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

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Civic VX, VTEC-E, D15Z1, etc

I thought I'd post up some diagrams to help clarify things and also to make them available for anyone else that wants to copy them into other threads etc. I hope that this thread will make things clearer to people and to help dispel some false assumptions and misconceptions that people make when they have only a partial understanding of VTEC-E.

This thread is wide open for any VX fanatics to contribute to in any way whether it's posting up info or simply posting a link. I'm not claiming ownership, I'm just kicking this off. MY ONLY REQUEST IS TO KEEP EVERYTHING IN LAYMAN'S TERMS.

VTEC-E is very simply explained as a method of switching from 12 valves to 16 valves on a 4 cylinder engine. One intake valve per cylinder is closed under certain conditions in order to improve low end torque and decrease fuel consumption. Then when load and RPM have increased, both intake valves open up to allow more air so that the engine doesn't choke up; giving you better mid range power. The cam lobes are optimized for BOTH low and mid range.

Normally no power is sent to the VTEC solenoid resulting in 12 valve mode. When RPM conditions are met, the VTEC solenoid is energized resulting in 16 valve mode. In other words, when the solenoid is ON, VTEC-E is OFF.

https://suspendedhatch.thecarthing.co...z1_diagram.gif
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.

https://suspendedhatch.thecarthing.co...-E_diagram.gif
This is a good demonstration of how closing one intake valve per cylinder swirls the incoming air into the combustion chamber in order to spread the fuel evenly for a complete and uniform burn. This is how it is possible to run a very lean mixture which would cause a lean misfire in conventional engines, even the very closely related D series engines from the same time period.

https://suspendedhatch.thecarthing.co...xplanation.gif
https://suspendedhatch.thecarthing.co...planation2.gif
Notice that "lean burn" occurs in the very low load (high vacuum / low pressure) portion of the fuel map. There is a wide range of driving where you're in 12 Valve mode but not lean burn.

https://suspendedhatch.thecarthing.co...xplanation.gif
Here is the SOHC VTEC description (D16Z6) for comparison purposes. Though the switching mechanism for VTEC is exactly the same as that for VTEC-E, using the same parts and wiring, the purpose behind these two technologies is different. Honda just happened to have this particular switching apparatus available and in production at the time. But don't make the mistake that you can simply put an Si/EX ECU into a VX and it's converted to VTEC. The cam and valve train are fundamentally different.

https://suspendedhatch.thecarthing.co...xplanation.gif
VTEC by comparison optimizes both mid and high range RPM power combining racing cam lobes and daily driving cam lobes so that you not only have impressive high RPM power, but a smooth steady idle, low emissions output, and low fuel consumption.

Some interesting features of the D15Z1 motor.

It has roller rockers for less valve train friction. exclusive to VX and HX.

It uses special piston rings for less friction like those found in the Type R.

Federal models use a wideband O2 sensor.

The engine uses 190CC vs the 240CC injectors found in the VTEC motors.

It uses the same distributor as the D16Z6 and other OBD1 SOHC D series engines.

It uses the same VTEC solenoid as the D16Z6 and other OBD1 SOHC D series engines.

The valve cover is interchangeable with other OBD1 VTEC SOHC D series engines and all 96-00 D series engines.

The 94 and 95 had "VTEC-E" on the valve cover similar to the D16Z6's "VTEC".

It uses a lightweight crank pulley with no harmonic balancing (as a result of this engine not revving high).

Transmission has a lightweight flywheel. exclusive to VX.

Transmission has low gearing resulting in less acceleration (but theoretically a higher top speed). These features allow for low 1000 RPM cruising.

Some interesting features of the VX chassis.

It has a lightweight aluminum lower alternator mount. VX exclusive

It has a lightweight aluminum front driver's side lower engine mount mount. VX exclusive

https://suspendedhatch.thecarthing.co.../vx_mounts.jpg

It has a rear diffuser. VX exclusive

It has lightweight alloy rims.

It has a front lip spoiler. exclusive to the Si and VX. The EX models also have a front lip spoiler but it is not interchangeable with the hatchbacks.

It has less sound deadening. exclusive to VX and CX.

It lacks a rear wiper / squirter system.

It doesn't have shopping cart bumpers on the doors. exclusive to VX and CX.

It comes with a tachometer.

https://suspendedhatch.thecarthing.co...cono_light.jpg
Some models came with a upshift light.

