rynberg

I know exactly how a boost controller works. I also agree that a relief valve should be used when running a single turbo (I don't know if it's REALLY necessary with the twins..).

However, what I disagree with, is your statement that a relief valve is a good option to avoid boost creep. That's a poor bandaid instead of properly addressing the situation. Installing a restrictor plate in the exhaust is a much better option if one can't port the wastegate right away. With a restrictor plate, there is nothing to fail and it also prevents the turbos from spooling way too high. A relief valve can fail and also doesn't stop the turbos from spooling too fast. I don't consider it a reliable measure to eliminate boost creep.

FDNewbie

iTrader: (10)

DCrosby, i feel wut ur sayin, esp. w/ employin multiple saftey mechanisms

wut is the max relief provided by the stock wastegate?

and when ported, i take it u have to specify wut boost level u want the wastegate to handle, so it can be ported accordingly, correct?

wouldn't a drawback of that be that if u get it ported to handle a certain boost level, then later down the road ur boost levels change significantly...then wut? or is it simply that u get it ported to handle a large amount of boost, more than ud expect to need...?

and on that note....is there an advantage to porting the wastegate, vs. getting an upgraded wastegate, say the HKS ones?

also...from wut ive read/heard, aren't wastegates effective at controlling boost creep, but not boost spike, cuz it's instantaneous? and that's wut can cause u damage the fastest?

rynberg...is a restrictor plate basically somethin that restricts exhaust output, which would be in effect the same as replacin the MP w/ a high flow cat that's still high flow, but much more restricted than the MP to eliminate the boost creep/spike probability?

yy4u

Get a Profec B and be done with it, does a good job controlling boost, easy to install, easy to settup, etc.

The PFC does NOT do a very good job of controlling boost.

A relief valve after the turbo is simply a safety measure and was NEVER meant as a boost controller.

DCrosby

This is the Missnomer that I'm talking about for some starnge reason, the problem to everybody's boost problems is an AVC-R or Profec-B ...

DCrosby

I do agree that a restrictor plate is a viable option, but you've just negated the whole reason to get a MP... is to free up more natural HP... by letting the motor breathe... (out)

Porting the wastegate, here's the thing you can run 20+ PSI, on stock twins, maybe not for long but you can, on RACE gas mind you. The wastegate on the stock wins is part of the assembly, so this means porting.
As to adjustment, the ECU will adjust the wastegate based on the boost it sees on the map sensor, it's sort of a check and adjust kind of system the wastegate opens, once the desired PSI has been reached, and then it tries to maintain that pressure... allthough I don't know the intrecacies of the stock ecu, the aftermarket ones you usually, set the door to be open a certain amount, to get a certain amount of pressure, and then the ECU with the help of the MAP sensor tries to reach those values...

So when you port, you're more wooried about porting too much to make the manifold crack or break, due to thinning walls. All that will change is that the wastegate will no longer have to open say 95% to get 10 psi, it'll open 75% so it has more room to open wider to remove exhaust that will cause boost creep.

BTW spikes are more dangerous, since they come on suddenly and are hard to react to, creep you can see and let off the gas... it takes time to build....

when you go single you can make sure you have a large enough wastegate, or if it's a kit it will make sure that the boost that can be run on it will be supported by the wastegate.. so this really only applies to people doing one mod at a time, and can't afford to buy a whole single turbo system, which would need larger IC, Better Rad, Battery Relocation, Cold Air Intake, larger Injectors, DP, wastegate, Manifold, Turbo, ECU... a lot of $$$ what I'm trying to do is save the man some $$ so that he won't blow the engine, and still have some fun with his new setup while he saves for the other things on his list for the "Perfect Setup" we all want...

