Small Turbo vs Large Naturally Aspirated Engine

[ctechbob]

100% Disagree on towing with a small turbo engine @Jetronic.

The 'little' 2.3L turbo in my Ranger was flat out astounding in every way when we were towing with it. And I'm talking a full size 8 foot wide travel trailer weighing in around 65-6600#s. That engine performed fantastically, and with the 10 speed it was far from revving out. Usually at 70mph on the highway we'd be in 8th gear somewhere between 2300-2600 RPM. I had no intention of getting rid of the truck until a stellar deal came along on my Powerboost, and I really wanted the Pro-Power onboard.

If Ford ever brings the PHEV Ranger (2.3 with turbo) to the US, I'll probably get rid of the F150 provided they offer the PPOB on the Ranger as well.

The 3.5TT with the hybrid system is a whole other world again. It out-grunts the 5.0 (And most if not all of the other V8's) pretty much everywhere when towing, and I get 23-25mpg driving back and forth to work.

 

[Hohn]

This, for me.

I’ve had a low pressure turbo in a gen 1 s60 Volvo, and that did it. the twin turbo ford 2.7 which followed was a delightful motor, and the Tacoma I have makes excellent use of its small turbo. There was a 1.5t civic in the family which was also a delight (manual trans).

All of these are smaller displacement motors, obviously.

For me too. The K20c4 in my Accord is the best engine and driveline I've ever owned likely will be the best I ever own in my entire life.

270lb-ft (370Nm) at 1500 rpm. Artificially limited to that value until 4000rpm. Will annihilate the front tires to 40mph easily, so more torque isn't really beneficial.

Matched to the 10sp auto, I can get 32mpg for a tank with individual commute legs pushing 38mpg. Or it will do 0-60 under 6 seconds if traction permits.

In a naturally aspirated engine, you'll looking at a Coyote or a Hemi to get that kind of low RPM torque. And I promise that a Coyote or Hemi isn't giving 32mpg for a tank on its best day.

 

[Hohn]

100% Disagree on towing with a small turbo engine @Jetronic.

The 'little' 2.3L turbo in my Ranger was flat out astounding in every way when we were towing with it. And I'm talking a full size 8 foot wide travel trailer weighing in around 65-6600#s. That engine performed fantastically, and with the 10 speed it was far from revving out. Usually at 70mph on the highway we'd be in 8th gear somewhere between 2300-2600 RPM. I had no intention of getting rid of the truck until a stellar deal came along on my Powerboost, and I really wanted the Pro-Power onboard.

If Ford ever brings the PHEV Ranger (2.3 with turbo) to the US, I'll probably get rid of the F150 provided they offer the PPOB on the Ranger as well.

The 3.5TT with the hybrid system is a whole other world again. It out-grunts the 5.0 (And most if not all of the other V8's) pretty much everywhere when towing, and I get 23-25mpg driving back and forth to work.

It really comes down to how the turbo integrated-- to the engine, and to vehicle overall.

Obviously, since every hard working industrial diesel is turbocharged, it's not the case that turbocharging excludes heavy duty usage per se. But huge diesel and small gas engines aren't quite apples/oranges.


It's is entirely possible to design a combination the tows quite well and quite effectively with a small turbo. The problem is efficiency. LSPI is the bane of pushing limits with small engine pushing bit loads at low RPM. So if you let them rev a bit to make the power (ala current Tundra, Ford 2.7, etc) they are absolute guzzlers of fuel when highly loaded.

The guy designing a tuning big-boost-at-low-rpm gas engine has to make it stupid rich to suppress knock. Which burns gobs of fuel. Or he has to let the engine rev a bit more-- which ALSO burns gobs of fuel.

NO surprise then that lots of folks buying newer trucks with small turbo engines find that towing heavy with them is an exercise in constant searching for the next fuel station. They handle lighter loads reasonably well if the transmission actually loads the engine a bit. But mostly the newer auto transmissions are tuned to kickdown at slightly hint of work, rev the engine into boost, and gobble up the fuel. Because it's safe and make knocking impossible and that saves warranty dollars.

 

[meep]

It really comes down to how the turbo integrated-- to the engine, and to vehicle overall.

Obviously, since every hard working industrial diesel is turbocharged, it's not the case that turbocharging excludes heavy duty usage per se. But huge diesel and small gas engines aren't quite apples/oranges.


