Missing Boost
 

Been outside the US for the last 2 months, drove to work today and the car only makes 4 PSI. Looked at all the clamps, all good, I'm thinking the BOV could be opening?

Any ideas? I'll look under the car at the discharge to intercooler stuff later this week.

Could my PS cooler have rubbed a hole in the intercooler? It Looks Very Close!!! OUCH!!!??? JB Weld...

Thought it might be a bad Vac/Boost sending unit, still may me but the vacuum readings look good.

Still seem to run good, I'll log some data on the way home tonight and check the A/F ratios. should be way rich if there is a leak.

Thanks

First try checking your bypass valve and see if it needs to be cleaned and lubricated. I've had similar issues in the past.

change the BPV, if that fixes it, then you solved your problem, if it doesnt then check the intercooler where you patched the hole and do a boost leak test and see if it is leaking from there(you can usually feel the leak if its really bad) switch the intercooler, if it isnt then you might need to tighten down clamps around all the silicone sleves

What lube did you use?

Adjusted my BOV and now I have 7PSI, It's leaking and I am so HAPPY it just the valve. Thank for all the help.

OK, when cleaning of my BOV it looks like someone put the a ultra-heavy spring in the valve and when it could not be opened by vaccuum he cut it down.

I bought this kit used from a 370z sponsor, not GTM, a very big mistake I might add, $1500 worth!!!! It was for a G37 and not a 370z.....

Just get a new one. Maybe HKS, GFB, or turbo smart.

I use GFB respons on my turbo eclipse and it holds all the boost I throw at it. Plus it was cheap, $200

New one is onthe way. The fix for now was Ace hadware springs. After the new spring install the valve is half-way open at idle. Under full boost it sould be full open from the SC pressure and the high vaccuum. At cruse it should be full closed. It should closer sooner as it is only part open at 15-18 inches of vaccuum. The old valve has never held up to full 1.5 SC boost. It will be fun to see if my new setup can handle 10PSI.

Sorry to hear about the issues you had with your bpv. The lube I used for my bpv was from TurboSmart and can be found here:

TurboSmart Multi-Spray

You may want to check the bpv at least every six months because mine was dirty and it needed some lubrication!!

Did you buy it from this website?
I have been trying to get this stuff, but everyone website I end up on looks shady.

Street Unit is legit. They're pretty much the go-to source for all things Mazdaspeed.

You can buy with confidence from them.

Excellent, thanks.

It should be open at idle,closed when you floor it and it will flutter under part throttle cruise.

It is open 1/2 at idel with 17 inchs of vaccuum. When I tested it with my vaccuum pump it was bypassing so much I could not generate enough suction to pull it open using my standard brake vaccuum bleeder hand pump. New one is on the way, tomorrow??? maybe today???

Hmm. My understanding of such things from my experience with my various F.I. cars, is that the BOV should be closed at all times, except when there is a pressure differential between the intake manifold and cold pipe, meaning the TB is closed but there's still boost in the cold pipe(s).

If it were open at idle, and you ran an un-recirculated BOV, you'd be sucking unfiltered and unmetered atmospheric air at idle...

I could be completely wrong though. Wouldn't be the first or last time.

He is supercharged. You want it open at idle. You're correct for turbo cars.

Mine sounds like a sewing machine at part cruse.

Gotchya, to bypass the compressor since it doesn't free spin in a vacuum like a turbo would.

Thx for clearing that up! :)

i have always been told this as well, with a BOV you want to keep it closed until you let off the throttle which would release all the pressurised air and prevent compressor surge

with a BPV you can have slightly open at idle or completely closed because you are recirculating after the MAF so either way, you are taking in the same amount of air since its been accounted for via MAF

also there is no such thing as a recirculated blow off valve since a blow off valve, blows off the pressurised air into the atmosphere while a bypass valve, allows the compressed air to bypass the turbo/supercharger and is recirculated in the system, since internally they are the same, the set up ultimately determines what the valve will function as(IE remove the recirc hose from the BPV and you now have a BOV and vise versa)

if im wrong about anything though, anyone please feel free to correct me but afiak bov and bpv are the same internally, just depends on how it is set up

could you explain why?

i have always been under the impression that centrifugal superchargers are basically belt driven turbos, so wouldnt anything that applies to a turbo setup apply to a supercharger setup(except for obvious stuff like boost controllers and other turbo specific parts)

Because the supercharger would restrict airflow and affect idle quality etc.

The turbo can just spin freely in the relative vacuum created by being off boost, so it isn't an issue, the supercharger effectively functions as an air restrictor in a feedback loop... limit air, engine slows down, engine slows down, supercharger spins slower, air is more limited, repeat.

There are ways to compensate around it, but the simplest is to leave the BOV open.

And I refuse to use a different acronym for BOV simply to differentiate between recirc and non-recirc. :P

Since the supercharger is driven by the belt, the rpm of the supercharger is dictated by engine rpm regardless of throttle position. Therefore, at small throttle angles, the supercharger is trying to push air into the engine against the throttle. Since the bypass valve operates on the differential pressure between the intake manifold and the pressure in the pipe, it will be open when the manifold is seeing vacuum while the pipe is pressurized. This condition will occur at idle and at low throttle angles. Once the throttle is opened enough, the manifold will see pressure and so will the pipe. In that case, the bypass valve will close since the differential pressure will not be high enough to overcome the spring inside the bypass valve.

