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  #1 (permalink)  
Old 01 Apr 2004, 01:51 pm
Steve
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Default Re: V-TEC/Non-V-TEC?

M C wrote:

>
> I knew about VTEC for a long time but never really read about it. I think it
> is a brilliant design for getting the best of 2 worlds of valve timing.



Its brilliantly simple and well-engineered, but the way its implemented
you have to rev the engine to insane RPM levels to get any real
advantage out of it. I would have thought that it would be better to use
the technology in such a way that the LOW rpm profile is the "special
case" (say, maximum possible duration at a minimum lift to get zero
overlap, thus maximizing compression pressures) and use it to give a big
boost in usable torque below, say 2000 RPM and then switch over to a
normal profile for higher RPM operation. That would make a small engine
feel "bigger" off the line, rather than boosting it on the high end
where small engines already do pretty well as it is. My gripe with VTEC
engines is that they feel utterly gutless on the low end. Just no torque
AT ALL. Admittedly, I'm biased by years of driving big-block V8s, but
non-VTEC Honda 4-cylinders feel reasonbly acceptable on the low end to
me and VTECs feel weaker. They go like a rocket above 6000, but there
are only limited circumstances where that's practical. But every
stoplight is a place where more torque would be nice.

I do
> wonder a about the reliability issue. More parts means more stuff to wear
> out and fail. Also, the high RPM lobe actuates double duty for the other 2
> when it is used.


Its so simple there's really no reliability issue. As for excessive wear
on the radical profile lobe, forget it. A VTEC engine spends probably
less than 2% of its life operating in that mode, so wear on that lobe is
negligible. Yeah, it sees twice the spring pressure, but only for 1/50th
the time. It comes out the winner by a long shot in terms of wear.

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  #2 (permalink)  
Old 01 Apr 2004, 02:06 pm
dold@V-TECXNon-.usenet.us.com
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Default Re: V-TEC/Non-V-TEC?

In rec.autos.makers.honda Steve <no@spam.thanks> wrote:
> advantage out of it. I would have thought that it would be better to use
> the technology in such a way that the LOW rpm profile is the "special
> case" (say, maximum possible duration at a minimum lift to get zero


There are several models of VTEC. There are specifically some that are
"low end" as you note. My Civic Hybrid has a cylinder idling system where
the valves on three cylinders are shut off altogether during deceleration.

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

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  #3 (permalink)  
Old 01 Apr 2004, 02:31 pm
John Ings
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Default Re: V-TEC/Non-V-TEC?

On Thu, 01 Apr 2004 12:51:25 -0600, Steve <no@spam.thanks> wrote:

>> I knew about VTEC for a long time but never really read about it. I think it
>> is a brilliant design for getting the best of 2 worlds of valve timing.

>
>Its brilliantly simple and well-engineered, but the way its implemented
>you have to rev the engine to insane RPM levels to get any real
>advantage out of it.


What's insane about 8000 RPM?
You must have cut your teeth on Detroit iron that floats it's valves
at 4500.

>I would have thought that it would be better to use
>the technology in such a way that the LOW rpm profile is the "special
>case" (say, maximum possible duration at a minimum lift to get zero
>overlap, thus maximizing compression pressures) and use it to give a big
>boost in usable torque below, say 2000 RPM


Who says they didn't?

> and then switch over to a
>normal profile for higher RPM operation.


Why not a hotter profile, as they did.

>That would make a small engine
>feel "bigger" off the line, rather than boosting it on the high end
>where small engines already do pretty well as it is.


What boost? My VTEC engine (GSR 1.8 litre) has a virtually flat
torque curve from 3000 to 8000

> My gripe with VTEC
>engines is that they feel utterly gutless on the low end. Just no torque
>AT ALL. Admittedly, I'm biased by years of driving big-block V8s,


Exactly. You expect it to pull like crazy at 2000 RPM.

> but
>non-VTEC Honda 4-cylinders feel reasonbly acceptable on the low end to
>me and VTECs feel weaker.


Never mind the numbers on the tach, just treat the tach as an
indicator of percent of maximum RPM. The fact that half way
up the scale is way over what you'd rev a V8 to is irrelevant. If you
math out the piston speeds you'd find they are about the same.

>They go like a rocket above 6000, but there
>are only limited circumstances where that's practical.


Like anytime I leave a stop sign.

>But every stoplight is a place where more torque would be nice.


Why? In first gear I have to be right on the ball to go for second
before the rev limiter cuts in.




