Need help on choosing the right turbo size

What's wrong with a 72/75 for a "street car"? Not trying to get into a pissin match, but it seems that there are several, one could even say numerous 70mm+ turbos on "street cars". I have a 75mm on my car.....it's a car...I drive it on the street.... Am I doing something wrong? Still don't quite understand why people put labels such as "street car, or street/fun car, not a track car". I think, or at least it sounds like most of the people on this board drive their cars on the street regardless of turbo size. And, if the combination is right, it shouldn't matter where you drive it. Maybe I'm not old school enough.....I dunno.


Many years ago people in Salem all thought that it was a good idea to burn a few women at the stake because it was commonly accepted that they deserved it because they were witches.

A majority, and I mean over 90%, of the Buick community uses turbos that are significantly larger than what they need in order to achieve their goals, yet it is common practice to do so, since everyone else does. People do it because they see other people do it, and it becomes commonly accepted. A self-perpetuating practice. People do it because other people do it, thereby causing other people to do so.

Any honest person that knows what type of airflow is required to run mid 9s, would tell you that with today's technology, a 72mm turbo is exxeptionally large for our Buick motors.

If the OP is telling us he wants a "street" car turbo to run mid-9s, a 64mm can accomplish that. Or a PTE or BW 66/66 or 66/67, or a WORK 67/65, or PTE 67/68, or BW 69/68.... PLENTY of options with much better spooling characteristics and broader power bands, than a 72/75.

(Please note that I did not solely mention WORK, but also provided Precision options as well..for those who claim that I constantly "knock" PTE...)

You have a 70mm+ turbo on the street, so therefore what is the issue? That same process of thinking is why people over-turbo their cars.

Is it a newer turbo, or an older unit?

Just because other people do it, does not mean it is the correct choice. However that is a increasingly unpopular approach around these parts, but it is the truth, in certain instances, this being one of them.
 
Lag is exactly what I want. Right now with a 67/68 three bolt turbo, the thing frys the tires at 70mph kick down!

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You do not want to fundamentally build lag into your setup. If you need less boost at-or-near launch, you need to get a boost controller that allows you to progressively increase the boost over time, or by a switch, or by rpm/gear.

Something like a Boost Leash or an Eboost 2 allows just that.

It is such backwards thinking to purposely buy a slow-responding turbo so that you don't get wheelspin. Get a properly sized turbo, and get a proper boost controller, and tune the boost levels to where you do not spin at launch.

It is as simple as that. No need to buy a vastly oversized turbo just because you haven't bought the correct boost controller yet.

Yes, I have dual adjustable viking coil overs, and 295/55-15 drag radials. Dead hook at the track at 3500rpm. But not on the street at 70mph.

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Are your coilovers in the rear, or front?

What type of rear control arms and swaybar do you have?

What spring rate are your springs for the front and rear?

What shocks are you using in the front of your car?


then you got the right turbo.frying the tires is handled other ways not oversizing the turbo

EXACTLY!!!

It is such backwards thinking to do so!! It is like shooting yourself in the foot just prior to racing a 100 meter dash!! THAT is how much of a crutch you are giving yourself...

If you cannot hook on the street, then first thing I would do is get a proper electronic boost controller to allow multiple stages (pressures) of boost. Controllable by; time, rpm, gear, push-button.

Turn your boost down at launch on your controller to where you will hook up, and then ramp-in boost on the controller progressively as your car gains more and more traction.

FOR EXAMPLE of TIME based boost control:

If your target max boost is 30psi, and you know on the street that the first 60ft on the street you cant make more than 15psi of boost otherwise you will spin, and then after 60ft all the way to the 330ft mark you cant make more than 25psi, but after 330ft you can make your 30psi. I would set up your boost controller like this:

1) find out the average time it takes you to reach 60ft with 15psi of boost. For this example let's say 1.5 seconds.
2) set your 1st stage to 1.5seconds long, with the boost pressure at 15psi, with a quick ramp-up rate (meaning how quick your turbo builds that 15psi).
3) after you get the timing for 60ft, then you will have to make multiple test hits to see how long it takes you to hit the 330ft mark. Refer to your track timeslips as a base timing gauge. For this example let's say it takes you 2.5seconds from the 60ft mark to the 330ft mark.
4) set the 2nd stage duration on your controller to 2.5seconds, with the target boost at 25psi, and a slower ramp rate.
5) if the 1.5seconds and 2.5seconds are on average pretty correct times to use, then set your third stage to 1second because this is how quick we will ramp the boost up to 30psi. Then set the 4th stage to any duration of time, because now you are already at 30psi and have reached there in a timeframe that does not cause your tires to spin, but still brings in the boost quick enough to win your race.

Does that make sense?

Also...Id look at your front and rear shocks (those Vikings may not be the best selection for what you are doing) along with the rear control arms and rear swaybar. Lastly, what the spring rate is for your front springs.
 
Many years ago people in Salem all thought that it was a good idea to burn a few women at the stake because it was commonly accepted that they deserved it because they were witches.

A majority, and I mean over 90%, of the Buick community uses turbos that are significantly larger than what they need in order to achieve their goals, yet it is common practice to do so, since everyone else does. People do it because they see other people do it, and it becomes commonly accepted. A self-perpetuating practice. People do it because other people do it, thereby causing other people to do so.

Any honest person that knows what type of airflow is required to run mid 9s, would tell you that with today's technology, a 72mm turbo is exxeptionally large for our Buick motors.

If the OP is telling us he wants a "street" car turbo to run mid-9s, a 64mm can accomplish that. Or a PTE or BW 66/66 or 66/67, or a WORK 67/65, or PTE 67/68, or BW 69/68.... PLENTY of options with much better spooling characteristics and broader power bands, than a 72/75.

(Please note that I did not solely mention WORK, but also provided Precision options as well..for those who claim that I constantly "knock" PTE...)

You have a 70mm+ turbo on the street, so therefore what is the issue? That same process of thinking is why people over-turbo their cars.

Is it a newer turbo, or an older unit?

Just because other people do it, does not mean it is the correct choice. However that is a increasingly unpopular approach around these parts, but it is the truth, in certain instances, this being one of them.

For the most part I don't really disagree with what you're saying. You're right, people bolt these giant turbos on there cars and then wonder why they don't perform well. That's not my situation at all. Like I said, it's all about the correct combination.
 
For the most part I don't really disagree with what you're saying. You're right, people bolt these giant turbos on there cars and then wonder why they don't perform well. That's not my situation at all. Like I said, it's all about the correct combination.

100% agree. It is ALL about the correct combination.
 
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