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Vacuum

10K views 50 replies 22 participants last post by  ONE BAD 442 
#1 ·
Help me understand this concept of "tuning" or monitoring vacuum on a nitrous set up? I have heard guys on here talking about it, referring to losing vacuum because of detonation(?) Where is it being measured at? Intake manifold? Crankcase?
If i understand a motor at WOT should have little to no vacuum in the intake?
:confused:
 
#5 ·
if you run a racepack the crankcase vacuum signal can tell you when or if a cylinder is rich, pinched or hole'ed
 
#11 ·
it will look like a quick signwave decending to a lower than normal vacuum reading, yes you should be able it pick up a map sensor and monitor this but the lowest made is -15 to my knowledge.......
 
#13 ·
I'm interested in knowing this as well, because my NOS Launcher instruction sheet says that in race car setups with a vacuum pump, you can connect the integral MAP sensor to a crancase vacuum source and log the vacuum signal during a run and that vacuum signal spikes will indicate detonation. Is this true? Would that be so with mild detonation, or would it have to be very serious detonation?
 
#14 ·
Hope i dont sound stupid here. If i run a vac pump on my motor, and it has a pressure relief valve set at say @ 14in,If a single cylinder was to detinate would i see that on a log? Does the relief valve somehow let the motor maintain 14in. If it does how bad would the detonation have to be to upset the valve.

Thanks
 
#15 ·
That's what I'm wondering as well, as every vacuum pump setup I've seen uses a vacuum relief valve to regulate the vacuum in the crancase. However, I suppose it takes a few micro seconds for the valve to respond and regulate pressure if there is a spike (up or down) in vacuum and the MAP sensor can see this. What I'm wondering is, does this occur with even mild detonation, or does it have to be pretty serious detonation to rattle the rings enough to change crankcase vacuum? Obviously, if it happens with mild detonation then it would be useful to use a MAP sensor to log for it, but if it takes serious detonation, then it may already be too late when you see spikes in a log.:confused:
 
#17 ·
You will see even the slighest hint of ring flutter, in a vacumn trace, especially with a RacePak, because the sample rate is very high. As someone else said, the motor should maintain, or make vacumn during a pass. If it is dropping, or has dips, the motor is NOT happy.

With all 3 kits spraying on our 632, it has 10" when he drops the button and 13" at the stripe.

Think about it, on a nitrous motor, with a gas ported piston, the more cylinder pressure you make, ie, more nitrous, the better the motor should seal. If this is not happeneing, there is a reason. As I mentioned in another thread, about what a plug "should" look like, you will see an unhappy motor MUCH quicker in the vacumn trace, as opposed to watching plugs. Rich, or overtimed, will unseat the rings and even the slighest flutter, will show up in the trace.

Monte
 
#23 ·
If you have a 7531 box you can get a 1 bar sensor and monitor your vacuum. MSD used to sell it but I've heard they no longer do, however you can use a GM sensor and modify the plug connection slightly so the MSD cable can plug into it. We use a RacePak vac sensor that's hooked to a fitting at the back of the intake manifold floor.
 
#25 ·
its not a cure all but just another club in the bag to find the sweet spot for your combo and monitor if you are having an issue.......
 
#29 ·
Yep, The NOS Launcher is the most versatile progressive conroller out there, IMHO. As well as being able to program either time or RPM based progressive curves, you can log vacuum (it has a built in map sensor with can be used to switch on/shut of the nitrous) and AFR (with a plug in module and O2 sensor - which I am about to install). You can load files to and from your laptop, and the LCD touchscreen also has an SD card that you can store your files on. A really neat feature is that you can program it to shut off the spray if it exceeds a set AFR. This an awesome little piece of equipment.
 
#33 · (Edited)
No, unless you have a block that does not have the opening for a block-mounted fuel pump. I think some of the GM blocks look like they have a mechanical fuel pump mount but it is blocked inside.


1 bar is for no boost.
2 bar is for up to 14.7 psi and 3 bar is for up to 29.4 psi of boost (or something similar).

To measure crankcase pressure you want a 1 bar sensor.
 
#31 ·
If you have a 7531 box you can get a 1 bar sensor and monitor your vacuum. MSD used to sell it but I've heard they no longer do, however you can use a GM sensor and modify the plug connection slightly so the MSD cable can plug into it. We use a RacePak vac sensor that's hooked to a fitting at the back of the intake manifold floor.
What is the difference between a 1 bar, 2 bar, or 3 bar sensor? I have a 7531 and want to monitor vacuum and not sure which one to use.
 
#35 · (Edited)
1 bar= -30 to 0 atmospheric pressure
2 bar= -15 to +15 ap
3 bar = 0 to +30 ap
i think thats how the gradient works
also a ton of factory gm vehicles have them as 1bars and 2 bars are availible in salvage yards for testing purposes.....once you get the feedback set up you can toss cash for spanky new stuff.....plus you can get the male side connector for the map from the donor car........
 
#38 ·
for straight motor (no boost) you are losing -30 to the -15 readings, you will only be able to track -15 to 0 with a 2bar
 
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