"As far as you know" is already not a good sign better be safe than sorry, get some measurements done

the clearance between pistons & head is a topic discussed on hybridZ with many different versions. I went with 0.8mm (0.032") and so far, so good. It was a direction given by Brian Blake (a.k.a "1 Tuff Z" who did the L28 DOHC DETT)

Top rpm so far has been 5500rpm until I'd got bigger chokes or better: bigger carbs.

Regarding head shaving, it is hard to tell. Some say 0.040" is good but I have less on my build and I'm above 200wph. Head builder (Braap on hbz) did not push comp ratio. There's little gain to get vs. ping safe conditions.

I think you should focus on cam grind vs. comp ratio => meaning, talk to cam builder for proper setup - it should be a match.

Surface treatment done on cam lobes are usually very thin (0.5mm deep - 0.020") so if you perform a regrind, a new hard layer made with some treatment is mandatory.

FWIW, Bryan Blake goes by "1 fast Z" on hybridz.

L28ET (F54 block and a P90 head) ....The block has new rings and bearings, stock turbo pistons. The head has been shaved .074", with the proper single cam tower shim, multi angle valve job, intake runners ported and polished, slight deburring of combustion chambers, exhaust side just had behind the valve seat cleaned.

Don't know how well the P90 cam would perform either.

I don't know if it would be worth the effort to change the pistons and go NA, but the sound of a nice NA L6 is so...

Seems like there's been some effort put in to building a nice turbo long-block. You could probably sell it for good money and pick up a complete NA F54/P79 engine, refresh it and come out money ahead. The NA engine will already have the flat-top pistons and the correct cam for NA.

Or you could swap the head for an N42 or N47, keep the pistons and new rings, get the CR you want with the smaller N42/N47 combustion chamber, probably along with the right cam, and sell the rebuilt turbo head or keep it as an option for later use.

FWIW, Bryan Blake goes by "1 fast Z" on hybridz.

You're right! I should have doublechecked

A lot of numbers being thrown around here. As far as 1fastz , he actually says optimum clearance of piston head is more like .021-.025. This requires shaving the block and or mating the right HG size. 1fastz doesn't put all of his info because he's afraid of steering someone into precision they can't pull off.

I'm running around .025-.027

I would just order a Nismo gasket and know what your getting- pricey-yes!

I believe .040 is too much for an NA engine.

Sounds like a good engine combo- good luck

A lot of numbers being thrown around here. As far as 1fastz , he actually says optimum clearance of piston head is more like .021-.025. This requires shaving the block and or mating the right HG size. 1fastz doesn't put all of his info because he's afraid of steering someone into precision they can't pull off.

I'm running around .025-.027

I would just order a Nismo gasket and know what your getting- pricey-yes!

I believe .040 is too much for an NA engine.

Sounds like a good engine combo- good luck

Dave Rebello is the one that threw out the .040 inch number......seems like a lot to me too, but I really can't argue too much with him. I think a down shift at high rpm could stretch the rods somewhat......no idea how much. Maybe John Coffey could clarify or give his clearance preferences. Does anyone know what the stock gasket compressed thickness is?

Edited October 15, 201212 yr by Diseazd

I've measured mine - a new ishino gasket - at exactly 1.00mm compressed (while others said over the web it should be 1.25mm).

link: http://www.amazon.com/gp/product/B001G7GT5G/ref=oh_details_o00_s00_i00

I thought stock compressed is .047, which is 125mm I believe. As far as an Ishino gasket, I'm not sure.

When i removed my old HG, which I can't be certain, but I think it came from an old MSA kit, it measured right at

.047 compressed.

I wouldn't want to argue with Rebello either-I'm just a hack mechanic:0

I have searched the Hybridz pages for hours, especially on the squish issue. The numbers that I quoted came from a post deep inside a thread that 1fastz commented on about squish. HE acted asif he had devulged his best secret about these motors!

But then you get into the argument about what standard deck height is on the flat-tops, and then numbers start flying around again. Braap chimed in saying that he measured countless blocks and the flat-tops averaged .019 above deck-so is this true? I guess every engine needs to be checked by someone with some good skills and mics.

this is what I've measured. For my rebuild, I bought 4 different gaskets before giving up. I then torn down the bottom end again and milled pistons to match Felpro gasket.

Compressed thickness on headgasket needs to be measured if we want to be 100% confident. I've done it with calibrated gauges so I know how reliable my measurement were (minus my skills).

I advice everyone to build an engine to check those dimensions, it is not hard to do but some tools & time are required.

I just googled stock gasket thickness for Datsun L series. The answer given was they come in two sizes.....1.5 mm ( .060 inches )and 1.25 mm ( .050 inches ), so you should be able to deck the block .010 to .020 inches and still get a cheap gasket.

I thought stock compressed is .047, which is 125mm I believe. As far as an Ishino gasket, I'm not sure.

When i removed my old HG, which I can't be certain, but I think it came from an old MSA kit, it measured right at

.047 compressed.

I measured the compressed fire ring of the HG I removed from what looked like a never disturbed, original (numbers matching), engine in my 1976. I got 1.25 mm also.

better be safe than sorry, get some measurements done

Yes, I will check it if I decide to change the pistons.

Now when I have more information I've started to to think that maybe I just should keep this L28 as a turboengine, becouse it should be a nice setup as it is. As Zed Head wrote I could sell it and buy a stock NA L28 and build it instead.

I got to make a decision. I'll let you know if I start to work on this engine