Turbo theory
12-17-2010, 09:47 AM
#21
Jake your only thinking on one side of the motor here. True there are some additional pumping losses incurred from the additional "restriction" in the exhaust side of things, but efficiency deals with the whole engine and under part throttle and light loads on a FI set-up the intake stroke will also see much less resistance. A quarter of the work done on a 4 stroke engine in the intake stroke which requires quite a bit to "suck" in the intake charge. TURBOHOE mentioned it before, even when the turbo isn't creating boost it's still helping, quite a bit actually and what it does more than off-sets the little restriction that is seen during part throttle on the exhaust size.
Take your own example that you mentioned with straws and instead of breathing out for half hour, breath IN...and tell us which one tires you out more. You gotta remember there are 4 strokes and in each stroke there is the ability to gain and lose pumping loss efficiency. The exhaust stroke might lose some a frational amount of efficiency under part throttle but the intake stoke will gain quite a bit more than the exhaust side loses. Hence why the saying goes that a turbo will make a engine more efficient while cruising.
Take your own example that you mentioned with straws and instead of breathing out for half hour, breath IN...and tell us which one tires you out more. You gotta remember there are 4 strokes and in each stroke there is the ability to gain and lose pumping loss efficiency. The exhaust stroke might lose some a frational amount of efficiency under part throttle but the intake stoke will gain quite a bit more than the exhaust side loses. Hence why the saying goes that a turbo will make a engine more efficient while cruising.
12-17-2010, 09:51 AM
#23
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As well as the straw demonstrates nothing. You think me haveing psi forced into my lungs will make me fast? you comparing one way flow to 2 way
As well as the straw demonstrates nothing. You think me haveing psi forced into my lungs will make me fast? you comparing one way flow to 2 way
12-17-2010, 10:29 AM
#25
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...
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...
how much power does your truck make? whats the max rpm? is the 5.3 stock of built? how much boost are you running?
12-17-2010, 11:24 AM
#26
Jake your only thinking on one side of the motor here. True there are some additional pumping losses incurred from the additional "restriction" in the exhaust side of things, but efficiency deals with the whole engine and under part throttle and light loads on a FI set-up the intake stroke will also see much less resistance. A quarter of the work done on a 4 stroke engine in the intake stroke which requires quite a bit to "suck" in the intake charge. TURBOHOE mentioned it before, even when the turbo isn't creating boost it's still helping, quite a bit actually and what it does more than off-sets the little restriction that is seen during part throttle on the exhaust size.
Take your own example that you mentioned with straws and instead of breathing out for half hour, breath IN...and tell us which one tires you out more. You gotta remember there are 4 strokes and in each stroke there is the ability to gain and lose pumping loss efficiency. The exhaust stroke might lose some a frational amount of efficiency under part throttle but the intake stoke will gain quite a bit more than the exhaust side loses. Hence why the saying goes that a turbo will make a engine more efficient while cruising.
Take your own example that you mentioned with straws and instead of breathing out for half hour, breath IN...and tell us which one tires you out more. You gotta remember there are 4 strokes and in each stroke there is the ability to gain and lose pumping loss efficiency. The exhaust stroke might lose some a frational amount of efficiency under part throttle but the intake stoke will gain quite a bit more than the exhaust side loses. Hence why the saying goes that a turbo will make a engine more efficient while cruising.
Unless it is creating positive manifold pressure, a turbo is still a restriction in the intake side as well as the exhaust side. I did not mention the breathing in side of things because its essentially the same thing...mildly induced vacuum as opposed to mild backpressure. WOT, things change, obviously..
I understand that the turbo helps create more power than it consumes while it is making boost...otherwise we wouldn't be having this conversation at all. Efficiency is the use of as little resources as possible to make maximum power in the case of engines. But power is NOT synonymous with efficiency. And because the turbo does not make boost while cruising and is therefore a restriction in the intake side and exhaust side, it works very much the opposite in terms of efficiency.
I'm talking fuel efficiency here; of course the turbo turns the volumetric efficiency around once it spools up, but its not all of a sudden making more power per X amount of cylinder air mass. Air is proportional to fuel in a gas engine, and the whole mixture gets richened up a point or two before it even starts making positive manifold pressure. That in itself should explain why fuel efficiency can't magically go up.
12-17-2010, 01:40 PM
#28
I have never calculated the mpg of my truck with the 408 but it has got to be somewhere in the 10 mpg range. Send me some funds and I will drive to Arizona and back and calculate mpg then I can go up a mountain pass and back down with some street driving mixed in and get another mpg range. That would be with the 408 and a tune already in there.
After I install the turbo I can do the same and see if mpg improved or not. No WOT runs though as that would skew the results.
After I install the turbo I can do the same and see if mpg improved or not. No WOT runs though as that would skew the results.
12-17-2010, 01:47 PM
#29
I think the turbo increases efficiency. My mpg has been basically unchanged over the years from non turbo to turbo. But I had a very good tune before the turbo. But as far as the engine doing work it comes with great ease now. Cruising through the hills I no longer have to down shift or unlock the tcc. It's not often I even have to go about 33% throttle. I think just because there is no boost shown on the boost gauge doesn't mean the turbo isn't at work.
I missed the other thread though.
I missed the other thread though.
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.
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.
This is what I wrote in the other thread.
Using that same scenario two identical trucks are at the light. They both want to get to 45 MPH(speed limit) so when the light turns green they both hit the gas peddle to 35%. The truck with the turbo gets to 45 in 5 seconds then lets off the gas enough to maintain that speed. The other guy has to stay in it an extra 2 seconds to reach the same speed. The turbo truck would have used more gas in the 5 seconds than the non-turbo truck but the later has to stay on it for 2 more seconds. So the non-turbo truck has to have the pedal to 35% for 7 seconds vs 5 for the turbo truck. Somehow, the turbo truck manages to save some fuel because of that.
Also, if the two trucks are on the highway and want to overtake another car or are going up a hill and want to maintain their current speed or both they would have to give it more gas. At one point the non-turbo truck would give it sufficient gas to cause the truck to kick down to a lower gear where the turbo truck would stay in gear and still be able to pass or maintain the speed.
On the Black Hemi whenever I would go up a hill I would get sucked into boost(3-5 psi) really fast because of the load. This was not good because there was no tuning originally so you would have boost at 14.7 A/F. The only time the A/F would go down was at WOT.
Those are two possible reasons why you might get better mpg but I can't say for sure as I have never personally tested to confirm.
12-17-2010, 01:47 PM
#30
I have never calculated the mpg of my truck with the 408 but it has got to be somewhere in the 10 mpg range. Send me some funds and I will drive to Arizona and back and calculate mpg then I can go up a mountain pass and back down with some street driving mixed in and get another mpg range. That would be with the 408 and a tune already in there.
After I install the turbo I can do the same and see if mpg improved or not. No WOT runs though as that would skew the results.
After I install the turbo I can do the same and see if mpg improved or not. No WOT runs though as that would skew the results.