A few car questions....

[Gamingphreek]

I am desperately trying to begin learning a lot about cars. I know enough to get by right now (change oil, and carry on a decent conversation) but not enough to really grasp everything.

Having read multiple articles on "HowStuffWorks" for the past 1.5 hours, i have a few questions:

1. If VTECH is so good, and HEMI is so good, why not combine them. It would seem to me that your car would be very efficient, yet even more powerful due to the VTECH's modification of the camshafts.

2. Exhaust. Currently the exhaust runs the length of the car. According to the article the air resistance causes the car to lose power because it cannot exhaust air as fast. Why do manf put the exhaust on the back of the car. Why not have it right below the engine witha huge exhaust blowing straight down (or perhaps with a slight angle to the rear)?

3. Can someone try to explain to me exactly what VTECH does. From what i understand it modifies the camshafts, but i am having trouble grasping how it does that.

-Kevin

 

[Demo24]

1. think HEMI does have variable cams
2. you know how freakin loud that would be? Yes more efficent, and also more polluting. Thus why the big fart can mufflers came to being. The bigger the exhaust diameter the less back pressure and thus more power. However the ricer crowd is to cheap to go the whole length and tend to stick to rear add ons that do nothing but make a crap load of noise.
3. Vtech bascially adjusts the cams to provide more high end power, and supposed its also set for low end torque which is still to be determined. If you really feel a Honda when you drive it theres certain RPM points where you can feel it kick in for high end power. My accord kicks in at 4500 but you have to be good to feel it, and I rarely do actually. Auto box tends to shift right before unless you put your foot down

 

[Gamingphreek]

I forgot to ask something real quick also:

Because i had so many places to go and my car was in the shop (starter was indeed gone just like in the thread), i was "forced" to drive my moms minivan. That, my friends was REAL SEXY . At any rate, driving it i noticed something that was slightly disturbing. WHen i hit the gas pedal, the tachometer, climbed a little bit and then fell a little before it accelerated, almost as if it slips and then catches. The car is a 2003 Chrysler Town and Country (Fully loaded). My dad said that while he thinks it could be slipping, that it is common in Chrysler cars. Is the transmission in Chryslers really that bad. Sometimes i could downshift or shift better in my manual transmission.

(FYI: That car really does, SOMEHOW, haul ass, im sure nothing on the Honda Oddessy though (T&C- 4Speed, Honda- 5 speed). The car redlines at 6 grand, and it shifts at 5500 RPM when accelerating fast. Probably would beat my truck )

-Kevin

 

[Demo24]

that Im not so sure on, but Id have to say investigate torque convertors

 

[Pepsi90919]

Originally posted by: Gamingphreek
I am desperately trying to begin learning a lot about cars. I know enough to get by right now (change oil, and carry on a decent conversation) but not enough to really grasp everything.

Having read multiple articles on "HowStuffWorks" for the past 1.5 hours, i have a few questions:

If VTECH is so good, and HEMI is so good, why not combine them. It would seem to me that your car would be very efficient, yet even more powerful due to the VTECH's modification of the camshafts.

2. Exhaust. Currently the exhaust runs the length of the car. According to the article the air resistance causes the car to lose power because it cannot exhaust air as fast. Why do manf put the exhaust on the back of the car. Why not have it right below the engine witha huge exhaust blowing straight down (or perhaps with a slight angle to the rear)?

3. Can someone try to explain to me exactly what VTECH does. From what i understand it modifies the camshafts, but i am having trouble grasping how it does that.

-Kevin

cordless 2.4GHz engines FTW

 

[swtethan]

you can barely feel Vtec on a honda.... but it is there... (used to drive a 2004 s2000)

 

[Kalvin00]

Another point is that if the exhaust is under the car, guess where the exhaust goes when youre stopped? Yep, right up and into the cab.

 

[Gamingphreek]

Originally posted by: DEMO24
1. think HEMI does have variable cams
2. you know how freakin loud that would be? Yes more efficent, and also more polluting
3. Vtech bascially adjusts the cams to provide more high end power, and supposed its also set for low end torque which is still to be determined. If you really feel a Honda when you drive it theres certain RPM points where you can feel it kick in for high end power. My accord kicks in at 4500 but you have to be good to feel it, and I rarely do actually. Auto box tends to shift right before unless you put your foot down

So a HEMI does, essentially, the same thing that a VTECH would do.

I was thinking noise might be a concern lol. Is that why when people are "pimping" their car out, they get these enormous exhausts?

While driving the Accord i felt VTECH kick in ~5k. I may be hearing things, but once you hit a certain RPM does the engine almost sound like a turbo is in there, as in accelerating rapidly then a WAAAAAH at the end (hard to put that noise into words without it looking funny).

