DAW

I think round ports are more of a problem re no abundant round port headers vs square ports. Also, if one is using cast iron manifolds, there are much better square ports than round, including turbo manifolds. I have removed liners before and it's a pain. I found a round port ceramic-coated header in a JY and I'll leave liners in for that one, but I want to use a square port manifold on another round port head and it appears that the porting for manifold gasket match will be better without the liners there, both for machining and flow. Any experience adapting round port head to sqare exhaust? DAW

They'd look better if they didn't angle down towards the bottom, are they flipped R to L and upside down? BTW, two other questions: 1) Has anyone converted a 280Z rear tailight/panel to a 240Z style? 2) I've been trying to come up with a simple projector headlight conversion for the Zcars and a Toyota MR2 Spyder headlight looks about 7" round and beneath a plexiglass cover. Any experience with this? DAW

Thanks. 40cc must be about right, working back from the Maxima c.r. of 8.9:1 and assuming flat top pistons. Looking at the chambers next to E31, N42, & P79 heads it appears closest in volume to the E31. Actually, it looks most like a W58 L20B combustion chamber (40cc) in size and shape. The Maxima N47 looks like an excellent choice for updating a 240- 260Z, given it already has hardened valve seats and L28-sized (35mm) exhaust valves (but means must notch the top of the cylinder bore on L24s, L26 comes notched from factory), and if converting to f.i. later, it's a bolt-on to this head. The drawback is it's got round/liners vs rectangular exhaust ports. Also, must get rid of Maxima cam, it has reduced intake lift vs Zcars. If using on L28 & larger, L28 intake valves (44mm) would need to replace Maxima (42mm). There are some strange finds at some of the Japanese engine warehouses. I have a rectangular port "N47" on one of my cars that is essentially an N42, and I've seen P90 heads on na stock L28 f.i. engines from Japan, so I wouldn't be surprised if there are f.i. L24s from Japan with the Maxima 40cc head but with rectangular exhaust ports. DAW

Note to "Bobby", above...your site is a wealth of info, presented in an articulate, straightforward manner. Thanks!! DAW

Of course a significant difference in displacement makes more power, but that's apples & oranges like "my 454 chevy will beat your 350 chevy". The question is will your 302 chevy beat my 305 chevy? I think it will. As to the comparison between the configuration of the old Nissan 3L V6 to the new, it doesn't matter if it's a V6 or an L6, I think it may allow for more tuning and power using a multivalve head and variable cam timing re the characteristics of a long-rod engine vs short (new r/s = 2.00, old = 1.86). The important factor is the intended use of the engine, road race vs drag race vs autocross vs street, the budget of the builder ($/hp), and the fun factor for the effort/ingenuity/uniqueness in building the engine. Different strokes for different folks. DAW

re LD28 block in 240-280Z, it was stated that it won't fit under the hood. I'm not sure about that, I checked hood clearance by sticking a stack of modeling clay on the highest point of the engine of my '72 with L28, sprayed vegetable oil on top of the clay to prevent sticking to the hood, and closed the hood. The LD28 with L28 head is 19.7mm taller than the L28 and although it's close, it looks like it will fit. If not, I've got a '67 Vette 427/435 hood scoop that looks good on the car. My concern is the clearance to the strut bar. There's no way that it's going to clear without modifying the strut bar and using a hood scoop; or, dropping the engine by slotting the mounts. DAW

So why did Nissan change the configuration of their 3 Liter V6 from 87mm bore x 83mm stroke, to 93mm bore x 73.7mm stroke?...Hey, wait a minute, those stroke specs look familiar..83mm = LD28, 73.7mm = L24. DAW

Hands down: 280ZXT motor, with the complete wiring harness & ECU & sensors. Add an intercooler and compressor bypass valve and start working on brake upgrades. DAW

