Civic VX, VTEC-E, D15Z1, etc - Page 2 - Fuelly Forums

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Old 05-30-2008, 10:29 PM   #11
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Maybe I'll finish it someday.
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Old 06-12-2008, 03:04 AM   #12
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You're talking about the Helms (that's where I pulled all those diagrams). I left it out because people get too caught up in how VTEC-E is actuated rather than the purpose behind it. Fuel pooling up behind the valve is a problem the engineers ran into and opening the valve slightly was the solution. It's really not related to VTEC-E at all.

It's not opening the valve partially that causes the swirl effect, but closing it. Pretty much the same thing though. "Glass is half full..."

Hence the arrow in the piston diagram. If both valves are open, air rushes into the combustion chamber from the intake side and travels straight across to the exhaust side. If you only open one of the intake valves, it rushes in and follows the outside of the combustion chamber until it reaches the closed valve. In other words, it swirls in like a whirlpool.
How come the CX (the 8 valve engines) don't benefit from this then?
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Old 06-12-2008, 08:19 AM   #13
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Because in place of four small valves per cylinder you have two large valves. You don't have intake air coming in from one "corner" of the combustion chamber and swirling around, but all from one side, just like you would on a normal 4 valve-per-cylinder engine.
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Old 06-12-2008, 09:34 AM   #14
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Because in place of four small valves per cylinder you have two large valves. You don't have intake air coming in from one "corner" of the combustion chamber and swirling around, but all from one side, just like you would on a normal 4 valve-per-cylinder engine.
Yeah but what prevented honda from just using a base of 4 valve but only use two of those valves?
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Old 06-24-2008, 07:37 PM   #15
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Here's a diagram of the D15Z1. Not very educational but very interesting to look at. The most obvious difference between this and its contemporary D-series motors is that the catalytic converter is mounted directly to the exhaust ports to light it off faster and decrease emissions.

WAIT SO, Where is the catalytic EXACTLY located on the VX? Reason I ask is because when I bought my VX it came with an aftermarket exhaust, the ones the racers put on. As in Loud muffler, no resonator and no catalytic supposively per the muffler shop I took the VX to get the stock exhaust put on.

They put everything stock EXCEPT the catalytic because they did not have it in stock they said. BUT funny thing is, I took my car to get a New York State Inspection where they do emissions tests and all, and it PASSED

How did the VX pass the emissions test without the cat?

So as per that diagram, do I have a catalytic somewhere by engine?

Last question is, in the VX or any car in general, do you waste more gas if the catalytic is missing?

THANKS!
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Old 06-25-2008, 09:34 AM   #16
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In the diagram the cat converter is in the bottom center with the O2 sensor sticking out the top.

Running no cat converter sounds and smells horrible. It decreases your low RPM torque. It's required by federal law so if your car passed emissions, you have to have it.
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Old 06-25-2008, 09:40 AM   #17
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Yeah but what prevented honda from just using a base of 4 valve but only use two of those valves?
I don't understand this question.

The CX has an 8 valve motor; 2 per cylinder. This poor head design was implemented SOLELY for cost savings.

The VX has a 16 valve motor; 4 per cylinder. This motor has a special VTEC cam that allows one intake valve per cylinder to be remain closed for 12 valve operation or opened for 16 valve operation. This head design was implemented to maximize FE and power in the driving range.

*edit, if you're asking me why the CX engine isn't using small valves like those found in a 16 valve motor the answer is because it wouldn't make any power. The CX only makes 60hp as it is. It would not run or idle well. It would make no sense having that size combustion chamber with those small valves because you'd never be able to fill it. A static 12 valve motor also makes no sense. The purpose of 8 valves is to reduce cost and 12 valves is overly complicated when you're trying to simplify head design.

Honda does not lack for imagination however. I am alluding to the L-series engines found in the Fit. They've considered every possible valve arrangement even mixing in spark plugs and injectors in place of valves.

Then of course there's the possibility of 5 valves per cylinder as was the case of a silver-top Toyota 4AGE engine that I had for a short time in an old Corolla. If your valves and your pistons are circle shaped, 5 valves allows the most possible airflow.
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Old 08-25-2008, 08:33 AM   #18
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I found something interesting in the Honda Repair Manual for the HX. Apparently, the HX/D16Y5 uses the CKF sensor as a means to lean out the mixture until it detects a misfire. Since the VX/D15Z1 doesn't even have a CKF sensor, this means theoretically that the HX runs leaner and is in lean burn more often.

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Old 11-26-2008, 07:15 AM   #19
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Some interesting features of the D15Z1 motor.
Rods with built in piston oilers.



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Old 05-04-2009, 07:53 AM   #20
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D15Z1 indicated (VX) red line is 6,000 rpm... what is the ECU limit?
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