l33-l35 stroker...

[devilsbullet]

so I've been tossing around building a stroker for my z for a while now.  already have an f54 block and unknown head in my parts car that's dying to be put to use.  only thing is...I don't want it to be the run of the mill 3.1l stroker.  I've had it in my head for a bit that I want to try for a 3.3-3.5l build. so what i'm looking for now is the math to figure out piston size, rod size, bore, etc. to do this. also, what would be the best material to fab those out of, my dad is a machinist and I have a buddy that does 3d modeling with solidworks, so as long as I con pony up the cash for materials and the beer to keep my buddy interested, I can have those custom built and as bulletproof of a bottom end as possible. outside of potentially to thin cylinder walls, are there any problems I would run into with this idea?  oh, and last but not least...if we can figure out how to either adapt one or have my buddy design and build one from scratch, it will be supercharged :devil: . hopefully. anyone with ideas or equations, they would be more than welcomed.

[datzenmike]

You need a Maxima diesel crank and overbore the L28 block the maximum practical limit is just under 3.2 If you re work the crank for more stroke by welding and re-grinding the rod journals it could be made larger. You may need custom rods and pistons for this. You cannot over bore the L28 forever. 3-4mm it barely possible so that only leaves a stroke increa$e. Your machinist buddy won't be making pistons and rods on a lathe.

 

http://www.zhome.com/rnt/L28conversion/3031FAQ.html

[devilsbullet]

planning on a custom crank too. and I dunno which machine my dad would use, i'd leave that up to him to decide, but his shop has made everything from medical equipment to parts for a space shuttle. i'm sure one of the 20 some odd machines in his shop will be able to make pistons and rods, and thankfully he knows how to run every one of them.  that was a helpful article, running the numbers down i'd have to have a 90mm stroke to pull off what i'd like. that would be a 3.4l or 3435cc.  next question is what material to use.

[72240z]

lol sigh... 

[Xnke]

Ok, Having assembled a 3.4L shortblock by offset grinding an LD28 crank and selling it, this is what you would end up doing.

 

You will need to obtain a RB30e crankshaft, and have it fitted to the L28 block. Doing this will net you more stroke than the LD28 crankshaft, but you will have to modify the crank snout and there is some work to be done on the bearing surfaces. This is a much more viable solution than modifying an LD crankshaft.

 

The F54 block is absolutely useless for a big overbore. They won't handle more than a 1.5mm overbore...I wouldn't go over 87.5mm piston diameter. You need an early N42 block, 1975-76 blocks are reported to handle the bigger bores better than 77-80, which will hold a bigger bore than the 80-84 F54 blocks.

 

You MUST have the block sonic tested to see how far you can bore it. Some N42's with core shift or casting flaws, or blocks that got run with no anti-freeze and are all rusty, won't handle a large bore either.

 

The largest bore I've ever seen in an L28 was a 90.5mm bore. Going any larger, even if the block *could* handle it, compromises headgasket sealing. The largest headgasket available has a 91mm fire ring, so that's the practical limit.

 

There is an aftermarket 85mm crankshaft available for about 3500$. There are a few companies in the US that will cut you a custom crank, Moldex will do a custom forging, maybe...they used to do them. The 85mm stroke unit is a custom forging from Kameari Engine Works, and accepts standard rod and main bearings, and could be offset ground to accept a smaller rod journal to increase stroke further still. Even with the LD28 crank, you have to clearance the block a little...the longer the stroke the more clearancing you'll need to do to the block.

 

The RB30 crank is 85mm stroke, and can be offset ground to 90mm. 90mm stroke, 90mm bore, that's 3.435L displacement...and that's pretty much as far as you can take it.

 

And as far as making your own pistons...forget it.

 

Billet pistons are not suitable. Not only that, but did you know pistons are not circular? They are an ellipse. They are also not the same diameter top, middle, and bottom. A standard lathe can't cut an aluminum piston, very few CNC lathes can cut an aluminum piston, and even if you have the machines to do the final machining...can you make the forging? By the time you make all those parts in-house, you could have bought the engine already built.

 

I have machined custom rods, custom engine blocks, and custom crankshafts. Was machinist for a team that built a 1.0L V8 with said custom rods, blocks, and cranks, and then spun it to 18,000RPM. We used motorcycle cylinder heads, and we tried to make pistons. None of them, regardless of material or method of machining, were as good as even a stock motorcycle piston was...which is what we ended up using.

 

Custom rods, though...that's doable. They are not terribly difficult to do, if you have access to a CNC machining center then they're not even all that time consuming. If you've never made rods before, though, the first designs will be thick, heavy, and not any stronger than a properly designed, tested, lightweight rod.

 

Remember...Rods don't break from compression. They break on the exhaust stroke...They bend on overcompression...then they only break if they hit something.

[devilsbullet]

I've heard some back and forth on which blocks are better for boring over(I have both an f54 and an n42, ones in the parts car, ones in the running car.) out of curiousity why wont the f54 handle any more than 1.5mm? good to know about sonic testing, one more thing to research and have done. thank you!

