Hey guys, I know that this topic has sort of been covered before, but my search turned up threads with motors basically stock. I am trying to decide between a 52mm and a 58mm. My motor is in my sig. I noticed that ricktpi is running a 52mm on his HSR383 and runs a 12.0, so they obviously can support some kind of horsepower.

 

You'll get different answers depending on who you ask. I don't know of anyone that has track/dyno tested only a 52mm vs 58mm TB on a highly modded motor. I have heard of a few people that claimed lower performance with the larger TB but they were running near stock motors that wouldn't benefit. I'm curently running an Accel 58mm on my setup and I honestly can't say I could tell a difference from the stock TB. Once I get more track passes with my current setup then I may put the stock TB back on to compare.

 

I'd go with the 58mm. What the heck right? It won't hurt with your induction system and that cam, LOL. If anything it will make your throttle seem more responsive. I've read several posts about the throttle body, and the stock one flows about 650cfm, which will easily support 450hp at about 6,000rpm. That's just an estimate, but I know it's something like that. I don't see how a 58 will hurt over a 52, so get the 58, if price doesn't matter.

 

Tom Keliher and one of the 2 dozen magazines I read tested a 52 and 58 on his 13 second (or somewhere thereabouts) 350. He slowed down with the 58, which really isn't much of a surprise.

The 52 can support well over 750 dry cfm, which is more air than any 350 can use unless it's turning ridiculously high rpms.

 

Tom isn't running the XE 288 last time I heard either. Like I said, the 58, would be better for throttle response and it would also be good for the future, in case you nitrous, sc, etc. We all know that most are here for the long run.

 

See sig. The Holley 58mm is the only way to go!

And since you have a stealth-ram, there's a reason why the stealth ram's plenum comes with 58mm bores!

 

Same goes for the SR and the MR.

 

I would get the 58mm. Since you need to buy one, get the larger of the two. It won't hurt anything at all. I highly recommend the AS&M piece. I just installed one on my car and absolutely love it. Either way you can't go wrong though.

 

big cam or not, if you're not exceeding the cfm capacity of the 52 (which you're not), you're not benefitting from the 58, and if anything, your throttle response will suffer.

 

too large of a TB might cause the velocity to drop.

GM feeds the GM RAMJet 502 with a 48 MM TB?!?!?!How? Velocity.

 

Oh, brother, I can't believe Ram jet 502 got brought up again, when throttle bodies are the issure.. This subject has been treaded on second to only the MAF/SD debates.

Jim, how the hell do you think a 58mm throttle body will hurt throttle response???? I, myself run a 58mm tb, others run it, and we all agree, if you're making good hp, it doesn't hurt power, and it DOES give the gas pedal a more lively feeling. You guys should talk to people who run the 58's instead of speculating on how they perform. If they don't work, why do all the fast cars run them?? I guess David, Mike, and myself have slow cars or something. All three of us have 12 flat or better cars and they all have 58mm tbodies.

Poncho, velocity of air going in the engine will be dictated by the intake runners on the heads more than anything else. Maybe a smaller tb may help w/ velocity on a tpi setup, but remember gixxer is running a st.ram.

 

Over throttle bodying is like over carbing....to much air for the amonut of fuel you can efficiently burn....

not saying you or anyone else for that matter has this problem, you just need to figure out how much air you need for your heads/cam, instead of just simply purchasing the largest throttle body available.

Rule of thumb you usually need a slightly larger TB than theoretically calculated, that's why a 52MM on an engine like mine(mild 350) could actually help, where a 58 for sure will hurt me

 

I still stick to what I said. The cam this guy's running is pretty big cam for the street. 236/242 dur at .050 is gonna need all the air it can get, especially if he wants to sping the engine up to 6500rpm, which it could easily with that cam.

 

AND, the 58mm isn't the biggest TB available !

The TPIS 1300 cfm mono-blade TB is the largest one I know of available.

Here's the TPIS catalog listing for it:

Part # 100-169 Throttle Body, Mono Blade, 1300CFM, Custom Order........$650.00

 

You took the words right out of my mouth except I was thinking of the AS&M Monoblade. And speaking of the Monoblade, I have a friend that just tested this throttle body on a stock bottom end heads/cam LT1 car. Going from the 52 to the monoblade only picked up like 3rwhp, but he said you blip the throttle now and it just revs like crazy. The car was a test vehicle and they were trying to ring out every bit of hp which is why they wanted to try the TB. Since the testing I'm starting to believe you can't really oversize a TB. Now granted, I wouldn't be slapping a mono on a 305 but when the motor is healthy enough and you need to purchase a TB, go with the 58. It won't hurt! And to compare a throttle body to a carb.....is like cumquats and onions. They don't!!!

