___ BOOST: WHAT YOU SEE... MAY NOT BE WHAT YOU GET

mountainhorse · Nov 14, 2016

When it comes to what your gauge is reading that is... :face-icon-small-hap

This thread is intended to be a DISCUSSION... The opinions presented here are just that OPINIONS... Especially mine :face-icon-small-coo

This conversation was started in another thread and was off topic (my bad)... so I thought I'd "bust it out" and bring it here for discussion.

In this day and age of new turbo systems... More Pull-N-Go than we have ever been... this may help some to understand what is going on in terms of Boost pressure and what you see on a gauge and what is happening.

Some Acronyms:
IMO = In My Opinion

PSIG = Pounds Per Square Inch GAUGE
PSIA = Pounds Per Square Inch ABSOLUTE

EBC or EABC =
Electronic Boost Controller
or Electronic Altitude Boost Controller

MAP = Manifold Absolute Pressure

From This page: Click

hobbes said:
That is incorrect. The amount of oxygen molecules per square foot (or whichever area measurement you prefer) is going to be less at higher elevation. This is easily overcome by increasing the boost level as you climb in elevation. The MAP (manifold absolute pressure) sensor incorporated into the system will read the air pressure, which not only changes with altitude change but with temperature and weather changes as well, to the electronic boost control. The EBC will keep the pressure at the manifold the same by increasing or decreasing the boost accordingly. This is why it only takes @3 lbs of boost at sea level to make 200 hp but 6+ lbs of boost at 9000 feet to make the same 200 hp.

A boost gauge does exactly what Hobbes is saying.... reading PSIG

I'll refer here to "EBC" as an electronic boost controller that will adjust, automatically, for changes in altitude (barometric presure) as well temperature.

The "EBC" systems work off of ABSOLUTE pressure sensors to read manifold pressure.

So, your Gauge will read higher boost at higher altitudes when the "EBC" is functioning as intended as compared with the same EBC functioning as intended at lower altitudes....

While is is true that your "boost gauge" is reading "higher boost pressures" at higher elevation... the "EBC"/Turbo is NOT making more boost at altitude... although the turbine/compressor ARE spinning faster.... actually the MAP remains constant (or at least that is the target that we are shooting for)

AND...
The pressure on the charge side of the system (charge-tube/airbox/throttle bodies/BOV) , ABSOLUTE PRESSURE, which the MAP sensor is reading... That pressure will remain constant at WOT... and thus the oxygen content in that air-charge will also remain constant (or increase if target boost is dialed-up)... for our intents and purposes here.

Now... some well equipped people will have a gauge that reads PSIA.... like an AEM X gauge with MAP-sensor... or other PSIA gauge.

I wonder why 2-stroke turbo mfgs have visual-gauges that read PSIG... when the "EBC" system reads PSIA.

I'd rather know what the manifold is reading, rather than the gauge-pressure which is compensated with ambient atmospheric pressure.

Although most don't need a system... And I would argue that it can take away from that pull-n-go motif... It would be nice to have a MAP-gauge avail as an option.

It is true that there is the same PERCENTAGE of oxygen in a given volume of 'air' at altitude.

Example... blow up a balloon... which is a 'container' that can expand...at sea level, that balloon will be smaller in size than it will be at 10000 feet (as long as it doesn't burst)... That balloon contains the same air at both altitudes...only the density changes (units per given volume).

Since a turbo must spin more to collect less dense air at high altitudes.... the efficiency drops at higher altitudes.
Analogy.... How many 5 gallon buckets of blower powder would you need to collect 10 gallons of water once melted... how many buckets of spring snow would you need to collect that same 10gallons of water.

A given PG turbo sled with a funtioning "EBC", running MAP at 20.7psi (1.4 bar) , will have a different throttle response at sea level than at higher elevations with the same 20.7psi MAP.

So long as the kit mfg did their homework in selecting the correct compressor/turbine/housing... and the sled is working inside of those parameters that the mfg used to select the turbo... all is good.

That being said, there can be improvements made in HOW well a turbo kit works by narrowing down the 'window' of altitudes that it is designed to Optimally perform in. Even with an "EBC" some compromises are made if the turbo is selected to have optima response and power at, for example, sea level compared to, say, 9,000 ft.

In a well designed sled turbo kit, I would expect a slightly different turbo configuration for customers who run mostly at lower elevations than at higher elevations...so that the sled has optimal running characteristics (throttle response, minimal lag, lower charge temps, outlet backpressure...etc... etc) for that target range of elevations most ridden in...and any 'compromises' are made only when you are operating outside of you preferred range.

hobbes said:
Either way, you are NOT MAKING THE SAME HORSEPOWER AT 9000 FT THAT YOU ARE AT 1500 FT unless you are adjusting your boost pressure.

