If you're looking at an 85 102 turbo, you're probably chasing some pretty serious horsepower numbers and wondering if your drivetrain can even handle the abuse. We aren't talking about a small upgrade for a daily driver here; we're talking about a massive piece of hardware designed to move an incredible amount of air. When you get into the realm of an 85mm inducer and a 102mm turbine wheel, you've officially left the "bolt-on" world and entered the world of custom fabrication, big fuel systems, and hopefully, a very strong roll cage.
I've seen a lot of guys try to jump straight to a turbo this size because they want the "big number" on the dyno, but there's a lot to consider before you pull the trigger. It's not just about the peak power; it's about how that power comes on and what you have to sacrifice to get it.
What Exactly Are We Dealing With?
To keep it simple, the 85 102 turbo designation usually refers to the dimensions of the compressor inducer and the turbine exducer. An 85mm inducer is a hefty size. To put that in perspective, many high-performance street cars are running 62mm to 72mm turbos. Moving up to an 85mm unit means you're looking to flow enough air for anywhere from 1,000 to 1,500+ horsepower, depending on the rest of your setup and how much boost you're willing to cram down its throat.
The 102mm side of the equation—the turbine—is equally important. This is the "hot side" that drives the compressor. Having a 102mm wheel means the engine can breathe. If you had a tiny turbine wheel paired with that huge 85mm front wheel, you'd run into massive backpressure issues. The 102mm wheel ensures that the exhaust gas can actually get out of the way, which is crucial for making big power at high RPMs without melting your valves.
The Reality of Turbo Lag
Let's be honest for a second: a turbo this big is going to have some lag. If you're putting an 85 102 turbo on a small-displacement engine, like a 2.0L four-cylinder, you're basically going to be waiting until next Tuesday for the boost to hit. But on a large-displacement V8 or a high-revving 2JZ or RB26, it starts to make a lot more sense.
Even on a 6.0L LS engine, you're going to notice that it takes a moment to spool up compared to a smaller S300 series turbo. But once it hits? It hits like a freight train. That's the trade-off. You lose that instant "stoplight-to-stoplight" punch, but you gain a top-end pull that feels like it's never going to end. For drag racing or half-mile events, that's exactly what you want. For a tight autocross circuit? You'd probably hate it.
Supporting Mods: You Can't Just "Plug and Play"
You can't just bolt an 85 102 turbo onto a stock motor and expect things to go well. Well, you could, but it would be a very short-lived experiment. When you're moving this much air, everything else in the system has to be up to the task.
Fueling is Everything
First off, you're going to need a fuel system that looks like it belongs on a small ship. We're talking dual or triple fuel pumps, massive injectors (probably 2000cc or larger if you're running E85), and a rock-solid fuel pressure regulator. If you lean out while an 85mm turbo is at full tilt, your pistons will turn into expensive paperweights faster than you can blink.
The Drivetrain Dilemma
Then there's the transmission. If you're running a stock manual or a basic automatic, the first time that 85 102 turbo hits full boost in third gear, you're likely going to leave a trail of gears on the pavement. Most guys running this size turbo are looking at built Powerglides, TH400s, or heavily reinforced manual gearboxes with multi-plate clutches.
Plumbing and Space
Don't forget the physical size of the thing. An 85mm turbo is physically large. You're going to need 4-inch or even 5-inch exhaust piping to really let it breathe. Finding room in a cramped engine bay for that kind of plumbing often requires a "cut first, ask questions later" mentality. You'll also need a massive intercooler to drop those charge air temperatures, because compressing that much air creates a ton of heat.
Why the 102mm Turbine Side Matters
I want to circle back to that 102mm turbine for a moment. A lot of people get caught up in the compressor size (the 85mm part) because that's what determines the ultimate "potential" for air intake. But the 102mm turbine is the unsung hero.
In many older turbo designs, the turbine wheels were relatively small compared to the compressors. This created a lot of heat and backpressure, which is a recipe for engine failure. By having a 102mm turbine, the 85 102 turbo setup allows for a much better "pressure ratio." This means your engine doesn't have to work as hard to push the exhaust out, which actually makes the whole system more efficient. It also helps with reliability because you aren't trapping nearly as much heat in the combustion chamber.
Is It Overkill for the Street?
This is the million-dollar question. Is an 85 102 turbo overkill for a street car? Usually, yes. If your goal is to have a fun car to drive to work and occasionally "show off" on the highway, a 76mm or an 80mm turbo is usually plenty and will be a lot more responsive.
However, "overkill" is a subjective term in the car community. If you live in a place with wide-open highways and you enjoy "roll racing" (safely, of course), then the 85mm might be exactly what you're looking for. There is a certain intoxicating feeling when that giant turbo finally spools up and the car just takes off like it's been shot out of a cannon. It's a different kind of fast. It's not "jumpy" fast; it's "relentless" fast.
Choosing the Right A/R Ratio
When you're buying an 85 102 turbo, you'll also have to choose an A/R (Area/Radius) ratio for the exhaust housing. This is basically the "size" of the tunnel the exhaust gas flows through before it hits the turbine wheel.
- A smaller A/R will help the turbo spool up faster, but it might restrict top-end power.
- A larger A/R will feel laggier but will allow for the absolute maximum horsepower at the top of the RPM range.
For a heavy street car, you might lean toward a slightly tighter A/R to help get that big 102mm wheel moving. If it's a dedicated drag car that's going to spend all its time on a trans-brake or a two-step, go big. You won't care about lag if you're already at 20 psi of boost when the light turns green.
Maintenance and Long-Term Care
Big turbos like the 85 102 turbo generate a lot of heat and put a lot of stress on their internal bearings. Whether you go with a journal bearing or a ball bearing version, you cannot skip out on oil quality. You need clean, high-quality oil and a proper feed and drain line.
One of the most common ways people kill these big turbos is by having a drain line that's too small or kinked. If the oil can't get out of the turbo fast enough, it backs up and blows past the seals. Then you've got a smoke show that looks like a forest fire. Also, always let the car idle for a minute or two after a hard pull before you shut it off. This lets the oil circulate and cool down the bearings so the oil doesn't "coke" (turn into crusty carbon) inside the turbo.
Final Thoughts
Stepping up to an 85 102 turbo is a big move. It's a commitment to a certain type of build—one that favors raw, top-end power over low-end grunt. It's for the person who isn't satisfied with 700 horsepower and wants to see four digits on the dyno sheet.
It's definitely not the easiest path to take. You'll deal with more heat, more lag, and more broken parts along the way. But the first time you feel that 102mm turbine screaming and the tires fighting for grip at 80 mph, you'll probably decide it was worth every penny and every headache. Just make sure you've got the fuel, the block, and the guts to handle it. Happy boosting!