I am in a bit of a bind trying to find info on A/R sizing. Is there any good and stadardized way to figure out the best A/R for a given engine size? I think i have my turbo sizing narrowed down to a GT3071 but now i need to figure out my A/R so i don't have a choke up high or lots of lag down low. I am working with a 1.9L, 4 cylinder, 4 valve per cylinder engine if that helps anyone. Any info would be helpful.

 

what kind of power does it make n/a ?

 

125hp current n/a rating. Expecting 300-325hp when done.

 

Peak Torque @ rpm would give a better idea of how the engine breaths and how it will spool a turbo.
Redline rpm would give an idea of how much the turbine has to breath.

Valves per cylinder don't change much when under boost, it's about how much air can flow into the cylinder and how much exhaust can flow out. A 16V 4I has the advantage of dual cams allowing adjustable cam gears to make changes between intake and exhaust timing without changing cams.

I assume the factory 125 n/a HP are block hp ratings, are your goals 300 to 325 wheel or block hp.
The GT30 turbine chart
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What I see from this chart is the faster you reach your set pressure ratio the less rpm or when you shift mater.

I feel like you oversized your turbo for your goals and engine size, I am no expert but I like a turbo to spool as quick as possible and pull to redline, I think a turbo with a rated flow closer to your goals would spool faster and turbine housing options would become when do I want to spool the turbo (rpm) and how much peak flow do I need instead of when can I spool the turbo.

Is this a track car with power adders to spool the turbo or a street car you can enjoy, peak hp doesn't make a car fast, torque below 5252rpm and hp above 5252rpm make a car accelerate.

For any four cylinder running a GT3071 that is fun to drive I would run .61 or maybe a .63a/r housing.

 

This is a street car. Yeah stock hp of the car is rated at 125hp. I have not bought the turbo as of yet. I was hoping to get a t3 with a built in 3" v band outlet. The smallest i could find that covered that was a gt3071. A bonus on that was the pressure ratio for my top boost was right in the middle of the efficency curve. I am almost certain if i tried to get a turbo sized for 20psi at 4k rpm it would choke out before 8k. I might be wrong. If you guys have a better option i am all ears. Thank you for all the input.

 

The a/r controls flow through the turbine section. Low boost needs a bigger a/r, high boost needs a smaller a/r.

Need way more info to determine what a/r you need, hp at rated rpms, redline, any other airflow mods?

 

The post above was waiting on moderator approval before it could be posted. Not complaining. Just letting you know. All of the stuff below is 100% custom as the car and engine in question has no Mod support at all anymore. When people were customizing these it was still janky.

2.5" full intercooler piping
FMIC
3" exhaust
Large Throttle Body
Extended Plenum

I do not have the confidence to not blow through a water jacket while porting so no head work has been done to this. I built one of these in 2008 that ran 18PSI. I had an old RHC62 off of a chevy 6.5L turbo diesel. I made it spin but it was not a great ride. According to the stand alone fuel table, data logs, gearing and speed it was making approximately 320hp. If i can get back to about there then i will have to either dial it back or start building more custom parts. I guess if i could max out around 275hp i might be able to keep a clutch in it and not build one. With the lack of flow mods force feeding the engine is my only real shot. I am attempting to use up a bunch of parts in my garage. The turbo is the only thing i do not have dialed in. I have a t304E sitting rebuilt at the house but i cannot find an exhaust housing for it that would fit and use the 3" vband exhaust i already have for it.