I found an N47 head in my garage while spring cleaning and it is not the same as the N47s I have from 280Zs. I think it's probably from a Maxima L24. It has 35mm ex. valves, 42mm int. valves, and the peanut-shaped combustion chamber of a P79. My question is, what is the cc volume of this head? I don't see how it could be equal to the 53.6cc volume of the P79 because with flat top pistons, the L24 would have to have a much lower c.r. than the '81-'83 L28 (8.8). Anyone know the cc of the Maxima N47 head, or the c.r.? DAW

Typo above re Z20E connecting rod length: should be 152.45; not 154.45. BTW the truck (Z20S) engine rod is 148.6 (r/s = 1.73); while the car (Z20E) r/s = 1.78. The point is that a difference in r/s of .05 is significant enough that Nissan engineers separate rod & pistons to use in the same block, tailored to application. DAW

It's not a project for everyone. I've done an L28 stroker both ways. Why did Nissan increase the height of the L18 block when they increased the stroke? Rod/stroke. The L18 is essentially an L28 minus two cylinders (85mm vs 86mm bores, too), with rod/stroke = 130.4/79 = 1.65. Nissan retained the 85mm bore in going from the L18 to the L20B, but increased the stroke to 86mm and at the same time increased the block ht by the same distance as L28 vs LD28 ht, thus allowing use of longer rods which improved rod/stroke (L20B = 145.9/86 = 1.7). Nissan went further with factory long-rod engines by changing the 145.9 rod to 154.45 in the Z20E (car) engine which has a r/s = 1.77. The rod length differences are taken up by the differences in piston compression ht. When they further stroked the shortblock in the Z22 to 92mm, they increased the rod length in the car engine (Z22E) for a r/s = 1.62; while the truck engine (Z22S) kept L20B rods. With the increased stroke the r/s = 1.59 (a low r/s is OK for a pulling/lugging truck). In order to stroke that engine any further, they again had to increase the block ht (Z24 = 96mm stroke, r/s = 1.72), or the r/s would have been too low. I used a mule car ('82 Maxima) for the initial LD28 block/crank stroker development. I took a diesel Maxima shortblock (84.5mm bore, 140mm rods with 23.5mm pins!) r/s = 1.69, and adapted an N42 head (10:1) with 280Z injection & 280ZX distributor. 280Z wrapped header with 3 into 2 3ft collectors into 2.5 exhaust. The engine runs smooth, strong & torquey, and reliable. The shortblock has 225K miles on it. I've driven it regularly for over a year. I don't go racing around in this Maxima but on occasion I've seen dropped jaws in the rearview mirror. This engine is going into a '72 240Z daily driver. My only concern is hood clearance in the Z due to the taller block (19.7mm). A turbo top-end assy combination onto an LD28 shortblock is next, then some overbore/longrod combinations using LD28 block. I think this taller block would have been the next natural evolution of the L6 by Nissan had they not gone with the VG30. DAW

addendum above, the L28E pistons are flat tops that the factory uses with the p79 head; they come in an F54 block. DAW

Stroker short-rod engine or long-rod? That's the main decision you need to make because one involves using your 280Z block with the LD28 crank, and the other uses the LD28 block and crank. Read up on rod/stroke ratios and why a long-rod engine is better suited to high rpm use and tuning. The usual stroker L6 is an L28E block bored .120" over, to 89mm; LD28 crank; L24 or L16 rods (9mm bolts, 133mm length); Z24 or KA24 pistons, machined down a bit on top to reduce both compression ht and dish cc; and L28E cylinder head and gasket/cc of choice for desired compression ratio. Rod/stroke = 133/83 = 1.67. An alternate stroker engine is LD28 block bored 0.60" over, to 86mm (or larger if using o.s. L28 pistons); LD28 crank; Z22E (E not S) rods (9mm bolts, 148.6mm length); L28E (p79) flat-top pistons; L28E cyl head of choice, head bolt holes drilled from 10mm to 12mm; BMW headbolts; L20B front cover; L20B timing chain; drill block boss for rear dipsick/rear sump use (Maxima is front sump); Z car oilpan. Rod/stroke = 148.6/83 = 1.79. DAW

