240 to 260? pistons and boring

[clutchdust]

o.k. let me see if i understand how this works. the 240 was the smallest engine they used in the Z (at least in North America). then, to increase to the 260, nissan increased the stroke but the bore dimensions were the same (correct?). does that also mean the pistons in the L24 and L26 are interchangeable? now, when they released the L28, it had the same stroke as the L26 but a bore of 86mm vs. the 83mm used in the L24 and L26. do i have that right?

dan, your really raining on my parade here! this is what i've found out so far. the L28 replacement pistons speedpro listed in their catalog are being discontinued so those are out of the equasion. now i'm going back to another idea i had, if the block can hold up. i talked to speedpro yesterday about the comparison of these two pistons and here's what i have. the pistons from the L4 1.8L are a compromise. it's listed for '74 LD truck, '73-'74 car and '76-'71 car and LD truck.

these are the dimensions that are the same as what's listed for both this 1.8L and the L6 2.6L:

rings: 2-2.00mm, 1-4.00mm

pin diameter: 21.0mm

piston clearance: .04mm @ 56.3 from head

1.00mm pin offset

these are the dimensions that are different:

piston diameter: 85.0mm, available with .50,.75, 1.00, 1.50mm overbore vs. 83.00mm for L24/L26 and 86.0mm for L28

recessed head: 1.3mm deep x 73.5mm versus 1.2mm x 71.5mm

comp. dist.: 38.3mm vs. 38.2mm. (still unsure what this means)

from what i gather, this will yield a displacement in the 2700cc range and compression approximately 9.5:1 without milling of any hard parts.

now what i need is an L24/L26 piston to compare. if you have an old, unserviceable piston lying around, i'd like to have it. i'll pay for shipping (US only) and it doesn't have to be in good shape, just needs to be whole. i'll get one of these new pistons, make some measurements and let everybody know what i've found

[Phred]

clutchdust,

I explained what comp. dist. is in my first post, go to the back of the class. Your last post indicated the the comp. dist. between the two pistons is .1mm. thats only .004 in. Insignificant.

The displacement of an L-24 bored out 2mm would be 2507.2cc

compared to 2394.6cc stock. Not 2700cc.

The pistons are not interchangeable between the L-24 & L-26.

Remember they have different strokes. Therefore the comp. dist. is shorter on the L-26 to keep the piston from popping out the top of the block at TDC. If you can operate a calculator, use these figures to compute displacement.

1mm= .03937

1 cubic inch= 16.387cc

divide millimeters by 25.4 to get inches

multiply inches by 25.4 to get millimeters

Displacement:

bore x bore x 16.387 x .7854 x stroke x # of cyls

(bore and stroke figures entered in inches)

I used to hate math in school, but it comes in handy now & then.

Phred

[Dan Baldwin]

Get an L28 block and build on that. It sounds like you're planning on a rebuild anyway, the additional cost of getting an L28 should be very small. If you want hypereutectic pistons, overbore .120 and use KA24E pistons with L20A rods. or use the LD28 crank and L24 rods for 3.1 liters.

If you're rebuilding the L24, just give it a .040 (1mm) overbore and use Nissan L24+1mm pistons is my official recommendation.

Go here for more info on Z cylinder heads, and bore/stroke combinations for the L28

http://www.zcluboftexas.org/

Click on "about the Z car", then "L28 bore/stroke combinations".

[clutchdust]

damn phred, i feel like i've been virtually bitch-slapped!

i read your explanation when you first posted but it just didn't register then, got it now. must just take a little rattle of the cage to clean out the cobwebs. so if i now understand you correctly, the L26 pistons had a different wrist pin location than the L24. correct? aside from that, was there any other difference? if so, do you know what the location was for the L24? i'm hoping these are specifications i will find in my manual, when i get it.

dan, the only other engine i'm buying to put in here is gonna be a chevy. not that i have anything against the little nissan, but the old hot rodder addage says, "there is no replacement for displacement". 2003 and that still hasn't changed.

i was hoping to get a decent bump in compression cheap. i wanted to tinker with this engine and get it putting out some decent power until i had the rest of the chassis sorted out and could put together a good odd-fire v-6. man, if you've never heard an odd-fire chevy v-6 at 6000rpm, you haven't heard anything! it's a creepy sound, cool as hell, but creepy.

since i just got the car, i don't even have a manual for it yet. figured i might just as well put it on my christmas list since that's only a week away anyhow. i don't know what the factory rated bore and stroke on these cars is. i was waiting on the manual to get that information just to get some decent ideas of what i was looking at. so apparently, i didn't understand the difference between the L24/L26/L28 engines correctly. hey, it's a learning curve. only owned a Z for a whole week now.

[boltmans]

Sorry to be another person to rain on your parade, but if I were you I would look for a used 280 engine and run that and save your $$ for the big engine. You can probably find one in good shape for $200 or less and put the rest towards the new engine. You could even freshen up the 280 with rings/bearing/timing kit amd probably stay within you budgetary limits. As you said your self, there is no replacement for displacement.

