KLG4 Intake Manifold Porting and Modification
A How-To Guide For The DIYer


     I discovered the KLG4 intake manifold quite a few years back by accident when I purchased a newer Mazda 626 engine from a very low mile roll-over.  The car was barely off the show room floor.  The engine didn't look like the standard KL but I could see that underneath it's somewhat similar exterior appearance that it was a true KL underneath.  So I tore down the KLG4 and began studying the differences and experimenting with the parts and pieces.  After a thorough examination of the new and odd-looking intake manifold I concluded that it could be a good performance performer with some modifications.

A little about the KLG4 Engine:

     The KLG4 comes in the 1998 to 2002 2.5L Mazda 626 cars.  The major differences are that it has Solid Lash Adjusters (SLA) vs. the Hydraulic Lash Adjusters (HLA) of the standard KL motor.  This change was made by the engineers to reduce problems inherent to HLA's when the tiny oil ports would become clogged.

     Then there is the crank which is cast iron vs. the forged steel and hard nitrided crank of the standard KL motor.  The crank is slightly lighter weight than the standard steely but this is not necessarily a good thing.  I would never exchange the durability of the hard nitrided -forged steel crank just for a slight difference in weight.  Lighter pistons, rods make the crank lighter when you have it balanced because of the weight that is removed to counter the lighter pistons/rods.

     The rear head has a machined place in the front cam cap/truss for a camshaft sensor as well as a mated cam pulley with a nub on the inside of it for the sensor to pick up.  And the cam lobes have a slightly different profile to accommodate the solid lifters as well as narrower surfaces where the lash gap is found.  Since the SLA's do not put pressure on the no-lift area of the bottom of the lobes then the area does not need to be as substantial as with HLAs that put pressure on the camshaft on the bottom of the lobes.  There is actually a small gap at zero lift.  This is called your valve lash.  Hydraulic adjusters actually maintain zero lash when they are operating correctly.

     The harmonic balancer on the KLG4 has a 36-1 ring on the back side vs. the 6-lobe of the standard KL motor.  This is because the KLG4 cars have distributor-less ignitions.  So instead of a distributor on the front head there is a blocking cap that goes in the hole and a bracket that ensures it does not pop out.  This bracket also serves as a mount for the coil pack.  It is a three-coil-pack where each coil fires two cylinders at the same time.  One of them is at the power stroke and the other is fired on the exhaust stroke.  So the  exhaust cycle cylinder that gets a spark is just a wasted spark and thus the system is known as a wasted spark system.  Three coils fire 6 cylinders by sharing a coil between two of them.

     The intake manifold is very much improved from the KLDE design.  It has a more open design.  Also with the KLDE and the KLZE long neck/curved neck the air enters the plenums nearest to the number 5 & 6 cylinders.  It has a longer path to the number 1& 2 cylinders.   And as many people know - longer path means more torque and lower top end.  Shorter path means less torque and higher top end.  Well the KLG4 intake manifold dumps air closer to the center of the plenums so that it is more equally distributed.

The How-To:

     To modify the KLG4 and help it to breath even better then there are a few things that need to be done.  The runners of the G4 are rectangle shaped on the outside just like the KLZE runners.  But the inside of the G4 runners have some added material just past the downwards bends on the flange end to help transition to the oval shape.  So if you remove this material to match to the KLZE heads and do a little polishing work then you can make them basically into KLZE runners.  So then the one thing that the KLG4 has that the KLZE does not is a shorter neck and more equal air velocity between cylinders.  The shorter neck can mean increased top end.  However -the throat of the KLG4 is a bit restrictive in un-modified form.  This can be remedied by a way of modifying the center wall that I found works very well.  To the right is a photo of an unmodified G4 throat area.


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     To make the throat area capable of more airflow I decided to combine the potential flow of both plenums by removing enough of the center divider so that it would share the same airway back to where it begins to open up some.  But I didn't want to loose much of the torque that the center divider creates.  So I came up with the Idea of "U" shaping the cutout so that it still produces some reasonable torque while allowing air to pass from one side to the other in the critical area.

