Jeff7181
Lifer
- Aug 21, 2002
- 18,368
- 11
- 81
location of the camshaft only affects the number of components in the engine. OHV have more breakable parts than OHC and DOHC provides better airflow control at the sacrifice of reliablilty.
I'd still take that 732ci chevy BB with twin 1600cfm davinci carbs and twin VORTECH V-4 XX centrifigal superchargers and some nos over a ricer with V-tec and DOHC.
http://www.gmpartsdepot.com/store/produ...px?SID=2&Product_ID=458&Category_ID=2&
drool...
Not sure what he ment by that except DOHC can adjust airflow at different rpms, perhaps letting it breathe easier? I think on the japanese vehicles, V-Tec Dohc switch form lowrpm cam lobes to high rp,m cam lobes at 6000rpm and so you get better airflow at both ends of the spectrum.
False. It does.
read
"Engines modified with extremely high-flow cylinder heads, intake and exhaust systems, and longer-lift, longer-duration camshafts can operate near 100-percent efficiency. Add supercharging or turbocharging, and volumetric efficiency can exceed 100 percent."
And another link
"The ratio of this volume of outside air to the engine displacement is what is usually referred to as Volumetric Efficiency (VE). VE rarely exceeds 100% for normally-aspirated engine. VE exceeds 100% for forced-induction engines."
In my Z, the variable cam timing consists of advancing the whole cam a bit. But on Honda's engines, it's a more complicated system and they actually switch to a completely different set of lobes.
Interesting hearing people talk about lift here, when duration and overlap are just as important.
Picking the right cam can work wonders...
Here's a pic of a motor I just had built, and the dyno sheet to go with it.
Not bad for a 9.3:1 motor that runs on 91 octane. Notice how it makes over 400ft/lbs from 3000rpm right up.
383 Mopar
Dyno Sheet
Picking the right cam can work wonders...
Here's a pic of a motor I just had built, and the dyno sheet to go with it.
Not bad for a 9.3:1 motor that runs on 91 octane. Notice how it makes over 400ft/lbs from 3000rpm right up.
383 Mopar
Dyno Sheet
Jimmah
Golden Member
- Mar 18, 2005
- 1,243
- 2
- 0
91TTZ:
Sadly thats also incorrect, adding air density doesn't increase efficientcy, it just increases density, just like if atmospheric pressure was higher than 14.7psi it wouldn't increase VE. VE is only increased through air path efficiency, not through mass of the air itself. Try reading a physics textbook or a mechanical engineering text and you'll understand. Its actually a myth that VE increases through turbo or supercharging, the engine cannot ingest more total air than its VE will allow, but the air's mass/density can be higher while not effecting this rating.
Sadly thats also incorrect, adding air density doesn't increase efficientcy, it just increases density, just like if atmospheric pressure was higher than 14.7psi it wouldn't increase VE. VE is only increased through air path efficiency, not through mass of the air itself. Try reading a physics textbook or a mechanical engineering text and you'll understand. Its actually a myth that VE increases through turbo or supercharging, the engine cannot ingest more total air than its VE will allow, but the air's mass/density can be higher while not effecting this rating.
Jeff7181
Lifer
- Aug 21, 2002
- 18,368
- 11
- 81
Volumetric efficiency (VE) is used to describe the amount of fuel/air in the cylinder in relation to regular atmospheric air. If the cylinder is filled with fuel/air at atmospheric pressure, then the engine is said to have 100% volumetric efficiency. On the other hand, super chargers and turbo chargers increase the pressure entering the cylinder, giving the engine a volumetric efficiency greater than 100%.
More correctly, volumetric efficiency is a ratio (or percentage) of what volume of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Therefore, those engines that can create higher induction manifold pressures - above ambient - will have efficiencies greater than 100%.
<a target=_blank class=ftalternatingbarlinklarge href="http://64.78.42.182/sweethaven/MechTech/Automotive01/default.asp?unNum=1&lesNum=3&modNum=1">Increasing volumetric efficiency increases engine performance. Volumetric efficiency can be increasedin the following ways:
- Keep the intake mixture cool by ducting intake air from outside the engine compartment. By keeping the fuel cool, you can keep the intake mixture cooler. The cooler the mixture, the higher the volumetric efficiency. This is because a cool mixture is denser or more tightly packed.