Hobbes.... You are talking about "Gauge Pressure".... not MAP, Correct?

An "EBC" works to maintain near consistent MAP at different elevations....so long as the turbo is capable of handling those variations.

IMO... From a consumer aspect... it would be great, from an intuitive level, to talk about boost as MAP...Rather than Gauge boost readings that are "compensated".

Most people that own turbo sleds don't know, nor should they need to know, how the system works... unless they are really are 'tuners'.... 90% of the people, IMO, that buy a turbo kit for their sled really just want a "pull and go" system. Having a gauge that reads 10 lbs of boost when they are riding and they purchased a "6 lb PG" system just makes them nervous.

Correct me if I'm wrong... a sled will have the same power at all elevations if the MAP is consistent at those different elevations. You are not actually making "more psi"... you are keeping the MAP at a consistent psi number.

Example... if you were to hook your typical boost gauge to a sealed bottle... and pump that bottle, at sea level, to say 10 psi reading at the gauge.... and you took that sealed bottle with your boost gauge to 9,000 feet (using Max's 10.5 psi ambient number).. Your gauge would now read 14.2 psi, at 9,000 feet... without changing a thing in the bottle.

Of course the turbine section is affected as well from the changing differential of exhaust pressure and ambient baro... which changes how the turbo works as well. A properly selected turbo and functioning "EBC" will help to mostly negate this effect.

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mountainhorse · Nov 14, 2016

hobbes said:
Manifold absolute pressure per say, is the pressure measured at the manifold. Which in our case, describes air pressure available to the motor in the airbox or charge box. Boost pressure would be referring to the air pressure leaving the charge side of the turbine, and what most people put a gauge to. I've always been fond of your propensity to over complicate things MH, but sometimes the KISS approach works well LOL. Everything you have stated is perfectly correct IMO. Even if a bit over stated. Your bottle example is a good way to think about it, however, a bit misleading because you have the gauge on the sealed bottle and are noting the change there. We aren't dealing with a sealed bottle(or charge box) in our scenario. The question to ask is WHY did the pressure INCREASE in the bottle? It's because of the DROP in the ATMOSPHERIC pressure around it which causes the air in the bottle to expand and increase your bottle pressure. And in hook's case, the only way to replace the atmospheric pressure we've lost as we gain altitude is to increase the boost pressure to compensate for it. Restoring the manifold pressure to a similar pressure he saw at 1500 ft.

I completely follow your logic on wanting to see MPA pressure gauge. We throw so many variables at the manifold when boosting a motor it's almost beyond comprehension. Boost, temperature, air density, humidity, intake pulse etc. But again, I think we're over complicating the issue. Which is another reason having a simple low boost, no hassle turbo kit is all the more appealing to me.

Good discussion... I sincerely like your presentations too Hobbes.:face-icon-small-hap

My take... in a presentation for our members here...and fodder for discussion... not trying to tell you stuff that I believe you already know.

In the case of the bottle example above, it is a 'sealed system' ... the pressure in the bottle remains constant and is unaffected by ambient pressure. Pressure inside the bottle, the force that the air pushes against the inside of the bottle, does not increase because of a drop in ambient pressure.

In order for the pressure inside the bottle to change, the bottle itself would have to deform (think a ballon rather than a rigid bottle) The air in the bottle will not expand unless the bottle itself expands.

The gauge reads differently because the atmosphere has dropped in pressure, not the gas expanding in the bottle. That is, using the most common, "needle type" boost gauges that we all see on sleds and pickup trucks.

If the bottle doesn't crush or rupture or deform... you could take that bottle to the bottom of the Marianas trench or mount it to the Hubble telescope... and the pressure inside the bottle would remain constant.

The pressure that is displayed on the gauge changes because most boost gauges are referenced against atmospheric pressure... if that atmospheric pressure drops, as does when you climb in elevation, then a fixed pressure (as in the bottle example above), will read against an atmospheric presure referenced by the gauge. A typical boost gauge actually measures differential pressures... not absolute.

The pressure that the engine 'sees" in a turbocharged sled is, in effect, that same sealed system... much like passengers in an airliner at 40,000 feet... the pump (turbo) maintains a pressure that the people/sled-engine feel.

The goal of the turbo is maintain or increase the amount of oxygen the engine can intake... which will allow you to burn more fuel than that engine in a N/A condition.

The EBC reads info from the actual pressure, using a MAP-sensor, on the charge side of the compressor (charge-tube/airbox/manifold)... and then directs the wastegate to spin the turbine faster or slower by adjusting how much is bypassed.... and relies on the BOV to bypass any pressure spikes when the throttle plates are snapped shut.

