: Revisiting Airflow = Torque



codewize
12-02-06, 07:43 PM
Ok so after installing my Volant CAI and lots of discussion about torque I wanted to revisit the topic. I have some questions.

We have proven that by installing the Volant CAI the power band of the Northstar is moved higher in the RPM range. This is supposedly caused by additional air flow.

Can someone explain why that happens.

Secondly if this is in fact the case then I should be able to adjust where in the RPM range the power occurs by altering the airflow in the box. No?

Anyone have any insight on this?

danbuc
12-02-06, 08:33 PM
Alot of it has to do with the velocity of the air as it enter the cylinders. reducing the restriction allows for more overall volume, but results in a loss of overall velocity. Here's an example. Take a regular garden hose. Hold the open out and turn the water on all the way. It's going to just pour out in a big stream. Lot's of volume, little velocity. Now place your thumb over the end of the hose. The water will shoot out quickly and cover much more distance. Litle volume, lot's of velocity. At low rpm's, for the maximum amount of torque, you want lot's of velocity, and not a hole lot of volume. Installing an air intake that flows more freely can (and sometimes will) adversely affect your low end torque. The air is no longer flowing into the cylinders as fast, resulting in less low rpm power. The flip side of this is that at high rpm operation, volume is key in making power, so the less restrictive intake is going to build more power at higher rpm's. This is what you see as a "shift" in the usable powerband of the engine. You sacrifice low end torque, for more high rpm power. It's the reason dual plane intake manifolds, and variable valve timing were invented. They help balance the high velocity. low volume airflow needed for low rpm power, with the high volume, low velocity airflow needed for high rpm power. In affect, it creates a broader power band, and a much flatter torque curve.

If the question your really asking is this, "By installing the volant did I sacrifice low rpm torque, for high rpm hp?"...the answer quite simply is yes.

It's the reason why the K&N filter I tried once stayed on my car for about 10 minutes. Low end torque was more important to me than high rpm hp, since I spend most of my time at WOT at lower speed where more torque is needed.


edit: to more directly answer the the question you posted above....no. The only real way to gain back the power you had is to either re-install the old intake, or find away to adapt the VVT head to your engine (which is basically impossible). I'm sure you could shove something in the airbox to restrict the flow, but that would be somewhat counterproductive.


edit#2: As for all those who thing that a different intake is not enough change to adversely affect the torque curve of the Northstar, even th smallest changes can have a huge impact on the way an engine breathes.

eldorado1
12-02-06, 10:21 PM
We have proven that by installing the Volant CAI the power band of the Northstar is moved higher in the RPM range. This is supposedly caused by additional air flow.


We have? Did you post back to back dyno results in some other thread? I'm not going to trust a butt dyno. The calibration on those things is terrible ;)



Can someone explain why that happens.

I can explain what you saw... The MAF measures airflow in grams/sec with a fairly high resolution. If you disrupt that flow (i.e. installing a turbonator, or cone air filter, etc), it basically throws the MAF calibration tables out the window. Especially if the MAF doesn't have a screen to create laminar flow across the heating element. (I don't know if the 2000 does or not) Another potential problem is oil spray from the air filter contaminating the MAF. I think there was a TSB issused for that.

On a properly installed intake, on a tuned vehicle, a cold air intake will NOT AFFECT LOW END TORQUE. You can put a 10" semi air filter on it, it doesn't care.

On a stock intake, there is a little bit of restriction at WOT. I think I measured it to be a few kPa. Not a lot, but it's there. Airflow increases with HP. Higher rpm's mean more HP and more air the engine is trying to pull in. If you remove this few kPa restriction, you get more air into the engine, which the MAF registers, and you get more fuel, and more power...

However - at low RPM, the air filter/intake isn't going to be a restriction, so it will not affect low RPM torque positively or negatively. It's like that other thread we had a while back - changing an air filter won't affect the fuel economy. The airflow is always less than the capacity of the air filter.


Secondly if this is in fact the case then I should be able to adjust where in the RPM range the power occurs by altering the airflow in the box. No?


