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BlackGuard Motorsports
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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
sweet!
 

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Discussion Starter · #22 ·
finished the teardown today!

looking at the rear main seals, they are almost perfectly identical sans lettering on the backs of them that on the 6g74 says '-2', the MIVEC's says '4-2 487'


6g74 on the left, MIVEC on the right


back of the MIVEC rear main seal


back of the 6g74 rear main seal


and onto the mainbolts


MIVEC on the left, 6g74 on the right, almost the same right? Well



6g74



MIVEC

yeah, they are basically identical, it's also entirely possible that I mixed a few of those pictures up


all of the 6g74 bolts, I came across a weird sort of optical illusion, maybe my camera picked it up, when I had all the bolts in a pile, the threads of surronding bolts made the threads of the bolts on top look very stretched, but they weren't, just something worth noting


and onto the girdle, as I have mentioned before, the girdle won't come off on its own


and as I couldn't find the 2x4 I used last time, I tried using the handle of one of my mallets, the girdle disagreed


finally found a 2x4, if memory serves, the MIVEC girdle (with the MIVEC block) has a slightly larger gap, with the 6g74, I could just get the corner of the board between the girdle and the oil pan rail


just push down lightly on the 2x4 and the girdle seperates from the block


and there we go, now comes the really difficult part, getting the pistons and rods out so the crank can be removed, due to the geometry of the rotating assembly, you have to have at least 2 pistons and rods (and all the rod caps removed) before the crank can be lifted out


and the MIVEC girdle drops in very nicely, I would like to get some main studs because there is a very small chamfer on the ends of the outboard most caps outwards towards the oil pan rails (if you understand what I'm describing, more pictures will follow tomorrow), so I could evenly line up all the bolt hols that go through the girdles


and finally the the crank is out, I must note for everyone tearing down a 6g74 or 6g75 variant engine, grab a towel that your not attached to, cut small holes in it, put head bolts through the holes with washers, you must remove multiple pistons+rods to remove the crank, as the 6g74 uses higher tension ring packs (and that mine disn't have much oil on the cylinder walls, although I should have applied some penetrating oil on the cylinder walls), if you don't, you will literally send a piston+rod flying out of a cylinder, luckilly every single time, each one landed in the drain pan below the engine into the vat of oil and antifreeze that has accumulated


and finally everything is out of the block


here's a 6g74 piston and connecting rod, I frankly have no idea who or what ART is, I'm guessing they are a subcontractor Mitsubishi uses
scratch that, they are, I found their website, this is a Japanese manufactor that makes them for OEM builders
anyway, I'll post ring and piston specs tomorrow compared to the MIVEC piston, I'll try to get my dad's letter scale again so I can ge the weight of the 6g74 rods, pistons and wrist pins
 

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Discussion Starter · #23 · (Edited)

here's all of the pistons and rods, sans one rod nut that fell off an oil pan rail (I had a flawed but seemingly good idea for organizing which rod nut goes to which rod bolt for each rod) down a cylinder and bounced to I don't know where
anyway, these will be for sale soon, with a set of ARP rod bolts, these would a very good budget alternative to aftermarket connecting rods


the 6g74 crank, this is one heavy bastard, but it is very well designed with a shorter stroke over the MIVEC crank at 85.8 millimeters rather than 90 millemeters, the 3S boys have machined down the main jounals of these and used them as stroker cranks for years, you can see the wide fillet on the rod and main journals, more pics to follow


the MIVEC crank drops in perfectly, I'll be letting my machine shop work with crank and rods to sort out clearancing, it looks like from the factory they did some clearancing work to begin with, which those pictures will follow later


a 6g74 main bearing half (that is in the block, not the main girdle) on the left and a MIVEC main bearing half on the right, not how very similar they are, at this point in time, all I can tell is the MIVEC bearing is more silver and has green on one edge to tell you which way it sits in the race and the 6g74 bearing is darker in color


and one more shot of a 6g74 piston, note that carbon got bast the first ring, I'll have more information later
 

