Intake Manifold - Explained 

You are the best teacher ever really appreciate your efforts thanks from my deep heart

The Intake Manifold design doesn't only involve a larger diameter. While a larger diameter will allow more volume through, it also slows down the air speed. Slower air speed through the runners, naturally won't allow for complete cylinder filling at high rpm. The length of the runners are a major factor, these are tuned specifically to take advantage of the pulsing effect when the valves are opened and closed (i.e. harmonics). Larger volume of the plenum is a benefit as it allows for more air "available ".

Just awesome. You've helped me a lot with your videos. Never had I so much information about engine.

Engineering Explained, Hey EE, I enjoy your videos and regularly share them with customers so they can easily grasp certain systems. One thing though, when approaching the PCV system, you pointed at flow being from the intake manifold to the valve cover. That is false. The PCV valve on the valve cover is a one way check valve stopping pressure from entering the crankcase and only allowing flow from the engine to the intake manifold in order to burn the oil vapors. If flow were as you said it was, every boosted engine would suffer from gasket/seal failure every time it made boost (positive pressure in the crankcase would push the seals out). I've seen this happen on a 300ZX-TT where a customer didn't reinstall the PCV system and had cam and crank seals blow out on the first drive post rebuild. Keep up the good work, the Internet needs a reliable source of info, and you're it. Cheers

Jason, your channel is awesome! You've been a huge help throughout my entire semester. Your explanations are really easy to understand and very informative. Keep up the good work. Looking forward to learning more.

I'm pretty sure that air travels out of the valve covers through the pcv hose rather than in

When I was in middle/high school I really enjoyed cars but didn't bother learning the actual mechanical aspect of them. Now that I'm a bit older I find alot of interest into learning stuff like this. Love your videos 👍

Question, you said the air flows into the PCV valve from the intake manifold, isn't it the other way?

Torque and horsepower are directly related, so you won't simply produce one without the other. Higher HP may come from higher RPM without changing the torque, so if that was the case torque could remain the same.

Jason, I so enjoy watching your videos that I re-watch them to learn even more (today's Presidents Day 2021). You are a true talent in so very many ways!

Thanks for the great informative video! I may be mistaken - but I believe that runners can be tuned (like headers) so that the +/- pressure waves will be aligned nicely at a certain RPM to give a pressure slightly higher than atmospheric just as the intake valve opens, thus increasing power (albeit only for a certain part of the rev range). A video on this and the basic (or just some rule-of-thumb) calculations associated with finding optimal runner length, diameter, etc would be great! I know it was mentioned but I would also love to see video on independent throttle bodies. Keep up the awesome videos!

@Engineering Explained , the PCV system hose you pointed out actually sucks air from the valve cover, the valve cover casing needs to be under vacuum, this helps in ring seal. Also this is why you see oil coating the inside of your intake plenum, oil vapors from your valve cover gets sucked into your plenum to be re-consumed by the engine to some degree, for emissions purposes. Also, you said increasing the the volume of runners...Thats not quite accurate. The fact is, longer/thinner runners benefit low end torque, shorter/wider ones benefit high RPM power....Usually a stock intake will be tuned for more low end than High end, or have a variable system. The type of intake you have is a static runner size. BMW engines for example the m54 has variable runner system, controlled by the DISA valve which switches from the longer set of runners to the shorter ones as the RPMS rise. Anyway this video was two years ago, and I like you later videos so thanks for those, please keep it up.

All your videos explain automotive systems very well. I may pass my exams because of you. Keep up the great work! My first subscription of all my years on youtube.

1) The piston pulling down on the compression stroke, as well as any vacuum remaining from the exhaust gases leaving. 2) Only 1 valve is open at a time, so the incoming air flows to the open valve, thus it is fairly even.

Again, thank you. You've increased my knowledge of engines and car engineering tenfold just with five minutes at a time and a simple whiteboard.

Thank you so much for the quick, thoughtful, and educational reply! I continue to have a greater appreciation for the internal combustion engine.

I am indeed learning as I make each video.

I agree with some of the other comments. The PCV system flows from the valve cover to the intake manifold, opposite your explanation. The valve itself is a check valve to ensure flow only in that direction. It's the blow-by from combustion going into the crankcase that creates pressure in the oiling system, which would pressurize the valve cover since the valve train oiling system drains down into the crank case area. Those gases are drawn into the intake manifold via the PCV system an recirculated into the subsequent intake charge, as I understand it.

