6G72 DOHC 2/4 bolt 3.0 with 6G75 3.8 SOHC MIVEC heads.

[Blackmount]

Me and a few people have been talking about this so i want to try and gather more data on it. Ive got a few word files on my computer but i want more

So far im pretty sure it will work. 75 heads bolt on 74 block and 74 heads bolt onto 72 block. So 75 heads should drop on 72 no problem. I know there is a select few who have a 74 stroker with these heads. I want 72 for maybe a pretty much bolt on upgrade. As the the 75 mivec heads are some of the best flowing heads out there (or so im told) and have some great cam options (again so i am told) plus it would just be badass. U can get a new set of these heads for a pretty decent price in relation to new TT heads/major machine work on stock heads

As far as controlling mivec im sure a 99 flash ecu could do the job if not AEM. There are also Mivec/vtec/vvti piggy back controllers

My snag is the timing components and related on the block. Would one use a 72 water, oil pump, tensioner crank pulley etc with a 75 timing belt? Is it that simple?

Now that i am working 50+ hours aweek again and have decent income im going to pick up a 2nd motor and maybe try some of this stuff to figure it out myself. But i thought itd make a good thread

[MR2]

Been a while since I've played with the crap in my garage, keep in mind when I say parts fit, I mean the Gen 2 upwards parts. Itallo would have more info.

the 72 water pump fits
72 water neck does NOT fit
I doubt the 72 upper intake will fit
From memory you NEED the 74 lower intake with the 75 heads to allow the 72 Upper to bolt on, but seeing as the 75 heads have massive PCV I assume this was necessary to comply with emissions, you may fine the Pajero MIVEC heads are lower.
the 74 lower also allows you to use 72 spec injectors as opposed to having to have them angled as per the 75 one
I can't see why you need to do anything special with timing, just use the 75 timing belt you will however need to grind down the front mount and come up with some engine covers since none of the stock stuff will fit without leaving gaps. as per the 74 heads you will need to make power steering and alternator brackets, cannot remember but I'm pretty sure the 74 ones are not high enough (and the engine is reversed in the 380/Eclipse/Pajero).
probably the most expensive adjustment will be the exhaust headers, the 75 heads use round ports and the bolt pattern is upside down compared to 74/2
the 75 uses coil on plug so it's up to you if you keep that or just throw some wires on the stock stuff
From what Itallo said in the past the timing from a Gen 2 car plugs right into the sensor on the 75 or he adjusted the harness or something he made sound easy

here is me attempting to fit 72/4 accessory brackets on to the 75 heads

http://3000gt.com.au/car/74%20vs%2075/Accessories/

[Blackmount]

Thanks for the info. Im gonna post what info i have in a organized fashion to my best ability when i get home and can get on my laptop.


Biggest thing im focusing on is the initial engine assembly.. 75 heads on to stock 72 shortblock (to see how simple the process can be) and get all the timing and much needdd companants such as WP and OP installrd and everything together perfectly. Im not worried about the alternator and pws that stuff will be the easy part.

[mehrshadvr4]

you can't bolt 75 head on 72 block. you need 74 block because the block are a little taller and farther apart and the heads need modifying to fit on 74 block, but you need 75 lower manifold and upper manifold. the lower 72 won't work because it's too narrow and 74 won't work because the porting are different. same with upper manifold. i tried to buy 75 manifold for my car and later i found out the lower is different than dohc engines.

[Blackmount]

why wouldn't it work? if 74 heads bolt onto a 72 block then why won't 75 heads bolt onto a 72 block but they will a 74?? that makes no sense. and Yes I am aware of a light modification to get them to work but it was very minor iirc.

[Blackmount]

Most of what I had is about doing a 74/75 SOHC MIVEC Stroker, so it's missing some of the more relevant info but it can be a good source.

Just some things I pulled from my Notes, some of it may need correction, but if claimed false please provide a reliable source that says so.

6G75 Deck height 228
6G74 Deck height 228
6G72 Deck height XXX (?)

6G75 Bore 95
6G74 Bore 93
6G72 Bore 91

6G75 Main journals 64
6G74 Main journals 64
6g72 Main Journals XX (?)

6G75 Rod Journals 55
6G74 Rod journals 55
6G72 Rod Journals XX (?)

6G75 Stroke 90
6G74 Stroke 86
6g72 Stroke 76

6G75 Pin downset is 29.75
6G74 Pin downset is 31.75
6G72 Pin Downset is XX.XX

Custom 3.8 Stroker

Parts
6G74 Block
6G74 Rods
6G75 3.8L Crank
6G75 Pistons or Lower/Higher Compression Custom Pistons.
Bore Block to 95mm
CUstom Upper Intake Plenum
6G74 Oil Pump
6G74 Water Pump

NOTE:

*3.8L Crank is a direct drop in replacement into the 74

*When the custom pistons are built for this application, the pin downset will need to be changed from 31.75 to 29.75 if we are basing it off of a stock 93mm 6G74 piston.

*Heads: Mivec Heads are a direct bolt on and just need a switching system to activate them

*Aftermarket cam gears: These are the same part # being used on 6G72/74/75

*Custom/Modified Waterneck needed

*Custom Headers/Turbo/Exhaust manifolds needed (Modified Stock 72 manifolds will work)

* 74/75 Connecting Rods are the same
* 74 lower plenum will bolt to 75 heads allowing use of 72 TT plenum (maybe)

MYTH?

Supposedly they outflow LS7 heads...I think it was Matt or Ray that mentioned that once.

Flow data pulled from Sources





Other semi-important shit for reference.

Exhaust ports



Timing Set up and components.



Intake ports



Lower plenum Intake ports (Upper plenum side)

[mehrshadvr4]

you can put the head on but you won't be able to bolt the lower intake manifold because the heads are closer together. you are going to need a totally redesigned manifold.

[Greg E]

Cam and Crank sensors absolutely will NOT work with a flash/stock ECU. Writing the code to control the MIVEC isn't difficult though.

72 pistons will not work with the 75 head valves. Custom pistons are needed too.

[MR2]

good point on the heads being closer, forgot that one maybe you can use the 72 lower intake then? seeing as the intake ports on the 74 and 75 ports are the same?

I assume you already realise that the 75 heads have a 65cc chamber and the 74/2 have a 43, so you'd need to re-work your compression numbers..

when you say "good cam's" available, the only people I've seen to do them are RPW, and when a few people who know a lot more than me looked at they they did not seem convinced as to their suggested numbers etc.

[mehrshadvr4]

are you sure the ports are the same? i'm sure the 75 has bigger ports and probably different shape and angle too.