F54 and P90

[Kimi]

I begin with saying that I'm sorry that I make a question that has been several times asked before. Been reading the topics, but still felt that I wanted to ask you guys for help with my engineproject.

I bought a L28ET (F54 block and a P90 head) for my 240Z. 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.

So this should be a nice turbo-engine, and when I bought the engine I thought that I would use it as it is+EFI, but lately I've been playing with the idea of making it a NA with the flat-top pistons.

In that case I probably would go with:

- F54 block + stock F54 flat-top pistons

- the shaved P90 head

- MSA header + 2,5" exhaust

- early SU carbs

- aluminium flywheel

But now to the question, would the stock flat-top pistons clear the shaved head and what kind of compression am I looking at. Would it be near 9.5:1?

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...

Edited October 13, 2012 by Kimi

[Diseazd]

The F54 block with P79 flat top pistons and .080 shaved head would give you approximately 10 to 1 compression ratio. The pistons will clear the head. What cam do you plan to run? I run stage III Isky cams in all 3 of my L28's with the above mentioned combinations. You will enjoy that combo if you decide to go that route.......it's a great engine combo.

[Kimi]

Thanks Diseazd

Ok, sounds good. The compression should be pretty ok with this head then I know that the engine won't have the same hp as with the turbo setup, but it should be enough for me and my series 1 240Z

Haven't thought about the cam yet, just been thinking about the pistons. Probably going to change the pistons first and try to find all the parts I need, and then choose a cam.

Thanks for the tip too, I have to look at the Isky stage III specs. I think I will find Crane cams locally, but I have to check that too.

[Lazeum]

As Diseazd say, pistons would be ok.

The combustion chamber looks like a bean, there's a flat area that would end up in front of the piston anyhow. This zone will allow the engine to have a quench effect at TDC improving air/fuel mix (= efficiency + ping resistance).

To make sure, you'll be ok, you will have to measure some parameters: piston top vs. deck for each pistons, head gasket thickness compressed.

head gasket thickness is usually given by manufacturer. if nothing is written, don't trust Internet value. Felpro gasket for instance are given sometimes for 1.2mm or 1.0mm, I measured it at 1.0mm but Ishibo gasket (the stock unit) is given by internet users for 1.25mm, I measured it at 1.0mm also.

The gap at TDC for each pistons should be min at 0.023" (0.6mm) & max at 0.032" (0.8mm). If you're too short, pistons will hit the head, if you're above max, you will lower quench effect. For your info, I was conservative with my build, I shoot for 0.8mm nominal; I'd rather loose some hp than an engine.

In stock form, if nothing has been machined on your engine block, you should be right on.

My block has been surfaced before rebuild, I had the milled the pistons by 0.3mm with Felpro gasket.

Without measuring gasket thickness, I would have ended up using Ishibo gasket, I would have over-estimated quench gap that could have led to engine destruction...

Edited October 14, 2012 by Lazeum

[EuroDat]

Thanks Diseazd I think I will find Crane cams locally, but I have to check that too.

I thought Crane stopped making cams in 2005 and sold their inventory to S&S cycle in Wisconsin. I remember reading it somewhere...

Dont go cheap on the cam. The extra money for a post treated cam (Nitride treatment) is well worth it in durability of the cam lobes. A lot of regrinds dont have it.

[Diseazd]

The metal to metal compatibility of the Datsun cams was excellent. The Z Doctor in Roanoke, Virginia is an expert on Z engines and firmly believes you should regrind your stock cam to maintain that durable relationship. He recommends Isky. I've used them on all 5 of my motor builds. They all perform perfectly. With a new cam, you'll want to install new or remanufactured rockers and new Isky valve springs with a lift over .460 inches. The cam is what makes the combo you refer to work so well.....go with Stage III IMO.

[Diseazd]

As Diseazd say, pistons would be ok.

The combustion chamber looks like a bean, there's a flat area that would end up in front of the piston anyhow. This zone will allow the engine to have a quench effect at TDC improving air/fuel mix (= efficiency + ping resistance).

To make sure, you'll be ok, you will have to measure some parameters: piston top vs. deck for each pistons, head gasket thickness compressed.

head gasket thickness is usually given by manufacturer. if nothing is written, don't trust Internet value. Felpro gasket for instance are given sometimes for 1.2mm or 1.0mm, I measured it at 1.0mm but Ishibo gasket (the stock unit) is given by internet users for 1.25mm, I measured it at 1.0mm also.

The gap at TDC for each pistons should be min at 0.023" (0.6mm) & max at 0.032" (0.8mm). If you're too short, pistons will hit the head, if you're above max, you will lower quench effect. For your info, I was conservative with my build, I shoot for 0.8mm nominal; I'd rather loose some hp than an engine.

In stock form, if nothing has been machined on your engine block, you should be right on.

My block has been surfaced before rebuild, I had the milled the pistons by 0.3mm with Felpro gasket.

Without measuring gasket thickness, I would have ended up using Ishibo gasket, I would have over-estimated quench gap that could have led to engine destruction...

Good advice Lazeum.......if the engine block is decked, the pistons will come out of the cylinders. The way I've heard it, you need .040 inches ( 1 mm ) clearance. Does anyone know the compressed height of the stock Nissan gasket. Also, how much is a safe shave for a stock P79 piston ( you could shave the top of the piston versus a thicker head gasket ). If there is no decking, you have no problem.

Edited October 14, 2012 by Diseazd

[AlexS13]

As Diseazd said, you should regrind your stock nissan cam. The durability of the oem nissan cam is much better than the new billet cams. I myself sent my cam to a company called Web Cams and had them regrind my stock cam. You have to be careful with the base circle of the cam after the regrind, some regrind's are able to maintain the stock base circle measurement, in my case the base circle ended up being smaller so I had to compensate with thicker lash pads in order to get the correct "wipe pattern" on the rocker arms.

[Diseazd]

Thanks Alex.....I forgot to mention that you'll need thicker lash pads......failure to geometry the rockers (center the wipe pattern) will destroy your cam and valve train.

[EuroDat]

A lot of regrinds dont have it.

Just to clear up what I meant by regrind. There are a lot of aftermarket billets that shops will grind to your specs. The quality of these billets is sometime questionable. Nissan billets are very good and can be identified by "japan" stamped on the end. I reground mine and had no problems with the geometry, but my profile was mild. Hi lift would probably change that.

[Kimi]

A lot of good information here, thanks

Ok, I got to check the mentioned things and then choose the headgasket after that. As far as I know the block should be stock, but that will be seen when the pistons are installed.

[Lazeum]

"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.

Edited October 15, 2012 by Lazeum