No. (aside from doing something stupid like completely blocking off airflow, then yes) However, you can tune where the intake (manifold) affects the powerband. Generally speaking shorter runners are tuned for higher RPM, longer runners are for low RPM torque. However, outside of the intake manifold, there isn't anything you can do to move the power band around. You can add to the high end by using a free flowing air filter, or subtract from the high end by using a restrictive air filter.... but that's about it.

dp102288
12-02-06, 10:42 PM
^^ Both excellent posts! :thumbsup:

danbuc
12-02-06, 11:34 PM
On a properly installed intake, on a tuned vehicle, a cold air intake will NOT AFFECT LOW END TORQUE. You can put a 10" semi air filter on it, it doesn't care.


Excellent point which is overlooked by the vast majority of people too many times. For optimal performance, the engine must be calibrated to the amount of airflow coming in. Like you said, on a Properly tuned engine, a less restrictive intake should have only beneficial affect on performance. The problem is we can't really tune these engines for that extra airflow, which is why people see (or rather feel) the drop in low end performance after putting one of these high flow air filters on.

As for butt dyno, seeing as how the number of people reporting this affect keep growing each time someone tries it, I think it's pretty much common knowledge at this point that a less restrictive air filter on a stock N* = no low end performance gain.

codewize
12-03-06, 12:50 AM
Wow most of that I knew and understood already but you definitely clarified WHY? Which was the big question. No as far as the proving thing.

It's not the butt dyno that we're talking about here it's pretty obvious and dramatic to say the least. Bot myself and Hitmoney have the same experience and I haven't touched anything BUT the CAI.

Stock DTS hits the power at 3k. After installing the Volant CAI the power doesn't even come close to turning on until 4k. At least. Yes it's that dramatic. I believe that Hitmoney claims even higher with the Corsa added to the mix.


Ok so what's being said here? The N* isn't properly tuned? My 01 does have a MAF screen BTW. So you're saying that the MAF doesn't know how to deal with the extra air so no extra fuel is added? Do after market MAF's overcome this?

On a properly installed intake, on a tuned vehicle, a cold air intake will NOT AFFECT LOW END TORQUE. You can put a 10" semi air filter on it, it doesn't care.


The question is what IS more important? Do you want the low end torque to mess with the idiots at the lights or do you want the all out HP at the top end for the hi-way. It's a big decision and a big sacrifice.

eldorado1
12-03-06, 04:46 PM
Stock DTS hits the power at 3k. After installing the Volant CAI the power doesn't even come close to turning on until 4k. At least. Yes it's that dramatic. I believe that Hitmoney claims even higher with the Corsa added to the mix.


Ok so what's being said here? The N* isn't properly tuned? My 01 does have a MAF screen BTW. So you're saying that the MAF doesn't know how to deal with the extra air so no extra fuel is added? Do after market MAF's overcome this?


Post some pictures of the stock and aftermarket intake, and I might be able to help you. I think we discovered the IAT is in the MAF, right? Can you get a scan tool to read the intake air temperature at idle when hot? If you wanted definitive back to back tests, you can find a scan tool that can take datalogs, and make a scan of a WOT run with the volant and with the stock intakes. I'd be interested in seeing several sensors' data... PM me if you want in depth info.



The question is what IS more important? Do you want the low end torque to mess with the idiots at the lights or do you want the all out HP at the top end for the hi-way. It's a big decision and a big sacrifice.

Can I have both? :)

Actually, I've said this before, but the only time you're below 3000 rpm is when you're going slower than 20mph in 1st gear.

I would rather have more HP than torque. Actually I'd rather have a v8 that winds to 9000 rpm, but one step at a time... You can shift the power curve around a lot through the choice of cams, intake runner length, header length, etc... Usually what happens is this: You swap in new high lift, long duration cams. Low end torque takes a hit, high end torque gets a boost. They're not necessarily equal.

So lets say every point from 1000-3000 rpm loses 40lb ft. That's a LOT of torque you just lost. But, every point from 5000-7000 rpm gains 20lb-ft.

