05HD

The one that eats the most lightbulbs the fastest.

Mr. Sir

This is what I've been trying to prove for the last page!

Oh, and it is airflow related. (That'll be my question, how is horsepower NOT airflow related?)

pwrtrip75

iTrader: (8)

What gears? tranny? converter? there is more to making a car go down the track than HP.

05HD

Calm down, you haven't proved anything other than I am drunk enough to continue replying.

Horsepower isn't airflow related because it isn't real. Engines make torque to do work. Somebody (Watt?) decided it would be a good idea to relate how much work an engine could do in a set period of time to how much a horse could do as a marketing tool, hence, horsepower. Now, you are confused and I am drunk and trying to teach you.

Orr89rocz

iTrader: (13)

Whichever one is geared best to get the most average power down to the tires.

slow67

iTrader: (2)

X2. A lot of stalled autos only have a 1000rpm shift extension.

Mr. Sir

By this logic, horsepower shouldn't be considered at all. It isn't real, right? So why ever run your engine any higher than peak torque? after all, that's the point of greatest volumetric efficiency, right?

What about F1 cars? Only around 230 Torque at peak, so they should be slow, right?

Perhaps you wouldn't like to acknowledge horsepower as a real number, but it does indeed exist, even if you choose to call it "how quickly you can repeat a given torque value" (another accurate description of horsepower).

And horsepower, or "how quickly you can repeat a given torque value", IS based on airflow.

05HD

Ok, you win. Put a 76/75 and 1 inch i/c pipes on a 454 and make 1,000 rwhp to prove it.

While you are busy with that project, think about this:

I never said making torque at high RPM wasn't an advantage.

Nick V.

iTrader: (1)

so as far as altitudes with turbo systems, is a sea level atmosphere better than a above sea level or a below sea level?

So.jerZ-28

iTrader: (20)

I just lul'd ... and lul'd ....and lul'd.... lul'd.
Absolutely best way to get your point across but I would have said a 106mm just to make it more rediculous!!!



p.s. Mr. Sir reminds me of my old boss, guy had like 10yrs of schooling, Masters in Engineering & Development, but couldn't change a lightbulb if his life depended on it. He was so smart, He was stupid.

Mr. Sir

Yet denied that it was airflow related.
An engine requires X grams of air per revolution, and spins at Y revolutions per minute, so you need XY grams of air/minute. Now it's spinning at 2Y revolutions per minute; so it requires 2XY grams of air/minute. Now nY rpm; so it requires nXY grams of air/minute. Directly related to airflow. Agreed?

And I know you'll say no, because you only look at 1 out of Y revolutions (or 2Y, or nY) to get your torque value (which is the correct way to do it). But engines don't operate in a theoretical world where time stands still as you leisurely measure torque output; they operate at given rpm values, and flow a given mass of air per unit of time, a mass that varies based on rpm.

So far everything you've said has made sense, except how you continually try to deny the existence of horsepower. (you don't have to call it horsepower, call it whatever you want; it's a unit of measurement for how much air an engine will flow in a given time period.)

Fbodyjunkie06

iTrader: (10)

Your a ***** dave. LMAO

427

iTrader: (3)

What he said cause the boost will be higher!

Kurt

Zombie

iTrader: (2)

To really understand the relationship between engine size/flow and turbo compressor / turbine matching you have to remember to deal in a constant unit in order to make the proper comparisons. That unit is Mass Flow. A centrifugal compressor is a mass flow device (just like an engine) which is one of the reasons you can compound them to increase pressure ratios. You just feed one with a gas (air) that is already at a higher mass density (psi) and it will continue to compress it further (more psi).

The turbine side is also a mass flow device and if you exceed it's flow capabilities it becomes a bottleneck in the system and you get lots of back pressure. To compensate for this you can run a larger turbine housing to bypass more exhaust around the turbine (a little improvement) or a larger turbine wheel (usually a better improvement) or a larger turbine housing and larger turbine wheel (best improvement) of exhaust flow. Down side to going larger on the turbine side is more mass flow = more exhaust (energy) is bypassed from doing work on the turbine wheel. Since the amount of exhaust mass that comes out of an engine at a given rpm is fixed the only way to get more work out of it is to keep the gas as hot as possible (more energy) so it can push on the turbine wheel harder (think of exhaust molecules as bullets, a .22 bullet being shot from a derringer, cooler exhaust vs shot from a rifle, hotter exhaust. The bullet is the same but the one from the rifle has a lot more energy when it hits it's target) while the rest of it is bypassed around the turbine wheel in the housing and through the waste gate. None of this has jack to do with exhaust velocity, exhaust size / etc. The shape of the turbine housing is what increases the velocity of the exhaust flow to help drive the turbine wheel.

The compressor side needs to be matched to the operating range of the engine based on size and desired pressure ratio.

How well a given turbo will spool depends on how good you are at matching the proper turbine wheel/housing (and transferring as much of that exhaust energy into work) with a given compressor wheel for the goals you are trying to achieve for a an engine that has a known mass flow at normal atmospheric pressure.

I hope I got most of that right, I'm jet lagged, sick and it's been a while since I talked compressors so I hope that made sense.

jbhotrod

Finally someone gets it right. Its not about CFM with turbos, its about MASS! Completely ridiculous that so many people called so many other people wrong and then posted some crap thats also wrong. Thank you zombie, I registered just for the purpose to reply to this thread.