 

Right on fellas. Thats yet more proof of where a bigger throttle body helps with the throttle responsiveness, which makes the car a lot more fun on the street.

 

agree'd. ive had the 58 on my stock motor, and throttle response definately feels better.

i can wait to see how it feels with this whole new tpi setup going on...hey thanx for the edlebrock base gixxer, i can't wait to put it on and get back to the track.

 

Thanks for all the input guys. I also want to point out that my cam is the XR294hr... 242 248 at .050.... I understand the concept that an engine of a given size can only move a certain amount of air. My biggest dilemma is that my engine analyzer states that a 52mm throttle body is too small for my motor configuration and shows tremendous power increases above 4500 rpms. I shift my car at 7000 rpms at the track and drive very spirited on the street. The reason I asked for some insight on the throttle body selection is that an engine analyzer is just a program. They're usually very close to real life but I wanted to hear from people who are actually using the 52mm and 58mm.

Josh, I'm glad you got the intake and wish you the best at the track!

 

7000 RPMS?? That's too high for even a miniram better yet a Stealthram. Why are you shifting so high?

 

Wow, I just remembered that the 236/242 is the xe 288 cam. You're running the one up from that, which is even a little bigger than my cam. :hail:

My point exactly. With your shifting habbits, which are higher than mine (6500), a 58 mm is a must.

 

Dannyt, I shift at 7000 rpm because my motor makes max power at around 6700 rpm. Its peak is higher than I was hoping for when I went with the stealthram. I figured it would be a bit lower. Keep in mind that I don't have a stroker like you. Your motor will not rev as freely as mine does with the same components. As far as your statement that the miniram or stealthram don't work that high, you need look no further than my car because it revs more than I want.

 

58 is mega huge, and a 52 should do you fine. 58 is very large. You dont see guys with mild street motors running 1200 cfm carbs do you? Too much air is a bad thing. 52 or a bored 48 toa 50 could actualy give you better velocity, and will supply plenty of air for any type of street/strip motor. Like it was said above, unless your suckin in tons of air all over the band, dont waste your time with teh big 58.

 

just some input. ive talked to the guys at tpis on the phone when i got my throttle body. they dont recommend going to a 58mm until you are at 400 cubic inches or more, no matter how many rpms youre turning. they told me a 52mm will easily outflow a 350 and will handle a 383 with no restriction whatsoever. they said they dont recommend the 58mm for small blocks under 400 cubes because it takes away some low and midrange power due to the slowed air velocity from the bigger throttle blades. but if you are more worried about dragging than street manners, it doesnt really matter.

 

Well, my motor pulls HARD low, mid, and high rpm and has ALL the throttle response you want! I seriously doubt I would see ANY performance increase by stepping down to a 52mm throttle body.

But, I fully ported my TB openings on the upper plenum to match the 58mm bores of my 58 TB. I DO believe this is a must if you want to run the 58mm or you "could" lose a little bit of performance otherwise due to plenum restriction of the throttle bores.

Just my $.02

 

I didnt read the hole post, but I assume
if your engine doesnt require the 58 mm,
you're only gonna slow down the velocity.

 

This is a really hot topic! I talked to Terry at TPIS and he says he is running a 52mm on his 383. I like that company and all, but I don't agree with some of their philosophies. If a 52mm is in fact enough, and it should be if it flows over 750cfm, I will probably go the route of a stock TB modified to 52mm. All of the engine calculators I have used say that I only need 700cfm, but those are carb numbers and I believe there may be a difference. The only reason I am questioning this is because my Engine Analyzer Pro 3.3 shows a huge difference between the 52mm and 58mm throttle bodies. I know it is just software but it has me thinking and second guessing. Once again, thanks for all of your input on this matter.

 

software isnt true life, so just remember that. Its good for what its worth, but dont entrust in it. Now, this book i have basicly breaks it down to what you need.
It says a 52mm(750cfm) will support up to 400hp and a 1k cfm up to 470. I think TB manufactures should have rated TB's by flow and not diameter.

 

But how is putting on a bigger TB going to give it more air?

