Help. Eaton on a Probe

benfica88

Registered User
Hi, i have a 94 probe gt v6 2.5l. I mounted a eaton m90 from a SC a while some months ago. Ever since the initial install i've had boost dropping problems. I get about 6-7 psi with a custom intercooler and as i hit about 4500 rpms it begins to drop off. By the time i hit 6500 its like at 2psi. I've checked for leaks and everything else. My final conclusion is that maybe the supercharger is ruined, even though i don't know if that is possible, or the belt is slipping at high rpm's.I've checked it and eveything seems good, i don't hear any squeeling either... I aslo know some other people who have a m90 on a probe and they don't have this problem. We rebuilt the charger before the install so i asumme everything should have been good. Another note it the more boost i make,the lower it drops. for example i hit 9 psi on a really cold day once and it ended up droppig to 0 psi. Help! I can't figure this out.

p.s.Also my exhaust is about 2.75'' is that too small, maybe increase it to 3"?
 
While a certain amount of boost drop is expected, this does sound excessive. My personal suspicion is belt slip, I think a couple of other things should be checked into.

What the pressure drop is telling you is that the engine is more able to move air than the air can enter it. At least at the location where you took your pressure reading, that is. Where is the throttle body, before or after the SC? On the inlet side of the SC did you use any rubber hose?

Anyway, assuming that nothing is being sucked closed I would want to see pressure readings between the SC and the intercooler, intercooler and intake if the TB is ahead of the SC, if the TB is still on the intake then I'd look for a pressure drop across the TB.

It also sounds like you haven't got it pullied very aggressively so that might perhaps be the issue, but I'd only look into that after the other items checked out.

Also, more efficient exhaust tends to lower intake pressure unless the exhaust is no restriction at all. As a rule forced induction is more able to move air into an engine than exhaust systems can move it out, so you get a certain amount of exhaust backpressure showing up as "boost".
 
drive ratio

have that figured ? with your pulleys 2 to 1 ratio ... it could be ..not spinning enough... to move the volume air ....needed at higher RPM ...dave
 
What have you done with the two-stage manifold? I would have it open the short runner tubes as soon as you go into boost instead of waiting to whatever rpm they normally switch at. I could be that your motor's efficiency at higher rpm requires more blower rpm. Are you sure that the bypass is staying closed? Is it possible that the bypass is connected to the vacuum source that normally actuates the butterfly in the intake manifold?
 
I dontthink the motor is going to swallow up that 7psi at high RPMs..Possable..But I just cant see it..Probably belt slippage

However I wonder how he has the blower setup drive wise...Id up the ante a lil with the boost

What size blower pulley do you have?
Crank pulley???
 
DamonSlowpokeBaumann said:
I dontthink the motor is going to swallow up that 7psi at high RPMs..Possable..But I just cant see it..Probably belt slippage

However I wonder how he has the blower setup drive wise...Id up the ante a lil with the boost

What size blower pulley do you have?
Crank pulley???

Thanx for your help. you guys put out some pretty good points. I should have been a little clearer though. Ill make this less of a mystery. First the setup is in this way. Air fitler->blower->intercooler->tb->Manifold. Pressure readings are at manifold. And it is loosing boost at the point. You can literally feel the car go back to stock form and i have a dyno that also prooves it.I have rubber hoses all around but they are all double clamped very tightly.(i had no idead these blew so much are and they kept popping off). I also thought it could have been the pulley ratio but a couple of other guys have done this and they get in the 6-10 psi range but obviously withought any dropp off (this is with stock probe pulley and stock from SC pulley).I actually hae a normal by pass and blow off valve. For some reason the by pass would not vent enough air by itself. I thoughg the valves could be leaking but i tested them one at a time and still hade the same issue.I also tested them and they seem to be worknig properly, they close when i give it gas.Dave if your refering to the VRIS as the two stage i completly removed that crap as for boost its in the way. I guess i have to might have to check out the belt slippage although i do not hear any noise at all. But then again these blowers are extremly LOUD withought being attacthed to the manifold. I get people literally telling me my car sounds like a F1 race car.

I'm trying to get a digital camera to post pics.
 
The reason that the bypass was not venting enough air is that you are running the blower under boost at all times. The bypass is only intended to operate while the blower is under vacuum. The stock bypass cannot flow 4-500 cfm.

I suspect you are having the bypass or your blow-off valve opening under boost. The supercharger simply does not stop working. I don't see any other explanation. In order to achieve a -0- boost condition it would require a grossly loose belt.
 
