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resident crossplatformer
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Discussion Starter · #1 · (Edited)
I promised to do this thread, I know nobody really said that I should but as I am probably the only person to date that has or had no less than 4 different versions of 6g7 SOHC 24 valve cylinder heads sitting in my garage, I might as well while I'm at it

for the sake of cutting down on time typing and for my own sanity
6g74= SOHC 6g74
MIVEC = 6g75 MIVEC
the purpose of this thread is two fold; first to show the differences between the 6g75 MIVEC and the 6g74, and second to show the usability of the 6g74 with the use of 6g75 MIVEC parts (and vice versa). My goal is to give data to give the reader information to build a lower cost built engine while reducing down time with your car as well as providing a potential source of low cost performance parts. Any and all internal engine work should be done by the highly skilled and/or by professionals, this is not for beginners (other than for research) and I will not take any kind of resposibility for any mistakes that can lead, or have lead to engine and/or vehicle damage nor any monentary loss, I can at least help with some troubleshooting but not much else, I will document and post as much as I can, but for anything that I might have gotten wrong, which if you find anything that is incorrect, let me know, I will correct it after I can confirm it. While there are some parts that can't be considered performance parts over the OEM 6g75 MIVEC items, such as the stock 6g74 injectors, lower intake manifold, upper intake manifold, heads, and so on, these will mostly be documented just for comparison sake, however if anyone plans on doing a two injector per cylinder set up, using OEM fuel injectors would at least be theoredically a reliable way of going about it.


let's start with my most recent big purchase, my 6g74

I already took the time to take off the upper intake manifold, throttle body, engine cover and a few other parts, I won't be covering these parts in the comparo for reasons I will mention later, the upper IM is in the lower left hand corner, my Galant is the grey car in the background


here the 6g74 lower intake manifold, it is of a similar design, ports are smaller to suit the smaller displacement, but it is completely incompatible with 6g75 MIVEC parts


here is a 6g74 fuel injector, it has a smaller flow rate than a 6g75 fuel injector, rated at 270 cc's
this is because there is 4 holes for fuel to travel through versus the 12 the 6g75 fuel injector, I wish either of my camera's are able to pick up this detail making it at least theoretically possible to have several different variations of the same fuel injector with different flow variations which is only different sprayer disks (basically a flat nozzle with several ultra fine holes drilled in it)


and this is a 6g75 MIVEC fuel injector, if memory serves, the none MIVEC's are rated at 305 cc's, I would expect the MIVEC's fuel injectors to be rated at least as high


and it appears that the 6g75 fuel injectors are compatible with the 6g74 fuel rails, I should note that these fuel rails are for cars from the factory (such as my galant) or are converted to with a return type fuel system


here is a MIVEC 6g75 (I'm just going to refer to the 6g75 MIVEC as just 'the MIVEC' from here on) lower intake manifold gasket on the 6g74 cylinder head, it does fit, not conformed to the intake port shape, but it fits


here is the MIVEC lower on the 6g74 heads with the 6g74 fuel rails, as is clearly present the 6g74 rails DO NOT work with this lower, however the MIVEC lower intake manifold is compatible with these heads


and vice versa


here is the MIVEC's upper intake manifold gasket on the 6g74 lower, more parts that are incompatible, however for me, this just further reenforces the shear size of the MIVEC's breathing capacity


here is something for those of you short on cash, if you need a new rear upper timing cover (or a new front upper and lower covers) and can't afford to go to the dealership, it is possible to use these parts in combination


shot of the 6g74's front head without the valve cover, I have seen this sight waaaay too many times with my 6g72 than I feel like I should, this is an engine with fixed cam timing, therefore is simpler, also the cover is off as I was originally planning on this being an ending point of part 1 when I first shot this, but I didn't get around to making the thread then, also the head is coming off


a side by side comparison of the 6g74 head and the MIVEC head, I will take a picture comparing (actually a full comparison) a none MIVEC 6g75 head next to the MIVEC head and the 6g74 head later on


close up of the 6g74 combustion chamber


close of of the MIVEC combustion chamber, needless to say, the 6g75 valves are HUGE, the exhaust valve on either version are about the same size as the 6g72/6g74 SOHC 24 valve's intake valves, which is directly related to how much more 6g75 heads can flow


most importantly the MIVEC heads are compatible with the 6g74 block


as are the MIVEC valve covers to the 6g74 heads


but not the other way around


for those of you curious, or those googling around and ignoring the existing flow potential of the 6g75 heads, you can in fact use the COP coil packs with the 6g74 heads


