VTC Dyno graph

[Stinky]

There has been some discussion about setting the VTC rpm and I figured I'd share this. I did some runs with the 450sx with the VTC set to stock, set ON, and set OFF. You will notice that with the VTC OFF you lose power under 4800rpm. With the VTC left ON you lose some power after 4800rpm. So basically the 4800rpm set point is right where needs to be.

[irax]

can you make it so at 4800 rpm the vtc will turn off?

[hannibal]

^ Isnt that what its doing there?

You can see the the red 'stock VTC' line follows the 'VTC on' line, then starts following the 'VTC off' line after ~4800rpm. Seems to me that its doing its job quite well. It may not make more peak power than leaving it on or off, but it makes more across the range...

[sijoko]

That's very good info to have. So there's no reason to mess with the Valve Timing Control shut off point.

I was reading in the SAE paper on the VH45DE that Nissan spent 3 years on this engine. I guess they spent quite a few hours on setting up the VTC.

[autoworkz]

from what i read, it was more like 5 years, project was launched in 1984 and delivered in 89.

[sijoko]

from what i read, it was more like 5 years, project was launched in 1984 and delivered in 89.

The Q45 project was launched in 1984 with the engine development taking 3 years as per the SAE paper #900651 submitted by Nissan on the VH45DE.

Some other tidbits:

- Included angle of the valves: 46 degrees.- Ratio of valve diameter to bore: 0.41.- Engine torque @ 800 rpm: ~ 240 ft. lbs.- Coil-on-plug capability: 37 kv @ 9000 rpms.- Engine block construction: Hypoeutectic silicon alum. w/ 7-10% silicon.- Crankshaft construction: Two-plane forged steel.- Crankshaft features: Fillet rolled journals, Radio frequency hardened.- Crankshaft journals width: Rod = 44.2 mm, Main = 26.5mm.- Low pressure cast-in iron cylinder liners: 3mm thickness.- Piston weight and height: 402 grams & 62.5mm.- Connecting rod construction: High-strength, micro-alloyed free-cut. - Intake runner diameter: Tapers from 46mm to 42mm.- Intake runner length: 420mm.

I understand everything except the description of the connecting rod construction. What do they mean by high-strength, micro-alloyed free-cut? From what I have read so far, the rods are supposed to be forged.

[Ezekial]

i wonder what the effect of forced induction will be on VCT power / rpm

[sijoko]

i wonder what the effect of forced induction will be on VCT power / rpm

I have been thinking about this alot lately.

My take on VTC and its effects on turbocharging: The valve overlap will send more raw fuel out into the manifolds where it would combust and increase the energy available to spool up the turbo.

The key is to size the turbo with a large enough a/r that it does not become restrictive before the VTC cut-off point. This way you minimize the potential for hot exhaust gases being pushed back into the cylinders due to the valve overlap.

On the other hand if a too small turbine side is used, the VTC can actually be a liability because the excessive backpressure would cause exhaust gases to work their way back into the combustion chambers. Of course, the fix would be turn off the VTC feature in that case.

[Clifton]

My take on VTC and its effects on turbocharging: The valve overlap will send more raw fuel out into the manifolds where it would combust and increase the energy available to spool up the turbo.

The key is to size the turbo with a large enough a/r that it does not become restrictive before the VTC cut-off point. This way you minimize the potential for hot exhaust gases being pushed back into the cylinders due to the valve overlap.

On the other hand if a too small turbine side is used, the VTC can actually be a liability because the excessive backpressure would cause exhaust gases to work their way back into the combustion chambers. Of course, the fix would be turn off the VTC feature in that case.

I think the a/r would have to be so large that vtc wouldn't even matter. Boost would come on so late. I measured turbine pressure on a T66 with .70 hotside with P and O trims. With the larger P trim I was still 10 psi higher than inlet pressure on a 3l at high boost. Most large overlap n/a cams don't work well with turbo because of the high turbine pressure, and lower manifold pressure.

What's the power dip around 5200 rpms? AFR?

[Stinky]

The power dip is from the stock ignition timing. Maybe they dropped the timing to allow for smoother shifts or something? Anyway, you can see here zerothread/194518 that they can be tuned out.