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VTEC.. is this for real?

trucke

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Yes, the Type R has VTEC on the exhaust side. You have a turbo pumping in air/fuel on the intake side so the VTEC is there to help those exhaust gases get removed at a similar rate. Sounds like the same concept is being employed on the Si.
 

Boostez

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Yes, but the mere presence of profile switching doesn't mean much by itself.

The "intake VTEC is useless since it's turbo" bit of info people like to regurgitate is bullshit, too.
Explain why it's bullshit on a technical level. VTEC is used to make the flow of the engine at a given point in time be at it's maximum efficiency. Since we are already well above 100% efficiency with a turbo car, valve overlap doesn't make much of a difference since the valves will get plenty of air into the combustion chamber at peak torque from the forced compressed air. I'd wager that the more you turn up the boost, the less intake VTEC plays a role in the engine's efficiency level to the point where it's completely negligible.
 

D-RobIMW

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Explain why it's bullshit on a technical level. VTEC is used to make the flow of the engine at a given point in time be at it's maximum efficiency. Since we are already well above 100% efficiency with a turbo car, valve overlap doesn't make much of a difference since the valves will get plenty of air into the combustion chamber at peak torque from the forced compressed air. I'd wager that the more you turn up the boost, the less intake VTEC plays a role in the engine's efficiency level to the point where it's completely negligible.
Sure. :)

"VTEC" has been used for a bunch of reasons over the years by Honda for numerous reasons; not all of them for power. The moniker is nothing more than buzzword to describe a system that allows for multiple lift/duration profiles (whether or not those profiles are to change the shape of a torque curve or to simply create a swirl in the combustion chamber for fuel economy purposes is completely dependent on which engine we're talking about).

As far as your comment goes, we need not look any further than the previous generation of engines Honda used on a large number of vehicles - the K24Z. The K24Z lacks VTEC on the exhaust side entirely, yet has it on the intake. The exhaust outlet is a very similar configuration to the K20C/L15 engines, with an integrated "manifold", also. This engine is very popular to turbocharge in the aftermarket (I've tuned countless, personally), and I can tell you with 10000% certainty that without switching on the "high cam" lobes on the intake, it's completely useless as engine speed and boost pressure climb.

Here's a quick example of a turbocharged K24Z. The orange line is a run without high cam engagement on the intake, and the gray line is with VTEC engaged on the intake cam. The test stops earlier on the orange line because torque is already falling hard by 5,000rpm, but you can see that it carries much better with the high cam engaged. There's a 40wtq delta @ 5,550rpm from the difference in cam profile in this instance. The spread gets larger and larger as boost pressure goes up, also, as the camshaft's profile is literally a restriction to total flow through the engine.

IntakeVTEC.png


There is no downside to having "VTEC" functionality if a broad torque curve is what you're after.

I hope this helps shed some light on why making broad generalizations like "VTEC on the intake cam with a turbo is unnecessary" is bullshit.
 

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Yes, the Type R has VTEC on the exhaust side. You have a turbo pumping in air/fuel on the intake side so the VTEC is there to help those exhaust gases get removed at a similar rate. Sounds like the same concept is being employed on the Si.
It's not, though. Again, "VTEC" is never used at wide open throttle on the L15's with it. Accord, Civic (non-Si), and Civic Si. None of these engines are using VTEC at high load, ever. The "engage" RPM is literally 32,767rpm in the ECU for these models.

They're likely using it in this case for something similar to "VTEC"s purpose on the R18 and K20A3 engines of the past.
 

Boostez

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Sure. :)

"VTEC" has been used for a bunch of reasons over the years by Honda for numerous reasons; not all of them for power. The moniker is nothing more than buzzword to describe a system that allows for multiple lift/duration profiles (whether or not those profiles are to change the shape of a torque curve or to simply create a swirl in the combustion chamber for fuel economy purposes is completely dependent on which engine we're talking about).

