[slow6goat]

Guys, the heat is mainly a function of:

PV=mRT

I don't know where this talk about rotor pack and temps come from, except maybe conductive heat from the rotors???


Sent from my local E85 station.

PV=nRT
Someone mentioned cooler IAT with snout porting and/or larger throttle bodies.

No offense, but I didn't underarm what you just said.

Laws of thermodynamics still apply, whichever blower design is being addressed.




Sent from my local E85 station.

I'm waiting on clarification with you.

Your not creating boost with blower speed. Your creating boost with air porting. Manipulating the air to make it more efficient. Efficiency is heat loss on s tvs.

At least from my learning on blowers.


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I never said anything about blower speed. My statements were regarding an increase in inlet size/efficiency, pertaining to iat2.

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[Jokerz]

Boost is direct result of porting your supplying more air. boost will go up. Efficiency by porting the snout and supplying more air through a bigger throttle body. This means a drop in iat2.

People can't compare boost increase from the result of porting vs the boost increase from the result of increasing blower rpm(running smaller upper or bigger lower). Ones a efficient mod the other is not.



Boost can go up with blower rpm increase. This is not an efficiency mod which means more heat. at a given point in which the blower in its current state will become an issue as you increase the rpm of the blower. It will get the point it becomes no longer efficient because the air it's moving becomes to hot regardless of the boost its creating. Cause if you take a cammed headed stroker motor car with this blowers and your trying to make 18 psi. That blower is ten seconds away from cooking itself for breakfast.


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[slow6goat]

That's what I was saying. I simply forgot to add "with porting" to my comment. I'll fix it.

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[TriTexan]

Guys, the heat is mainly a function of:

PV=mRT

I don't know where this talk about rotor pack and temps come from, except maybe conductive heat from the rotors???

Not to be picky brother Karch, but "m" vs "n" in this case does kinda have specific and different meanings to me as a physicist.

But as you noted, and which I totally agree with - the laws of thermodynamics apply. It's often the case with situations like this that the simplified scenarios we were taught in 101 in college don't account for things like conductive heat, transfer heat from other components, and so on.

So the simple thing that Karch is after here - in the most basic form, is the relative relationship between compression and heat. Double the pressure, double the heat. So if you take a given mass of air and reduce it's volume by one half, it's absolute temperature will double. Don't use Fahrenheit - 30 degrees is NOT twice as hot as 15 degrees. Nor is Celsius. We gotta go hard core with Kelvin. Once you do that, you realize that the percentage difference in temps is not nearly as much as we think.

Example: 81 degrees F is about 300 Kelvin. 120 F is about 322 Kelvin. So the difference in total heat between 80F IAT2 and 120 IAT2, in absolute terms, is only about 7%, not 50%. But that's still substantial in engine world, right?

What Karch is expressing is called the "Ideal Gas Law", which merges together the relationships between temperature, pressure, and volume. VERY applicable to our FI cars and worth every member on here knowing at least the fundamentals of. Here's the basics, as concisely as TriTex can do:

1) If you change the volume, you change the temperature inversely. Compress a gas to half its original volume, you double the temp. Expand it by a factor of 2, the temp goes down by half.

2) Likewise, if you increase the pressure of a gas - without changing the volume, the temperature behaves in exactly the same way. Double the pressure in a fixed volume, the temperature will also double.

3) If you HEAT a gas, while holding the volume of space it occupies fixed, the pressure will increase. As before, proportionately. Double the temp (in Kelvin) and the pressure will also double. Remove heat and the pressure drops accordingly in the same ratio.

In Karch's example, you can see P,V, and T - which represent Temp, Volume, and Pressure. The other bits are there to make all the math work out and we can assume they are constants and/or extraneous for now - just to keep things uber-simple. But as you can see, pressure and volume are on one side of the equation, while temperature is on the other side. As long as you remember that increasing pressure increases temps and/or decreasing volume increases temps, then that's half the battle.