- Modify the intake passages (fig. 2-23). Changes to the intake passages that make it easier for the mixture to flow through will increase the volumetric efficiency. Other changes include reshaping ports to smooth bends, reshaping the back of the valve heads, or polishing the inside of the ports.
- Altering the time that the valves open or how far they open can increase volumetric efficiency.
- By supercharging and turbocharging, you can bring the volumetric efficiency figures to over 100 percent.</a>
A turbocharger is an exhaust driven supercharger. All superchargers have a gas compressor in the intake tract of the engine which compresses the intake air above atmospheric pressure, greatly increasing the volumetric efficiency beyond that of naturally-aspirated engines.
Do you have any sources to back up your claims that forced induction doesn't increase volumetric efficiency?
More correctly, volumetric efficiency is a ratio (or percentage) of what volume of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Therefore, those engines that can create higher induction manifold pressures - above ambient - will have efficiencies greater than 100%.
<a target=_blank class=ftalternatingbarlinklarge href="http://64.78.42.182/sweethaven/MechTech/Automotive01/default.asp?unNum=1&lesNum=3&modNum=1">Increasing volumetric efficiency increases engine performance. Volumetric efficiency can be increasedin the following ways:
- Keep the intake mixture cool by ducting intake air from outside the engine compartment. By keeping the fuel cool, you can keep the intake mixture cooler. The cooler the mixture, the higher the volumetric efficiency. This is because a cool mixture is denser or more tightly packed.
- Modify the intake passages (fig. 2-23). Changes to the intake passages that make it easier for the mixture to flow through will increase the volumetric efficiency. Other changes include reshaping ports to smooth bends, reshaping the back of the valve heads, or polishing the inside of the ports.
- Altering the time that the valves open or how far they open can increase volumetric efficiency.
- By supercharging and turbocharging, you can bring the volumetric efficiency figures to over 100 percent.</a>
A turbocharger is an exhaust driven supercharger. All superchargers have a gas compressor in the intake tract of the engine which compresses the intake air above atmospheric pressure, greatly increasing the volumetric efficiency beyond that of naturally-aspirated engines.
Do you have any sources to back up your claims that forced induction doesn't increase volumetric efficiency?
That's not true.
"Volumetric efficiency (VE) is used to describe the amount of fuel/air in the cylinder in relation to regular atmospheric air. If the cylinder is filled with fuel/air at atmospheric pressure, then the engine is said to have 100% volumetric efficiency. On the other hand, super chargers and turbo chargers increase the pressure entering the cylinder, giving the engine a volumetric efficiency greater than 100%"
Note the "in relation to regular atmospheric air" part.
Jimmah
Golden Member
- Mar 18, 2005
- 1,243
- 2
- 0
I remember back when I was in my first semester of mechanical engineering, the prof was a rear gearhead and somehow we got talking about VE, even had a referrence in my machines and tools text. He explained how increasing air pressure/density doesn't do anything to the VE, how the engine is still pulling in 87% (or whatever) VE but at a different pressure. Now I'm not going to believe a bs website which probably has no true credentials saying VE is modified via forced induction vs what the prof said, he who IS a real engineer and HAS the masters degree + experience to back it up. You may keep your misconceptions.
Originally posted by: Nebor
Originally posted by: LordMorpheus
Originally posted by: Brutuskend
American V-8's OWN all imports!
(well, MOST imports at any rate.)
don't the really quick Grand Nationals use turboed V-6's? I might be wrong, but thats what I thought they had.
but its a cool vid. check out the minivan site, some funny stuff there.
I believe all the grand nationals use a turbo v6.
Yep....but the GNX had two turbos (and seating for five, and a trunk big enough for your wife's fat mom....etc, etc, etc)
Show me some references OTHER than one guy that you "heard" it from. We've showed you quite a few links that say the same thing. If you choose not to believe one specific reference I can see why you'd do that, because one source may be flawed. But so far we've shown you many sources while you are only referencing one, and not even providing proof of that one.
Also, just because one person has a master's degree and is a professor means nothing. The Unibomber was a professor with a Phd, and had a degree from Harvard. Would you believe what he had to tell you?
So far, it seems to be you who has the misconceptions. You are wrong. I find it sad that you continue to deny reality even in the face of proof, all the while failing to provide even one iota of proof supporting your belief.
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