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Discussion Starter · #25 · (Edited)
Great posts, thanks very much for taking the time to do this.
*you must spread more Reputation around before giving it to z80 again*

foiled again

thank you


I've been doing research lately, in a weird twist, the pistons that are out of my 6g74 aren't OEM (or as far as I can dig up), they are aftermarket replacements, meaning that my 6g74 was rebuilt at some point in time. Interestingly, when I checked the bore diameter with my calipers, the cylinder bores all fell in line with factory spec sizing (just a couple tenths of a millimeter below 93 mm, which is normal anyway as once the engine is warmed up, the cylinder and the piston expand out to spec), this means that whoever did the rebuilt must have used a honing brush. This also explains why there appears to be some clearance work done on the block already and what appears to be uneven sanding on the bottoms of the connecting rods, meaning that the bottom end was balanced as well.


I seem to have the weirdest luck with engines

edit: I might have pointed this out with later posts, my 6g74 engine was not rebuilt previous to when I purchased it, the odd manufacturers logo on the pistons (which there is also a Mitsubishi logo on them as well) were what was primarily throwing me off, even my machine shop was surprised the engine was not rebuilt, it kind of says something about the long term durability with the cross hatch pattern being that visible and the bearings being is such good shape
 

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MIVEC Cam Specs

Hey Fox, can you measyre the MIVEC CAM base circles for INTAKE (Low/Med/High) and Exhaust Lobes with pictures? I'm trying to go with a more aggressive cam profile and have lost this data form the stock cams.

Thanks!
 

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Discussion Starter · #27 ·
Hey Fox, can you measyre the MIVEC CAM base circles for INTAKE (Low/Med/High) and Exhaust Lobes with pictures? I'm trying to go with a more aggressive cam profile and have lost this data form the stock cams.

Thanks!
that I can, I'll be measuring cam specs tomorrow if I am not working, I also will have piston, connecting rod, wrist pin and piston ring info up tomorrow, also if I'm not working

by the way, aren't you the fellow that has a 6g75 MIVEC heads on a 6g74 block? Could you answer me this question, I can say in 99.9% confidence that no mods to the block need to be done to use these heads, but as a second opinion, did you have to have any mods done to your block to use these heads?
 

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that I can, I'll be measuring cam specs tomorrow if I am not working, I also will have piston, connecting rod, wrist pin and piston ring info up tomorrow, also if I'm not working

by the way, aren't you the fellow that has a 6g75 MIVEC heads on a 6g74 block? Could you answer me this question, I can say in 99.9% confidence that no mods to the block need to be done to use these heads, but as a second opinion, did you have to have any mods done to your block to use these heads?
I used a 74 JDM DOHC 3.5L block so i had to modify the coolant and oil passages on the MIVEC heads to work, not sure what needs to be done with the SOHC 74 you have. I also bored and stroked my 74 by utilizing the 75 crank (it dropped right in) in the 74 JDM block. The 74 rods and 75 rods are the same length, same pin diameter and same journal diameter..I believe the 75 rods are even stamped 74. The difference in pistons is the pin location, the 75 has ~2mm pin moved closer to the piston top.
 

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Hey fox, any luck with those cam base circle numbers? sorry to be a pain I just have the the cams on the grinder and they're waiting for that info.
 

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Discussion Starter · #30 ·
yep, just give me a couple minutes and I will have them up, well, the only hiccup I encountered was getting the base circle of the low lift low speed profile, my calipers can only reach so far and the profile is nearly just a base circle
 

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Discussion Starter · #31 · (Edited)
ok, the picture quality is pretty shitty, so here are the specs
low speed A (the super low lift profile): not able to be recorded
low speed B: 30.99 mm
high speed: 30.97 mm
with the typical error of my calipers, this should come out to 31 mm base circle for the intake profiles with a higher accuracy tool and/or for a new cam, it's safe to say that both the high speed and low speed profiles have the same base circle

exhaust profile: 31.96 mm, recorded on other profiles at 31.93 and 31.98 mm, with some better calipers and/or new cams, 32 mm base circle

this info at this point in time the base circle of the low speed profiles are different, other than that, the intake high speed base circle is confirmed to be 31 mm, the exhaust profiles have a base cirlce 32 mm, as recorded by itman3s, the low speed prolife base circles are ~32 mm


have a few pictures up regarding the valvetrain, still not that good quality, it's pretty weird to be honest, I know the complexities of VVT systems, but there are some really weird features I have just got to share