It's is entirely possible to design a combination the tows quite well and quite effectively with a small turbo. The problem is efficiency. LSPI is the bane of pushing limits with small engine pushing bit loads at low RPM. So if you let them rev a bit to make the power (ala current Tundra, Ford 2.7, etc) they are absolute guzzlers of fuel when highly loaded.

The guy designing a tuning big-boost-at-low-rpm gas engine has to make it stupid rich to suppress knock. Which burns gobs of fuel. Or he has to let the engine rev a bit more-- which ALSO burns gobs of fuel.

NO surprise then that lots of folks buying newer trucks with small turbo engines find that towing heavy with them is an exercise in constant searching for the next fuel station. They handle lighter loads reasonably well if the transmission actually loads the engine a bit. But mostly the newer auto transmissions are tuned to kickdown at slightly hint of work, rev the engine into boost, and gobble up the fuel. Because it's safe and make knocking impossible and that saves warranty dollars.

Solid, solid post.

I guess part of the equation then, if towing, is to tow within the performance thresholds for the engine. I never had an issue with the ford 2.7. The tow programming was arguably better matched for my f150 than the normal DD mode. It handled itself that well. With a travel trailer behind it, it yielded nearly identical mpg figures than the naturally aspirated 4.7 I’d had before it. The 2.7 averaged 10-11 while the 4.7 yielded 9-10. I guess the 2.7 still had a 10% improvement. But I was likely well within the parameters of that engine. I also didn’t hammer on it, and often tucked in with big trucks in the mountains not because of power limits but just because I had a 4500 lb trailer behind a 4700 lb truck on twisting roads and didn’t need to be doing anything stupid. If I did put the pedal down, with a load back there I could feel the chassis become unsettled - whether it was frame flex or simply torque against the axle, so for what I was doing, probably within fords expected use, it was awesome. For me then, the savings from the 2.7 wasnt really while towing, but when I wasn’t towing. It was regularly between 20.9 and 21.9 average, in a full-size 4x4, oem wheels and tires, no lift.

But everything youve said is spot on. Run them hot and they have to run rich to avoid detonation. But then also, even in NA motors they do that as well, though probably not to the degree as a boosted motor??

It was Impressive how much heat the 2.7 could put out when run hard. Mine never leaked coolant as a DD, but absolutely wept from the cooling line o-rings when towing in the hills, and man it threw a lot of heat for a while after too.

 

[tblt44]

I like a large v8 no turbo.
Less to go south for the few of us that keep a truck/car 250k plus

 

[Hohn]

Solid, solid post.

I guess part of the equation then, if towing, is to tow within the performance thresholds for the engine. I never had an issue with the ford 2.7. The tow programming was arguably better matched for my f150 than the normal DD mode. It handled itself that well. With a travel trailer behind it, it yielded nearly identical mpg figures than the naturally aspirated 4.7 I’d had before it. The 2.7 averaged 10-11 while the 4.7 yielded 9-10. I guess the 2.7 still had a 10% improvement. But I was likely well within the parameters of that engine. I also didn’t hammer on it, and often tucked in with big trucks in the mountains not because of power limits but just because I had a 4500 lb trailer behind a 4700 lb truck on twisting roads and didn’t need to be doing anything stupid. If I did put the pedal down, with a load back there I could feel the chassis become unsettled - whether it was frame flex or simply torque against the axle, so for what I was doing, probably within fords expected use, it was awesome. For me then, the savings from the 2.7 wasnt really while towing, but when I wasn’t towing. It was regularly between 20.9 and 21.9 average, in a full-size 4x4, oem wheels and tires, no lift.

But everything youve said is spot on. Run them hot and they have to run rich to avoid detonation. But then also, even in NA motors they do that as well, though probably not to the degree as a boosted motor??

It was Impressive how much heat the 2.7 could put out when run hard. Mine never leaked coolant as a DD, but absolutely wept from the cooling line o-rings when towing in the hills, and man it threw a lot of heat for a while after too.

Sounds like you did a good job respecting the 2.7’s design limits and had a great experience.

