Hot Air vs Stock Intake/Open vs Normal Exhaust

[CajunCC]

No, this is not your usual Intake and Exhaust thread. Think more of an intelligent discussion of what's REALLY best for our cars. Let's start with the intake side.

The stock setup is quite restrictive. On my vacuum gauge, I've registered almost 5 in.-Hg of vacuum at WOT over 4000 RPM. You should have ZERO manifold vacuum at WOT. Most intakes are centered around better flow to make it easier for the engine to get the same amount of air. The thing is with our stock intake the engine isn't even getting ENOUGH air.

That being said, I'll give up my conclusions after back-to-back testing of the stock intake vs. and open K&N filter stuck right on the VAF. No matter how you look at it, the filter on the VAF is the better way to go. The difference in volume of air and ease of flow more than makes up for the difference in temperature. When I first took the cone filter off and put the stock intake back on, I felt more low end but a lot less top end. I left it on because I liked the better low end. Then I swapped the cane filter back on after I ran a 17.0 and had horrible top end power on the dyno at the DC Dyno meet. I've swapped the intakes back and forth and the stock intake does not provide more power anywhere in the band. The cone filter DOES provide more low end power and a LOT more top end power. The only problem is that I'm still pulling about an inch or so of vacuum as I approach redline, even with the open filter. So now the restriction is not the intake. I'm thinking it's either the VAF, throttle body, or part of the intake manifold. I'm thinking the VAF may be part of it. I'm not absolutely sure though. I need to remove my intake manifold and clean all the gunk out of it so I know it's not the manifold. Same with the throttle body. Then I'll research one component at a time and figure it out.

Now let's figure temperature into the thing. With a hotshot-style intake, you've still got the wide-open filter, it's just on the end of a pipe. If you use 3" pipe, like most people do, then you shouldn't run into any restriction there, but I'd like to test that out. You should also gain power from the lower air temperature, depending on where it's pulling air from. The lower temperature obviously means a higher concentration of oxygen. This is always good. But the point remains that if you can't afford a true CAI or you can't figure out how to make one effectively, then an open cone filter on the VAF is still better than the stock intake.

Now let's talk about exhaust.

Larger piping. Mandrel bends. Straight-through mufflers. What is all this crap and why do we really need it?

Stock exhaust is about 2 1/8 inch crush-bent pipe through a resonator into a chambered, glasspacked muffler.

"Don't make your piping too big or you'll lose back-pressure and the engine needs back-pressure to make low-end torque."

That statement is NOT true. The engine would like to have NO back-pressure at all. Any back-pressure means the engine has to work harder to push out the exhaust. Suppose you unbolt the exhaust at the end of the y-pipe. You'll lose some low end torque because you'll lose the scavenging effect through the exhaust pipe. You would need a VERY large pipe to disturb the scavenging effect. Two and a half inch pipe is not too big for a 2.5 liter engine. I've seen 5.0 liter mustangs running dual 3" pipes. That means that each bank is pushing 2.5 liters through a 3" pipe. They aren't having problems. I've even heard of someone with a 3" exhaust on a KLD with no noticeable loss of low end toque. Even if you would lose some low-end torque compared to a slightly smaller pipe size, you'll still make more than the stock exhaust because of freer flowing mandrel bends and a less-restrictive muffler.

Again, I'll give my case. When I put my Pacesetter exhaust on, I noticed more gains in the low end than I did in the top end. I had more power on tap in 4th gear than I did before. Even if it's just an illusion, I certainly didn't LOSE torque from the 2.5" pipe. It would be interesting to measure pressure inside the exhaust and eliminate restrictions like I can do with the vacuum gauge in the intake.

"Now the muffler. Look, you can see right through this one, it's gotta flow better than this other one that you can't see through."

That's also wrong. Try an experiment. Go to Pep Boys. Ask for a Cherry Bomb Turbo II muffler. It costs about $30. Grab a friend. Stand face-to face with the friend and hold the muffler between your faces. Have the friend blow into his end of the muffler. You will feel his breath on your face as if he was blowing through a straight pipe. And that's a chambered muffler with an offest inlet. On a side note, it sounds pretty good on a car too. That's just a $30 Pep Boys value muffler too. I'm sure better-designed mufflers will perform just as well as a straight pipe or a straight-through muffler.