FDNewbie

iTrader: (10)

DCrosby...thanx 4 the concern =)

yea...i figured a restrictor plate would negate the whole point of the MP...

i actually dont plan on goin single... im one of those diehard fans of twins... like some BNRs...

so is boost spike as big a concern w/ twins (vs. goin single)?

my bad bout the 1001 ?s...newbies...wut can i say? =P

sub-zero

I did not pay much attention to the twin setup and went single right when My motor went. I am not sure if the HKS EVC will work with the twins, I think I read it works fine? Ramy PM Me and I have a like new one for 140.00 shipped if You think it will help. It controlled the boost on My car great. With the fuel You have You can run those twins at a good boost level if they can take it. Port that engine and start running some 11`s with Your setup.

I just checked the HKS instructions and it will work.

Steve

DCrosby

I know people have been having troubble with the AVC-R with the twins, and there were soem issues with the Profec a while back when they were using a fuzzy logic circuuit, the transition screwed up it's programming, so be carefull when you buy a boost controller, since the twins are a complicated setup, and most controllers assume you have 1 turbo or 2 Turbos on two intake manifolds. .. it's rare if not unique to have twin sequencial turbos...

FDNewbie

iTrader: (10)

<< it's rare if not unique to have twin sequencial turbos... >>

now u know why im so fond of it =)

is fuzzy logic a prob across the board, or just w/ the profec? cuz the HKS EVC has it too...

DCrosby

The way I understand "Fuzzy Logic" is it tries to learn what amount of input to the wastegate gives you the most consistant results etc... the issue comes in when the turbos transition, and it diverts some exhaust for prespool, this freaks the Fuzy Logic out, and since it's trying to learn your setup, it never gets used to it since it's not anticipating the dip in pressure.
But if you do a search on either unit, some people have posted experiences with controllers, and how well they work...

-DC

DamonB

That's all true but the relief or pop-off valve is meant to be used like the fuse in an electrical circuit. It saves your engine from seeing boost higher than the relief valve's setting, but in the meantime while the relief valve is open your turbos are spinning like mad trying to overcome what is essentially a boost leak in the system. A relief valve is a tool to prevent accidental overboost, it is NOT a means of controlling boost.

Since a relief valve never opens the wastegate the turbos are trying to fight the "leak" the relief valve creates. This results in wildly reving the turbos; not a good idea to do constantly.

rynberg

THANK YOU. Someone else sees the points I was bringing up.

DCrosby

I understand the point when you're talking about say a mechanical failure in teh wastegate or map sensor or whatever, but if the wastegate is open all the way, all you're doing is venting what excess pressure is causing you to creep, possibly getting past the point where the creep is occuring, breaking the cycle, and getting your boost back under controll. Since it is rare, yet occurs to not creep when you put a MP on some FD's... and without it you're still reving the turbo just as much, the difference is that you're seeing that pressure in the intake.

I guess I don't see the corralation that the tubos would change speed, due to the boost leak, since the ecu isn't trying to reach a higher boost than what the relief valve is set to, it's just that the wastegate isn't efficient enough to divert enough exhaust to maintain proper boost levels. The relief valve in fact helps keep the pressure in the combustion chamber eual, so as not to change an allready bad situation at the wastegate to worse by adding more flow....

And as soon as you break that cycle, the valve snaps shut... so I doubt on a street you'd see more than 1-5 seconds if that due to transitioning / shiting etc... of the valve's use / excess turbo spinning.
I'm not advocating doing this for a track vehicle, I'm saying it's a cheap safe alternative, to porting the wastegate in the short run, and that the point someone else made to use a Boost Controller is poinless with creep due to the mechanical limitations that are reached....

DamonB

That's exactly what happens.

Let's simplify all this and leave out the idea of a pop off valve and just say you have a boost leak in an intercooler hose for instance. Let's say the wastegate is set to open at 10psi. Let's say you get on the gas hard and begin building boost but due to a slit in your intercooler hose the system can't hold more than 6 psi (the turbos are making 10+ psi, but the system can't hold it due to the leak). Now the ecu knows there is only 6psi of pressure in the manifold so it holds the wastegate shut and tries to bring up the boost. The turbos continue to spool like mad because the wastegate is fully shut but they cannot overcome the leak in the intercooler hose and ever build enough boost to begin opening the wastegate. Therefore every time you accelerate the car hard you're are practically burning up the turbines because they are trying to pressurize the system to 10psi and yet never can, so they run at full bore the whole time your foot is in the gas. Not good for the turbines.

