A disapointing way to add horsepower to a Prius

Hi Jimbo,

EdtheFox in Florida has bypassed his throttle plate heating with a tube for years.

Have not heard if anybody has done the thermostat yet. If I remember correctly, somebody said Jaguar had a bimetallic valve thermostat all built into the throttle plate.

As to if the cold throttle is best for mileate, or not, I think that is undetermined. Hobbit's experiments with intake air heaters resulted in no better mileage. The colder air results in more charge mass, more power, and less engine operating time in the hypermiling driving regime. Its probably a practical trade-off...

 

Throttle body heaters are normally used to prevent icing between the throttle plate and body. It can get really cold as the air is expanded by being pulled past the throttle plate.

 

I assume we are talking about more horsepower only at Wide Open Throttle.

 

Power is roughly proportional to intake air density.

Density is inversely proportional to absolute air temperature.

On the F scale, absolute temperature on an 80F day is
80 + 459 = 539R

Removing the heater won't reduce the temperature increase to 0 at full throttle, let's say it's a 5F increase.

So air temp in the manifold with the heater =539+15=554
Without the heater = 539+10=549.

Relative air density = 554/549 = 1.009 at the 10F lower temperature. A bit less than a 1% increase at full throttle.

It's not quite that simple but the exact answer would be closer to 0.9% than it is to 0% or 2%.

 

Aren't you getting the free power by effectively leaning out the a/f mixture? But then, I assume that since the car is measuring the IAT and using a MAF sensor, it's going to try and meter the same total volume of air?

 

I think Scangauge reports the IAT all the time even if the ICE is stopped, ie; intake air is stationary in the throttle body.
Please refer to the attached chart.

The ICE breathes more than 10 liters/second of air, and it's huge.
I don't think the throttle body has such huge heat exchange capability (+25 degree heating up of 10 liters/second).

Would you please check the IAT during the highway driving (ICE always runs)?

Ken@Japan

 

What I'm thing of is all the feedback loops involved that sort of counteract this.
1- The fuel Oxygen monitoring system would adjust fuel to maintain the optimum stochimetric ratio.
2- The Engine Control would adjust the power to match the accelerator command.
3- The Hybrid Control would balance the Engine/Motor contributions
4- The driver would change accelerator setting based on see the police car monitoring the horsepower test.

So, while it is a worthwhile theory discussion, is there any practical point?

 

Got it. Thanks for the overview I was missing.

 

I don't believe the throttle body heating is for reducing air density.
I agree with patsparks saying "Throttle body heaters are normally used to prevent icing".

The cooled EGR is the way to reduce pumping losses on the Gen3 Prius.

Ken@Japan

 

You did see that part where the post you liked to reads:

Maybe it's not all that free, or in fact all that safe.

 

Hi Gray, et al,

If there was an Outlaw Engineering kit for the Prius, it might be a way to keep the intake air charge colder, yet not disconnect the throttle body coolant loop. Of course the computer will adjust charge to the proper stoiciometric or lean, as required. Its not about changing that. More air molecules into the engine means more gas gets injected. The engine will have slightly more torque.

This can be used for boy-racing, or hypermiling. Its just dependant on what the driver wants to do with it.

With more torque, you can run lower RPM more efficiently, making SHM more stable and easier to hold, for example.

Now what I am not real sure about is cold-weather emissions. As you may know cold weather polution from cars is much worse. Back when I was a college freshmen, one of my dorm mates (who later went on to work at Amoco Research and NASA) did a paper on car emissions for advanced credit in Mechanical Engineering. He found a publication that dealt with all this. Back then, the cold air did not vaporize fuel from Carborators well, and people drove slower , at less power, which exacerbated the issue. Also, air going around corners would cause fuel to seperate from the mixture stream. There was a brisk buisness in performance aftermarket intake manifolds because of this problem.

Now, does the Prius fuel injectors finely atomize the fuel sufficiently to make this a non-problem when intake charge is below freezing? Or even at 0 F? Hard to say.

But, for summer driving, especially in the high 80's and 90's, my guess is there is no change in polution output of the engine with ambient temperature intake air with a port fuel injected car.

The heating from the intake manifold is probably due to the coolant loop to the throttle body also heating the intake manifold. But also the engine heats up the intake manifold as well.

 

It still comes down to a more gas = more power equation, so I'm a little confused as to how this would apply to increasing MPG (since it still results in increased gasoline consumption). I know you can super-lean out an engine for the lowest gas consumption, but that comes at the cost of much greater NOx emissions.

 

Hi Gray,

Its not about power, its about energy to get to speed. Energy is power times time . More power, less time to speed. same energy. From a first-order point of view, more power does not conflict with fuel economy.

Of course a bigger more powerful engine uses more gas, due to thermo-dynamic issues. But were are not talking about a bigger engine. We are talking about what is called the "volumetric efficiency" of the same engine. Or the fraction of mixture that gets into the cylinder while the engine is running, as compared to what would fill the cylinder in a purely static situation. The cold air improves volumetric efficiency.

 

Jimbo, if I had the knowhow and resources, I'd definitely do this mod.

Your critique of "modders" is a little unfair...most modders make changes that are generally easy to do (or if kits are available), well publicized (read as advertised) and or common knowledge. This mod of yours is one I'd never real heard of (sounds similar to a cold intake mod, though I'm guessing that's different). Point being, now that I know about your post, I'll definitely be looking into it as an option.

Very few mods actually deliver and the chrome etc. DOES give offa vibe of false pretense, but it doesn't mean that, as you say, modders looking for more power would pick chrome-pretense over an actual working HP mod. Most modders simply don't know about the options you presented.