So how does all this academic crap boil down to superchargers and porting and shit?? Well as some have noted - perhaps porting increases the volume in some parts of the airflow path. By having a larger volume, perhaps the pressure is lower, which would also lower the temperature proportionately. But Karch - in his wisdom (or to his demise...we shall see!) cleverly included that lowercase "m" in his equation - which is the mass of the gas we are dealing with.

What is more difficult to figure out is just exactly how much of an effect the porting has on total airflow (which would alter the mass of air involved, and hence our equation results).

But in a very simplified view, all of the porting is "after" the rotors (save the snout I guess...). If you boil this down to pre and post rotors, we can talk about temperature, volume, and pressures before the intake gas is compressed (in the intake) and after it is compressed (in the blower lid and the runners, more or less.

If the porting creates substantial or measurable changes in pressures after the rotors, we might conclude that restriction into the heads has been reduced. And along with lower pressures we get a liner change in intake temps. But a sharp person might say, "But wait Tri - that gas has already passed the rotors, and you said lower pressures mean less mass, but conversely lower temps mean higher mass - aren't these effects kinda canceling each other out?"

And that person would be correct. Karch notes that thermodynamics can't be skirted. Once you have a given and fixed mass of air, that's what the engine is going to get. If the blower was forcing the air into the lid and runners faster than the heads can eat it, the pressure in the lid would just grow and grow until something bursts. But it doesn't. It quickly finds equilibrium.

So as you think through all this - and I am going to leave this post "Duck Style" for you to do some basic math if you aren't an engineering / propeller head type like me, Karch, and others - just remember that power is all about how much MASS of air you can stuff into the cylinder. More mass of air = more oxygen = more fuel you can burn with that oxygen = more power. Now heat DOES factor in, but in an engine, that heat is all about safety and not as much about power. If we had different fuels and infinitely strong components, we could dramatically change the heat points and get far greater power AND efficiency at the same time. Remember that an internal combustion engine is, at the end of the day, a simple heat engine - it does work based on the transfer of heat from one mass to another, imparting some mechanical force in the process. The first mass is the intake air, the second mass is the exhaust. All heat engines produce greater and greater power when the difference in temperatures between mass 1 and mass 2 are greater. That's fundamentally why cooler intake air is good. But hotter exhaust is also good - take for example an engine tuned for mileage instead of power. They run leaner and hence hotter - by leveraging a hotter exhaust temp, the engineer is effectively increasing the difference between intake air temp and exhaust temp, increasing power (in this case, power is traded for efficiency, but they are effectively the same concept - get as much as you can out of the fuel you have).

To get you guys started, let's re-arrange Karch's formula this way:

m = PV / RT

Why did I do it this way? Well - in our cars, we want MOAR POWAH! How do we get it? By maximizing the amount of air and hence fuel we can burn. So in Karch's equation, we want to get "m" as big as we can. You can do that by increasing the "P" or "V", or by lowering the "T".

This is where Duck needs to come in and talk about choke velocities and some more advanced concepts. Realize that Karch's formula is actually for static systems, not dynamic ones - but the core concepts are completely valid and good starting points. Duck and others need to bring in a few simple concepts around when increasing intake pressure does NOT cause a corresponding increase in the mass of air delivered.

And to bring my lengthy post full circle - THAT folks is what porting is all about - not about increasing volumes or even trying to optimize the pressure / volume / temperature relationship. Let's assume - for Jokerz sake - that we tell him we want to keep the volume of the lid, blower case, snout, runners, etc exactly the same - we only want him to change the SHAPE. A good porting job is about finding any point in the airflow path where the good old relationship between temp, press, and volume would get compromised. How about an example we are all familiar with?

