Suppose I was fed up with the boost drop off...
 

Right now I have to spike to 12 psi for it to settle to hold 10 psi above 5.5k rpm. Greddy 15G, stock wastegate, ebay ball and spring MBC. Basically this is an issue of too weak of a wastegate right?
Let's say I want quick spool up and then for it to hit a set psi and hold it strong. What's the surefire way to do it? Don't tell me to use EBC with MS - I've already ruled that out as it's far too finicky.

I've heard amazing reviews about the Greddy Profec-B (not type II).

I've also heard of HKS and similar brand wastegate which are supposed to be stronger..

New ideas? One of the ones above?

-Ryan

EDIT: SOLUTION AND RESULTS ON PAGE 2

You are using the fitting on the side of the compressor to feed into your MBC, right? Nix that. Cap the fitting, drill a hole into the cold-side charge pipe (between the intercooler outlet and the throttle body) and install a 1/8" NPT to hose-barb adapter (available from your local ACE hardware store in the plumbing section). Use that to feed your MBC.

The problem is that intercoolers are inherently restrictive. Yes, even ones the size of a Peterbilt truck's front grille. Thus, for any given airflow, the pressure after the intercooler will be lower than the pressure before it. Now, a fundamental tenet of fluid dynamics is that pressure drop across a restriction increases with flow. Assuming a constant load, flow (volume of air per second) increases linearly with RPM. If the engine is passing 100 CFM at 3,000 RPM, then it'll be passing 200 CFM at 6,000 RPM. (made-up numbers.) So, the pressure drop across the intercooler will be roughly double from 3,000 RPM to 6,000 RPM.

(Physics majors, please ignore the fact that I'm pretending all these relationships are precisely linear. It's easier this way.)

So the problem is that since you are feeding your MBC pre-intercooler, it's probably doing a nice job of regulating the pre-IC pressure to a steady state. But since the drop across the IC increases with RPM, MAP decreases with RPM. Move the fitting to a position after the intercooler, and then the MBC will be regulating pressure after the intercooler.

I've heard that if you drill a tiny hole in the MBC that it will help smooth out spikes, is this true?

Excellent info and thanks Joe. Just one question arises about the suggested change: I've read that it is crucial to keep the vac line to the MBC and from the MBC to wastegate as short as possible to increase response. Obviously a line from my coldside to the wastegate instead of running off the compressor is going to be 5x-6x longer than it currently is. Is this an issue?
-Ryan

I've not heard that one before.

The reasoning behind it is understandable, though fallacious. The volume of air inside a length of 3/16" vacuum hose is relatively minuscule- approximately 0.33 square inches per foot. This is going to have next to no effect on the operation of the boost controller or the wastegate canister.

From a practical standpoint, I went down this path myself. Initially, I used the stock compressor nipple on my turbo to feed my MBC, and spent a lot of time troubleshooting boost drop-off. First, I went through a series of "helper springs" on the wastegate arm, but all these did was raise my base pressure. Next, I thought my cheap hardware-store MBC was at fault, so I bought an expensive TurboXS unit and had exactly the same result. (Incidentally, this is the one with both the ball-and-spring as well as the variable bleed- functionally equivalent to drilling a hole into a cheap MBC.) Then I replaced the wastegate canister that came with the Greddy turbo with a big one from Garrett. Nothing helped.

Finally, Abe suggested that I relocate the MBC pickup to a port after the intercooler, and that's when a light went off in my head. Duh! My dropoff was caused by the pressure drop across the intercooler! Moved the line, and problem solved.

As to line length, you should see my setup. The vacuum hose goes from the coldside up pipe, along the radiator, down to a brass "T" fitting mounted behind the headlight, up to the MBC which is mounted on the valve cover, back down to another "T" fitting, and back up to the wastegate canister. (The "T" fittings are mounted to either side of an air solenoid, which disables the MBC as a failsafe if my water injection doesn't come on.) Total line length is probably close to 10 feet.

Excellent info. I'll give this a shot and post results as soon as I do.

Got a pic? ;)

Since we are talking vacuum/boost sources.

Getting the wastegate signal from the vacuum booster supply line should be safe too? I was going to install BEGi's 3 port vacuum splice at the booster, and run my wastegate, boost gauge, and MAP sensor off it.

