Theoretical long rod turbo L-series, L26ET?

[DAW]

I've yet to transfer the LD28 bottom-end/N42 topped hybrid I put together in '96 or so from my '82 Maxima into the '72 240Z waiting for it but one of these days I'll get around to it. The front sump/oil pickup vs rear is not a big deal, but it is an issue in the transfer between cars.

 

Meanwhile, I use the car as one of my family cars, running my kids around to school, soccer, getting groceries, etc. It's very reliable, starts instantly every time. This is my "mule" for setting up the LD6/L6 engine and it's the "budget" prototype with stock bore (84.5mm), rods (140mm, large floating pins), and pistons (46.5mm c.ht.) which yields just over 10.0:1 c.r. with the N42 head. Cranking pressures are 210-220 p.s.i. with the stock N42 cam. I've never heard it ping. I've just done some crude tweeking of the stock N42 e.f.i. by changing sensor resistance values, thermostat, AFM door spring tension, etc. I'm using 280ZX headers with long secondaries into a 280ZXT rear pipe & muffler.

 

BTW, the chassis components have been substituted on the Maxima with 280ZXT components and I cut the diesel springs down all around (the nose was pointing up without the LD28 upper end on the LD28 bottom end). I'm using the LD28 torque convertor (the Maxima trans has a hydraulically-activated lock-up convertor that the 280Z/ZXs didn't get). The stall speed is lower than the gas engine convertor but with the stock cam it works fine. With the high compression ratio the throttle response is excellent and the power goes right to the ground. The car is just a daily driver and looks like a stock Maxima except it has Infinity 15x6.5" wheels with 205/55-15s, an Audi 4000S front air dam and later year Maxima trunk-lid spoiler, and it has a lower-than-stock stance. Basically, it makes a good "sleeper".

 

The plan was to swap it straight across to the early Z which is an A/T car and substitute an '84 300ZXT 4LN71B trans for the L3N71B, sort it out, then put a mild cam in it and select the best final drive ratio with that combination. I guess that's still the plan for the first stage hybrid, but the Maxima makes a very practical vehicle as-is and too useful to take off the road right now.

 

What I may do instead, is to remove the N42 top portion and modify and install a P90 L28ET top onto the stock LD28 bottom-end. I'm confident that the bottom-end, built for 22:1 or so c.r. can handle a significant static c.r. increase and boost increase vs L28ET. Since the LD28 pistons have a tiny dish vs the 10.9cc dish of the stock L28ET, with equivilant 2.8L displacements the P90 head yields an increased but manageable c.r. on the LD bottom-end. I don't foresee getting by with the LD28 torque convertor, but I may choose a n.a.-range convertor rather than a turbo-range since the static c.r. will be higher and throttle response good; turbo lag lower.

 

Intermission. I'm not going to risk losing this book to some computer glich or crash, so I'll post part II separately. DAW

[Cody 82 ZXT]

So how long is the intermission?

[DAW]

Part II.

 

So the LD28 bottom-half/P90 top-half is the "budget" stage II project and both of these engines (stage I and II) have decent rod/stroke improvements over the L28, and far better than the 83mm stroke/133mm rod formula. The next stage is to optimize the performance capabilities through increasing displacement (bore) of the LD28 and selecting piston/rod combos to get the best rod/stroke that the taller LD6 block affords.

 

Stage III is still budget-minded as it uses stock Nissan L4, L6 and LD6 components rather than custom pistons, rods, etc. It is an overbore from stock 84.5mm to 86mm (unlikely that this is the max overbore, discuss later), use L28ET pistons (38.1mm c.ht.), L20B rods (145.9mm, same pin size, 21mm), and the P90 top-half. The 10.9cc dished turbo pistons keep the c.r. reasonable when the displacement is increased by the overbore, and the rod/stroke is now 145.9/83mm = 1.76.

 

I've heard a lot of hearesay about the hybrid engine I'm talking about (like it can't be done, the LDblock which is built for 22:1ish c.r. can't be overbored [right! makes sense to me]), but haven't compared notes to many fellow builder/users of this engine hybrid. I'd like to compare notes to others out there who have actually built and driven cars so equipped with LD28 bottom-half/L6 top-half.

 

I discussed my plan with a NISMO tech-rep (Ron) over the phone back in '96 or so and he was helpful but told me it couldn't be done. I wouldn't have pursued it if I had unlimited access to custom forged pistons and rods in order to have a decent rod/stroke performance engine but since I don't, poverty is the mother of invention. You have to crunch all the numbers, measure and search for a part to fit what you need (BMW headbolts, L20B timing cover, etc.) to make this work. Hey, what about marketing a kit requiring a customer's good bare L6 head core to exchange for a bolt-on conversion bare head and Stage package of choice? Not difficult, but I don't have the time to do it. Better do it yourself before the LD28 blocks become valuable. Most are discarded when the crank is taken out. DAW

[Doug71zt]

Report on the 2.2 dodge pistons - They were made by TRW, forged flat-top in 87.5mm bore or 88mm oversize. Compression height is 1.610 inches or 40.8mm as far as we can tell. I don't have the engine calc. on this computer so I can't verify that number. They are not available from D/C mopar performance. Dis-continued like all the rest of the good stuff.

 

I'm sure that some other company makes these pistons.

 

Doug

[DAW]

My posts should be moved to the "six-cyinder" forum or "other engines" as they fit better there than in the "turbo" forum where they sprung up, but if the moderators could library articles or FAQs somehow, rather than defer to "search", I think it would benefit all as we look for answers to our questions.

