[Alloytec] Designing tuned length alloytec 190 extractors

[Not_An_Abba_Fan]

The front O2 sensors will need to go as close to the collector as possible and the rears just after the cats. But on long tube extractors, if you want the best results, you will need 6 wide band sensors, one for each port up near the heads.

 

[OS-Mike]

I was thinking the wide bands just after the venturis and the other 2 about a foot downstream from the 1st ones. Im not running cats in NZ we dont have to (and im a authorised vehicle inspector) from the collectors its something like 30" to the resonator boxes with a cross over somewhere in there after that ill probly run 2 x 2 1/4 into a single 3" out the back ill try it without a muffler 1st and see how loud it is.

 

[Not_An_Abba_Fan]

You won't need the second set of sensors if you're not running cats, they only measure the change in O2 concentration after the cats to make sure they are working. Have them turned off in the tune.

 

[OS-Mike]

You won't need the second set of sensors if you're not running cats, they only measure the change in O2 concentration after the cats to make sure they are working. Have them turned off in the tune.

Worked it out ill put in 4 o2 sensors and put diodes in the after cat ones they use like 0.4-0.5v so ecu sees perfect working cats. Have you ever made pressure wave termination style resonators? iv worked out i need 2 x between 4600-7200cc ill probly just make some empty hotdogs using a 3.5"pipe down to 2.25" crimped in a swager but was wondering if i could use 4 x 2.25 pipes using a y merge on each end? i have heaps of 2.25" tube and would have to buy some 3.5" tube about 3-4 meters im guessing.

 

[OS-Mike]

Done apart from one collector flange now time for exhaust system

link to build pics r32driftking's Library | Photobucket

 

[Not_An_Abba_Fan]

Splitting into twin pipes then going back to single will quieten it down, but it will also create back pressure, what you will be doing is splitting the pressure wave into two then trying to cram them back together into the single pipe at the same time. If you can spiral the pipes first, then the exhaust gas is spinning when it comes back together, less turbulance.

I would keep the pipe size the same as the collector outlet, you have reduced the pipe after the flange to fit into the flange by the looks of it. It will be fine if you don't run an exhaust, but what will happen there is the gas will expand and slow down after it comes past the flange then into the larger pipe. You want it moving as fast as possible for as long as possible.

If you are going to fit the second set of O2 sensors with a resistor, all your work will be for ****, as the tune will think there are working O2 sensors there and adjust fuel to suit the fact there are cats. The whole purpose of those sensors is for emission control. Tune them out.

 

[OS-Mike]

This is all a bit new to me but iv made sure to add in all the things that make a complete exhaust system as a bit of an experiment. From what i worked out my primaries have to be 1 5/8" x 36 1/2 from the ex valve to the point they merge. There is no real collector length with a merge collector its all just angles and the diameters determine the length. The collector outlet should be 2 1/4" and have a 33" tail pipe then exit to the atmosphere. So im trying to design around these specs and from what iv learnt you have 3 options for tuning. Primaries, collector and tail pipe. This should give me peak torque around 4500rpm from the primary length & tail pipe lenght the primary diameter is more to not be restricting at higher rpm and the venturi collector for low down torque.

The collectors iv made have 15 degree taper down to 2" then they should have (mine don't yet but there close) a 7 degree taper out to 2 1/4 to give it a venturi effect for a wider power band or more low down torque. They look like this without the flanges and iv put flanges where i have so i can change them if i want.

116 0304 Merg 1 Z Photo 2

After the collector a x pipe then 33" tail pipes that end half way under the car so i have to trick it into thinking they have exited by having a pressure wave termination box (a resonator with at least 8x the volume of 1 cylinder displacement 11x to 15x is best) so for the resonators im going to make something like these. In theory the headers wont see back pressure after the resonators.

And as for the o2 sensors i dont have vcm suite yet and im thinking the the ecu will probly be happier being tricked in to thinking there is working cats the me just unplugging them and having a fault code. My plan is to get my intake and exhaust sorted then tune.

 

[OS-Mike]

Quick sound clip of extractors installed still making exhaust system to suit extractors.

[video=youtube_share;HtTJYVjP5FI]http://youtu.be/HtTJYVjP5FI[/video]

 

[vy1tonnerbloke]

Sounds not too bad aye. The dog is unsure though.