control solenoid to both the hot and cold side wastegates so that they'd open at the same time, perhaps with some type of MBS before the hot side one additionally, so that it would tend to open just a second later, that way the cold side would open, and then very shortly after that, the hot side would open, reaching an equilibrium point where there would be no spiking?

I realize that this is not an easy thing to figure out "on paper" but with some tinkering, it seems like such a system could be developed and be effective. . .

Thanks for all the input guys
ryan

NissanConvert

iTrader: (1)

As i said before i would set the pop off valve (however you do it) to open *at least* 1psi higher than your boost controller set maximum boost. when your (hopefully) EBC sees that you've over boosted it will open your wastegate and lower boost past your pop off valve, past the safety 1psi and the pop off will close.

Example:

You want to run 15psi so you set up your EBC to run 15psi.

You set the pop-off (2nd wastegate in your case) to 16psi.

Set up like that there's no reason why your turbo, ebc and WG #1 will fight WG #2 because WG 2 won't even open until after the ebc has failed. once it regulates boost down to 16psi it closes.

The EBC *should* have the WG open 100% if you're over boosting so with the WG2 open venting boost pressure then closing at 16psi that only leaves 1psi (and WG1 has been open the whole time venting away from the turbine)

I don't see the fail point unless both WG1 and the "pop-off" WG2 were both set at the same pressure.

calculon

iTrader: (29)

What about this. . .

Let's call the hot side wastegate WGH and the cold side WGC.

have a substantial length of pipe coming off of WGC, with a bung in it near the opening to take pressure from. Have an EBC or MBC take that pressure and plumb it to the WGH which would be set to open at a pressure substantially lower than the WGC.

My reasoning is that if the WGC didn't vent DIRECTLY to atmosphere, but instead was forced through some length of pipe, the length of pipe near the WGC's valve would be at a pressure very near MAP. By setting the WGH to open at a pressure substantially lower than the desired MAP, it would open immediately after WGC opened, preventing the turbo from overspinning. As WGH closed, WGC would tend to reopen and cause WGH to open again. . .In this way, the turbo would be fluctuating between the desired boost output, and an output slightly higher, thereby saving the turbo's life, but also ENSURING that your motor never saw more boost than you wanted... additionally, your turbo would spool more quickly because it would be seeing 100% of the exhaust all the way up to (actually a little past) the desired boost level.

It's my understanding that the WGH tends to crack before the desired boost level is reached so that it slows down the boost level increase in the last ~couple psi of the desired setting. That is another reason why a setup like this would be desirable. . .the motor saving insurance that your intake would NEVER see spikes is the added benefit. Why this setup (assuming it would work of course) is preferred over a standard pop-off valve is that it would allow MUCH finer control of your boost level than is allowed with a pop-off valve, which is just a one setting type of device.

Thanks again for the input.
ryan

BLUE TII

iTrader: (9)

Hmm, you are crazier than I thought for sure :P

If you are simply looking for a very good boost control there is no substitute for a properly sized wastegate with properly run wastegate runners and a manual or electronic boost controller.

Problem is almost no one sizes wastegates large enough on rotaries and fewer properly route the waste gate runners off the main manifold runners to direct FLOW out the wastegate.

Once you have a proper wastegate set-up you can use a high quality manual boost controller like the Hallman Pro with its fast acting cermaic ball and play with bleed hole sizes while data logging to get it to peak without a spike.

Or you can get a cheap electronic boost controller and play with the gain settings to do the same.

Or get a fancy electronic one and let it learn to do the same.

Any way you do it you should only have a few tenths of a second response time and what does that really matter since 15psi at 3,500rpm isn't going to net much less HP than 16psi at 3,500rpm during those 10ths of a second...


For engine safety in case of catastrophic over boost-

Use a pop off valve
Map your fuel very rich above your desired boost (but DO NOT retard timiing excessively, it will cause more boost)

I forget where I got my Greddy Pop-off valve, 4 years ago when I bought it everyone was selling it.

It comes with a chart for how many turns (from initial adjuster screw contact) to give it for desired opening pressure- though it is in Japanese

It sounds like a fart fart noise when it cycles open and will cause erratic boost and power so you will know when it is working and back off.

