4.556 Final Drive with a Turbo Setup
 

Currently running a 4.556 Final Drive with my Auto 86 from back in my NA days and have since been turbo'd for over a year running a Garrett GT3076r on 7psi. Planning to run a boost solenoid to run dual maps so I can up the boost to 11psi for my high boost map.

Been thinking about going back to the stock 4.1 Final Drive. My understanding is that turbos work on load and with the shorter gears, I won't be building enough boost and will just end up shifting too much? And especially since I'm looking to increase my boost, I should be wanting to stay in gear for longer?

Side question; does shorter or longer gearing have any impact on the reliability of a turbo setup?

Fd / gearing shouldn’t have an impact on reliability.

What is the goal and or use for your car? Track? Autocross? 0-60? 0-100/60-100? 1/4mile? Or just a “fun” DD?

You'll have more wheel spin with a shorter fd and turbo. It depends what you want. In general the rule should be that when you have more power, then you should go to a longer fd. You are losing time by shifting too much.

At least your running an auto, otherwise I imagine you'd have gotten tired of wheel spin by now. Is your block built? Do you have upgraded valve springs and retainers?

I would look for a 4.1. Surely someone would love to trade with you (however you'd organize that...)

Just a weekender, sometimes driven on weekdays. No real intention for the drag strip or any track days.

Completely stock engine. Only supporting mods I have is an oil cooler and catch can.

Dibs on 4.5 FD

With out a more specific “goal” it’s hard to say. With lower boost and especially on a turbo with sticky tires I doubt wheel spin is an issue?
Based on what you said, Fixing wheel spin would be the main reason to swap. Unless you can do the swap cheaply I’d just stay the same.
Choosing the best final drive for your setup is entirely based on your goals. Your 4.5 will
Be faster to 88mph but slower to 94mph then faster again to around 105mph. 4th gear is so unusable on autos with the 4.1. But you may not care about going 100+ then maybe the 4.1 is better if you just want to do 0-94mph pulls or whatever.

Especially running a 30r, I'm surprised getting shot into the rpm limited hasn't had you floating a valve yet! That's great to hear, not enough success stories. I've already got my catch can and oil cooler for when I go FI. I think you'll love being able to hang in a gear longer with that turbo.

What wtq figure ? I don't mean to derail, I'm just surprised you've gone a year with that turn with only basic supporting mods especially with that fd. It'll take away your initial launch being in an auto, but you'll more than make up for it with gearing

Current at 230kw/365nm on a hub dyno. I try not to go too hard in 2nd gear, most of my fun is done in 3rd gear and above so wheel speen is generally not an issue. Have heard too many stories of people breaking their transmissions by launching too much and flogging it in 1st/2nd.

I think the stock AT final drive and JRSC power match very well on my car. Acceleration at any speed is perfect for me. Power is just one tap away. If I don't need the power, the engine is so quiet at low rpm. Just reinstall the stock final drive.