Q45 intake tract

[EWT]

When I put my transmission oil cooler on, I noticed that the air intake terminated in a location that seemed awfully restrictive, but I didn't have enough time to play around with it much. I had some free time today, and pulled the driver's side headlight and end of the intake pipe off. I don't remember if my 93 had the same design, but on my 95, the end of the intake terminates into what amounts to a sealed "box" next to the headlight. It's hard to describe in words, but there isn't any obvious large place for air to get in. The intake inlet is probably about 4 x 2", and it terminates into a "box" made up of several plastic trim pieces and the side of the headlight. Obviously, air gets in somewhere (probably from the junctions between pieces), but it has to be really restrictive. I'm guessing Infiniti did it that way for noise reasons and to ensure that water wouldn't get sucked into the intake. I pulled the last part of the intake off (a roughly U shaped piece that is about 2' long), so that I'm now pulling air from behind the bumper. I'm really hesistant to say this since "butt dynos" are so unreliable, but the car really feels like it picked up high rpm power. It always felt like it was weaker above 5K rpms or so than my 93, and just didn't have the same surge to redline. Now, it feels strong all the way to the redline. As an added bonus, the strange hollow "sucking" noise my car made at idle is gone as well. It was starting to drive me crazy since it sounded like a vacuum leak, but I couldn't find anything loose or leaking. The fact that it made that much noise confirms that it had to be pretty restrictive even at idle.

Surprisingly, the car isn't much louder at WOT if at all. The only downside I could see is that you'd have to be more careful driving through deep water. Hot air isn't an issue since you're still pulling air from outside the underhood area from a good cool air source right above the opening below the bumper.

Has anybody else noticed this or played around with it on a 94-96 (or maybe 90-96) car?

[maxnix]

A great discussion here.

[EWT]

A great discussion here.

I'll have to take some pictures of it. Contrary to what I initially thought, there actually is a little opening to the box but it is only a roughly 1 x 2" hole above the headlight, which is very small compared to the intake pipe on the other side of the "box." I don't have a vacuum gauge sensitive enough to measure intake restriction, but it seems impossible to me that the way it was setup on my car wasn't restrictive at high rpms when the engine is pulling a lot of CFM. Everything seemed to be designed to fit together the way it was assembled, but perhaps my car had the wrong pieces or something. If I get some free time again, I may try timing some 60-100 roll-ons with and without the last intake piece to see if the seat of the pants improvement is real or not.

[Q451990]

The only downside I could see is that you'd have to be more careful driving through deep water.

That is a big concern... I'd check your air box from time to time even in moderately rainy conditions to see if you see any water in there.

I know Dennis has played around with the airbox quite a bit and concluded that it's pretty much optimized from the factory, but who knows... there's always room for improvment - you just have to find it!

Heath

[EWT]

That is a big concern... I'd check your air box from time to time even in moderately rainy conditions to see if you see any water in there.

I probably wouldn't do it if I still lived in Florida or SC, but living in Northern CA where .25" of a inch qualifies as the lead story (with 3 followup stories, and 5 teases of the followups) on the news, I'm not as worried.

Quote »I know Dennis has played around with the airbox quite a bit and concluded that it's pretty much optimized from the factory, but who knows... there's always room for improvment - you just have to find it!

Heath [/quote]

I could be wrong, (wouldn't be the first time), but I'd be surprised if an opening that small wasn't at least somewhat restrictive. I forget the formula to compute CFM, but the engine is probably sucking in the neighborhood of 500+CFM near redline, which is a lot of air to pull through an opening that small. When I originally posted, I hadn't noticed the little opening at the top, and it's pretty hard to argue that a sealed box isn't restrictive. I'm a little less certain I've made a brilliant discovery at this point. I'll try to time some roll ons or better yet quarter mile passes at a dragstrip with and without the piece to see if it really makes a difference or not.

[Q45tech]

The Q air intake system from the inlet to the air filter has a 5.5" W.C. restriction [probably better [less than 95% of any cars].

In fact there is some minute BOOST above 60 mph! as the losses decline at same load rpm 50 mph vs 95 mph at 6500 rpm.

Measure things to be sure as you never know what problems you create by relying on your senses.

You must understand that the air flow at idle /cruise is very minute vs that at 4,000 rpm or the maximum rpm where it can be 12-15 times more.......in grams or CFM.

Nothing you can do, even setting the MAF atop the hood with nothing in front of it will be significant until say 4,000 rpm.

I know everyone wants [prays] that the factory is hiding HP and doesn't want you to have it but not true.........if anything they are running out of tricks to get more from same sized engines.

CFM is not accurate as the CFM can go up while the density goes down what you want to know is the weight of air per second of flow.......grams per second!

This is how they [aftermarket cheats they use HOT air in more ways than one].