XR7 Dave said:
The reason that the bypass was not venting enough air is that you are running the blower under boost at all times. The bypass is only intended to operate while the blower is under vacuum. The stock bypass cannot flow 4-500 cfm.

I suspect you are having the bypass or your blow-off valve opening under boost. The supercharger simply does not stop working. I don't see any other explanation. In order to achieve a -0- boost condition it would require a grossly loose belt.

Unless you are spinning the SC pulley counterclockwise :rolleyes:
....dave
 
vba928484c6.gif
 
Last edited:
Do you have a blowoff valve of a bypass?..Yeah zero boost you would have to be slipping a hell of a lot...Check for black dust around your blower snout
 
XR7 Dave said:
The reason that the bypass was not venting enough air is that you are running the blower under boost at all times. The bypass is only intended to operate while the blower is under vacuum. The stock bypass cannot flow 4-500 cfm.

I suspect you are having the bypass or your blow-off valve opening under boost. The supercharger simply does not stop working. I don't see any other explanation. In order to achieve a -0- boost condition it would require a grossly loose belt.

Ya i thought that could have been a problem, but like i have both the bypass and a turbo xs blow off valve. I tried one at a time and it was still the same problem. I even verified to make sure the bypass was working right and it opened under vacum, closed under boost. I drove the car for about 3 months before winter and no belt dust at all. :confused:

Also, the weird thing is it doesn't always go to 0 psi. The more boost i make the more it looses. When i hit 9psi (wich was in the middle of the cold winter) it dropped to 0 psi. But i usally make about 6 psi and normally drops to about 1-2 psi.

p.s. could a intercooler cause this problem?
 
benfica88 said:
p.s. could a intercooler cause this problem?

Not impossible. If belt slip is not an issue and other similar setups make more boost then that leaves a (big) restriction. thats' why I would like to see pressure readings between the SC and intercooler, intercooler and TB, along with vacuum readings between the SC and the air filter assy.

FWIW, I really think you should move the TB to the inlet side of the SC ASAP, and then run your bypass between the inlet of the SC and the tube between the intercooler and intake. This is like the SuperCoupe set-up and like that set-up it will dramatically reduce parasitic drag of the SC in off boost conditions. Just for grins one day I forced the bypass valve closed on the Cougar at idle. Immediately, I heard the SC make a burrrrr sound and the engine bogged from the increased load, and that was with a closed throttle! (ie minimal air available to the SC)

Consider what's happening right now when you're part-throttle. The SC is still moving air at full capacity but it's stacking against a partially open throttle plate. This is resulting in a lot of unnecessary heat build up in the intake tract, perhaps to the point of detonation until that heated air stacked between the SC and the TB gets used. This assumes, of course, that you're using a SuperCoupe SC that does not have an internal bypass like the later model Lightning and Cobra units do. Anyway I would think that if you managed to fab up the SC install, then fabbing up a TB before the SC should be easy

Oh I don't know what you've got on the inlet side of the SC but if it's a rubber hose then it needs to have some sort of wire reinforcement since it is possible for the hose to be sucked shut if it isn't reinforced. Little bit of SVO trivia there :)
 
Parker Dean said:
Not impossible. If belt slip is not an issue and other similar setups make more boost then that leaves a (big) restriction. thats' why I would like to see pressure readings between the SC and intercooler, intercooler and TB, along with vacuum readings between the SC and the air filter assy.

FWIW, I really think you should move the TB to the inlet side of the SC ASAP, and then run your bypass between the inlet of the SC and the tube between the intercooler and intake. This is like the SuperCoupe set-up and like that set-up it will dramatically reduce parasitic drag of the SC in off boost conditions. Just for grins one day I forced the bypass valve closed on the Cougar at idle. Immediately, I heard the SC make a burrrrr sound and the engine bogged from the increased load, and that was with a closed throttle! (ie minimal air available to the SC)

Consider what's happening right now when you're part-throttle. The SC is still moving air at full capacity but it's stacking against a partially open throttle plate. This is resulting in a lot of unnecessary heat build up in the intake tract, perhaps to the point of detonation until that heated air stacked between the SC and the TB gets used. This assumes, of course, that you're using a SuperCoupe SC that does not have an internal bypass like the later model Lightning and Cobra units do. Anyway I would think that if you managed to fab up the SC install, then fabbing up a TB before the SC should be easy

Oh I don't know what you've got on the inlet side of the SC but if it's a rubber hose then it needs to have some sort of wire reinforcement since it is possible for the hose to be sucked shut if it isn't reinforced. Little bit of SVO trivia there :)

that sounds like a good idea about the readings. What would i use to stick my gauge int here though? Is there certain fittings i could use?

also just for fun, i also tried the charger witht the bypass closed all the time :D . There would would start and die out within a second everytime.

