Turbo vehicle exhaust size
03-02-2012, 04:19 PM
#1
Senior Member
Thread Starter
Turbo vehicle exhaust size
Can one have too big of an exhaust on a turbo vehicle? Specifically the Ecoboost F-150. I'm planning on installing a 4" system, (modifying the y pipe), but thought I'd ask first. The headpipes from the turbos/cats are 2 1/2", so the rest of the system needs to be at least 3 1/2" single pipe to equal that. Seems to me one would want the least restriction possible downstream of the turbos/cats. Please correct me if I'm mistaken, I have no previous experience with turbos.
03-02-2012, 04:33 PM
#2
I Like Tires
Depends on what you want. If you want a drag strip truck go big.
If you want to use it as a truck with low rpm torque then keep it around stock.
A smaller pipe will allow for easy engine scavenging at low rpm which = good power in low rpm but will restrict you in high rpm.
A larger pipe will make scavenging exhaust harder in low rpm but will be non restrictive to high rpm equating to an increase in redline rpm.
So if you want high rpm power and lose a little low end get the 4", if you want to keep it where it's at now then keep the pipe sizing equal and get a free-er flowing muffler
If you want to use it as a truck with low rpm torque then keep it around stock.
A smaller pipe will allow for easy engine scavenging at low rpm which = good power in low rpm but will restrict you in high rpm.
A larger pipe will make scavenging exhaust harder in low rpm but will be non restrictive to high rpm equating to an increase in redline rpm.
So if you want high rpm power and lose a little low end get the 4", if you want to keep it where it's at now then keep the pipe sizing equal and get a free-er flowing muffler
03-02-2012, 04:33 PM
#3
Senior Member
The inlet into the turbos is about the size of a quarter the cat back pipes are more than addaquate for the out flow the resonater and muffler are both straight thru design. unless you just want noise[that little 6 aint never gona sound like v8] or mine is bigger than yours bragging rights. save your money. the above statement applys to the eco boost and may not hold for other turbo apps. but experiance shows that larger exhaust slows gas velocity and could lose low end power. you might see a slight gain at WOT and near max Rpm. over all its a compromise at best
03-02-2012, 09:56 PM
#4
Boost :)
I answered your thread on the other board already but ill answer here too.
With a turbo vehicle, the turbo itself IS the restriction and creates the backpressure the motor needs. There have been several documented reports of these trucks picking up 30rwhp or more with just a 4" catback.
Bigger exhaust is better on a turbo vehicle. Even if the stock exhaust is already straight through and relatively good, you can still pick up power with just increasing the pipe size with a good muffler.
I've been working with and have owned turbo Supras for 10+ years and have personally dyno tested and tuned cars going from 3" to 4" exhaust and with that change only, they saw very good increases in power as well. You may lose a LITTLE bit of low end, but the restriction the turbos provide can make up for that too.
With a turbo vehicle, the turbo itself IS the restriction and creates the backpressure the motor needs. There have been several documented reports of these trucks picking up 30rwhp or more with just a 4" catback.
Bigger exhaust is better on a turbo vehicle. Even if the stock exhaust is already straight through and relatively good, you can still pick up power with just increasing the pipe size with a good muffler.
I've been working with and have owned turbo Supras for 10+ years and have personally dyno tested and tuned cars going from 3" to 4" exhaust and with that change only, they saw very good increases in power as well. You may lose a LITTLE bit of low end, but the restriction the turbos provide can make up for that too.
03-02-2012, 10:36 PM
#5
Senior Member
BassAckwards, you're thinking NA. The rules change for turbocharged.
TJ, you're right on.
Optimum exhaust pressures on NA engines depend on a lot of things, but 5+ psi is considered too much. 3-5 psi is about right. <3 psi risks losing some low-end. On a turbo engine, the exhaust pressure the engine sees (upstream of the turbine) runs 2-4 times boost. So, on the EB, the exhaust pressure will be 30-50 psi!!! This is WAY beyond what an engine needs to make good low-end.
Turbines (hot side) operate at a "pressure ratio". In other words, the turbine might require 4/1 pressure ratio in order to produce enough power to spin the compressor. This is the pressure in the header divided by the pressure between the turbine and cat. So, if you reduce the pressure downstream of the turbine by 1 psi using a big exhaust, the engine sees a reduction of 4 psi. Big gains can be had by reducing pressure downstream of the turbine.
Now, IMO 4" may be overkill. I was running respectable exhaust pressure (34 psi exhaust @ 17 psi boost) using a 3.5" exhaust on a 950 hp combo. Of course, it won't hurt anything except noise and maybe weight.