[supergoat]

Since you have the gauge, it's easy to tell WHERE the restriction is. :)

*Run the car at WOT without an air filter to see the gauge registers lower or 0. If it does then the air filter is still restrictive. Find a bigger air filter. If the reading is the same as before though with no air filter than it's either the VAF or plumbing that restrictive.

*You can also see if the throttle body is a restriction by testing manifold pressure. :tup: Once you get rid of the other restrictions that is. :)



:tup:

[CajunCC]

Exactly what I'm doing. :tup:

[CajunCC]

TTT

[mgloomis]

This is interesting.:tup:

My bet would be that the VAF is the next restriction. I mean... compare a VAF to a MAF.

I saw a VAF for the first time last night when putting on my PRM. I can NOT believe what I saw! The VAF has a cone shaped plunger type thingy that blocks basically all of the airflow when it's fully extended! Then, as the airflow increases (I.E. increase in vacum behind the VAF), the "plunger" moves back into a more open area of the VAF housing. While it does provide more area for air flow back in there, it still has a 2" piece of solid plastic sitting in the center, blocking air flow.

Somebody told me (the person that answered the phone when I called to inquire about the PRM), that when he switched from VAF to MAF, he saw only 3 HP increase, but an 8lbft increase in torque. :???: He also had to make some sort of "controller" for the MAF to work correctly.

Mike

[Drag On]

c mon.. lets make this sticky and debate it.. I'm going to be honest though, the name of your topic sucks.. mosy big names arent even going to look at it.. the only reason I looked into it, is because I saw that you posted it and you are a valuble member with a lot of information.. let the debate begin..

[CLPCLD]

My $.02-
From what I remember the engine does need some back pressure to function properly. I think you're forgeting that we don't drive 5.0 Mustangs, because first of all it is much easier for a RWD car with a V-block to be free-flowing, since the headers can go straight back with gentle curves as apposed to the almost complete circle my rear haeders piping makes before it joins with the other, and second of all, the engines are barely even made by the same company, not to mention that you can't really compare one bank of a 5.0 to both banks of a 2.5L. As far as flowing, obviously size isn't everything, since the Borla is almost the same size as stock and the Greddy is about 2.5" (if I remember correctly) then how come the Greddy makes less than 1 HP more than the Borla?

Also, speaking as someone who has driven their car with open headers (not by choice, that's just the way it had to be) and having an ATX, so I have no real control over shifting, my car definitely felt bogged down and went very much slower.

[Nuke]

Flow is all about differential pressure, without it there is no flow. Any piece of pipe or intake manifold has some internal friction and a differential pressure must be developed to generate flow. With that said.....if you are measuring manifold conditions and there is any kind of restrictor at all (TB, MAF, air filter housing, etc.), then you probably will see some vacuum in the manifold since there is obviously air flow. You can measure flow across a TB, a nozzle, even a mere bend in a pipe simply by measuring the differential pressure (DP)across it. And there will be a DP, otherwise there isn't any flow.

I don't know where you're measuring the manifold vacuum but even if you measured immediately before the TB and immediately after it you would see some DP, it's simply an indication of the flow passing through it and the characteristics of the TB. Granted, you might have to have digital indicators that can read very fine increments but you'll see something.

Even those monster big block Chevys with mechanical fuel injection and individual injector stacks probably register some vacuum just after a wide open butterfly.

The only normally aspirated engine I can think of that might not show some manifold vacuum is a new one being developed by Porsche (or is it BMW?) that can vary the lift of each valve and thus does not need a butterfly to throttle the engine. The variable valve timing and lift does away with the TB.

[CLPCLD]

BMW, if you're talking about "valvetronic". I believe the new 7-series already features this, or maybe the 5-series that is supposed to come out soon, but at any rate all the new models introduced over the next few years will also feature this according to the article in SCC or Car & Driver or Motor Trend, whichever one it was.

