Automotive Forums .com - the leading automotive community online! Automotive Forums .com - the leading automotive community online!
Automotive Forums .com - the leading automotive community online! 
-
Latest | 0 Rplys
Go Back   Automotive Forums .com Car Chat > Engineering/Technical
Engineering/Technical Ask technical questions about cars. Do you know how a car engine works?
Reply Show Printable Version Show Printable Version | Email this Page Email this Page | Subscription Subscribe to this Thread
 
Thread Tools
Old 05-23-2002, 01:12 PM   #31
SaabJohan
AF Enthusiast
 
Join Date: Nov 2001
Location: Borlänge
Posts: 1,098
Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally posted by 454Casull

Why not?
That's what tests have shown, doesn't have an explanation why.
SaabJohan is offline   Reply With Quote
Old 05-23-2002, 03:25 PM   #32
454Casull
AF Enthusiast
 
Join Date: Mar 2002
Location: Toronto
Posts: 615
Thanks: 0
Thanked 0 Times in 0 Posts
All else being the same, having an extra spark plug in there would increase the compression ratio slightly, would help cool down the engine (an additional heatsink), leads to more efficient burning, so what's to lose?
__________________
Some things are impossible, people say. Yet after these things happen, the very same people say that it was inevitable.
454Casull is offline   Reply With Quote
Old 05-25-2002, 07:29 PM   #33
SaabJohan
AF Enthusiast
 
Join Date: Nov 2001
Location: Borlänge
Posts: 1,098
Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally posted by 454Casull
All else being the same, having an extra spark plug in there would increase the compression ratio slightly, would help cool down the engine (an additional heatsink), leads to more efficient burning, so what's to lose?
Since compression ratio depends on cylinder volume and volume when piston is at TDC I can't se how the c.r. would increase with an extra plug.

A sparkplug is rather a hotspot than heatsink.

Twin sparkplugs is used when a cleaner and more efficient combustion is wanted at low and mid rpms, and if there is hard for one plug to ignite the fuel and/or if the fuel is burning slow like in Top Fuel dragsters.
SaabJohan is offline   Reply With Quote
Old 05-26-2002, 12:03 AM   #34
454Casull
AF Enthusiast
 
Join Date: Mar 2002
Location: Toronto
Posts: 615
Thanks: 0
Thanked 0 Times in 0 Posts
Sorry, I forgot.

Why are there heat ratings for spark plugs then?
__________________
Some things are impossible, people say. Yet after these things happen, the very same people say that it was inevitable.
454Casull is offline   Reply With Quote
Old 05-26-2002, 01:29 PM   #35
texan
Writer Mod
 
texan's Avatar
 
Join Date: Jan 2001
Posts: 714
Thanks: 0
Thanked 0 Times in 0 Posts
They're for controlling tip temperature, to prevent them from becoming so cold that they foul and so hot that they cause ignition pre-ignition.

There's nothing wrong with two spark plugs per cylinder, it's just that they don't really fit properly if you have more than three valves per cylinder. Mercedes found it beneficial for efficiency and emmisions to remove one valve in order to add a spark plug, which isn't surprising given that it does help low to midrange engine operation (where their engines spend about 90% of their life).

SaabJohaan- For combustion to travel fastest and exert maximum pressure on the piston crown during high RPM operation, a large bore and small stroke are what you're looking for (not the other way around). Additionally, such a setup has a smaller surface area to volume ratio, which if you're that worried about efficiency would be the way to go. Remember its not just about surface area, its about volume vs. surface area. On a displacement vs. surface area basis, old pushrod 2 valve V8's have a significantly better ratio than most any modern four cylinder motor.
__________________
'03 Corvette Z06
'99 Prelude SH
texan is offline   Reply With Quote
Old 05-26-2002, 02:37 PM   #36
454Casull
AF Enthusiast
 
Join Date: Mar 2002
Location: Toronto
Posts: 615
Thanks: 0
Thanked 0 Times in 0 Posts
On a another note: Why is the Viper's V10 still using pushrods?
__________________
Some things are impossible, people say. Yet after these things happen, the very same people say that it was inevitable.
454Casull is offline   Reply With Quote
Old 05-26-2002, 04:05 PM   #37
texan
Writer Mod
 
texan's Avatar
 
Join Date: Jan 2001
Posts: 714
Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally posted by 454Casull
On a another note: Why is the Viper's V10 still using pushrods?
If you're looking for the positive aspects of it, the pushrod configuration naturally lends itself to a lighter and more compact engine package. They probably decided early on to make the motor a 2 valve per cylinder setup, and given the height and width considerations didn't see the need to move to SOHC valvetrain. The Viper V10 is actually closer in design and tune to a truck engine than a performance car motor, but it's so damn big it can still hurl a car around at ludicrous speeds.
__________________
'03 Corvette Z06
'99 Prelude SH
texan is offline   Reply With Quote
Old 05-27-2002, 06:29 AM   #38
454Casull
AF Enthusiast
 
Join Date: Mar 2002
Location: Toronto
Posts: 615
Thanks: 0
Thanked 0 Times in 0 Posts
It's already big enough...

