Stock boost ?

[Bullett]

Ok so I'm running a notchtop s14 with greddy FMIC, Cx piping, greddy type s (unrecirculated), Wally 255 and Isis tubular. Saturday I installed a profec bII and have been using it to monitor boost only. the solenoid is not hooked up and the vac lines have been left in the locations that I bought the car in. the hose connected to the controller is running to a nipple on the intake mani. that was previously blocked off.
I noticed that my boost increases steadily with rpm all the way up to 12psi, +/- with error. I have been lead to believe that stock Max on the gate is 11 psi, so it seems about right. my question is, is this a normal behavior for an SR with only factory boost control? Seeing as how it steadily rises to Max I figured maybe something has been bypassed. And will simply Tuning the new boost controller remedy this?
BTW, idle is normal even unrecirculated. car runs perfectly.

[Mikester]

Ok so I'm running a notchtop s14 with greddy FMIC, Cx piping, greddy type s (unrecirculated), Wally 255 and Isis tubular. Saturday I installed a profec bII and have been using it to monitor boost only. the solenoid is not hooked up and the vac lines have been left in the locations that I bought the car in. the hose connected to the controller is running to a nipple on the intake mani. that was previously blocked off.
I noticed that my boost increases steadily with rpm all the way up to 12psi, +/- with error. I have been lead to believe that stock Max on the gate is 11 psi, so it seems about right. my question is, is this a normal behavior for an SR with only factory boost control? Seeing as how it steadily rises to Max I figured maybe something has been bypassed. And will simply Tuning the new boost controller remedy this?
BTW, idle is normal even unrecirculated. car runs perfectly.

First of all, you are 'setting' the boost controller- NOT tuning ;)

Normal gate pressure varies from 10-12psi IIRC; so that's about normal. If you've got all direct lines from intake vac/boost sources to the WG actuator, then nothing has been bypassed.

[Bullett]

lol got ya. Sorry I'm a reformed muscle head. still learning the Jap lingo. so the consistent rise in boost to redline is normal? figured it would hit 7psi and stick there. And is it safe to monitor the boost with only the controller? didn't quite understand the point of having a gauge if the controller has a readout..

[Mikester]

lol got ya. Sorry I'm a reformed muscle head. still learning the Jap lingo. so the consistent rise in boost to redline is normal? figured it would hit 7psi and stick there. And is it safe to monitor the boost with only the controller? didn't quite understand the point of having a gauge if the controller has a readout..

I misunderstood. If stock turbine, yes it should hit max boost by 3,000-3500 and stay there... not creep up with rpm. Could be a minor vac/boost leak somewhere, or maybe it would behoove you to go ahead and connect the rest of the boost controlling system and see if you can iron it out. While you're at it, never hurts to change out all of your vac/boost lines for silicone... and reroute/clean them up at the same time.

As far as a gauge is concerned, it's generally a lot easier to read a gauge in real-time than the readout on the controller. I use the controller for the 'obvious' controlling boost/response/limiting; and for monitoring my maximums when making minor adjustments. Each to their own I suppose. I have 2 gauges (boost, oil pressure) and like the simplicity.

[Bullett]

ok I thought something was funny. It only has about 4 lines and they all look good. may just try to sort it out with the controller after I check for other leaks.

[Fuego]

Just here to confirm 7lbs is correct for stock actuator. Creep like that sounds like a bad actuator, boost solenoid (which you said was disconnected), or a leak. Follow what Mikester said and good luck!

[jr_ss]

Just here to confirm 7lbs is correct for stock actuator. Creep like that sounds like a bad actuator, boost solenoid (which you said was disconnected), or a leak. Follow what Mikester said and good luck!

Correct, factory wastegates are 7psi. The factory boost control solenoid allows up to 10-11psi.

[Bullett]

ok, as I'm still learning here, how is it that one can get 12-20+ psi if the gate controls the boost?