[Not_His]

I know all abou thte specifics of vacuum and such, but on the scale you're talking about with before and after a throttle body or a pipe bend, 1 or 2 inches of mercury is a HUGE amount of vacuum. And that much vacuum will have a definite effect on performance. My vacuum gauge isn't anywhere near precise enough to measure the minute vacuum that a free-flowing throttle body will make. I'm more looking at serious restriction in volume of air getting to the engine.

As far as backpressure in an exhaust and the 5.0 vs. 2.5 thing, You're wrong. Sorry. Backpressure is the enemy of performance. I did go through all this in my original post. The reason huge piping can harm low end torque has nothing at all to do with backpressure. Smaller piping increases the temperature and velocity of exhaust gas. As an exhaust pulse travells down the pipe, it leaves a slight vacuum behind it, which pulls the next pulse along behind it. With a huge pipe or open headers, you totally lose that scavenging effect. But the huge pipe or open headers are great for high-rpm power because at that RPM, you just need to get as much gas out as possible as easily as you can. Make sense? It's velocity and scavenging, not backpressure.

GRRR!! I posted under Kim's name again and can't delete the stupid post to put it under my name! :( Oh well

-CajunCC

[CLPCLD]

I thought a small amount was better, though. For example, a car with a Borla XR-1 muffler usually has more power than with open headers. All I'm saying, is that with open headers, my car was much slower and got about 10 mpg, driving normally and in no traffic. Make of that what you will.

[CajunCC]

Open headers means you have no exhaust pipe which means you have no scavenging effect. Unbolt your muffler. That'll keep the scavenging effect but lose the backpressure from the muffler. You'll see no decrease in low end torque.

[Not_His]

Sorry, Matt. I'll never sign on to PT on your pc again! :(

This is very interesting. And very informative. I really wish it would be made sticky, so some of the other GT guys would get in here and give their opinions.
I can't really say too much, because this is where I'm gaining knowledge from ... you guys. All I can do is read, think, and read some more. Maybe Matt'll let me help him with some of his testing of ideas? ;)

So is an open air filter fitted directly on the VAF still better performance-wise than a CAI with 3" piping? Do you pull more air still?

~Kimberly

**EDIT - yeah, I sound like a 'tard. :darin: I'm tryin' at least.

[Probe 2C]

I retitled the thread in an attempt to get more flow in here.

Also, it seems as though you're trying to get to something here, but you just aren't getting there.

For starters, our stock intake and exhaust aren't really that restrictive. Much less so than most cars. Improvements can be made, but nothing is going to be spectacular.

Second, the open headers. You say yourself that the scavenging effect aids in 'sucking' out the exhaust by creating vaccum between pulses. That would continue throughout the RPM range, not only at idle/low RPM. Infact, the vaccum would be greater at high RPM's causing it to enhance further performance (assuming the correct size exhaust was used).

The Vaf is not restrictive to air flow. It is a restriction when going Forced Induction mainly because of the way it reads the air, not because it blocks the air. The method it uses to read information about the air makes it harder to 'trick' a car not normally force fed into running correctly while air is being shoved into it.

For most na cars hardly noticable gains will be had by switching to MAF, most of them will be due to the extra management which you will have as a result of the switch.

Either way, on the intake, just go Cold air and you're better than stock or Hot air.

[mgloomis]

Originally posted by Not_His


So is an open air filter fitted directly on the VAF still better performance-wise than a CAI with 3" piping? Do you pull more air still?

~Kimberly



Well.... I would think that with just the filter on the end of the VAF would be less restrictive therefore flowing better, which would normally equate to an increase in HP and TQ. But then factor in that the air that it will be sucking in will be between 30 and 60 degrees hotter (even more I think) than a cold air setup, and that negates any horsepower increase via. flow advantage that you would have had. The colder air (because it's so much more dense than the hot air at the top of the engine bay) seems to make more HP and TQ.