 

You aren't giving the necessary info for the turbo experts that are on this forum to make suggestions.
What you have told them so far is:
-1.9 L 4cylinder
-125 block hp (At what RPM?)
-Goal is 300-325 hp (wheel or crank?)
-Red line 8000rpm (you mentioned 8k, is this factory or your goal?)
-Air flow mods: Large throttle body

What is "extended plenum" ? are the runners longer? this would move your powerband lower in the rpm's.
What is peak torque and at what RPM?
What is factory redline.
At what rpm did the engine make 125hp in factory stock form? If it's at 8000rpm that's like 82ft/lbs torque, If it is a low torque high rpm engine like honda's you might not spool that turbo until 5252rpm or higher, by the time you build boost the guy you wanted to race is long gone.
The make, model, year of the engine even the bore and stoke can be useful info, longer stroke than bore usually breathes better at lower rpm, shorter stroke than bore usually performs better at higher rpm.
What powerband rpm range are you looking for? Transmission gear ratios and final drive ratio play a role in the powerband, say the transmission has short gears and you drop about 2200rpm shifting gears (3rd to 4th) no matter if red line is 6000 or 8000 rpm when you shift from 3rd to fourth you have 2200rpm before redline and shifting to 5th. With the right sized turbo and A/R's it wouldn't matter what rpm you put the powerband duration at acceleration will be the same, top speed in each gear will be lower at lower redline..

BBI turbo introduced me to this turbo:
The amazing Garrett G25-660 turbo, I spent about 4hours reading up on it and watching videos about it (I swear I didn't drool once, well maybe once), apparently VW 1.8T's can spool these turbos at 3000rpm with the largest or second largest A/R turbine housings available, that's incredible spooling a turbo capable of flowing 660cfm at 3000rpm running the larger end of turbine housings with a motor that can barely flow enough to blow a kazoo.

The G25-660 is for engine from 1.4L to 3.0L and flows up to 660cfm, comes internally/externally wastegated, flange or v-band selections of different sizes .
The GT3071 is for engines from 2.5L to 3.5L and flows less cfm than the G25.

BBI turbo offered me a quality reproduction at a very good price but I'm so broke I can't afford to pay attention.

 

May I save that and use as a sig?

 

Yes you may.

 

I think I half plagiarized it from the lyrics to this song:
KMFDM Lyrics
"Dogma"

All we want is a head-rush
All we want is to get out of our skin for a while
We have nothing to lose, because we don't have anything
Anything we want anyway...

We used to hate people
Now we just make fun of them
It's more effective that way

We don't live
We just scratch on, day to day
With nothing but matchbooks and sarcasm in our pockets
And all we are waiting for is for something worth waiting for

Let's admit America gets the celebrities we deserve
Let's stop saying, "Don't quote me" because if no one quotes you
You probably haven't said a thing worth saying

(Sex, drugs, God, cash
Sex, drugs, God... America)

We need something to kill the pain of all that nothing inside

(Sex, drugs, God, cash
Sex, drugs, God... America)

We all just want to die a little bit
We fear that pop culture is the only kind
Of culture we're ever going to have
We want to stop reading magazines
Stop watching TV
Stop caring about Hollywood
But we're addicted to the things we hate

We don't run Washington, and no one really does
Ask not what you can do for your country
Ask what your country did to you

(Sex, drugs, God, cash
Sex, drugs, God... America)

The only reason you're still alive is because someone
Has decided to let you live

(Sex, drugs, God, cash
Sex, drugs, God... America)

We owe so much money, we're not broke - we're broken
We're so poor, we can't even pay attention
So what do you want?
You want to be famous and rich and happy?
But you're terrified you have nothing to offer this world
Nothing to say and no way to say it
But you can say it in three languages

You are more than the sum of what you consume
Desire is not an occupation
You are alternately thrilled and desperate
Sky high and fucked

Let's stop praying for someone to save us and start saving ourselves
Let's stop this and start over
Let's go out - let's keep going

(Sex, drugs, God, cash
Sex, drugs, God... America)

This is your life - this is your fucking life

(America...
Sex, drugs, God, cash
Sex, drugs, God... America)

We need something to kill the pain of all that nothing inside

(America... America)

Quit whining, you haven't done anything wrong because frankly
You haven't done much of anything

(Sex, drugs, God, cash
Sex, drugs, God... America)

Someone's writing down your mistakes
Someone's documenting your downfall