I've got a question though - why does it only make ~60HP/L?
__________________
Some things are impossible, people say. Yet after these things happen, the very same people say that it was inevitable.
454Casull is offline   Reply With Quote
Old 05-27-2002, 11:29 AM   #39
SaabJohan
AF Enthusiast
 
Join Date: Nov 2001
Location: Borlänge
Posts: 1,098
Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally posted by texan
SaabJohaan- For combustion to travel fastest and exert maximum pressure on the piston crown during high RPM operation, a large bore and small stroke are what you're looking for (not the other way around). Additionally, such a setup has a smaller surface area to volume ratio, which if you're that worried about efficiency would be the way to go. Remember its not just about surface area, its about volume vs. surface area. On a displacement vs. surface area basis, old pushrod 2 valve V8's have a significantly better ratio than most any modern four cylinder motor.
The flamepath will be shorter for an engine with small bore since the flame path is from the sparkplug to the furtest point which is the cylinderwalls when using a centrally placed spark plug.

Large bore with small stroke have a larger surface area/volume than small bore and large stroke, but is anyway better in a high rpm operation like you said.

A four cylinder engine will always have better surface to volume ratio than an eight cylinder engine if they have the same volume and have the same type of head.

I didn't mentioned the volume since my comparison was between few and large cylinders against small and many cylinders.
SaabJohan is offline   Reply With Quote
Old 06-08-2002, 01:08 PM   #40
GPrince
AF Newbie
 
Join Date: Jun 2002
Posts: 31
Thanks: 0
Thanked 0 Times in 0 Posts
Smile

these are generalizations.
larger displacement makes more torque
air flow makes more power
it's easer to get air in to a small cylinder than a larger one at higher engine speeds.
also larger bore size can make it easer to get air into an engine. for a given dispalcement.
a V12 6 L is just 12 smaller one cylinder engines added together.
a V8 6 L is just 8 larger one cylinder engines added together.
torque is about the same.
the v 12 will almost aways be able to breath better at higher R.P.M. and make more HP.
every thing else being the same.

.........ft/lb of torque * R.P.M.
HP= --------------------------
....................5252...............
how does one get sucked in to answring a question. that has no real answer?
GPrince is offline   Reply With Quote
Old 06-08-2002, 05:52 PM   #41
454Casull
AF Enthusiast
 
Join Date: Mar 2002
Location: Toronto
Posts: 615
Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
a V12 6 L is just 12 smaller one cylinder engines added together.
a V8 6 L is just 8 larger one cylinder engines added together.
You missed the whole point.
__________________
Some things are impossible, people say. Yet after these things happen, the very same people say that it was inevitable.
454Casull is offline   Reply With Quote
Old 06-08-2002, 06:22 PM   #42
GPrince
AF Newbie
 
Join Date: Jun 2002
Posts: 31
Thanks: 0
Thanked 0 Times in 0 Posts
i THINK

I think I got my threads crossed.
I was repling to something else.
GPrince is offline   Reply With Quote
Old 06-21-2002, 10:58 AM   #43
Hudson
Old Mod
 
Join Date: Aug 2001
Location: None
Posts: 1,525
Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally posted by 454Casull
On a another note: Why is the Viper's V10 still using pushrods?
Just for additional information:

When the Viper's engine was designed, it was derived from an existing OHV V8. In order to develop the V10 as a SOHC unit, it would have been much more expensive and taken longer. The Viper went from concept to assembly line in 3 years. Very good for a vehicle that was on a unique platform using a unique (albeit based on an upcoming volume engine's design) engine.

I forget the exact numbers, but the cost of the Viper project was relatively low.
Hudson is offline   Reply With Quote
Old 06-21-2002, 05:26 PM   #44
GPrince
AF Newbie
 
Join Date: Jun 2002
Posts: 31
Thanks: 0
Thanked 0 Times in 0 Posts
yeah I know what ya meen.

the v 10 iis big enough already.
I have been thinking about this
so what if your engine is smaller on the inside
it matters how big it is on the outside. that and weight. and fuel consumption are the only real things worth thinking about
GPrince is offline   Reply With Quote
Old 06-22-2002, 02:10 PM   #45
Steel
AF Fanatic
 
Steel's Avatar
 
Join Date: Aug 2001
Location: Tucson, Arizona
Posts: 4,027
Thanks: 0
Thanked 0 Times in 0 Posts
fuel consumption schmuel consumtion! When i get me a deuce and a hlaf, ill be mkaing a good 8 miles a gallon! If that! or mabbe an M1 abrahms, 2 gallons a mile...hmm
__________________
Steel is offline   Reply With Quote
 
Reply

POST REPLY TO THIS THREAD

Go Back   Automotive Forums .com Car Chat > Engineering/Technical

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -5. The time now is 03:49 AM.

Community Participation Guidelines | How to use your User Control Panel

Powered by: vBulletin | Copyright Jelsoft Enterprises Ltd.
 
 
no new posts