If you are stuck on the 240 engine, I would be surprised if you can do all you want to do for <$1000 unless you have a full machine shop in your back pocket, and your getting the pistons for free. Also if you realy want to bore 0.120 over on an L24, you better find a "tuned" torque plate when you do the honing and make sure you use a fresh headgasket with the torque plate, not just a slab of steel. The cylinder walls are going to get pretty thin so your bore distortions are going to get much worse. This will give you terrible oil control and increased blow-by since the rings won't seal as well, which will rob your power, possibly enough to get you back to the power level you started with or even lower.

Another way to get yourself some torque is to just put in a much lower gear 3.9 or 4.11 R200 rear end. It won't increase the available engine torque, but will increase the available torque at the wheels, but you will trade off top speed. You are probably going to need to upgrade the rear anyway for the chevy engine. I believe that the production R180 rear end is marginal for the V-8 swaps, but maybe someone else can elaborate on that.

[Dan Baldwin]

I agree that there is no substitute for cubic inches. But in that case why even BOTHER with the L24? You're talking about a full rebuild, no? My point was that it'd be just as easy and not much more expensive (if any) to drop in an L28.

Also, why bother with a v6? A small-block with aluminum heads reportedly weighs about the same as the Nissan inline 6. BTW, is the GM 2.8 an "odd-fire" v6? If so, it's one of the few internal combustion engines I've ever heard that positively turns my stomach! The worst exhaust note EVER! I'm sure you must be talking about the 3.8 or maybe the 4.3 liter v6, no? Still, I don't know why you would choose that over a small-block V8.

My recommendation remains: if you're going to do any tweaking on a Nissan OHC inline 6, it may as well be the L28. They're still easy enough to find, and one from the junkyard shouldn't cost you as much as the pistons, anyway. Or you could just buy a running one and cut your effort and costs and get the same hp results you would've gotten tweaking the L24.

[Phred]

Clutchdust,

You know, were all just a bunch of hotrodders who like the Z. One of the fun parts is doing your own thing with your own machine. Many of us have been down the same road your on, and we just don't want to see you loose your wallet along the way. Thats why most of these posts have advised you to drop in a L-28 till your ready for something big. The L-28 would be cheaper, and have more grunt than a bored out L-24. So, do your own thing, have fun, and let us know how it goes. Then, you can say to us ,"see, it worked", or we can say, "see, we told you so!".

Merry Christmas

Phred

[clutchdust]

o.k. guys. you've sold me. i may re-ring the original L24 (depending on the condition of the cylinders) and shave the head just a bit, but no more major components. probably just exhaust, pertronix and pretty much call it good.

dan, i was and still am talking about the 4.3. it's pretty much a 350 minus two cylinders. in fact, many of the parts interchange: pistons, rockers, lifters, timing chain, well, you get the idea.

why the v-6 as opposed to the v-8? well, both GMHP and brodix makes aluminum heads for the 4.3. so now instead of a SBC v-8 that weighs about the same as a stock L24, i'm talking about one that weighs ~100# less. and sits further back. don't forget, for what i want to do, power means alot but balance is everything.

speaking of power, it's pretty easy to get 300hp out of a N/A 4.3, even on pump gas. how can you beat that?

so i'll get it running and go from there. struts, swaybars, brakes and so on and so forth. once the rest of the car is ready, then i'll drop the v-6.

[clutchdust]

well fellas, the wifey-poo did come through on the manual for christmas. so i've been reading up a bit and noticed a couple things. thing number one: the haynes manual lists the CR for the 240 at 8.8:1 but the CR for the 260 at 8.3:1. from what i've seen so far, it would appear the 240 and 260 share the same deck height, piston diameter and dish size. so did the 260 come with a different head with more open chamber?

thing number 2: dispite the lower compression, the manual lists the 260 at 14hp more than the 240, at the same RPM no less. how so? are the peak HP numbers closer at different RPMs?

if i went ahead and had the head shaved, say, .020-.030" for an increase of CR, can i take advantage of that with the original cam? or should i consider a new cam while i'm at it.

once again, the goal is just a slight bump in power while freshening up a motor that hasn't run since George Bush was in the White House. oh wait! i mean the first one.

looking for an honest 165-170hp. is that unreasonable for a mostly stock 2.4L with just headers and some tweaking?

[Phred]

clutchdust,

The difference in C.R. between the L-24 & L-26 is only .3 (three tenths). Not worth fussing over. The reason the L-26 has more HP is simply a result of larger displacement, and a cam with 8 degrees more duration. To my knowledge all 260's came with the E-88 head. Which also came on the later 240's. The early 240's came with a E-31 head which had less cc's in the chamber. If you surface the E-88 head .020 you will gain a half a point (.5) of compression. If you do this, make sure to have a three angle valve job done at the same time. The extra compression won't do anything unless you can get the valves to flow a little better too. If you do all of this plus a good header & exhaust, make sure to run some SM needles in the carbs. At that point, I'd be interested to see some chassis dyno numbers, before doing anything else.

Phred

[clutchdust]

sounds like i'm beginning to build a plan here. :classic: i haven't pulled the valve cover off yet so i don't know which head i have but i hope to do that in the next week or two. still have plenty of projects to tie me up around the house now.

would anyone suggest going with a 260 cam then? if i just bought a 260 or even 280 OEM grind cam from one of the aftermarket cam grinders, would i need to change out springs, rockers and retainers? would it even be worth it?