I have heard that certain death may result from sourcing your wastegate signal from a throttled location (ie brake booster line or manifold) because then the turbo is free to create as much boost as it possibly can when the throttle is only partially open creating a potentially dangerous situation.

No.

If you do this, the wastegate will be closed damn near all the time. When you're at part throttle, just tooling along at 3 or 4 PSI up a hill, the wastegate will be closed and the turbo will be spinning like mad, putting as much pressure into the intake piping as it possible can, trying desperately to get to a limit it'll never reach, and making gobs of heat in the process.

With the reference taken before the throttle plate, the turbo will never make any more than the set pressure in the pipes. (Minus loss across the intercooler.)

Here's the best one I can find at the moment.

The hose coming off the top of the throttle body goes to the BOV, which is just to the left of the circular saw blade on the crank pulley. (You can't really see it.)

The hose stretched across the top of the radiator fans goes down to a brass nipple installed in the side of the coldside pipe. The nipple itself is hidden behind the upper radiator hose in this pic.

The pneumatic solenoid with the brass T fittings on it is mostly obscured behind the power steering fluid bottle. If you look hard, you can see the big brass Tees on either side.

The hose goes from the radiator fan, loops around the long way, and goes into the brass tee on the right. The fat blue goes go to and from the MBC (bolted to the front of the valve cover) and then the skinny blue hose on the left tee goes to the wastegate can.

http://img33.picoodle.com/img/img33/...em_6418bd8.jpg


Also, since we're in a picturey mood, here is a tray of sliced pork uteruses:

http://img19.picoodle.com/img/img19/...3m_1940776.jpg

Joe, are you on the garrett wastegate or did you go back to the Greddy one? I have always read about the Greddy one being crappy, is this also the case, or could I just relocate the nipple to after the intercooler, run a MBC and get 14-15psi with the Greddy wastegate? Or would I need to upgrade to a better one/use a helper spring? (yes...I have bigger injectors, fuel pump, MS, etc. I am focusing on the wastegate)

um joe i have run with my shit hooked to a manifold vac line for a long time with no issues man the manifold boost is overall your most reliable source. And the vacuum from time to time will not hurt the diagphram either.

That doesn't mean it's ideal, does it?

Why wouldnt be ideal? It is the endall be all pressure pre combustion chamber barring leaks whats your problem? The further i had my mbc from the boost source the more reliable of a pressure i could maintain up top, or idle once i went with a vented unit.

I don't have a problem man, chill, it's just a discussion.

I'm just saying, Joe has laid out an argument against sourcing boost signal from the IM, and all you've said is that you run it that way. That doesn't make it right in and of itself, so I'd be interested to hear more specifics from you about this.

Lol no worrys koto u know i respect u and joe. Ok i will do an indepth analzyes and get it to you guys.

Ok joe i take particular exception to this the turbo wastegate is always closed until u reach a boost lvl capable of moving the diaphram and opening it. So no matter where u source ur WG line from it will stay closed at 3-4 psi until ur desired psi even at part throttle. The reason we run ebc and mbc etc is to make sure this happens at a pressure higher than WG and or that we can garner a better spool from what our wg gives us becouse sometimes the valve will flutter everso slightly on the way up to maximum boost and this will cause an inconsistant climb in boost and with it tourque and hp. Also u know as well as i do turbos are laod driven. They make boost determined via the restriction of the intake tract and the output of the exhaust, the more laod your motor is under the more exhaust gasses it will expell thus making the turbo spool. By sourcing from the intake vaccuum sources u eliminate the gues work on pressure loss from all the stuff u stick between your compressor and your motor. This rather large chamber of final waiting for our intake tract is the ideal place to take readings on what goes in our motor.
One could also argue that since it is post the cooling process either IC or WI etc the density of the intake charge and its pressure would also bemore reliably measured in the intake manifold. As anyone familiar with the ideal gas laws knows volume is variant given pressure and relative temperature since we have a fixed volume then our pressure and temp work inversly and quite readily in the way that the lower the temperature the more density and relative pressure. Where as when we measure at the outlet of the compressor and the air is at its thinest and hottest our pressure readings will be much lower than that of the cooled charge. Assuming the compressor has the capacity to fill the entire intake tract at a rate to keep the pressure and heat up. If your turbo was going out of its effeciency range then your compressor wheel spinning at maxx rpm would simply be recompressing the same air results in less movement and intake velocity overall and the same or less pressure than when u where in your effeciency range. This ultimatly generates exponentialy more heat than flow and even when cooled u are facing a loosing equation in terms of performance.
I hope that wasnt to horrib man i havent done it like this in a while.
If some of the sciency stuff went over your head the wiki can help u understand it abit better http://en.wikipedia.org/wiki/Ideal_gas sadly im not as good as my highschool chem teacher.

