BOOST Tuning

[tici]

discharging the bypass air would mean you have a pretty serious vacuum leak when the bypass opens. No way around it without using an electro-mechanical clutch of some sort on the blower to actually stop the rotors/impeller. Believe it or not this is getting a serious look at by a lot of euro manufacturers as they try and come up with low down torque and no lag combinations vs. traditional turbocharging.

Sorry but I don't get it :-[
I was thinking at a blow-off valve instead of a bypass.
Blow-off = when you close the throttle the manifold vacuum opens the valve and the air goes back to the nature.
Bypass = the air goes back to the suction side of the blower.
Blow-off = you need a MAF after the valve or SD with a 2 bar MAP
Bypass = you can leave the MAF before the blower.
...to my understanding...

Grate movie! I guess every supercharger owner did dream about that electric clutch. I'm not sure if it really exist or if faisable (costs) or if it makes sense (to safe fuel?)

mediumrareintexas: I would leave that valve alone: if it remains closed for some reasons when you close the throttle youll'have a backpressure in the pipe and the SC won't like it.

Here my Vortech setup with bypass valve

[Chris@HPTuners]

yeah two different beasts, a BOV only vents under positive pressure (usually in turbo apps) when you suddenly snap the throttle shut under boost. This is because the turbo keeps spinning when you close the throttle leading to overboost, flutter, and even damage. A BOV never vents under vacuum conditions. It really makes no difference to airflow if you vent to atmosphere or have it plumbed back in as long as the MAF is after the BOV and hence ideally would be a blow thru system.

a bypass valve only relieves mechanical load from the engine when the s/c is operating under vacuum conditions not boost. This is for effciency and also quiet the damn things down (especially true for roots type s/c)!! The bypass can also be used for boost control (eg. the V6 s/c engines use the bypass to control boost as a form of engine protection).

[tici]

True, the bypass is a grate thing but when not under boost the air mostly recirculates and gets really hot. Also the piping and the blower, and when you mash on it it takes a moment to cool.

I know, it was better to get the intercooled (or better aftercooled kit).

[mediumrareintexas]

So how much boost do you guys feel that a LS1 with stock heads and cam can handle?

[mediumrareintexas]

I think I am going the direction of SD because the MAF does impede airflow which impedes performance. So I'm going to replace the MAF with a straight bellows. Then I'll play with the SD tune.

By the way, I passed the emissions test so now it's time for the fun to begin.

[MadMax350]

Also, keep in mind on turbo setups that when you close the throttle and have a long intake path (via an intercooler) the turbo's will continue to draw/blow air thru the MAF, however this air is not going into the engine, it is in effect pressuring the intercooler. This can lead to rich conditions on throttle closure at idle (eg. after a burnout as the turbo's spool down).
Chris...

I actually had this problem the first time I put a turbo on my MAF-only 95 3800SC computer system. The 3" MAF (off a 3100V6, but similar to the 3.5" LT1 MAF) was mounted between the turbo inlet and air filter. I was using a GN turbo with integral wastegate. What happened was any time the turbo was making boost and I closed the throttle, pressure built up in the intercooler/induction system and back-fed thru the turbo and back out the air filter past the MAF. This told the PCM that there was excessive airflow at closed throttle which created 2 problems. The first was a overly-rich condition. The second, and most troublesome was the PCM saw the increased airflow and commanded the IAC completely closed. Of course what this caused was a STALLING condition nearly every time I let off the gas after boost, unless I was going fast enough or in manual 3, 2, 1, etc...something that kept the RPM's up.

What I did to fix the problem was to relocate the MAF sensor to right before the throttle body, to use as a blow-thru. NO MORE ISSUES. Better throttle response, and the MAF doesn't seem to mind the hot-boosted air.

Keep in mind I couldn't use the stock 3800 TB-mounted MAF because it did NOT like the boost pressure differential due to its design, since it is uses an indirect-method of measuring airflow.

[tici]

MadMax350: are there any problems related to continuosly discharge the eccessive air? (non boost condition).
I'd like to try it once but I saw a tread on LS1tech about that. Apparently the open bypass valve makes a lot of noise and blows dust everywhere.
I'd like to try it because my non intercooled kit gets really hot ad idle.

mediumrareintexas: not to tell you what to do, but installing a SC is a pain by itself. SD + boost is an additional headache. Why not first install the kit following the instructions and see how it works?
THe MAF is a grate thing! To remove it won't give you so much additional power. Remove it only if it's maxed out.

[MadMax350]

MadMax350: are there any problems related to continuosly discharge the eccessive air? (non boost condition).
I'd like to try it once but I saw a tread on LS1tech about that. Apparently the open bypass valve makes a lot of noise and blows dust everywhere.
I'd like to try it because my non intercooled kit gets really hot ad idle.

