My prof today was asking me about the turbo kit i am planning on installing this coming spring. He asked me what im planning on "boosting" and after some clarification I realized he meant how many pounds i was planning on running. I told him around 10-12 lbs. He then told me that i wouldnt need bigger injectors because that amount of boost would be safe on stock injectors!!!!!

Then i asked him how he knew what size injectors i needed if he didnt even know the trim or type of turbo i was using. He said that 10 psi is 10 psi and no matter what i wouldnt need bigger injectors for a larger turbo.

The question im asking is how can i sensibly explain to him that a t-25 turbo will force less air into an engine than a gt35R would. I know that may sound vague but just need a lil help with this haha.

 

your professor is correct that 10psi is 10psi no matter the size of the turbo but incorrect on injector size you will find out during tuning.

Different size turbos exerts different volumes of air. It's not a matter size but how long it takes for your turbo to pressurize the intake manifold to see 10 psi.

 

so r u saying that 10psi of air coming from a t25 is different from the volume of air that a gt35r is producing or just that it fills it faster?

 

just tell him there is a difference between how much air pressure (psi) a turbo is producing and how much air a turbo is flowing (cfm), so the convo should go something like psi is the amount of force pushing outwards (towards ambient air pressure) and cfm is the volume of air that will be forced into the cylinders, so a bigger turbo can not only produce more psi, but can also flow a greater volume of air...but he is correct you will need to upgrade your injectors. here is rc's injector worksheet http://www.rceng.com/technical...heet_

 

10psi is 10psi, but;

A small turbo will spool up quickly and suffer from little lag, however it may have trouble producing 10psi at high rpm because it simply can't flow enough air, so performance may fall off at higher rpm.

A larger turbo will spool up more slowly so may suffer from significant lag, however it should have less trouble maintaining 10psi at higher rpm because it can flow a larger volume of air.

A small turbo will be more drivable, and give better low rpm response / performance. A larger turbo will be less drivable but give better power at higher rpm. All else being equal...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by srmofo &raquo;</TD></TR><TR><TD CLASS="quote">just tell him there is a difference between how much air pressure (psi) a turbo is producing and how much air a turbo is flowing (cfm), so the convo should go something like psi is the amount of force pushing outwards (towards ambient air pressure) and cfm is the volume of air that will be forced into the cylinders, so a bigger turbo can not only produce more psi, but can also flow a greater volume of air...but he is correct you will need to upgrade your injectors. here is rc's injector worksheet http://www.rceng.com/technical...heet_</TD></TR></TABLE>
Ok i can understand that but is it also true that 10 psi with a smaller turbo will flow less air per psi than a larger turbo at the same psi rating

 

the simple answer is yes, but that all depends on alot of different variables like your rpms aka how much air the engine is consuming. restriction is what causes pressure, not the turbo. dont confuse psi and cfm. and also with a smaller turbo you are gonna heat the air more and have the same pressure but even less cfms. I guess you could compare it to 2 different size garden hoses, say the first is 1/2in I.D. Its gonna take less flow to produce 10psi inside that hose than a hose 1in I.D.

 

that does help to clarify it haha this is the point i was trying to get across like 10 pounds from a small turbo is completly dif from a larger one bc of the fact that it flows more air at the same psi. I think that is a correct statement at least correct me if im wrong.

 

Someone correct me if I'm wrong here,

You have 2 turbo cars running at 2000 RPM. 1 Has a small turbo set at 10psi 2. has a larger turbo also set at 10psi

(remember I'm not a turbo guy. this is just a hypothetical flow vs volume vs psi = AFR theory. It is not a trim theory)

Car 1 has 2195cc's of volume to be filled and the small turbo does it in 2ms @ 2000rpm.
Car 2 has 2195cc's of volume to be filled and the larger turbo does it in .5ms @ 2000rpm.

Now the total volume for both cars is still only 2195cc's. How does filling it faster require more fuel when the volume of air is still the same @ 10psi?
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Edit* I'm not saying whether or not you will need larger injectors, I'm sure you probably will. A tune will tell you for sure what size injectors you will require.


Modified by GhostAccord at 10:16 AM 9/30/2008

 

Read my sig, down at the bottom. Bigger turbos make more power for a given pressure because there is "more" air available to the engine. Think of it this way: an 8 inch fan(small turbo) that can create a 200 mph breeze vs. a 2 foot fan(big turbo) that can create a 200 mph breeze. Which one moves more air?


Modified by King V at 6:04 PM 9/30/2008

 

I do see how the "Bigger turbos make more power for a given pressure". because they can sustain the required volume of air to keep filling the cylinder to 10 psi higher into the RPM range.

But back to my original question, how does a 2 foot fan filling an engine with 2195cc's of air @ 4500 RPM in .5ms require more fuel than the 8 inch fan filling the exact same volume but in 1ms. They both fill the cylinders to 10psi before the valves close. So the same volume of air and fuel would exist in the cylinder correct? Doesn't any excess air that the big fan tries to cram in just get blown off? Isn't that what a BOV is for?

