Serious Boost Q's

[Razz]

I gotta be honest. I'm salavitating from the mouth over getting a turbo. I've got the cash, but I don't like gettin' into anything I don't completely understand, and there's still a few points about turbos that I don't get. Yes, I've used the search function over and over at several mod sites, and still I've yet to find difinitive answers to these questions, namely:

1. What exactly is a BOV? I think I understand that it vents off excess intake pressure. But how? Does it use a simple spring loaded diaphram, or a vacuum line, or what? Is this how you adjust boost pressure? Also, where in the system does it go? Anywhere in the intake line? Is it the same thing as a wastegate? If not, what's the difference?

2. I've gotten tidbits from here and there, but I still don't understand how exactly more fuel is proportionately added to compensate for the boost. I understand how fuel injection works, but I've heard of people just putting in bigger injectors (larger cc) to compensate, and I don't see how this works without somehow changing the ECU. Will the ECU adjust the injector pulse width according to the reading of the O2 sensor, if you were to add larger injectors without reprogramming or changing the ECU? I've studied on the Power FC units, but can't seem to get definitive answers on what it does, either. When the word 'stand alone' is used, what is that referring to? Why isn't the stock ECU a 'stand alone' too? Where would you 'plug-in' and mount a Power FC? I understand you can program one with a laptop. I like that, being a programmer already. Please fill in any blanks that I'm not getting here. I'm sure there's plenty.

3. Why is the stock fuel pump not adequate? Is it because of lack of volume or lack of pressure, or both?

4. When the turbo is not spooled up and increasing intake pressure, where does the engine get air from? Does the air still flow thru the IC? Does all incoming air still flow thru the vanes of the turbo even at idle?


Please don't flame my ignorance. Try to respect the fact that I'm not someone who is gonna slap something on my car unless I completely understand how it works. Thanks ahead for any answers to these Q's.

[vvtlikick]

I'll try too answer some of your questions, but I don't have all the answers.


1. What's a BOV?

A blow-off-valve (BOV) sits in the INTAKE, after the compressor half of the turbo. The purpose is to vent excess pressure, such as when the throttle plate is suddenly closed during an upshift. It is not normally used to control boost pressure. I don't know what precise mechanisms are used.

A wastegate sits in the EXHAUST. It allows exhaust gas to bypass the turbine half of the turbo. It is used to control boost pressure, by limiting the turbine's supply of exhaust gas.


2. Fuel Management?

Any ECU that can run the engine by itself is a "stand-alone" ECU, so I suppose the stock ECU qualifies But the APEX-i S-AFC would not qualify, because cannot be run by itself.

I don't want to comment on the big injectors, becuase I'm liable to be wrong

I know some other engines' kits use a fuel-pressure riser, indexed to boost pressure, to provide additional fuel , but that strikes me as a very sloppy solution. Also I believe the fuel-pressure riser goes on the return line to the fuel tank, but the Celica has a returnless fuel system.

I think the XS turbo originally added a return line and fuel-pressure riser, but now they have appear to have moved on to the Power FC ECU for fuel control.


3. Why is the stock fuel pump not adequate?

I don't know the specifics.


4. Air path?

The intake air always comes through the compressor half of the turbo and then the intercooler, even at idle.

More Info: http://auto.howstuffworks.com/turbo.htm

[nyoneway]

3. Stock pump is only good for around 5psi, after that they do not pump enough fuel at higher RPMs.

4. Air can still get thru the blades of the turbine on the turbo and IC.

[Razz]

Thanks, guys! I noticed the XS kit includes a new Walbro fuel pump. That's why I asked. I'm wondering how hard that's gonna be to install, compared to the IC and exhaust manifold.

It seems strange to me that the intake air still flows adequately thru the turbo vanes at idle. It know the turbo vanes allow blowby, but it seems like it would restrict it enough to interfere with normal aspiration, before the turbo spools and boost is created. But I guess no more than a stock air cleaner would. Is the turbo normally at 0 rpm's at idle?

[Razz]

Another Q to add to the list:

When 'tuning' is mentioned, what does that entail? It seems rather complicated, and only possible with a dyno and exhaust gas fuel/air ratio measuring equipment. I would think that tuning would mean getting the car running as close to lean (more power), and as safe as possible, thruout the rpm range. And all this has to be 'mapped' into the Power FC. So tuning would only entail making changes the the PFC program. Close?

[Masayver]

The stock fuel pump is good for over 5 psi, as shown in the SF turbo setup on kireisceli's car.

[larryd]

Originally posted by Razz
Another Q to add to the list:

When 'tuning' is mentioned, what does that entail? It seems rather complicated, and only possible with a dyno and exhaust gas fuel/air ratio measuring equipment. I would think that tuning would mean getting the car running as close to lean (more power), and as safe as possible, thruout the rpm range. And all this has to be 'mapped' into the Power FC. So tuning would only entail making changes the the PFC program. Close?

Tuning is changing your cars fuel trims to a set air/fuel ratio.

[cool2miketlu]

Originally posted by Masayver
The stock fuel pump is good for over 5 psi, as shown in the SF turbo setup on kireisceli's car.

This could be true, it may be our stock Fuel Pressure Regulator that is keeping fuel pump to go past 5psi. Because I am not sure about SF kit, they may take out stock FPR and use a different one (they must have for this fuel system to work). Thus the stock fuel pump may be good for alittle bit more higher boost, as to how high I am not sure of because I had pump and FPR changed out already.

[minhtin]

Another thing you should be aware of is smog issues. Most of these kits except maybe alpine's kit are not smog legal. I am a full time student but i work part time as a part delivery person so i know ltos of shops and stuff. even then i have a hard time frinding a place to do crooked smog. Lots and lots of shops been hit by the gov for crooked smog. so it's almost impossible now to find someone that's willing ot pass you. just a note.

[Razz]

Does anyone understand how exhaust flow is able to spin up a turbo? I've taken a turbo on the bench, and tried to spin it up with a leaf blower, and the thing will only get to about 10k rpm's. It's hard for me to understand how exhaust makes more flow than a leaf blower, especially when you can stall most cars just by sticking a potato in the tailpipe.