no personal experience per say for the m90 here, however, when I ported my LIM I ended up with better air flow and velocity through the engine. The result of this was less boost and more power. To make up for the roughly 1-2 psi drop in boost, I dropped back to my 2.5" pulley to take boost back up and then some(as i had no issues with heat and knock). TO me it makes sense that porting of the LIM, exaust work, and valvetrain work would all do their bit to increase air-flow through the engine and result in more power and less boost.


The resulting lower boost that some people have observed with ported m90 blower housings; I have my own opinions here.
I've spent countless hours looking up info on these eaton blowers and the various opinions of how to (and not to) port them and my opinion falls to the side of those who feel that too aggressive porting in various areas of the blower housing makes it less efficent.(however the lowering in heat buildup leaves the person using it to feel that it increased power) Specific areas that I feel are trouble areas for lowering efficency are the two silencer slits, any cleaning/polishing of the outside circumfrence of the bores where the two rotor lobes turn, and too much deformation to the shape of the V outlet.

my own thoughts are that if boost has gone down from a ported blower, and nothing else on the engine has changed, you have just sacrificed some efficency in exchange for less heat buildup. For some people this is a good thing as it allows through the lowering in heat to run full strength with no KR and the engine preforming better. A smaller pulley could be then be added depending on case, but its really to bring the boost back and the resulting heat that will bring must be taken into effect.

as always, we end up with the same story with these engines where we want to process as much air through it as efficently as possible, but keep temp down.

anyway thats my 2c....

Thanks, Karma. Your cents make sense. I agree that there is a wrong way to port/polish a blower that lowers efficiency, and boost. I want to steer clear of making such a mistake. From the photos on page 1, do you see any that look correct? I'm leaning towards ZZP's approach, but not sure.

the first photo on page one looks the best IMO. It keeps the lines and angles for the V while opening it out a bit more. Maybe could use a little more agressive rounding and smoothing on all edges on the BOTTOM facing side of the housing. I like how the silencer slits are largely unchanged, a slight rounding of the edge can be done there as long as it does not change the original hole size, but making NO changes other than a slight break of the corner from the inside edge where the rotor lobes will pass by. Also a good hard polishing at the inlet end when the air comes from the TB(near where the EGR lets in) will reap the most benifits in regards to heat, as flow testing on these eaton blowers shows that is where the greatest buildup of heat is due to friction.
anyway, thats how I would do it.

If you realy want to increase the efficency and maybe remove a little fricional heat you could look at plugging the scilencer ports themselves, but that is its own bag of worms as to how to properly do it.
here is a link on porting these things with various points of view, also discusses the plugging of scilencer holes..:
http://www.eatoninside.com/showthread.php?t=156

Kemps

Thanks, Codith!

Codith what did u use to fill in the silencing ports

looks like old fashoned JB, or maybe perma-steel, or magnum steel, or cold-weld or all that good stuff... as long as the sides of the ports are scuffed up to be nice and rough it should hold no problems.

-still best porting of m90 IMO that i've seen ever...

I'm with AA on this one. If changes are made to the supercharger and nothing else, and boost goes down, you have lost efficiency. Maybe gained a bit cooler running, but efficiency is down period. Since these are positive displacement superchargers, boost is built up in the LIM ONLY. So it you made a change upstream(the SC itself) so the SC could flow more air, and boost goes down, you have lost efficiency. The idea of a good P&P is to improve how the air flows through the SC so there is less heat, but without sacrificing efficiency; otherwise you have wasted your time and might as well just put a bigger pulley on the SC as it would accomplish the same thing: less boost, less heat.

I could have two blowers: perfectly the same. making say 13psi.
lets say on one engine one gives the 13 psi, but on the other it gives 10psi. This is because the second engine flows better from the LIM on, and hence makes better power. A decreased boost number is only proof of increased efficiency of the ENGINE and how it flows from the LIM on(because these are positive displacement SCs)

I agree with AA on this. The goal is to make less heat, increase potential flow of the unit, and increase the target efficiency range of the blower. At WOT with the motor in its power band, there should be equal or more boost. If its equal, we assume its pushing a cooler charge in and using a little less torque to do so resulting in more power for at least two different reasons.

As I see it, if done right, there is no drawback to porting blowers like this. Most of what is done is correcting factory limitations. The second part is, in a sense, re engineering the unit to work to a higher power demand.

The only way I can think of that you might see less boost and I can't imagine it would even be enough of a difference to see is by opening up the intake manifold and blower housing for an I/C without putting the I/C in, effectively increasing the volume of the intake manifold. Theory: The same amount of matter (boost or not) occupying more available space means less pressure.

I basically did that but since the cam happened at the same time, there is no way to make a judgment on its effect on boost.

My head is going to explode!!!
Can anyone just recommend who does the best porting job?
which company should get our business? ZZP? WBS?

Erik, that would be nice to know, but I want to understand the science behind this so I can do it myself - the right way.