Fuelpak FP3 and Exhaust

[jeffjeney]

Is anyone using the fuelpak with stock Headers that have had Cat removed? Someone at Vance and Hines told me if I did this that the Fuelpak Autotune would not work properly because of Crosstalk because of the exhaust sampling. I am wanting to buy the decatted header from wildpigpipes for $100 with $50 core charge, but not if I will have tuning issues. This would be much cheaper than $600 V&H Dresser duals. Not really looking for major power performance, just removing heat from Cat. I already have V&H Air and SE Street Cannons.

Hopefully someone has experience with the FP3, want to make decision soon.

 

[lah2420]

I am running a stock pipe that somehow seems to have lost its cat and Screamin' Eagle mufflers along with the FP3. My mileage went down and it wasn't running as well as it should. Just on a whim I installed a set of DK's Thunder Torques and I am happy. I was skeptical of them doing anything for me. But the trike runs great now. Mileage went from about 31 average to about 35 average. Lower rpm torque is better. I felt like I went backwards when I just went with the pipe and mufflers. Just by mileage it went from about 33 mpg to 31 mpg. But the TTIs pushed it the other direction. Like I said, my average mpg is about 35, but I have seen as high as 38 with 2 up.

I have not done an auto tune because I am happy with the way it runs now. Don't expect them to be a miracle pill, but I feel like they were worth the money for my setup.

 

[Jack Klarich]

This post I made errors when I posted it, I did not preview it SORRY, The following post is accurate

 

[Jack Klarich]

There are SO many after market so called fixes IMO. The constant is this

How do you calculate specific impulse?

To calculate the specific impulse, we first need to calculate the exhaust velocity. Since the real exhaust velocity is exceeding complex to calculate, we will be using some simplifying assumptions to make a simpler equation. Assume that the exhaust velocity follows the following formula:

V[SUB]e[/SUB][SUP]2[/SUP] = kR[SUB]gas[/SUB]T[SUB]c[/SUB] [1 - (p[SUB]e[/SUB]/p[SUB]c[/SUB])[SUP](k-1)/k[/SUP]] / (k-1)​

where

k = ratio of specific heats, c[SUB]p[/SUB]/c[SUB]v[/SUB]

p[SUB]e[/SUB] = nozzle exit pressure

p[SUB]c[/SUB] = combustion chamber pressure

T[SUB]c[/SUB] = combustion chamber temperature

R[SUB]gas[/SUB] = exhaust flow specific gas constant RR/MM

RR = universal gas constant

MM = exhaust gas molecular weight

​

Note that k is typically between 1.21-1.26 for a wide range of fuels and oxidizers. Also note that the subscripts (e, c) stand for exit and chamber. Therefore, p[SUB]c[/SUB] stands for temperature of chamber and p[SUB]e[/SUB] stands for pressure of exit.

Because we are just approximating, we can simplify the above equation. The second half of the equation:

[1 - (p[SUB]e[/SUB]/p[SUB]c[/SUB])[SUP](k-1)/k[/SUP]] / (k-1)​

typically ends up as a small number which we will approximate with 1. Since anything multplied by one is itself then a rough guess of a specific impulse is:

V[SUB]e[/SUB][SUP]2[/SUP] = kR[SUB]gas[/SUB]T[SUB]c[/SUB]​

and since k is typically between 1.21-1.26 then we will also remove that term and approximate it as 1 giving us:

V[SUB]e[/SUB][SUP]2[/SUP] = R[SUB]gas[/SUB]T[SUB]c[/SUB]​

This result gives us some interesting observations:

• to get a high exhaust velocity and therefore a high isp we want both a high temperature in the chamber (T[SUB]c[/SUB]) and a large exhaust flow gas constant (R[SUB]gas[/SUB])
  
• for a given temperature (T[SUB]c[/SUB]), because R[SUB]gas[/SUB] is RR/MM, then if we reduce the molar weight of the exhaust gas then we get a higher velocity.
  

This then tells us that for better performance (high exhaust velocity), we want fuel-oxidizer mixtures that burn very hot and have a low molar mass exhaust.

---

The specific impulse is:

I[SUB]sp[/SUB] = u[SUB]eq[/SUB]/g[SUB]e[/SUB]

​

where

I[SUB]sp[/SUB] = specific impulse

u[SUB]eq[/SUB] = total impulse / mass of expelled propellant

g[SUB]e[/SUB] = acceleration at Earth's surface (9.8 m/s[SUP]2[/SUP])

​

And since we are approximating the speed of a gas with a constant velocity; the momentum of the escaping gas is:

p = mv

​

where

p = momentum (kg m/s)

m = mass (kg)

v = velocity (m/s)

​

Notice how masses cancel out and therefore we the I[SUB]sp[/SUB] is just the velocity of the exhaust gas (V[SUB]e[/SUB]) divided by the gravitational attraction of the Earth (g[SUB]e[/SUB]).

Now, if U want the condensed version find this book and read it

This book has almost every formula including cam choices and intake formulas

 

[DK Custom Products]

Is anyone using the fuelpak with stock Headers that have had Cat removed? Someone at Vance and Hines told me if I did this that the Fuelpak Autotune would not work properly because of Crosstalk because of the exhaust sampling. I am wanting to buy the decatted header from wildpigpipes for $100 with $50 core charge, but not if I will have tuning issues. This would be much cheaper than $600 V&H Dresser duals. Not really looking for major power performance, just removing heat from Cat. I already have V&H Air and SE Street Cannons.

Hopefully someone has experience with the FP3, want to make decision soon.

As lah2420 noted, the TTI's will eliminate/reduce reversion. This has a very beneficial effect on preventing crosstalk of the 02 sensors, as well as increasing low and mid range power.

Additionally, it is always a good practice, when removing a cat, to put a 1/4" weld bead around the interior of the header, right at the location of the front of the removed cat. This also helps to prevent crosstalk.

Kevin

 

[lah2420]

Dang Jack! Now I am not only cross eyed, but my head is spinning too.