How quickly the waste gate responds, and how the spool rates of the turbo match demand, plays a large roll in maintaining consistent charge-side pressures with constantly varying throttle positions.

"How does the motor respond to the flipper"?
That is where thoughtful/experienced design plays a huge role in how the majority of consumers enjoy the ride !

In the end... the turbo system that is designed best will maintain consistent charge side boost pressures for constantly varying throttle position with no spikes or depressions in boost pressure.... Minimal lag as we like to call it.... "Linear response" :face-icon-small-sho

We've not touched on Temperature here either... which adds even more dimensionality to the equation..:bowl:

Trying to keep it as simple as possible. :face-icon-small-win

Here is a good one from AEM's site that elaborates better than I can.

Absolute (PSIa)
PSIa is referenced to absolute zero. Absolute zero is the pressure measurement when all the pressure exerted by the atmosphere has been removed. The most common use for absolute pressure sensors is reading manifold pressure. PSIa sensors are required of you wish to measure vacuum. A PSIa sensor will read about 14.7 PSI when the sensing element is exposed to atmospheric pressure at sea level however they can be recalibrated to read zero at atmospheric and a negative number at values less than atmospheric pressure.
.

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mountainhorse · Nov 14, 2016

If I WERE wanting to monitor Boost on a sled-turbo-system with an "EBC" ... or even no EBC...

I'd want to monitor MAP ONLY because of the drastic changes in elevations that we operate our sleds in. I would want to know what the actual pressure in the system was... rather than trying to remember what the changes in elevation are doing to my readings and trying to work that out in my head. :face-icon-small-con

Something like the AEM 30-0309; which comes with it's own MAP-sensor and has Peak/recall as well as changeable warning alarms would be cool.

https://www.summitracing.com/nv/parts/avm-30-0309

mountainhorse · Nov 14, 2016

By reading a gauge that displays the ACTUAL (Absolute Pressure) on the Charge-Side of the turbo... you will have a better idea, IMO, of what is actually going on in your system.

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gmustangt · Nov 14, 2016

Simply put if you are running "6psi" at sea level. With an altitude compensating feature. Rough numbers:
Typed on my phone .. Hopefully it lines up.

Elevation. / Atmosphere PSI. / Turbo PSI. / PSI Absolute

0ft ...... ...... 14.7 .................. 6 ............ 20.7

1000ft. ...... ...... 14.2 ...... ...... 6.5 ...... ...... 20.7

2000ft. ...... ...... 13.7 ...... ...... 7 ...... ...... 20.7

3000ft. ...... ...... 13.2 ...... ...... 7.5 ............ 20.7

4000ft. ...... ...... 12.7 ....... ...... 8 ...... ...... 20.7

5000ft. ...... ...... 12.2 ...... ...... 8.5 ............ 20.7

6000ft. ...... ...... 11.8 ...... ...... 8.9 ............ 20.7

7000ft. ...... ...... 11.3 ...... ...... 9.4 ............ 20.7

8000ft. ...... ...... 10.9 ...... ...... 9.8 ............ 20.7

9000ft. ...... ...... 10.5 ...... ...... 10.2 ............ 20.7

10000ft. ...... ...... 10.1 ...... ...... 10.6 ............ 20.7

mountainhorse · Nov 21, 2016

The topic of this thread is related to turbo gauges and what they are actually telling the pilot.

So, to keep this on topic... I'm moving this "complicated" discussion to it's own thread.

Click this link to go to that new thread
http://www.snowest.com/forum/showthread.php?t=420372

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mountainhorse · Dec 11, 2016

Re-Visting this.

So for you guys with Boost controllers or NOT....

To get consistent performance from your sled in terms of clutching, response power output... the goal would be to maintain air density in the charge side of things.

Density is related to pressure and temp.... For say a low boost system, "3 lbs" (17.7 MAP).... more than sea-level performance... you wont have as much air heating issues IMO as on a high boost system.. So temp plays less of a role.

So, for me... I'd want to have a gauge that I could look at and know if I need to dial up or down my boost... or, if a bare spring controlled WG... weather or not I would need to shim or increase preload on that spring at altitude to get consistent performance....

Even on a higher boost system... you would only have to intuitively understand 2 variables: the effects of temp on the charge pressure and the charge pressure itself.... rather than 3 variables of how to interperet the "boost pressure" (PSIg), what is that pressure, and temperature. A PSIa gauges, IMO, makes things less complicated to monitor what is going on.

my 2¢

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___ BOOST: WHAT YOU SEE... MAY NOT BE WHAT YOU GET

mountainhorse

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___ BOOST: WHAT YOU SEE... MAY NOT BE WHAT YOU GET