This is the exact scenario using a pop-off valve as a boost controller would provide everytime the pop off valve opens. Sure the valve slams shut after the boost bleeds off to the set level of the valve, but since you are still accelerating the boost will merely climb high enough again to pop the valve open once again. The pop-off valve CANNOT maintain a set level of boost, it will just keep see-sawing back and forth. Definitely not the traits you would like your system to have.

rynberg

And I'm saying that it's not, a cheap band-aid is not a good approach with this car.

Yes, that is true and not what I am arguing about.

FDNewbie

iTrader: (10)

Wow...you guys wouldn't believe how much I'm learning from all this...seriously

DamonB, I completely understand the scenario you described...but here would be my question

If my wastegate is set at say..10 psi (i have no idea what the stock wastegate is set at), my PFC is programmed for 12 psi, and i have a relief valvue set at 12 or 13 psi...because all I'm worried about is boost spike past 12 psi... in such a case, wouldn't the relief valve work well, since anytime I boosted over 10 psi my wastegate would be wide open, and the ECU would realize there is 10 (or more) psi of pressure in the manifold, and thus would stop the turbines from spinning to generate any more boost?

rynberg

You have some more learning to do...

In you scenario, how exactly would the ecu "stop the turbines from spinning"? The wastegate actuator naturally opens at 7 psi. Without any signal from the ecu or boost controller, this is what it will open at. With the PFC or a boost controller, you have a device managing the wastegate. Unless you exceed the flow of the wastegate, the ecu/controller does NOT keep the wastegate wide open but cycles it open and closed to maintain the desired boost pressure.

Unless you are exceeding the flow of the wastegate, there is no NEED for a relief valve, other than for safety reasons.

sub-zero

No, You want the PFC to control Your boost. You can either use the factory setup or get an boost control kit for the PFC or another boost contoller. You want the PFC to be able to control boost and if it does not, something with the solenoid setup or something else is wrong. The releif valve will cause You very unsatable driving if it is ulaways opening and closing.

DamonB

First let's make certain you know how the wastegate works. The engine exhaust is routed into the turbines, making them spin. Obviously the more exhaust going through the turbines the faster they will spin and therefore the faster they will drive the compressor wheels which will make more boost. The wastegate is basically a switch that is between the engine exhaust and the turbos. The switch will let exhaust flow into the turbines until they are at the speed to produce our set boost limit. Once that limit is reached the switch will bypass some of the exahust around the turbine, thus regulating turbine speed and hence boost. The more exhaust bypassing the turbine through the wastegate, the slower the turbine will spin. The wastegate is on the hot side of the turbo regulating exhaust gas volume through the turbines. A relief valve or BOV is on the cold side of the turbo, inline with the pressurized air.

The only way to actively control boost is by opening the wastegate. If the wastegate is already fully open, then the ecu is at the end of it's rope so to speak. Once the wastegate is fully open and boost still builds, there will be trouble. We call this "boost creep". What happen is exhaust flow is so great that the wastegate even when fully open cannot vent enough exhaust to slow the turbine speed, so boost continues to build and is effectively unregulated since the only means of controlling boost is the wastegate. The only way to solve boost creep is to make the wastegate larger so it can vent a greater volume of boost, or to restrict the exhaust somehow and therefore reduce the volume of exhaust gas making its way through the turbines, thus spinning them slower.

