Long Rod I6 Hybrid (long)

[DAW]

In the spirit of Hybrid Z I'm offering some food for thought. The problem with putting the LD28 crank (stroke = 83mm) into the L28 block is that it's too cramped in that vertically-challenged block. The standard conversion uses Z24 or KA24 pistons (modified) with L24 rods (133mm). This gives a rod/stroke ratio of 133/83 = 1.6024, which sucks. I'm not going to go into rod/stroke and performance here, read-up on your own, but that's good for a truck, not a performance unit that could hit the track.

 

OK...so here's the crux, I crunched the numbers prior to taking this project on and I decided it was worthwhile, I consulted NISMO and they said "forget it".

 

So, take a LD28 engine and get rid of the cyl head, cast iron and it weighs a ton! Get rid of the diesel fuel pump and front cover (keep the water pump), keep the oil-to-water cooling unit on the oil filter assy. Massive alternator unit has an integral vacuum pump on its tail-end, could be useful if going turbo. Specs on internals: 84.5mm bore, 140mm rods, massive, with 1" floating wrist pins (not unlike a set of rods available from NISMO). Compression ht of pistons = 46.5mm and that's alot. Block ht. is the same as L20B and that's where the front cover is going to come from for our hybrid engine.

So, the first phase of my experimentation was to put a N42/N47 series cyl head onto the LD28 block. This requires the aluminum head to be drilled for a 10mm headbolt to a 12mm headbolt. Nothing special here, most of it was done by hand. Headbolts were from BMW, some washered, 3.0 inline 6 cyl or 2.5 4 cyl (I think); but they were the right thread pitch and length, and 12mm dia. Reuse the diesel head gasket. Said head makes about 9.8:1 as I recall. L20B front cover and LD28 water pump will go together with a bit of grinding to the water pump.

 

Anyway, it runs good. Presently it's coupled to an L3N71B A/T. One notable quirk is that the diesel A/T has a LOW stall speed.

Luckily, with the good compression ratio, it's ready to jump off the line with good response and torque.

 

So, rod/stroke @ 140/83 = 1.686, better already than the L28 block/LD28 crank hybrid, and that's with a HUGE compression ht of 46.5mm on those diesel pistons.

 

Stage II is to fit a P90/P90A head to the LD28 shortblock and turbocharge.

 

Stage III is to overbore the LD28 and fit with longer rods and pistons with more std compression hts; let's choose L28ET pistons (bore =86mm, dish = 10.9cc, comp. ht.= 38.1mm). So, with comp. ht. 46.5 - 38.1 = 8.4mm; then you can add 8.4 to the rod length of 140mm and that's = 148.4. Well, the closest Nissan rod is the 148.6mm rod from the Z22E engine (not to be confused with the Z22S truck engine with its 146mm rod), and there you have it.

DAW

[DAW]

BTW, 148.6/83 = 1.781 is a much-improved rod/stroke and something impossible with a L28 block stroker.

DAW

[TimZ]

I've often thought of doing the same thing - there are lots of attractive attributes to the LD28 block. I stayed with the L28 block and crank, because that's what I had - for me the LD28 crank wasn't that big a deal. I had 136mm rods made, with arias forged pistons - the rod ratio comes out to 136/79 = 1.7215.

 

I have never investigated it myself, but someone had said that the LD28 block was incompatible with the Z engine bay - something about the oil pickup being in the wrong place, maybe? Any truth to that? If I ever do another turbo motor, I would seriously consider using the LD28 block.

[BLKMGK]

Other OEMs, most notably GM, made their V8 diesel blocks stronger. I wouldn't be surprised if that block has more beef to it too. Diesel's (sp?) generally run pretty high compression to auto-ignite thus the added strength. Honestly this sounds like a good candidate for a gasturbo motor. I'm surprised NISMO blew it off! Can you put a stick behind it? How far are you going ot take it and when will you be slapping turbos on it? Sounds like a neat project!

[DAW]

I should add a few addendums:

I am using a "mule" to do the work on this project, it's a Diesel Maxima that I bought specifically to do the diesel/gas conversion. It's also a lot less conspicuous during road testing than a Zcar. Once I'm satisfied that it's right, it is going in a '72 240Z a/t car (and hope the taller engine clears the hood). The Maxima is a front sump engine so I'll have to switch pan & pick-up. One thing nice about the turbocharging coming up is that the Maxima pan already has an oil drain (for the alternator-mounted vacuum pump) which I can use for the turbo oil drain. Presently, it has 240Z headers on it in the Maxima, and the Maxima has 280ZXT struts and sway bars and Infinity 15 x 6 1/2 wheels. I cut the springs a bit, the change from the diesel to gas cylinder head alone must be a 60-70lb wt loss.