 

 

lol sigh... 

sorry that we're not all as brilliant immediately as you are and some of us would rather ask questions and be (hopefully) pointed in the right direction.  if you see a problem with my idea, I would be more than happy to hear it and why it is a problem. if all you're going to do is make smartass snarky comments like I normally see out of you, go somewhere else and let someone who's willing to explain why it wont work tell me, or tell me where to go to find out why it wont.

[72240z]

Damn you assume and talk a lot of shit from a simple sigh, no need to get your panties in a bunch over it.

Your very fortunate Xnke felt like taking the time to type and teach you whats been discussed 1000 times over on hbz, czc, zc etc...

[Xnke]

The F54 is a non-siamesed block. Cut one down the middle and you'll immediately see that whatever the book was that people quote is absolutely wrong, the block has six seperate cylinders and nothing between them. It cools better...which for a stock 86mm bore is great...but the walls are thinner to start with.

 

The N-42 block has cylinders 1-2-3 cast together as a block, all joined together between 1-2 and 2-3, then a gap between 3 and 4, then 4-5-6 are all joined together between 4-5 and 5-6. This means inherently that the walls are thicker to start with, and that they are better supported and more rigid. That allows for better wall stability for the same amount of wall thickness..which you are going to want a minimum of 0.120" wall thickness all the way around the bore, top to bottom, for any kind of engine life. Get thinner and you'll be down on power due to poor ring sealing, and have a short engine life.

[72240z]

Xnke you have a vid of that 1L v8? I love small displacement v8s. 

[devilsbullet]

makes sense, and thank you.  means i'll have to add getting another car to drive around while the z is down to the list of things to do.

 

 

Damn you assume and talk a lot of shit from a simple sigh, no need to get your panties in a bunch over it.

Your very lucky Xnke felt like taking the time to type and teach you whats been discussed 1000 times over on hbz.

don't have to assume, I've already dealt with you talking down to me once, and watched you do it to others. that attitude is exactly why i'm on ratsun, and don't even bother going to hybridz. and I wasn't talking shit, I was stating my preference that you either explain why its a bad idea so that I can learn, or just shut the fuck up if you're going to act like I've seen you normally act. since you're obviously going to just sit and talk down to me, i'd prefer that you just leave the thread alone, but since I cant force you to, i'll just pass by you comments as I've started to do since I watched your little spat with Tristan. makes it easier that way.

[Xnke]

Yeah, you need to ditch ratsun and go BACK to HybridZ if you're looking to get away from getting talked down at. There's a reason I have only about 40 posts here...I read through the forums and saw how a lot of the "old timers' here are and decided it wasn't worth the crap I'd take for speaking against some of the well-established fallacies that you find here and a lot of other datsun forums, ClassicZcar and Zdriver and Zcar.com included. We do expect you to own the books and KNOW the material when you show up at HybridZ, though, it never has been, and never will be a datsun-basics forum.

 

If you want professional information, you need to make an effort to ask in a professional manner.

[72240z]

 

 

 

don't have to assume, I've already dealt with you talking down to me once, and watched you do it to others. that attitude is exactly why i'm on ratsun, and don't even bother going to hybridz. and I wasn't talking shit, I was stating my preference that you either explain why its a bad idea so that I can learn, or just shut the fuck up if you're going to act like I've seen you normally act. since you're obviously going to just sit and talk down to me, i'd prefer that you just leave the thread alone, but since I cant force you to, i'll just pass by you comments as I've started to do since I watched your little spat with Tristan. makes it easier that way.

 

You mad? lmao

[EricJB]

As far as pistons go, I think the reason a billet piston wont work is because of grain orientation. Even a raw crank forging starts out as something that looks like a crank. And as previously mentioned, the skirts are not usually round. But pistons would be easy to have custom made. Many companies will do that for you.

 

The Silvolite catalog is a good resouce for finding something that might work. With application they list all the specs as well. I would not use their pistons for this project, but it might get you closer to knowing what might work.

http://www.kb-silvolite.com/assets/09_silvolite_catalog.pdf

 

Just a thought, if you ditch the blower idea and decide to run it N/A, you will have to build a monster of a top end or it will be all torque and no top end. If it cant breath, it wont spin. 

 

[Xnke]

If you build this engine and don't spend at least 3000$ in the port job alone, you will be making about 220HP. The L6 heads need some work, and you need to be *very* familiar with them or own several heads of the same casting code and a flowbench. It is possible for a 2.9L L28 to put down 400RWHP naturally aspirated, but you will spend 30K$ to do it, and it doesn't take the OS Giken head.

 

I missed the supercharged earlier. Don't do it. There is a reason you don't see turbo or supercharged L28's in Japan displacing more than 3.0L...bore stability. There are folks who do it in the US because "more displacement! WHOO!" But then they wonder why their engine blows oil all over the bay and power takes a nosedive about 6000RPM...You loose ring sealing.

 

Turbo San Gata lives forever.

 

Personally I'd run a set of custom 88mm bore forged flat-top pistons, the 85mm crankshaft, and a custom connecting rod if I was going to be doing a blown stroker. I'm not, I'm building a supercharged +2mm bore L28, and I expect to put down about 250RWHP at 8PSI. I also expect to drive the car every day, without failure, and without early engine demise.