 

Anyway, Kenny, I just used an extremely unscientific and crude method to assess the cyl wall thickness of some L6 and LD6 blocks lying around and these are the relative values of comparative wall thickness, not in units, but as related to each other. Personally, I'd feel comfortable with a .120" overbore of a F54 block, 0.080" of an N42, and .120-.160" of an LD28 based on my crude approach. I doubt there are many machine shops that would overbore a Nissan block much more than .120" so I'd limit my overbore on my LD28 blocks to 87.5 to 88mm bore. I'd recommend that anyone boring a block more than 0.80" over, have it sonic-tested rather than using my assessment.

 

I've worked up combinations with larger bores and longer rods which should work OK, but the greater the displacement, the greater the demands on piston dish volume and combustion chamber volume, especially if you want forced induction. DAW

[ToplessZ]

What about using a head plate to shim up the head. I wouldnt think it would be hard to make. Maybe weld to the block. What about using aluminum with head gasket on each side. I would think it would be easier to do that then all the LD28 conversion mods. Also what would happen if you used an LD28 crank with turbo rods and pistons. Could that be done with say a 2mm headgasket or is that going to cause the pistons to be too tall. I want to hear more options. I really want to run a long rod high revving turbo engine yet still keep it reliable.

[DAW]

A plate is an excellent idea as long as the total block ht. without the top head gasket is equal to the LD28/L20B/LZ20/LZ22 blocks as you want to be able to use the L20B front cover (probably just forget about providing a top hole for the L20B cover, or put one into the end of the plate).

 

Finding head bolts or studs 20mm longer than L6 bolts with same dia. and thread pitch is the quest. Slightly longer bolts are OK with doubled hardened washers, but not significanly shorter. Any metric source can be explored...you take a set of calipers to a JY and start the search.

 

Ultimately this may make more sense as there are no front oil sump/pump issues and no machining the bolt holes of the L6 head to enlarge for larger dia. LD6 headbolts. DAW

[JMortensen]

In order to do this, they were forced to increase the L20B block ht by something like 19.7mm more than the L18.

A plate is an excellent idea as long as the total block ht. without the top head gasket is equal to the LD28/L20B/LZ20/LZ22 blocks as you want to be able to use the L20B front cover (probably just forget about providing a top hole for the L20B cover, or put one into the end of the plate).

 

I'm missing something. If the block would be 19mm taller, then presumaby the plate would also be 19mm tall. How are the piston rings going to pass over from the block to the plate. Seems like a recipe for ring failure. I don't think you'd want a piston with 20mm height to the first ring either, since you'd then have a really low pin height on that piston, which is also something to be avoided.

 

What am I missing?

 

Jon

[DAW]

You'd have to use a F54 block, fix the plate to the block for overboring both the block and plate, and drop in a sleeve. DAW

[JMortensen]

That makes more sense... thanks.

[ToplessZ]

I think if you welded the head plate around each bore then it should be able to be honed just as if the block were taller. You would definatly want to find a good welder but I think it would work. Any more ideas. And anyone want to come up with some different dollar figures and usable components. I really like this thread... for those of us that dare to be different I also havent been able to calculate on my own what would happen if one used the ld28 crank with l28et rods and pistons. How many more mm of deck height would be needed on the f54 block for that to work? I still like the idea of the l24 crank and Rods in the f54 block with a big turbo and alot of boost.

[DAW]

You have to do the math. There's no way L28 turbo piston and rods will work. You'd be looking down into the bore saying, "anybody down there"?

 

You could use the piston but you'd need a longer (e.g., L20B [= 145.9mm]) rod to bring it up to deck ht.

 

B.T.W., 186.5mm is the magic LD28 deck ht. (46.5 + 140mm) from the center of the LD28 rod crank throw. L28ET piston (38.1mm) + L20B rod (145.9mm) = 184.0mm deck. Better to use the LZ22E rod = 148.6mm. That's the correct formula and it puts everything exactly to deck. I wrongly cited the L20B rod in an above post. I meant LZ22E; (note the LZ22S rod is 145.9, same as L20B; LZ22E is 2.7mm longer at 148.6mm, [and piston c.ht. adjusted accordingly]). DAW

[ToplessZ]

Daw I think we are misunderstanding each other. I didnt mean l28et rods and pistons in the deisel I mean in the f54 block with the ld28 crank. In that combination how much piston are we talking about peaking over the deck surface? Also when using a headplate wouldn't it be possible to retain the stock timing cover?

[DAW]

The L28ET piston/rod assys are way too long if you use the LD28 crank in the L6 block. The L28 is 130.4 + 38.1mm from crank pin center to a zero deck ht. Putting in an LD28 crank means increasing stroke from 79 to 83mm which adds half of that increase at the top of the TDC distance from crankpin center to piston deck ht.; in this case, there would be 2mm of excess piston deck ht. Using an extra thick head gasket might compensate (if the rings aren't protruding out of the block at TDC), but the main drawback is the bad rod/stroke which would result. It would be worse that a stock L28, which is a compromise for a performance engine as it is. You'd be making it 130.4/83 = 1.57. Why even bother building an engine with that kind of geometry? DAW

[ToplessZ]

hmmm didnt know the rod and stroke would be that bd. Well hopefully we can figure out something. I have an l24 crank and rods and a p90/f54 combo they could go into. I think that with t61 turbo might be rather interesting.