 

Software doesn't take into account velocity....or barely does. It simply assumes that the air charge will be as efficient with a 52 MM as with a 58 MM and therefore the 58 will deliver more air.

Unfortunately that's not real life. A 52 MM can flow as much air as needed for a 350 or even a 383 but because it's a smaller opening it will flow it with greater velocity. It's like the science behind our TPI runners and more recently the great working vortec heads. They have small 170 cc intake runners, yet they flow very well and with great velocity.

 

The engine will only pull as much air as it needs. The cam/heads/intake are the limiting factors, not the TB. You may not need a 58mm, but it won't hurt you either.

 

Uhh...comparing the size of a tb openings does NOT apply to the same science of tpi runners and vortec heads regarding velocity. If you truly believe this, then re-read some physics books.

 

nicely heated topic

 

Really? why are the TB openings any different from intake runners or the intake runners inside heads? They all serve to flow air into an engine.

The only difference is that a TB fills/maintains a plenum with air. But if the air charge entering the plenum is too slow it might not be able to maintain the proper air charge for the intake runners. A smaller TB flowing the same amount of air that a larger TB will flow will do it with increased velocity, resulting in almost a "charging" effect. The idea is to have the highest velocity possible with the highest CFM possible. A 58 MM might flow X amount of CFM for a given engine at Y ft/sec, where a 52 MM might flow the same X amount of CFM at a higher rate than Y ft/sec.

Which is better? Well if your engine can even use X CFM than the higher rate ft/sec is preferable to the lower rate. Isn't that what "charging" does, whether it be super or turbo?

Camarojoe....it's not about what I beleive, it's about how it is.

 

Have any of you actually watched the map sensor VS throttle % change from stock TB to a 58MM TB?

I have. the change is incredible... moving the throttle SLIGHTLY on the highway practically gives me WOT (98~KPA) on the MAP even though im only stepped 1/2 way down.


A bigger throttle body is same as a bigger carb. more air with less throttle opening, more overall äbility" for flow (CFM). but if your engine only moves 650CFM, having a TB flowing 1000 CFM isnt going to do diddly.

The change in power and throttle response can be attributed to other factors; velocity i wouldnt even consider since if you actually have "velocity"you have some sort of restriction, like putting your finger over the end of a hose will increase the velocity of the water shooting out. But your entire intake system and the pressures within are going to be the primary factors in just how fast the air moves... not the size of the hole feeding it.

You can say throttle response is better because you simply have more of a throttle opening with less of a throttle position. in fact with a 58MM TB about half-way down on the pedal and thats all the air my engine can use. I actually LOSE "resolution" of control over my motor since i basically cut my useable TPS in half... therefore i need more fuel and AE enrichment, sooner, and theres more of a % VS TPS fuel added since a small movement is so much more air than stock.

But on the other hand, launching the car and overall performance "seems" to be better just because i dont have to slam my foot down to get WOT...

so basically all im saying is when you hit that 98KPA on your MAP sensor (if you have one..) thats as much air as your engines going to take at that RPM. any more throttle opening and all your doing is dropping the velocity even further, sort of like when you nail the gas with your carb and the pump shot is too small... but this is EFI so we determine our "pump shot"through AE... so its really not a problem at that point. I can see people "losing" power with a bigger TB if they just slap it on and expect the factory TPS % AE to be enough shot to keep the motor from leaning out. and if you assume oh im flowing more air now and enrich the base map suddenly your rich all over for no apparent reason. Camaro Joe is right, you cant really OVER TB a motor, but you can screw up the tune by just slapping one on, and it gives you less control over airflow if the motor doesnt need the extra CFMS.

 

If you are worried about not enough air being supplied to the throttle body to fill the plenum at speed, you can always do this !

 

The grill openings are plenty large enough to supply the throttle with all it wants, the faster you go, the more air available!

 

This topic is gay. It's been beat to death over and over again. The two things I hate about this argument are ...

1) The BBC RamJet argument. Duh. This is stupid. Put a 58mm TB on that motor and see what happens.

2) STOP COMPARING dryflow throttle bodies to carbs!!! This is pure stupidity. Oversized carbs run like crap for a reason .... and that reason has more to do with fuel than the air inlet size of the carb.

3) There's tons of us running 58mm TBs and making over 350hp to the rear wheels. Wanna bet that I would make less horsepower with a 52mm TB? I'll take that bet. If anybody is close enough to Frederick, MD (which is where I dyno) and IF you have a 89-92 TB in the 52mm size then let me know. I am going to dyno again soon and this will be an easy test for me to do.

