Ford Power Stroke Nation banner

1 - 20 of 26 Posts

·
Registered
Joined
·
175 Posts
Discussion Starter · #1 ·
Hey guys not sure about this so lets talk about it. Would a bigger turbo on stock injectors give better Fuel Economy? In theory you are increasing the air in the combustion chamber offering a better chance of complete combustion... but would it really work like that? Maybe with compound turbos so that you dont have the lag? or Maybe a Supercharged/Turbocharged combo in order to get the extra air in (I dont believe the supercharger would help much since it uses a lot of the engine power to drive it...)

So what do you guys think?
 

·
Premium Member
Joined
·
1,097 Posts
That's a good question.

I run at a very low RPM, so have a very low gas flow rate through the turbo. At 60 MPH (1450 RPM) my boost gauge is barely off the peg. At 70 MPH (1700 RPM) I'm showing 3-4 PSI. No black smoke at either speed, so I don't think I'm short of air.

With a smaller turbo, I'd probably get more boost, but it would impose more back pressure.

If I slow it down even more, I'd probably need a smaller turbo.

This is a part of the performance envelope that few guys think about.
 

·
Registered
Joined
·
14,568 Posts
Less psi seen by the map causes less fueling right? I would venture to guess that a larger exhaust housing on a stock turbo would net more MPG, maybe not a large gain.

Dave, have you tried messing with your wastegate at all?
 

·
Registered
Joined
·
175 Posts
Discussion Starter · #4 ·
In furnace they use about 10% excess air to make a complete combustion
 

·
OBS junkie
Joined
·
8,249 Posts
Generally the rule of thumb is that "less boost while cruising will = better MPG", so long as your EGTs are under control. Something like an H2E, or a similar size turbo would be able to do both. In theory at 0lbs of boost with 500-600* EGTs, we should get our best mileage on the highway. That is as long as the tune your in doesn't start dumping extra fuel when you hit a hill or a strong head wind. But once again that part is left up to the tuner. There are plenty of guys out there with big injectors, big single turbos, & proper tuning that get great mileage on the highway with their setups.
 

·
Registered
Joined
·
4,865 Posts
I have read and seen that you can watch your egts. Lower usually means more complete burn. Anything that could aid better atomization of the fuel or more air. Diesel unlike gasser do not have to worry about detonation from to much air. They will eventually just stall as I understand it.

A centrifugal SC such as a Pro Charger might be interesting as even at cruising speeds its supposedly still is creating more power than what is lost from crank drag. The one I have seen numbers on with a 38R was showing 10 boost at cruising RPM and egts were crazy super low. Even in the most aggressive race tune EGTs never made it to 1000.

straight water injection may also show a small gain even with careful lite driving 1 mpg?
 

·
Registered
Joined
·
233 Posts
I makes since that a bigger turbo (less backpressure) would let the motor run a little more freely. BUT i think diesels like a little boost. Even tho you may not have any back pressure and letting the motor flow good i thnk a little bit of boost is needed for the extra power to keep the truck going with less skiny pedel. I think its just a fine line between it some one who knows alot about turbo sizing could tell you better than i can
 

·
Registered
Joined
·
745 Posts
These trucks are pretty slugish with out boost. I think you would find a decreas in MPG with a bigger turbo. the lag would be to much and you would find yourself on the skinny peddle more to light the turbo thus taking more fuel to get the truck rolling. A supercharger on the other hand would not require as much fuel and would create boost instantaly and you would not have to apply as much fuel to get the truck rolling. But than you are taking HP to turn the supercharger.
 

·
Registered
Joined
·
2,897 Posts
A bigger turbo will not flow more air necessarily, if sized right it will move an equal amount with lower backpressure.

This means for the same charge air less hp is required/lost in the turbine.

I got +1-2 mpg on stock injectors with a large frame turbo. The boost going down the highway was actaully lower most of the time. Backpressure was half what it was.
 

·
Hater Club
Joined
·
3,602 Posts
Hey guys not sure about this so lets talk about it. Would a bigger turbo on stock injectors give better Fuel Economy? In theory you are increasing the air in the combustion chamber offering a better chance of complete combustion... but would it really work like that? Maybe with compound turbos so that you dont have the lag? or Maybe a Supercharged/Turbocharged combo in order to get the extra air in (I dont believe the supercharger would help much since it uses a lot of the engine power to drive it...)

So what do you guys think?
That's a good question.

I run at a very low RPM, so have a very low gas flow rate through the turbo. At 60 MPH (1450 RPM) my boost gauge is barely off the peg. At 70 MPH (1700 RPM) I'm showing 3-4 PSI. No black smoke at either speed, so I don't think I'm short of air.

With a smaller turbo, I'd probably get more boost, but it would impose more back pressure.

If I slow it down even more, I'd probably need a smaller turbo.

This is a part of the performance envelope that few guys think about.
Using single shot style injectors and a larger turbo will "improve" fuel mileage with proper tuning and PROPER DRIVING habits.