Like, say, for instance that annoying little flow restricter in "water saver" faucets. They INTENTIONALLY put a precisely sized hole in a flat disk and installed that in your faucet. But what is really going on in your faucet? Well at the most simple level, that little hole is fully capable of passing all the water you need - without creating one of Duck's "choke points" - up to about 2 gallons per minute. Faucets use a type of restrictor called an "orifice plate" - you've seen 'em...just flat disk with a hole in the middle. But to illustrate my point about porting and how and why shape is so important, check out this video. Yes, it's VERY long, but just watch the first minute or two and you'll see something VERY interesting. The "choke point" in a system like this actually occurs AFTER the hole in the plate. Wait - what?!? You mean that little hole is NOT the point of greatest resistance, that it is actually downstream of the hole where the pipe is many, many times wider and more open? Yep - that's actually what happens.

So how does this apply to porting? Well - a good porter understands these very fine points about the flow characteristics of compressible fluids like air. Water, by comparison is also a "fluid" in physics terms, but is incompressible - so my previous example of water in the video isn't exactly applicable, but the point is that fluid dynamics isn't always intuitive. You can't always just use your intuition and logic skills to figure out how to port something - the physics matters and there's no way around that.

The porter knows enough about the nature of flow dynamics to know exactly where and how to change the shape of the flow path to avoid as many choke points as possible because we know these will muck with our beloved PV=mRT equation, making the mass delivered less. Ever wonder precisely why some cars make more power on 16psi of boost and others don't, even with the same cam and such? One way or another, its quite possible that even though both cars produce the same pressure behind the choke point, the flow after the choke point is reduced. The whole point of these flow restricting faucets is exactly the opposite of what we want in our cars - these faucets are designed to flow NO MORE than about 2 gallons per minute - NO MATTER HOW MUCH PRESSURE (i.e. boost) you put in the supply line going into the faucet.

The same principle used to choke off a faucet at a known rate of water flow can also choke off your engine. It flows just fine, right up to some magical-seeming cutoff. And what's effectively happening is there is some point in your airflow path that - no matter how much boost you use, just like the faucet is going to refuse to flow any faster.

Ok - I hope that was helpful to some of you out there and not too confusing. When you talk about porting - just remember it's not likely or even necessarily advisable to expect the porter to dramatically change the boost or other pressures in your system. His goal is to eliminate any point where your boost level is not producing the maximum amount of flow that is is theoretically capable of. How would I measure a good port job? Ultimately its not that hard - I would expect to see exactly the same peak boost levels, but with a greater mass of air flowing into the cylinders, with a corresponding increase in fueling needs and hence, power output. If the porting did not cause this direct and measurable effect, it means one of two things: 1) the porting job was not done right, or (hopefully), 2) Choke points are NOT a restriction in your build - so you can increase your power by adding more pulley, going with a larger cam, opening up the exhaust, and so on. All this talk about heat IS a valid topic, but its a good simplification when talking about porting to focus more on improving the mass airflow amounts at a given boost pressure. If you hold boost constant ("P" in Karch's equation) and the porting doesn't have much overall impact on the volume of the components, then ultimately the "m" or mass of air should improve.

Realistically, practical considerations mean its easier to remove metal than add it - but the SHAPE is what we are after, not enlarging anything.

Verbosely yours,

-=TriTexan=-

 

[TriTexan]

Ones a efficient mod the other is not.

This proves to me that Jokerz gets it. Like I said in a thousand more words - porting is about improving how efficiently air is move by eliminating the most restrictive parts of the flow path. Boost increases heat when you have more pressure that the rest of the system can effectively flow - like the faucet example. In your house, it's perfectly fine to have 60 or 70psi in your water supply pipes. But if that faucet flows the same even if the supply line has just 30 psi, the additional 40 psi are pointless and don't deliver more water. Same goes in your car - ideally you should only increase boost to the point that it stops generating more mass airflow. When the mass of air delivered stops increasing, more pulley is likely to be HARMFUL. The mass of air delivered, again back to Karch's formula, can be affected by pressure or temperature. So your mass of air could top out because of increasing heat OR because of a flow choke point. Either way - mods that don't increase the mass of air delivered are likely to be doing more harm than good.