 

pressure is not the same as volume

 

No. A BOV is for when the manifold sees the pressure spike from the throttle closing.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GhostAccord &raquo;</TD></TR><TR><TD CLASS="quote"> So the same volume of air and fuel would exist in the cylinder correct?</TD></TR></TABLE>

In theory, yes. But, what is the temperature of the air charge?....hence the bigger turbo needing "more" fuel, more being relative. It doesn't heat the incoming charge as much as its not working as hard as the smaller turbo is to fill the cylinders. And yes, intercoolers do cool the charge, but thats after the turbo. It cools the charge, the charge "shrinks", turbo works "harder" to sustain the airflow, air gets heated from turbo, goes into the intercooler....

 

10 psi at 200 degrees is less air mass in the cylinders than 10 psi at 100 degrees.

 

Thanks King V,
I'm learning bits and pieces about FI as I go. N/A is still my choice for now. Need to learn a lot more about boost and all theprinciples behind the scenes before I toss one on my car.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mmuller &raquo;</TD></TR><TR><TD CLASS="quote">pressure is not the same as volume</TD></TR></TABLE>

Yeah I know that, but thanks for your input!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GhostAccord &raquo;</TD></TR><TR><TD CLASS="quote">

But back to my original question, how does a 2 foot fan filling an engine with 2195cc's of air @ 4500 RPM in .5ms require more fuel than the 8 inch fan filling the exact same volume but in 1ms. They both fill the cylinders to 10psi before the valves close. So the same volume of air and fuel would exist in the cylinder correct? </TD></TR></TABLE> I assume this is also an example where these numbers were just pulled off the top of your head. therefore you are assuming that the smaller turbo does in fact get the cylinder filled to 10psi before the valve closes. which hypothetically speaking it may not.


Modified by srmofo at 6:20 PM 10/1/2008


Modified by srmofo at 6:21 PM 10/1/2008

 

Good luck!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GhostAccord &raquo;</TD></TR><TR><TD CLASS="quote">Thanks King V,
I'm learning bits and pieces about FI as I go. N/A is still my choice for now. Need to learn a lot more about boost and all theprinciples behind the scenes before I toss one on my car.

Yeah I know that, but thanks for your input! </TD></TR></TABLE>

it is as simple as that

read turbo maps to know

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mmuller &raquo;</TD></TR><TR><TD CLASS="quote">read turbo maps to know</TD></TR></TABLE>

Now now, no need to throw him to the wolves.....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mmuller &raquo;</TD></TR><TR><TD CLASS="quote">

it is as simple as that

read turbo maps to know</TD></TR></TABLE>

And you have tuned how many boosted cars?

This guy feed me to the wolves...yeah right!

I think I would rather learn the principles of how everything works in a boosted system than to go throw a turbo on and "watch maps to know". But hey if that's how you roll with your builds that's great. I do a bit reading first. Reading for the win!


Modified by GhostAccord at 7:27 PM 10/1/2008

 

pick ya up a copy of corky bell's book "maximum boost"...it'll teach you everything you could ever wanna know....for now

 

Thank you for some more good info!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GhostAccord &raquo;</TD></TR><TR><TD CLASS="quote">

And you have tuned how many boosted cars?

This guy feed me to the wolves...yeah right!

I think I would rather learn the principles of how everything works in a boosted system than to go throw a turbo on and "watch maps to know". But hey if that's how you roll with your builds that's great. I do a bit reading first. Reading for the win!
</TD></TR></TABLE>

e thugging... i have tuned a decent amount of them...internet dummy..
i dont see how my answer pissed you off. if it doesnt help u go about your way kid; or at least u act like one.
you must watch me work you seem to know lots about me...hahahaha

 

e thugging...lol your a hoot.

You never even answered my original question. That is great that you feel comfortable around boosted cars. You must be one of those omniscient H-T members that just sit back and wait to give as little information as possible. And then say that it's as easy as that.

I was asking a theoretical question about boost that had nothing to do with tuning to begin with. It had to do with how they work.

But thanks again for your totally useless information as it pertained to my question!

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mmuller &raquo;</TD></TR><TR><TD CLASS="quote">pressure is not the same as volume
</TD></TR></TABLE>
Yes I too remember that from grade 5.

& another one......

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mmuller &raquo;</TD></TR><TR><TD CLASS="quote">

it is as simple as that

read turbo maps to know</TD></TR></TABLE> This is real useful info for someone just learnign about boost as well! thanks again

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by srmofo &raquo;</TD></TR><TR><TD CLASS="quote">pick ya up a copy of corky bell's book "maximum boost"...it'll teach you everything you could ever wanna know....for now</TD></TR></TABLE>

Agreed xInfinity

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mmuller &raquo;</TD></TR><TR><TD CLASS="quote">read turbo maps to know</TD></TR></TABLE>

Thats like saying "Here, read this Latin dictionary and you'll know Latin"

Maps are more for choosing a particular turbo/compressor for a given engine combo/application. You have to know what kind of pressure ratio you're dealing with and how much air you want to move thru the engine to really be able to utilize a compressor map. If you just take a gander at them without knowing what you're looking at, it looks like a bunch of lines and numbers, and can be a little confusing, hence my comment.