Now... take a Jackson racing supercharged car, for example a Honda Civic Si, and watch it lose HP as soon as you put the AEM (or any brand) CAI on. This is because the super charger has to work to pull the air through the long CAI (it's like 3' long on those cars) which means an increase in vacum (backpressure was only in exhaust I thought). Kind of like if you took a straw that was 1 foot long, and then take a straw that is 3 feet long..... it is MUCH more difficult to suck water through the long one, than the short one. Physics..:wtf:

Mike

[jones93pgt]

ahhhhh!!:eek: he said HONDA...such vile language...i am forever scarred:cry:

[HowLeTT]

Originally posted by CajunCC
The difference in volume of air and ease of flow

:lol:


After reading this thread I went outside and superglued my VAF to the end of the throttle body, put a thin mesh screening over the end of the VAF for a filter, and unbolted all the exhaust after the heads. ;)

n/a, 2.5" is too big. There really is no way to argue that matter other than dyno plots. The mediocre displacement of the KL doesn't provide significant exhaust gas through that piping to get it up to speed and take advantage of the lessened backpressure until almost the absolute peak of the powerband, and by that time the benefits are outweighed. Obviously how true these statements are varies depending on the car. A ZE with it's higher powerband and hp levels is going to benefit more from a less restrictive exhaust than a bone stock KL will. The more modified the car is, the better. If I ever felt like my borla + test pipe combo was choking the car when it was running mid 13's at the track, I would have done something about it.

[94probester]

i cant really say that my 2.5" pacesetter w/ testpipe is too large of piping because i never really had a borla laying around to slap on to compare. when i installed the pacesetter, i was looking to feel a little loss low end because of the piping, but i really couldnt. maybe if my car was bone stock the piping might be a little big, with adding a few air mods, i think the bigger piping would be fine. My brother has a '99 mustang v6 and the other day i unbolted the exhaust from the y-pipe(suprisingly sounds great for a v6). but when i drove it i could definitely feel a loss low end. because he really has little mods, it is probably best to run the exhaust through the muffler, but he just wanted it louder. but for our cars i assume that without major work like turbo/n20, open piping would be pointless IMO

[roadrunner@rps]

Open headers actually cause an over scaveging effect. With the reduction of so called "backpressure" there is a higher low pressure area behind the exhaust port when opened due to less resistance to flow in the exhaust. Due to an engine operation speed this low pressure area can be found sometimes even when there is no pipe(header). Overscaveging will usually hurt an engine unless cobated with an agressive cam, and still then it can be a problem.

In theory less backpressure is always ideal for an engine. The key word being ideal. For a streetable engine that operaties in lower rpm resistance to flow does play an effect. Not a huge one but small in combating over scaveging. Mostly the problems with larger size is ehxuast velocity. A smaller pipe can flow faster than a large pipe, while a larger pipe can hold more, but will flow at a slower rate. In cars the mass of exhaust gas is rapidly changing due to the vaarying rpm. That is why typically a larger size pipe will always flow better at high rpms than a smaller one. The excess mass of the exhaust gas makes use of the pipe and creates less backpressure. At lower rpms the small pipe plays a huge role by allowing the exhust gas to flow faster resulting in lower backpresure.

Also to take into accont is exhaust length. From the basic physics formula W=F*D show that pipe length plays a huge key in flow rates. If considering W the work the engine has to do to press the gas out of the pipe, the longer D is the more power is lost due to the exhaust. Also this shows that the resistacne force or as called "backpressure" drops the engine has to put less work into pressing exhaust out of the pipe and then that work can be placed into the driveterain.

[CajunCC]

I retitled the thread in an attempt to get more flow in here.

Thank you.

For starters, our stock intake and exhaust aren't really that restrictive.

I dunno about the exuast, but if you re-read my original post, the stock intake is VERY restrictive. So restrictive, you'll pull up to about 4 in-HG of vacuum at WOT above 4000 RPM. I've proven that with my vacuum gauge. I replaced the intake with a cone filter on my VAF and now I pull about 1 in-Hg and only at about 6000+ RPM. That's PROOF that the engine is getting a LOT more air with the cone filter. No matter how cool or hot the air is, 4 in-Hg of manifold vacuum = less power than 1 in-Hg. You're just plain getting more air.