Set it per the chart and several psi above desired boost levels. You can put grease or Hylomar on the piston where you can see it in the port, this way you will be able to see if it is creeping open in normal use as there will be a clean spot on the piston.

You do not want it to open under normal circumstances as it will shorten the turbo life though the erratic boosting and even possibly overspeeding the turbo.

calculon

iTrader: (29)

I agree with you Blue, I just was trying to avoid hacking up my manifold, but that is probably the wrong way to do things. I just need to bite the bullet and work it out.

Thanks everyone for the discussion.

If anyone knows where to get pop off valves other than the spot NissanConvert listed, more like the type Blue described above. . .I'd love to know.

thanks again
ryan

calculon

iTrader: (29)

Is yours like this one Blue?

http://www.autocarparts.com/part/320/4/

Busted7

I just found out some of the track racers run the wastegate in the ic pipe to do exactley what has been said. They use o2 to open the ic wastegate wich spins the turbo way up and on launch it closes and gives big boost. I would not say this is for street cars!!! A friend does this on his 2200.00 h/p Camaro.

SPOautos

Yea that isnt for a street car setup. They are actually overspooling the turbo to spin the crap out of it on purpose off the line, so just as they are starting to launch the WG snaps shut and it will build huge boost instantly. Like he said, this is definitly not for a street car, its very hard on the turbo and isnt used to control boost but rather to build boost.

BLUE TII

iTrader: (9)

Nope, that is the Greddy blow off valve I have :P.

The pop off valve is this one

http://www.turbowholesale.com/produc...productid=7135

Note: I don't know this vendor just the 1st one I found when I googled Greddy pop off valve...

I feel your pain of talking your car apart to fix the wastegate issues- I had an epic struggle with boost creep and went through five iterations of wastegate design to fix it...

EDIT: the picture, price, name and pressure relief range are correct in that ad, but the description is for the blow off valves... bad site!

BLUE TII

iTrader: (9)

Correct descriptions-

http://www.racingworks.com/greddy_relief.htm
http://www.2kracing.com/product_info...oducts_id/2887
http://www.mimousa.com/home.asp?dir=products&prod=2122

again, don't know the sites, just first Google results.

The thread on it is same as 1" conduit (1" pipe thread). I used an aluminum conduit nipple to weld it onto my compressor outlet pipe.

You can see it just behind the strut tower in this pic
https://www.rx7club.com/attachment.p...3&d=1160386579

Zero R

iTrader: (1)

You wont overspin the turbo if setup properly and if it is a larger frame turbo. A simple way to not overspin the turbine is to run both a WG and a POV, This will also allow you to not have a need to run a grapefruit for a WG. Setup properly you can get a much larger turbo work like a much smaller one, and the engine will breath a lot better as a whole because of it.

-S-

calculon

iTrader: (29)

Thank you Blue TII for the sites. . . much appreciation
ryan

calculon

iTrader: (29)

Blue, do you happen to have the chart you decribed? I got my hands on the Greddy POV, but my instructions were nothing but a bunch of Japanese text. Nothing I could make heads or tails of.

How do you set it? Do you know if the boost it opens at is linear in terms of the number of rotations?

In other words, if I tighten it all the way down, I assume that is the maximum boost it will hold (2.2kg/cm2 i believe) and if I then loosen it all the way (Counting the number of turns required to do so) I will be at the minimum boost it will open at (0.8kg/cm2 I believe). Will half the total number of turns required to go from all the way tight to all the way loose then set the boost level at which it cracks open at 1/2 way (~1.5kg/cm2)?

Any elucidation would be greatly appreciated. Thanks
ryan

BLUE TII

iTrader: (9)

I will look for the Greddy POV instructions so I can translate the little chart for you, I don't remember if it is linear.

It is pretty straight forward once you know what you are looking at though. One one column you have Kg/cm2 and the other column has number of turns of the adjuster screw.

Remember to start counting from when the adjuster screw comes in contact with the spring (you will feel it go from no resistance to some).

Now, actual opening pressure will vary some due to pressure difference between where POV is and your MAP sensor, etc. That is why I suggest you put some hylomar on the exposed portion of the piston at the exhaust port to make sure it is not opening under normal use.