I am not aware of any problems with the continuous discharge of excessive air, other than your air filter will be processing more air which means it would gather dirt and debris at a faster rate. Not exactly sure what else you are asking here (specifically, pertaining to what type of forced induction setup you are using and what design of bypass system is has); but I will be happy to explain my setup plus what the 3800SC's use.

My turbo setup uses the stock GN turbo and integrated wastegate. When the wastegate opens, it allows exhaust pressure to bypass the turbo turbine and dump straight into the exhaust. The wastegate opens once boost pressure reaches a preset point.

The bypass system used on the GM 3800SC engines has a dual bypass actuator. It can be opened with boost pressure (via the computer controlled boost solenoid) or with manifold vacuum. At low loads, there is manifold vacuum present which causes the bypass valve to open which won't allow significant pressure to be built by the SC. This helps remove the load from the SC and increases gas mileage as well as extends SC life.

As far as temperature, most of the heat created by supercharging and turbocharging comes from compression of the air charge. It idle, there should not be any significant amount of pressure being created therefore there should not be a temperature increase in the air charge. Unless of course your SC is capable of building boost at idle speeds. Now if you have a turbo, there will be some temperature increase because of the thermal transfer from the exhaust to the induction system within the turbo itself, but this should not be that much.

[tici]

Look at my setup (a couple of posts ago).
Everything sits on top of the engine and gets hot just because of exhaust heat, engine heat and so on.
The SC is lubricated by the engine oil and I'm not sure if this is a kind of cooling or an additional heat source.

At idle or during low load part of the air will recirculate (bypass valve) from the outlet back to the inlet of the SC and will be warmed up by the metal parts (piping, impeller and so on).
As long as you drive around there will be a certain cooling under the hood (from the Ram Air opening) and the charge air won't be too hot. But when the car idles for a while, especially in summer the IAT will rise up to 160F.

So this is not heat caused by compression (you're right - no boost at idle) but just because of underhood temperature.

If air goes just once through the blower it will probably cool the unit a little and also cause lower IAT: this means I have to move MAF (blow through) and fabricate some new piping. I don't know if this modification will really help or not: maybe the air will remain hot no matter if it recirculates or if it's discharged ???

[Chris@HPTuners]

Look at my setup (a couple of posts ago).
Everything sits on top of the engine and gets hot just because of exhaust heat, engine heat and so on.
The SC is lubricated by the engine oil and I'm not sure if this is a kind of cooling or an additional heat source.

At idle or during low load part of the air will recirculate (bypass valve) from the outlet back to the inlet of the SC and will be warmed up by the metal parts (piping, impeller and so on).
As long as you drive around there will be a certain cooling under the hood (from the Ram Air opening) and the charge air won't be too hot. But when the car idles for a while, especially in summer the IAT will rise up to 160F.

So this is not heat caused by compression (you're right - no boost at idle) but just because of underhood temperature.

If air goes just once through the blower it will probably cool the unit a little and also cause lower IAT: this means I have to move MAF (blow through) and fabricate some new piping. I don't know if this modification will really help or not: maybe the air will remain hot no matter if it recirculates or if it's discharged ???

wasting your time, also it impossible to vent anything under vacuum. Heat soak is your main enemy here not the very minor reculation of air at idle. Even NA cars will see 140+ temps at idle on warm days...

[mediumrareintexas]

My SC is internally lubricated with no connection to the engine oil supply. It is also mounted in the right front of the engine just behind the radiator, not on top of the engine. The SC blows into twin intercoolers before the air enters the MAF and the intake.

There is a bypass valve which is open to allow air to recirculate through the blower until 0 vacuum at which time the bypass valve closes and all the air is blown into the engine.

Tici, you seem to be a big fan of the MAF. How do you feel about removing the screen in the MAF? That would allow the MAF functionality to continue but also allow more air to enter the engine.

[tici]

I love my MAF :-*

MAF is an improvement, not a regress.
It measures what really goes in to the engine, no matter if you have ported heads, cam blower or whatever.
It's pretty accurate from idle to WOT, winter to summer, high to low pressure. VE alone isn't that good.
The PCM always check the MAF values with the VE and if there is too much difference it will set an error or just go straight and use the VE alone.
This happens if the engine is high modded and its function is not the same as GM planned (a car and not a rocket!).
At this point it's better to go VE: the PCM will make less confusion.

Descreening: I wouldn't. THe MAF needs a laminar flow to work correctly.
If you look around you'll find a lot of posts from people that regret having descreened it. If you want more air going through, better put a smaller pulley.

[Chris@HPTuners]

I love my MAF :-*

MAF is an improvement, not a regress.
It measures what really goes in to the engine, no matter if you have ported heads, cam blower or whatever.
It's pretty accurate from idle to WOT, winter to summer, high to low pressure. VE alone isn't that good.
The PCM always check the MAF values with the VE and if there is too much difference it will set an error or just go straight and use the VE alone.
This happens if the engine is high modded and its function is not the same as GM planned (a car and not a rocket!).
At this point it's better to go VE: the PCM will make less confusion.