here is a near side by side comparison between the 6g74 (or 6g74M, I have no idea if that makes a difference) piston and that of one out of the MIVEC, note the complex crown shape of the 6g74 piston, if you look closely, the pistons aren't exactly dished, they have a mild dome as well as shallow valve reliefs, compared to the MIVEC piston, in addition to being slightly larger, that it has mostly a flat top with a millimeter scale dome with valve reliefs immediatly present, weather the 6g74 pistons have coated skirts like the MIVEC pistons, I cannot say yet, but more pictures will follow


next time, bottom end and exhaust manifolds
 

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chucknasty
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in order to use 6g75mivec heads on 6g74 either heads must be scaled down or use of 6g75 crank due to very low compression
 

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resident crossplatformer
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Discussion Starter · #3 ·
Custom forged pistons would be a requirement in that case to correct for the drop in compression
 

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What I am most curious about is the possibility of a straight "bolt in" all-wheel or rear wheel drive transaxle. say out of a 3000gt vr4.
 

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resident crossplatformer
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Discussion Starter · #6 · (Edited)
the 3000gt VR4 / Dodge Stealth R/T awd transmission will bolt on no problem, however like a lot of (if not all) Mitsubishi's built after 1999 that are based around a FWD platform, our transmissions are on the opposite side opposed to the 3s transmissions (ie, if you use one of there transmissions, you will have at least 5 gears in reverse)

however, I suppose with enough money you can make it work, a gal on c3g has spent over 30 grand on her car, she uses a 2g AWD automatic gearbox, iirc that conversion alone cost in the neighborhood of 12 grand (lots and lots of custom work), which, honestly if I had that much money I would spend on a transmission and parts to go AWD, I would get a billet case that could still use the 4g GT or 3g GT input and output shafts (or use EVO components so I can use a multi plate clutch), differential and so on, a custom cast or machined OE cross member to allow for the use of a transfer case, all with the ability to use an Evo or 3000gt transfer case


and thank you

I promise at least around when I am done with finals (2 weeks on Thursday) I will get to the bottom end, sooner or later I will compare blocks, but first the former, oiling system and the exhaust manifolds
 

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chucknasty
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i just found out yesterday in 1997 mitsu made a 6g74 dohc mivec that made 274 hp stock. i want that engine!!!
 

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resident crossplatformer
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Discussion Starter · #8 ·
I don't blame you, I know a guy on 3si swapped one of those in (engine was imported), shame that he didn't take many pictures of the heads disassembled, I'd love to know more about the design, or at least know the flow numbers and cam specs, there was also a direct injection and MIVEC version that was put into production

I also know there is a MIVEC version of the 6g72 that produces 266 hp @7000 rpm and 222 lb/ft of torque @ 4500 rpm
shame those weren't released over here, but I think that the reason why these engines produce so much power compared to, you know, a factory 6g75 MIVEC is that the former cases weren't built for the emissions standards of just 6 years ago, rather than 15 years ago

people, please (including those googling around, I know the pictures of this thread can be found on google images), if you get ahold of any of the MIVEC DOHC 6g7 engines, please at least flow bench these cylinder heads and post the results on any major Mitsubishi forum, it will at least help educate everyone the potential of these heads
 

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For that kind of money I would just by an Evo X. The chassis of my 46 Chrysler kustom has over $60k in it! Ridiculous. Anyway, people like you, who take the time to do these kinds of comparisons, are the reason new solutions are found. Thanks.
 

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The 6G74 and the 6G75M injectors you have pictured above have the same flow rate. You can also exchange the injectors between the two without any adverse effect.

There's also a second variation of the 75 mivec heads with only the one mivec control valve mounted on the rear head with a feed line crossing over to the front. Have these heads fitted to my engine.

Otherwise great effort, looking forward to more.
 

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resident crossplatformer
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Discussion Starter · #12 ·
I don't entirely doubt you, right now I'm playing off existing values, I do plan on getting all 12 of these fuel injectors flow tested so we can also work out the factory variances as well
 

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resident crossplatformer
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Discussion Starter · #13 · (Edited)
well, been awhile since an update, and school starts for me today, so I might as well update this thread

today we will be looking mostly at the oiling system


first, as a reccomendation for anybody tearing down an engine, I strongly suggest getting ahold of some very high viscosity oil and lightly coat the outer surfaces of the block after spraying it down with WD40 and then coat the cylinders, this is to protect these surfaces from rust

I got a free quart of racing diesel oil from a friend


here's the lower oil pan removed from my 6g74, I actually had to on this engine as the drain plug was completely siezed to the threads, also when tearing down engines, I suggest buying a ton of lunch baggies of several sizes or a multi pocketed box to keep bolts, nuts and other hardware orginized


obviously you first will have to remove all the bolts connecting the upper pan before you can take it off, but because of the adhesives that are part of the gasket, you can't directly pull it off, Mitsubishi in a stroke of genius put threaded holes on each side of the super long bolts, weirdly on this specific side of the pan, this bolt hole is threaded for a 13 mm, which in my teardown of my MIVEC and various projects with my Galant, I don't think Mitsubishi has every used any 13 mm bolts


but a 14 mm bolt works just beautifully on the other side


you just need to tighten this bolt with a 14 mm wrench or ratchet head


and there you go, in this phase, DO NOT tighten this bolt extremely fast or you will score or scratch the cast iron, just go slowly and cut various bits of silicone that are hanging between the gap between the mating surface of the block pan rails and the oil pan


there we go, the upper oil pan is off


a close up of part of the main girdle, crank and a connecting rod, note the shiny surface, this is because the engine was balanced at the factory


this is the the 6g74 windage tray and oil pick up, note the pick up screen has a near hemispherical shape, the SOHC 24 valve 6g72 used the same design, I'm not confident that in heavy cornering that this will work well against oil starvation when oil is sloshing around


and here is the pick up from the MIVEC, while it does have less surface area, the relatively tiny pick up opening should resist oil starvation considerably more


a random shot looking up towards the bottom of a piston, note that part of the piston skirt is protruding from the cylinder


this is the MIVEC's windage tray on the 6g74 main girdle, yeah, not compatible here


here's the MIVEC's windage tray and the 6g74 windage tray


here is the 6g74 windage tray on top of the MIVEC's, note that not all the bolt holes line up and the MIVEC's has another bolt hole



here's the main girdle from the MIVEC, this thing is very, very thick and beefy, I'm guestimating it weighs at least 15 pounds


here is the MIVEC main girdle on top of the still installed 6g74 girdle, yep, they are interchangable, also visable in this picture is that part of the 6g74 girdle tapers down, while I can't say this makes the 6g74 girdle is weaker as the 3s boys have gotten JDM 6g74's to put out over 1000 awhp, just for me, I will be using the MIVEC's girdle since I have access to a stronger part, that might change depending on is and if line honing is required to run the MIVEC girdle on the 6g74 block, it's a future conversation with my machine shop
also when tearing down these engines, note that there is an arrow denoting which way the girdle should be bolted on, which it is pointing to the front of the engine


on to the oil pump! also at this point back when I was tearing down the MIVEC during the summer, I poured some oil directly into the pump then rotated the engine by hand a few times so fresh oil is within the passages, I did the same here
also in my opinion, removing the oil pump from these engines is one of the most aggrivating things in the tear down phase


here are the 6g74 oil pump and the MIVEC oil pump, the only external differences between the two are that the MIVEC unit has 2 threaded bolt holes near where the filter threads on and the 6g74 oil pump does not
 

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BlackGuard Motorsports
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what a bunch of malarky! no turbos! ? wtf...


just kidding! great thread man.. good read for sure!:bigthumb:
 

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In your first couple of pictures, there is an additional coolant passage across each port of the exhaust side of the MIVEC of which the 6G74 does not have. 6G74 Rods will fit into the MIVEC. The MIVEC Engine is approximately 10mm taller than the 6G74. I'm pretty sure the oil pans are different due to exhaust routing. The 3000GT Vr-4 trans has alignment issues with the oil filter housing and the axle on the 6G75 engine. Along with if rotated, none of the engine mounts line up anymore.

As far as the cylinder head goes, the 6G75 MIVEC flows about 277 CFM on the intake and 179 CFM on Exhaust. Cylinder 2 shows a port and polish job on this same head. Stretching out the intake to flow 352 CFM Intake and 228 CFM on the exhaust. Granted these are peak numbers (i don't know what the max lift is on these heads so I can't quote exactly realistic numbers based off of cam profile. Pics or it didn't happen? I got cha covered ;)

 

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resident crossplatformer
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Discussion Starter · #16 · (Edited)
*you must spread more Reputation around before give it to Wingo171 again*
darn

thank you

I hope when you mean there is an additional water passage across each exhaust port, you mean those are internal to the heads and aren't changes within the blocks

also, is that extra 10 mm's just the total height of the engines or the deck heights?

edit: how I missed the additional water passage, I have no idea, it is very obvious when veiwing the mating surfaces, before I though these were some kind of oil passage, but coolant makes sense, when I have time I will measure the height of the oil pans, although I think this might be a combination of the intake manifold and the oil pan
 

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resident crossplatformer
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Discussion Starter · #17 · (Edited)
well, I said I wasn't going to compare the intake manifolds, but I though screw it and show this

by the way, upper= upper intake manifold, lower = lower intake manifold, gasket = gasket between the upper and lower intake manifolds

I'm going outside my normal format of text talking about what's in each picture for the first one

these are the upper intake manifolds, the MIVEC at the top, the 6g74 in the middle, and my factory 6g72 (SOHC 24 valve) intake manifold at the bottom, sadly this picture doesn't say much for the shear scale of each manifold, the 6g72 is easily the smallest of the three and I won't be in the rest of this section of the comparo, this also gives a decent view of the runner design and part of the plenum design, I don't need to say how much the 6g72 upper sucks in the total design, tiny plenum (I'm guessing one third the volum of the MIVEC upper and half the volume of the 6g74 upper), the squashed runner design



the MIVEC upper and lower with the gasket and the 6g74 units opposite


here is the 6g74 upper (top) and a MIVEC upper (bottom) flanges, note the difference in length


here is another shot of the MIVEC gasket on the 6g74 lower, although the port shape is the same, the MIVEC manifold has the runners spread even more


MIVEC lower and gasket (left) and 6g74 lower and gasket, you can see some more changes in design other than the spread runners, the fuel injectors are at a radically different angle than the 6g74 unit, also I must note my camera was slightly tilted so this gives a false view of what the angles on each unit is


the 6g74 upper runners, note how straight they are


the MIVEC upper runners, note they have a velocity stack profile cast into them


the lowers of the 6g74 and the MIVEC lowers, the 6g74 lower has a rail for positive cranshaft ventalation cast into it (which the MIVEC has cast into the upper) for providing each cylinder PVC, also take note the overall shape of each runner, there is also a good view of each port profile even with my camera's poor low light capabilities


close up of the 6g74 lower, you can pick out more details such as external casting flash, ports off of the PCV rail are pretty large, which I would think would give a high level of in engine vacuum


and the MIVEC lower, I'm falling back in love with this engine, there is a mild velocity stack profile cast into the runners, which perfectly suits the upper's design, I need to check again, I think this might have a reversed profile, which would radically increase air mass charge velocity, the casting quality reminds me of a high performance racing product


for shits and giggles I shot a picture of the 6g74 and MIVEC uppers next to the runners of a G6AU upper intake manifold (the unit off a Hyundai xg350's engine, which is basically a DOHC 6g74 but not as good as the JDM stuff), you can see a good range of runner designs over the years, also how massive the MIVEC upper is


a 6g74 fuel injector within a boss of the 6g74 lower, note the huge volume around the injector nozzle that isn't directly in the runner volume, the fuel injector is also at a steeper angle than the MIVEC's


speaking of which, here is a 6g74 injector in a MIVEC injector boss, note the very shallow angle, it is very nearly perpendicular to the ground when viewing from the top, also note the very small area around the injector nozzle, among the many, many design changes with the MIVEC makes me see how much work Mitsubishi put into this engine and how over the years how much has changed, the change with the fuel injectors sets the nozzles closer to the flow along with setting the injected fuel more directly into the airstream thus improving fuel atomization and therefore power, emissions and fuel economy rather than with the 6g74 lower where there would be a thick rich fuel seperated flow of gases directly paralell to a very lean in fuel seperated flow of gases, each making up the air charge, which would make the engine run richer overall and leading to a direct opposite of what I just describe with the MIVEC lower


you can directly see the differences in the runner profiles

conclusions: compared to the MIVEC upper, the 6g74 manifold is just dwarfed by it on top of the massively improved runner and plenum designs, the angled throttle body on the MIVEC upper is also a significant change that I could list off any number of them, most importantly this improves air distribuition, 24 valve SOHC 6g72 intake manifold is just adorable compared to the MIVEC's upper
 

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chucknasty
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should compare the nonmivec to mivec as there are differences
 

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resident crossplatformer
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Discussion Starter · #20 ·
I really wanna see a huge power all motor 6G
soon, I have a few parts to order and there is machining that needs to be done before this


all I have are the none MIVEC heads (which I will do a comparison to the MIVEC heads soon enough) , if I had the intake manifolds, I would gladly include them in my last post
 
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