Turbo BS Thread

@Blackdawg is correct.

Here is another example.

 

And yet another reason why I like my EFR turbo so much.

 

Bad ass turbos. Would boost

 

So what exactly is wrong with these two examples

 

Yours is clearly on the other side. Or is his????

 

First of all let’s understand that the ECU doesn’t “remember” air measured by the MAF and somehow anticipate it...

The ECU bases its fuel mapping off instantaneous voltage readings from the MAF. If the air flow into your engine (through your TB) and the air flow over the MAF doesn't match, you will have issues regardless how you vent or rout your BOV.


So visualizing the system, there is pressurized air on the hot side and a vacuum on cold side (pre turbo). The turbo is spinning down but remember it’s still spinning and still pushing air.

When the TB closes, we have to somehow equalize everything but limit as much as possible any extra air flow over the MAF.

When the BOV opens to the atm, if it’s vented too fast, you can initially create a vacuum from the velocity of air flow out of the BOV. This vacuum as well as the spinning turbo will cause air to continue to flow through the pipes, over the MAF, and out the BOV. So right off the bat, we need to make sure the BOV doesn’t just open wide and dump all the air. It needs to be tune to minimize extra air flow. This is the biggest issues with BOV’s; people don’t realize they need to be tuned and adjusted.

Now let’s look at recirculating.

Recirculating the pressurized air behind the MAF will equalize pressure on hot and cold side of the turbo without any extra air flow over the MAF which is good. The turbo is still spinning and drawing in air but instead of drawing in extra air, it will recirculate some of the pressurized air that was vented without any extra air flow over the MAF. This is why so many people run this setup; even with an un-tuned BOV the recirculating air isn’t flowing over the MAF. However, if (and it generally will be) the total air pressure is still higher than 1atm after the hot and cold side equalize, that extra pressure will still have to vent out the air filter, flowing over the MAF. This is why Jason is still stalling with this recirc setup. Just as above, a tuned BOV can limit the “shock” of venting so much air too quickly and can prevent you from stalling. IMO this is the 2nd best BOV setup.

Now, if you rout the recirculated air to the filter side of the MAF, we get the same thing but now the recirculated air is flowing over the MAF and the extra pressurized air is not. HOWEVER, just like above, if we tune how quickly the BOV opens and make sure the hot side pressure draws down slowly to match the drawdown of the Turbo blade speed, we will limit the “recirculation” of the air and therefore limit extra air flow over the MAF. IMO this is the best BOV setup.

Either way its done, if your BOV is not properly tuned and it just opens and dumps all the air, you will have issues. In all three setups, I bet you my truck that a properly tuned BOV will stop the stalling.

Personally I prefer to have the MAF mounted on the charged pipes as close to the TB as possible as that limits how much air will back flow over the MAF, regardless of how the BOV is mounted (as long as it’s not between the MAF and TB). May not be the most effective way but it’s definitely the easiest.

I also don’t like BOV’s or think they are necessary. Stalling turbo blades don’t put any additional pressure on the thrust bearing

Just my two cents.

 

I will have to politely disagree about the stress added. Equal and opposite pressure. Fundamental of physics. As well as proven by engineers in that respective field.

 

Man I've missed alot...I wonder why Im not getting notifications? O whale

 

I don't see anything wrong with your setup. You blowing off post MAF and Recirculating post MAF as well. Should function properly. The air that has already been metered is staying in the system.

 

His setup is right. He just probably has an air leak somewhere so when he lets off the gas he is pig rich and stalls.

 

It means that something else is affecting the setup. Something with the bov, or other.

 

Equal and opposite pressure is exactly my argument. When you are building boost, that pressure is pushing back on the turbo blades and thrust bearing.

I'll have to find it but someone actually measured the pressure on the thrust bearing when the TB closes w/ no BOV.

The pressure pushing back temporarily builds by ~1psi. So if you are boosting at 8psi, you have 8 PSI pushing back on your blades and thrust bearing. When you let off the gas, the charged pressure will initially spike by ~1 psi to about 9psi

 

How is it staying in the system? Unless there is a one way check valve somewhere all that pressure is flowing back out the air filter. The extra flow over the MAF is causing him to go rich.

 

Chris, its basic motor mechanics. The motor is a vacuum a huge air pump. Its still taking in air. the TB never close 100%, that would kill the whole motor.

 

B/c of this ^^^^

If the motor is running, it will be sucking in air. This will minimize the amount of air that flows back over the MAF in the opposite direction. I would guess that there isn't going to be any more air flowing back through the MAF than there would be in a blow through set up.

 

Today I tried venting to atmosphere and it didn't run well at all less power so I put it back the way it was. I have a stiffer spring coming and I'll go from there. I'll let everyone know what happens.

 

Think about what you are saying. I understand the engine is still running and air is flowing through the IAC valve but all that presurized air still needs to be vented, hense the need for a BOV. The pressurized air isn't going to run circles through the recirc valve.

Also remember, all the pressure is built with the TB wide open in most cases. If you have positive presure despite your engine runing at 5000 RPM's, how is an idle engine going to draw in all that extra air?

The BOV is meant to vent that pressure.

Put some streamers on your air filter and run a dyno, WOT, let off the gas, and watch how much air is expelled through your filter. Or use smoke to visualized the air flow. Or if you are brave, hold your hand by the filter.

 

Here is a quick wot log of my car. x- axis is the column number logging at about 10hz. y axis is maf voltage. I didn't show rpm but I started @ 2.5k to a pull to about 6.5k with an immediate throttle let off. My bypass valve is recirculating. maf voltage peaks at 4.3v and only dips to about 1.5v. I'm still pulling in air into the motor while the motor is slowing down. I cut off logging about 5k rpms. So at 5k I'm pulling in 1.5v closed throttle. Closed throttle my throttle body is open at 2.3% No air is being vented off for this entire log.

 

That spike proves my point. Its not always going to cause you to stall but you can clearly see a spike in the MAF voltage right after your let off the gas. Do you happen to have a map of your ARF's to conincide with this? I'd be curious to see how rich you were at that spike.

It looks like with the TB closed, and at idle MAF should be around 1.4V (its hard to see the numbers).

When you closed your TB, the MAF voltage droped to ~2.05 then spiked back up to 2.5V as the air flow reversed, before dropping again.

 

I logged everything. I can post the excel file. You are right that it is going to be pretty violent. My afr is showing full lean because of fuel cut. Keep in mind that each dot is a 1/10 second log with no smoothing. The maf voltage will fluctuate a bit, but you aren't going to be leaking air out the maf with a recirculating bov. I'm going from 290g/s to high 20 g/s in a quarter second.

I don't run my car aggressive compared to the big hp guys. Front wheel drive can only handle so much, lol.