Second, the open headers. You say yourself that the scavenging effect aids in 'sucking' out the exhaust by creating vaccum between pulses. That would continue throughout the RPM range, not only at idle/low RPM. Infact, the vaccum would be greater at high RPM's causing it to enhance further performance (assuming the correct size exhaust was used).

Correct in a way, but at high RPM, you're moving a LOT more air per given unit of time. That means you'll get the same velocity and scavenging effect with a larger pipe. Basically if you have a big pipe, you'll get better top end. If you have a smaller pipe, you'll have better low end. But if you go too small, you'll choke the engine. If you go too big, your motor won't be able to put out enough gas to fill the pipe and that itself will create backpressure within the pipe. But that's really not the point of my argument in the original post. My point there was that people argue to death the difference between the borla's 2.25 or 2 inch pipe and the Pacesetter's 2.5" pipe. Bigger is not always better, true, but 2.5" is NOT too big for our cars.

The Vaf is not restrictive to air flow. It is a restriction when going Forced Induction mainly because of the way it reads the air, not because it blocks the air. The method it uses to read information about the air makes it harder to 'trick' a car not normally force fed into running correctly while air is being shoved into it.

Right, it flows plenty. But think of a 2.5 liter engine at 6500 RPM. You're flowing 271 liters per second. That's a LOT of liters. Consider pushing that much through our VAF. Sure, it's not as restrictive as it looks, but for sheer volume of air at that RPM, it DOES get in the way and WILL restrict airflow. I'm not saying it's worth it to replace it though. Just providing a little information.

Either way, on the intake, just go Cold air and you're better than stock or Hot air.

Some of us have serious issues coming up with a way to do cold air. An ATX MX-6 has almost no room in the engine bay for a cold air intake. It requires battery relocation at the very least. Besides, it's obvious that cold air is better than hot air. That is, again, not my point. My point is to disprove the myth that a "hot air intake" makes less power than stock.

[FASTFRANK96-PGT]

Well after reading all this info. I have concluded that I am going to autozone on my lunchbreak and going to get one of those cheap 20 dollar cone filters and take off my stock setup and bolt this cone filter directly to the VAF. For now what can it hurt. Our motors run so hot anyway I just can't imagine that a CAI can be that much more beneficial. Don't get me wrong I will be purchasing one this summer but for now I don't see any reason not to try a filter on the end of the VAF. People with this set up what do you think? Anybody out there tried both setups? How did it perform and how did it sound? Just curious. I am not saying that a CAI is not the better route to go, but in regards to air flow a cone filter on the end of the VAF has to be better than the stock setup....agreed? or do you disagree, I see quite a few different opinions on this issue. Thanks, Frank

[CajunCC]

Frank, I wholeheartedly agree. While you're not making as much power as you could be with a hot-air setup, you're definitely making power over stock because the increase in volume and flow GREATLY outweighs the difference in heat.

[FASTFRANK96-PGT]

Thanks Matt,
Well I did it last night, actually I did 3 cars. Put the nice polished $20 dollar filter on the end of my VAF, Put one on a Jetta w/ a VR6, and put a whole CAI on a Civic. Out of the three mine is definitely the quietest. :( The VR6 in my friends Jetta sounds bad-ass. I can't believe how much sound it gave his car. His exhaust is quieter than mine so you can hear his intake growl alot more, my exhaust is louder so I can't really hear the intake growl quite as much, still noticeable but wish it was a little louder.
I must say I am disappointed in Ford (Mazda) for even designing anything like that VAF. I mean what the hell, how is the car even running with that dam restrictive sensor there. I would like to do a Mass Air Flow conversion. I think it is possible I will do some searching and see what's up. But until I get the $$ for a CAI setup the Autozone Special will do for now.

