high comp. vs. low comp.
11-22-2004, 07:15 PM
#1
Thread Starter
Join Date: Jan 2004
Location: essex, ct, usa
Posts: 86
Likes: 0
Received 0 Likes
on
0 Posts
high comp. vs. low comp.
What are the advantages and disadvantages of low compression w. high boost and high compression w. lower boost. What will make more horsepower, what is more reliable, what would be your choice.
11-22-2004, 07:19 PM
#2
Join Date: Jul 2004
Posts: 1,049
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (turbo89civicb18hatch)
Advantages of High Compression:
SLIGHTLY more power at a given boost level
More off-boost power
Disadvantages of High Compression:
Harder to tune
less boost on pump gas
much smaller margin of error in terms of a bad tank of gas or whatnot.
Advantages of low compression
More boost, more power on pump gas
safer motor
easier to tune
Disadvantages of Low Compression
SLIGHTLY less power under boost
SLIGHTly less power off boost
I'm running 7.8:1 compression in my B16. H-T says high compression spools your turbo quicker. My turbo spools the same from stock 10.2:1 to 7.8:1. H-T says you make more off boost power on high compression. I say, do you want more power when you're driving normally from stoplight to stoplight, or do you want more power when you're aggressively driving and boosting hard?
For a street car I would run NO HIGHER than 9:1 compression.
SLIGHTLY more power at a given boost level
More off-boost power
Disadvantages of High Compression:
Harder to tune
less boost on pump gas
much smaller margin of error in terms of a bad tank of gas or whatnot.
Advantages of low compression
More boost, more power on pump gas
safer motor
easier to tune
Disadvantages of Low Compression
SLIGHTLY less power under boost
SLIGHTly less power off boost
I'm running 7.8:1 compression in my B16. H-T says high compression spools your turbo quicker. My turbo spools the same from stock 10.2:1 to 7.8:1. H-T says you make more off boost power on high compression. I say, do you want more power when you're driving normally from stoplight to stoplight, or do you want more power when you're aggressively driving and boosting hard?
For a street car I would run NO HIGHER than 9:1 compression.
11-22-2004, 07:24 PM
#4
Join Date: Jul 2004
Posts: 1,049
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (9psiTurboSI)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 9psiTurboSI »</TD></TR><TR><TD CLASS="quote">this topic has been covered too many times... do a search!</TD></TR></TABLE>
A lot of the "info" being "shared" are just spreading misconceptions. A lot like the "LS transmission is better for turbo" and "VTEC doesn't work well with turbo" myths that were passed around.
A lot of the "info" being "shared" are just spreading misconceptions. A lot like the "LS transmission is better for turbo" and "VTEC doesn't work well with turbo" myths that were passed around.
11-22-2004, 07:44 PM
#5
Thread Starter
Join Date: Jan 2004
Location: essex, ct, usa
Posts: 86
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (b16coupe)
wat wuld be a better choice for an ls vtec w. rods pistons stock sleeves being a street car w. a t3/t04e turbo and hondata
11-23-2004, 09:20 AM
#6
Honda-Tech Member
Join Date: Feb 2003
Location: Margaritaville
Posts: 7,355
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (b16coupe)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b16coupe »</TD></TR><TR><TD CLASS="quote">
I'm running 7.8:1 compression in my B16. H-T says high compression spools your turbo quicker. My turbo spools the same from stock 10.2:1 to 7.8:1. H-T says you make more off boost power on high compression. I say, do you want more power when you're driving normally from stoplight to stoplight, or do you want more power when you're aggressively driving and boosting hard?
For a street car I would run NO HIGHER than 9:1 compression.</TD></TR></TABLE>
H-T is right.
Higher C/R = more exhaust gas energy = more work through the turbine = faster spool up. Period.
I'm running 7.8:1 compression in my B16. H-T says high compression spools your turbo quicker. My turbo spools the same from stock 10.2:1 to 7.8:1. H-T says you make more off boost power on high compression. I say, do you want more power when you're driving normally from stoplight to stoplight, or do you want more power when you're aggressively driving and boosting hard?
For a street car I would run NO HIGHER than 9:1 compression.</TD></TR></TABLE>
H-T is right.
Higher C/R = more exhaust gas energy = more work through the turbine = faster spool up. Period.
