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Yes Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 28 Apr 2006 05:39:28
In Reply to: Does turbo condition effect gas mileage?, Goyo, Thu, 27 Apr 2006 11:18:42 Members do not see ads below this line. - Help Keep This Site Online - Signup |
A turbo in better condition improves gas mileage. A turbo actually improves engine efficiency by reclaiming some energy that would have been lost in the exhaust. Now, more power is more fuel, so if you wail on the car, you'll use more gas. But a turbo car with a marginal turbo system is wasting fuel.
It may not be the turbo that's the problem. The typical failure of the turbo is for the bearings to fail, and either leak oil into the intake (which burns as blue exhaust), or for it to just stop spinning. Turbos themselves usually don't loose efficiency. If you aren't getting full boost, it's most likely something else, something that may be easy to fix.
The boost gauge tells you the pressure in the intake manifold. Depending on year, the colors change, but let's say that the left side of the gauge is green (sometimes white), the middle is yellow, and the right is red. With the car off, the needle should be right at the gap between green and yellow. That's atmospheric pressure. Makes sense - the engine isn't running.
At idle, the needle will be in the left side - vacuum. Depending on idle speed and the like, it may be way to the left (like 8:00). That's because the throttle plate is almost closed, but the engine is running, sucking in air through that almost closed plate. The turbo isn't spinning (much) because there is very little exhaust.
In a non-turbo car, the intake pressure is always at least some vacuum. With the throttle partially closed, there will be a low pressure area behind the throttle plate. Even with the throttle wide open, the intake is at a slight vacuum - otherwise air wouldn't be pulled in.
As you drive, the turbo will spin up with engine speed and flow. By definition, once the needle gets into the yellow, you are not boosting - the turbo is pushing air into the intake at above atmospheric pressure. The actual boost pressure will depend on engine speed and load.
Red is too high - you shouldn't see the needle in the red unless there is a problem with the system or the car has been modified.
So, as a driver, what do you do with the boost gauge? Nothing - watch the road. You don't need to drive to it, or otherwise change your driving habits.
It will tell you if you have turbo issues. First, you want to know your full boost level. Find a nice long uphill. Accelerate hard up the hill - I find around 45 mph is pretty good. See where the needle goes.
If the needle goes into at least the yellow, then the turbo is working. It should go right up to the edge of the yellow/beginning of red. That's full boost.
If the needle only goes to the middle of the yellow and then stays there (until you back off the gas or run out of hill), then you are at Base Boost. The turbo system adjusts to keep the engine from knocking. If it doesn't detect knock, it will go to full boost. If it detects knock, it drops the boost back to about half-yellow - base boost. This reduces knock.
If your engine is at base boost, there can be a lot of reasons. The first would be that your car needs a higher octane fuel than you're using. To at least diagnose the problem, put in a tank of premium, if you aren't already running it. If that gives you more boost, you know your engine is kocking and the APC (automatic performance control) is adjusting for it. Your engine may or may not require premium, but at least you've diagnosed the problem. If a tank of premium doesn't fix it, then there are other things to look at. See the Base Boost FAQ.
If your car takes premium, you may be able to run a lower grade of gas. How are your spark plugs? The right plugs in good shape, properly gapped, is critical. You don't mention the year of your car - if you have a car with adjustable timing, make sure the timing is correct. Too advanced, and the car will knock. When you pulled the plugs, how did they look? They should be a nice grey. If they're white, you're running lean, which can cause knock (and overheating, burned valves, etc.). Lean running is usually due to one or more vacuum leaks - bad hoses, etc. There can be other issues, like a bad fuel pressure regulator, old and clogged fuel filter, or old and clogged air filter.
At a minimum, a tune-up before chasing other issues is a good start. And a great way to improve gas mileage.
posted by 192.249....
, Fri, 28 Apr 2006 05:39:28 <-- Viewing This Message
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