It’s possible to design a turbo gas engine that has gobs of low end torque AND will have somewhat reasonable efficiency, but it ends up being a VERY costly design that has pretty poor empty MPG. Sort of a one trick pony. Lots of extra coolant and oil plumbing, heat exchangers, etc. Think of a miller or atkinson cycle with undersized turbos coming into boost just off idle.

 

[ctechbob]

It really comes down to how the turbo integrated-- to the engine, and to vehicle overall.

Obviously, since every hard working industrial diesel is turbocharged, it's not the case that turbocharging excludes heavy duty usage per se. But huge diesel and small gas engines aren't quite apples/oranges.


It's is entirely possible to design a combination the tows quite well and quite effectively with a small turbo. The problem is efficiency. LSPI is the bane of pushing limits with small engine pushing bit loads at low RPM. So if you let them rev a bit to make the power (ala current Tundra, Ford 2.7, etc) they are absolute guzzlers of fuel when highly loaded.

The guy designing a tuning big-boost-at-low-rpm gas engine has to make it stupid rich to suppress knock. Which burns gobs of fuel. Or he has to let the engine rev a bit more-- which ALSO burns gobs of fuel.

NO surprise then that lots of folks buying newer trucks with small turbo engines find that towing heavy with them is an exercise in constant searching for the next fuel station. They handle lighter loads reasonably well if the transmission actually loads the engine a bit. But mostly the newer auto transmissions are tuned to kickdown at slightly hint of work, rev the engine into boost, and gobble up the fuel. Because it's safe and make knocking impossible and that saves warranty dollars.

I got the same mileage as just about every other (gas) truck out there. 10-12 mpg when towing. Same as I get with the F150.

 

[ctechbob]

It really comes down to how the turbo integrated-- to the engine, and to vehicle overall.

Obviously, since every hard working industrial diesel is turbocharged, it's not the case that turbocharging excludes heavy duty usage per se. But huge diesel and small gas engines aren't quite apples/oranges.


It's is entirely possible to design a combination the tows quite well and quite effectively with a small turbo. The problem is efficiency. LSPI is the bane of pushing limits with small engine pushing bit loads at low RPM. So if you let them rev a bit to make the power (ala current Tundra, Ford 2.7, etc) they are absolute guzzlers of fuel when highly loaded.

The guy designing a tuning big-boost-at-low-rpm gas engine has to make it stupid rich to suppress knock. Which burns gobs of fuel. Or he has to let the engine rev a bit more-- which ALSO burns gobs of fuel.

NO surprise then that lots of folks buying newer trucks with small turbo engines find that towing heavy with them is an exercise in constant searching for the next fuel station. They handle lighter loads reasonably well if the transmission actually loads the engine a bit. But mostly the newer auto transmissions are tuned to kickdown at slightly hint of work, rev the engine into boost, and gobble up the fuel. Because it's safe and make knocking impossible and that saves warranty dollars.

I got the same mileage as just about every other (gas) truck out there. 10-12 mpg when towing. Same as I get with the F150.

Physics is a cruel mistress.

 

[Hohn]

I got the same mileage as just about every other (gas) truck out there. 10-12 mpg when towing. Same as I get with the F150.

Physics is a cruel mistress.

Quite true, but towing technique plays a role too. The key is to drive as if you have no brakes whatsoever. Leave as much space in front of you as is practical, coast as often as you can. Understand there are indeed practical limits to what this can achieve, but using brakes stopping 6k lb wastes a lot less energy than stopping 12k lb.

 

[CKN]

Solid, solid post.

I guess part of the equation then, if towing, is to tow within the performance thresholds for the engine. I never had an issue with the ford 2.7. The tow programming was arguably better matched for my f150 than the normal DD mode. It handled itself that well. With a travel trailer behind it, it yielded nearly identical mpg figures than the naturally aspirated 4.7 I’d had before it. The 2.7 averaged 10-11 while the 4.7 yielded 9-10. I guess the 2.7 still had a 10% improvement. But I was likely well within the parameters of that engine. I also didn’t hammer on it, and often tucked in with big trucks in the mountains not because of power limits but just because I had a 4500 lb trailer behind a 4700 lb truck on twisting roads and didn’t need to be doing anything stupid. If I did put the pedal down, with a load back there I could feel the chassis become unsettled - whether it was frame flex or simply torque against the axle, so for what I was doing, probably within fords expected use, it was awesome. For me then, the savings from the 2.7 wasnt really while towing, but when I wasn’t towing. It was regularly between 20.9 and 21.9 average, in a full-size 4x4, oem wheels and tires, no lift.