500 CFM is smoking something as that would be 413 HP!!!!!!274/2= 137 x 4,000 rpm=548000/1728= 317 CFM x VE [93%]= ~~295 CFM

at 6700 rpm= 531 x VE [72%]=382 CFM maybe on a perfect day.At 7300 rpm the engine might just exceed 400 CFM

A good rule of thumb is:HP x 1.21= CFM..,JWT ECU 307/HP [@ 6300] x 1.21= 371 CFM278 HP x 1.21= 336 CFM

Easy just monitor the MAF voltage vs rpm, what ever the largest number is [4.41.........4.444 volts] is the rpm at max flow!All my test show by 6600-6750 the flow has maxed.

Generally the intake tract cleanliness [frictional restriction to airflow] starts to be meaningfull above 5500 rpm when the flow gets above 350 CFM.

What you might note from above is the VE of 93% at 4,000 rpm is the point of maximum efficiency as rpm increase less and less air in cylinders due to time.......the valves are open 248 degrees but as rpm goes up the TIME of opening gets smaller and smaller thus the air in runner speeds up towards the speed of sound and the higher the speed the more friction as it passes through the valve curtain.

Remember the HP peak is the intersection of two graphs a rising rpm and a falling VE [usually where the VE has fallen 20% from torque peak rpm] [93 x 0.8= where it become a VE of 74-75%].

[Q45tech]

If you graph the flow [or dyno the engine] you will find TWO HP peaks one at 5500 and another at 6,000 rpm both being equal with a valley [of 10 HP] between them due to the tuning of the runner length from plenum to heads and the design of the dual input ports.........the 94 oval port is different with a single peak at 5700-5800.

The above rpm will vary depending on air temperature in runners as the speed and tuning wave varies with temperature by 5-7% from 30F to 100F.

The use of Nitrous which cools the air on evaporation [by 30-50F at the heads -- amount declines as rpm increases] can make for some interesting happenings on a cold day.

[PalmerWMD]

Having to build a 3.5 V6 was the last thing they wanted to do same with the up coming 5.6 V8.].

Q45tech:

Are you saying we are expecting an Infiniti 5.6L V8 soon?

Fred...

[Q45tech]

Well if you want a truck engine I'm sure they'll offer it in a few years--- note MB has the 5.5 liter currently available.......think they have to retrofit VVT to get the HP numbers up from 300 to 370............to sound competitive.

The current 4.5 at 333 lb/ft vs 375...........hey an extra 40 is another 0.4 secs depending on what the engine weighs extra.

The 507E transmission is still the bottleneck! Wish they would just spend the extra $1200 and use the ZF 6 speed AT.

[reggiegsd]

5.6 liter, aluminum block, aluminum heads, 4 cams 32 valves, TRUCK motor.

[EWT]

Measure things to be sure as you never know what problems you create by relying on your senses.

That's exactly why I plan to measure acceleration with and without the piece. Seat of the pants measurements aren't very accurate. If I had a dollar for every modification that felt like it made my car faster and didn't, I'd have a lot of $.

Quote »I know everyone wants [prays] that the factory is hiding HP and doesn't want you to have it but not true.........if anything they are running out of tricks to get more from same sized engines.[/quote]I agree with you that there's not nearly as much power leftover as the aftermarket industry would like you to believe, but that's not universally true. Power is not always the primary concern for car makers. As an example, there is are a couple of restrictions in the intake on first generation Talons/Eclipses that can be easily removed, and result in significant gains on a dyno. The downside is that intake noise is increased slightly, which apparently was a higher priority than extra power. Taking the lid off the airbox on a mkiv Supra results in about 7 rwhp on the dyno, and intake temperatures are not increased if the car is moving. A freer flowing exhaust frees up large amounts of power on either car at the cost of more noise. If the Q45 intake is already optimized for maximum power though that's great. I just have a hard time believing forcing the car to inhale through an opening that small isn't restrictive.

When you're measuring vacuum are you measuring it before or after the MAS?

Quote »CFM is not accurate as the CFM can go up while the density goes down what you want to know is the weight of air per second of flow.......grams per second![/quote]That's true, but not relevant here since you're still drawing in outside air of about the same temperature in either case. If you remove that final piece, you're drawing air in from right behind the bumper, which is right above the opening for the radiator and is an excellent source for cool air.

Quote »500 CFM is smoking something as that would be 413 HP!!!!!!274/2= 137 x 4,000 rpm=548000/1728= 317 CFM x VE [93%]= ~~295 CFM

at 6700 rpm= 531 x VE [72%]=382 CFM maybe on a perfect day.At 7300 rpm the engine might just exceed 400 CFM[/quote]Like I said, I didn't have the formula at hand, but even 400 cfm sounds like a lot of air to pull through that opening. I've seen 200 hp cars with bigger intake openings than what my Q45 has, and they didn't have the many bends and twists along the way. I wonder why they didn't just run the intake straight down into the fenderwell rather than the convoluted setup they ended up with? I'd guess it might have been a noise issue, although a little more intake noise would be a good thing as far as I'm concerned. The Aurora that I had the misfortune of owning had the airbox in the same location and had a nice big opening (probably ~ 4 x 6") on the bottom of the box that lead to the fenderwell. It had a nice intake growl to boot.