Small Turbo vs Large Naturally Aspirated Engine

[AdmiralYoda]

One thing I've noticed with many modern cars (especially GM) is that the gas pedal is dead. It has such a lag and is so non-linear that it gives the impression that the engine is a dog. The transmission shift logic and tuning also leaves much to be desired.

The combination of both tends to make the engine feeling gutless unless your foot is to the floor. It is like they designed it so grandma wouldn't be intimidated by the 308hp in her SUV but leaves the rest of us going..."where's the beef"???

I've put an aftermarket tune on my 2021 GMC Canyon w/GM 3.6L and an Equinox with the 1.5L turbo. The response was completely different. It feels like your foot is connected to the throttle body via a cable again and the transmission shifts like it knows what it is doing, really brought the cars to life!

GM should make them all drive like this from the factory. Put an ECO button somewhere for those who want a dead gas pedal and a lazy transmission.

 

[GenSan]

I've yet to truly open up and enjoy the 3.5L twin turbo motor in my 2025 Nissan Armada. I'm awaiting a Fumoto Valve and then I'm putting a 0W-40 Porsche A40 spec oil in it. Whatever is available at Wallys. Most likely Mobil 1. Then I'll have a little fun.

 

[BMWTurboDzl]

Depends on the car. Most day-to-day cars will have small turbos to make boost down low compared to a sportier car where they will look more at mid and high range power.

I don't know about now, but ~10 years ago in some amateur class racing like NASA TT, there was a limit in HP but not TQ. Corvettes were dominating the field because the naturally aspirated v8 made gobs of torque everywhere compared to having a high-strung 4 cyl making low tq but high HP; so you'd have a 430hp/480tq V8 versus a 430hp/250tq I4 turbo.



Depends on the tune and turbo size. BMWs have a very straight hp/tq; VWs have a lot of low end; my evo had a lot of low-mid and none past 5.5k rpms. A stock tune or early-era tune on the evo is low-end tq heavy but tuners have been able to smoothen out the curve like an NA V8 now.

Loosing torque over 5.5k rpm is normal because this is whether the smaller turbos run out of room but at that rpm you're relying on HP anyways and the vast majority of drivers are never at that range anyways. For daily drivers almost all driving is under 3k rpms anyways so the point is rather moot.

 

[JHZR2]

Turbo lag totally varies per manufacture and design. For example

My Tacoma = No lag
My WRX = Lots of lag

Not all turbo engines have that power down low.

Efficiency is a crapshoot. Stay in the boost and you're gonna have terrible mileage. Putter around you might get more over NA, likely not.

Turbo cars are going to be more sensitive to maintenance and won't tolerate missed services like NA.

As I understand it, that’s a design consideration.

A truck wants power down low, so the turbo is optimized for fast spool, fast transients, low lag, but is limited in max flow as a result.

A sports car wants that power down low, but cares as much or more about max hp and max speed and making power at high engine RPMs, so the turbo design is different.

Then you get compounding and twin turbos so you get smaller faster units which spool faster, but have more total flow. And low inertia turbos that aren’t really intended for max boost at any rpm, but optimize for fast spool while also optimizing economy and providing seamless performance (my Saab 9-3 was set up this way).

Longevity also comes into play at higher pressure ratios.

 

[raaizin]

I really like small turbos 2.0 and up, the low end torque really helps drivability.

I agree we had a Q5 A4 and now an Atlas with the 2.0. The low end torque is fantastic. The AudiVW is a fantastic engine. They have been at it a long time. When I ordered my Cayman S I specifically wanted the turbo over the NA 4.0 .

spk2000​

if your looking for a long life vehicle avoid the turbo anything. Increaased pressures lead to increased wear , oil leaks, etc which kills the engine sooner with the possibility of costs for a failed turbo too


I wouldn't worry about modern turbos failing they have come a long way

 

[Oillover]

if your looking for a long life vehicle avoid the turbo anything. Increaased pressures lead to increased wear , oil leaks, etc which kills the engine sooner with the possibility of costs for a failed turbo too


I wouldn't worry about modern turbos failing they have come a long way

Interesting conclusion.

 

[Carmudgeon]

Good stuff.

I’ve got solid respect for how Volvo pulled it off. They already had a stout block in their 5 cylinder. They lowered the compression ratio and added a low pressure turbo - and with reasonable care theres s60s rolling with a quarter million miles on them with the original turbo, head gaskets, etc. granted, those were lower performance mills, and probably lower rpm turbos as well - as pressures were usually capped at 6-7 psi and still had lag - but it showed it could be done with longevity in mind.

I had a red block B230FT, which I guess could be characterized as v1.5 of the B21FT. It ran cooler once the dealer upgraded the original 2-row radiator with a 3-row version under warranty. Despite being oil-cooled only, had 180k+ on of the original turbo before the car was victimized in a hit-and-run. On a diet of dino oil, but with proper care. Only thing I had to fix on it was a broken vacuum line to the wastegate.

