Imrc
#3
08-30-2005, 10:15 AM
Posted this in the other forum, hope it helps.
Make sure that the IMRC controller is functioning...you should be able to feel the cables behind the passenger side of the intake move (careful putting your fingers in a running vehicle engine bay) when the RPM's rise above ~3250 RPMs. And in my car...if all is quiet I can hear a distinct "click" when passing 3250 rpms.
IMRC cleaning is a fairly simple process. There are several writeups over at the Corral. And i've been meaning to do one for quite some time.
IMRC's stand for Intake Manifold Runner Control as stated above. Only 96-98 Cobra's had it. But "similar" setups are seen on the FR500 Intake, and the Lincoln Aviator Intake.
It was Ford's attempt to create (or salvage) Low end torque on these huge head DOHC cars. The early 4V Cobra heads...known as the "B-series" or "Swirl Port" Heads are unique, in that they have 2 seperate intake Port runners. A square shaped Primary port, and a round shaped Secondary Port. The IMRC's sit between the Lower Intake Manifold and the Cylinder Heads, and a shaft is attatched to butterfly valves that reside inside each secondary Intake port.
The reason for this is because, the B series cylinder heads have one of the largest intake port volumes ever produced. The primary Intake port is 107cc's, secondary being 115cc's. That's a total Intake Port of 222cc's of intake volume. Large intake volumes = poor intake charge velocity. The volume is too large on the B-series head. Which is why they make for amazing Forced induction heads...but comparatively speaking "****-poor" N/A heads (when compared to 99-01 C heads, FR500, or 03/04 Cobra heads.)
INTAKE VOLUMES OF VARIOUS MOD ENGINES (cc)
96 - 98 C 107 Primary/ 115 secondary 222 total
99 - 01 C 177
03 Cobra 177
FR500 160
96 - 98 GT 146
PI Heads 159
SVO 173
These butterflies remain closed from idle to ~3250 RPM's, an IMRC controller engages a motor that pulls 2 cables that open the butterflies (much like your throttle plate on a throttle body.) This subseqeuntly reduces the effective intake port volume, and enhances low RPM velocity. It is only moderately effective at improving low end torque.
The reason that the IMRC's become a problem is because the B series heads only inject fuel into the primary intake port. The PCV valve spits oil into the intake, and it becomes caked (anyone who has pulled the intake hat on a B series Car knows what i'm talking about.) The primary port is crystal clean...when compared to the secondary port, and that is because the primary port see's fuel. This fuel and air cleans the port, and the oil doesn't have the ability to stick or "gunk" up on the plates like on the secondary port.
So what happens is over time this Crud cakes up on the IMRC Butterflies..but more detrimentally on long turn radius and back of the secondary intake valve.
This decreases power significantly, and the IMRC's should be cleaned at least once a year. What's more is...if the IMRC's become so dirty that they cannot open...you are losing your other intake valve...and performance will suffer greatly.
IMRC's can be deleted, but on a stock or near stock car it isn't worth the driveability issures, and loss of low end torque. Only on Short runner cars, pulling more RPM's or significant Rear end gear with many bolt on's...or Forced Induction cars should delete IMRCs.
Anyway...know you all know!
__________________
Make sure that the IMRC controller is functioning...you should be able to feel the cables behind the passenger side of the intake move (careful putting your fingers in a running vehicle engine bay) when the RPM's rise above ~3250 RPMs. And in my car...if all is quiet I can hear a distinct "click" when passing 3250 rpms.
IMRC cleaning is a fairly simple process. There are several writeups over at the Corral. And i've been meaning to do one for quite some time.
IMRC's stand for Intake Manifold Runner Control as stated above. Only 96-98 Cobra's had it. But "similar" setups are seen on the FR500 Intake, and the Lincoln Aviator Intake.
It was Ford's attempt to create (or salvage) Low end torque on these huge head DOHC cars. The early 4V Cobra heads...known as the "B-series" or "Swirl Port" Heads are unique, in that they have 2 seperate intake Port runners. A square shaped Primary port, and a round shaped Secondary Port. The IMRC's sit between the Lower Intake Manifold and the Cylinder Heads, and a shaft is attatched to butterfly valves that reside inside each secondary Intake port.
The reason for this is because, the B series cylinder heads have one of the largest intake port volumes ever produced. The primary Intake port is 107cc's, secondary being 115cc's. That's a total Intake Port of 222cc's of intake volume. Large intake volumes = poor intake charge velocity. The volume is too large on the B-series head. Which is why they make for amazing Forced induction heads...but comparatively speaking "****-poor" N/A heads (when compared to 99-01 C heads, FR500, or 03/04 Cobra heads.)
