M112 Porting Project - Winter/Spring 2008

Winter of 2008 found my car up on blocks again. Since I planned on reworking my fuelrails I desided to do a couple other things:
1.Port/polish work on the throttle body, inlet manifold, and Eaton to see if I can bring the ACTs (air charge temps) down a little and may be gain 1-2psi using the stock 3.55" diameter Cobra pulley. With the crank/blower ratio of 1.55, normal bypass intake temps have been around 85-90*F while my boosted temps have been a little higher. At 6.5-7psi they were peaking ~180*F (90* ambient). With the Lightning 2.93" diameter pulley, crank/blower ratio change to 1.88, at 10.2-12psi I was seeing it peak ~225-230*F (85* ambient) out of the old Easy-Bake Eaton.
2. Rework the upper rad hose.
3. Build an air filter housing and inlet tube.
4. Rework the MachI side skirts.
5. Rework/rebuild the PCV catchcan. There was still too much oil getting through my seperator and ending up in the intake.

PROJECT SUMMARY - After datalogging many times for the past months I have concluded the M112 port and polishing show small performance gains. After correcting my a/f, I'm seeing a slight acceleration increase during WOT pulls (average of 1.35 seconds quicker from 30 to 100mph - all 3rd gear pull). My intake temps are about the same as before during normal driving, but during high speed runs (throught the gears shifting at 6k rpms) the max temp I see is ~160* (I have seen as high as 180*+ before) with an increase in MAF counts (40-50) and a peek manifold pressure of 8psi at the end of the pulls. This is with an ambient temp of 73*. The decrease in peak intake temps are showing a difference in final max timing from 13.5* to 15*. If I altered the motor to allow for greater volume efficiency I'm sure the gains would be more noticeable. I think the Mustang GT exhaust has to go for better flowing system. My highway economy has increased slightly. I'm observing ~27MPG with 90highway/10city and all highway trips have shown 30-31MPG. I believe I'm also seeing greater engine vacuum than before. Deaccellerations are showing 23-24" and normal cruising has averaged 1-2" greater than previously recorded.

Throttle Body/Inlet Manifold/Blower

I drained the gear case oil and set it aside to reuse it later. This stuff smells like puke. The gearcase/rotor assembly pulled out of the housing case rather easy. Before I started porting on the case I took a small amount of RTV and some aluminum foil and sealed off the bearings to avoid getting aluminum shavings in them. When I'm ready to assemble the Eaton, and it's completely cleaned, I'll remove my sealant patches. Some before and after pics:

Air outlet before, and after enlarging. The 4 small oval ports are for pressure backflow. They're there to help quiet the blower by widening the pressure vector of the outlet port. A side effect of this is a reduction in pressure output. So these ports are not enlarged. The outlet porting isn't as massive as a Steggy porting because that type of volume increase isn't needed for the little 3.8. Good porting takes into account volume and velocity. Over porting decreases performance when the air charge velocity (energy) is lost.

Air outlet from inside before, and after. I repacked the rear case needle bearings with the hi-speed synth grease Eaton uses. I ordered the grease from zzperformance. The grease for the M112 is the same as the M90 used in the Pontiac GTP.

A couple shots of the case air inlet before, and after. Material was removed from the lower pressure/inlet floor. Material was also removed from the back of the inlet cavity, quite a bit actually. A contour was created before the large opening that is now the IAC valve inlet. When I first installed the Eaton, this cavity was cleaned of oil residue and operational discoloration. After putting 20k miles on the car with the blower on, the discoloration (darker brown areas) indicates where the air flow had to make abrupt flow/direction changes leaving heavier deposites on the cast.

Stock throttle body before and after. The hard edges of the bores were given a nice large, smooth radius and polished as well as the outside. I also filled the IAC valve port holes in the thottle body and inlet manifold with a silicone sealant. They're no longer needed because I use a remote valve.

I reinstalled the blower back on the car and took it for a quick spin. No vac leaks and it ran great, despite not liking the 7 month old fuel still in the tank. The blower whine at WOT is noticably louder. I won't know any tangable performance effects the porting has until I run the rest of this old gas out and start datalogging/tuning. I ordered the Innovate XD-1 wideband gauge to help me tune and fill the last opening in my triple gauge pod.

I took the car out today for a couple of short 15-20 minute putts around town. Just enough to warm things up good and let it cool down for a hour or so. The last time, I took it down the freeway to let it sit at cruising speed. Turning around to get back on the freeway to head home, I got into the throttle and cranked it up. At ~5k rpms the Eaton was pumping out ~9psi, and climbing. Before the porting, the best I could get with the 3.55" pulley was between 6.5-7psi. Now, between 5.5-6k rpms it reaches 10psi. That's an increase of 2.5-3psi! NOTE: this was with ambient temps around 58-60*. With temps in the 70*s and higher I have not seen it reach this manifold pressure.

And the tuning begins

The Innovate XD-16 is now connected to my LC-1. This is a great little gauge. The color sweeps are programmable and it can be setup with a warning function. It came programmed with a sweep of 9 to 20. I don't see a need to have it dancing around all the time in the 14.7 area, so I set it to sweep from 10:1 to 13:1. During average driving the sweep is pegged to the right (13) which is fine with me. The numberical display still shows from 9 to 20. I programmed the warning function to alert me for readings between 11.8 to 12.8. any reading in this area for .5 seconds causes the gauge to flash.

It was great weather Saturday for datalogging/tuning. Ambient temps were in the low 70s. Originally I thought I had a lean condition, but it turned out I had a slight air leak around the throttle body/inlet tube seal. Datalogging four 3rd gear WOT pulls (35-100mph) show an increase in MAF counts, Air#/min, IAT and manifold pressure. My air filter housing is still letting engine/rad heat into the engine. The temp sensor I installed in the filter housing shows and increase in inlet temp from 0-30mph and 70mph and up. This is adding to my intake temps which are pulling a lot of timing to keep it safe. By ~5.5k rpms (~100mph) I've got IATs reaching 160* (inlet temp of ~90*) with a final spark of 13.5* and an A/F of 10.6. With 92oct it should be safe to lean it up a tad to 10.8-11.0. With all the pounding and testing I did this weekend, I still averaged 26mpg on this fill up - not bad.

Page 1: In the beginning - Fall 2003
Page 2: Let the modding begin - Fall/Spring 2004
Page 3: Deer hit damage - Summer 2005
Page 4: M112 Blower Install - Spring/Summer 2006
Page 5: Suspension/Drivetrain - Winter/Spring 2007
Page 6: Eaton M112 Porting Project - Winter/Spring 2008 (you are here)
Page 8: Modification List