As I go further into the cooling mods of my srt, the more I find out. I wanted to pass the following info on so that there will be less confusion about the operation of our car's Supercharger (s/c) .

Many speak about the s/c cutting in below 3000 revs etc, well yes, if starts almost immediately. The intercooler circulation pump runs constantly upon start up and the reason is the supercharger is engaged as soon as you start to drive, FOR REAL.

Let me try to describe it this way, the supercharger does not run when the car comes to a stop, wheels not moving.

When you start the car, the supercharger will not run if you rev the motor in neutral. When you go in gear ( wit a buddy driving ), you will see that if you torque up the transmission using both feet, as you goose the throttle the s/c will kick in, and when you let off the gas it will back kick out.

In gear, driving very easy the supercharger will not kick in until about 1500 revs, then its on for the trip. Coasting for about 20 seconds does not kick the s/c out from my indicators, only when you roll to a stop.

This should get some scratching their heads, and I hope that I have gotten useful information to the forum. As this first came to light, I was taken back a bit myself but it makes sense. You dont wanna kick the throttle, have the transmission downshift, the engine rev up and then apply the clutch of the supercharger.

City diesel busses have their superchargers operate full time. [ BTW: Thats where hot rodders first got their supply of blowers for the hot rods. ]

To prove this, I added a LED across to the supercharger and another across the I/C pump some time ago, watching their operation during drives and traffic.

Enjoy; Woody

 

I'm going to respectfully disagree. I know it would kick in when accelerating but I'm pretty sure that while cruising at say highway speed with little or no load demand on the engine that the supercharger would disengage as long as the RPM signal permitted so. The only way to tell for sure would be to datalog the MAP sensor and see if there is more pressure then the surrounding atmosphere.

 

Thanks for the heads up woody... I wonder if a cutout switch on the s/c would increase gas mileage on a long trip... hmmm...

So about 1,500 RPM is the switch on point eh... yeah, that's pretty easy on the drive line then. Also, if that's true, cruising at highway speeds keeps the s/c on because the RPMs are just above 2,000 or so.

 

Well I wrote up this ditty so that we could get this information out there.

Iam here to tell ya that the clutch magnet on my SRT-6 2005 is fully on as stated in the above article. I had to do some checking to prove it, so do the following, please.

Get your bud or squeeze to run up the motor in drive without moving and watch the S/C clutch kick in and out in concert with the gas pedal. As my son said early on : NO TRICKING. You won't have to go as high as 2000 revs also........................

Its a bit of a revelation is it not? Thats what I do is to test the boundrys. I found another in that I have gotten over the edge with my 170 degree stat, too cold for weather below 63 degrees, more on that later.

Remember that once it (s/c) kicks on it won't go off till you stop the vehicle, even if driving at 1000 rpm, LEDS dont lie. Its on regardless of the revs when set, it's off when stopped or out of gear. I will have to test this when driving and I shift into neutral on the roll at speed.



TA TAA, Mate

Woody

 

There is really no switch-on RPM (unless it has not already kicked in by 2,900 RPM, then it will engage by default). I think it's more throttle position and/or load based. When my car is warm, I can get the supercharger to engage at about 600-700 RPM (according to tach) while loading up on the brakes.

 

Best way to tell when your SC engages

Get a boost gauge and watch the needle go from vacuum to boost when you get on it and back to vacuum when you let off. Drive like a law-abiding citizen and watch the needle stay in vacuum.

Get an IAT gauge and watch the temps rise when the SC engages and peak when you stay on the gas. Then watch the temp slowly drop when you let off the gas and then stabilize..

 

I just went out to check the coasting response as it relates to the supercharger. Please remember that I am measuring the voltage applied to the clutch of the supercharger unit. See the photo, the leds are powered by the power source feeding the pump and the supercharger clutch

THe supercharger is off when:

The car is off
The engine is on and the transmission is in park or neutral (idle) or in reverse.

The supercharger has the clutch power on, ie it's ON

When the car is in gear, not moving and the throttle is above 1500 revs.