If i were, not that i ever have or ever will, drive at ~120; the idea that the car is driving at around 5 Grand. Would that mean VTECH is always on? Does VTECH consume more gas at all, or is it just a more efficient way of moving it from point A to point B.

Finally, i rode in my friends car (old Civic he is restoring and "fixing up"). In the car he has a VTECH "tuner" (for lack of a better word). He said it allows him to set the RPM point at which VTECH kicks in. I think he shifts at 9 grand (10 grand is max), and he has it set for 4.5k. Is there any advantage to setting this at a lower interval (ie: set VTECH to kick in as soon as you hit the gas). Also i assume that this "tuner" is only their because the car uses a VTECH and not an i-VTECH.

-Kevin

 

[Xyclone]

Originally posted by: Kalvin00
Another point is that if the exhaust is under the car, guess where the exhaust goes when youre stopped? Yep, right up and into the cab.

But this would only get your car dirty, right?

 

[Gamingphreek]

Originally posted by: Kalvin00
Another point is that if the exhaust is under the car, guess where the exhaust goes when youre stopped? Yep, right up and into the cab.

So why dont they design more cars with engines in the rear? What are the disadvantages to a rear engine?

-Kevin

 

[funboy6942]

Originally posted by: Kalvin00
Another point is that if the exhaust is under the car, guess where the exhaust goes when youre stopped? Yep, right up and into the cab.

WHAT they dont want you to die of CO2 poisoning?

 

[Demo24]

Originally posted by: Gamingphreek

Originally posted by: Kalvin00
Another point is that if the exhaust is under the car, guess where the exhaust goes when youre stopped? Yep, right up and into the cab.

So why dont they design more cars with engines in the rear? What are the disadvantages to a rear engine?

-Kevin

a)cargo room
B)driving characteristics
c)most cars with engine in rear are 2 seaters

 

[deadlyapp]

Hemi is the design of the pistons IIRC. Most cars are now hemi's, but not quite the same as dodge's formula. Vtec has something to do with variable timing I believe, and many other cars now have it. IIRC MIVEC is essentially the same, and the butterfly valves on Naturally aspirated dodge stealth's and 3000gt's are both the same, they allow for long runners for low end torque, then open up to make them shorter on the upper end of the powerband.

Having the exhaust underneath the car is a bad idea. You want cold air to allow for more air to enter the engine and be compressed, all this hot exhaust gas directly under the car is not only very inefficient but is also drastically dangerous. There are still gas particles in that exhaust. The best idea is to have side exits that exit directly after the front wheels. But that gives you no room for mufflers or catalytic converters.

I would check the honda technical documents, i'm sure they have something that explains it indepth.

 

[Demo24]

Originally posted by: Gamingphreek

Originally posted by: DEMO24
1. think HEMI does have variable cams
2. you know how freakin loud that would be? Yes more efficent, and also more polluting
3. Vtech bascially adjusts the cams to provide more high end power, and supposed its also set for low end torque which is still to be determined. If you really feel a Honda when you drive it theres certain RPM points where you can feel it kick in for high end power. My accord kicks in at 4500 but you have to be good to feel it, and I rarely do actually. Auto box tends to shift right before unless you put your foot down

So a HEMI does, essentially, the same thing that a VTECH would do.

I was thinking noise might be a concern lol. Is that why when people are "pimping" their car out, they get these enormous exhausts?

While driving the Accord i felt VTECH kick in ~5k. I may be hearing things, but once you hit a certain RPM does the engine almost sound like a turbo is in there, as in accelerating rapidly then a WAAAAAH at the end (hard to put that noise into words without it looking funny).

If i were, not that i ever have or ever will, drive at ~120; the idea that the car is driving at around 5 Grand. Would that mean VTECH is always on? Does VTECH consume more gas at all, or is it just a more efficient way of moving it from point A to point B.

Finally, i rode in my friends car (old Civic he is restoring and "fixing up"). In the car he has a VTECH "tuner" (for lack of a better word). He said it allows him to set the RPM point at which VTECH kicks in. I think he shifts at 9 grand (10 grand is max), and he has it set for 4.5k. Is there any advantage to setting this at a lower interval (ie: set VTECH to kick in as soon as you hit the gas). Also i assume that this "tuner" is only their because the car uses a VTECH and not an i-VTECH.

-Kevin

1)no, HEMI is bascially a term for Chryslers sacred V8 engine, came about in the drag racing era of the 50-60's. Research there to know what the name means. What I meant was Vtech is an advanced form of variable cams, which most engines have today

2) yeah makes engine a bit more waily

3) probably is always on, however efficency is likely worse and thus why its set so high

4) Well theres a boost when i kicks in so in theory youd get more ummpph outta your engine. Also I doubt there is a significant difference in adding an "I" to Vtech, likely means the ECU monitors stuff and can kick it in at some different times.