That might be a typical scenario. When you drive the two cars, the one with more torque is going to feel faster. Probably a lot faster. The butt dyno can't register that high rpm 20lb-ft you just gained... but take a look at what you've actually gained (using N* numbers):

RPM Stock(HP) Mod(HP)
2000 100 85 (yes, 40lb-ft at 2000 rpm is 15hp...)
3000 150 127
4000 200 200
5000 250 269
6000 300 322
7000 (~270) 297

So what have you gained? Well lets assume your torque converter has a 2000rpm stall. (Pretty close to stock) You've lost 15hp@2000, 22hp@3000, and gained 19hp@5000, 22hp@6000 and about 27hp @7000, assuming a stock engine could rev that high without valve float.

You lost 20hp over 1000rpm (from 2k-3k) and gained 20hp over 2000 rpm(5000-7000). Since it's area under the curve that counts, this would be a beneficial mod because you can hold the gear longer.

danbuc
12-03-06, 06:09 PM
IAT sensor is on the intake tube between the airbox and maf sensor...at least that's where it is in my '98 Seville. The maf can be used as an IAT sensor, but I don't think the vehicle does, unless the actual IAT sensor is faulty.

codewize
12-03-06, 08:08 PM
Yes we proved that the IAT is built into the MAF on the 01 and probably beyond.

So I guess I now have the all important question. Which will yield better 1/4 mile ET's

danbuc
12-03-06, 08:25 PM
You'll have better 60' times with the stock filter, but your trap speed will probably be higher with the Volant (maybe 1mph or so difference). I would expect most of the change to be seen in your 60' times. Overall 1/4 time probable would change much.

codewize
12-04-06, 12:12 AM
Does anyone have record of before and after 1/4 mile runs?

What the heck do I care about 60' marks for? Just wondering?

eldorado1
12-04-06, 07:47 AM
Yes we proved that the IAT is built into the MAF on the 01 and probably beyond.

So I guess I now have the all important question. Which will yield better 1/4 mile ET's

If the volant is screwing something up like I think it is... probably stock.

Only way to find out is with a scantool or going to the track.

codewize
12-05-06, 12:55 AM
Why do you think it's screwing something up? And I have another question

Will I have the same effect by adding the Corsa exhaust? How about the Corsa with the stock intake? I can't wait until the track reopens.

eldorado1
12-05-06, 09:15 AM
Because you said you have less torque.

That means it's screwing something up, because it shouldnt.

Reasons why are infinite..... only way to find out for sure is start checking variables.

codewize
12-05-06, 12:01 PM
I have some ideas I'm going to play with, I think the real answer is running on the track. When summer comes I'll put the stock air box on and make a pass or two. The I'll put the Volant back in and make a pass or two and look at the results.

It's pretty easy to change especially since the idiots at Volant don't give you any way to fasten the thing to the car, which I have also worked out.

codewize
12-06-06, 11:18 AM
I would also like to say that I think I've learned form this thread that..

Torque is created by pressure

HP is created by volume

:) Hows that for an analogy

eldorado1
12-06-06, 01:37 PM
I would also like to say that I think I've learned form this thread that..

Torque is created by pressure

HP is created by volume

:) Hows that for an analogy

As long as we're not talking air anymore, but something like fire hoses vs garden hoses....... yes.

Torque is like the pressure at the nozzle. You can have a fire hose and a garden hose at the same pressure. But they can't do the same amount of work. One can just blow away leaves, the other can knock people down. That's like horsepower

dp102288
12-06-06, 10:09 PM
^^ I am trying so hard to get this concept...I will keep reading! Too interesting to pass up.

codewize
12-07-06, 08:32 AM
LOL it's the same as discussing bandwidth really. We talk about the size of the pipe all the time.

If you have x amount of pressure and you put it through a 1/2 pipe it's going to feel like a lot of pressure.

If you us the same pressure of x and put it in a 2 inch pipe it's going to feel pretty week. That's the torque relationship

Now if you go back to the 1/2 pipe, say a garden hose, the water coming out of that won't do much damage to anything even at a very high pressure simply because there's not enough of it.

Now with the 2 inch pipe there is so much water, even though the pressure feels like it's less, the shear volume alone will knock people over or push objects along the ground. That's HP

eldorado1
12-07-06, 09:02 AM
exactly. Torque is a force.. Horsepower does work.

dp102288
12-07-06, 09:03 PM
I am getting it! :D

This is an excellent thread.

codewize
12-07-06, 09:14 PM
:blurock: :wes: :grouphug: