L24 stroker build (yeah...I know)

[Murch240z]

Okay, let me start this off with a short disclaimer. I know what you're going to say about choosing to build the L24 instead of the L28, so I'll say up front that I don't care. I am not trying to build the highest power number that I can within a certain budget, I'm trying to build the best L24 I can within my budget. Feel free to consider me as much of an idiot as you like but please don't share your thoughts in this thread because there is nothing you can say (short of "I'll give you an already built L28 for free" ) that is going to change my opinion on what I want to do. I'm not a new owner that just doesn't know any better, I've had the car for 4 years now and been gathering all of the information my brain can hold since the initial purchase. So yes, I am in fact knowingly and intentionally going to spend the same amount of money to get less power.

 

Now that I've gotten that bit out of the way, if anyone is still reading I'll get to the point of the thread. After 4 years of working towards this point, I'm finally getting close to having all of the necessary funds to begin my engine build so I figure it's about time to start gathering parts. Therefore I came to the conclusion that it was finally time to post here rather than just silently observe.

 

The basic plan I have right now is to use L28 crank and rods along with a 2mm overbore (as I remember that being the common sense limit of the L24 block as I don't want to sink the money into sonic testing or sleeving) and a somewhat mildly built MN47 head. I do have a couple of things that I'm looking to get clarification/advice on.

 

From the info that I have found, L18 pistons are what are normally used with the 2mm overbore. I am curious as to whether anyone knows about how well the L18 pistons mate with the quench of the MN47 head. I'm hoping to maximize said quench as much as possible to offset the potential detonation from my sticking with carbs (once again yes, I know MS would be more stable and maybe I'll eventually convert it to EFI but not with the initial build). I hope to be able to keep the 3 screw SUs, possibly even have them overbored if necessary for them to deliver enough fuel.

 

My other main curiosity is in regards to the crankshaft. Despite my warped desires for the engine build I'm fully aware that it would be a waste of an LD28 crank even if by some miracle I managed to come across one for a price I would pay. That leaves the V06 (that's the L28 crank code, right?). I have read that the V06 can be modified to increase its stroke (can't remember the original poster, but I think it was Tony D or 1_fast_z that pointed to the Rebello 3.2L and 3.3L engines as an example thereof) and I was wondering if anyone knows the cost effectiveness and availability of having said crankshaft modification done.

 

The '73 is my daily driver and the only S30 I've ever owned (so far) which I think explains my hairbrained engine desires. I don't want to build the fastest 240z on the block, I want to build MY 240z and for me that requires keeping the L24 block (Insane or inane, take your pick but it's what I want). If anyone has ideas/knowlege/exprience (and I'm sure that pretty much everyone one here can outmatch me in all three arenas) that falls outside of my build ideas I'm more than happy to take in any extra information available.

 

I know that a lot of threads get started here by people thinking they want to build the L24 simply because they don't know any better, but I've known better for 4 years now and it hasn't changed my opinions. I'm open to any and all suggestions as long as it's not "Go buy an L28 block and build that instead". The information I have as of now has been gained from a bunch of disjointed sources (which is completely logical considering how few Z owners are as hairbrained as I am about block selection) so my plans could REALLY benefit from a cohesive discussion of the subject. Thanks in advance.

[aarang]

I won't try to tell you what to do or what not to do, but Nissan already made an L24 'stroker', it was the L26 in the 260Z. L24 bore with L28 stroke. Just some info.

[Murch240z]

And your point is what? That because the L26 is the same dimensions as the L24 the term "stroker" is no longer applicable to the L24 engine in any way even though block is stamped L24 and has a crankshaft with a larger stroke than stock installed in it? Well that just plain defies all linguistic sense, not to mention being irrelevant in every way. I understand if people just plain aren't interested in the subject but please don't pop in just to make a snide remark, I think I plainly stated that I'm looking for technical discussion, not to banter about basic semantics.

 

Now, does anyone have an actual opinion/knowledge pertaining to an effective way to build an L24? Whether you agree with my decision or not surely someone must have the technical knowledge to form an "if you had to for some freakish reason" opinion. Perhaps if I pose it in the theoretical sense, say I am limited to the model specific engine block, if you need to include the E31 for the head into your thoughts then go right ahead as I haven't ruled out that option (assuming I managed to come across one, that is).

 

Hell, for those of you that think I'm completely batty just play devil's advocate and help me figure out the best way to follow through on my concept simply in the hopes of seeing me disappointed with the results. Moreover, feel free to tell me that I'm an idiot as long as it's immediately followed by something applicable to the subject at hand.

 

I know this is only my second post here and all and I am probably coming off like more of a prick than I intend to but I don't understand why everyone just dismisses the concept outright. It's not your car, I'm not even wasting an engine block anyone else would want so why not have a theoretical discussion and lend a hand to a guy that just wants to set his Z up *his* way?

[alexdeprat]

Hello Murch 240z,

 

There are several reasons why one wants to stroke the L24, I for one did it many years ago, and I truly was very happy with the performance; Nevertheless please check on the link below, since your question has being address before, hope this help and good luck with your built.

