What mod is this? reduces dip between change over" Warning long read

[ardasaliah]

http://www.armond30.com/adp/smartquestions.html

 

Found this -scroll down near bottom of page

 

. Sounds intrested however its a long read!!

[Clarkey]

May I suggest that you edit your post and add some carridge-returns.

 

I think the techies will be more inclined to read your post if it was abit more friendly on the eyes.

[carl0s]

Why does my 93.5-98 Toyota supra drop psi when the second turbo kicks in, and what can I do to fix it (LONG)?

 

Well, this question is one of those "etched in stone" questions where people only used information that was acquired years ago and left alone, until now. Most people would say "buy a single turbo and replace the stock twin turbos.........that will get rid of the dip", or "do TTC like MKIV.COM says........that will get rid of the dip". both of these answers are absolutely correct. Putting on a single turbo WILL eliminate the dip in pri at 4K rpm, but think practically for a second.......do you really want to do ALL that work to get rid of a dip??? Also, doing TTC WILL get rid of the dip at 4K.........but again, you loose the basic aspect that Toyota wanted the car to have......optimal power and torque over a large driving range using sequential control. Plus, you get excessive turbo lag from trying to spin both turbos at lower rpms.

This hurts the automatic guys more than the manual guys, but it is stil VERY annoying. Well, We at ADP have figured out a new, fairly similar mod to TTC to eliminate the dip. First, you need to understand how the Sequential turbo setup works.

 

Basiclly, you have 2 Hitachi CT12-B turbos mated up with both turbos connecting to a central manifold. These turbos are similar to the HT-12 turbos used on 93-95 Mazda RX-7's, also made by Hitachi. The turbines from the turbos both empty into seperate Oxygen sensor housings. the front turbo housing goes straight to the downpipe, whereas the rear turbo has a large flap-valve which blocks exhaust flow from exiting the second turbine/o2 sensor housing, thus keeping the turbine wheel from spinning.

There is also a smaller flap valve which connects the o2 housings of both turbos. This valve is used for "Pre-spool" which will be explained later. The compressor housing for the back turbo is connected to a valve box which also closes to restrict air flow from going backwards through the rear turbo compressor when it is not being used.

 

All of these valves are controlled by individual electronic solenoids or "VSV's" as toyota calls them (vacuum switching valves). These vsv's control pressure being sent to each valve's respective actuator.

Each actuator resembles an internal wastegate actuator with a vaccuum pump looking mecanism on top with a rod comming out of the bottom of it whis ic pushed out at a certain pressure. The MAIN exhaust valve's actuator can be found under the turbo/manifold combo. it has 1 vaccuum nipple and has 1 vaccuum hose connected to it. the compressor's actuator can be found beside the compressor valve box near the rear of the engine in between the intake and charge pipesby the rear turbo. it also has 1 vaccuum nipple and 1 hose going to it. The actuator for the "pre-spool" valve is located behind the rear turbo. this looks like a standard toyota wastegate actuator with 2 parallel vaccuum nipples with 2 hoses connected to it.

 

If you follow each actuator's vaccuum hoses, you will find that the vsv for the main exhaust acutator is located by the front turbo, the vsv for the compressor is located on top of the rear turbo charge pipe, and the vsv for the pre-spool actuator is located by the rear turbo intake pipe. The ecu controls when it should use the pre-spool acutator based on engine rpm and current boost puressure read via the stock toyota 2 bar map sensor. The map sensor is located on the intake manifold (engine side) near the center. It should have something like "pressure sensor" or something like that written ont it, and it has a vaccuum hose connected to it.

 

Now that you know what the ecu uses to control your stock turbos, you figure "ok....kool......I still don't know what to do, and there are no pretty pictures to look at". I'm getting to the good stuff . Just in case you don't have a boost controller yet, I would reccomend you get one. they are pretty useful to have. the stock supra only has 1 wastegate. The actuator for the wastegate has 2 nipples, and is located on the front turbo. one nipple will be connected to the compressor housing, and the other nipple will be connected to a VSV. this is the factory boost control solenoid. what you will want to do is run the compressor nipple to the "in" port on your new boost controler's solenoid, and run the "out" port on the new solenoid to either nipple on the stock wastegate actuator. PUT A VACCUUM CAP ON THE NIPPLE THAT ISN'T USED, AND ON THE NIPPLE ON THE FACTORY VSV THAT USED TO CONNECT TO THE ACTUATOR. The supra ecu will cut fuel if it sees over 15 or so psi of boost (stock boost pressure is 12 psi).

