cjg454ss

iTrader: (27)

this guys got it.

TURBHOE

iTrader: (4)

i agree but i'm talking out of boost low throttle mid loads. like unloaded through appilachain mountains. my trailer was small and at maybe 2000-3000 pounds. it was easier to climb the grades with out even having to roll into boost. some hills i did have to you 1-2 pounds but that was it. where as before i would have to go half throttle unlocked in third. again tune is key also. with only 1-2 pounds i left the tune to run around 13:1 afr, with no kr. but the fact still remains that the turbo is moving more air than normal under same load and throttle positions as no turbo while not in boost. thats might point to all this.

now, i did tow a 30ft camper through some steep *** hills in arkansas (yes they have a few). i think had it not been for the turbo it would have been a looong ride. i had to (via data loging) shift down to second and use the turbo to pull the hill with the tcc locked. but i did this mostly to keep my trans cool. it was peak of the day heat middle of summer. and i didn't like riding the torqueconverter out for that long of a grade. it just made too much heat for my liking. of course my dad with his cummins and even heavier trailer walked me like nothing. but my uncle with the ford and lighter trailer behind me showed up about 30 mins after us. lol. but i have never pulled this load with out the turbo so i can't prove anything here.

smokeshow

iTrader: (16)

Tune comes into play again Part throttle is what I am getting at here too. Fuel mileage and efficiency go out the window at WOT, so thats out of the question. It is difficult to illustrate because there aren't a lot of long grades like that where you can actually calculate average mileage up the grade. Your Tahoe downshifted before because it couldn't creep into boost and stay in OD. If the grade was steep enough, and long enough for you to calculate fuel mileage, you'd be able to see that when you shifted into 3rd, your mileage would have increased versus you lugging along at 1-2psi in OD. It's sweet to be able to do that, but it doesn't mean you're getting better mileage just because you're turning a few less RPM.
This is why trucks with towing packages typically come with lower gearing in the rear end. More mechanical advantage means less load on the engine, and therefore better mileage when you drop a heavy *** trailer behind it.

cjg454ss

iTrader: (27)

think of it like this....

on an n/a motor it takes say 15hp to spin the rotating mass of the engine at and produce 300hp.

turbo motor takes 15hp to spin and now makes 500.

Hemitruck04

So if you live in a world that has limited part thorttle tuning for boost would it be wise to go with a LARGE unit lets say this S400sx unit that supports 850 hp with a T6 1.10 AR with a 83mm compressor, who thinks this may be too big for a 5.7 liter?

smokeshow

iTrader: (16)

You said it yourself, a turbo provides backpressure. A hell of a lot of it at that. Let's do a little math... Take your 50psi of backpressure for example, coming from a T4 turbo at WOT at x RPM. Your engine is a 6.0, so the bore is 4" even. To find area of that piston, use pi*r^2=12.56 square inches. When your piston is running up the cylinder with the exhaust valve open, it is experiencing 50 pounds per square inch of pressure. 50*12.56=628 pounds of force on the top of the piston. For simplicity's sake, I won't get into how to calculate how much energy is expended pushing the exhaust out of the cylinder over the entire duration of the exhaust stroke because that would require calculus, and you don't want to read through that. SO...we'll just use the piston's position halfway up the cylinder, where the crank is nearly 90° with the rod. Stroke of the 6.0 is 3.62", so half that for radius of crank is 1.81/12=.151 feet. Torque is T=force*radius*sin(X°), force being pounds, and radius of the crank. Torque required by the engine to expel exhaust gases at 50psi is T=.151*628=94.8lb-ft of torque. This is instantaneous at 90° crank angle...doing the calculation on paper, the torque consumed by backpressure over the entire exhaust stroke is 94.8*.636=60lb-ft. So you can figure each cylinder is making 60lb-ft less than it could be because of backpressure created by the turbo.

These are called pumping losses, which take away from the engine's ability to create maximum torque. While backpressure is not often/ever as high as 50psi, it is always higher in a turbocharged application regardless of manifold pressure because the exhaust is no longer free-flowing like N/A engines. Therefore, you make less power out of boost with a turbo.

So I just proved it mathematically...saying that both a turbocharged and naturally aspirated engine take the same X amount of horsepower to run at x RPM is incorrect.

chpspecial

iTrader: (1)

This is fine and dandy at WOT when a turbo see's full load, so therefore at full load, the turbo consumes 60lb-ft of torque to make 700+at the wheels. But at part throttle when the turbo is "free spinning" there is no 50psi of back pressure, there should be little to no back pressure, therefore the turbo shoul not be consuming any torque. This is also why turbos have delay...

Edit, I do agree that there is more pumping losses on a turbo vehicle over an N/A one

charcold-bowtie

iTrader: (10)

I cant believe you still think this is an argument lol.

cjg454ss

iTrader: (27)

also 50psi of back pressure is horrible. a t4 70mm turbo will never see 50psi on a 5.3 at 5500rpm with 10psi of boost. it may be 15psi or so.
thanks you. back pressure is not exsistant at idle. i know my camaros turbo wont even spin when its cold and idling. but just to recap, PER PISTON STROKE a turbo wil lmake more power thus increasing the efficiency and even though the boost gauge doesnt read boost.. it still is increasing efficiency and will little to NO BACK PRESSURE. no if you put a T6 flange turbo on a 5.3 you will lose mpg because unless you building a track racing 4 door silverado a t6 turbo is a poor choice. a turbo that provides instant boost would be better for towing and general performance.

also 50psi was an extremely poor setup. a t67 on a 5.3 at 55rpm might see 15psi at 10lbs of boost.

smokeshow

iTrader: (16)

If you shove exhaust down a 3" pipe, its going to flow better than through the tiny T4 scroll. Less backpressure, less pumping loss, more torque available from the engine.

Efficiency can be difficult to understand. More power simply does not mean more efficient. As I said before, if power=efficiency, we would ALL have monster CI big blocks with some sweet gas mileage.

You're right, backpressure at idle probably can't even be measured with a gauge. But what is the cylinder air mass? It's extremely small. The engine at idle only consumes enough air and hence fuel to keep it rotating. As soon as you load the engine though, the engine WILL begin to flow more air. That's where your backpressure comes from.

Tell you what, give this a shot if you don't believe me. Get a drinking straw and something a little bigger in diameter, like a piece of 1" PVC or something. Spend a few minutes breathing out through each of those. Hell if you're up to it, do it for half an hour. Then you tell me which requires more work from you, the tiny opening of the straw or the larger PVC. I'm sure you'll be exhausted and nearly asphyxiated breathing out through the straw. It is no different with an engine. The more work YOU (the engine) have to spend blowing out through that tiny straw (a T4 turbo), the less you have available to use elsewhere. Like propelling a vehicle...