Excellent and simple observation J!

Now I am wondering - is there such a thing as a flow bench for superchargers? While more complicated that a standard flow bench, it should be possible to spin the rotors at a given rpm and observe CFM delivered, pressure differentials, and so on. And such a flow bench should be able to test out how adding boost pressure changes the CFM and mass of air delivered. I would not be surprised if the big boys have toys like this in their R&D secret bunker...

 

[TriTexan]

PV=nRT

I noticed this too, but I've seen it stated both ways, albeit with different meaning obviously. But in our case, I kinda like expressing it this way - especially for those without an advanced degree in fluid dynamics, physics, etc. Because optimizing for total mass of air is really the goal to a large extent. Anyway - I would seriously doubt Karch would throw that down without knowing it was going to stand out like a new girl member on this forum. He had to anticipate these kinds of responses so I assumed that he posted it that way intentionally...

 

[slow6goat]

I'm pretty sure this is Karch's way of compensating to standardized units.

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[blubyu]

I just want to say that even if Tri can type 100 words a minute his post still take him half a day to complete. LOL

 

[ttboost]

He started typing after dinner...cut and pasted at 1am...

 

[Karch]

That a boy!

Tri, wow!


Glad I didn't try to type out Bernoulli's equation.

Thanks for explaining the ideal gas law.

BTW, orifice plates are my biggest competitor in my day job, it amazes me how many companies use them to measure flow.

The delta in pressure from the upstream side to the downstream side is proportional the the volumetric flow rate, given a constant fluid.


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[VVVROOMTX]

The easiest way to visualize this is,

The air isn't being forced into the supercharger, its being drawn in by a vaccum/suction. Any way to smooth the flow of air from the time the air enters the filter, or increase the area the air can take up, will benefit the charge air to the rotors.

After the rotors is different. The air is being forced at that point because the air has a confined space to fill, (ie how you read boost PSI).

Interesting tidbit i found as well..... Volumetric Efficiency (VE) is how efficient a motor can move/displace air in one full cycle.

Our LSA has a displacement of 6.2L or 376ci. So 100% VE would mean the engine took in 376ci of air and expelled 376ci by means of NA. Well that's impossible since IC engines have a VE of about 80%. Bring in FI to make up the difference. I found that every 14.7lbs of boost supplied to an engine the VE doubles. So i guess this mean just make as much boost as possible

 

[Hotrod-Realtor]

Now I am wondering - is there such a thing as a flow bench for superchargers? While more complicated that a standard flow bench, it should be possible to spin the rotors at a given rpm and observe CFM delivered, pressure differentials, and so on. And such a flow bench should be able to test out how adding boost pressure changes the CFM and mass of air delivered. I would not be surprised if the big boys have toys like this in their R&D secret bunker...

My buddy has one. It's powered by a blown big block on alcohol to spin the blower to replicate a drag car. I can't afford to have him dyno my blower. The blowers he works on are big money billet blowers.

 

[Jokerz]

You can Dyno the blower all you want guys. Restrictions in front of the rotors make that testing pointless. Throttle body is your guys biggest weakness. Also the fact you can't test 75 mph of air hitting your cold air intake which also adds to flow on the Intake side. There are ways but damn to set it up like I have scene at Roush. We are talking millions of dollars to test for 4-6 hp. When it comes down to it either you know what the hell works and how air travels and you make that air travel the best it can. Or you just take a sawzall and make a port and say I makes the big horsepowers. I have done simple testing on how air travels in the inlet and sometimes simple is always better. I take a go pro. Pvc ball flange in front. Behind that I have a ring I Fill with sanding dust or whatever using a ring I made that holds the dust in place. Basically like a fogger nitrous plate. As the air travels across the ring it grabs the dust and I can see how the dust acts enter the blower to some extent. I watch this with the camera on my computer as it comes into the inlet. No rotors Involved. Now this same concept I use for testing air flow. I can test using electric motor spinning at a 1-1 ratio with the blower. I just need a flow meter in the box under the blower outlet side. And meter on the inlet side. Install the cold air intake throttle body with no blade. Adjust the Rpms of the electric motor with a throttle based switch. Flip the sensors on you have flow before and after the blower

