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  • 10/4/2012
Upper Intake Manifold This is a very common upgrade for many of you out there. The "standard" option for upgrading these parts has been the Diamante, Eclipse GTS, or XG350 manifold. The reason for this switch is due to the design of the OEM V6 Galant and Eclipse GT intake manifold having "squished" intake runners. This design can affect how efficient the air flows into the combustion chamber, as well as how much air is taken in. Also between the "squished manifold" and one of these upgrade manifold options is that they can increase better mid-range to upper mid-range performance. 3.5L 6g74 Diamante Upper Manifold Below shows pictures of the stock Galant/Eclipse GT upper intake manifold side by side with the Diamante manifold. You will see the obvious difference is the intake runners between the two. Also the other clear difference is the size of the air inlet section of the manifold before it goes into the runners. The throttle body mounting plate is also a different size (bore is larger on Diamante than the stock unit). The differences with swapping from the stock manifold are fairly limited and "minor." When you look at a stock manifold side by side with the Diamante manifold you will clearly see how the stock intake runners are "squished" and the size of the manifold where the throttle body bolts to is smaller.The stock MAP Sensor will fit onto the Diamante manifold, but you will have to fabricate a longer EGR tube to run from the rear exhaust manifold to the upper intake manifold. This is something that can be "blocked" if the build requires that route, but for the majority of people who need to pass emissions it is in your best interest to have a piece fabricated. The manifold is also going to set your throttle body off more to the driver's side of the engine bay due to the straightened intake runners. This is only a minor issue and you should be able to fabricate the correct intake piping for the bend needed. For some, depending on the specific build you may need to relocate the battery from the stock location. The Diamante Upper Intake manifold has an inlet size of about 69mm, with the potential to safely increase the bore 3-4mm. The stock manfiold has an inlet size of only 60mm. XG350 Upper Intake Manifold This is another manifold option for those who want to make the swap. In my eyes, and even in your own (as you can see in the photos), this is the "best" choice for a manifold upgrade. The throttle body inlet size is the same as the Diamante unit (roughly 69mm). With the 3 piece type design of this manifold it is a better option for those seeking to build even more performance of the 6G72/6G74 platforms. If you are building a heavily modified N/A engine, or a boosted engine, the manifold can be seperated and a custom intake plenum assembly fabricated to fit the runners section. Doing this type of fabrication is generally needed for those running a larger throttle body such as one from the Infinity Q45 which is a stock 90mm unit (largest production TB made). Below pictures the XG350 manifold side by side with the early model Diamante manifold. You will notice a sizeable difference between the two in the plenum areas. Also note that the MAP sensor locations are on opposite sides of the manifold as well. The EGR mounting location is about the same, but the EGR valve from the Diamante (or stock manifold too), cannot be used on the XG350 as you will see in the photo they are different. The XG350 actually uses a EGR valve that has the exhaust gas pipe running directly into the EGR valve (which makes it easy to fabricate a piece for those with emissions). The Diamante manifold has a plenum diameter of roughly 91mm (3 9/16"), whereas the XG350 manifold has a diameter of roughly 125mm (4 7/8"). There is additional volume in the XG350 plenum as you can see in the photos of the Middle section of the manifold. Note, I have removed the valves within this section as these are not needed for my specific build. This is something I do want to look into further to make it fully functional for others who could benefit from the functionality in the entire range of this manifold's intended design. The XG350 uses a sensor/motor control on the valves to regulate the amount of air that flows through the manifold assembly and into the combustion chamber. The primary section (Red colored area in cutaway photo) utilizes the smaller runner diameter internally to help increase the low end-mid range torque. With the higher RPMs the sensor/motor will open the secondary valves (unpainted area in the cutaway photo) to allow an increased amount of air flow that assists with increased torque in the mid range-high end. This photo shows you the material that can be removed to combine the primary and secondary runner ports into one large runner section out of the plenum Looking into the center section, with the rear part of the plenum attached you can see the plastic dividers inside that feed the primary runners when the valves are closed up. When the valves are opened the majority of the incoming air flow will enter through the larger ports of this section. Here the rear part of the plenum is removed and shows you the plastic runner inserts mounted, and then with them removed for applications such as mine where they are not needed; Intake runner length also has an affect on performance as well. Below shows the runner length (within 1/4") difference between the Diamante manifold, and the XG350 manifold. The Diamanter manifold (first photo below) has a length of roughly 12" to from the lower manifold mounting surface to the edge of the plenum. The XG350 manifold has a length of approximately 10" from the same locations (in this case to where the middle section bolts to the runner section). 