Missing Boost

theDreamer · 08-09-2013, 07:12 AM

Quote:

Originally Posted by Sh0velMan

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.

Chuck33079 · 08-09-2013, 01:11 PM

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

Sh0velMan · 08-09-2013, 01:16 PM

Quote:

Originally Posted by Chuck33079

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

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

Thx for clearing that up!

luigi90210 · 08-09-2013, 02:49 PM

Quote:

Originally Posted by Chuck33079

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

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)

Sh0velMan · 08-09-2013, 03:05 PM

Quote:

Originally Posted by luigi90210

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

Mike@GTM · 08-09-2013, 03:14 PM

Quote:

Originally Posted by luigi90210

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)

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.

Sh0velMan · 08-09-2013, 03:30 PM

Quote:

Originally Posted by Mike@GTM

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!

luigi90210 · 08-09-2013, 03:43 PM

Quote:

Originally Posted by Sh0velMan

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

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

Quote:

Originally Posted by Mike@GTM

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.

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?

Sh0velMan · 08-09-2013, 03:47 PM

Quote:

Originally Posted by luigi90210

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?

elperuano · 11-06-2013, 09:27 PM

How many miles on the SC?

pokeyl · 11-07-2013, 08:14 AM

Quote:

Originally Posted by elperuano

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!

pokeyl · 12-21-2013, 07:48 PM

I don't know if anyone is following this but the SC change did not fix it. But today I started looking at the "tune" as the car ran fin as a Stage 1 and never as a Stage 1.5 and after looking for hours I found the problem?

See the highlighted line, is is set to "off" in the 1.0 tune and "on in the 1.5

I understand that all 3 of the codes in this frame need to be set to off (FI cars) or you will get a "LIMP MODE" AKA missing boost as the throttle is 20% MAX

pokeyl · 12-23-2013, 09:28 AM

Fixed

After a new BOV, belt change Pulley change, Supercharger change, leak test and many other things. It was the tune. Thanks for all the help.

Mkai0 · 12-23-2013, 10:42 AM

Thank you for sharing your progress.

08-09-2013, 01:11 PM	#2 (permalink)
Chuck33079 A True Z Fanatic Join Date: Nov 2011 Location: Houston Posts: 12,265 Drives: 2011 370ztt Rep Power: 29539	He is supercharged. You want it open at idle. You're correct for turbo cars. __________________ 2011 MB Touring-Sport-6sp-Nav/GTM TT/FI TT TDX/JTran/Kosmic/Eibach/Hotchkis/SPC/CSF/RPS/SoThatsWhereAllMyMoneyWent

12-21-2013, 07:48 PM	#12 (permalink)
pokeyl Track Member Join Date: Nov 2010 Location: DFS Posts: 900 Drives: ??? Rep Power: 55	I don't know if anyone is following this but the SC change did not fix it. But today I started looking at the "tune" as the car ran fin as a Stage 1 and never as a Stage 1.5 and after looking for hours I found the problem? See the highlighted line, is is set to "off" in the 1.0 tune and "on in the 1.5 I understand that all 3 of the codes in this frame need to be set to off (FI cars) or you will get a "LIMP MODE" AKA missing boost as the throttle is 20% MAX jaytirbhaw and Mkai0 like this. __________________ It's not my fault I'm old, I was born a very long time ago! Last edited by pokeyl; 12-21-2013 at 08:11 PM.

12-23-2013, 09:28 AM	#13 (permalink)
pokeyl Track Member Join Date: Nov 2010 Location: DFS Posts: 900 Drives: ??? Rep Power: 55	Fixed After a new BOV, belt change Pulley change, Supercharger change, leak test and many other things. It was the tune. Thanks for all the help. Mkai0 and jlo370z like this. __________________ It's not my fault I'm old, I was born a very long time ago!

12-23-2013, 10:42 AM	#14 (permalink)
Mkai0 Base Member Join Date: Dec 2010 Location: Somewhere in Texas Posts: 209 Drives: 2008 G35 Sedan Rep Power: 15	Thank you for sharing your progress. __________________ Eibach, Tanabe, Blitz, Vertini, GTM stage 1.5 SC, Aquamist, Invidia, Alto built 5AT, Edge Racing, Racelogic, GTM driveshaft, 440 whp in 101F TX heat..

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11-06-2013, 09:27 PM	#10 (permalink)
elperuano A True Z Fanatic Join Date: Oct 2011 Location: Southwest FL Posts: 1,374 Drives: G37S Rep Power: 29	How many miles on the SC?