Now the relief valve will work in that it will prevent the engine from ever seeing more than the boost level you have the valve set it, but it has absolutely no interaction with the ecu or wastegate and so does absolutely nothing for turbine speed. No sense in making the turbines work hard if you're just going to waste their work. A wastegate is not wasteful, a relief valve is. The relief valve is meant to save your engine "when everything goes wrong", and it will do that. But it is not to be used as an actual boost control device because this will constantly overwork the turbines every time the relief valve is open. If you tried to use the relief valve as an actual boost controller it would also give you poor boost response because everytime the relief valve opens the boost will have to recharge the intake tract again, making response laggy at best.

yy4u

1) DamonB is probably one of the most informed individuals on this board, i've been around a while and read a lot. You can pretty much take what he writes as true. Rynberg is not far behind. Look at their post counts and how long they've been members

2) The Profec B does NOT use fuzzy logic, only the profec A does. The profec B is a cheap, simple, effective way to control boost and works perfectly well with a twin sequential system, assuming your wastegate is big enough - which i realize the stock one is not - thus the need to port the wastegate

3) There is a reason NO one on this board that i know of is using a pop off valve to control boost. Sure, use it as a safety measure if you want to, but not as a boost controller.

I'm done with this thread, good luck, FDNewb, you seem to have a genuine interest in learning and pick things up quickly. Just keep reading. THere is a lot of good info out there and lot of questionable stuff too, so make sure you get your's from a reputable source.

FDNewbie

iTrader: (10)

<< You have some more learning to do... >>

lol yea..i imagine you had a little chuckle on that one =) i definetly recognize that I have a LOT to learn, but unfortunately in my field of study, I hardly have any time to just sit and read up on my 7...(I'm already killin SO much time on this forum haha)

in the meantime, just please be patient with me, because im one of those guys who's not afraid to ask about somethin they're not sure of, even if it might make me look like im retarded =P

but really..i sincerely appreciate all your guys' help.

rynberg and DamonB, my understanding of the wastegate was actually right on with your explaination...

but see the reason I said the part about the ecu and the turbos spinning was because DamonB said

<< Now the ecu knows there is only 6psi of pressure in the manifold so it holds the wastegate shut and tries to bring up the boost. The turbos continue to spool like mad because the wastegate is fully shut but they cannot overcome the leak >>

so im thinking, okay, if the ECU will cause you to continue to spool if you aren't reaching your max boost, then if you ARE at max boost (as set by the ECU), wouldn't it stop the turbines from trying to create more boost? (i didnt mean STOP the turbines...rather i meant it would stop them from producing MORE boost)

If im still way off, lol...my bad. help me out with what I'm missing...

yy4u..thanks. im trying =)
would you happen to know if there's an Idiot's Guide to RX7s? lol I'm looking for a simple read that'll give a good overview of how everything works...rather than me trying to peice together threads from here and there...?

oh and DamonB and rynberg...WOW. 3000+ posts?! im speechless. =)

Herblenny

iTrader: (13)

Ramy, You started something..
I learned quite abit too.. No wonder when i put my silencers, I got rid of my boost spikes (i kind of knew it before)..

Well, I'm porting my wastegate for my new turbos..

DamonB

I guess someone could just as well make the argument that we have no life

Don't let post count mean anything to you. There are plenty of people who know what they're talking about who don't post much.

FDNewbie

iTrader: (10)

Phil...

I was just thinkin the same thing... here I am askin what I thought was a real simple yes/no newbie question, and I got a much better in-depth understanding of my car. Good stuff =)

And DamonB...I feel you. But I figure there's now way you'd last 3000+ posts if you were full of it... =P

btw was I correct regarding the ecu preventing the turbos from trying to create even more boost in my scenario?

and anyone got any ideas regardin the idiot's guide/good read bout FDs?

thanx

DamonB

Yes. As long as the system is functioning within its limits (no boost creep or large leaks) the ECU will slow (actually just maintain a constant) turbine speed by opening the wastegate. The higher the engine rpm the more the wastegate opens to maintain a constant turbine speed and not overboost the motor. That's why a stock FD has 10psi of boost at 4500 rpm as well as 6500 rpm. At 4500 the wastegate is closed or barely cracked open; at 6500 rpm the wastegate is more widely opened.