intake/exhaust theory questions
12-16-2009, 06:52 PM
#11
D.R. THE PATHETIC DORK
Join Date: Jun 2007
Location: West Virginia
Posts: 30,863
i'm questioning this theory because of the 302/306 n/a builds over on sbftech.com have huge intakes and large exhaust with normal heads/custom cam. they are running crazy times based on their suspension set up. some peeps with complete set ups on their suspension on slicks running 10's.
12-17-2009, 08:35 AM
#12
in limbo
Thread Starter
Join Date: Jan 2007
Location: Iowa
Posts: 7,300
Compression has to do with power production, see bottom of reply:
Yes exactly parade rain - this changes the density of the air and therefore power. But not solely on atmospheric pressure unless you are just cranking the engine with the ignition turned off. Scavenging significantly contributes
----bottom of reply, see below----
---------------------------------------------------------------------------
Article By David Vizard
http://www.popularhotrodding.com/tec...ech/index.html
At least 150hp of a Pro Stock engine is due to the use of ultra high compression ratios (CR) of 16:1--or more. 110 octane race fuels make this possible, but don't be fooled into thinking that the use of 93 octane pump fuel in any way diminishes the importance of the CR used. Understanding how the CR affects your street or race engine can easily net as much as a 50hp benefit.
---------------------------------------------------------------------------
Compression Ratio Information / Calculation / Comparison
http://www.442.com/oldsfaq/ofcrc.htm
The rule of thumb for the compression ratios run in most street engines is: for every point change in the compression ratio your power output will change by 2%. Using this rule of thumb on an engine that produces 400 hp, every 1 point change in compression ratio will result in approx. a 8hp change in output.
---------------------------------------------------------------------------
Finally
http://en.wikipedia.org/wiki/Compression_ratio
A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency. High ratios place the available oxygen and fuel molecules into a reduced space along with the adiabatic heat of compression - causing better mixing and evaporation of the fuel droplets. Thus they allow increased power at the moment of ignition and the extraction of more useful work from that power by expanding the hot gas to a greater degree.
Yes exactly parade rain - this changes the density of the air and therefore power. But not solely on atmospheric pressure unless you are just cranking the engine with the ignition turned off. Scavenging significantly contributes
----bottom of reply, see below----
---------------------------------------------------------------------------
Article By David Vizard
http://www.popularhotrodding.com/tec...ech/index.html
At least 150hp of a Pro Stock engine is due to the use of ultra high compression ratios (CR) of 16:1--or more. 110 octane race fuels make this possible, but don't be fooled into thinking that the use of 93 octane pump fuel in any way diminishes the importance of the CR used. Understanding how the CR affects your street or race engine can easily net as much as a 50hp benefit.
---------------------------------------------------------------------------
Compression Ratio Information / Calculation / Comparison
http://www.442.com/oldsfaq/ofcrc.htm
The rule of thumb for the compression ratios run in most street engines is: for every point change in the compression ratio your power output will change by 2%. Using this rule of thumb on an engine that produces 400 hp, every 1 point change in compression ratio will result in approx. a 8hp change in output.
---------------------------------------------------------------------------
Finally
http://en.wikipedia.org/wiki/Compression_ratio
A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency. High ratios place the available oxygen and fuel molecules into a reduced space along with the adiabatic heat of compression - causing better mixing and evaporation of the fuel droplets. Thus they allow increased power at the moment of ignition and the extraction of more useful work from that power by expanding the hot gas to a greater degree.
not needed though. i wasnt disregarding compression for power increase. i myself run higher compression than a stock 5.0now there are some instances where what i said isnt true because of cam events where some air is lost due to if the valve is closed or not. yadda yadda yadda. just all depends on the build. but generally speaking... my question was if you made the intake and exhaust as free flowing as possible....would your heads/cam flow/perform to their max potential?
Last edited by FivePointOhh; 12-17-2009 at 08:47 AM.
12-18-2009, 01:17 PM
#13
3rd Gear Member
Join Date: Nov 2007
Location: Orange County, CA
Posts: 614
Yeah I read what you wrote, to be clear: I just didn't agree with it. I pre-apologize for the following text no hurt intended and I'm kinda slow, so don't read it as an attack or a know-it-all, I'm just giving it my best here
My understanding is that your compression ratio does absolutely have to do with airflow, netting a higher(more) compression ratio also a result of more (higher) flow for one.