INTAKE VOLUMES OF VARIOUS MOD ENGINES (cc)
96 - 98 C 107 Primary/ 115 secondary 222 total
99 - 01 C 177
03 Cobra 177
FR500 160
96 - 98 GT 146
PI Heads 159
SVO 173
These butterflies remain closed from idle to ~3250 RPM's, an IMRC controller engages a motor that pulls 2 cables that open the butterflies (much like your throttle plate on a throttle body.) This subseqeuntly reduces the effective intake port volume, and enhances low RPM velocity. It is only moderately effective at improving low end torque.
The reason that the IMRC's become a problem is because the B series heads only inject fuel into the primary intake port. The PCV valve spits oil into the intake, and it becomes caked (anyone who has pulled the intake hat on a B series Car knows what i'm talking about.) The primary port is crystal clean...when compared to the secondary port, and that is because the primary port see's fuel. This fuel and air cleans the port, and the oil doesn't have the ability to stick or "gunk" up on the plates like on the secondary port.
So what happens is over time this Crud cakes up on the IMRC Butterflies..but more detrimentally on long turn radius and back of the secondary intake valve.
This decreases power significantly, and the IMRC's should be cleaned at least once a year. What's more is...if the IMRC's become so dirty that they cannot open...you are losing your other intake valve...and performance will suffer greatly.
IMRC's can be deleted, but on a stock or near stock car it isn't worth the driveability issures, and loss of low end torque. Only on Short runner cars, pulling more RPM's or significant Rear end gear with many bolt on's...or Forced Induction cars should delete IMRCs.
Anyway...know you all know!
__________________
#5
08-30-2005, 12:08 PM
Yes the gaskets are infinitely reusable as long as they are not torn or bent. Follow all the proper torque seqeunces and values and you'll be fine. Double check all your connections, PCV, EGR, IAC valve...and everything.
#8
08-31-2005, 05:27 AM
Originally Posted by cobra4123
Okay question..... they vavles on the butterflies look ****ty (black or as rick james would say DARKNESS!!) is that common in a cobra with over 100,000 miles?
#9
08-31-2005, 05:31 AM
not yet goin to do that tonight. heard you need to index the crank to close the vavles in a single port and do them one at a time as to not get anything in the motor. is that from the gas only going in the main port? would larger injectors be better to increase fuel?
#10
08-31-2005, 05:41 AM
Yes at 100k miles the butterflies will look horrible...the secondary intake port and valves however is going to be the gunky part. You need 6-7 cans of Carb cleaner (cheap stuff works just fine), and I made a little scraping tool using a large screwdriver with an angle head tooth brush Duck taped to the end. This helps get to the back of the port and valves on secondary.
Indexing the cran is necessary...and fortunately I got them lined up so that all Intake valves were closed except for 2 cylinders. I then taped off cylinders as I went around cleaning. (It makes a mess)
Take your time and be patient and it'll go smoothly.
The reason the secondaries are so dirty is because they see no fuel. Larger injectors on an N/A car would be a waste of money...and would require a tune. There is no solution to this except some put an inline oil seperator on the PCV valve, but oil still gets past it. Just have to live with it.
Indexing the cran is necessary...and fortunately I got them lined up so that all Intake valves were closed except for 2 cylinders. I then taped off cylinders as I went around cleaning. (It makes a mess)
Take your time and be patient and it'll go smoothly.
The reason the secondaries are so dirty is because they see no fuel. Larger injectors on an N/A car would be a waste of money...and would require a tune. There is no solution to this except some put an inline oil seperator on the PCV valve, but oil still gets past it. Just have to live with it.
#12
08-31-2005, 08:04 AM
Seafoam is a temporary fix...it might take the edge off...but once you see the backs of the ports and valves you'll realize the only way that the Caked Deposits are coming off is with good old fashioned Carb Cleaner and Elbow grease.
If you do it properly, the secondary ports, IMRC,s and intake will all be squaky clean...no need for Seafoam.
The In-Line oil seperator will help, but people have put 2 separators inline prior to the intake and still see deposits on the intake runners...so it's definitely on the valves as well. A wet shot of nitrous might help
Philip K.
If you do it properly, the secondary ports, IMRC,s and intake will all be squaky clean...no need for Seafoam.
The In-Line oil seperator will help, but people have put 2 separators inline prior to the intake and still see deposits on the intake runners...so it's definitely on the valves as well. A wet shot of nitrous might help
Philip K.
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