I hope that helps
 

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Wow, I thought for sure that the base circle of the B and high lift would be different. Crap well I guess I was wrong...when you visually inspect he base circles do they also look the same.. Sorry for the stupid question, just very surprised...
ok, the picture quality is pretty shitty, so here are the specs
low speed A (the super low lift profile): not able to be recorded
low speed B: 30.99 mm
high speed: 30.97 mm
with the typical error of my calipers, this should come out to 31 mm base circle for the intake profiles with a higher accuracy tool and/or for a new cam, it's safe to say that both the high speed and low speed profiles have the same base circle

exhaust profile: 31.96 mm, recorded on other profiles at 31.93 and 31.98 mm, with some better calipers and/or new cams, 32 mm base circle

I'll have a few pictures up regarding the valvetrain, still not that good quality, it's pretty weird to be honest, I know the complexities of VVT systems, but there are some really weird features I have just got to share

I hope that helps
 

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Discussion Starter · #33 ·
no, no, it wasn't a stupid question at all, this was on my to do list, but much later on, I guess in a way I take requests to measure specs and some comparisons :p

by the way, this was done with the cam still in the head, and yes, visually the base circles are identicle, although the exhaust profiles are between the high speed lobe and the low speed lobes makes it a little difficult

well, think of it this way, for the valve lash to be accurate for both the high speed and the low speed profiles, it makes sense for the base circles to be the same, either that or Mitsubishi could have altered the rocker ratio (well, made it larger) for the high speed profile and reduced the base circle and keep the same lash, buuuut in the respect to the valve lash, well, you'll see shortly
 

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Agreed, I thought the same about the valve lash but the roller on the high lift is larger then the other intake rollers and thought the ratio might be Different..
no, no, it wasn't a stupid question at all, this was on my to do list, but much later on, I guess in a way I take requests to measure specs and some comparisons :p

by the way, this was done with the cam still in the head, and yes, visually the base circles are identicle, although the exhaust profiles are between the high speed lobe and the low speed lobes makes it a little difficult

well, think of it this way, for the valve lash to be accurate for both the high speed and the low speed profiles, it makes sense for the base circles to be the same, either that or Mitsubishi could have altered the rocker ratio (well, made it larger) for the high speed profile and reduced the base circle and keep the same lash, buuuut in the respect to the valve lash, well, you'll see shortly
 

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Discussion Starter · #35 · (Edited)
first up a complete comparison between the MIVEC pistons and rods and 6g74 pistons and rods


6g74 rod and piston assembly on the left, MIVEC rod and piston assembly on the right, you can already pick out differences between the two, the 6g74 rod is thicker, the piston is a little taller. Meanwhile the MIVEC unit is thinner, the piston is shorter, has coated piston skirts and somewhat has a slipper skirt design


first up ring specs, the top ring for the 6g74 is 1.45 mm thick

6g74 second ring is 1.49 mm, or with the margin of error typical of my calipers, would be right at 1.5 mm

oil control ring is 2.98 mm, well, or 3 mm once error is acounted for

and a shot of the oil control ring expander

and the 6g74 bare piston, weighing in at 377 grams, also I made note earlier that it appeared these weren't OE pistons, I might have corrected this, well, they are and they aren't, the Mitsubishi logo is one side and ART's logo is on the other

weight of one true arc retainer, just one gram

weight of all the rings, 30.5 grams

weight of one 6g74 connecting rod (sans the bearing), in at 745.5 grams

lastly, the 6g74 wrist pin, in at 135.5 grams
combined weight of above, 1290.5 grams
 

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Discussion Starter · #36 · (Edited)
ok, time for the MIVEC parts

I have no idea where the picture went, the MIVEC piston weighs 382 grams bare, I really, really like this design, shame it is cast, it has a semi slipper skirt design, and accumulator groove

MIVEC wrist pin: 108.5 grams
ring specs, 1.21 mm top ring, 1.26 mm second ring, 2 mm oil control ring