11-23-2004, 09:25 AM
#7
Member
Join Date: May 2002
Location: TurBlowVille, SC, USA
Posts: 3,719
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (RyanCivic2000)
High compression and boost imo is wonderful. Find a high compression set up and a low compression set that is very similar and tell me which make more power and lower boost levels and tell me which one's power band is alot more effiecent.
Trending Topics
11-23-2004, 10:02 AM
#8
Join Date: Sep 2002
Location: SR20 Specialist
Posts: 164
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (RyanCivic2000)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 »</TD></TR><TR><TD CLASS="quote">
Higher C/R = more exhaust gas energy = more work through the turbine = faster spool up. Period.</TD></TR></TABLE>
Errr...nope. the #1 factor in the work you can extract out of a turbine is...
MASS FLOW
not exhaust gas energy.
Say we even ignore that fact. Higher compression engiens make better use of the energy contained in the charge. thus theoretically there is less energy in the charge after combustion because you have converted more of it into work.
but...here's what everyone misses. you think there is going to be more "pressure" in the exhasut stroke becasue the compression ratio is higher. not true. the crank is still displacing the same mass of air at the same velocity on a 8.0:1 motor as on a 10.5:1 motor. think about it... either way on a 2.0L engine the exhaust stroke expels 0.5L worth of air/fuel combustion byproduct per cylinder per 2 revolutions. and for a fixed RPM it has a set amount of time to expel that quantity of air. regardless of compression ratio.
in reality ont he exhasut stroke there is no compression ratio...becasue...the exhaust valve is OPEN!! your just displacing air/fuel...not compressing it.
Modified by Enthalpy at 2:18 PM 11/23/2004
Higher C/R = more exhaust gas energy = more work through the turbine = faster spool up. Period.</TD></TR></TABLE>
Errr...nope. the #1 factor in the work you can extract out of a turbine is...
MASS FLOW
not exhaust gas energy.
Say we even ignore that fact. Higher compression engiens make better use of the energy contained in the charge. thus theoretically there is less energy in the charge after combustion because you have converted more of it into work.
but...here's what everyone misses. you think there is going to be more "pressure" in the exhasut stroke becasue the compression ratio is higher. not true. the crank is still displacing the same mass of air at the same velocity on a 8.0:1 motor as on a 10.5:1 motor. think about it... either way on a 2.0L engine the exhaust stroke expels 0.5L worth of air/fuel combustion byproduct per cylinder per 2 revolutions. and for a fixed RPM it has a set amount of time to expel that quantity of air. regardless of compression ratio.
in reality ont he exhasut stroke there is no compression ratio...becasue...the exhaust valve is OPEN!! your just displacing air/fuel...not compressing it.
Modified by Enthalpy at 2:18 PM 11/23/2004
11-23-2004, 10:06 AM
#9
Honda-Tech Member
Join Date: Nov 2003
Location: South Florida
Posts: 3,711
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (Enthalpy)
talking to Earl I was told that compression has nothing to do with spool, just exhuast and turbine size. so with this info I personally feel low compression is the best.. more power on pump gas, more power on race gas, more room for error and spools just as fast.
11-23-2004, 10:24 AM
#10
Honda-Tech Member
Join Date: Feb 2003
Location: Margaritaville
Posts: 7,355
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (Enthalpy)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Enthalpy »</TD></TR><TR><TD CLASS="quote">
Errr...nope. the #1 factor in the work you can extract out of a turbine is...
MASS FLOW
not exhaust gas energy.
Say we even ignore that fact. Higher compression engiens make better use of the energy contained in the charge. thus theoretically there is less energy in the charge after combustion because you have converted more of it into work.
but...here's what everyone misses. you think there is going to be more "pressure" in the exhasut stroke becasue the compression ratio is higher. not true. the crank is still displacing the same mass of air at the same velocity on a 8.0:1 motor as on a 10.5:1 motor. think about it... either way on a 2.0L engine the exhaust stroke expels 0.5L worth of air/fuel combustion byproduct per cylinder per 2 revolutions. and for a fixed RPM it has a set amount of time to expel that quantity of air. regardless of compression ratio.
in reality ont he exhasut stroke there is no compression ratio...becasue...the exhaust valve is OPEN!! your just displacing air/fuel...not compressing it.
Modified by Enthalpy at 2:18 PM 11/23/2004</TD></TR></TABLE>
More exhaust gas means more mass flow.
Errr...nope. the #1 factor in the work you can extract out of a turbine is...
