I’m amazed how little attention people pay to boost leaks – as if they have no effect on the way an engine runs. It is 100% critical that a turbocharged/supercharged engine have no boost leaks if you want to have any hope of enjoying a responsive and reliable car.
Any leaks that exist in the charge piping are constant pressure bleeds that the turbo has to overcome to maintain the target boost pressure. This means spinning the turbo faster, which means increased air temperature and more lag. Don’t think that just because you have T-Bolt clamps or you just recently installed your intercooler that you have no boost leaks. Almost EVERY car I test has boost leaks. In fact – T-bolt clamps tend to be the worst offenders!
A vehicle with a mass airflow sensor simply will not run with any significant boost leak. Since the MAF measures air as it comes in through the intake and calculates how much fuel to inject, if any air is lost along the way to the engine the fuel mixture will be totally wrong.
What happens is this: while operating in boost the pressure in the charge piping bleeds out through the boost leak. This bleeding air was metered by the MAF, and is expected to enter the engine. When the air doesn’t arrive (it bled out the charge piping) there ends up being way too much fuel at the engine. The motor goes rich, and the engine loses power or misfires. The same thing happens with a blow off valve that is vented to atmosphere. Metered air is blown out the charge piping and as a result the engine goes rich – usually while decelerating which is why it is not uncommon for engines with atmospheric BOVs to often stall.
I’ve seen boost leaks so bad where the engine simply cannot achieve its target boost pressure, and boost leaks that have delayed spool by over 500rpm.
You need to understand that a car tuned with a boost leak will have entirely different boost response and as a result different boost control tuning than one with no leaks. As a result a dyno tune with a boost leak is a waste of your time and money. If that won’t convince you to boost leak test your car, I can’t think of what will.
Here comes the shameless plug! The reason we developed our boost leak tester 4 years ago was because people didn’t have an easy way to detect and fix boost leaks. Our tester allows the user to pressurize the system from wherever he/she would like using a 3 step tester that has accepts 2”, 2.5” and 3” couplers.
Here’s how you use our boost leak tester:
You can either pressurize the charge piping right off of the turbo, or you can pressurize the system through the intake pipe. If you use the intake pipe however, you MUST plug any hoses that run to crankcase breathers or oil catch cans. Otherwise you will be pressurizing the crankcase which is a big no-no (and will act as a huge pressure leak so the boost leak test will not work correctly).
Once the tester is hooked up and any crankcase ventilation is capped, remove the oil cap and simply connect air pressure to the valve on the tester and watch the gauge. Build 5-10PSI and listen for leaks. It is common for pressure to drop fairly quickly, as air bleeds past the piston rings and valves. However, it should hold pressure long enough to hear and locate any leaks.
See the sample boost leak tester connections:
A few notes on using our boost leak tester:
- There is no need to deactivate the valve-train. The engine will always seal either on the intake valves, or if the intake valves are open, the engine will seal on the piston rings and exhaust valves. In some very rare instances using an engine with high overlap cams the engine may be in a position where both intake and exhaust valves are slightly open. In this case bump the starter motor and try again. Usually you won’t end up in a position where one cylinder is at overlap, but if you do turning the engine over should fix that problem.
- It is always suggested to pressurize through the intake that way you do not disturb the charge piping and can have full confidence that there is no pressure leak.
- Make sure the boost leak tester is securely fastened to the coupler. You don’t want the boost leak tester to let go at 15psi, it has a scary amount of energy behind it.
Preventing boost leaks:
- It’s great to know that we don’t want boost leaks. It’s even better to be able to test for boost leaks, but I’m going to give you a few tips to help prevent boost leaks. I have lost a few races because of a charge pipe popping off, and it was a frustrating learning experience. Learn from my mistakes – follow the points below:
- ALWAYS use charge pipes that have rolled beads or welded beads to provide a mechanical lock for the coupler. Without a bead, its only a matter of time before the pipe slips out of the coupler.
- ALWAYS tighten the clamp square and after the bead. Tightening a clamp crooked gives it the opportunity to work itself square which will result in the clamp loosening up.
- ALWAYS clean your couplers before installing. There should be no oil residue on the coupler or the components to be clamped. If your couplers are saturated in oil, it’s time for new ones.
- Forget T-bolt clamps. They are way too wide to do a good job of creating a sharp clamp on the piping and in many situations there is not enough depth from the rolled bead to the throttle body / intercooler for proper clamp engagement after the bead. This is asking for trouble! Always use high quality stainless steel clamps. Home Depot sells Trident clamps and they are fantastic.
- If you do not have solid engine mounts, ensure there is a provision for the engine movement in the charge piping. Hump couplers allow for this kind of engine movement.
- All of the above notes will help prevent boost leaks. But only one thing will guarantee you will not pop a charge pipe off. That is by mechanically attaching the charge pipe to the component. This is THE MOST IMPORTANT thing you can do. A small boost leak is survivable – a charge pipe that has popped off will surely ruin your day. You can use safety wire, home made brackets, or products available from the after market like these nice boost braces from Vibrant performance.
After reading this, you have NO excuse to have a boost leak or intercooler pipe come out. Happy racing.