At 60-65mph, I barely push more than 2psi and EGT's are below 600* on relatively flat ground. A lot depends on weight and gearing as well. As another general rule, keeping the engine under 2000rpm's helps out as well.
 

·
Junior Mint
Joined
·
2,461 Posts
If you found yourself often having a fair amount of boost on the stock turbo (I'd gander anything over 6-7 psi) when you were cruising for mpg, then yes a larger turbo would reduce back pressure and therefore up effieciency. If you were looking for better mpg for your hot-shot rig that is usually loaded than there is no doubt that a larger turbo would improve efficiency and therefore mileage.

If your cruising boost is already very low (say less than 3 psi) than no, it would not help and could quite likely lower mpg to go larger on the turbo because of a lack of air flow and the need to push the skinny pedal more to get moving.
 

·
Registered
Joined
·
14,568 Posts
If you found yourself often having a fair amount of boost on the stock turbo (I'd gander anything over 6-7 psi) when you were cruising for mpg, then yes a larger turbo would reduce back pressure and therefore up effieciency. If you were looking for better mpg for your hot-shot rig that is usually loaded than there is no doubt that a larger turbo would improve efficiency and therefore mileage.

If your cruising boost is already very low (say less than 3 psi) than no, it would not help and could quite likely lower mpg to go larger on the turbo because of a lack of air flow and the need to push the skinny pedal more to get moving.
That's exactly my thinking.
 

·
OBS junkie
Joined
·
8,249 Posts
A bigger turbo will not flow more air necessarily, if sized right it will move an equal amount with lower backpressure.

This means for the same charge air less hp is required/lost in the turbine.

I got +1-2 mpg on stock injectors with a large frame turbo. The boost going down the highway was actaully lower most of the time. Backpressure was half what it was.
What turbo were you running with stock injectors?
 

·
Registered
Joined
·
2,897 Posts
How did it run with stock sticks & an auto?
Much better than the stock charger. The low end smoke was exactly the same (spooling very slightly slower if any) with the same programming. Top end is where the biggest difference was noticed, instead of that rough doggy sound (high backpressure 70psi absolute w/stocker) it ran super smooth with the same exact boost pressure and less than half the baclpressure. It gained a tremendous amount to power on the top end and towed a whole lot better.

The ONLY time I had spooling issues with that charger were with the hybrids in the heavier fueling programs. The low end fuel can completely snuff a large charger, the way around this was to bring the fuel in slower. (not matting it) A tuner could have fixed this for me easily.

Empty mileage was +1-2 better, cruise boost/egt's both went down a considerable amount.
 

·
Haters Gonna Hate
Joined
·
5,868 Posts
Much better than the stock charger. The low end smoke was exactly the same (spooling very slightly slower if any) with the same programming. Top end is where the biggest difference was noticed, instead of that rough doggy sound (high backpressure 70psi absolute w/stocker) it ran super smooth with the same exact boost pressure and less than half the baclpressure. It gained a tremendous amount to power on the top end and towed a whole lot better.

The ONLY time I had spooling issues with that charger were with the hybrids in the heavier fueling programs. The low end fuel can completely snuff a large charger, the way around this was to bring the fuel in slower. (not matting it) A tuner could have fixed this for me easily.

Empty mileage was +1-2 better, cruise boost/egt's both went down a considerable amount.
how would i go about reading the bp on my 6.0? id like to try and get a few more mpg's outa the ol girl so im thinkin gears and different charger, any reccomendations?
 

·
OBS junkie
Joined
·
8,249 Posts
Much better than the stock charger. The low end smoke was exactly the same (spooling very slightly slower if any) with the same programming. Top end is where the biggest difference was noticed, instead of that rough doggy sound (high backpressure 70psi absolute w/stocker) it ran super smooth with the same exact boost pressure and less than half the baclpressure. It gained a tremendous amount to power on the top end and towed a whole lot better.

The ONLY time I had spooling issues with that charger were with the hybrids in the heavier fueling programs. The low end fuel can completely snuff a large charger, the way around this was to bring the fuel in slower. (not matting it) A tuner could have fixed this for me easily.

Empty mileage was +1-2 better, cruise boost/egt's both went down a considerable amount.
That's exactly the info I've been looking for Andy, glad to hear from someone that's run a larger frame turbo on stock sticks.
 

·
Registered
Joined
·
2,448 Posts
the only way it would is if you could stay outta the skinny pedal.
also, a few spooling mods (ceramic tubular headers, ported heads, etc) I think would help with that as well.
 

·
<----Nice headlights!!!
Joined
·
1,868 Posts
all things considered and equal(which our trucks are all ever so different) in perfect driving conditions the larger turbo would be more efficient in terms of fuel combustion. You'd not gain alot of mpg's so you'd have to do TONS of driving to justify it that way. Towing or in unperfect condition(most are) the larger turbo with stock inj would be beneficial. Throw in a tuner and good intercooler and the gains would be substantial. Not to mention all of these things would negate pumping losses(heat) which is our #1 enemy.
 
1 - 20 of 26 Posts
Top