To fix this electronically, you will need to either install a Greddy BCC (boost cut controller) or a Split Second VC-2 (fuel cut eliminator). these 2 units are both hard adjustable voltage clamps, and teh BCC usu. sells for 80 bucks. the VC-2 usu. sells for 55 to 60. For a cheaper, less accurate way fof controlling map sensor output, you could install a HKS FCD or a Split Second VC-1. both are soft clamps and begin to reduce voltage at a limit of 5 volts (approximately 14.5 psi = 5 volts from 2 bar map sensors). These don't always/usually work well. If you don't want to install either of these, I would suggest doing the fuel pump voltage mod from MKIV.com to keep your input voltage to your fuel pump at a constant 14 volts. The variable voltage to your fuel pump is also partially controlled by the map sensor.

 

Now, you know how to hook up a boost controller, and you have read MKIV.com to do the fuel pump voltage mod, and you know more about why your car has a map sensor........"BIG DEAL" you say, wait.........it gets better. now, your factory ecu usu. opens the pre-spool valve for the rear turbo at 3K rpm and the big valve for the exhaust and compressor at around 4K rpm under wide open throttle. The rear turbo is allowed to spin with the compressor valve closed during pre-spool because the compressor valve box contains a reed valve which allows a pressure balance between both sides (compressor1 and 2). even though it doesnt' have the air flow, the turbo is allowed to spin enough to pressurize the rear compressor housing until it is needed. At 4K, the turbo is "supposed" to only need to be accellerated a slight ammount to compensate for beign added to the system. when increased flow work is done (downpipe, gutted cats, exhaust, intake, etc) this acceleration gap becomes BIGGER. that's why when you dynoed yoru supra, yoru car dropped about 50 hp for a second at 4K. Toyota didn't design the control system for all that extra flow, so the control is less than optimal. that's also why your boost pressure drops 2 psi or so at that point. the best way to ensure you don't burn out your rear turbo at a very early age by hitting it so frequently and changing the acceleration of it so suddenly is to either keep the turbo spinning all the time, or continue reading;).

[carl0s]

The Main exhaust actuator responds to 5 psi of pressure. the compressor actuator responds to 6 psi of pressure. Basically, what you need to do is take the 2 hoses that go to the main EXHAUST VALVE ACUTATOR'S VSV (solenoid) and connect them togehter with a hose connector. Again, this vsv is located near the front turbo. Then, do the same for the COMPRESSOR VALVE ACTUATOR'S VSV (solenoid) but use a vaccuum T instead of a straight connector. IT is good if your vaccuum T has a restrictor on one end. if not, buy a restrictor hose connector as well. Now, what you want to do is run the nipple on the T that has the restrictor on it to your intake manifold. you can find a vaccuum hose comming stright out the back or from teh side fo the manifold easily. just get a regular T and connect a hose to it. so now you have a hose connecting the t in front of the actuator for the cold side to the intake manifold. you hav eto do this becasue toyota equips teh supra with a pressure tank with a built in check valve. this pressure tank routes before both the hot and cold actuators in the vaccuum hose diagram, and only allows aor to flow one way, meaning that once you build pressure in your lines, it holds it.

The way that pressur eis relieved is when the vsv's click over and vent the pressure off. since there are no more vsv's in the system fo rsequential control, you must have this pressure balance hose. the Restricto ris important because without it, pressure would beed off way too fast if you dropped pressure (i.e. while shifting gears or decellerating for a moment). If pressure drops in the line too quickly, then both hot anc cold actuators close and your turbo still gets started and stopped abruptly. when the pressure is allowed to bleed off slowly, then the actuators will close slowly when neeed be. this way your rear turbo doesn't have to slam stopped and it doesnt' get compressor surge, but it still goes back to single turbo after a couple of seconds of no boost. this essentialy takes the RPM dependency away from the second turbo's control, and makes it strictly boost dependent. also, since yoru rear turbo will become fully operational at 6 psi, there is really no need for a pre-spool actuator anymore, so you can kinda ignore it (it won't hurt anything to leave it hooked up, it just wont' do anything important. you will notice that your car is now louder at idle and when you fre-rev the engine. you may also notice that the engine seems to rev a bit faster than before. this is because the stock ecu sometimes leaves the car in twin turbo mode after boosting, so when you calm down after a run, the exhaust flowing through both turbos silences the car a bit. now, you can guarantee, that if your car is BELOW 6 psi of manifold pressure, exhaust is ALWAYS ONLY flowing through the front turbine. this results in a little more backpressure under little/no load and a slight bit more torque (hince quicker revs).