 

Alex

 

http://forums.hybridz.org/showthread.php?t=138857&highlight=L24+stroker

[zedman240]

I'm actually in the process of rebuilding my L24 as we speak. Like you have had everyone around me ask why I haven't chosen the L28 to throw money at. Reason is its the original engine in a low numbered car (#121) and been told the L24's behave differently to other L's. When I delivered the disassembled motor to the builder, he told me this engine already has been modified; L26 crank with other pistons. The original E31 head was found to be unsuitable, alloy has gone too "soft" and a later head from a 80's L24 equipped Skyline will be used. The L26 crank will stay but 1mm overbored pistons will be used and the above mentioned head to achieve some decent power. Still have my current TB's from my RB25DE conversion to use. I'm not expecting 250hp at the wheels but I'm hoping for around 200-220 (or 130ish rwKw's) Not sure how many $$$ you want to throw at yours, but I can let you know what sort of power I get when my setup is done. Most likely stick a little video of it on youtube...

[Tony D]

Wow, I was going to be helpful, but with the attitude, I can pass. I see this headed somewhere...

 

I just wonder where the L28 crank came from...

[aarang]

I was only trying to give you some info, not being snide in any way. Please don't lambast me for chiming in. It seems from your first post that you already know what you want to do, and are demanding people answer you as long as it agrees with what you want. Being defensive from the getgo on this forum will get you nowhere. Sorry

[Drax240z]

After seeing the video of MonZter's 240z, I know exactly why people like the L24!

[Murch240z]

Like I figured, I came off like more of a prick than I intended to, for that I do apologize. It just seemed like the statement was made to belittle the way that I presented myself (mainly the way he put 'stroker' in quotations, usually such punctuation is used to indicate a sarcastic tone in regards to the term within) and I overreacted. I shouldn't have.

 

Thanks for the link, alexdeprat. zedman240, sounds like you've got quite the unique build going, I'll definitely be interested in seeing the finished product.

 

Tony, if you're referring to the comment about modifying the L28 crank it's probably a memory misfire on my part, I can't seem to re-find the thread with the bits of info my brain logged in amongst all the others. If my initial reaction put you off from posting that's unfortunate (though understandable, all things considered), yours was an opinion I was quite hoping to get.

[AkumaNoZeta]

I don't really see the big deal from using the L24 block compared to the L28. Aren't they the same thing? I always thought that Datsun kept the original block design and just bored, stroked, and turboed it as years went by.

[Murch240z]

Same basic design, yes, but not the same block. The L24 doesn't have the meat to be overbored to match the stock L28 displacement, not to mention past that.

[Tony D]

The L24 doesn't have the meat to be overbored to match the stock L28 displacement, not to mention past that.

 

Who says?

[woldson]

Somehow I kinda like you, although not sure why, can't rightly put my finger on it.....

 

I'm interested in seeing what you come up with.

 

And now Tony just put his knuckle in your shoulder blades, teehee.....

[Murch240z]

It was a gross oversimplification, Tony, I know that lots of things are possible. I should have clarified with by conventional methods, or basic methods. Or perhaps simply that there is not as much room for displacement increase as in an L28?

 

As I remember (though I've already proven that faculty flawed once already in this thread), doesn't one usually run into water channel issues in the L24 block when overboring past 85 or 86 mms? That was my thought process and if you add the 'by basic methods' onto it, the statement holds at least a fair amount of water, I think. Perhaps, "it takes highly complex modification for the L24 to match the stock displacement of the L28". Or a crankshaft as long as the LD28 to go with a 2mm overbore (I think I got it up to almost 2.9 playing around on the ozdat calculator once).

 

Right...I grossly oversimplified in response to a simple question when nothing in regards to these engines is truly simple.

[Tony D]

It's basic machining, there's nothing complicated about it. Punch the bores. Stick an LD in there. You get 2.9l SAME as with an L28 having an LD.

 

I was just curious where the information came for such a definitive statement that the "L24 doesn't have the meat to bore to the stock L28 Displacement"

 

Not if you are using an L24 crank maybe, but you stated you already had an L28 Crank.

 

Cheapest thing to do would be boring to, and using stock L28 Pistons. Oversize L28 pistons if the sonic checking reveals a sound unshifted core casting.

 

If it cuts through in a couple of spots...then it's liner time with standard size L28 Liners I guess.

 

There is nothing complicated about this.

 

But I'm still curious as to who says it can't be done because of boring limitations to stock L28 bore size...

[Murch240z]

I don't have some specific source that made the absolute statement that it can't be done. It's simply that from the disjointed information I have gathered so far that the cost and difficulty went up considerably after 85mm, therefore implying more complicated and expensive procedures needing to be done. If that is incorrect then great, I have more options than I thought.

 

Like I said, it was a gross oversimplification, not something I meant as a definitive statement of absolute fact.

[Xnke]

Ok, to answer the 85mm bore thing, yes, it is a Nissan spec according to the Hanyes manuals. It's quoted in a table in the engine rebuild section as being the "Maximum Factory Recommended Overbore". I assume this means that you should be able to cut 2mm oversize bores in any L-series without an issue, as long as they aren't compromised in some other way, like being eaten by corrosion, or cracks.

