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Big Head Building idea


Z_FromDownUnder

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Ok, so i've been thinking about the l28 head(s) and what options there are. i think i've come up with a plan to develop my own head, it will be based on the head of a RB25-26, i want to base it on this because it has DOHC and there are readily available headers suitable for twin-turbo. so to anyone out there who knows the similarities of the l28/RB25 heads and possible problems with this plan please chime in. also this head will be completely built at a custom head shop so everything can be changed eg. valve size. Just thinking about it, im guessing the RB head will be shorter than the L28 because of a smaller block (i dont actually know its smaller just a guess because of smaller displacement.)

 

If this was to go ahead (in the far future) it would be a damn the expense exercise.

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yes i agree it would be easier and cheaper (maybe) to just stick a RB25 in there. But thats not what i'd want in a Z, its been done before, if this was ever done then there is a certain satisfaction to having built a one of a kind car. but in saying that anyone can take my idea from here and put it into work, that whould also make me happy.

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There's nothing wrong with dreaming about 'what if....' The big problem you have is that you haven't done any investigating for yourself. You'll generally find that people will comment if you start off with some solid idea or concept, not some general statement about what might be possible if you win the lottery.

 

I agree with Bart, buy yourself an RB and drop that in if your so keen on the twin cam option. Perhaps a 2JZ if you want something even more unique. The purists will hate it.

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*hides in fear*

 

If you want to do it, I'm not going to stop you, either method you go with will be a crazy amount of work. I will tell you with my project here's what you're going to need to do.

Find a MB 104.98x cylinder head (no air-pump).

Get all the timing schtuff.

Turn crank to SBC demensions

Machine off the oil sprocket so you just have the timing chain.

Sleeve the timing gear and re-insert.

Put in SBC Internally balanced pulley on it.

take oil out of main gallery, run to back of head (split in to 4 galleys, externally accessable from back of head).

Fill parts of head to Z HG using favorite aluminum filler.

Pull rear freeze plug and tap to use AN for front and rear for cooling return.

Tap Oil returns on exhaust side and run AN branch back to pan for oil return.

Head bolts on using "b" length (long) head bolts in stock bold holes (with centering dowel pins removed)

The valves are big, so an 87mm bore would be a must at least.

Drive.

 

My project is currently on hold since I'm holding out to put it on an 810 Coupe and for my Z I found all the bits to make a 3.4-3.6L AMG M104 for the same price as a hard run L28ET long block, and I couldn't pass up 600+ cc's in displacement for nothing.

 

Your best bet is build it then post it. I tried the build in progress and it just didn't fly here. I'm all for something that's the long, hard way around (watch it) so PM me if you ever need a hand from the other side of the world ;)

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Thanks MAG58 and everyone else for the info :)

 

i have to say though that the DOHC thing will come second to the redesign of the exhaust ports to suit a RB26TT header so that i whould now have twin turbo (and yes this would be a long/expensive/difficult way to get twin turbo but if you don't take the harder options, what sort of journey it that?)

 

anyway still wondering what the dimension differences between the two head would be?

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  • 2 weeks later...

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