 

[NutBucket]

Setting the crossover point lower is useful to smooth out power delivery. If you look at stock dynos of say an H22 or B16/18 there's a big jump in power when VTEC engages. Lower the engagement point and power delivery smooths out a lot.

VTEC on an Accord is VERY different from VTEC on the aforementioned motors. On Accords its used for economy/emissions purposes whereas on the H22 and B16/18 its used to boost power delivery at high revs.

For example the stock 2.2L, F22B1, Accord motor (well, from 94-97) was about 145hp. The H22 on the other hand had 190hp from the same 2.2L

EDIT: Ok, using VTEC will consume more gas only because more air is being moved through the engine. More air = more fuel for combustion. The high-profile cams are inefficient at lower RPMs and also lead to more emissions.

EDIT 2: iVTEC is COMPLETELY different beast then VTEC. The i stands for intelligent and basically adds the ability to adjust the cam phasing. Therefore the ECU can adjust the overlap between the intake and exhaust cams. Normal VTEC cannot do this.

EDIT 3: Having VTEC or iVTEC has zero effect on whether you run a "tuner" or not. Both systems can have positive benefits from a properly tuned piggyback computer.

 

[nakedfrog]

Rear-engine RWD, as far as your exhaust question.

 

[skyking]

Hemi = hemispherical combustion chamber. The plug is dead center, with the intake and exhaust valves placed symmetrically to either side.
VTECH = two different cam profiles. One for high RPM and power, the other for low RPM and smooth operation under normal conditions.
The two profiles are ground into the cam next to each other. The default cam position is the smooth, low RPM one. When the RPM gets to the switchover point, the cam is shifted hydraulically so the followers are now on the radical high RPM profile.

 

[Gamingphreek]

iVTEC is COMPLETELY different beast then VTEC. The i stands for intelligent and basically adds the ability to adjust the cam phasing. Therefore the ECU can adjust the overlap between the intake and exhaust cams. Normal VTEC cannot do this.

I know it uses the ECU to determine when to kick in, but aside from that how is it different. Not many places have articles on this that go in depth.

-Kevin

 

[NutBucket]

cam phasing.

http://asia.vtec.net/article/k20a/

That explains the basics of iVTEC. In "normal" VTEC and most other cars the cams are solidy affixed to the gears; no rotation is possible between the two.

 

[OS]

Originally posted by: NutBucket
cam phasing.

http://asia.vtec.net/article/k20a/

That explains the basics of iVTEC. In "normal" VTEC and most other cars the cams are solidy affixed to the gears; no rotation is possible between the two.

I've been wondering for a while how much more power honda will get out of their motors if/when they add cam phasing to the exhaust cam also, since only the intake cam has it right now.

 

[Gamingphreek]

Another question:

In reading about Limited Slip differential could you tell me if i am right. In a car without it there is actually only 1 tire that is recieving power, but the axle is locked so the other tire automatically gets the same power the other one gets. So it is impossible for them to spin at different speeds. In a SD this, when the tire with the torque begins to slip, it transfers some of that power to the other wheel. So they can, somewhat, operate independently.

Finally, i read about the Torsen type. It would seem, that this is better than the SD. How is the Torsen/LRD better?

Nutbucket...thanks for the link, ill read it

-Kevin

 

[NutBucket]

An open differential transmitts equal power to both wheels provided they have equal traction. If one wheel slips the power is diverted to the wheel with the LEAST amount of grip.

A LSD, whether it be a clutch type or Torsen (gears) attempts to maintain equal power delivery to both wheels even if one is slipping.

NOTE: Obviously we are using a 2wd car as an example but the same principles apply to 4wd and AWD cars as well.

 

[Gamingphreek]

I see, i was thinkingn of an Open Differential as transmitting power to the wheel with the most traction, for some God unknown reason.

Why wouldn't someone design something that diverts power to the wheel(s) with the most traction? Or has that been designed (is that the basic Torsen gearing?)

-Kevin

 

[NutBucket]

There is no simple, purely mechanical method to transmit power to the wheel with the most traction. Advanced SUVs like the X5 and Range Rovers and the like have the ability to power the wheel with the most traction by using the abs system to sense which wheels are slipping, applying the brakes the those wheels which therefore sends the power to the wheels that have traction. In these vehicles the differentials are typically open however on Range Rovers they have the ability to be electronically locked.

 

[AgaBoogaBoo]

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