Sweet! Thanks for this video. I'm becoming a pilot and intake manifold is an important part of what I need to know in the plane.

I'm pretty stoked about it!

Thanks for subscribing, glad you could learn from it!

Finally! A video that shows you where the inlet vacuums go

So glad I found this channel, you make great vids keep it up! Could you please make a vid explaining what happens when a heel toe/double clutch shift is used to switch into a lower gear

Im just learning the whole process and parts of cars and found your videos. I appreciate the way you explain stuff, im learning a lot from you thank you

You can't even imagine how useful your channel is. Thank you for your explanations!!!

If I may make a suggestion, I think after you show something zoomed in, please zoom out to show where that part is in relation to everything else. I love your videos and I have learned a ton from them. You are one of the reasons I am pursuing an ME degree when I get out of the military. Thank you.

Thank you for the videos. You've got a gift for teaching!

That's the goal! Appreciate everyone's patience, as I didn't expect to be doing anything like this for another year, but parts started coming in so I started making videos.

Like always, an informative video, but I was a bit surprised you didn't discuss runner length and it's impact on power, since it's one variable that is a factor in performance engines.

You look like the happiest person holding that manifold! :)

I really admire your knowledge of cars and how they work. Teaching is the best way to learn some say, I was wondering if your learning about how cars work as you make each video?

I would say yes, the PCV or Positive Crankcase Ventilation takes the gas from the case to the intake, an emissions control rather than just vent gas to the atmosphere, I learned this replacing the PCV system on my Saab 9-5

i agree with some of the commenters on here. combining theoretical explanations with hands-on installations will be a sure way to win over a huge audience! great video as always man. i like how you are direct and straight to the point.

I thought the same though the service manual showed the opposite, perhaps it was simply an illustration "typo."

I love that you're using the standard airbox. I'm not a fan of those cheap after market air filters, they look cheap and warm up the inlet temps.

Best channel on youtube. Hands down.

Watching your videos is not wasted time but learing thanks man!!

Eventually, yes. I have long term goals for my channel which involve doing so - but I don't want to simply install it and call it a day. I want to show the actual impact of what is installed. I also need the time to do all this, and the beautiful northwest summer prevents me from working on my car during the weekend, when there's so much to do out here in my few months of sunshine.

I checked the Honda service manual to verify, it shows flow from intake manifold to the valve cover. (Arrow pointing from intake to valve cover).

I thought so too but the Honda service manual showed airflow the other direction. I'll have to look back into it.

You should do an episode on breather filters, why would some use it, pros and cons and all that good stuff you normally do in your videos

really nice work, you take the time to explain the little things most people wont.

Awesome, thanks for watching!

Take your time man. We'll still be here :D

Thank you! You're making it possible for me to enjoy my car So much more😁

I've often heard of this being done, though I haven't seen any data to see if it's worthwhile or not.

i just came here after watching his videos in 2020 and lemme tell you, this is not the same man

It flows from the cam cover to the manifold. When combustion products accumulate in the crank case and head due to blow-by (tiny leakage through piston rings and valve stem seals etc) this is vented through the PCV system back into the intake manifold to undergo combustion in the case of unburned hydrocarbons and conversion in the catalyst in the case of combustion products rather than venting either to the atmosphere.

I'd say that the air is drawn thru the air intake system instead of saying the air just goes thru it. Engine's are merely air-pumps that pull air in and then push the air out. Sometimes more plenum volume is not always a good thing and can actually hurt performance due to the fact that you have not added any more fuel to add to the extra air that is being drawn in. No more fuel + extra air will equal a leaner condition than just using the stock intake manifold. In order to fully take advantage of a performance intake system would be to have the car re-tuned to accomodate for the additional air. Cheers! EDIT: Btw, I have that exact cross bar on my CRX. Oh and I'm running an S2 IM and S2 TB.

You fill a great gap which is very helpful for DIYers! Thank you so much for your videos. By the way, thinking of the cracking direction of my PCV valves, it seems like there may be an error with your fingers pointing out the direction of flow. I was thinking that the unburned gasses in the CC get directed back through the intake for burning.

a very helpful video for newbie in cars or any vehicle...very educational

Just want to thank you for you´r great video´s. You explain all things so that even a dude from Sweden gets it. Thank´s and don´t quit

Straight from the plenum to the cylinder head, but there is certainly a curve for the quick 90 degree transition. Space is likely the reason it's designed as is.