I also wanted to try the TB on the inlet before the charger but I don't know if its worth the work and $$. I mounted the charger right in front of the engine, very far from the throttle. To move that thing im assuming it would be kind of hard since there are some electronic components that have to be moved too and are not easy to deal with. One being a p.o.s. called a VAF instead of the usual MAF and this thing is a pain. Some people have tried putting it on the inlet of the blower but the car ran like ****. If it doesn't have accurate readings of air, the car runs like ****. Even how you position it makes an effect. It has to sit at about 45 degree vertical angle.
 
benfica88 said:
that sounds like a good idea about the readings. What would i use to stick my gauge int here though? Is there certain fittings i could use?

You'll just have to find some sort of small plumbing fitting and drill and tap the tubes in the needed locations. No magic available here.

also just for fun, i also tried the charger witht the bypass closed all the time :D . There would would start and die out within a second everytime.

OK, we REALLY need pics because this what I'm thinking you've done, and some things you say you've done are not matching up. It's confusing at best.

I also wanted to try the TB on the inlet before the charger but I don't know if its worth the work and $$. I mounted the charger right in front of the engine, very far from the throttle. To move that thing im assuming it would be kind of hard since there are some electronic components that have to be moved too and are not easy to deal with. One being a p.o.s. called a VAF instead of the usual MAF and this thing is a pain. Some people have tried putting it on the inlet of the blower but the car ran like ****. If it doesn't have accurate readings of air, the car runs like ****. Even how you position it makes an effect. It has to sit at about 45 degree vertical angle.


Interesting about the poor performance stories. The only thing I can think is that the Naturally Aspirated (N/A) fuel map isn't even close to the ballpark for a positive displacement blower which moves a lot of air at low speed. Then when they're running the SC under boost at all times, but bleeding it off, the VAF "sees" the increased airflow and fattens it up and the two situations meet somewhere around the middle. Not the way I'd like to see it but anyway, nothing says you have to move the TB over to the SC. I would think that it could be easy enough to move the TB out and over bit so that a tube could be run over to the SC inlet and then the output from the SC can be bolted to the intake where the TB mouted. Probably have to fab up a couple of flanges and weld them to the pipe
 
VAF and MAF do the same thing so if you can get the SC behind the throttle it would work pretty well. If you are going to spool the engine to 6000+ you don't want to get silly witht he pulley size either. I would copy the Super Coupe position of the blower behind the throttle and rig a bypass that work simular to our setup.

I think it would work much better for you. Down the road you could always get a custom chip and maybe even bigger injectors. Get us some pictures, we all would love to see that M90 in the Probe engine bay.

Jerry
 
What i meant about trying the bypass closed, is that all i did was unhook the vacum line from the bypass so it would just stay shut. I started teh car and the little turbo xs valve was screaming. The little thing couldn't vent enough air out so the car would just die out at idle. If i kept tapping the gas quickly as soon as i started the car it would obviously stay alive. About the VAF it has to stay in a position to read the air. It can't read the air and then vent it out so basically the VAF has to stay put before after teh blower. Some people have tried it otherwise and the car "runs like ****". I guess this would be a lot easier with pics. My friend just took some so hopefully he will e-mail them to me later tonight so i can post. Then you guys can see how it is setup.
Sockwave, im also working on the fuel right now. I also looked for bigger injectors but a ECU reprogram or Standalone would be necesarry but they were just to much money for me and also i have to keep the car in check for emissions.So as of now, i just got a Greddy Rebic and am working on installing extra injectors on the manifold for when boosting. At least this way when i have to go to emissions i can just reroute the belt the old way withought the blower and run stock again.

btw. I appreciate all the help you guys have given me so far.

p.s. In case your wondering about the power increase. I had the car dynoed last summer. These cars pretty much make power until 6700 rpms. I made 212whp and 212wtq but this was at about 4000rpms and 6psi. After that power would just drop to about 160 whp. Not bad considering stock is 130whp.
 
Last edited:
Back
Top