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Bypass actuator in magnacharger

7K views 20 replies 8 participants last post by  Blown7 
#1 · (Edited)
I read that if the actuator is stock, no vacuum and leads to no boost.
But what if the actuator is the other way around. What if it was loose than normal state? What happen then? How is the boost behavior?

The reason I am asking is that Shem I am cruising or 1st or 2nd gear I feel the boost is kicking in with a minimum throttle which is annoying me.
Also I remember the installer told me that the actuator was stuck and they had too fix it.

I am wondering if the actuator and the sensitivity of the boost are related to each other.

What o you guys think?

Note:
On a stop light my MAP is 9-10 psi and BARO is 29.75 hg
On wot my MAP is 21 psi and BARO is the same 29.75 hg
And while cruising or in 1st or 2nd I feel the boost kicks in with normal throttle press and my MAP goes up to 16-18 psi and BARO is the same 29.75 hg
 
#2 ·
The Bypass actuator does control when the bypass closes, which does dictate when you start building boost.

From Magnusons website:
When vacuum is high (idle-cruising) the actuator opens the bypass valve, equalizing the vacuum pressure throughout the system. When boost is required (accelerating) the vacuum is decreased and the bypass valve instantly closes, causing pressure to increase into the cylinders. This equalized vacuum condition virtually eliminates the normal parasitic power loss of a forced induction system.

It's not uncommon with a positive displacement blower (Magnuson, KB, Whipple, or even a turbo for that matter) to get part throttle boost early in the pedal travel. When you say you feel the boost kicking in, what do you mean? Do you see it on the guage or do you actually feel the truck accelerate more without any pedal input?

From your MAP number (I'm assuming you ment MAP not MAF since the Hemi doesn't have a MAF sensor), your Barometric pressure is approxiamtely 14.61 PSI. When you go WOT you are at 21PSI. 21psi (MAP at WOT) -14.6psi (Baro) = 6.4 PSI Boost at WOT. Using the same math for your part throttle MAP readings shows 1.4-3.4 psi of boost at part throttle. That is completely normal for a positive displacement supercharger or Turbo system. Centrifugal superchargers (Vortech, Paxton or Procharger) dont' do this because they rely on engine speed to build boost. At lower cruise speeds, you are not spining the SC fast enough to build any boost so it behaves just like a normally aspirated vehicle.

Alot of good info over here

Part1
http://www.musclemustangfastfords.com/tech/mmfp_0412_ford_modular_motor_forced_induction/index.html

Part2
http://www.musclemustangfastfords.com/tech/mmfp_0501_ford_modular_motor_forced_induction/index.html

J
 
#8 ·
Thanks for the links JB. Real interesting reading.
 
#7 ·
The only time my jeep will do this is when climbing a hill from a stop etc. Otherwise I can cruise around all day long without boost at low RPM.


Sent from my iPhone using Autoguide
 
#9 · (Edited)
JB, thanks for great info and yes I meant MAP not MAF.
On my driving style, I can never be in hurry or I will spin the tires. On other words, I don't really need to step on it hard to start spinning. I will just let the rpm reachs 1.5k fast on 1st gear and it will noticeably spin.

JB, how accurate is this formula against the actual boost gauge?
On dyno it made 5.8 psi and this is the best my installer could reach as he said.

Also to answer your question, I feel the boost and also the MAP reading goes up.

@AL, let say you are in hurry and you are on a stop sign. Lights goes green and you drive just a little fast on 1st gear. Do tires spin? Also when do you start feeling the boost is kicking ( rpm wise)?

Thanks guys
 
#13 ·
Maansy, what are you trying to accomplish? As I explained above, being in boost at light throttle is a product of a Positive Displacement Supercharger. The spring rate of the bypass valve is actually tailored to each application at Magnuson. Buying a generic one may actually cause you more tuning issues. Have you spoken with Abdullah about your concerns?

J
 
#11 ·
Note:
On a stop light my MAP is 9-10 psi and BARO is 29.75 hg
On wot my MAP is 21 psi and BARO is the same 29.75 hg
And while cruising or in 1st or 2nd I feel the boost kicks in with normal throttle press and my MAP goes up to 16-18 psi and BARO is the same 29.75 hg
OK quick primer........

Chrysler engineers designed the NGC PCM to only sample Barometric pressure on start..
jthe juries still out on when and how many times the PCM will update that given the same sensor is used for Manifold Pressure and Ambient Barometric pressure (can't get an accurate ambient Barometric pressure when engines running)


Although the ambient pressure shouldn't change quickly unless a storm front passes thru when the engines running.

Your Baro will never read right anyway as the Jeep PCM calibration doesn't understand boost like a SRT4 PCM would.
 
#12 ·
Actually Baro gets updated at WOT also Jeff. That is when MAP is closest to what actual ambient pressure is. There are some tables that account for pressure drop across the aircleaner to get it more accurate. When you start playing with new air induction systems it throws the calculation off but it's only a few kPa so it's not a big deal.

That being said, when you add forced induction to a late model hemi, you need to turn off the Baro learning so it will not learn Baro at WOT or else it will learn an artificially high number (whatever your boost is actually). Under this instance, it will behave as you describe and only update at Key-on.

But then again, what do I know ;-)

J
 
#18 ·
#16 ·
I told him to do that in another thread.
 
#19 ·
I think humidity plays a role as well.
On a very rare case I saw BARO dropped from 29.85 to 29.75 driving to different city (almost 2hrs away) without restarting the engine again.

Knowing that temp was almost the same and humidity was 20% less in the 2nd city.
 
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