While its hard to get the research while only having the www and a few minutes to illustrate my disagreement I will try by way of example:
http://www.physicsforums.com/showthread.php?t=244434
Less cylinder filling also lowers the compression ratio. Compression ratios are calculated assuming 100% cylinder filling
http://forums.turbobricks.com/showthread.php?p=2837187
When static compression can be higher, overlap allows more cylinder fill and head flow with engine vacuum.
As the static compression is raised, the effect of reduced dynamic compression is minimized as rpm's increase. It is the lower dynamic compression that occurs when overlap provides greater valve opening off of the compression stroke that is of note, and allows unburned fuel to go out the exhaust valve.
------------------------------------------------------------------
also "volicity stuff is old school and mostly crap"
if we were to say that old school stuff is crap, *the wheel* is pretty old school, so is icing the intake, are they are not mostly crap
Velocity is important to consider, it can gain a dynamic momentum that will flow better than a static test would indicate is possible
you did type exactly "what does compression have to do with anything?" how would you like me to interpert that? I have to assume that what you type is what you are communicating. You say you meant to say that "<compression has nothing to do with the> amount of air being sucked into the cylidner" but I cannot read your mind.
OK so IMO this is a tired statement and a bit of a cop out on my part but its the combo that will allow the BEST flow for your app (car type, rpm range etc), max flow might not be best. there is always a limiting factor in any system. Identifying the limiting factor (such as Holley's Systemax I to replace the 5.0 lower intake) will net the highest results, but as soon as you address "the" limiting factor there is instantly a different limiting factor. This is why the combo is important to address as a whole. If you keep removing the limiting factor to flow on intake and exhaust you will have the intake and exhaust capacity of a 747 engine while the center is still a SBF or whatever.
My understanding is that your compression ratio does absolutely have to do with airflow, netting a higher(more) compression ratio also a result of more (higher) flow for one.
While its hard to get the research while only having the www and a few minutes to illustrate my disagreement I will try by way of example:
http://www.physicsforums.com/showthread.php?t=244434
Less cylinder filling also lowers the compression ratio. Compression ratios are calculated assuming 100% cylinder filling
http://forums.turbobricks.com/showthread.php?p=2837187
When static compression can be higher, overlap allows more cylinder fill and head flow with engine vacuum.
As the static compression is raised, the effect of reduced dynamic compression is minimized as rpm's increase. It is the lower dynamic compression that occurs when overlap provides greater valve opening off of the compression stroke that is of note, and allows unburned fuel to go out the exhaust valve.
------------------------------------------------------------------
also "volicity stuff is old school and mostly crap"
if we were to say that old school stuff is crap, *the wheel* is pretty old school, so is icing the intake, are they are not mostly crap
Velocity is important to consider, it can gain a dynamic momentum that will flow better than a static test would indicate is possible
you did type exactly "what does compression have to do with anything?" how would you like me to interpert that? I have to assume that what you type is what you are communicating. You say you meant to say that "<compression has nothing to do with the> amount of air being sucked into the cylidner" but I cannot read your mind.
OK so IMO this is a tired statement and a bit of a cop out on my part but its the combo that will allow the BEST flow for your app (car type, rpm range etc), max flow might not be best. there is always a limiting factor in any system. Identifying the limiting factor (such as Holley's Systemax I to replace the 5.0 lower intake) will net the highest results, but as soon as you address "the" limiting factor there is instantly a different limiting factor. This is why the combo is important to address as a whole. If you keep removing the limiting factor to flow on intake and exhaust you will have the intake and exhaust capacity of a 747 engine while the center is still a SBF or whatever.
Last edited by Hamutoff; 12-18-2009 at 03:07 PM.
12-18-2009, 04:18 PM
#15
2nd Gear Member
Join Date: Sep 2005
Location:
Posts: 246
since we all know that volicity stuff is old school and mostly crap. and we all know an engine is basically a giant air pump... what would happen in this example.
lets call this an average build.
stock 302 bottom end.