TJ, you're right on.
Optimum exhaust pressures on NA engines depend on a lot of things, but 5+ psi is considered too much. 3-5 psi is about right. <3 psi risks losing some low-end. On a turbo engine, the exhaust pressure the engine sees (upstream of the turbine) runs 2-4 times boost. So, on the EB, the exhaust pressure will be 30-50 psi!!! This is WAY beyond what an engine needs to make good low-end.
Turbines (hot side) operate at a "pressure ratio". In other words, the turbine might require 4/1 pressure ratio in order to produce enough power to spin the compressor. This is the pressure in the header divided by the pressure between the turbine and cat. So, if you reduce the pressure downstream of the turbine by 1 psi using a big exhaust, the engine sees a reduction of 4 psi. Big gains can be had by reducing pressure downstream of the turbine.
Now, IMO 4" may be overkill. I was running respectable exhaust pressure (34 psi exhaust @ 17 psi boost) using a 3.5" exhaust on a 950 hp combo. Of course, it won't hurt anything except noise and maybe weight.
03-02-2012, 10:47 PM
#6
I Like Tires
I answered your thread on the other board already but ill answer here too.
With a turbo vehicle, the turbo itself IS the restriction and creates the backpressure the motor needs. There have been several documented reports of these trucks picking up 30rwhp or more with just a 4" catback.
Bigger exhaust is better on a turbo vehicle. Even if the stock exhaust is already straight through and relatively good, you can still pick up power with just increasing the pipe size with a good muffler.
I've been working with and have owned turbo Supras for 10+ years and have personally dyno tested and tuned cars going from 3" to 4" exhaust and with that change only, they saw very good increases in power as well. You may lose a LITTLE bit of low end, but the restriction the turbos provide can make up for that too.
With a turbo vehicle, the turbo itself IS the restriction and creates the backpressure the motor needs. There have been several documented reports of these trucks picking up 30rwhp or more with just a 4" catback.
Bigger exhaust is better on a turbo vehicle. Even if the stock exhaust is already straight through and relatively good, you can still pick up power with just increasing the pipe size with a good muffler.
I've been working with and have owned turbo Supras for 10+ years and have personally dyno tested and tuned cars going from 3" to 4" exhaust and with that change only, they saw very good increases in power as well. You may lose a LITTLE bit of low end, but the restriction the turbos provide can make up for that too.
BassAckwards, you're thinking NA. The rules change for turbocharged.
TJ, you're right on.
Optimum exhaust pressures on NA engines depend on a lot of things, but 5+ psi is considered too much. 3-5 psi is about right. <3 psi risks losing some low-end. On a turbo engine, the exhaust pressure the engine sees (upstream of the turbine) runs 2-4 times boost. So, on the EB, the exhaust pressure will be 30-50 psi!!! This is WAY beyond what an engine needs to make good low-end.
Turbines (hot side) operate at a "pressure ratio". In other words, the turbine might require 4/1 pressure ratio in order to produce enough power to spin the compressor. This is the pressure in the header divided by the pressure between the turbine and cat. So, if you reduce the pressure downstream of the turbine by 1 psi using a big exhaust, the engine sees a reduction of 4 psi. Big gains can be had by reducing pressure downstream of the turbine.
Now, IMO 4" may be overkill. I was running respectable exhaust pressure (34 psi exhaust @ 17 psi boost) using a 3.5" exhaust on a 950 hp combo. Of course, it won't hurt anything except noise and maybe weight.
TJ, you're right on.
Optimum exhaust pressures on NA engines depend on a lot of things, but 5+ psi is considered too much. 3-5 psi is about right. <3 psi risks losing some low-end. On a turbo engine, the exhaust pressure the engine sees (upstream of the turbine) runs 2-4 times boost. So, on the EB, the exhaust pressure will be 30-50 psi!!! This is WAY beyond what an engine needs to make good low-end.
Turbines (hot side) operate at a "pressure ratio". In other words, the turbine might require 4/1 pressure ratio in order to produce enough power to spin the compressor. This is the pressure in the header divided by the pressure between the turbine and cat. So, if you reduce the pressure downstream of the turbine by 1 psi using a big exhaust, the engine sees a reduction of 4 psi. Big gains can be had by reducing pressure downstream of the turbine.
Now, IMO 4" may be overkill. I was running respectable exhaust pressure (34 psi exhaust @ 17 psi boost) using a 3.5" exhaust on a 950 hp combo. Of course, it won't hurt anything except noise and maybe weight.
Thanks Guys!