 

I was curious, so I sliced the three P30 blocks I have, one '72, one '73, and one '74. One cut lengthwise, and then cross cuts across the bores. Measurements of the cylinder walls (83mm bores) were made at four points, per cylinder. The 72 block averaged 4.2mm wall thickness, so a 2mm bore would make the walls approx. 3.2mm thick. The 73 block was the same. The 74 block had 5.3mm thick walls, which I knew already from sonic testing, but the testing also confirmed a suspected crack in cylinder 5. (so much for the 2.8L P30 turbo project...see below.) I didn't feel as bad about cutting it up as I did the functional 72 and 73 blocks...

 

Anyway, If you're gonna do this, an 85mm bore should be just fine, but check for excessive corrosion and cracking or other general unsuitable traits.

 

My recommendation for a 2.7L *P30* block Bang/Buck combo would be as follows:

 

P30 Block at 85mm

L28 crank

L24 rods

Z20S pistons

MN47 head, unshrouded and chambers opened up ALOT to 44.5cc's OR P79/P90 cut down to 44.5CC's or so, this will give approx 10:1 compression. Unaltered MN47 would put you at 11:1 or so, possibly workable with EFI and GOOD tuning, I wouldn't try it myself. N42 will give 10:1 compression unaltered, but open chamber head, so detonation problems are likely.

 

The reason for using the L24 rods and Z20S pistons is to get a flat top piston, because the 85mm pistons for the L18 and L20B are both dished, 4cc's and 11 cc's, approximately. A side effect is a better rod/stroke ratio, but really, I think it's neglegable at this level.

 

If you really want to get crazy, try this 2.8L one:

 

P30 Block at 85mm

LD28 crank

L28 rods

Z20S pistons

 

You'll be .59mm down in the bores, so quench is gone. Good enough for most turbo setups, I guess. MN47 produces a 10.5:1 compression ratio, P90 gives 8.3:1 compression. Looks like a good turbo setup, compression ratio wise, if you are stuck with a P30 Block and want L28 displacement.

[Murch240z]

Excellent, I'd been trying to figure out a combination to get flat top pistons but never figured out that the L24 rods matched up to the Z20S pin height. What are your thoughts on the bang/buck combo using an E31 head instead of MN47?

 

I still haven't decided between the two and I'm not sure about my ability (or that of local machine shops) to match the tight clearances in order to maximize the quench of the MN47 to allow higher compression without detonation, which as I understand it is the biggest bonus of said head. Whichever head I choose is going to get a professionally done port etc job so that end I can be confident in (as I've no issue shipping a head to wherever the pro is) but as for the bottom end work I'm aiming to do all of the assembly myself.

 

If I'm going to buy and have an MN47 built I'd really like to do it in such a way as to maximize the quench as much as possible. I already pump nothing but 93 octane into it so I'm going for a premium gas build regardless.

 

If I were to go with an E31, would I be aiming for the same general CR, about 10:1, or do the detonation qualities differ?

[Xnke]

Well, Monzter is running the MN47 at 11:1, I'd PM him and get details, and I'd ship the head to BRAPP, or 1fastZ, either can do a really excellent job with them. Keep in mind that the MN47's are prone to cracking between the valve seats, and the E31 head is prone to serious erosion to the water passages. I'd get an E88 and weld it up, myself, but I have lots of cores to screw up.

 

Do some more reading on the subject here, and you'll find more answers. I seem to recall that when properly set up and run, the oversize markings on the piston will 'ghost' imprint on the quench pad, not actually contacting the head, but so close that the burr from the stamping causes the ghosting. Don't quote me on that one though, it may have been a fluke.

[Murch240z]

Hrm...according to his Dyno thread he has a one-off N42, but he is running about that CR.

 

Now, my understanding of the subject is extremely flawed as I haven't made it through much of the Racer Brown Article but am I correct in the idea that cam selection has a great deal to do with how an engine runs at a particular CR? I have to admit that the more I think about it the more I like the idea of an E31 with an old-school asymmetrical grind cam.

 

Am I correct in supposing that the erosion issue with the E31 is to do with the age of the core rather than an under load issue?

 

As for the quench pad with the MN47, I remember reading once (and again I might be completely mistaken, I'll do a bit of searching and see if I can dig the thread up) that someone (think it was 1_fast_z) assembles the motor and uses a marking agent when "bump"ing the piston against the head to mark out a custom dish area on the piston to allow higher CR without detonation. That's my hesitancy with the MN47, I'd want to get the very most out of the quench but I don't know if I could find a machine shop locally that I could trust with such delicate work and I would think it's something that has to be done on an engine-by-engine basis otherwise it could do more harm than good.

 

Now, to search for the thread...

 

 

Found it! He mentions the P90 head in his description of the process but it's in a back and forth about the MN47 and maximizing the quench. I'm not sure if I could manage it locally and be confident in the results of such sensitive work and outsourcing the entire motor just really isn't an option for me. This might all be something I should be discussing with whoever I end up paying to do the head, but I suppose it can't hurt to muse.