Descreening: I wouldn't. THe MAF needs a laminar flow to work correctly.
If you look around you'll find a lot of posts from people that regret having descreened it. If you want more air going through, better put a smaller pulley.

ever tried using a MAF on one of these rockets ? ;D

[SideStep]

...
Descreening: I wouldn't. THe MAF needs a laminar flow to work correctly.
If you look around you'll find a lot of posts from people that regret having descreened it. If you want more air going through, better put a smaller pulley.

NEEDS???

Then why is the ZO6 maf screenless from the factory??? I am using one, works great.

[tici]

:P
...didn't know... ouch!
Maybe if it's that way from the factory it will be calibrated correctly.
Good point.


Hey Chris! why not 8x MAF's?

;D ;D
;D ;D
;D ;D
;D ;D


By the way: what car is it? The brake boost is on the left... ???

[Dellz06]

Hi,

So SD tuning on a supercharged vehicle is impossible without a 2 bar MAP and the software upgrade? How then, would one tune the VE table?

If the VE/MAP/IAT numbers are essentially used as a check for the MAF numbers - and the stock MAP is useless above 105kPa - what does the VCM do? Throw codes? Ignore it?

Or since the VCM exclusively uses the MAF at some point (>4000rpm?), do we assume the MAP is accurate until it maxes out?

I'm contemplating a maggy this fall and I'd hate to make my HPTuners useless by doing so.

John.

[tici]

Hi,

So SD tuning on a supercharged vehicle is impossible without a 2 bar MAP and the software upgrade? How then, would one tune the VE table?

If the VE/MAP/IAT numbers are essentially used as a check for the MAF numbers - and the stock MAP is useless above 105kPa - what does the VCM do? Throw codes? Ignore it?

Or since the VCM exclusively uses the MAF at some point (>4000rpm?), do we assume the MAP is accurate until it maxes out?

I'm contemplating a maggy this fall and I'd hate to make my HPTuners useless by doing so.

John.

Under boost the PCM will think to be at 105 kPa (mine does).
MAF, RPM and PE will take care of fueling.
The Vortech (Superchip) programmer modifies the "DTC0101 Allowed Error" table as in the picture.
This may take care of the difference VE - MAF reading (but I'm not 100% sure)
I don't know how other boost tunes look like.

[Dellz06]

Hey Tici,

Thanks for the response -- I checked the magnacharger file I have and the P0101 table is modified like you describe.

The odd thing is that the VE table is the same as the stock Z06 table. From what I've read and from what DynoSim says, the VE table goes over 100% on boost. My VE tables tops out at about 105 with the Vararam at speed. So I'm guessing the superchips magnacharger tune ignores the VE alltogether and opts for a purely MAF tune.

The other odd thing is that MAF table has been barely touched either. They seem to be tuning mainly off the IFR table for the bigger injectors. It's just a little weird. I would hate to see what happens if the MAF fails while under boost.

SD tuning makes sense to me. Of course, I guess I'm looking at the 2 bar upgrade and a new MAP sensor when I do drop the supercharger in.

John.

[Chris@HPTuners]

:P
...didn't know... ouch!
Maybe if it's that way from the factory it will be calibrated correctly.
Good point.


Hey Chris! why not 8x MAF's?

;D ;D
;D ;D
;D ;D
;D ;D


By the way: what car is it? The brake boost is on the left... ???

Its a Holden, which are right hand drive.

[tici]

Hey Tici,

Thanks for the response -- I checked the magnacharger file I have and the P0101 table is modified like you describe.

The odd thing is that the VE table is the same as the stock Z06 table. From what I've read and from what DynoSim says, the VE table goes over 100% on boost. My VE tables tops out at about 105 with the Vararam at speed. So I'm guessing the superchips magnacharger tune ignores the VE alltogether and opts for a purely MAF tune.

The other odd thing is that MAF table has been barely touched either. They seem to be tuning mainly off the IFR table for the bigger injectors. It's just a little weird. I would hate to see what happens if the MAF fails while under boost.

SD tuning makes sense to me. Of course, I guess I'm looking at the 2 bar upgrade and a new MAP sensor when I do drop the supercharger in.

John.

As long you have the stock MAP sensor the VE table will have to remain the same: the boost range is outsite of the stock VE table.
You'll have higher numbers if you extend the table to show more pressure (2 bar).
Also Vortech leave the VE alone.
Because of the higher air temperature the VE should be reduced a little but I wouldn't bother. Too many variables and the IAT will make some correction also.

Same for the MAF table: there is no reason to modify it unless you change something that will change the air flow (porting, descreening, different filter system).
I just saw the MAF hitting higher frequencies than without the blower, but other than that no problems at all. No MAF under boost would be bad!

The main changes made by Vortech were IFR, PE and timing.

Stefano