You are driving forward and the engine is above about 1500 rpm the first time. It stay on until:

You come to a stop or
You shift out of gear while still moving
It goes back on when you go back into gear and the transmission re-engages or
You coast over 30 seconds ( not speed related )

The manifold vacuum is possible with the supercharger clutch engaged, because the throttle body controls the air ( mass flow ) into the "engine". If the engine did not have a vacuum with the supercharger running the motor speed would be high and largely uncontrollable. Try to take the throttle body off of the engine and start it up for less than ONE SECOND or it will over rev terribly due to the loss of air control.

I expect some 'blowback' on this topic because it is AGAINST the common wisdom, but it is true. Just meter the cable feeding the clutch and you will see.
This is why my temperature reading did not make sense because I thought the s/c was under control of the driver (silly me) and therefore on and off etc.

Busses are full time superchargers and so are hot rods, they have no problem, its just a pump to add more air (density) to the motor to increase the output power.

The left LED is across the clutch magnetic coil
The right LED is across the I/C pump windings

ENJOY, Woody

 

My favorite martian! Heh, heh...he's supercharged. Great work Waldig!

 

Full time supercharges and Turbos have by-pass vavles or wastegates. Our SC's don't

These pictures were taken in sequence - from what you are saying - there is no way at 70 MPH my boost gauge could be showing vacuum.


Just cruzing at 70MPH


Kick'er down an jump to 100MPH



Crank' er up to 115MPH



Max'n er out WEEEEEEEEEE!

 

Turbos like my old super sixty have wastegates to limit boost typically for detenation.

Some superchargers have bypass valves but most don't like the old 6-71 GMC blower.

It is totally possible for the supercharger to be running even at 70 in a partial vacuum, because you are making enough power to satisfy the needs at that road speed / load. Open the T/B more and the air density will increase until the pressure goes atmopheric and then into the boost region as more power is desired.

Please check at the driveway to see that the S/C kicks in when torquen the transmission, like 1500 rpm. Also meter the clutch to see for your self. Note the power is positive on the brown wire and negative on the other, reversed from the I/C pump motor color code. You have to measure differentially across BOTH leads, not from chassis to one lead or the other.

Wee this is going to be interesting as more add in on this topic. Where's Splinter???

Hot damn, Woody

 

Woody - I'm going to respectfully disagree - go make myself another cocktail - put on my new Jazz CD - come back to the computer and reply to the PM that you sent me a yesterday on a different subject. (I have a back log of PM to answer - so much for going to concerts)
I will end with this - how can my boost gauge go from vacuum at 70 MPH to 18 PSI at 100MPH if it was engaged in both pictures? There is no partial SC engage - its either on or off - with no bypass valves to bleed the uneeded PSI...

Also - My boost gauge never reads 5 PSI or 8 PSI -- It either reads vacuum or 10+ PSI which tells me once my SC kicks in - - its WOW time!!!

At what voltage does the SC clutch kick-in?

At what voltage does your LED light up?

Perhaps there is millivolts on the wire and thats enough to light up your LED?

 

The high intensity leds (RED) have a zener voltage about 2.2 volts and I added a 1200 ohm resistor in series to limit the current. My Fluke indicates about 13 volts, sorry it really is on, give me your address and Ill send you a couple of leds and resitors if you wanna check it out that way.

It is slightly amazing but you have to measure it possibly to get to the truth. Also watch the clutch operate in drive with a bud working the loud pedal while easy pushing at 1500 in drive, stand on the side.

I WOULD NOT HAVE POSTED IT TILL I CHECKED IT MORE THAN ONCE. I HAVE MADE MODS THAT DONT WORK AND THEY NEVER SAW THE FORUM. DONT TAKE MY WORD FOR IT UNPLUG THE CONNECTOR, ADD A FEW THIN LEADS TO THE PINS AND THEN GO FOR A SLOW AND SHORT SPIN TO SEE FOR YOURSELF, I KNEW THAT IT WAS GOING TO GET ATTENTION. ENJOY..........wEEEEEE

 

If the supercharger is almost always engaged then what's the purpose of having it driven by a clutch?

 

Why not just "hard" wire to be on all of the time?
I'm guessing gas mileage.
The 8/71 on my (496ci) Chevelle is always ready for action!

