Turbo sizing
 

I'm about to undertake my first turbo project, and have a question on sizing and style of system. First question is twin or single turbo? Second is what sizes? I was looking at a single 76 of twin 57s. Car is a 1985 olds cutlass with a 5.3, 4:10s and a t56. Car weighs about 3200 lbs. Thoughts?

Also, it's used for street, autocross and track days

A lot goes into this. Hard to sell what works for each setup. Gotta have power goals and budget. Single will be cheaper than twins. You also may end up changing that gear, turbos like load. Higher gear may be a nicer car to drive.

William

I forgot to mention, looking for about 600-700 rwhp. I know there is a lot of variable to consider. I am just looking for any guidance I can get being that I don't even know where to begin with figuring out the turbo sizing. I have no experience sizing turbos, so any help would be appreciated.

For that power are you stuck to a turbo route or considering supercharger as well?

Not stuck with a turbo, it just looks like that is what my budget will allow. I've got a friend with a 76mm 1.10 A/R turbo who is giving me a good deal on, I don't want a too bad of a mismatched setup. I was advised against a turbo by a local machine shop who said that super chargers are overly abusive to the bottom end, I understand thousands of people have used super chargers, but was just worth a note. Also, I know a supercharger is more compatible with a standard shift. So moral of story is I am not completely opposed to a supercharger, just opportunity has arisen for a turbo setup at this time.

at that power level either will do the trick easily and reliably ! i run my 63 belair as a twin turbo simply for my OCD. i love the look of semetrical things. and also because of my car has an x frame and routing twins was my only option. however your car you could go either way . some of the questions that need answering before going any further what is going to be your full intention with the car? Autocross? road racing? drag racing? everyday driver? what pecentage of each ? there is trade off's in each your gear ratio is great for autocrossing but not road racing or everyday driving with that power level all you will do is fry tires what are you running for a rear suspension? tubbed? i have over 20,000 miles on mine with twin 56mm on a 5.3 the car weighs 4,700 # and i pull a camper with it too.a friend of mine runs a small shop called one guys garage this is all he does he would be worth a call. here is a link to his shop. no matter what you will never regret what ever way you decide!

http://www.one-guys-garage.com/

The car is 80% street driven, 10% road race, 10% autocross, though I am trying to increase my track time.

I'm upgrading to a quick performance 9 inch and I am getting two center sections to change ratios for track and autocross. Rear suspension is stock as of now, but have control arms and coil overs for the new rear. Running a 27/45/17 now, waiting for new rear before I put some stickier tires (10 bolt rear currently).

Now my question for you, what is the deal with your 5.3, SBE? Also, what rpms do you make power?

And thanks for the number.

I recently finished a twin 62mm build on a 5.3 in a 66 Chevy II. We've since updated to a 6.0 but, the 5.3 performance wasn't far off. While I'm partial to Garrett based turbos, there are very nice Borg Warner options out there to support this very deal. I'd think twin 62-65mm would be a great choice.

Btw...that 4.10 gear should be on the list of things you'll change with the turbo update. They make a lot of torque which you will not need to multiply anymore.

https://youtu.be/CTKhP1tU0l4

https://youtu.be/4MiLkisn-2k