I would expect all the lessons learned were carried over to the white blocks, and their turbos.

Many different ways to skin the turbo cat.

 

[meep]

yes, but not usually right at idle. But you will only be in that rpm range when you start from a stop and if you use all the torque you just get tire slip.

For towing, and especially getting going on a hill, a big NA engine is better. Best is a big engine with a turbo.

I have no comparison to agree or disagree, theres a lot of love for displacement….

But towing with the 2.7L ford we had was “luxury class” towing. They /nailed/ the tuning on that thing. It simply didn’t have to rev, ever. The torque converter locked by third gear, the engine stayed around 1800-2200 rpm, and the gas pedal basically drove the turbos. I’d just tuck in with traffic and the camper behind me and the torque was simply there. If I needed to pass uphill on a mountain pass, there was a no-drama downshift to 3000 rpm and done. The turbos in both the 2.7 and this little Tacoma (which is crazy, I pulled 3660 pounds with it last week, smaller pull), really provide a better drivers experience. I don’t have to listen to a V8 wind up to make power on every climb. Drawback - turbo “drone” gets old /fast/. Dental drill can drive you mad.

 

[meep]

I had a red block B230FT, which I guess could be characterized as v1.5 of the B21FT. It ran cooler once the dealer upgraded the original 2-row radiator with a 3-row version under warranty. Despite being oil-cooled only, had 180k+ on of the original turbo before the car was victimized in a hit-and-run. On a diet of dino oil, but with proper care. Only thing I had to fix on it was a broken vacuum line to the wastegate.

I would expect all the lessons learned were carried over to the white blocks, and their turbos.

Many different ways to skin the turbo cat.

You did GOOD with that. Red block turbos used bushing bearings if I recall and could experience buildup issues affecting the bearings. That said, man I always wanted one … RWD wagon with a turbo 4?? Drool.

 

[RDY4WAR]

I have a soft spot for turbos. Our new F150 has the 3.5L ecoboost. We test drove the 5.0L which had good power but doesn't quite plant you in the seat as well.

2025 F150

5.0L V8
- 400 HP @ 6000 rpm
- 410 TQ @ 4250 rpm
- Fuel economy
-- 17 mpg city
-- 22 mpg hwy

3.5L TT V6
- 400 HP @ 6000 rpm
- 500 TQ @ 3100 rpm
- Fuel economy
-- 18 mpg city
-- 23 mpg hwy

What's new to me is how quickly and easily these turbos spool up. I'm used to my aftermarket turbo'd cars being fully spooled at 3500+ rpm. Going up a hill today, the F150 made 7-8 psi at 1400 rpm. It never even dropped out of high gear and climbed the hill seemingly effortlessly.

 

[SubieRubyRoo]

My wife's BMW has a 2.0 twin scroll turbo and is a mild hybrid with an 8 speed automatic. The hybrid mask any turbo lag and the transmission is dialed in perfectly. It supposedly does a 13.9 1/4 mile. The only thing I dislike about her car is the brake feel.

That being said, I don't have the same feeling for her BMW as I did years ago for the 3 series of old.

Other notes, my VW Jetta GLI has a 2.0 turbo and a 6 speed manual. My GLI has lousy engine braking. My wife once had an Accord Coupe V6 with a 6 speed manual and that car had excellent engine braking.

Brake pads are cheaper than any possible engine work besides an oil change. You’re doing it wrong.

 

[skyactiv]

Brake pads are cheaper than any possible engine work besides an oil change. You’re doing it wrong.

There are times I'm on the freeway and need to slow down a touch and don't want my brake lights showing, not because I'm doing anything stupid. Other stick cars I had managed engine braking better when letting off the gas even if in 6th gear compared to my GLI. But yes

 

[SubieRubyRoo]

There are times I'm on the freeway and need to slow down a touch and don't want my brake lights showing, not because I'm doing anything stupid. Other stick cars I had managed engine braking better when letting off the gas even if in 6th gear compared to my GLI. But yes

Plus, generally speaking, reduced engine braking will result in improved mileage, all other things equal…

 

[Carmudgeon]

You did GOOD with that. Red block turbos used bushing bearings if I recall and could experience buildup issues affecting the bearings. That said, man I always wanted one … RWD wagon with a turbo 4?? Drool.

Often got a lot of weird reactions to doing the brief cool down before ignition off, and it was a hassle, but it paid off. Over the course of its life, it did need more than one muffler replacement, though.

If I could do it now, and have use of the time machine mentioned in one of the other topics, I'd bring something like this back with me.

https://bringatrailer.com/listing/1990-volvo-740-turbo-3/