Just out of curiousity guys/gals Who out there has tried the filter on the end of the VAF, and a Hotshot CAI setup. I mean if I am not going to gain anymore sound or performance from the HS setup then I am not going to spend the $200 for it. Is it louder over the Filter on the end of the VAF, I know that it will be a slight performance gain since it is Cold Air, but is it worth it for $200. If I can expect a decent gain and sound equal to my bud's VR6 in that Jetta I would put one on the Credit card today!LOL Just let me know guys thanks!!

[CajunCC]

Adding a pipe to your intake wil make it slightly quieter from the increased distance to the motor. It'll suck cooler air, giving you better performance.

The VAF isn't anywhere NEAR as restrictive as it looks. It's actually a very good design. A mass air conversion is basically more trouble than it's worth unless you have a LOT of mods.

[FASTFRANK96-PGT]

Well it just IMO looks restrictive but hey I guess if it was so bad then they would have designed it differently. well I tried to make another post to just see what people had to say about HAI VS. CAI and it was closed. Figured it would be just thought somebody might have had the setup like me and then put a CAI on. I have searched numerous times just thought I might get even more input but oh well. No Big Deal. Well appreciate the info. Matt. Guess when I get some extra $$green I will go ahead and get the HS CAI. For now I will stick with what I got. Thanks, Frank

[mgloomis]

Originally posted by FASTFRANK96-PGT
Out of the three mine is definitely the quietest. :(

Can you say, "No overlap in the camshafts"??? If my memory serves, there is actually 3 degrees of rotation between the exhaust valve closing and the intake valve opening. On most cars (I'm pretty sure most.... anyone?), the intake valve is open/opening as the exhaust valve is closing. This allows the air/fuel mix to be drawn in by the vacum created by the escaping exhaust gases (kind of like scavenging). The ZE cams have this, and is why they are such a power +.

It kinda seems like the whole VRIS thing is used to "simulate" that effect.... maybe not.:shrug:

Mike

[hudnut]

I may be thinking backwards here but, could a smaller diameter intake increase air velocity? Also, what about turbulance right at the end of the VAF? I was looking at my setup today and noticed that the part of the VAF that I had my pipe clamped onto (far back, towards the mount) has a curved lip that could cause intake air to curl backwards. Just tryin to put in a few more variables to think about here.

[slink]

i have run a large k&n cone filter right off the vaf and definently noticed a loss in power over the stock setup as the car warms up. now i run a ractive heat sheild filter off the vaf with a pipe leading down to the bottom of the splash sheild and notice a definate improvment especially a higher rpms.

[FASTFRANK96-PGT]

Well I have been running the filter directly off the VAF for couple of days now and I have not noticed any loss in power. If anything it seems to me that car is running better. Not to say I have a big gain or anything but hell I do feel somewhat of an improvement.
I still agree CAI is the better setup just don't have the cash right now. 60k service coming up along w/ VCG's etc. so the VAF filter w/ do for now. I just wonder if I will get any better sound w/ HS CAI instead of the HAI I got right now.


One more thing while I am thinking about it, Now out of the CAI setups I have seen on other cars, Jetta, civics, etc. It looks like to me that the probe's setup is probably the best towards "Cold Air". Shit a civic CAI isn't nothing but a tube right over to the right of the engine bay, he isn't getting cold air, Same for a Jetta, at least the probe's is down close to the ground. For those two cars IMO a CAI is a waste of cash, just throw on a filter and that is enough. what do you think??? Frank:rolleyes:

[Jeff_Jeske]

I had a hotshot CAI. I sold it and went back to a HAI right off the VAF and it is a noticable downgrade.

You might not feel an upgrade but you sure do feel a downgrade.

The stock intake is AZZ so definatlely go to Autozone and pick up a filter.


At the track I used a 3" PVC pipe feed down to the pavement and I use a thigh-high nylon as a filter. Thats right no filter just some womens pantyhose!

I have tested various configs at the track and the are all about the same, however, the legging filter produces the highest trap speeds....even thougth the time is close the speeds are higher without the filter on there.

Keep in mind I run 2.5" exhaust with TESTPIPE and a 64mm Throttle body.