showing my friend how to read compressor maps the other night, he brought up a good question. how does vtec affect lbs/min that your motor flows. the equation i was using had rpm and engine displacement in cubic inches as the main factors for how much flow you have...but vtec helps flow more air- moreso the dohc than single cam, but they both flow more air- how much does this affect the lbs/min? its it substantial. sorry if this doenst make sense, but im kind of curious on this

 

um yes?

higher lift = more flow = more LBS/min

am i right?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Turbo E 604 &raquo;</TD></TR><TR><TD CLASS="quote">

higher lift = more flow = more LBS/min </TD></TR></TABLE>


Seems right to me...

anyone else that knows a lil more on the subject...

 

good question..bump for a good answer

 

vtec effects the volumetric efficiency of ur engine, the displacement stays the same.. when you plot a compressor map use 100% volumetric efficiency for the rpm's after vtec kicks in.

 

VTEC itself does not effect airflow. What does effect airflow, is cam profiles, ad someone mentioned above. All the VTEC does is allow you to have multiple cam profiles for multiple situations, so that you don't have to have a cam that is optimized for 8000 rpm, which would suck at 2000 in traffic.

The point is that a motor with VTEC will not flow any more air than a motor without VTEC but with the same cam profile as VTEC's high rpm cam.

When you calculate the airflow of the motor, just do it from 4000 rpm (or whatever VTEC switchover point you have). The only difference you will see with a VTEC motor, is the VE curve is going to be broader and might have a little bit of a weird shape to it.

DIRep covered it pretty well too.

 

wow 100% VE is nice. i think i was using 80 or 85 %, calculating at 3000,5000,7000 rpm's

 

You will find it is in the 95% range, not quite 100. Damned close though.

With mods, you can go over 100.

 

i have a 12lb flywheel and a larger throttle body- will that help? dont forget the honda tech sticker hhahahahahhaha just kidding.

back on track now, i just recalculated some **** using 95% VE, and that brings my little z6 between 9.8 and 13.7 lbs/min from 5000-7000rpm's. putting these values into the compressor map for t3 50 trim that i just orderred, ill be between 70 and 75% efficient for the boost levels im intending on running

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackeg &raquo;</TD></TR><TR><TD CLASS="quote">i have a 12lb flywheel and a larger throttle body- will that help? dont forget the honda tech sticker hhahahahahhaha just kidding.

back on track now, i just recalculated some **** using 95% VE, and that brings my little z6 between 9.8 and 13.7 lbs/min from 5000-7000rpm's. putting these values into the compressor map for t3 50 trim that i just orderred, ill be between 70 and 75% efficient for the boost levels im intending on running </TD></TR></TABLE>

That's airflow without boost man, you need to calculate airflow with boost.

 

i thought the question was "when vtec activates, does the airflow through the head increase"???

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Turbo E 604 &raquo;</TD></TR><TR><TD CLASS="quote">i thought the question was "when vtec activates, does the airflow through the head increase"??? </TD></TR></TABLE>
the question i had originally was how much does vtec increase the flow in lbs/min. now my question is what do i have to do to calculate under boost???

i was doing displacement * rpm *.5 * VE(started using 80, then went to 95) / 1728.


that gives me cfm i think, then i multiply by .07xxxx depending on air temp to get lbs/min.... that goes on the x axis and pressure ratio is on the y axis...please lemme know what im doing wrong...thanks guys

 

vtec-e and 3 stage vtec-e would be interesting in this discussion as they use swirling to promote its efficiency, they do this by deactivating one intake valve (making it a "lean-burn" 12 valve). however in vtec it uses the inactive valves to increase airflow (making it operate with the full 16 valves)... and in the case of 3 stage vtec-e it also has a 3rd stagefor the more wild cam profile that activates seperately from the now active 2nd intake valve assemblys.

that has to affect airflow.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kpt4321 &raquo;</TD></TR><TR><TD CLASS="quote">You will find it is in the 95% range, not quite 100. Damned close though.

With mods, you can go over 100.</TD></TR></TABLE>

How is it possible to go over 100% volumetric efficiency?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by NB &raquo;</TD></TR><TR><TD CLASS="quote">How is it possible to go over 100% volumetric efficiency?</TD></TR></TABLE>

The air will actually compress as it enters the cylinder, due to several factors (like inertia).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by twkdCD595 &raquo;</TD></TR><TR><TD CLASS="quote">vtec-e and 3 stage vtec-e would be interesting in this discussion as they use swirling to promote its efficiency, they do this by deactivating one intake valve (making it a "lean-burn" 12 valve). however in vtec it uses the inactive valves to increase airflow (making it operate with the full 16 valves)... and in the case of 3 stage vtec-e it also has a 3rd stagefor the more wild cam profile that activates seperately from the now active 2nd intake valve assemblys.

that has to affect airflow.</TD></TR></TABLE>

VTEC E actually still opens both intake valves before VTEC kicks in. One valve only opens a very little bit.

 

have a reference for that info... curious cause I was under the impression that it was different. thanks?

 

Yea, I ripped my old hx engine apart, and rotated the cam with a wratchet....each intake valve opened...one only opened a very small amount.

 

thats not reference material... I was more looking for a reputable source.

btw I have broke down my fair share of engines... including the d15 and d16's... and so I personally have not seen what you describe.

sorry my 2 cents.

 

um, ok...guess I'm a liar.

Have you ripped apart a D15Y5?? It is different then the d16y7, y8, z6, d15s, etc.

 

just remember you said it, not me.

dont take it personally btw... I jst cannot agree with your conclusions without more info.

on a side note I drank way to much amber bock to care really at the current second. another side note... 6.00 pitchers are cool.

 

ah whatever, neither can prove what is right or wrong right now.