MASS FLOW
not exhaust gas energy.
Say we even ignore that fact. Higher compression engiens make better use of the energy contained in the charge. thus theoretically there is less energy in the charge after combustion because you have converted more of it into work.
but...here's what everyone misses. you think there is going to be more "pressure" in the exhasut stroke becasue the compression ratio is higher. not true. the crank is still displacing the same mass of air at the same velocity on a 8.0:1 motor as on a 10.5:1 motor. think about it... either way on a 2.0L engine the exhaust stroke expels 0.5L worth of air/fuel combustion byproduct per cylinder per 2 revolutions. and for a fixed RPM it has a set amount of time to expel that quantity of air. regardless of compression ratio.
in reality ont he exhasut stroke there is no compression ratio...becasue...the exhaust valve is OPEN!! your just displacing air/fuel...not compressing it.
Modified by Enthalpy at 2:18 PM 11/23/2004</TD></TR></TABLE>
More exhaust gas means more mass flow.
11-23-2004, 10:34 AM
#11
Member
Join Date: May 2002
Location: TurBlowVille, SC, USA
Posts: 3,719
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (RyanCivic2000)
If the compression in no way affects spool time or anything else for that matter, why do most of the pro's run 10.1 plus on there motors. Seems funny to run such high compression if it does nothing.
11-23-2004, 10:52 AM
#12
Join Date: Sep 2002
Location: SR20 Specialist
Posts: 164
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (RyanCivic2000)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RyanCivic2000 »</TD></TR><TR><TD CLASS="quote">More exhaust gas means more mass flow.</TD></TR></TABLE>
your original post stated that you have more exhasut gas energy. exahsut gas energy = pressure and temp.
besides...compression raito does not increse mass flow. changes in RPM or displacemtn increase mass flow.
if you would like to tell me how an increase in co,pression ratio can significantly increase mass flow i'm ready to learn....
your original post stated that you have more exhasut gas energy. exahsut gas energy = pressure and temp.
besides...compression raito does not increse mass flow. changes in RPM or displacemtn increase mass flow.
if you would like to tell me how an increase in co,pression ratio can significantly increase mass flow i'm ready to learn....
11-23-2004, 10:54 AM
#13
Join Date: Sep 2002
Location: SR20 Specialist
Posts: 164
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (FOrSfEd)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by FOrSfEd »</TD></TR><TR><TD CLASS="quote">If the compression in no way affects spool time or anything else for that matter, why do most of the pro's run 10.1 plus on there motors. Seems funny to run such high compression if it does nothing.</TD></TR></TABLE>
bceasue you get 3% thermodynamic efficiency out of each point of compression ratio.
and i dont agree with your statement that "most pros" are running 10.0 + compression ratio...
bceasue you get 3% thermodynamic efficiency out of each point of compression ratio.
and i dont agree with your statement that "most pros" are running 10.0 + compression ratio...
11-23-2004, 01:08 PM
#14
Join Date: Jul 2004
Posts: 1,049
Likes: 0
Received 0 Likes
on
0 Posts
Re: high comp. vs. low comp. (FOrSfEd)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by FOrSfEd »</TD></TR><TR><TD CLASS="quote">If the compression in no way affects spool time or anything else for that matter, why do most of the pro's run 10.1 plus on there motors. Seems funny to run such high compression if it does nothing.</TD></TR></TABLE>
Motor design when you have enough octane to support basically any compression ratio under 12:1-ish revolves around more than just what compression ratio you're running, it's based a lot around the efficiency of the combustion chamber design, and a flat top piston promotes a better burn. I had a nice talk with Jeff and others at FastTimes about this, but a lot of it was way over my head.
Take it from me, I had my B16 boosted at stock compression, and I have my B16 boosted on 7.8:1 compression, you cannot tell a difference in spool.
Motor design when you have enough octane to support basically any compression ratio under 12:1-ish revolves around more than just what compression ratio you're running, it's based a lot around the efficiency of the combustion chamber design, and a flat top piston promotes a better burn. I had a nice talk with Jeff and others at FastTimes about this, but a lot of it was way over my head.
Take it from me, I had my B16 boosted at stock compression, and I have my B16 boosted on 7.8:1 compression, you cannot tell a difference in spool.
Thread
Thread Starter
Forum
Replies
Last Post
-iLLuZioN-B18C1
Forced Induction
2
03-04-2003 04:46 PM