6g75 3.8 Non-MIVEC Upper Intake Manifold This manifold currently has shown excellent power increases over the other manifolds (though I need to verify if XG350 manifold has been compared still). There are people who have seen an increase of 15whp from swapping this manifold onto their 3.0L or 3.5L engines, with a tune. The runner length of the 6g75 Non-MIVEC manifold is about the same as the Diamante (12"), though with a slightly larger plenum volume and design (not rounded like Diamante or XG350 Manifolds). Photo below shows the inlet diameter of the 6g75 Non-MIVEC manifold (I have not yet measured this but will as soon as I find my digital calipers). The manifold has a Q45 TB adapater bolted to the TB flange which reduces the 89-90mm opening down to the 6g75 TB flange size; Throttle Body Now before you jump into purchasing these items it is important to know the details of the upgrade, and there are some differences you need to know about. The stock 3.0L 6g72 throttle body has an internal diameter of 65mm whereas the 3.5L 6g74 Diamante is 68mm. There is obviously only a 3mm difference in size here, so you have decide if the upgrade is worth the extra 3mm. Also, the Diamante throttle body is sometimes labeled as a "Bigger Bore" throttle body upgrade. This is in a sense true as it is larger than stock, however not one to be considered a true Big Bore Throttle Body. The majority of big bore throttle bodies will step the internal diameter up anywhere from 5-10mm, or more depending on the requirements of the engine. Another issue with the Diamante throttle body is that the sensors (TPS and IAC) are different from the OEM sensors. The Diamante throttle body sensors have the same pin out as the stock ones, so you will need the pigtails for these sensors from the donor vehicle. The difference between the Diamante IAC and TPS sensors and those on the 1999-2003 Galants, or 2000-2005 Eclipse differ as shown in the photos below. The IAC plugs have the same number of pins (6), but the plug size is completely different. As current options are limited for a larger bore throttle body without additional fabrication, the increased size of 3mm is minimal and hardly worth the cost when you look at what these normally sell for. With any one of the options for upper intake manifolds out there, combined with a stock throttle body the improvements will be justified in just the manifold swap. There is another option for a larger throttle body (Infinity Q45 90mm TB), but it will require farbication and really only suited for those with heavy engine modifications to demand the increased air flow.
BlackHeart Motors (BHM) - Mitsubishi Certified Technician - Enthusiast - Owner www.blackheartmotors.net
  • 10/10/2012
Very excellent read! V6 Mitsu owners shall appreciate this!
If you talk the talk, you better crankwalk the walk.
  • 10/10/2012
Agreed. Have any knowledge on the lowly 4 cylinders?
  • 10/10/2012
I know a little... lol What kind of stuff are you looking for?
BlackHeart Motors (BHM) - Mitsubishi Certified Technician - Enthusiast - Owner www.blackheartmotors.net
  • 10/12/2012
Originally posted by SPDFRK
I know a little... lol What kind of stuff are you looking for?
Hmm, anything really I guess. I know the cyclone manifold is a variable length manifold of sorts, but it does not get much attention or praise by the DSM community. I would think something that would help broaden the torque curve and doesn't require a full standalone computer would be more sought after.
  • 10/15/2012
Originally posted by drxlcarfreak
Hmm, anything really I guess. I know the cyclone manifold is a variable length manifold of sorts, but it does not get much attention or praise by the DSM community. I would think something that would help broaden the torque curve and doesn't require a full standalone computer would be more sought after.
But the cyclone is jdm bro, broseph, brotato, brodie bro broman. Yeah the DSM community does not give it much praise. It almost reminded me of the age old 1st gen manifold vs 2nd gen manifold.
If you talk the talk, you better crankwalk the walk.
  • 10/15/2012
Originally posted by talonIV
But the cyclone is jdm bro, broseph, brotato, brodie bro broman. Yeah the DSM community does not give it much praise. It almost reminded me of the age old 1st gen manifold vs 2nd gen manifold.
Haha, yeah it is JDM, just like most awesome things we don't seem to get... Pal... Lol, supposed to be the best of both worlds right?
  • 2/11/2020
Nice, good to hear it is running better!
  • 3/11/2020
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  • 6 months ago
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