How much would a small turbo affect MPG?

**xinthenight** · 01-13-2008, 08:41 PM

I've read that it helps and it hurts. I've heard that it hurts no matter what, that it helps when you're not pushing it for boost, and just so many different stories.

So what is the case? I'm looking to put a small 5-8 psi turbo on my DD that gets about 28 MPG on premium as it is now.

**jimmybling31** · 01-13-2008, 08:48 PM

Originally Posted by xinthenight

I've read that it helps and it hurts. I've heard that it hurts no matter what, that it helps when you're not pushing it for boost, and just so many different stories.

So what is the case? I'm looking to put a small 5-8 psi turbo on my DD that gets about 28 MPG on premium as it is now.

it will hurt it. when not in the boost it causes resistance in the exhaust. when you get in it, it take increased gas to account for the extra air being forced into it. 5-8 psi is a pretty good bit on an american car.

**Frost** · 01-14-2008, 03:30 AM

If the cost of fuel is a concern or limiting factor, I couldn't imagine that you'd wanna go FI; especially turbo.

**cailey37** · 01-17-2008, 03:46 PM

Ok...first, the idea of a turbo is to force more air into the cylinder. The more air, the more fuel you can add to create more power. It's not that just by adding a turbo it hurts your MPG...it's because you've added more air into the mix so you have to go in and add more fuel in your tune....unfortunatly with more HP comes less MPG....

**2mchtoy** · 01-25-2008, 06:40 AM

If you get a turbo that is a 70mm, it will give you great response and power, As long as you keep your foot out of it, it will drive just like a stocker, get past 3 grand and boost comes in. Get it dyno tuned and you will be fine, That way the computer will tell it when to dump fuel and when not to. My mustang gets 23mpg when not in boost.

**TajMan** · 02-08-2008, 03:25 PM

Take a car that comes in both turbo and non-turbo, like a Mitsubishi 3000GT.

The N/A engine has a 10:1 compression ratio
The twin turbo engine has an 8:1 CR (allows for higher boost and more power, however engine can be making less power at certain rpms)

Because of this, cruising on the highway in 6th gear and out of boost the TT car might get 30mpg where as someone racing their N/A around town is getting 20mpg.

just to give you the idea

however, NOT-rebuilding an LS1 engine and just adding boost- turbo or SC- you will ALWAYS use more fuel than you did N/A.