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[theory]A stock Honda ecu can send enough additional fuel to produce 10-15% more power than is originally programmed into it. This is why bolt-ons like intake header exhaust can make an otherwise stock d16a6 spin the rollers to the tune of 120 flywheel hp. In completely stock configuration, 108 hp is recognized through pushing the limits of that configuration. When IHE is added, various sensors tell the ecu that more air is entering and exiting the combustion chambers. The ecu in turn sends a proportionate amount of fuel to meet this air. Added horsepower is the end result.

Additional HP was created because the intake and exhaust plumbing was opened up allowing for better flow. Applying this idea to the intake manifold, increasing its size and interior smoothness or contour will yet further open up more room for better flow. There is however a limit to how open is too open before it starts having adverse affects on Hp and torque production at certain RPMs. This limit can only be determined by engineers with fancy degrees. For our purposes, imagine the IM in this manner: inhaling air through a straw versus inhaling mouth wide open. Yes, you can fill your lungs much faster with your mouth wide open but the air entering doesn't have nearly the same velocity compared to the straw. This velocity is what can affect HP and TQ production inside an engine. In essense, if the intake plumbing is too open, you will likely lose low rpm TQ in exchange for high rpm HP.

Remember that many smart men sat down and designed our cars from the ground up. They chose a certain size intake and exhaust to achieve the best compromise of power/driveability and efficiency. When we go in and start rearranging various parts of this design we change that compromise. In closing, I think you'll make more high end power at the expense of low end torque and thus driveability. At the same time, I don't think it'd be so drastic to the point as say a skunk 2 camshaft which would only be useful for high rpm drag purposes. I personally would clean up the inside contour and port match a bigger TB to possibly push the limits of the stock ecu a bit more yet.[/theory]
 

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The EACV also controls hot or cold idle. it can be bypassed, but if the car is cold, it will only idle at 750, not the 1200 rpm cold idle.
 

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Discussion Starter · #23 ·
I gave it to him last night, should get it back just after dinner tonight. I asked him to clean up the castings at the ends of the runners and TB, where there are big sloppy lines in teh aluminium. He's also going to blast the outside clean so I can coat it or paint it. I'll check the distances on the lines tonight, but I won't be able to install anything until I get the new gaskets to go with it. I'm going to replace my vacuum lines at the same time. I'll do a write up on the whole thing too, though it doesn't seem like a terribly difficult job (of course I saw 3 thread on HT about how to do this in the last 2 days).
Heu, I understand what you're saying about the balance of efficiency/power and getting more from the stock ECU. So, I should expect the fuel economy to go down?
 

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I wouldn't really think so, since the car would be putting out a bit more power, it doesn't need to work as hard to cruise. I have no clue if thats really a valid thought, I just hope so, lol. Of course, once we do this stuff to our engines, we just can't resist the, ummm, "occasional" throttle mashing.

Seriously, if the engine is making more power throughout the RPM band, the engine shouldn't need to run as hard to maintain a speed. Thats my theory.
 

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Tom, I think you wont lose too much if anything in the way of fuel mileage. That is of course if the car is driven normally (2.5 - 3.5k shifts) In this rev range, you foot isn't asking too much out of the engine so there shouldn't be a huge change in fuel consumption there. If however, you're sprinting all over town, you can be sure that that newly reconfigured induction system will suck alot more fuel over stock sprinting. Again, this is all theory but I'm pretty sure the likes of say Mr. Composimo will at least somewhat agree with me.
 

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Discussion Starter · #27 ·
Checked the fitting out last night. Seems like I am going to have to extend that plug, but the brake booster line will be ok. I forgot how bad the stock A6 manifold looked! I'll get some pictures before and after. I love the Z6 fuel rail, it looks like an I-beam! My friend also didn't bring back the manifold, should get it tonight or tomorrow.
 

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Discussion Starter · #28 ·
Well I was waiting on some parts, but the local Honda dealer called me today with my throttle body gasket. I also happened upon a new Z6 intake manifold gasket from a friend at the shop. It took a while, there were a couple problems I ran into during the install, but it's on now, and I can't say for sure that it's a lot better, but it does feel a little better in the low end, I actually managed to spin the wheels by accident.
The new mani didn't have a MAP sensor on it. I didn't even notice it wasn't there. It also didn't have the EACV, like I mentioned, and the A6 one didn't bolt up at all. I got both of those from my friend who sold me the manifold. The black plastic thing that holds the wires above each injector won't fit, it bumps into the FPR, but that's ok because... I had to pull the air temp sensor a little out of the harness, but it fits. The booster line fit fine. I'll get some pictures tomorrow, I have to clean it up a little still, the MAP plug needs to be freed up a little bit.
FWIW, the Z6 mani has a bigger diameter. I wasn't sure at first, but comparing the Z6 gasket to the A6 manifold it's pretty obvious. Also, does anyone know if any Z6 powered cars came with cruise control, there's an extra plate with a wire spot on the throttle body, I had another Z6 manifold I was using for vacuum/coolant line reference, and it didn't have it, neither did my A6.
My A6 manifold was filthy dirty, but the ports on the head were just as clean as they were when I put it on after the rebuild in August, I was pretty happy about that. The rear of the bay is really dirty too, but a friend of mine who details cars in the summer helped me clean it up a little, and he wants to fully clean my engine bay. While I was assembling the manifold, he cleaned up my resistor box, some of the fasteners, the new throttle body, and a few other misc things. When it gets nicer I'll have a spotless bay to work in... can't wait.
 

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Discussion Starter · #30 ·
No problems at all. I'm still using this manifold with the Z6 TB, the only difference is the TB mounted MAP sensor. I am now converted to OBD1, but I was running it for a while on OBD0, I don't see how it would make a difference. B series TB's will work, I have a DA OBD0 one I'm trying to sell, I just don't want to use it because it requires a firewall-mounted MAP sensor.
 
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