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NOS Launcher manual said:
Once a dry run is performed, the system can be activated with the nitrous and fuel solenoids hooked up.
The following are some basic guidelines for tuning. Every engine will be slightly different:
• Nitrous typically should not be activated below 3000 RPM or possibly higher depending on the engine.
If activated below 3000 RPM, use the progressive controller to meter less amounts of nitrous/fuel
as to not create excessive cylinder pressure causing detonation.
• Nitrous should only be activated at wide open throttle (WOT).
• If using a wideband A/F sensor, use the lean cutoff feature.
A delay of approximately .5 seconds should be past the typical lean spikes seen from nitrous activation.
The leanest it is recommended to run an engine at with nitrous would be between a 12-12.5:1 A/F ratio.
A/F ratio’s in the 11’s are typical with nitrous when trying to get a safe tune.
• Use the RPM cutoff to help shut the nitrous off when using a manual transmission.
On race engines that use a vacuum pump and sealed crankcase, connect the [Launcher's] vacuum port to the crankcase.
This can be used to monitor the vacuum and detect any detonation by showing vacuum fluctuations in the crankcase.
I'm contemplating the installation of a crankcase vacuum/pressure sensor (2 bar MAP sensor) for my Holley Dominator EFI system.
I found the blue quote above very interesting. What kind of vacuum fluctuations/changes (detonation) have you seen in your data logs?

Also, the Holley EFI software indicates there will be a stainless steel 3.5-bar MAP sensor/transducer available at some point.
I know I'm supposed to use a 2-bar MAP sensor, but the transducer would be a nice fit and look a lot better too.
(I don't run a vacuum pump.) Will it be sensitive enough around 100 kPa? If so, I'll just wait for it.
 

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Danny, you only want/need a 1 bar sensor. You will never be looking at boost inside your crankcase. Well, if you DO have boost inside there, it won't be there for long!

I just use the generic GM 1 bar MAP sensors available everywhere. The SS units are nice, but the other sensor is free in most bone yards. ;)

When you have detonation the vacuum signal in the crankcase starts to fluctuate. If you are rattling the engine hard enough the vacuum swings up and down 4 inches, or more, easily. My vacuum stays rock-steady during a pass. It starts low, until the pump has come up to speed, and then increases going down the track. If it decreases, IE: starts at 10 inches and falls to 5 inches, there is a problem, usually a leak, or a tired engine with a lot of blow-by. If it is bouncing, then it's getting hurt.

I run a vacuum pump. Without one, I have no idea what kind of pressure you will measure in a crankcase. If you have NO exhaust evac of any sore, then maybe a 2 bar sensor will show you what kind of pressure is in there. You will also have oil leaks too with positive crankcase pressure.
 

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Thanks for a very informative post.
I don't run a vacuum pump, so I image there's zero (idle & cruising) to two PSI (WOT) of crankcase pressure in my engine.
That's why I think I need a 2-bar MAP sensor. Or maybe I won't benefit from a crankcase pressure sensor at all?
I just want it for data logging purposes; if something ever goes wrong with the engine, I'd like to analyze the data.
 

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If you have watch it for a long time and know what it looks like, you can see the very smallest amount of detonation going on. For most with vacuum pums it's a steady line going up to it reaches full vacuum, and anything that makes it flaten or did is detonation!!! On boosted cars where it common to have prussure in the crank case where they don't have vacuums pumps your read the amount of psi, again with you set up you know what is normal and anything above that is things you should be looking at. Good luck
 

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I also use a basic 1 bar GM MAP sensor. Just remember, a MAP sensor doesn't measure the same as a vacuum gauge.

With a vacuum gauge, it will always read zero no matter what the barometric pressure is at sea level or on the top of a mountain. A MAP sensor is always based on the current station pressure. It returns a 0-5v voltage signal based on how much pressure difference it senses.

With the engine off and the power on, the voltage returned will always be different depending on the station pressure. An exact amount of vacuum measured in the crankcase won't always be exact and how much it reads depends on the 0-5v calibration.

Since 1 bar is 14.7 psi, the sensor need to be calibrated from minimum volts to maximum volts to cover that pressure scale. Since the MAP sensor is measuring pressure and you want to know vacuum, a different calibration scale needs to be used. Typical calibration range is 0.5v to 4.5v. I believe the sensor returns 4.5v when the engine is off and voltage drops as vacuum is increased but it could be the other way around.

Instead of knowing an exact number, it's easier to just see how much pressure is detected when the engine is off and how much less is detected during a run. At the start of a race day, I turn on my data logger and record a session before starting the engine. That way I have a base number of what the MAP sensor is reading before the engine is started.

A MAP sensor is great for datalogging but a simple vacuum gauge is easier to understand providing you actually look at it during a run.

Without a vacuum pump or even a header evac system, the crankcase will always have a slight bit of pressure due to blow by past the rings. The lower the blow by, the less pressure there will be. Crankcase pressure is normally measured in inches of Hg. Anything under 6 inHg is considered good. Higher than that and the engine is considered worn out. Typical blowby is only 1-2 inHg unless you have a very low leakdown percentage.
 

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I use a standard GM 2 bar sensor as my Crankcase Vacuum sensor...
no issues with it

if you experience any positive pressure, the 2 bar will show it where as a 1 bar will only show that you are positive, but not how much over 105kpa you are.
a vacuum gauge would be a better option, but the map sensor is a cheap and readily available option and easy to wire into any aftermarket ECU


if you data logger is fast enough, you can see the individual pulses of the vacuum pump...
and if you have detonation, you will see a pretty good sized spike or a dip in the vacuum.
 

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This might be a stupid question, but where are you guys tapping in the engine for crankcase pressure? Meaning where in the Oil Pan or am I missing something?:rolleyes:

Thanks
 

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Im going to tap mine in the valley cover of my intake, AEM sells a brass 2 bar fitting for $60 bucks
 

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This might be a stupid question, but where are you guys tapping in the engine for crankcase pressure? Meaning where in the Oil Pan or am I missing something?:rolleyes:

Thanks
Valve cover for me...
Or valley cover if your engine has one.


I like to use a 2 bar map sensor so I can see if I should happen to get crankcase pressure which would reveal a problem..it should never have pressure if your vacuum pump does its job unless there is a problem.
 

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Valve cover for me...
Or valley cover if your engine has one.


I like to use a 2 bar map sensor so I can see if I should happen to get crankcase pressure which would reveal a problem..it should never have pressure if your vacuum pump does its job unless there is a problem.
Oh! I just assumed that to monitor crankcase pressure it would be in the crankcase. Thankyou very much!!! Won't a 1 Bar sensor be good enough since it is not seeing boost pressure since its a nitrous motor?

Thanks
 

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Oh! I just assumed that to monitor crankcase pressure it would be in the crankcase. Thankyou very much!!! Won't a 1 Bar sensor be good enough since it is not seeing boost pressure since its a nitrous motor?

Thanks
Heads are attached to the block...oil has to have holes to drain back to the pan..
All part of the internal pressure vessel..

A 1 bar sensor works.. if you don't care about pressure..
Without some sort of crankcase vacuum device, you will build some crankcase pressure...rings don't block 100% of all pressure..and you don't build vacuum without a pump or a header evac system.

Doesn't matter if you are naturally aspirated or nitrous or forced induction...
 

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Heads are attached to the block...oil has to have holes to drain back to the pan..
All part of the internal pressure vessel..

A 1 bar sensor works.. if you don't care about pressure..
Without some sort of crankcase vacuum device, you will build some crankcase pressure...rings don't block 100% of all pressure..and you don't build vacuum without a pump or a header evac system.

Doesn't matter if you are naturally aspirated or nitrous or forced induction...
Oh ok. That explains it! Makes sense since there is nothing removing the pressure such as vacuum pump or header evac. Thank you for the info!
 

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So will this 2 bar sensor measure crankcase vacuum?

http://www.jegs.com/i/AEM/017/30-2131-30/10002/-1
that one actually will read vacuum....
0.5v to 4.5v
-14.7 to 15.3

the Holley software will only allow -14.5 psi.....
so just set up the scale to be 0.53 to 4.5v
and -14.5 to 15.3

or you can set the values to be 1.234 format(to allow 3 digits) and you can enter
-14.475 to 15.300
and 0.53 to 4.5
 

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So how do I set it up for InHg?
I do mine so InHg is positive values for vacuum and negative values for pressure since I am measuring crankcase "vacuum"

so
0.53v to 4.50v
29.471 to -31.151

again... positive numbers would be Inches of Vacuum in this example.
 

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Interesting information on this thread, it's given me the idea to monitor my crankcase pressure. That's why I like YB, it's hard to know everything but on this site you get exposed to a lot of ideas that you may not have thought about.

My street/strip Mustang has twin turbos on a SBF, makes north of 1000hp when I push it. I don't have a vacuum pump, only two small K&N breathers on the passenger side valve cover. So I don't know if it will give me any useful data, but it's too easy to hook up not to try and see.

I have a spare map sensor in the engine compartment that is already hooked up to my Haltech ECU that I use to monitor/datalog various pressures that are in a map sensor's range. Right now it has a 3 bar sensor, but I have a 2 bar sensor that can be swapped in quickly. I'll throw a fitting in the opposite valve cover and see what kind of pressures it may register. With 2 breathers, it may not have any measurable pressure over atmospheric pressure at low loads, but under boost I might see enough positive pressure to use for long term analysis on ring seal.

If nothing else, it's an easy experiment that might give me some interesting data.
 
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