 

I've never inspected the internals of a screw-type supercharger, but I assume it is made to very tight tolerances. I do know from tinkering with carberators how quickly an engine loses power if you choke or throttle it. It would seem that a non-functioning s/c must really choke an engine at any rpm above idle. I can see the logic supporting waldig's findings, since our engines have power at any operating speed.

Brianbrave, as for boost or vacuum readings on your gauges, maybe the position of your sensor determines your reading. Upstream of the intercooler you might get higher boost readings because of the restrictive nature of the cooling passages. Downstream from the i/c you might read negative pressure because the throttle plate is wide open and the pistons are sucking air like crazy but the i/c is limiting the supply. The dynamics of the system are a bit beyond me, so this is just a theory. There are a number of you who would know if it has merit or is just caca.

 

You will see both vacuum and boost with a "blower". Depends on the load on the engine. In my Chevelle while I'm cruzin' or slowing down I see vacuum. As soon as you mash the gas you see boost.

 

Look again at this picture

I'm doing 70 MPH which means I'm running around 2200 engine RPM's (below every ones current notion of when the SC clutch kicks in)

With a 185mm crank pulley my crank to SC pulley ratio is 2.5

That means in the above picture - my Supercharger is spinning (if it were engaged) at 3,200 RPM - - and it's not even making 1 LB of boost?

How can that be done with out a bypass valve to bleed off pressure? I tore my SC apart - there are no bypass valves. It's direct linkage.

 

Where is the sensor located? What you are describing sounds similar to the reaction of my vacuum operated wipers on my old panel truck. It could use some boost!

 

The position of the throttle body (TB) controls the amount of air admitted to the "engine". The s/c is in the stream and is constantly turning to compress the air flowing thru it.

The condition that causes the manifold to have a boost or vacuum condition is the balance of the air supplied versis the amount consumed by the cyclinders. Internal combustion engines typically operate at high vacuum, ie up to 20 inches of mercury while running.

My 440 6 pack is 15 inches as I cruise at 50 mph. This is because the motor is being partially charged and the cyclinders are not operating at their full potential, I am at cruise. At wide open throttle I have 1 or 2 inches of vacuum and thus my volumetric efficiency (VE) is less that one. This inspite of 3 carbs that have a flow rate rated at 1050 CFM. Carbs aspirate fuel due to flow and the movement of air is the result of a pressure differential.

The TB controls the air and thus the motor speed, at Idle it has a high vacuum and as the power output is increased the vacuum falls until the net manifold pressure becomes positive and therefore becomes a boost condition. The s/c is after the TB and is along for the ride,when we go hard it assists the engine by drawing in more air and charging the cyclinders above atmospheric pressure to raise the VE above 1 so that we get 300+ hp out of 3.2 liters.

I forget the conversion, my pinto was 2 liters at about 122 inches so were in the neighborhood of 200 inches. And were making 300 hp, thats way over a VE of one to achieve that. At a boost of about 15 psig we are looking at an angine that thinks it is 400 cubic inches due to the 2 atmosphere intake charge pressures.

Bottom line is the I/C pump runs almost immediately from a cold start because the car is cooling the charge to reduce the intake tempertatures. The heat is part is from the abadetic compression and losses in the s/c.

Its too early to spell,sorry. The s/c cooling is marginal at best and from the interest in this thread, Ill let it sink in before I write up my styck about the overall cooling efforts I have now completed. Our cars are simply warm air engines and the simple act of adding heat to the atmospheric gases (air) in the cyclinders causes that air to expand.

As the air expands it liberates energy that we use to turn the wheels and gizmos in our cars. To make more power we only need to increase the amount of heat added(fuel, in the proper ratio of 13 so to one to air), the amount of air heated (displacement and or boost), the rate this happens (rpms), and the efficiency of this process (design of the internals).

Later, Woody

 

Hey Woody, I applaud your efforts in providing the information about the SC. I tend to believe in real data. If power is applied to the SC clutch then the clutch is engaged period. Now if there is some other mechanism bleeding off the excess pressure then I can understand the boost/lack of boost issue. Maybe we are missing something? I know from running turbo cars for many years that you must bleed off execess boost when the throttle is closing. Otherwise boost spikes etc. and that is never good. This is an interesting issue, keep up the good work from everyone involved in helping us understand. You have me curious and although I have too many projects at the moment this might be fun to investigate!