power lost from my exhaust?
06-12-2006, 02:53 PM
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power lost from my exhaust? I have 1 7/8" headers and 3" dumped TD's. my only other mod is an airlid. How much power do you think I'm losing because of the large size of the exhaust. I'm planning on doing much more h/c n20 or FI. So I think they'll be fine then just wondering if anyone could give me a ballpark figure of what I'm losing right now over smaller headers and exhaust.
06-12-2006, 04:02 PM
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not losing horsepower, but losing torque. not enough backpressure with that exhaust. ur actually gaining horsepower up in the high end
06-15-2006, 08:47 AM
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Originally Posted by emerica4601
not losing horsepower, but losing torque. not enough backpressure with that exhaust. ur actually gaining horsepower up in the high end
Back pressure is a bad thing and you don't want it. The only reason some say yo do is it means the fueling of the motor doesn't need to be adjusted.
A freer flowing setup will require calibration and tuning to make the most from it.
However a restrictive exhaust will alter the profile of the torque curve and move it more towards the lower end of the scale where as a freer flowing setup will move the profile towards the upper rpms.
Now as HP is a function of torque:
HP = torque x rpm / 5252
It means if you produce the SAME or MORE torque at higher rpms you will also produce more power. Alternatively if you produce the SAME or LESS torque at lower rpms HP will also drop.
On a fairly stock setup the only thing 3" duals are likely to do is reduce exhaust gas flow velocity. However not by enough to make any real odds.
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07-09-2006, 05:30 AM
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Yep, exactly, backpressure is NEVER good. However as mentioned you can lose velocity, velocity helps create greater negative pressure at the port which optimises scavanging. So what you are doing to reducing the benefits of scavenging. You are probably setup for optimal at like 7000rpm, so power should be good way up high, but you will be losing midrange and low end torque.
If you want the full low down take a read here http://popularhotrodding.com/enginem...exh/index.html
If you want the full low down take a read here http://popularhotrodding.com/enginem...exh/index.html
07-09-2006, 05:58 AM
#9
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As ringram said, velocity creates a sharper negative pressure behind the exhaust "pulse";
larger diameter pipe means the same volume of gas can flow with a reduced velocity;
small diameter pipe means the same volume of gas has to flow with an increased velocity (to move the same volume);
reduced velocity means the negative pressure behind the pulse will not be as great, meaning scavenging (sucking thru to the intake port) will be reduced;
but as Blur and 300 said, the difference should be small enough to not worry about;
large diameter pipes do allow larger flow at higher rpm (i.e. the maximum flow rate is higher).
larger diameter pipe means the same volume of gas can flow with a reduced velocity;
small diameter pipe means the same volume of gas has to flow with an increased velocity (to move the same volume);
reduced velocity means the negative pressure behind the pulse will not be as great, meaning scavenging (sucking thru to the intake port) will be reduced;
but as Blur and 300 said, the difference should be small enough to not worry about;
large diameter pipes do allow larger flow at higher rpm (i.e. the maximum flow rate is higher).