Oh god, Magna is going to do an in-depth -----zyes. Everyone pucker up!

lol :magna: is oficialy back :D oh and a ebay or home depot made mbc will do u as well as anything else man :D

Quite the story there! I'll keep it in mind for future plumbing. Looks like in the pic you use the factory barb that is for cruise control, or capped if you dont have it. Sounds good. Where is your vacuum source for your boost reading?

I'm going to be totally honest here- I didn't read your entire post as carefully as I might have otherwise, as I find it painful on the eyes. However I'd like to address a couple of specific points.

First, let us visualize the path of air from the compressor to the engine. I will refer extensively to the following diagram, which I have borrowed from Bell's "Maximum Boost" and modified to suit our discussion.
http://img02.picoodle.com/img/img02/...im_a867914.png

Here, we see the entire pressurized intake system. I have marked three points of interest. "A" is a point after the compressor but before the intercooler, typically the little hose nipple that comes stock on most compressor housings and is the classical boost reference. "B" is a point after the intercooler but before the throttle body, which is where my boost controller is referenced to. "C" is a point after the throttle body, within the intake manifold itself.

Now, putting aside arguments of boost threshold and such, can we all agree that, all else being equal, a boost controller is going to try to achieve the pressure to which it is set, at the point in the system being measured? And we'll also agree that the boost gauge on the dash is always fed from a point after the throttle body, such as the brake booster hose, the cruise control hose, etc.

Good. Let us assume that we have a hypothetical perfect boost controller (and a perfect wastegate) and that the boost controller is set to 12 PSI.

We'll start with point A, since that's where most people are referencing their wastegate to. In this scenario, the boost controller is always going to try to achieve 12 PSI at the compressor outlet. At relatively low speeds, the flow through the intercooler is relatively little, and thus the pressure drop across the intercooler is relatively small. Assuming WOT then, the pressure in the system at points B and C will be fairly close to 12 PSI. As RPM increases, the magnitude of the pressure loss across the restrictive intercooler also increases. So while the boost controller is ensuring that 12 PSI exists at point A (before the restriction), the pressure at B and C will decrease by the amount of pressure drop across the intercooler. By redline, we may be down to 9 or 10 PSI at points B and C, despite the fact that there is still 12 PSI at point A.



Next, we move the boost controller's feed to point B, and re-run the test, still at WOT. As airflow increases and pressure drops across the intercooler, the boost controller works to maintain 12 PSI at point B, and so we see 12 PSI being reported on the boost gauge, assuming zero pressure drop across the throttle body. (Give me this one for the moment on faith, and I'll come back to it.) Now, since we're still seeing 12 PSI at points B and C, and yet pressure drop exists across the intercooler, this means that the pressure at point A is steadily increasing. Under the same assumptions as in the first test (that 2-3 PSI of drop occurs across the intercooler at WOT at redline,) the pressure at the compressor outlet will have risen to 14 or 15 PSI by this point. This, of course, is because the boost controller is ignoring point A, and looking only at point B. Some extra heat is going to be generated owing to the fact that the compressor is now working harder than before, but as a percentage of the total heat being generated, this is relatively inconsequential.



Ok, now we'll move the boost controller to point C, and we'll also change one other assumption- we're no longer going to be at WOT. We'll be going up a fictitious hill (or accelerating past a fictitious truck on the highway) and so you are modulating the throttle with your foot to achieve, say, 8 PSI. What's important here is that we're added a second restriction in the system- the throttle plate. And there's going to be pressure drop across this. If boost starts to creep up, you're going to close the throttle a little, increasing the pressure drop across the throttle, and holding MAP at 8 PSI. Because you are actively holding MAP below 12 PSI, the boost controller is never going to reach its activation point, and the wastegate is going to remain completely closed.