By the way, the LD28 block is 19.7mm taller than the L28, the same ht difference between an L20B and L18. So, you use L20B timing chain & front cover.

As an aside, the diesel exhaust manifold is a nice unit, separate chambers, rectangular port, and alot like the early Z manifold but without air pump fittings. The intake manifold is also interesting, with long curved runners, the down side is that they have no injector mountings.

I'd like to have the LD28 block sonic tested to see just how much of an overbore would be possible. I believe that there is a lot of metal there. The bare block itself is not much heavier than an L28 bare block, it's the head, diesel pump, and accessory brackets, etc that add so much weight to the diesel engine.

The next step for this project is to change the L3N71B (3spd, lock-up torque convertor) for an L4N71B, and from a normally aspirated gas engine source. The stall speed on a turbo trans is too high; on a diesel, too low. Once squared away, I'll put the engine/trans into the 240Z and start again with diesel/gas hybrid #2: intercooled turbo.

The internals in the LD28 are massive but as such won't want to spin high rpm, but a turbo doesn't need high rpm to make good power.

DAW

[240Z Turbo]

Daw, food for thought. It is nice to have a higher stall converter in a turbo car if you are running a monster turbo. I ran a 2900stall with my T64 turbo and a built 4N71B and I thought the stall was too low. My new stall was built by protorque and it is a whopping 5700rpm. I know this is too high, but I am waiting to finish my new twin turbo setup to have it lowered to about 4000-4500rpm. The stall will not actually rise above 3200rpm unless you throttle and start building boost. It does not drive around slipping like hell and makes for an awesome ride. Anyway, if you need any info on the 4N71B buildup just let me know, it is very cheap and easy and will survive 500hp in a 240z with no problem.

[DAW]

Thanks, and yes I'd like some info on the build-up. I presently have one E4N71B from a normally aspirated 300ZX, and one from a 300ZXT. My info says the na has 2150-2450; and the turbo 2500-2800 stock stall speed. I was going to fit either with the Lseries A/T bellhousing. I guess if I get the urge to run an autocross course I'd be better off with the higher stall speed even with na engine. I'm not a big A/T type, but I know the '82-'83 280ZXTs were faster than the 5spds (turbo revs are kept up better with gearshifts in an A/T vs M/T), either one benefits from a compressor by-pass valve (left off by Nissan along with the intercooler).

If you have any budget-minded tips for the L4N71B, please pass them along. I can fix the tran(s) up before installing in the car.

DAW

[fast240z]

There is a fellow who lives in Santa Rosa, CA who used to run a Datsun shop by the name of Cam Lu. Several years ago, when folks were just waking up to the concept of using the LD28 Crank to stroke the L-motor, I spoke to him and found out his recipe for success. Cam, as I recall, did a lot of R&D work and was using the LD28 block as well as the crank. He mentioned doing extensive modifications to the Water and Oil passages. He was building them with high compression and large overbores to come up with some truly vicious street and track motors. I think he prefered 50mm Mikunis for this application. The last of these I saw, he was plumbing for nitrous. Sadly, Cam was injured and had to close his shop. He is still around, just tough to get ahold of. I always thought this would be a trick way to go building a long-rod motor using the LD28 block (see smokey Yunik's theorie's on Long rod motors) but was equally concerned with the extra height of the block giving away the "cheater" motor. That's all I need, some ambitious tech inspector measuring my engine height! Sounds like a great project, keep us all informed.

 

Michael

[DAW]

Thanks. I'm more interested in doing the technical experiments than in trying to squeeze through trackside inspections. I'm more likely to run an autocross for "time only" than to hassle with Street Prepared or Street Modified rules. Solo I is also a great place to flog the car.

I've got a few engine bay photos around on Kodak disc but I don't have an html. I'd welcome someone to help me post these.

DAW

[BLKMGK]

Shoot them to me but if they're HUGE in file size send me a noe offline for a better address. I'll shrink them down and post them on my site for linking here. I'll be out of town starting this coming Tuesday for a week so if it's not this weekend it might have to wait (shrug).

[DAW]

I dug up the photos and I guess I forgot just how bad they are. Let me shoot some more, in better light, and I'll get in touch.

Thanks,

DAW

By the way, I noticed that CA20E pistons share bore size with LD28 = 84.5mm; does anyone know pin size, compression ht, & dish of the CA20E piston? Also, there is a good discussion of rod/stroke ratio and effect on peformance in "How to Hot Rod & Race Datsuns", author is Waar, I think.

DAW