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  #4 (permalink)  
Old 01 Apr 2004, 04:26 pm
Steve
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Default Re: V-TEC/Non-V-TEC?

Disclaimer: I didn't mean to sound like I was insulting VTEC. Its a
great technology and EXCEEDINGLY well executed. As a contrast, look at
the disaster that Cadillac's first valve-deactivation engine in the 80s
was. They called it the "V-8-6-4" but it wasn't long before people
called it the "V-8-6-4-0." I'm just expressing personal opinion about
some things that don't appeal to me about VTEC the way its currently
implemented....


John Ings wrote

>
> What's insane about 8000 RPM?


The last 2000 RPM :-)

> You must have cut your teeth on Detroit iron that floats it's valves
> at 4500.


I didn't just "cut my teeth" on Detroit iron, I still drive it every
day. Just to be sure we're clear- there aren't any detroit V8s since the
mid 50s that REALLY float the valves as low as 4500 RPM. And quite
frankly, its not impractical or costly to build 8000-RPM 500 cubic inch
v8s with modern components. But the same argument applies- there are
very few circumstances in daily driving where I want to get to 6000 RPM,
let alone 8000. But I ALWAYS need torque from idle to 3000 or thereabout
EVERY SINGLE TIME I start from a dead stop.

>
>
>>and then switch over to a
>>normal profile for higher RPM operation.

>
>
> Why not a hotter profile, as they did.


There's nothing wrong with it at all, and in fact its great. I'm just
saying that for daily driving, I much prefer techniques that bump up low
RPM torque significantly, which is the inherent weakness of small
economical engines. I have no complaint about the top end of non-VTEC
4-cylinders (though VTEC is certainly more impressive), its the bottom
end that needs the help.


>
> Never mind the numbers on the tach, just treat the tach as an
>indicator of percent of maximum RPM. The fact that half way
>up the scale is way over what you'd rev a V8 to is irrelevant. If you
>math out the piston speeds you'd find they are about the same.



Don't bet the pink slip on it! VTECs are undersquare engines, and *most*
American v8s are oversquare with short strokes and big bores (obvious
exceptions are things like the Cadillac 500 CID and Olds 455 CID). Take
a Chrysler 383 or 400 CID v8 for example- the stroke is 3.38 inches
compared to a 1.8L VTEC stroke of 3.433 inches- at any RPM, the 383 will
have a LOWER piston speed than the VTEC. And a Chrysler 440 has a 3.75"
stroke so the piston speeds for it are only a few percent faster than a
VTEC. Small-block v8s have an even bigger advantage- a Chrysler 340 has
only a 3.31" stroke, and a 5.0L Ford a 3" stroke so the piston speeds
are gettinng substantially lower than the VTEC.

And to add insult to injury, a 383/400 has a 1.9 rod ratio compared to a
1.5 rod ratio for a 1,8L VTEC, meaning that the higher order piston
acceleration stresses (the stresses that generally cause connecting rod
or rod bolt failure) are a LOT lower. Even the 440 beats the VTEC in rod
ratio at 1.80. The "redline" on most V8 tachs has nothing to do with
the RPM where mechanical failure becomes likely, its just the RPM where
torque has begun to drop off because so much airflow has to be handled
and volumetric efficiency is tapering off quickly.


If you want to look at a wide varieety engines and how they compare in
terms bore, stroke (which directly determines piston speed) and rod
ratio, there's a neat table available at

http://users.erols.com/srweiss/tablersn.htm

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  #5 (permalink)  
Old 01 Apr 2004, 05:00 pm
John Ings
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Default Re: V-TEC/Non-V-TEC?

On Thu, 01 Apr 2004 15:26:46 -0600, Steve <no@spam.thanks> wrote:

>> What's insane about 8000 RPM?

>
>The last 2000 RPM :-)


Nah! You're thinking big heavy conrods, 2 big valves per cylinder,
pushrods and tappets, pistons the size of tomato cans...

>> You must have cut your teeth on Detroit iron that floats it's valves
>> at 4500.

>
>I didn't just "cut my teeth" on Detroit iron, I still drive it every
>day. Just to be sure we're clear- there aren't any detroit V8s since the
>mid 50s that REALLY float the valves as low as 4500 RPM. And quite
>frankly, its not impractical or costly to build 8000-RPM 500 cubic inch
>v8s with modern components.


For use at Daytona. Titanium conrods, overhead cams etc.
But then the F1 engines are turning 18,000 these days.

