Ordering the right boost leak tester comes down to one number: the size of the spot where the tester clamps on. Get it right and the tester slides on, clamps tight and seals. Get it wrong and you're waiting on a different size before you can test.
The good news is it takes about two minutes and a way to measure, a tape or idealy a caliper. Here's how to do it, plus the mistakes we see most often.
The Short Answer
- Find where the tester goes: usually the turbo inlet, sometimes the intake pipe in front of the turbo.
- Measure the outside diameter straight across the opening. The outer diameter O.D. and not including the bead on the flange.
- Testing at a flexible hose connection? Measure the O.D. of the pipe that slipped into that hose, since measuring the hose may not be accurate if it is not round.
- Match it to a tester size on our What Size Do I Need chart. If testing on a hard pipe or inlet that O.D. size is matched to the boost leak tester size youll need. If testing at a flexible hose connection youll need and end cap kit, and that end cap will slip into the hose you are testing at.
Step 1: Find Your Test Point
On most cars, the tester goes right on the turbo inlet: the opening on the compressor side where the intake hose connects. Pull the intake hose off and that's what you're measuring.
Some turbos are buried and hard to reach. That's common on Subarus and on a lot of V6 and V8 twin turbo engines. On those, you test at the intake pipe in front of the turbo instead, so that's the pipe you measure.
If you have a vehicle-specific tester for your engine, you can skip measuring. Check Shop by Vehicle Make first.
Step 2: Measure the Outside Diameter
Measure the outside of the inlet or pipe, not the inside. The tester's silicone coupler slides over the outside, so that's the number that matters.
With a tape measure
Hold the tape straight across the opening, through the center, from outside edge to outside edge. If you're a little off center, you'll read short, so move the tape until you find the widest point across the center.
With calipers
Calipers are the most accurate. Open the jaws, close them on the outside of the inlet, after the bead or lip. Check it in two or three spots around the opening in case it isn't perfectly round.
Can't get straight across? Use a string
If something's in the way, wrap a string or a strip of paper once around the outside, mark where it overlaps, and measure that length. Divide by 3.14 and you have the diameter. For example, a string that measures 9.4" around means a 3" inlet.
Step 3: Match It to a Tester Size
Our testers come in sizes from 1.5" to 6". If your measurement is in millimeters, this chart gets you there. Divide millimeters by 25.4 to get inches.
| Tester size | Outside diameter (mm) |
|---|---|
| 1.5" | 38 mm |
| 1.75" | 44 mm |
| 2" | 51 mm |
| 2.25" | 57 mm |
| 2.5" | 64 mm |
| 2.75" | 70 mm |
| 3" | 76 mm |
| 3.25" | 83 mm |
| 3.5" | 89 mm |
| 4" | 102 mm |
| 5" | 127 mm |
| 5.5" | 140 mm |
| 6" | 152 mm |
For testing at a flexible hose, the end cap sizes we have available are:
| End Cap size | Flexible hose Inner Diameter (mm) |
|---|---|
| 2" | 51 mm |
| 2.25" | 57 mm |
| 2.5" | 64 mm |
| 2.75" | 70 mm |
| 3" | 76 mm |
| 4" | 102 mm |
Pick your size on the What Size Do I Need page to see the single tester and the kits that cover it. If you work on a lot of different turbos, a shop kit covers several sizes in one box.
Important - If Testing before the turbo inlet
Look for any Positive Cracase Ventilation PCV return connections or vacuum hose connections. These need to be capped off! We have these in stock. This ensures that the boost leak test pressure does not go into areas where boost shouldnt be. For example, test pressure going in through the the connection and filliing the crank case, and putting pressure on all the oil seals and gasket surfaces.
Common Mistakes
- Measuring a plastic pipe. If the pipe is plastic and flexible, it will collapse when clamping the silicone coupler over it.
- Measuring the inside. The inside diameter is smaller than the outside because of the wall thickness. Measure the outside.
- Measuring the intake hose instead of the inlet. The hose you pulled off is sized to fit over the inlet, so it reads bigger. Measure the turbo inlet or pipe itself.
- Measuring off center. Anything not through the middle reads small. Find the widest point.
- Guessing on twin turbos. Measure both inlets. You'll need a tester on each one.
- Rounding when you're between sizes. If your number lands between two sizes, don't guess. Text us a photo (see below).
Not Sure? Send Us a Photo
Text a photo of your turbo inlet with a tape measure across it to 248-403-8512 and we'll tell you the size. And if you do end up with the wrong one, it happens. Reach out and we'll send a new adapter boot that works with your current end cap, plus the T-bolt clamp, with free shipping in the USA.
Find Your Tester
- What Size Do I Need? (size chart)
- Shop by Vehicle Make
- Shop Universal Testers
- How to Do a Boost Leak Test
Order by 5pm PST Mon–Fri or 2pm PST Sat and it ships same day!