A turbocharger's rpm, however, is dictated by exhaust flow. At low rpm and/or low throttle angles, there is insufficient exhaust gas flow to spin the turbocharger fast enough to develop boost. Therefore, the pressure in the charge pipe will not be significantly higher than the pressure in the intake manifold and the bypass valve will remain closed.

I hope that clears things up for you.

I had it backwards, S/C trying to increase boost pressure even at idle, not the other way around.

Thanks Mike! :tup:

lol, you're not alone with that one XD

i use to do the same all the time but i kept getting corrected by friends so i started using BPV and BOV

ok im still a bit confused about it but i get the basic idea, so even though the valve is the same internally, it will function differently on a supercharger setup vs a turbo setup?

could you in theory have a BPV designed for a turbo to work with a supercharger assuming everything fits? or would you need a different valve?

It's the same. The key you're missing is after the boost as been released on a turbo setup, generally there is no more boost being generated and the valve closes. The valve is "tuned" so that it requires a certain pressure differential between the manifold and the cold pipe in order for it to open. This is controlled by adjusting spring pressure inside the valve.

With the supercharger, boost is continuing to be generated at idle, so that differential is such that it holds the valve open slightly to release that pressure back to the pre-S/C pipe.

Get it?

[

OK I think that really cleared things up, since the supercharger is always creating boost, you want the valve open at idle because if it isn't, you will run into problems.

The valve

http://www.the370z.com/members/pokey...9-pict0082.jpg

http://www.the370z.com/members/pokey...1-pict0087.jpg

http://www.the370z.com/members/pokey...3-pict0088.jpg

http://www.the370z.com/members/pokey...0-pict0085.jpg

other, thanks Mike

http://www.the370z.com/members/pokey...2-pict0090.jpg

New valve is on, BUT, still missing boost. As soon as the traction fluid is warm the boost goes away.

If I WOT as soon as the oil temp is 160 I get 3 PSI at 3K

15 minutes later I get ZERO boost at 3K

outside temp is 75F

I looks like I may need a new supercharger. I have found other rotrex failures over at the BMW sight.

A lot of talk about overspeeding the SC causing the problem, and the user I bought mine from had the smallest pulley GMT makes on it with the stage 1 intake. He may have fried the unit and then sold it to me. As I did my install in the winter, the fluid was cool enough to keep the boost up.

I am working with Sam and Mike to come up with a solution. :(

Check to make sure you did'nt kink the SC hose coming out of the unit going to the SC filter.

I will look, I would think that a low oil flow would have destroy the SC.

Rotrex wants the belt changed and a smoke test for leaks after that.

The belt is old, my SC makes a high pitch whistle, I always though it was intake noise, I hope it is just a belt. Autozone will have one here tomorrow.

Inspected the belt, cracked, dusty and looks like it may be at the limit of the tensioner. So I stoppeed at Autozone and sprayed the belt with dressing. Boost now seems constant 3 lbs at 3K. It was raining and the racelogic had its hand full. Will test more this weekend with the new belt. If I hit over 10PSI I'll call it good.

Installed new belt, it is a 1045K7, GTM spec.

It looks longer than the one I pulled off. Belt wear indicator is not in range.

I had no squeal fro the first 20 seconds and then it came back. I think my belt is too long.

What a pain to change...

Now looking for a 1040 or 1035.

In my experience, it's really hard to find a 7PKXXXX belt if you need a non-standard length.

I ended up going with a 6PK (6 rib rather than 7) and it works fine.

Here's a 6PK1035 Amazon.com: Bando 6PK1035 OEM Quality Serpentine Belt: Automotive

What pulley are you running?

Underdrive crank pulley?

I can find 1040K7 and 1030K7, but no 1035K7 is this the one I need with a standard crank and the small GTM pulley or will the 1040K7 be short enough? 1045K7 looks long.

What is the difference from the 7PKXXXX and the XXXXK7 belts?

Did not work, as soon as SC fluid got up to temp boost fell off 6 PSI max and starts to build after 4K (1.5 to 2 PSI) and you have to twist past 6K to get to 6 PSI.

When the fluid is cold I build boost at 3 PSI at 2-3K...

Worked good 75F OAT for 45 min, 60-70 MPH. As soon as I hit city stop and go oil got to hot and boost fell off.


I am going to work on adding airflow to the coolers fan system.


Note: the under hood temp will burn you on any item you touch. The SC fluid in the tank is 155-160F (after a 1.5 hour heat soak drive and a 15 min cool down)
I took me 15 min to find my thermometer.

During the 15 min cool down the oil temp fell from 220 to 190F. If the SC fluid fell the same amount, my max temp is 185-190F is over the rotrex 175F limit.

Just got back home and spent the last 10 hours changing my SC unit. Fluid looked BAD milk/gray. Hope this fixes the boost falloff problem.

Then I can start back on this!

http://www.the370z.com/members/pokey...7-pict0010.jpg

How many miles on the SC?

15K on my car, but I bought it used from a 370z member/vendor and it was bad when he sold it to me. I took me 18 month to find out what was wrong.

I would have saved $2K if I had just bought a new one from GTM!. I was not trying to save the money, I was trying to help a member out.


No good dead goes unpunished!