MIVEC connecting rod, 625.5 grams


MIVEC piston, 382 grams


total weight of MIVEC piston/rod assembly (with wrist pin, true arc pin locks and piston rings), 1175 grams


length of the MIVEC pin

length of the 6g74 pin

inner diameter of the MIVEC wrist pin

inner diameter of the 6g74 wrist pin


and a shot of a bare 6g74 connecting rod and a bare MIVEC connecting rod, note both have ' 74 ' stamped onto it, the MIVEC unit has an ' S ' on it

thickness of the 6g74 rod

thickness of the MIVEC connecting rod, I should note these are slightly thicker than the none MIVEC 6g75 connecting rods

I don't need to post these specs, the 6g74 and MIVEC connecting rods are identical in bearing diameters and overall length

here, even look for your self, the 6g74 unit is on top of the MIVEC unit, they are perfectly the same length and journal specs



the connecting rods are both backwards and forwards compatible, seen here with the 6g74 rod mount with the MIVEC piston and vice versa


and here we can see some great detail on the bottoms of these pistons, the MIVEC unit has the pin towers moved pretty close together, the 6g74 unit has forced pin oiling both through the oil control ring and through these peep holes on the bottom


a more dramatic view of the differences in piston design, also this says a ton about the combustion chamber design, the 6g74 piston crown is covered in carbon deposits and the MIVEC unit has just a light coat, this means that fuel can be burned completely and thoroughly, thus much more power (on top of the higher compression ratio), better fuel economy and lower emissions, aslo clearly visable (usually not in any other angle) is the very short piston dome with the deepish valve pockets


it is also worth noting that even compared to the MIVEC rods, the very low weight of the Brian Crower connecting rods makes them look like they are made of aluminum, weighing in all at 559 grams
 

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Discussion Starter · #37 · (Edited)
time for the crazy valvetrain


here is a close up shot that we all know and possibly love, I wish a had a better picture for this masterpiece


exhaust side rockers are off, this lookeed absolutely awesome when I first took the exhaust side rockers off, shame my camera isn't high enough resolution for it, anyway, this is where things start getting weird


these are the exhaust side rockers and then some, the two outer arms for each of the triplets are the exhuast side rocker arms, that center one isn't a rocker arm, well, not exactly, my currect working theory on what the hell they are is that they maintain the lash for the high speed profile, meaning the high speed profile has self adjusting lash AND solid manual adjusted lash, which means the later is only used for the low speed profiles, in addition to this, it appears these tertiary rockers also prevent the high speed rocker from rotating backwards when it is not engaged and prevents said rocker from engaging when MIVEC isn't engaged

the intake side rockers, these are far simpler in operation than that tertiary rocker off the exhaust rocker shaft reaching over to the intake side, hydralic pistons are in the round portions of the rocker arms, when activated, the cylinders extend and the middle rocker moves with the pair of rockers according to the high speed profile

both sets of rockers are off, easy acces to the valvesprings and the camshaft is very easy to visually inspect, I have no other words for this, although I will take a picture of the 6g74 head in a few days

edit:
found a correct diagram regarding the function of the tertiary rocker arms, they aren't really what I was thinking they were, but still are required for the SOHC 2 stage MIVEC system
 

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Hey Fox, had another friend check out his cams as well and there is a little discrepancy in the info possibly due to you not removing the cams when measuring. My friend (Michael G.) measured ~31mm on the High lift base circle and ~32 mm on all the others which is what I suspected given the High lift roller is ~24mm and all the other rollers are ~20mm. Is it possible to re-measure your cams out of the head to confirm my thoughts? here are mike's pics..
 

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Discussion Starter · #39 ·
interesting, thank you for the more accurate information, also when I removed the MIVEC's rockers, I got the same roller specs you posted, I'll edit my post with the inaccurate info shortly

also if anyone has any specs or pictures (preferably with the engine apart) of any other 'exotic' 6g7 engine, weather it is a GDI, MIVEC DOHC, you can do so at any time
 

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Just finished carefully going through everything here, definitely one of the most informative threads I've read! However I have to say I'm curious as to the comparisons with the 75 non-Mivec, if you ever get another full one I want to see the differences.
 
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