Lost all backpressure and low end torque
07-05-2011, 09:58 PM
#11
Many folks never understand that low end torque is created through exhaust velocity. The high velocity gasses create momentum in the exaust that lets the flow actually create a draw on the exhaust port, evacuating the cylinders and during valve overlap, pulling the intake charge into the chamber. It's knd of a natural supercharging.
Now that you have big high flow pipes, you have to spin higher rpm to move enough volume of gasses to get back to that velocity level. This means the power band moves up the rpm range. Do you make more torque? Yes, but at at different rpm.
Too many people make changes like this, overshooting the usable range of their normal use and killing the daily performance. You may scream at the strip, but life sucks around town.
Now that you have big high flow pipes, you have to spin higher rpm to move enough volume of gasses to get back to that velocity level. This means the power band moves up the rpm range. Do you make more torque? Yes, but at at different rpm.
Too many people make changes like this, overshooting the usable range of their normal use and killing the daily performance. You may scream at the strip, but life sucks around town.
the reason hes most likely losing power is due to the resonance problem inherent with the SpinTechs (already stated)
if cars needed backpressure like you said, then top fuel dragsters would be running a full exhaust... which they obviously dont...
any car out there will not respond negatively to a DECREASE in BP but will suffer from an INCREASE...
NA cars will have a much less reduced increase from a reduction, FI cars LOVE taking all the BP away...
go drive a diesel truck with a stock exhaust and one with open pipes and see which one has more power...
07-05-2011, 10:33 PM
#13
3rd Gear Member
Join Date: Feb 2008
Location: Delaware
Posts: 801
I lost power by modding my car too. It sucks
07-06-2011, 12:14 AM
#14
1st Gear Member
Thread Starter
Join Date: Jun 2011
Location: California
Posts: 86
wrong
the reason hes most likely losing power is due to the resonance problem inherent with the SpinTechs (already stated)
if cars needed backpressure like you said, then top fuel dragsters would be running a full exhaust... which they obviously dont...
any car out there will not respond negatively to a DECREASE in BP but will suffer from an INCREASE...
NA cars will have a much less reduced increase from a reduction, FI cars LOVE taking all the BP away...
go drive a diesel truck with a stock exhaust and one with open pipes and see which one has more power...
the reason hes most likely losing power is due to the resonance problem inherent with the SpinTechs (already stated)
if cars needed backpressure like you said, then top fuel dragsters would be running a full exhaust... which they obviously dont...
any car out there will not respond negatively to a DECREASE in BP but will suffer from an INCREASE...
NA cars will have a much less reduced increase from a reduction, FI cars LOVE taking all the BP away...
go drive a diesel truck with a stock exhaust and one with open pipes and see which one has more power...
07-06-2011, 03:39 AM
#15
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
Here's another good read, it's a Headers 101 document from S&S who unfortunately are no longer in business. Some good "backpressure" and velocity info here as well...
07-06-2011, 07:22 AM
#16
4th Gear Member
Join Date: Jun 2010
Location: TEXAS
Posts: 1,452
I'm not a stang expert like some ppl are but I don't think the argument of a top fuel dragster vs the exhaust on a street car is a valid point at all. They both have motors and wheels but it almost stops there. What scotty said seems to make a lot of sense though bc you lose down low but gain up top.
07-06-2011, 08:04 AM
#17
6th Gear Member
Join Date: Aug 2009
Location: New Jersey
Posts: 6,028
Rocky....I have no idea what you just said.
07-06-2011, 11:11 AM
#18
Super Moderator
Join Date: Jul 2003
Location:
Posts: 14,917
All the original poster did was move the powerband.
A set of gears, 3.73 at the least will 'make up' for what you feel you lost down low.
Your car isn't making jack for hp/tq around 1500rpm anyway. Most likely what you are feeling is your butt dyno being confused by the increased vibration & noise. Quiet & smooth always 'feels' faster than loud & rough.
A set of gears, 3.73 at the least will 'make up' for what you feel you lost down low.
Your car isn't making jack for hp/tq around 1500rpm anyway. Most likely what you are feeling is your butt dyno being confused by the increased vibration & noise. Quiet & smooth always 'feels' faster than loud & rough.
07-06-2011, 11:46 AM
#19
5th Gear Member
Join Date: Nov 2007
Location: Maryland
Posts: 4,955
wrong
the reason hes most likely losing power is due to the resonance problem inherent with the SpinTechs (already stated)
if cars needed backpressure like you said, then top fuel dragsters would be running a full exhaust... which they obviously dont...
any car out there will not respond negatively to a DECREASE in BP but will suffer from an INCREASE...
NA cars will have a much less reduced increase from a reduction, FI cars LOVE taking all the BP away...
go drive a diesel truck with a stock exhaust and one with open pipes and see which one has more power...
the reason hes most likely losing power is due to the resonance problem inherent with the SpinTechs (already stated)
if cars needed backpressure like you said, then top fuel dragsters would be running a full exhaust... which they obviously dont...
any car out there will not respond negatively to a DECREASE in BP but will suffer from an INCREASE...
NA cars will have a much less reduced increase from a reduction, FI cars LOVE taking all the BP away...
go drive a diesel truck with a stock exhaust and one with open pipes and see which one has more power...
should be following this advice lol
All the original poster did was move the powerband.
A set of gears, 3.73 at the least will 'make up' for what you feel you lost down low.
Your car isn't making jack for hp/tq around 1500rpm anyway. Most likely what you are feeling is your butt dyno being confused by the increased vibration & noise. Quiet & smooth always 'feels' faster than loud & rough.
A set of gears, 3.73 at the least will 'make up' for what you feel you lost down low.
Your car isn't making jack for hp/tq around 1500rpm anyway. Most likely what you are feeling is your butt dyno being confused by the increased vibration & noise. Quiet & smooth always 'feels' faster than loud & rough.
07-06-2011, 12:16 PM
#20
for those of you that seem to lose low end power because of going with off-road pipe you might want to get some gears to remedy the situation 