Tim

 

thats not true.


ram air is a myth. you will never build pressure thru your scoops, and the amount of air thru there is going to be the same regarless of speed.....


athough that looks like more then enough air

 

oh and Kingtal0n is dead on with the resolution thing.



and why do they put 58mm bores on the aftermarket intake?


because you'll buy them.

 

im nowhere near there, but i WANT to see that test!!!!!

 

Yeah maybe at 5000 rpm you'd make more power, but when GM Engineers design there systems they used a 48 MM TB for a reason, I would assume because it works well throughout the RPM range and still makes plenty of power.

Listen noone is arguing that 58 MM don't make more power than 52 MM, they do if that much airflow is actually needed.


I'd love to see this, if for nothing else to have concrete evidence either way, but every engine will act differently to mods. Nonetheless this would help to qualify statements made here, by myseld included.

I am the first to admit when I am wrong, but I just don't like jumping on the bandwagon that bigger is always better.

I am sure overall performance with too large of a TB will be hindered except for possibly at the highest RPMs.

 

Hey I was just looking through the catalog for the 502 ramjet you're talking about. I found it but a couple of pages away they put a 75mm LS1 throttle body on a much smaller 350 engine and I just thought of something. Maybe since they are GM motors they just used the biggest GM throttle bodies that would fit the intakes? Could this be why they put a smaller TB on the bigger engine? Anybody know if GM makes a TB bigger that would fit on the 502 intake? I just wondered if that could be the reason

 

I always thought that the 48mm tb stood for that each opening is 48mm wide. therefor... 48x2=96mm > 75mm.

 

Ram-Air is not a myth. You're smoking crack. Want proof? Get on the highway and open your window. Now stick your hand out the window and cup your hand toward the wind. Do you feel the pressure? Ya. Me too. That's Ram-Air.

I am using the Random Technology Ram-Air kit....
http://www.celligent.com/tim/iroc/airbox/ramair1.jpg
http://www.celligent.com/tim/iroc/airbox/ramair2.jpg

Want real proof?
With this airbox installed I get an extra 0.1 and 1mph (stock heads cam at the time). Back to back testing showed this to be true. In BOTH cases the airbox was chopped. The only difference was installing and removing the Random Tech kit. Air temp was the same on both runs.

Tim

 

bullsh!t.

you will never generate any positive air pressure from putting a scoop in front of your car. thats physics.


cold air however is good for your car. so cold air intakes work.

go look it up.

 

No - that is not true. You need to take the AREA of the throttle blades into account.

Yes, 48mm is two 48mm blades. But the area is ...
Area of one blade = Pi*r^2
Area of one blade = 3.1416 * (48/2)^2
Area of one blade = 1809.5
Area of two blades = 3619

The 75mm blade is ...
= 3.1416 * (75/2)^2
= 4418

The 75mm TB has 22% more area for moving air. That is a huge difference.

FWIW,
a 52mm TB has an area of 4247
a 58mm TB has an area of 5284

A 75mm single blade throttle body is analagous to a twin 53mm TB (4412).

Tim

 

Blablablablabla. I have real world results. You have nothing. THAT's the fact. Furthermore, I understand the theory completely (I'm not some hilljack ... you have to have quite a few semesters of physics to complete a masters in science). YOU are forgetting things with regard to the theory. I'll give you some time to realize what you are forgetting before I post again.

Tim

 

enlighten me.

 

Ram air might work after 100mph or so.. It all depends onthe engine also..If you have a stock POS, then it might give you something. On LT1 cars, their ram air does see soem benefits through the 1/4 mile.. Anything under that and you will probally notice nothing more than a fancy cold air kit

 

nevermind, i dont have the time to wait.


just read:


There are many air intakes on the market today. Many claim "superior" performance over others.

Air intakes can be seperated into specific catagories:

- Those that take in warm engine bay air
- Those that are exposed to cooler/fresher air from the front.

The biggest bennefit of adding an aftermarket air intake is unshrouding the factory air box.

The last bennefit is exposing it to fresh air.

Ram Air is a myth, and many intake manufactures use the word Ram Air strictly for propaganda. They also try to show track results compared to other intakes that simply incur too many variables to make a meaningful and empirical determination. 60 foot times, atmospheric changes, shifting, etc, etc. So do not beleive anything you hear regarding such claims regarding air intakes.

