exhaust for m20b28

[abit]

seems like nobody is watching in exhaust subforum :D
so will try here, because I need some ideas :D

I have to repair my exhaust, so I thought this could be the best time to make it maybe liiiiiittle bit better than it is right now :D
engine is m20b28 with 285/285 degrees camshaft and other mods

I have 3 to 2 to 1 system, with 2 free flow silencers in middle and back

I have this exhaust manifold,

primary tubes are 42mm outside diameter, what size tube I should use from the place where these 3 primary tubes comes together as one till it goes to y-pipe ?

and how close or far from engine I should better place Y-pipe, to make it have more torque in middle/top rpms?

aaand, as I have been searching in many atmospheric engine exhaust people use these conic tubes, so they make better flow in exhaust by venturi effect,
for example here: how to calculate, how long it should be and what small diameter should be in the middle?


back end piping after y-pipe is 60mm outside diameter, what is as I know enough for 2.8 engine?

I'm ready and want to experiment, and hear some advice's, so please help, best regards

[digger]

Twin 2" in is pretty common. BTB manifold uses twin 1-7/8" and seems to give best dyno proven gains on stock engines by an off the shelf product. IE long tube use 2-1/4", so somewhere in that range.....you are unlikely to find anyone who as tested an otherwise identical engine with different collector/secondary diameters to see the effect on an m20.

With regards to the length typically for an engine with around 6500rpm peak hp the recommended tuned collector length are 16”, 32”, 64” give or take a couple inches. These numbers come from pipemax. This is measured from where the 3 tubes end at the end of primary pipes until the abrupt change in area of the y-pipe

Unless you have a pure race motor that is highly developed with an extremely large overlap cam and aren’t using a “street exhaust” then id use either 32 or 64” otherwise you could give up a fair bit of torque below 4000rpm for next to no topend gains. Horses for courses…
If you buy from burns stainless steel they will design the venture size for you. You fill out a form with all the details and they have a program to work it out. its usually smaller than you think. My guess is if you have a 2.5” outlet then venturi would be somewhere between 2 and 2-1/4”

these are rules of thumb and there is no substitute for actual testing

[abit]

wow, thanks.
about y pipe, Im little confused
like here, where 2 pipes comes together, is there should be like wall inside between both, or it should be just outside welded tubes?



crappy pics, but idea I think is clear. I believe that 1st is better, right?

1. just welded


2. wall inside


here is used 1st type, right?

http://www.r3vlimited.com/board/showpost.php?p=1004510&postcount=6

[digger]

First one is fine, that's how burns stAinless does it.