     Then to further increase the flow potential I knife edged the divider.  But this is where it might get a bit tricky.  The right side has a small amount of meat that can be removed only in the area where the throttle cable boss is located on the outside.  So I removed material in this area some (avoiding any beyond where the boss is located).  So to equal the increased flow potential of the right side - I removed material from the left side on the divider wall.  So this essentially shifts the divider wall over some to the right to give the left side a little more air.  There is no boss on the outside of the left side of the throat so you really cannot remove much material from the outboard side of the throat area.

     This view is slightly shifted to show into the right side of the neck area and a little better view of the "U" shaped center divider.  Also -notice how I ground down the two "Volcano" looking stubs for the EGR.  Since KLZE's do not have EGR then these only become an obstruction for airflow and so I have removed them.


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     I chose to use the KL47 throttle body that is found on the curved neck 2.5L Millenia cars in the US and on Eunos 800 cars in Europe.  This throttle body has the same round shaped area surrounding the throttle body bore.  So the only modification needed to make it work is for a notch in the flange for clearance of the Idle Air Controller (IAC) flange.  To the right is a photo of the KL47 sitting on a non-modified KLG4 flange


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     To the right you can see where the G4 intake needs to be notched for clearance of the throttle body compared to an un-notched manifold.  The notch needs to be approximately cut to a height 1/4 inch above the bottom of the flange and approximately 1/4 inch deep.  This can be done with a die grinder for the rough cut and then later finished a little cleaner with a square file.


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     To modify the runners to transition to KLZE heads you will need a port matching template.  I make my templates out of .050 thick aluminum sheet and cut them to fit a KLZE head precisely for best line-up.  You can make this by hand with a jig saw, drill and Dremel tool with a few hours of work.  You can either first trace it all out on paper and then cut the pattern out with a razor or you can use a printed template that I plan to add to this website under the references section in the somewhat near future.  I have a lot in-work so don't expect it to happen in just a few minutes.

     After you have your template then you can use this to mark your heads with a Sharpie marker for porting.  My choice of tools has always been a Dremel tool with the flex attachment (lets you get much further into the ports).  First start by removing material near the edge to obtain the general rectangle shape.  Then after you have gotten the shape started then begin to remove the material moving backwards from the flange face and further into the port.   Try to carry the rectangle shape all the way back to the bend if possible as this is where it naturally transitions to the rectangle shape as the factory fillet feathers out.


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     This is a view of the port matching on one of the front runners.  Keep in mind that after doing this porting work there may be a few areas where the port to flange edge is a bit narrow.  This can make for a bad seal with the stock gaskets.  So I make all of my own intake gaskets from gasket material that most auto parts stores carry.  With a little bit of sealant on each side of the gasket -it will seal more positively than the stock gaskets might with a possible mis-alignment.

     The aft runners have a different bend because of the manifold configuration.  So when I remove material from the rear -I remove it in such a way that it helps the air to make the turn-around that is more severe than in the front bank of cylinders.  Notice how the front runner wall nearest the injector boss in the photo above is more rounded and how in the bottom photo it is the wall away from the injector boss that is rounded and the one on the injector side is more flat.  This shaping of the port helps to minimize the effects of the sharper bends on the rear runners and equalize the two a little more than stock.  So it is not just about removing material to make it flow more.  More/larger/bigger is not always better!  With all of my own work - my emphasis is more on efficiency than just "more".


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     I will be adding some photos of the vacuum connections and perhaps a diagram of how to hook it up.  Remember that the #5 cylinder runner has a "vacuum looking" nipple on it.  But don't be tricked by this one!  It is a port for boost sensing for the OBDII cars.  If you have an OBDII car that has a boost sensor for emissions then you will need this port.  But if you have an OBDI car then this nipple should be capped.