> But the same argument applies- there are
>very few circumstances in daily driving where I want to get to 6000 RPM,


Because it makes you cringe. You know a big engine turning that fast
is at risk, and you associate high revs with risk. Maybe some time on
a motorcycle would have got you used to it.

>let alone 8000. But I ALWAYS need torque from idle to 3000 or thereabout
>EVERY SINGLE TIME I start from a dead stop.


I use the torque I find between 3000 and 5000. My engine has four
little valves per cylinder and a much smaller piston and conrod. The
inertial forces aren't near as great as in your big V8.

> I'm just
>saying that for daily driving, I much prefer techniques that bump up low
>RPM torque significantly,


Big displacement. Pass anything on the road but a gas station! :-)

> which is the inherent weakness of small
>economical engines.


I'm paying close to 90 cents a litre for gas. I don't want to have low
end torque AND the gas consumption such torque costs.

> I have no complaint about the top end of non-VTEC
>4-cylinders (though VTEC is certainly more impressive), its the bottom
>end that needs the help.


The bottom end, 3000 RPM and below, can only be helped by greater
displacement.

>If you want to look at a wide varieety engines and how they compare in
>terms bore, stroke (which directly determines piston speed) and rod
>ratio, there's a neat table available at
>
>http://users.erols.com/srweiss/tablersn.htm


Something's not quite right there, the numbers don't match my shop
manual.


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  #6 (permalink)  
Old 02 Apr 2004, 11:41 am
Steve
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Default Re: V-TEC/Non-V-TEC?

John Ings wrote:

And quite
>>frankly, its not impractical or costly to build 8000-RPM 500 cubic inch
>>v8s with modern components.

>
>
> For use at Daytona.


No, for use in a street/strip car that burns pump gas. The 358 CID
cam-in-block pushrod v8s in NASCAR are presently running 9600+ RPM, even
the restricted ones that run at Daytona.

> Titanium conrods, overhead cams etc.


Not at all. Stock forged conrods weight-matched and shot peened,
ordinary hypereutectic or forged pistons in modern short-skirt designs,
single chain-driven cam and pushrods are CERTAINLY good to 7000 RPM,
more if you get a little fancy on weight reduction. You're out of date
on v8 tech :-)


>>But the same argument applies- there are
>>very few circumstances in daily driving where I want to get to 6000 RPM,



>Because it makes you cringe. You know a big engine turning that fast
>is at risk, and you associate high revs with risk. Maybe some time on
>a motorcycle would have got you used to it.


Not because it "makes me cringe" at all. I'm an engineer, for pete's
sake, I'm not afraid of something "blowing up" if operated within design
parameters. I just don't like waiting a second or two before I get
anywhere near the power band.



>Something's not quite right there, the numbers don't match my shop
>manual.



Post the correct numbers then, and I'll calculate piston speeds- or you
can, its nothing more than 2*stroke*RPM/12/60 to give the average piston
speed in feet/second if the stroke is in inches. But I distinctly
remember being shocked when I learned how long the stroke on a VTEC was
way back when they first came out. Undersquare engines tend to have
long-ish strokes, and undersqure designs are back because small bores
reduce emissions- the Ford 5.4 is also small-bore as are more and more
modern engines. The price you pay is higher piston speeds for the
displacement. As I said before, older V8 engine "redline" RPM levels
rarely limitedby impending mechanical disentigration, they were set by
the limits of air flow through emissions-compliant cheap-to-mass-produce
cylinder heads.

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Old 02 Apr 2004, 01:00 pm
John Ings
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Posts: n/a
Default Re: V-TEC/Non-V-TEC?

On Fri, 02 Apr 2004 10:41:20 -0600, Steve <no@spam.thanks> wrote:

>You're out of date on v8 tech :-)


Not something I've kept up on since gas was 32 cents an imperial
gallon!

> I'm not afraid of something "blowing up" if operated within design
>parameters. I just don't like waiting a second or two before I get
>anywhere near the power band.


I don't ever recall having to wait "a second or two" to get above 3000
RPM. True, the V8 driver can be loafing along at 2000 RPM in high gear
and punch the throttle and get results. But he pays for that at the
pump. I just go from 5th to 2nd at any speed under 60 mph and get the
same results, AND good gas milage!

> >Something's not quite right there, the numbers don't match my shop
> >manual.

