How do gears effect turbo spooling?

joshw2890 · 10-23-2009

I have heard people say that changing gear ratios changes the way turbos behave, and it makes sense because I don't see as much boost in first as I do in second and up. So my question is how does changing rear end gears effect a turbo spooling? I want to maybe go 3.73 one day but what will that do for my turbo set up?

boosted stang · 10-23-2009

3.73 should be fine my brother in law has a 93 rx7 fd turbo with 3.73 spools great

Animal's 3rd · 10-23-2009

Are you running a boost controller?

Animal's 3rd · 10-23-2009

Just spoke with my boss, stay with the taller gear ratios. 3.55:1 would be a good one to go with. turbo motors are different than NA, you don't want to rev the heck out of a turbo motor.
You really should get a boost controller to hold that wastegate shut until you reach the desired boost.

joshw2890 · 10-23-2009

Right now I am running a boost controller yes.

Animal's 3rd · 10-25-2009

What boost controller are you running by chance?

joshw2890 · 10-25-2009

I am running the sts boost controller.

sonicmustang · 4 Weeks Ago

I had 4:10's before i put a turbo on. it was grate but now the turbo doesn't even spool up past 4-5 lbs tell 3rd gear. So i got a 8.8 with stock gears for now, its better than 4:10 but 3:55 would be nice. A locking diff is a must though. good luck!

burnrubber4.0 · 4 Weeks Ago

longer gears allow it to spool longer and build more boost and achieve higher top speed, the trade off with shorter gears is faster out of the hole accelleration. run enough at the track then run the street and try to decide a happy medium. 3:73s did it for me

Animal's 3rd · 4 Weeks Ago

3.73's would probably be ok, 3.55's would more likely be the better option with a turbo though. I do have the feeling that your boost controller isn't working as it should. A good boost controller will hit target boost every time and not go higher or lower in different gears, unless you have an electronic boost controller capable of being programmed like that.

DT444T · 4 Weeks Ago

Quote:

Originally Posted by Animal's 3rd

You really should get a boost controller to hold that wastegate shut until you reach the desired boost.

Be careful setting up your BC that way. If you tell it to hold the WG shut until it reaches the boost setting you want, you might over boost and go lean. Waste gates take some time to open up, so if you want, say 10psi, you tell the BC to open at 10psi, you might spike 11-12psi before it opens up, which can be bad.

Taller gears are better for boost. Short gears are for lower HP cars so that they have a chance. Plus, you'll retain your higher fuel economy. Are you also running larger injectors, or do you not need them?

joshw2890 · 4 Weeks Ago

I am running 39lb injectors. And its opening up at 6 fine. it stops there its just that I only see about 2 psi max in 1st. About 5 psi max in 2nd. And 3 and 4 I can hit 6 psi pretty early on. I was wondering if changing the 3.31 to 3.55 would change any way the turbo spools.

Animal's 3rd · 4 Weeks Ago

Quote:

Originally Posted by DT444T

Be careful setting up your BC that way. If you tell it to hold the WG shut until it reaches the boost setting you want, you might over boost and go lean. Waste gates take some time to open up, so if you want, say 10psi, you tell the BC to open at 10psi, you might spike 11-12psi before it opens up, which can be bad.

Taller gears are better for boost. Short gears are for lower HP cars so that they have a chance. Plus, you'll retain your higher fuel economy. Are you also running larger injectors, or do you not need them?

Thanks for clearing that up, I actually did forget about that because when I think to set the boost just slightly lower, I'm thinking electronic boost controller and not manual.

Animal's 3rd · 4 Weeks Ago

Quote:

Originally Posted by joshw2890

I am running 39lb injectors. And its opening up at 6 fine. it stops there its just that I only see about 2 psi max in 1st. About 5 psi max in 2nd. And 3 and 4 I can hit 6 psi pretty early on. I was wondering if changing the 3.31 to 3.55 would change any way the turbo spools.

Running 3.55's would help you to rpm a little faster so you get a quicker response, but don't go any lower than that. Also, I would have to say that your boost controller isn't working like it should if those are your numbers. If you are in the market for a good boost controller, contact Josh @ 3SX Performance, since you are in North Carolina. Tell him Chris from Turbosmart USA sent you. PM me if you have any questions on what we carry.

DT444T · 4 Weeks Ago

Quote:

Originally Posted by joshw2890

I am running 39lb injectors. And its opening up at 6 fine. it stops there its just that I only see about 2 psi max in 1st. About 5 psi max in 2nd. And 3 and 4 I can hit 6 psi pretty early on. I was wondering if changing the 3.31 to 3.55 would change any way the turbo spools.

What turbo are you running, that might have something to do with it. My gf's is an auto, and I've noticed that first SHOULD be plenty long to spool a turbo to a meager 6psi (Though pressure has nothing to do with amount of airflow). Where are you getting the 2psi at? Is it just hitting 2psi before you shift or does it hit 2psi and hold throughout the revs in 1st? I know in my Z, I get full boost by 2500rpm and holds, and my first goes to ~40mph.