Bigger Turbo Question

This is a pretty general question regarding turbocharged cars. If someone were to swap out their stock turbo with a larger turbo, would their cruising fuel economy (sayyy 60mph) with the larger turbo be better than their cruising fuel economy with their smaller stock turbo? Logic tells me since the larger turbo spools later and hits max boost later in the RPMs, you’d get better mileage with the larger turbo.. but I’m also not an expert on forced induction and I can’t find any literature online.

My particular setup is a North American Audi Q5 tdi with a dpf delete, 3” to dual 2.5” straight pipe exhaust, Darkside intercooler, and Malone Stage 2+ tune. I’m looking at the Darkside GTD2872VRZK turbo and I’m wondering about the outcome of mileage compared to stock. I currently get 39-42mpg on the freeway and I’m only willing to go with A larger turbo as long as it won’t hurt my mileage; my car is primarily a family trip car but also an all-in-one fun car for me. Thank you for any input!


Sent from my iPhone using Tapatalk

Here are my thoughts:


In a perfect world, with no wind, hills or anything else that can play a role in MPG we have starting point A and ending point B. With this perfect car and 100 HP and 200 lb ft of torque it works hard enough to get from point A to B using a certain amount of fuel. With the same perfect car and 200 HP and 400 lb ft, for it to go the same distance the engine is working less, thus more efficiently. More power, makes the engine work less, if the conditions remain the same. The problem is we have heavy feet and seem to hit the go pedal a little harder (well at least I do, lol), negating the MPG increase.

cuban11182 said:

The problem is we have heavy feet and seem to hit the go pedal a little harder (well at least I do, lol), negating the MPG increase.

Click to expand...

Lol I’ll definitely be hitting the go pedal and using that speed from time to time BUT when I’m not using all that power and just cruising at low RPMs (~1400 - 1500rpm), would I my engine be using less fuel? [emoji2955]



Sent from my iPhone using Tapatalk

Smaller turbo works with better efficiency while cruising which usually also effects in fuel consumption.

cuban11182 said:

With the same perfect car and 200 HP and 400 lb ft, for it to go the same distance the engine is working less, thus more efficiently.

Click to expand...

This is not true. Diesel engines best efficiency is usually near to max torque point. Google for "TDI BSFC" and you'll find some charts.

Definitely not going to improve fuel efficiency with a giant turbo. Well, maybe at speeds over 120 mph. How big of a hit at 80 mph? Dunno, maybe 2-4 mpg?

DieselDeeds,
Just buy a bigger turbo. It's not going to save
you any fuel, but it will be more fun to drive.
Lol, stop floundering around seeking justification,
this is the wrong place for that.

Rrusse lol for sure man. I just don’t want to get the bigger turbo and all of a sudden my mileage is cut in half. Just wondering if the mileage will be better, worse, or so close that it’s negligible. I want the power but without the cost of horrible mileage [emoji1360]


Sent from my iPhone using Tapatalk

No free lunch with more power. Drive it gently and you'll probably take
a mild hit. But what else can you get that returns anything like that FE?
At 75-80 on the highway I get low 40s with winter fuel. I'm pretty heavily
modded, I got no problems with the FE vs performance. You play you pay.

Calculate how much fuel you can buy and how many miles you could drive with the cost of the turbo. Hahahaha.

Do it for the fun and power. If you are worried about mileage, you probably are barking up the wrong tree.

I have a 2872 and have been pounding the piss out of it. Still well over 30mpg.

The 2872 probably isn't a good choice unless you are going to do a full build with CP3 pump,, injectors, valve springs etc. Otherwise you get all the lag of the big turbo but can't realize it's potential.

If you plan on keeping the stock head and fueling, the 2260 is a much better choice.

Errm... Turbo size will not affect for fuel effeciency quite much at all. Even turbo/NA differences are usually so small that it isn´t even noticeable, difference can be also one way or another. I have quite much stock effeciency with lowered CR, 0.341mm and HX35 on my Golf 3, 4-6 liters per 100km depending how i drive.

And if it would have any difference, who cares about few deciliters any way if you even think to make more power.

travis45 said:

The 2872 probably isn't a good choice unless you are going to do a full build with CP3 pump,, injectors, valve springs etc. Otherwise you get all the lag of the big turbo but can't realize it's potential.

If you plan on keeping the stock head and fueling, the 2260 is a much better choice.

Click to expand...

The OP has the 3.0L V6 not the 2.0. So it wouldn't be nearly as laggy in that application.

turbobrick240 said:

The OP has the 3.0L V6 not the 2.0. So it wouldn't be nearly as laggy in that application.

Click to expand...

Doh! Of course, that makes a ton more sense then.