Dude i know so much about cars now after watching your vids. I watch each one of your vids like twice just so i can truly understand excellent job keep up the good work now i can impress my dad ( car mechanic) how much i know about cars lol

Very clear explanation with clear examples

Wow dude u explain stuff soooo clear it's amazing! :)

Loving the use of the word "manifold" this time :D

PCV valves work off intake vacuum vs crankcase vacuum. The pcv only works at idle. That is when the vacuum is lower in the intake than it is in the crankcase. That difference pushes the ball valve on the pcv open and draws the blow by gas out of the crankcase and into the intake to be re-burnt. When not at idle the vacuum pressures are the opposite. When an engine is at anything but idle the intake vacuum can be higher than the crankcase. That would send the blow by right back in the crankcase.

Im waiting for an ITB video. Hoping to see the differences in design for an ITB than an intake manifolds

Some PCV systems do actually supply air in through the top cover/s, but usually they draw the air in from the intake hose/air box/somewhere before the throttle body/s. And then they have another breather hose running from the crankcase to an NRV mounted on the intake manifold, after the throttle body.

From what Ive heard, the air which escapes the piston rings go through the breather valve to the intake manifold and re directs to the engine.

I love your vids - but Aha! I spotted a mistake - at 4:24, you've got the direction of the airflow backwards. Positive crankcase ventilation involves recycling these gases through a valve to the intake manifold, where they're pumped back into the cylinders for another shot at combustion. Still, good work! You're entitled to an occasional error...

Very nice presentation. I hope you and your vids encourage people to hate Hondas a little less. :D I have a 2007 Si and the Skunk2 intake manifold isn't too effective unless I run bigger cams. For me, porting the stock intake manifold is more cost effective than buying the Skunk2 (over $500). -frugal engineer

I provided a link in the description.

This is probably one of the first vids from you that is a bit of a swing an miss... anyway here goes. like meny have stated the PCV valve takes built up / increased crank case pressure and relives it into the intake manifold so it can be burned off in the engine. Next runner length and overall intake design can affect lots of engine factors such as torque and horsepower. This is done not only through the volume of air that the manifold contains but also how it changes the velocity of the air moving into the engine. Another item that is lacking in this video is what's called helmholtz resonance effect and how intake manifolds are/can be tuned to use this effect. As the intake valve close in the engine a vibration is sent back to the throttle plate and will bounce back to the runners. A properly tuned intake will time this effect to the point the vibrations will force slightly more air into the cylinder. It is possible to get over 100% volumetric efficiency in NA engine with this effect. It is also worth mentioning that its also the intake manifold's job to equally distribute air and air pressure between cylinders evenly. That is why there is space for the air to accumulate, this way cylinders will have less of a tendency to run rich or lien. So to people out there that think you can just weld a pipe with runners to it. There are allot of factors that must be taken into account when building a intake manifold, it is not an item you can throw together in your garage.

That was very helpful how you had A separate intake manifold next to the 1 that was on the car. Thank you as always, You do such a clear job Explaining things with good voice projection. I consider myself to be a smart man. But I do not have the mathematical skills to be an engineer. At least not yet. Lol

I too would like more explanation on the pcv direction.. on my track car I have my pcv go through a one way valve and into the exhaust where the high velocity air draws a vacuum on it, and before that setup it used to make my intake dirty.

I wrote a reply agreeing with you both then came to realise i was thinking more crankcase breathing which usually does go into the intake to burn off hot oil vapours and any cylinder 'blow past' gasses which would otherwise cause positive crankcase pressure. the valve/cam breather is not internally connected to the crankcase with the same gasses or pressures.

I love these videos. I really learn a lot. Thanks!

You should do a dyno run before you install all of your parts, and then after. That way people can find out realistic gains available from bolt ons.

I love this channel so much man!

Because the current design may be optimal for the current power, but a larger design may be beneficial to a car which makes more power. (If it were turbo'd, new valvetrain, etc.)

Thanks for sharing you knowledge on this topic, it helped me a great deal.

Essentially you use the natural frequency of the air in the intake runners to cause a pressure wave at the intake valve as it opens. It's actually possible to get higher than 100% VE using this method. Of course, for any fixed runner length you'll have a set frequency so works best at a set RPM, hence variable length runners.