As far as your comment goes, we need not look any further than the previous generation of engines Honda used on a large number of vehicles - the K24Z. The K24Z lacks VTEC on the exhaust side entirely, yet has it on the intake. The exhaust outlet is a very similar configuration to the K20C/L15 engines, with an integrated "manifold", also. This engine is very popular to turbocharge in the aftermarket (I've tuned countless, personally), and I can tell you with 10000% certainty that without switching on the "high cam" lobes on the intake, it's completely useless as engine speed and boost pressure climb.

Here's a quick example of a turbocharged K24Z. The orange line is a run without high cam engagement on the intake, and the gray line is with VTEC engaged on the intake cam. The test stops earlier on the orange line because torque is already falling hard by 5,000rpm, but you can see that it carries much better with the high cam engaged. There's a 40wtq delta @ 5,550rpm from the difference in cam profile in this instance. The spread gets larger and larger as boost pressure goes up, also, as the camshaft's profile is literally a restriction to total flow through the engine.

IntakeVTEC.png


There is no downside to having "VTEC" functionality if a broad torque curve is what you're after.

I hope this helps shed some light on why making broad generalizations like "VTEC on the intake cam with a turbo is unnecessary" is bullshit.
Well, wait a minute. Let's discuss some more about this.

The engine in the K20 isn't the same as the FK8. So they don't have the same design flow. Also, there are many other cars with VVT that don't do any good once high boost and high lb/min turbos get introduced into the mix. Take the Evolution 9 for example. Taking the power levels up beyond what the stock cam profile can do requires removing cams altogether, abandoning the stock cam functionality in the ECU and getting fixed-profile aftermarket cams. I propose that the designers at Honda know more than you do when they designed the engine/cam system of the FK8 and felt that the best benefit for the FK8 was in doing a cam profile for exhaust side only.
 

D-RobIMW

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Well, wait a minute. Let's discuss some more about this.

The engine in the K20 isn't the same as the FK8. So they don't have the same design flow. Also, there are many other cars with VVT that don't do any good once high boost and high lb/min turbos get introduced into the mix. Take the Evolution 9 for example. Taking the power levels up beyond what the stock cam profile can do requires removing cams altogether, abandoning the stock cam functionality in the ECU and getting fixed-profile aftermarket cams. I propose that the designers at Honda know more than you do when they designed the engine/cam system of the FK8 and felt that the best benefit for the FK8 was in doing a cam profile for exhaust side only.
OK. :)

Have a good one.
 

charleswrivers

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I did like K20A3 base-RSX with its wild VTEC. And by “wild VTEC”, I mean completely-unnoticeable. The A2’s VTEC however… ?
 

HondaFan777

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Well, wait a minute. Let's discuss some more about this.

The engine in the K20 isn't the same as the FK8. So they don't have the same design flow. Also, there are many other cars with VVT that don't do any good once high boost and high lb/min turbos get introduced into the mix. Take the Evolution 9 for example. Taking the power levels up beyond what the stock cam profile can do requires removing cams altogether, abandoning the stock cam functionality in the ECU and getting fixed-profile aftermarket cams. I propose that the designers at Honda know more than you do when they designed the engine/cam system of the FK8 and felt that the best benefit for the FK8 was in doing a cam profile for exhaust side only.
I’m getting popcorn. Have you owned a 2.0T Accord or Type R?

I have and the motor is more similar than you know. DRob knows these platforms and has tuned the some of the fastest ones on the street and strip.
 

D-RobIMW

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Regarding the 22 Si, my understanding is the VTEC crossover happens at 4200 RPM. You can hear it crossover in some of the driving videos on You Tube. The crossover is not as loud and dramatic as my 08, but it's present and noticeable.
This is not correct.

VTEC is never used at wide open throttle on the 2022 Civic Si. As I stated previously, the engagement RPM for high load is literally 32,767rpm.
 
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