Lets take a look at the "Ram Air" Myth in automobiles:

The Ram Air Myth by Dave Rodabaugh

The Ram Air Myth is the most mythical of them all. It differs from the other myths, in that the other myths are misinterpretations of physical phenomena, whereas ram air simply does not exist.

MYTH: Use of a scoop on the front of the vehicle to collect intake air, or provide “ram air” can raise engine performance.

TRUTH: At automobile velocities, there is no ram air effect.

SIMPLE EXPLANATION

The "Truth" statement says it all. How much simpler can it be? The Ram Air effect is a total myth because it simply does not exist. “But Pontiac uses it on the Trans Am, and they know more than you do.” To those who offer this, tsk tsk. Careful reading of Pontiac’s statements on the matter reveal that the HP increase of the WS6 package are a result of a less restrictive intake, and a freer-flowing exhaust, NOT any ram air effect.

So why does Pontiac use Ram Air? Easy! To make people buy their cars! And they are quite effective with this strategy.

DEEPER EXPLANATION

Of all of the applied sciences, fluid mechanics is among the most difficult for many people to comprehend. It is a relatively youthful applied science as well, meaning that it has not had two or three centuries of work to mature into an applied science on par, with say, chemical combustion. To make matters worse, it is mathematically defined almost entirely by experimentally-determined mathematics.

This last point is the true differentiator between those who only understand concepts, and those who can quantify what they are discussing. Truly, quantification is the real skill of the engineer. It is one thing to speak about qualitative issues (the “what” of the physical sciences); it is entirely another to quantify them (the “how much” and “to what extent” of the same). In grade school, students are first taught about “closed form mathematics” and then that these mathematics are typical of scientific expression. A good example of this is Newton’s famed “law of action and reaction”, the mathematical expression of which is a succinct F=MA. So straightforward. So simple. Three variables in perfectly-defined harmony. Given any two of them, the third is easy to nail down.

Unfortunately, a vast, vast majority of the mathematics used in engineering are NOT closed form. Instead, they are multi-variable correlations valid only for a narrow set of circumstances. Deviate from those narrow circumstances, and a new expression must be experimentally derived. Fluid mechanics is almost entirely defined by these experimentally-determined expressions, further muddying an applied science not well understood.

And if there ever were an applied science for which common sense is wholly inappropriate, it is fluid mechanics. Virtually nothing obeys the “common sense” rules of observation, explaining why those who believe in ram air have extreme difficulty in believing that is simply does not exist.

The Deeper Explanation begins with a basic explanation of engine principles. Air and fuel must be combusted at a specific ratio, namely, 14.7 parts air to 1 part fuel (this is a chemical ratio). Stuffing more fuel into the cylinders without increasing the amount of air they also swallow will get no gain whatsoever. So the hot rodder’s adage “more air = more power” is proven correct. Figure out a way to stuff more air into the cylinder at any given RPM and throttle setting, and you can burn more fuel. Since burning fuel is what makes power, more air truly does create more power.

The amount of air which is inducted into a cylinder is a function of the air’s density. As the air flows through the intake tract, it loses pressure, and as the pressure decreases, so does the air’s density. (Denisty is mass divided by volume. Since cylinders are a fixed volume, increasing the density will also increase the mass of the air in the cylinder.) There are two ways to increase the pressure and density of the air inducted into the cylinders:

- Decrease the pressure drop from the throttle plate to the cylinders

- Increase the starting pressure at the throttle plate.

Ram air is an attempt to do the second. Under normal circumstances, the air at the throttle plate is at atmospheric pressure, and this pressure drops until the air reaches the cylinders. Ram air would start the process at some pressure higher than atmospheric, and even though the drop is the same, the cylinder pressure is higher because of the increase at the start.

Just how would this increase in pressure at the throttle plate occur? The oft-wrong “common sense” says, “If a scoop is placed in the airstream flowing around the vehicle, the velocity of the air ‘rams’ the air into the scoop, thus increasing the pressure.”

Why is this incorrect? There are two types of pressure: static and dynamic. Placing of one’s hand in front of a fan, or out of a moving car’s window, clearly exerts a force on the hand as the air diverts its path to flow around it. Most people would say “See? This is a clear indication that ram air works. Clearly there is pressure from the velocity of the air.” Well, this is correct, but only to a point. This is an example of dynamic pressure, or the force any moving fluid exerts upon obstacles in its path as the gas is diverted around the obstacle.