Now the problem is that at this load condition, you're generating more than enough exhaust gas to spin the turbo well beyond 8 PSI. If you were to measure the pressure in the system at points A or B, you might find that you've got 20 PSI. Or 30 PSI. Or 40? Who knows, really. A lot is going to depend on the size of the turbo, the exhaust system, etc. But it's going to be a hell of a lot more than 8 PSI, or 12 PSI, or even the 15 PSI we saw at the compressor outlet in scenario B. And this is going to generate a shitload of heat. And heat is the enemy. Granted, reducing the throttle opening is going to reduce the volume of gas available to spin the turbine, and there will be an equilibrium point somewhere, but remember that the whole reason turbuchargers work in the first place is that there is presumed to be a significant excess of exhaust gas available at all but the lowest load conditions- otherwise, we wouldn't need wastegates, and for that matter, the damn thing would never spool up.


"But" you ask, "won't this also be the case at part-throttle conditions in scenarios A and B?" And the answer, of course, is no it will not.

We'll step all the way back to scenario A. You're climbing the same hill, at the same part-throttle condition. You're making enough exhaust gas to spin the turbo up into orbit, however the boost controller is going to make sure that there is never more than 12 PSI in the pipes at point A. Doesn't matter if you are working the throttle to regulate MAP to 8 PSI, or 10, or 4. The pressure in the intake pipes will never exceed the boost controller's setpoint, because the boost controller is watching the intake pipes, not the manifold. Once the pressure in the pipes reaches 12 PSI, the wastegate will open to ensure that it does not exceed this. Thus, the compressor will never generate more heat than it would in a non-throttled run.

Same goes for scenario B. The pressure after the intercooler will never exceed 12 PSI, and the pressure before it will never exceed 12 PSI plus drop across the intercooler. And since the mass of air flowing through the intercooler at this part-throttle condition will be less than it was in WOT scenario B above, the pressure drop across it will be less and the pressure at the compressor outlet will be less.


Any argument here?



Yes, like the intercooler. Which is why taking the MBC reference from a point after the intercooler provides the same benefit of a manifold-sourced reference, with none of the disadvantages.



You are correct. However in this case, we are less concerned with what's going on inside the motor as we are with what's happening outside it- namely in the compressor.



كما يمكن للمرء أن يجادل بأن لأنه بعد انتهاء عملية التبريد إما يسكونسن جيم أو غير ذلك من كثافة استهلاك الاتهام والضغط أيضا موثوق يقاس في المدخول متعددة. أي شخص مطلع على النحو الأمثل للقوانين يعرف حجم الغاز هو البديل في ضوء الضغوط ودرجات الحرارة نسبيا منذ دينا ثابتة ، ثم لدينا حجم الضغط ودرجة الحرارة والعمل بسهولة تماما في الطريقة التي خفض درجة الحرارة أكثر كثافة والضغط النسبي. حيث عندما ننظر في منفذ من وضاغط الهواء في دورتها أرق وسخونة لدينا قراءات الضغط سيكون أقل بكثير من تبريد الاتهام. تولي ضاغط لديه القدرة على ملء كامل المدخول المسالك بسعر لمواصلة الضغط والحرارة. لو كان التوربينية الخروج من كفاءتها مجموعة الخاص بك ، ثم ضاغط على عجلة الغزل دورة في الدقيقة ببساطة نفس النتائج في الهواء واستهلاك أقل حركة وسرعة في نفس الكلية أو أقل مما كانت عليه عندما ضغط ش فيها في نطاق الكفاءة. هذا يولد حرارة أكثر مما تدفق وحتى عندما تبرد ش تواجه فقدان المعادلة من حيث الأداء

This is basically what I see when I look at the rest of the message. :D

woot i speack sans scrit.

One could also argue that since it is post the cooling process either IC or WI etc. The Density of the intake charge and its pressure would also bemore reliably measured in the intake manifold. As anyone familiar with the ideal gas laws knows volume is variant given pressure and relative temperature since we have a fixed volume then our pressure and temp work inversly and quite readily.

