4AGZE: Supercharger questions

[englishmike]

Supercharger questions

Being a new mr2 sc owner I have a few questions re the supercharger.

1. My mr2 has the bypass valve blocked, I believe this is due to sustain a higher boost level. Howcome there is a bypass valve fitted at the toyota factory in the first place?

2. How do I know if my supercharger has an upgraded pulley fitted?

3. What companies sell uprated supercharger pulleys and a matching belt?

4. My supercharger dashboard light is coming on whenever I press on the gas pedal. Someone has retrofitted a switch under the dash that is supposed to make the supercharger active all the time or just run at over 4000rpm. Has anyone heard of this? When I flick the switch either way, nothing seems to happen to the way the car drives. I can hear the SC at over 4000k under hard acceleration.

Is the purpose of the switch to disengage the electromagnetic clutch on the supercharger input shaft?

How can I remove this mod and how can I get the SC light to come on correctly? Could the light have anything to do with the throttle sensor?

[ToyotaTechGeek]

Originally Posted by englishmike

Supercharger questions

Being a new mr2 sc owner I have a few questions re the supercharger.

1. My mr2 has the bypass valve blocked, I believe this is due to sustain a higher boost level. Howcome there is a bypass valve fitted at the toyota factory in the first place?
well, the SC is clutch driven. your engine acts like an NA unless under boost, so it's not constantly under boost, the engine still needs air

2. How do I know if my supercharger has an upgraded pulley fitted?
have you installed a boost gauge?

3. What companies sell uprated supercharger pulleys and a matching belt?
NST still makes one (i believe) and others like Diaboliqe, Boost Junkies, HKS, Cusco, and Blitz will appear for sale in used ads from time to time

4. My supercharger dashboard light is coming on whenever I press on the gas pedalthis is a factory deal. . Someone has retrofitted a switch under the dash that is supposed to make the supercharger active all the time or just run at over 4000rpm. Has anyone heard of this? i've heard of some doing this as a defeat or as a way to keep the clutch engagedWhen I flick the switch either way, nothing seems to happen to the way the car drives. I can hear the SC at over 4000k under hard acceleration.

Is the purpose of the switch to disengage the electromagnetic clutch on the supercharger input shaft?

How can I remove this mod and how can I get the SC light to come on correctly? Could the light have anything to do with the throttle sensor?

i would seriously recommend buying a BGB as it seems many of your questions can be answered by a little bit of research (which means utilizing search functions and google searching along with going through the service manual).

[englishmike]

Hi, I have the BGB, it doesnt answer my questions however.

There is no boost guage installed.

[GrandpaGofast]

I'd get in touch w/ the seller, unless the mods were done previous to that owner.
Grandpa
P.S. My sc light comes on w/ all but the lightest pedal.

[ToyotaTechGeek]

Originally Posted by englishmike

Hi, I have the BGB, it doesnt answer my questions however.

There is no boost guage installed.

you'll find some of the answers you seek in the wiring diagram section.
you kind of want a boost gauge if you are unsure of how much boost you are running.

[mr2tim]

As Grandpa noted the ECU will activate the supercharger under somewhat light throttle as times and even 5th gear at very, very low RPM even.

Since our throttle assembly is mechanically operated I might suspect your switch breaks the circuit of the supercharger clutch operation. If so, your green dash light "supercharger light" will not come on indicating the supercharger is not working.

The green dash light is not directly connected to ANYTHING but the ECU which makes ALL the decisions to activate the supercharger no matter what you have heard or read on the "Internet".

If your crankpulley is 6" in diameter you have a HKS aftermarket pulley
" 7" " could have a NST "
otherwise your running stock Mike.


As for the Bypass Valve? Well, maybe you need to google that up and do some research good buddy.

You've got the Supercharged Model. You've got lots to learn.
Here's an article you can start with.

mr2tim

[GrandpaGofast]

...except - reread #4. light comes on whatever the switch position.
GP

[mr2_mk1.5]

have you checked the switch to see if its even hooked up to anything, I've seen people buy cars with a power adder switch or whatever they want to call it and its not hooked up to anything, not even wires

[ToyotaTechGeek]

Originally Posted by mr2tim

The green dash light is not directly connected to ANYTHING but the ECU which makes ALL the decisions to activate the supercharger no matter what you have heard or read on the "Internet".

i don't agree with you on this. it is directly related to throttle position (TPS)...which 'signals' the ecu. the ecu doesn't dictate the supercharger.

[englishmike]

I have not yet checked to see if the switched is hooked up to anything. It doesnt seem to change anything.



I was reading the 1987 car and driver review and it states

"If you're cuising along with the supercharger disengaged, a little pressure on the accelerator will summon full boost in just a fraction of a second. The supercharger makes the little motor feel much bigger than it is, from the liftoff right up to the 7500 rpm redline. Compared with the normally asporated engine, the blown motor has only one drawback (besides higher fuel consumption, of course); a groan from the supercharger at any speed beyond 4000 rpm. The melody just isn't as sweet."

From this text it seems the supercharged engages as soon as you press down on the gas pedal and then disengages when you take your foot off.

I was under the impression the supercharger only comes on over 4000rpm AND when the gas pedal is pressed.

It also says"Boost level is set at 8 PSI and achieved at 4000 RPM and higher, however the supercharger creates usable boost from idle through redline."

Does this mean max boost comes on at 4k rpm? Does this mean the supercharger runs from idle and comes on whenever the accelerator is pressed? If so then why is the sc light needed on the dash to tell me the supercharger is running?

I then read an article in grassroots motorsports 1988 "the supercharger is disengaged at cruising speeds by an electromagnetic clutch and air bypass system" This seems to contradict the above information.

Can someone explain this in simple terms.