What an engine needs is static pressure. This is the pressure the same fluid exerts on any vessel containing it at rest. For those who were physics/chemistry geeks, it is the pressure caused by the force of the molecules bouncing off of the walls of the container. The key to understanding the difference between static and dynamic pressure lies in the velocity of the gas. Dynamic pressure is only a momentum effect due to the bulk motion of the fluid around an obstacle. Static pressure is an intrinsic property of a gas or fluid just because the molecules of the fluid are moving around. Any fluid which is moving can have BOTH dynamic and static pressure, but a fluid at rest only has static pressure.

The point of ram air would be to increase the static pressure, which would correspond to an increase in the in-cylinder air density, and of course, more air. Superchargers and turbochargers do what the mythical ram air purports to do. A supercharger trades the power of the belt and uses it to compress the air in the intake tract. This energy trade-off results in an increase in intake air pressure, more air in the cylinders, more fuel burned, and more power. A turbocharger trades the power of the hot gases and uses it to compress the air in the intake. The overall effect is the same – an increase in intake static pressure.

For ram air to work, it would have to trade the energy of the air’s velocity (as the vehicle moves through the air) for an increase in static pressure (since static pressure is a part of a gas’s internal energy, we see this is TRULY a trade in kinetic energy for an increase in internal energy). Now for the true reasons why ram air is a myth:

- The way for air velocity to be traded for an increase in static pressure is to actually SLOW IT DOWN in a nozzle of some sort. This is easily the MOST counterintuitive part of fluid mechanics for most people. The “common sense” mind says “In order to increase the pressure of the intake, the velocity of the air needs to be increased, just as increasing the speed of a fan exerts more force upon the hand.” Not only does this confuse dynamic with static pressure, but is also misses the point, which is to trade the kinetic energy of the gas for an increase in internal energy. How can this trade occur if the kinetic energy of the gas is increased? It cannot, and in fact, the only way to trade it is to use the velocity of the gas to compress itself – by slowing it down.

- Below about Mach 0.5 (or about half the speed of sound), air is considered “incompressible”. That is, even if the correct nozzle is selected, and the air is slowed down (the official term is “stagnated”) there will be zero trade. No kinetic energy will be traded in as work capable of compressing the air. The reasons for this are not discussed here; the reader may consult any reputable fluid mechanics textbook for confirmation of this fact. In plain English, a car is just too slow for ram air to work.

Still not enough evidence? Here is a little test. For ram air to work, the nozzle must be of a specific shape. The “Holley Scoop” for the Fiero is the wrong shape, by the way. The fact that it has no net shape at all immediately means it cannot effect any kind of energy trade off, so it cannot possibly create ram air. This is also true for the hood scoops on the Pontiac Firebird WS6 package as well, by the way.

What shape must it be? There are two kinds of nozzles. Pick one:

- Converging. This nozzle gets smaller as the air flows through it. It has a smaller exit than entrance. If the nozzle were a cone, the fat end is where the air would enter, and the narrow end is where it would exit.

- Diverging. This nozzle is opposite the other; it gets bigger as the air flows through it. With a larger exit than entrance, the narrow end of the cone is where the air would enter, and the fat end is where it would exit.

So, which is it?

Without hesitation, most of the “common sense” crowd will answer “Converging.” BZZZZT! Thank you for playing anyway! We have some lovely parting gifts for you! Bill, tell ‘em what they’ve won….

The answer is “divergent”. Yes, the nozzle would have to shaped so that the skinny end is pointed into the air stream, and the fat end connects to the throttle plate. How can this be right? Remember, to increase the static pressure of the intake air (which is the true “ram air” effect), the kinetic energy of the air must be traded to compress the air. This is done by slowing the air down, or stagnating it, and the only way to do this is with a diverging nozzle. Ah, but since air is incompressible at automobile speeds, it doesn’t matter any way.

Conclusion

Ram air is a myth because it does not exist, for the following reasons:

- Air is incompressible at any automobile speed., meaning that the kinetic energy of the air cannot be used to compress the air and raise the static pressure.

- The “ram air” nozzles commonly employed on automobiles tend to be the wrong shape. A divergent nozzle is required for ram air. Straight-profile scoops cannot provide a ram air effect.

Select one of the two types of intakes, warm air, or cold air. Beyond that its just about looks.