TW heads
a good OTS cam dual pattern
holly/eddy intake (efi)
full exhaust shorties mid pipe and cat back all 2.5 inch
and supporting bolt ons 70mm TB egr 75+ mm MAF yadda yadda yadda
now take that average build and change it a bit
stock 302 bottom end
TW heads
a good OTS cam dual pattern
spider intake w/ elbow(or something large like it)
90mm intake
95+mm MAF
large exhaust 1 3/4 primary or something, then 3 inch all the way out
and supporting bolt ons yadda yadda yadda
all you did was open the intake and exhaust as wide open as you'll ever need on a regular 302. would you see a difference in power? in all honesty i dont think you'd see a decrease in power. in my head i see it as a air pump. previously in the first example i see the smaller intake runners may not flow as much as the cam will allow through the heads. basically in the second example you are supplying the cam and head with all the air they could possibly ever need. same with the exhaust, all the room they could ever need to flow out therefore the cam and head if they are properly matched would perform to they max potential correct? wouldnt the second example way out perform the first example? are there examples of this expriment?
lets call this an average build.
stock 302 bottom end.
TW heads
a good OTS cam dual pattern
holly/eddy intake (efi)
full exhaust shorties mid pipe and cat back all 2.5 inch
and supporting bolt ons 70mm TB egr 75+ mm MAF yadda yadda yadda
now take that average build and change it a bit
stock 302 bottom end
TW heads
a good OTS cam dual pattern
spider intake w/ elbow(or something large like it)
90mm intake
95+mm MAF
large exhaust 1 3/4 primary or something, then 3 inch all the way out
and supporting bolt ons yadda yadda yadda
all you did was open the intake and exhaust as wide open as you'll ever need on a regular 302. would you see a difference in power? in all honesty i dont think you'd see a decrease in power. in my head i see it as a air pump. previously in the first example i see the smaller intake runners may not flow as much as the cam will allow through the heads. basically in the second example you are supplying the cam and head with all the air they could possibly ever need. same with the exhaust, all the room they could ever need to flow out therefore the cam and head if they are properly matched would perform to they max potential correct? wouldnt the second example way out perform the first example? are there examples of this expriment?
Why dont you just post this at sbftech and get real answers?
12-18-2009, 06:24 PM
#16
4th Gear Member
Join Date: Jan 2008
Location: Louisville, Ky.
Posts: 1,326
You can go big as possible and it will be more than the engine can use. The draw back is that on a street car, you will lose a bunch of low end driveability. The longer runners of an intake such as the TrackHeat or SystemaxII or whatever will have better throttle response and lower rpm driveability because of the velocity of airflow in the intake air. The short runner spider type intakes are designed for high rpm power on a n/a engine. Much like the short runner Victor Jr. vs the Performer vs the Performer RPM.
So in therory, running the largest flowing parts possible would work ok on a drag car that runs from say 3500rpm -up. Not so good on a daily driver that also has to work from 1200rpm -up.
There is such a thing as too much of a good thing.
On the exhaust side, It won't hurt as much. But can still move the usable power band up.
So in therory, running the largest flowing parts possible would work ok on a drag car that runs from say 3500rpm -up. Not so good on a daily driver that also has to work from 1200rpm -up.
There is such a thing as too much of a good thing.
On the exhaust side, It won't hurt as much. But can still move the usable power band up.
12-19-2009, 05:14 AM
#17
6th Gear Member
Join Date: Jan 2008
Location: colorado
Posts: 6,395
your just going to get fustrated asking this question here.
I love where your head is at, but your not going to get the answer your looking for here.
I too would like to know a real answer for this. Not this volicity and "kills low down power" BS
I love where your head is at, but your not going to get the answer your looking for here.
I too would like to know a real answer for this. Not this volicity and "kills low down power" BS
12-19-2009, 09:17 AM
#18
M.A.D. Motorsports
Join Date: Jul 2006
Location: Indiana
Posts: 8,014
This thread is probably going to get out of hand......they always do............
As long as your cam is customized to your setup and it is tuned properly it would work. Those guys running those low numbers have a great suspension setup too and you know as well as the rest of us our cars react very well to an upgraded suspension.
Velocity does matter........... alot....
As long as your cam is customized to your setup and it is tuned properly it would work. Those guys running those low numbers have a great suspension setup too and you know as well as the rest of us our cars react very well to an upgraded suspension.
Velocity does matter........... alot....
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