[Kingtal0n]

Technical Articles | How A Boost Controller Works | Turbosmart USA (http://www.turbosmartusa.com/technical-articles/how-a-boost-controller-works/)

Hmm that article doesn't help much IMO. Oh well.

Its all about pressure. Atmosphere at sea level is 14.5~ Psi. In other words, the air molecules attracted to earth's center by gravity are held down, they cannot escape into space. Air density increases the closer you get to earths center, so if you were to fly up in the sky, there would be less than 14.5 PSI.

So when a naturally aspirated engine is breathing, the only thing available to push air into the engine is the atmosphere. That means all N/A engines are technically turbocharged at 14.5PSI. We just see this as 0"vacuum (0PSI) because we are ALSO sitting in the same 14.5PSI. So our frame of reference is the same as the engine's, so we detect no additional pressure.

A turbocharger adds to atmospheric pressure, some # of psi in additional to the 14.5 at sea level. A turbo producing 7PSI at the intake manifold is helping the engine receive an additional 7PSI above atmospheric. If you can squeeze a whole extra 14.5PSI in additional to our atmospheric 14.5PSI (15~psi of boost, 30~psi total) then the engine's torque output doubles. The reason that most engines running 15~psi of boost do not double their power, however, is because the air is usually hotter when boost pressure is applied.

SO, anyways, a given turbo will apply a given amount of boost pressure given the speed of it's compressor wheel, and is limited by a few factors, such as the speed of air leaving the compressor, air does not like to exceed the speed of sound, for instance, so plumbing diameter can become an issue (increase the size of plumbing to flow more air molecules per unit time if the flow is available). All A wastegate does is limit the speed of the turbine/compressor wheel by re-directing exhaust away from the turbine. It can do this because it has a boost reference port attached to the engine, that is balanced by a diaphragm with a spring at a specific resistance. A stronger spring allows more boost pressure before the spring is compressed and the wastegate opens.

A boost controller adjusts the amount of air pressure the diaphragm "receives" at it's boost reference side, limiting the amount of pressure exerted on the spring thereby allowing the wastegate to remain shut and forcing more exhaust through the turbine causing it to spin faster. If the compressor is not "maxed" then more flow is the result, and more power, and usually more boost as well.

[Bullett]

holy lamens definitions lol. thanks for the break down though, that was pretty thorough . I do know SOMETHING about how the system works, and the last car I built put down 503 to the wheels. there are just a few more basic theory points that I'm trying to understand w turbo engines.

[TheRealSy90]

STOCK BOOST IS NOT 7psi!!! That is the simply the wastegate pressure! The factory boost solenoid tapers the boost up depending on rpm and engine load to 11.5-12psi like it is SUPPOSED to be doing. Your car is doing exactly what it's meant to do from the factory.


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[Fuego]

the solenoid is not hooked up

The factory boost solenoid tapers the boost up depending on rpm and engine load to 11.5-12psi like it is SUPPOSED to be doing. Your car is doing exactly what it's meant to do from the factory.


:hey::hey:

[Bullett]

ok. here we go. lol

[Mikester]

^^Yea, my apologies for my initial post (thanks for keeping me honest, Glenn)... I had based my statement on stock boost (.7bar) with the solenoid hooked up. Didn't consider the disparity between the solenoid hooked up or not.

For grins, you can take a look at the wastegate actuator arm... If it's aftermarket, there will be an adjustment nut about halfway down... If the PO had it adjusted tighter, that could explain the higher 'stock' boost as well.

Be that as it may, your boost should not creep like that. It should hit full boost, then stay fairly stable throughout.

[Bullett]

actuator arm is stock. I have to wait for a new solenoid harness to get here and some silicone hoses and I'll give it a go.

[Bullett]

Problem solved! One tee on the manifold was blocked off with electrical tape (awesome I know), and the connection between the solenoid and intake on the intake side could be spun by finger. used a proper vac block and tightened the other and she's good as gold. low boost holding at 10psi high at 13ish. thanks for the pointers gents!