It sounds mean. also you will notice that boost doesnt' fall off when the second turbo starts (6 psi). that is because the turbos don't have to spin that fast to support 6 psi, so there isn't as extreme of a change in momentum for the rear turbo, making your rear turbo last longer. also, you dont' have to worry about trying to eek 12 psi out of the front turbo till 4K. this much power creates HIGH backpressure, and realistally isn't that great for your rear turbo in the past (which only felt the thrust pressure at that time, wearing out the turbo thrust bearings, reducing their life). Now, you still have sequential turbos, you have no dip, your car is louder at idle, it revs faster, and there is no question that the rear turbo is working at optimal conditions ad maximum momentum. This results in an increase of hp also. you have to be VERY CAREFUL now when driving. the stock supra 6 spd with this mod has a tendency to break traction in 2'nd gear EXTREMELY EASILY, and could get you hurt or killed. With Basic upgrades, plus this mod, you will be making more power than stock original vipers(with pump gas mind you), and the car must be driven as so. you can also easily toggle between this mod and True Twin turbo by blocking the pressure balancing hose as described above by either removign the hose and putting vaccuum caps on both t's or just replacing the t's in the manifold hose and the actuator hose with straight connectors. TTC gives an infanently smooth curve, but still remember you will have more lag and it won't be sequential (which is one of the coolest technical aspects about the car)

 

If you have done the sequential mod listed above, adn the fuel pump mod from MKIV.com, and the boost controller install as suggested above, then the simplist way to eliminate fuel cut at 15 psi is to put a check valve in place before the map sensor. The stock mass air flow sensor is responsible for fuel calculation, so you shoudl see no ill effects from this. we have run up to 21 psi with a supra in this form with no problems. Now you know even more USEFUL information about houw your supra works, and you have accessed some of the hidden power from yoru car. Personally, I think the car responds better in TTC while racing, but the sequential mod does make power more usefull for daily driving.

[carl0s]

Yup, that sure is long. Not very to-the-point but hopefully someone technical with the time and inclination will be able to give some useful comments.

[Alex]

Someone give us the edited highlights.

[carl0s]

I think this is the actual mod:

 

Basically, what you need to do is take the 2 hoses that go to the main EXHAUST VALVE ACUTATOR'S VSV (solenoid) and connect them togehter with a hose connector. Again, this vsv is located near the front turbo. Then, do the same for the COMPRESSOR VALVE ACTUATOR'S VSV (solenoid) but use a vaccuum T instead of a straight connector. IT is good if your vaccuum T has a restrictor on one end. if not, buy a restrictor hose connector as well. Now, what you want to do is run the nipple on the T that has the restrictor on it to your intake manifold. you can find a vaccuum hose comming stright out the back or from teh side fo the manifold easily. just get a regular T and connect a hose to it. so now you have a hose connecting the t in front of the actuator for the cold side to the intake manifold. you hav eto do this becasue toyota equips teh supra with a pressure tank with a built in check valve. this pressure tank routes before both the hot and cold actuators in the vaccuum hose diagram, and only allows aor to flow one way, meaning that once you build pressure in your lines, it holds it.

[Alex]

Is this the blue spaghetti mod then?

[carl0s]

Is this the blue spaghetti mod then?

 

Dunno. That was Ian C's brainchild wasn't it? Hopefull he'll be along soon

[Alex]

Not so much HIS brain child but yeah it's his post.

[SimonB]

Can't be arsed to read all that right now and figure it out, but it's not the blue spaghetti mod. It's something to do with bypassing the VSVs that control the IACV and EGBV so the actuators open on pressure and not under the control of the ECU.

[JohnA]

[...."ok....kool......I still don't know what to do, and there are no pretty pictures to look at". I'm getting to the good stuff . ....I would suggest doing the fuel pump voltage mod from MKIV.com to keep your input voltage to your fuel pump at a constant 14 volts. ........"BIG DEAL" you say, wait.........it gets better. .

...does it?.....

[JohnA]

...the simplist way to eliminate fuel cut at 15 psi is to put a check valve in place before the map sensor. .

...oh dear...

I've tried this early on, and I have now deleted every reference of the 'mod' because it is so very dangerous. AFRs 16:1 under boost anyone?

[carl0s]

...oh dear...

I've tried this early on, and I have now deleted every reference of the 'mod' because it is so very dangerous. AFRs 16:1 under boost anyone?

 

For a minute there I thought you were quoting ME :o (Wondered if I'd been posting in my sleep ).

 

I was briefly told to do the MAP mod.. then later told that it keeps the fuel pump high, amongst other things.

[JohnA]

The fuel pump mod is moronic in it's own right.

Forcing a lot more fuel through the rail when it is guaranteed that it cannot be consumed, can only succeed in overwhelming the fuel return.

 

The early US ECU has a funny fuelling dip during changeover, most likely for emissions testing conformity.

Performing the same 'mod' on a EuroSpec or a JSpec only shows lack of understanding of fuelling basics, and herd mentality.

 

(if the 1000bhp US beasts do it, hey...it must be kewl.

Every man and his dog have 1000bhp supras over there - give or take)