Um sorry PCV is a vacuum operated component. The excess crankcase vapors that build up in the crank case need somewhere to go to otherwise it can ruin rings and/or ruin seals. The vacuum of the engine sucks through the one way valve that sits on the valve cover and draws off the excess gasses and vapors via a port that runs down into the crankcase. Nothing goes from the intake manifold into the engine other than air and fuel through the main ports. In the olden days they would just have a breather on top of the valve cover that would vent to the atmosphere. The PCV was a means of just infinitely looping those vapors back through the engine. The advantage of having a vacuum source to draw out the crankcase and valve cover space was that it helped break in the rings when the engine was new or so I have hear and read.

Haha I'm surprised you think so. I've used some de-greaser before but well over a year ago. It just stays relatively clean on its own.

Intake Manifold also provides the vacuum for the diaphragm of fuel pressure regulator.

Assuming the ECU can't compensate for the additional air on it's own, then yes. But there are scenarios where no tune would be needed - especially if the ECU can properly calibrate the A/F on it's own, which I'm guessing most modern cars can do.

Could you if you haven't already do a video comparing individual throttle body to cold air intakes advantages and disadvantages?

Interesting, for the various Integras each of the Skunk2 manifolds are under $300.

Runner length plays a VERY important flow factor on intake manifolds. The skunk 2 one works better on N/A cars, while the edelbrock one tends to give better results on forced induction. They only have different runner lengths and shape. Dunno exactly why it works like that but that's what the dyno always shows between the 2. Could be something affecting velocity vs volume on both... Could be wrong, but that's just what I've experienced with these IM's... Very good video BTW

Not sure what you mean by types of air intakes. If you mean brands, there are quite a few. Unfortunately I don't have the time to help with projects on a case by case basis, too many people. Good luck!

That is a good point to make, simply letting more air in won't change your horsepower too much without the cams actually letting more air into the chamber or the ECU knowing to inject more fuel (although most cars can adjust fuel mix on the fly from O2 sensor feedback my race car uses fixed map injection, which means it runs richer than a overjetted carby but it has trumpets and straight pipes so...). Same for most engine mods, if you don't tune it to use the new part then its a bit of a waste.

It's very math intensive, yes, I'm won't sugar coat it. It's a ton of math, and plenty of theoretical math without actually using numbers, very logic oriented. I have a write up on my website regarding this subject. Go to my channel page, and the "about" tab. Then click on "Automotive Careers" for a link with some tips regarding this subject. Enough effort and you can get through it, best of luck!

I think he is saying: Short & long runners for the intake manifold. The long ones are blocked of by valves, and open up in higher rpm's to increase flow into the engine. At idle or under low load, they are closed so you have more vacuum(my assumption).

It would have been great if you would have showed where the evap purge valve mounts on the skunk2..

PCV from crankcase to intake...not the other way around. "The blowby vapors that end up in an engine's crankcase contain moisture as well as combustion byproducts and unburned fuel vapors. The crankcase is sealed to prevent the escape of these gases into the atmosphere, but the vapors must be removed to prevent oil contamination that leads to sludge formation. The PCV system siphons these vapors from the crankcase and routes them into the intake manifold so they can be reburned in the engine."

Agree w/ previous comments... great explanations! Thank-you very much.

Have you tried contacting tech support regarding the part? They should be able to offers solutions as they designed it.

This was very informing and easy to understand

do a vid on differences of intake manifolds (IE) plenum sizes, runner lengths and sizes and the effects on modified and stock engines

That was the same question on my mind. You keep showing parts for Integras. I'm guessing that you will do some heavy dyno runs to show what each part can do, can't wait!

I respect your professional knowledge greatly. In this case should more mention not have been made about the dynamic behavior of the shock waves and the effect of the length and diameter of the runners ?

Thank you for the informative video. This helped me understand my engine much better.

i just want to say ur awsome dude i never knew that part was the power brakes or what the heck a manifold was i have great respect for u man u are a great help to me thanks

The crankcase ventilation flow (“blowby”) travels FROM the valve cover into the intake manifold. Those vapors then get burned

Excellent description! I fully understood!

Absolutely.

In the beginning of the video, I was thinking "why is he holding up half an intake manifold?" Then, he said it was for an Acura Integra which has half a motor. Makes sense now.

I know nothing about cars, but now I know something about the throttle body and the air in take manifold