With regards to the air bypass valve being blocked on my mr2, does this mean the car will use more fuel because boost is being sent? Why did Toyota fit the ABV in the first place? If its to prevent overboosting, should I unblock it? Is it dangerous for the engine?

[goldluderay]

blocking the abv will not cause boost at all times(get a boost guage)
the abv is to prevent over boost it is sussposed to keep boost at 6-8psi(get a boost)guage)

if ur s/c clutch is working good,,,,then getting on th car at like 50% throttle you should see 3-5psi(get a boost guage)

i bypassed my abv on a stock pulley car and all i noticed was it stayed at 8psi alot better with abv it varried from 6-8psi but this could be because my abv valve has a malfunction(get a boost guage)

it will not hurt the car running w/o the abv
if u are going to run a pulley and want the exrta boost the abv bypassing and other things will need to be done to get the extra boost

get a boost guage and see if the s/c is opperating correctly

[englishmike]

There was a half fitted Greddy boost guage which I removed yesterday. Unless there are aw11 specific boost guage pods then I probably won't bother with one. Guages on there own look tacky as hell.

Mr2 mk1/5 was correct. It was just a switch that wasnt even connected up to anything.

[goldluderay]

u can just have a boost guage too test the opperation of the s/c
and after u test it just remove it

or mount it in the glove box,,,you cant see it then

[8589]

'Can someone explain this in simple terms'



From the bestseller SC for idiots (like me)

At the very top of SC is a plug n play connector, just look at SC from above and is right there at your fingertips, DISCONNECT n go for a ride..the lack of SC is evident at ANY gear/speed...no noticeable difference? SC is shot

[mr2_mk1.5]

That connector is for a clutch on the charger, when the wire is unplugged the clutch cannot engage and the supercharger won't engage either, if you mean there is no change plugged in or unplugged first check all the connections for corrosion and check all the electrical, also with the car idling and while watching jumper the wire at the supercharger with a 10amp powersource right from the battery and see if the clutch engages(the outside ring will slide toward the pulley and start spinning) if it does and the charger spins over while engaged then the charger is engaged and your problem is in the rest of the circut and you should get a wiring diagram and start tracing down, if it doesn't then your gap is wrong or the elctromagnet is fried, you should be able to see a little gap between the clutch and pulley, about 1/32 to 1/16 give or take, it should tell you the exact spec in the BGB, and somone correct me if I'm wrong but to adjust the gap you remove the clutch by the bolt in the center and there is shims in there you just remove or add however many you need.

[AE25]

digging out old threads here...
one main point that hasn't been brought up is the fact that the throttle is before the SC on a 4agze. This feature alone, will not allow the SC to create boost when throttle is closed due to creating a vacuum before the SC. if there is no air to move, it cannot create boost. it is also why a lot of mass production supercharged vehicles run this way, for safety reasons. Also why if the ABV is removed, it does not make too much difference if the system is operating as designed.
But if the throttle is after the SC, (as is often done to increase performance when larger intercooler is used), a bypass valve MUST be used to vent/recirculate air. also there is the danger of an over pressurised system if bypass valve failure occurs.

So why have an ABV then? there is another function of the ABV other than to vent excess pressure. that is to equalise the pressure before and after the SC on throttle transitions and closed throttle. the benefit of this is to take the load off the system. so less belt wear, less fuel consumption, longer life etc. also helps reduce noise.

It also says "Boost level is set at 8 PSI and achieved at 4000 RPM and higher, however the supercharger creates usable boost from idle through redline."

To explain in my understanding...
"creates usable boost from idle through redline" means if the SC clutch is engaged.. any throttle stomping will result in almost instantaneous boost at any rpm.
"set at 8 PSI and achieved at 4000 RPM and higher". not sure how accurate this rpm is.. but low down in the revs you'll have rotor 'slip' where air can get past the SC rotor tip from the rotor-to-housing clearances, so there will be 'some' loss of boost at lower rotating speeds. a used/worn out roots SC will have more noticeable boost loss and will take longer to reach the full 8psi if there is wear on the tips of the rotor lobes. So the system basically gets up to full boost once revs increase enough.

I then read an article in grassroots motorsports 1988 "the supercharger is disengaged at cruising speeds by an electromagnetic clutch and air bypass system" This seems to contradict the above information.

In cruise conditions, the ABV will be in operation due to part throttle. ie anything less than full throttle will have a vacuum after the throttle. the more vacuum there is, the less the SC is able to boost (less air available to push into the engine). vacuum also pulls the ABV open. this creates a progressive off/on boost transition. once vacuum is great enough (like cruising down a slight decline where there is little load on the engine), the ecu disengages the SC as it is no longer 'in use'.

i don't agree with you on this. it is directly related to throttle position(TPS)...which 'signals' the ecu. the ecu doesn't dictate the supercharger.

do you have any evidence to support this statement?
if this were true.. the sc will stay on in any situation other than idle and deceleration, which cuts out the possibility of SC disengagement in 'cruise' situations.
According to the interwebs, the sc engages around 8" of vacuum. this suggests the sc clutch relay is operated based on engine 'load' conditions. which would suggest ecu takes afm or map signal as a basis for clutch engagement.

[toyotaspeed90]

is this a factory supercharged car?

if not... maybe the switch was some aftermarket wiring to be in place of the stock fuel selector switch....?

[mista_mr2]

MR2_AW_1988_REPAIRMANUAL.zip

download this MR2 SC bible there are some troubleshooting help in there as well, also everything else you need to test all the components of various integral systems.

[scottohno]

i have a not factory SC car and i have a weird switch too. and it has wires going to it...

im also trying to figure out the REST of the switches, but one of them i think may be either the fuel selector switch or the SC switch...

[asj]

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