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[Hotrod-Realtor]

You can Dyno the blower all you want guys. Restrictions in front of the rotors make that testing pointless.

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This confuses me, easily done I might add. Don't you do the majority of the porting in front of the rotors? If so, wouldn't a before porting performance analysis compared to an after porting performance analysis prove useful?

 

[TriTexan]

I just want to say that even if Tri can type 100 words a minute his post still take him half a day to complete. LOL

He started typing after dinner...cut and pasted at 1am...

100 words a minute? That's the typing equivalent of a Prius. Predictive auto complete gets me to around 250 or 300 on my phone. Geez...amateur hour round here lol!!

 

[TriTexan]

That a boy!

Tri, wow!


Glad I didn't try to type out Bernoulli's equation.

Thanks for explaining the ideal gas law.

BTW, orifice plates are my biggest competitor in my day job, it amazes me how many companies use them to measure flow.

The delta in pressure from the upstream side to the downstream side is proportional the the volumetric flow rate, given a constant fluid.


Sent from my local E85 station.

I figured you were down...but it ain't for everyone. Gotta make this shit bearable.

 

[TriTexan]

This confuses me, easily done I might add. Don't you do the majority of the porting in front of the rotors? If so, wouldn't a before porting performance analysis compared to an after porting performance analysis prove useful?

Yes. And my post was wrong in that regard. I errant stated the porting is primarily after the rotors. My mistake....

 

[Jokerz]

This confuses me, easily done I might add. Don't you do the majority of the porting in front of the rotors? If so, wouldn't a before porting performance analysis compared to an after porting performance analysis prove useful?

I manipulate the air in the blower. But I can't control the fact that a 102 mm throttle body is still a 102 mm throttle body. I'll have to do some math on cfm of 1.9 LSA blower compared to a 102. I'm pretty sure the blower outflows the 102. Also air filters slow down air coming as well.

Hell I created a vacuum inside my air box and I collapsed my intake on itself. This was with my kennebell 2.6 on 24 lbs of boost


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[Jokerz]

I'm the biggest babbling idiot on the interwebs


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[LargeOrangeFont]

Jokerz-

I've been lurking on your work for the last few weeks. I'm really impressed.

I'm a HPDE guy, not a drag racer. I also am stuck in California running 91 octane. Can you talk about what your porting should do for IATs for someone doing 20 minute sessions? If I understand the theory correctly, you're removing a lot of restrictions/inefficiencies from the blower so temps should be lower at a given blower speed, correct?

And if I really want to reduce IATs I should do a full blower port, a cam, and headers to let the motor breathe a lot better?

Thanks,
Jason

Jason,

So you don't have to read a page of babbling- For HPDE the more power you make the hotter IATs will get... Period. For the road course porting the blower is one mod that has little penalty from a heat perspective. I'd port the blower and put on a 2.8 pulley. The car will make the power of a 2.4/2.5 pulley while keeping IATs notably cooler than that setup. Adding headers, cams etc are going to raise your IATs over a given 20 minute session. Unless you go to a 5 gallon intercooler reservoir in the trunk it is going to be a challenge keeping temps in check on hotter days when you start making really big power. You'll want to look at phenolic blower spacers as those will help keep IATs down.

This advice is from a fellow Southern Californian who tracked an 04 Cobra for 5 years. I fully ported the blower on that car and with a modest boost gain the car made lots of power without going into limp mode on warmer days.