But everything youve said is spot on. Run them hot and they have to run rich to avoid detonation. But then also, even in NA motors they do that as well, though probably not to the degree as a boosted motor??

It was Impressive how much heat the 2.7 could put out when run hard. Mine never leaked coolant as a DD, but absolutely wept from the cooling line o-rings when towing in the hills, and man it threw a lot of heat for a while after too.

10- to 12 towing (gas motors-newer trucks) seems to be universal for all half-ton trucks regardless of power train combo. Especially with the new ten speed transmissions.

 

[Nessism1]

whats more reliable and needs less maintenance small turbo or larger na?

Larger NA. We are painting with a broad brush here, though.

 

[Hohn]

Larger NA. We are painting with a broad brush here, though.

Yes, and preferably with low power density.

While the 6.7 Ram diesel (soon to be even larger) is nearly 60hp per liter, a large industrial engine designed to run a high load all day in and out is about 45hp per liter.

Unfortunately the marketing department doesn’t find any sex appeal in an engine that’s stone-axe reliable but 50hp less than the other guy.

A modern version of a trusty Ford inline 6 or or a mopar slant 6, something L6 and scaled up for 9L displacement to pull a reliable 300-350hp in a gas truck? Gotta be a V8, right? 40hp per liter, dead solid easy reliability. Gobs of long stroke L6 torque.

You know how many large industrial engines are V8? Almost none.

Marketing departments are convinced that truck engines have to be V8s. But that’s based on surveys of customers they have TRAINED to ask for V8s. Not exactly accurate polling! Engine that work for a living are L6 and stay that until they’re V12. The L6 is basically the perfect engine. Perfect primary and secondary balance. Easily packages very long strokes. Packages turbos and such very well.

I am biased. But that doesn’t make me wrong.

 

[RDY4WAR]

I've been impressed with my F150 3.5TT so far. No towing yet, but I've run 2 tanks of 87 (including dealer fill) and now 2 tanks of 93. Same daily route, about 45 minutes of mostly highway. The 87 tanks got 21.3 and 21.5 mpg. The 93 tanks got 22.8 and 23.6 mpg. It runs a lot smoother on 93 so I'll be sticking to it.

 

[4wd]

I've been impressed with my F150 3.5TT so far. No towing yet, but I've run 2 tanks of 87 (including dealer fill) and now 2 tanks of 93. Same daily route, about 45 minutes of mostly highway. The 87 tanks got 21.3 and 21.5 mpg. The 93 tanks got 22.8 and 23.6 mpg. It runs a lot smoother on 93 so I'll be sticking to it.

Try the mid grade?

 

[TiGeo]

Is the low-end torque of a small turbo engine higher than that of a larger naturally aspirated engine when both produce the same hp?

Yes.

 

[stanlee]

Small turbos with early boost are inherently harder on engines (high load at low rpm). This probably only matters if you're like me and keep cars/engines into the 250k plus mile range. Then down the road there's the potential for additional expenses like turbo coolant and oil line failures (pretty common and very expensive due to labor cost). Turbos also don't last forever, especially small ones working hard and hot (also not a concern if your a 5 year/100k mile get a new car guy). The advantages are the obvious: gas mileage when you aren't beating on it, weight and packaging if its the common 2.0L turbo that just about every manufacturer has. I've had 3 turbo cars and 2 of the 3 got bigger aftermarket turbos for reason one. The only one that didn't was an BMW N54 because I couldn't afford to.

 

[Khocke]

76 posts and no “no replacement for displacement” mentions?

 

[4wd]

76 posts and no “no replacement for displacement” mentions?

Perhaps a turbo is the replacement - and space is limited under the hood !

 

[Pablo]

A 400+ cubic inch smog mobile pumping out 150 hp
V.
150 cubic inch turbo beast making 400+ hp?

Come on man!

 

[BMWTurboDzl]

whats more reliable and needs less maintenance small turbo or larger na?

NA simply because turbos have oil and coolant lines to prolong the life of the turbo and the associated piping for the intercooler. If the intercooler is air-to-water then you have even more coolant lines. Turbos also have wastegates which will eventually fail but they're going away.