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Old 12-01-2012, 06:42 PM   #1 (permalink)
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Default Question for all you engine gurus

Was thinking the other day of how in the Skyline world, the guys have a way of mixing the engines together to make "new" types for better performance, strength and durability etc. I.e RB26/30 and so on.
Is there a way, in which the same principle can be applied to a 6G74/5 block, where you run 72 heads?
Seeing as the majority of 74/75's here in Australia are all SOHC and non turbo, that utilizing the Heads of a 72 would reap the extra benefits of higher reving motors etc.

thoughts?
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Old 12-01-2012, 07:24 PM   #2 (permalink)
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Default Re: Question for all you engine gurus

The reason they do the rb26/30 conversion is purely for the block size and the rb30 block has the same bolt pattern as the rb26 heads. As far as I know the 6g72 tt heads are pretty limited so if you intend on running big boost out of a 3.5l + you need better flowing heads to support that kind of capacity. Further more anything NA will have cast weak internals so either way you'd have the forge everything inside even if you could manage to get the 6g72 heads to fit on it. Mike or Mitch are probably the best people to answer this though. P.s the 6g72 revs pretty dam good for a 3L
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Old 12-01-2012, 08:45 PM   #3 (permalink)
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Default

Our heads bolt directly onto the 6G74 I believe. Just not on the 75.

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Old 12-01-2012, 08:55 PM   #4 (permalink)
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Default Re: Question for all you engine gurus

yeh you'd obviously be forging the shit outta everything, but more so to get that DOHC heads on a otherwise SOHC, effectively creating a 6G72/4 DOHC TT awesome!
and offcourse with flowing heads and forged internals, you'd make a shitonne of power!

so long as they bolt up thats the main thing.
I done a little bit of research in the interim and realised there isn't a DOHC 6G74 available whenever you want, only in the Pajero Evo? so this way would be much more cost effective and readily available.
I got no plans on doing this just a thought
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Old 12-01-2012, 09:28 PM   #5 (permalink)
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Default Re: Question for all you engine gurus

Let me start this one again...

From what I've been able to see all the 6g7x blocks share the same head stud pattern, the water channels change shape a bit but largely, it remains the same, so (and I've yet to find a single case opposing it) as far as I'm concerned any head is interchangeable.

with the blocks there are essentially two different types, and the difference largely comes down to two options for oil filter placement (left or right of engine) the GTO engines we're one of the rarer types that had the oil filter placement on the left side of the engine (looking from front) the reason for this seems to be the front half shaft, so if you find something like a pajero that's FWD chances are it'll be the same layout (called crossover oiling, which refers to the oil being picked up from the left side of the pump and then pushed through to the right side of the engine)

what you need to be aware of with the oil filter placement side of things is that the change in filter placement meant a redesigned oil pump and different (non interchangable) bolt pattern on the front of the engine...
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Old 12-01-2012, 11:15 PM   #6 (permalink)
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Default Re: Question for all you engine gurus

you made my delayed reply look like shit with your edit

ok, but end of the day, Heads can be mounted which was my initial question, and will work
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Old 12-01-2012, 11:48 PM   #7 (permalink)
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Default Re: Question for all you engine gurus

the old age thing of SOHC is crap does not apply to the 75 SOHC heads, see in past times SOHC meant that the head only had 8 valves, which in theory meant a reduced performance etc, the reality is that the SOHC head actually has 24 valves just like the 72/74 heads, the splitting from a single cam to all the pairs of valves is done inside the head as opposed to having a pair of shafts belt driven in each head, this leads to a more compact, easier to work on engine (less cam's to line up).

for a 75 head to 72/4 engine conversion you'd need to run a shorter belt, cut back the front engine mount to allow the slightly adjusted belt route to clear, get custom belt covers made, get brackets made for the alternator and power steering to lock into, get a 6G75 intake (lower + mid + upper or at the very least lower and then spacer so the stock 72 intake will clear the heads) and if you go the MIVEC version, get a 12v on/off RPM activated signal

I think that's most of it
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Old 12-01-2012, 11:49 PM   #8 (permalink)
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Default Re: Question for all you engine gurus

on the topic of 74/5 blocks I'm not sure what the differences are in water pump + accessories mounting brackets on the non "compatible" blocks, however you can get around the filter on the wrong side of the engine business by running a remote filter...
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Old 12-02-2012, 04:25 AM   #9 (permalink)
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Default Re: Question for all you engine gurus

Pajero EVO got the only MIVEC 74 DOHC.
The same heads are more commonly found on the Diamante 30M, 3L DOHC MIVEC 199kw and 300nm of torque.
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Old 12-02-2012, 06:09 AM   #10 (permalink)
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Default Re: Question for all you engine gurus

Spot on, but I just don't see the point of the 74 mivec, it's all that stuffing around (they are rare as hens teeth) when, if your going to all that trouble why not go with the 75 that have a totally revised design? (albeit you'd not put them on anything less than a full engine build, and if you DO do the engine build you need to remember that the 75 heads have 65cc of capacity in the head unlike the 72/74 that are 43cc iirc?)
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