In the way that the lower the temperature the more density and relative pressure. Where as when we measure at the outlet of the compressor and the air is at its thinest and hottest our pressure readings will be much lower than that of the cooled charge.

Assuming the compressor has the capacity to fill the entire intake tract at a rate to keep the pressure and heat up. If your turbo was going out of its effeciency range then your compressor wheel spinning at maxx rpm would simply be recompressing the same air results in less movement and intake velocity overall and the same or less pressure than when u where in your effeciency range.
This ultimatly generates exponentialy more heat than flow and even when cooled u are facing a loosing equation in terms of performance.

I see what u are saying joe but im not buying it the setup i describe will give u more power ultimatly and eliminate part throttle lag going to full boost. This is good and since i run a cooling method that is volume and heat dependant it works idealy for me in all situations. I can retain maxx boost longer and garner it in sooner comming from a partial throttle situation IE your hill etc.
This is all about what goes in your motor and makes the most hp man it was never any different.

I understood the sentiment of the latter half of your previous post, I simply don't find it relevant.

Let's say that in addition to an intercooler, you are also using water injection. And that like me, you have the nozzle located at a point just prior to the throttle body. In such a scenario, there will likely be a difference in air temperature and thus density between points B and C of the diagram.

However at WOT, there will not be a difference in pressure.

The ideal gas laws deal with the behavior of a gas of uniform temperature in a closed space. If you raise the temperature, the pressure increases, and so on. However I believe you are treating the volumes of the intake manifold and the post-IC, pre-throttle pipe as two separate spaces, and this is not the case. In order for a pressure differential to exist between two spaces between which a gas is flowing, there must be a restriction separating these two spaces.

While it can be argued that a wide-open throttle body does present some manner of restriction, it is relatively insignificant at the levels with which we are dealing and the argument is largely academic. Since there is no meaningful restriction between point B and point C, the pressure at these two points will always be the same, regardless of any difference in air temperature and thus air density that exists between them.

If temperature alone were enough to cause a significant change in pressure along the length of an open and relatively unrestricted path, than your boost gauge would read incorrectly, since the air at the gauge side of the tubing is a hell of a lot cooler than the air at the manifold side, particularly if you've got the top up and the A/C on.


Now, I do accept your argument that placing the MBC reference at point C rather than point B will improve throttle response somewhat in the part-throttle scenario discussed earlier- the "going up a hill" experiment. But this is because, as I stated earlier, the closed wastegate is going to ensure that you've got 20 or 30 PSI sitting in the pipe just waiting to flood into the manifold as soon as you floor the pedal. Unfortunately, this performance is not without cost- the whole time that the turbo was packing in the air, waiting for you to finally floor it, it was generating great gobs of heat, thoroughly heat-soaking your intercooler in the process. This wasn't so much an issue before, as the act of the intake air de-compressing as it passed over the throttle plate would have returned its temperature to a more reasonable level, but once you're at WOT, that benny is out the window and the interheater is in full effect. Where's the density advantage now?

Cliff's Notes: EBC reference taken after the throttle does give you the best throttle resonse on transition from partial boost to full boost, but at the expense of considerable heat production, increased exhaust backpressure, and decreased VE during part-throttle conditions. This is an unacceptable compromise in a street-driven car.

How much of a pressure difference is there at part throttle on each side of the throttle plate?

That depends on the throttle angle and the amount of boost in your charge pipes. Anywhere between 0 and 30psi, conceivably.

Looks like I'll be hooking up the magnehelic gauge or a secondary boost guage.

Yay! Empirical data!

I wonder if I could disable barometric compensation yet still datalog the second MAP sensor on my MS...

I would imagine one would need Hulk grade T-bolt clamps in order to even be able to run with the wastegate sourcing signal from the manifold.. 30 psi is not something I want to subject my pre-throttle body components to just yet.

I am curious to know whether all of the talk of the greddy wastegate being a feeble and weak part is actually based on a misunderstanding and in fact the problem is that the wategate's vac source is not optimal... given that a cheap and reliable MBC is still necessary to go over 6 psi.

-Ryan

Sorry I didn't answer these questions earlier- got wrapped up in thermodynamics.