See:

http://www.theturboforums.com/smf/ad...ssure-vs-flow/

http://www.theturboforums.com/smf/ad...ze-importance/

http://www.theturboforums.com/smf/ad...-engine-speed/

You will learn quite a bit by sweeping through the Advanced Tech section, and make sure you read everything posted by Andy Dorsett and Boost Engineer atleast two or three times. They will not lead you in the wrong direction. Theres also some other very interesting threads in there as well, such as viability of H2O2 and rocket fuels as power adders/oxidizers in piston engines, VAST amounts of cylinder head knowledge, 2v vs 4v vs OHC vs OHV, the infamous Turbonique rocket powered axle/how it works, etc. Im seriously not trying to sound like a jerk and apologize if I am as I am new here and love ls1tech, just saying that I learned a large majority of what I know by browsing that section..

Mr. Sir

.....Hey guys.....I have another question......related to small turbos on big engines.........

If you were to close the intake valve much earlier, say 130 degrees ATDC, could you emulate lower displacement? You could also try to close it much later, perhaps 66 degrees ABDC, but this would push fuel back into the intake, which I doubt is a good thing.

This could be achieved with either a 2nd intake lobe (vtec), or extensive use of VVT (there would probably be to many other inefficiencies caused by changing the other 3 valve events, so the 2nd intake lobe seems like the best way to go).

What'd this do for power? (maybe make the 6.2 have the same peak as the 4.8? maybe?)

qqwqeqwrqwqtq

My suggestion is to start reading one of the few thousand threads on this board that are related to valve events. After of say, a few months of reading if you still have a question make a thread about it.

Generally speaking, valve event changes will have similar effect on a forced induction engine as a naturally aspirated one.

The right way to go about things is to have goals.

Set a goal for power and drivability. What is the tolerance for drivability. What is the desired power curve. Than consider every other variable. Weight, fuel, gearing/etc.

Once you know exactly what it is you want to accomplish you put together a plan to achieve those goals.

The only thing you will emulate by clogging up your induction and having mad scientist cam specs is this-

Mr. Sir

Yeah, when I do start modding, I won't try to make an improperly sized turbo work.

But back to the original question, I was under the impression that the intake valve closed around 40 degrees ABDC, not 50 degrees BBDC (as I was suggesting). This would give the air less space to fill (perhaps only 4.8 liters of space) and therefore the engine would emulate being smaller, allowing it to make more peak with the smaller turbo.

I'm not going to do it, but it's an interesting thought. And unlike the last idea, this one doesn't really have any holes in it, since it's such easy thinking.

FSAE_Junkie

I'm not trying to pick a fight with you, but I must make address the above quote.

Air mass/cylinder = Torque

Air mass/second = Power
i.e. Airflow in its traditional form of lbm/min correlates to power

A given air mass in a cylinder will produce a given BMEP regardless of RPM. This pressure is applied over the area of the piston to produce a Force. This is the force that is applied over the 1/2 stroke (distance) to arrive at lb-ft or N-m of torque.

So, when RPM's are low, the air mass per second will be low and thus power will be low. As RPM's go up, so will the airflow and the power (until you hit the point where diminishing VE counteracts the effect of spinning faster).


As for power not being real, I can to some extent understand where you are coming from. You can't feel power per se. But you can feel force - which is directly related to torque.

But this isn't to say that power isn't still important. When you use a CVT and you target a specific engine RPM, you choose peak power RPM NOT peak torque RPM. The reason being is that it is wheel torque you are interested in, not engine torque. The peak power configuration will give you a higher wheel torque for a given road speed.

First, you've done a few odd things by imposing the hp and RPM limits on car A. Since car A makes peak power starting at 3000 RPM, you could shift at around 4000 RPM and be fine. No need to even go to 6000 as it wouldn't gain you anything. If you had a car that made the same hp from 2000 to 10,000 RPM's, you could shift at any RPM and have the same accelerative performance (so long as your shift time was ~0 seconds).

Anyways, because you provided such a large power advantage to Car B, it would be extremely hard to come up with a scenario in which it would lose. You would have to do something retarded and give it huge shift extensions. Had you given torque vs. several RPM's for each car, it would have been a much more challenging question.

But because power is RPM-independent, it makes this a semi trivial question. For example, you could also throw in 800 rwhp from 22 - 25 RPM scenario. It would have very similar performance to Car B given you had full control over gearing.

Doward

Mr. Sir, I believe I know your problem.

I must insist you track down a basic Physics book, stat.

Work = Force * Time.

Torque = force.
Horsepower = work.
RPM (Rotations per MINUTE) = time.

Therefore,


Horsepower = Torque * (RPM/5252)

Work = Force * Time.

That is your problem in this. You are severely confusing torque, which is a FORCE, with horsepower, which is a unit of WORK.

IE:

400 ft-lbs of torque in an engine system.

If this 400 ft-lbs happens when the engine is spinning 2000 rpm (a diesel, for instance) you have:

HP = 400 * (2000/5252)
152 hp, 400 ft-lbs of torque @ 2000 rpm.

If thiis 400 ft-lbs of torque is available @ 6000 rpm, you have:

HP = 400 * (6000/5252)
457hp, 400 ft-lbs of torque @ 6000 rpm.

Turbos make torque, period. The denser air/fuel mixture burns slower than at atmospheric pressure, and so you have a greater amount of pressure inside the combustion chamber as the crankshaft approaches 90 degrees ATDC.

More torque delivered at a higher rpm allows for more work to be done - and is represented as horsepower.