>
>Post the correct numbers then, and I'll calculate piston speeds- or you
>can, its nothing more than 2*stroke*RPM/12/60 to give the average piston
>speed in feet/second if the stroke is in inches. But I distinctly
>remember being shocked when I learned how long the stroke on a VTEC was
>way back when they first came out.


My Jags had a stroke in excess of 4 inches and I'm trying to remember
what the redline was. Something less than 6000 I think. Used a quart
of oil every 500 miles and 17 miles to the gallon of gas though.

> As I said before, older V8 engine "redline" RPM levels
>rarely limitedby impending mechanical disentigration, they were set by
>the limits of air flow through emissions-compliant cheap-to-mass-produce
>cylinder heads.


And valve springs that had to be really nasty to get big valves with
pushrods and lifters in train to close promptly. A modern cylinder
head with 4 valves per cylinder and OHC would solve that easily.



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Old 02 Apr 2004, 01:30 pm
ray
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Default Re: V-TEC/Non-V-TEC?

John Ings wrote:
> On Fri, 02 Apr 2004 10:41:20 -0600, Steve <no@spam.thanks> wrote:
>
>
> I don't ever recall having to wait "a second or two" to get above 3000
> RPM. True, the V8 driver can be loafing along at 2000 RPM in high gear
> and punch the throttle and get results. But he pays for that at the
> pump. I just go from 5th to 2nd at any speed under 60 mph and get the
> same results, AND good gas milage!
>
>

rrrrriight.
First off - the VTEC idea is a good idea and a step forward.

However, there is one part you guys keep overlooking - fuel consumption
for your VTEC engines when driven hard. Do a quick search for articles
on it... to get x horsepower requires y amount of fuel - a VTEC might be
more efficient, but it's not THAT much more efficient and when you get
on it... it's no better in the mileage dept than anything else with
comparable horsepower. It's a good idea, but it's not magic.

Ray

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Old 02 Apr 2004, 02:47 pm
Steve
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Default Re: V-TEC/Non-V-TEC?

John Ings wrote:

> My Jags had a stroke in excess of 4 inches and I'm trying to remember
> what the redline was. Something less than 6000 I think. Used a quart
> of oil every 500 miles and 17 miles to the gallon of gas though.


Oh, now if you're going to bring JAGUAR into the discussion, you might
as well talk about Lucas refrigerators that make beer warm while you're
at it :-)

4" is a really big stroke for an American v8. I'm not sure about all the
makes, but every single Chrysler entry in that table (barring the "early
hemis" that I'm not that familiar with) was correct. So were the Fords
and Oldsmobiles that I'm familiar with. The Chrysler "low deck" big
blocks in particular with their 3.38 stroke are amazing machines. I
think most people that don't deal with them regularly tend to think that
they have cylinder dimensions like scaled-up 4-cylinders, and they
really don't at all. And their downfall wasn't efficiency, it was
emissions. Big bore engines have a lot of quench area, and that pushes
up HC emissions.


>
> And valve springs that had to be really nasty to get big valves with
> pushrods and lifters in train to close promptly. A modern cylinder
> head with 4 valves per cylinder and OHC would solve that easily.


That's really an oft-quoted non-problem, probably spread by the
commonality of the small-block Chevy. A quirk of the SBC is that it has
small diameter lifters, and therefore the lift RATE of a non-roller SBC
cam is pretty limited compared to some other engines. That meant that
for a "big" cam, an SBC has to have a lot more total lift and duration
than an engine that can snap the valves open and closed quicker, so they
tend to float valves more than other brands.And also, the stud-mounted
rocker design was less stable and placed further demands on the valve
springs to prevent "bouncing." Not a problem with Chryslers, AMCs, and
other brands that used larger diameter lifters and/or shaft mounted
rockers, and not a problem with roller cams (although roller lifters
tend to add their own share of valvetrain inertia, which is a problem
too). And 4 valves per cylinder is a compromise too. Flow-wise, it
doesn't quite match a true Hemi head with 2 valves and a simpler,
straighter port layout with less port wall drag.


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Old 02 Apr 2004, 03:02 pm
John Ings
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Default Re: V-TEC/Non-V-TEC?

On Fri, 02 Apr 2004 12:30:20 -0600, ray
<bitbucket@rollingviolation.comnet.org> wrote:

>However, there is one part you guys keep overlooking - fuel consumption
>for your VTEC engines when driven hard.


The point is that you can get good fuel economy with VTEC when you
aren't driving hard. The horsepower is up in the high revs where you
can use it or not at your choice. The big displacement engine wants
more fuel ALL the time, you can't opt out.




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