In the picture above, the factory cruise control port is being used to operate the bypass valve, which is not visible (obscured behind the upper radiator hose) however it is just to the left of the crankshaft pulley, mounted midway up the coldside charge pipe that feeds into the throttle assembly.

The vacuum source for my boost control apparatus, as I said earlier, is a brass hose barb fitting mounted to the same charge pipe, just above the bypass valve. I drilled and tapped a 1/8" NPT hole in the pipe, and inserted a 1/8" brass hose barb fitting from the plumbing section of the hardware store. The blue tube that crosses the radiator fan is attached to this.

The vacuum source for my boost reading (both my in-dash boost/vac gauge, my MS's MAP sensor, and the MAP sensor for my WI controller) are taken from the large hose that feeds the brake booster. If you look just above the brake master cylinder reservoir (the plastic cup with the black cap) you will see a brass Tee fitting. (Yes, a lot of the stuff under my hood came from ACE Hardware.) That tee is located just before the check valve that's built into that hose. There's a thin semi-rigid plastic tube coming off of it (not visible) which passes through the firewall at the grommet for the cruise control, and is then split to feed the gauge and the MAP sensors. Yes, everything is fed off of one skinny plastic tube, of the sort that comes with vacuum gauges.


I threw away the original Greddy can after I installed the Garret one, so I'm unable to go back and make a comparison. All I can say for sure is that the helper spring on the stock Greddy can was not effective at combating the boost dropoff, however the Garret can was no better in this regard, given the same vacuum source at the compressor outlet.

I dunno, I've got a feeling, going up a hill with just maintenance throttle, it's not going to be 30psi difference. If that was the case you'd probably be able to hear a hiss like when a BOV opens every time you cracked the throttle, and there would be insta spike on boost guage.

But that's my hypothesis. I'll get around to testing probably in a few weeks (I know lame).

A few grammatical errors and misused words, but otherwise good.

http://smiliesftw.com/x/big_jihad.png

i would love to see imperical data. joe the ideal gas law realy only limits to a specific quantity of gas in most examples it is a mole.
This being said all variables that can change are subject to the unchanged and thus move inversely. For simplicity i assumed we had a constant or near constant mass of gass for the entire experiment.

Well, I would consider this a productive thread. Why? Here's why:

http://i175.photobucket.com/albums/w...gnalchange.jpg

I gained roughly 2.3 psi on the top end by applying the fix Joe clued me in on. Or in other words, I don't have to crank the MBC up to spike to 13 psi to get 10 at redline.

Wow, amazing info. You take any pics?

try it from a vac source and you will see even better performance man.

Win. :bigtu:

I did now:

http://i175.photobucket.com/albums/w...gatesignal.jpg

Left to Right..
Pic 1: Barbed fitting drilled/tapped and JB welded into coldside intake pipe just before the throttle body (the one that is higher up).
Pic 2: Vac line runs from barb under the coldside pipe up to front of valve cover
Pic 3: Line runs along front of valve cover to MBC and then out of MBC to wastegate.

-Ryan

Maybe the title of the thread should be changed to make it easier for noobs to find this great info.

I suppose I should re-do mine now, having to spike to 13lbs to hold 10-11 is annoying.

I re-did mine yesterday, and it doesn't drop off but I still get a spike at the beginning. It overshoots my target by a PSI or two and then settles (rock solid) at 13psi.

It's not perfect, as you can see on my datalog I do still lose about 1 psi from peak of boost point to redline but with the wastegate vac line ran the way it was before I was getting almost a 4 psi drop over the same range. 1 psi overshoot and then a solid X target psi to redline is pretty damn near spot on optimal.
-Ryan

Knowing you're losing 2.5-3 psi in your intercooler and plumbing should be annoying you now. 20-25 percent of the compressor's work being thrown away is not good.

If it helps, for every pound of boost you are losing, your charge air temperature is also dropping :)

Garrett Actuator
 

I just put on a Garrett actuator from ATP.

WG-ACT-28RS-14PSI: atpturbo.com

Made a bracket, used a 2" extension (also from ATP), and tightened it down. It ran 1Bar falling to only .98Bar on the first run. So it's as simple as a better WG, something closer to the boost levels you actually want to run. I'll hopefully have new dyno chart in a week or two running 1Bar. It pulls like a BEAST!!! It's back to being SCARY to drive. Even my wife shit herself, and she was only doing about 1/2 throttle.