Evolution of VTEC-E

The Civic HX / D16Y5
Power 115 hp @ 5600 RPM
Torque 100 ft/lbs @ 4500 RPM

The HX is a sixth generation Civic coupe featuring 14 inch alloy 8 spoke rims and the D16Y5 engine. This engine also has VTEC-E, EGR, roller rockers, a catalytic converter mounted near the exhaust ports, a wideband O2?, and long gearing. Another big difference besides switching from a hatchback chassis to a coupe with larger diameter wheels was that the 4 speed automatic option was replaced with a CVT.

How this engine differed from the D15Z1 is that it uses the same 1.6 liter displacement, head casting, throttle body, and intake manifold as the D16Y8 (a SOHC VTEC engine offered in the EX and early Si's.) Clearly Honda was prioritizing power in this implementation a bit more than they had on the previous generation which used a tiny throttle body, small intake manifold, and small intake and exhaust ports.

An obvious difference between the D16Y5 and the D15Z1 is the switch from OBD1 to OBD2 in 1996.

Seventh Generation HX D17A6
...

The 3 Stage VTEC (D15Z7)
Power 130 hp @ 7000 RPM
Torque 102 ft/lbs @ 5300 RPM

In Japan VTEC-E was pushed even further in it's ultimate implementation. VTEC-E and VTEC were combined to offer the best in mpg and performance in a single low displacement, SOHC engine. In Japan this engine is stamped "D15B" and can be found in the 1996-1999 Honda Civic VTi and Ferio Vi. In other European and Asian countries the same engine is stamped "D15Z7". This engine is identical in appearance to the D16Y5 except that it has a dual VTEC solenoid slightly to the side of where the VTEC solenoid is normally found (and a one-wire O2 sensor). This engine was also offered with a CVT (or 5 speed manual trans), but unlike the previous VTEC-E implementations it lacks roller rockers.

More Power / MPG Comparisons

D15B8 (92-95 CX)
1.5 liter 8 valve non-VTEC
Power 102 hp @ 6200 RPM
Torque 98 ft/lbs @ 3800 RPM
~? mpg combined

D15Z1 (92-95 VX)
1.5 liter 12/16 valve VTEC-E
Power 92 hp @ 5600 RPM
Torque 97 ft/lbs @ 4800 RPM
~43 mpg combined

D15B7 (92-95 DX/LX)
1.5 liter 16 valve non-VTEC
Power 102 hp @ 6200 RPM
Torque 98 ft/lbs @ 3800 RPM
~? mpg combined

D16Z6 (92-95 EX/Si)
1.6 liter 16 valve VTEC
Power 125 hp @ 6600 RPM
Torque 106 ft/lbs @ 5200 RPM
~30 mpg combined

B16A2 (96-97 Del Sol VTEC)
1.6 liter 16 valve VTEC DOHC
Power 160 hp @ 7600 RPM
Torque 111 ft/lbs @ 7000 RPM
~? mpg combined

D16Y7 (96-00 DX/LX)
1.6 liter 16 valve non-VTEC
Power 106 hp @ 6400 RPM
Torque 103 ft/lbs @ 4600 RPM
~? mpg combined

D16Y8 (96-00 EX)
1.6 liter 16 valve VTEC
Power 127 hp @ 6600 RPM
Torque 108 @ 5500 RPM
~? mpg combined

Good job suspended hatch Iv'e always thought of these engines as the pretacessor to the cvcc engines.

The GX also has vtec-e.

Also I had both a y5 and a z1 cam ran on the cam pro and it turns out they are the same cam. The z1 just has smaller ports and valves.

Quote:

(a SOHC VTEC engine offered in the EX and early Si's.)

z6 chambers had more tumble than swirl as apposed to the y8/y5/b5 swirl chamber. You probably knew that though.

There's much I don't know. That's why I'm here!

Post up what you know about the CNG.

Quote:

Originally Posted by topher (Post 98608)

Also I had both a y5 and a z1 cam ran on the cam pro and it turns out they are the same cam. The z1 just has smaller ports and valves.

That is very compelling.

I thought I've heard/read that the d15z1 actually partially opens the fourth valve during "12-valve mode" in order to create the swirl affect. Not 100% sure of this though. I'll have to post-up when I find the source of this info.

Quote:

Originally Posted by Danronian (Post 98867)

All vtec-e's do this. It's not to help the swirl but, so the gas does not pool up on top of the vavle.:thumbup:

Quote:

Originally Posted by Danronian (Post 98867)

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.