"I can't drive that, it's too fucking fast!"

She's been driving it around at 240whp (last tune) and never complained.

Let me bump this thread with a bit of manufacturer information for internal and external wastegates (disregarding the compressor outlet for the sake of this thread).

I was in the middle of trying to figure out what I was going to do for a source, but after reading Joe's explanation and seeing ThePass' information (good job btw!), I'll be installing a fitting post-IC/pre-TB.
Magnamx-5, I also took what you said into consideration because of Pat running his source off of the back of the intake manifold and because it makes sense, but after reading that quote from Garrett and a couple other places saying that vacuum can hurt the diaphragm, I'd rather be safe than sorry.

*edit* I just had a thought, what if one were to run a check valve so that the diaphragm is never exposed to vacuum?...

From what i see Vac hasnt hurt my diaphragm but the check valve would be a very workable solution for those who are worried.

does your seat still smell from your wifes shit?

Ray, this passenger-shit-effect, let me get this right, Greddy turbo, 1 bar boost, 1.6 with rods/pistons? Curious as I'd like to duplicate the effect eventually.

dont forget that he's using the aem. therefore his 240whp is way faster than a megasquirted 240whp. dont even think about disagreeing, its a fact.

Nah, she didn't get any on the seat.

It's still a stock 1.6l.

...the difference is the boost level that power was reached at.

What did you do to plug the source on the compressor housing ?

I just ziptied a little rubber cap on mine. So far so good.

1991 Eunos 1.6, t25 turbo, home made tubular manifold, home made 3" exhaust, 2" and 1 1/4" from turbo, intercooler, waste gate set to 5psi with switchable MBC 10psi.

Found this topic interesting I have sourced pressure for the waste gate/MBC from the cruise control port back of inlet manifold for the last 2 years. Didn't appreciate the potential problem with vacuum being applied to the actuator diaphram or the issue of potential over boosting/heat build up pre throttle body.

So I thought I would check things out. Does the pressure go high post compressor pre throttle body through the intercooler in part throttle situations as Joe suggests? Yesterday fitted take off point pre throttle body post intercooler and fitted second boost gauge to find out.

In part throttle running with the boost set to 5psi I was seeing almost 10psi on occasions from the pre throttle body gauge. On 10psi boost I was seeing over 15psi on a number of occasions. On each occasion I was not on anything like a real hill just a gentle incline. So Joe you got it right.... And of course with the extra pressure would have come unnecessary and unwanted additional heat.

So guess where I've now conected the take off for my boost control - yep post intercooler pre throttle body.


Malcolm

Having this second gauge fitted also showed something I hadn't appreciated - when you're running in vacuum (boost gauge showing this) there is already +ve pressure in the inlet pre throttle body. This fits in with why when a turbo is fitted and even driving technically off boost the engine feels more torquey, could this be because there is better cylinder filling.??

I think I'm going to give this a try today.

I currently take the boost signal from the compresser and have problems with boost overshoot, and holding boost until the redline.

I'm going to blank it off, then drill and tap the charge pipe pre throttle body and see what results I get.

I didn't realise taking the boost source from the manifold was a problem. I do now though! Good thread.

This was easy enough to fit so I had a go of it... but it was a bloody mess to make any sense of what was going on cuz in full boost, looking at two gauges was not too easy/useful.

THis sounded much better, so of course I asked Joe how to do it and thankfully he told me...

Logs attached... The first one is brief and includes a 2nd to 3rd shift WOT. THe second log is a boring mix of driving but includes a bit at WOT and also a part-throttle full-boost situation at about the 880 second mark, and some other dubious data for those much smarter than I to hopefully interpret.

Ideally, I suppose I should have tried a 4th gear pull from 2k rpm to redline but I didn't have the road for it. If you lot are interested, I can give it another go. I also may try to reference MBC post throttle just to see what's what.

Intercooler is a big Bell unit, MBC is set to ~10 with a reference just prior to throttle. THis was at sea level and the rest of the hardware is in my sig.


To overlay curves, "aux pressure" is what I called the second MAP sensor in MLV. The second MAP sensor is sourced at point "A" (compressor).

Enjoy.