SUs get my vote too. I've had both setups and the SUs are a lot more driveable. Check out the mini manifolds/adapters between the DGVs and the Z manifold. It curves down then up again like a sump in a sink drain and that can't be good for fuel delivery. There's a lot you can do to power tune SUs (more than just putting in "SM" needles). One place the Webers have it over the SUs is in the cold start: two accelerator pumps and butterfly valves vs none. DAW

It's good that there's no place for the Emergency Relief Valve, also known as the "source of confusion valve", you don't need it if you've got a functional wastegate. Besides, as another member pointed out, if you incorporate an Eclipse Compressor Bypass Valve in your system it can function as an inadvertant ERV (pop-off valve) anyway. DAW

I searched back too but it didn't come up. In it I recommended a book, "How to Build & Power Tune SU Carburettors" by Des Hammill, published by SpeedPro series. The Z Therapy video will be a great help too. When you say it runs fine when cold, do you mean with the chokes on or off? The chokes on these carbs is a linkage that mechanically pulls down the jet from the needle (like backing out the knurled mixture adjustment, except exaggerated). The choke linkage at the carb can stick, leaving the carb way too rich once engine is warmed. DAW

I went to a wrecking yard for parts for my rear disc conversion.

Do a search of this site for SU adjustment tips. I know I responded several months ago to a similar post. First of all, don't do anything else (timing, etc) until you've reversed what you know you did with the mixture adjustment. Think about what's happenning when you turn the adjuster: it's right hand thread; visualize looking at it from under the car while you turn it clockwise, you will be raising the jet and in its center is a tapered needle extending in it from above, as you raise the jet, less fuel can flow through the jet/needle so you are leaning the mixture. Get back on track by leaning (engine off) each jet in until it stops the out two turns. Good luck. DAW

Could be ignition system since it's falling down under load, but if it's been sitting then fuel contamination (esp water) could be the problem. Change the fuel filter anyway and use gas treatment in a full tank of fresh gas. Was the car running all right when it was parked, or is that the reason it was parked? DAW

Get a distributor from an'81-'83 280ZX or '81-'84 Maxima. Direct bolt-in and has the module on the dist. as part of the assy; one or two wire simple hook up. Forget points, forget the dual pickup 260Z and the 280Z with the module inside the passenger compartment. DAW

All 240Z heads have smaller valves than 280Z-ZX heads. Consider the 240 heads only if you're planning on installing L28 valves in them. DAW

It looks like you didn't get much of a response, so maybe I can give you some ideas. First off, a '75 L28 isn't a performer because it doesn't have much of a c.r. Bang for the buck, you'll get a lot from increasing it. Either swap the shortblock from your N42 to an F54 from an '81-'83 280ZX (or just the piston/rods). Better yet, get a set of '73-on L24 rods (9mm bolts), have your L28 dished pistons machined to take the rim down to the same plane as the dish (make them flat-tops), and put it together. That way you not only bump compression ratio up to about 10:1, you also improve the rod/stroke from 1.65 to 1.69. You'll need to richen up the fuel supply if you increase compression, and weakening the AFM flap spring slightly and add some resistance to the water temp sensor circuit to the CPU (change the 195 to 180 thermostat also). So far you haven't spent alot of money and may be able to improve the exhaust flow with some of the rest. There is another approach (which purists won't like) and that is to leave the internals of your 8.3:1 L28, with rectangular exhaust ports, stock and put on a turbo/exhaust manifold, injectors, cyl head temp sensor, knock sensor, and turbo CPU and harness. You'd have to make this a low-pressure turbo system (ala Volvo approach), but compared to a stock '75 L28...night and day difference. DAW

While on throttle bodies, does anyone know why the L28 Turbo is excluded from the Weber "big bore" T.B. applications in MSA catalog? DAW

It may be that the valve surface itself presents enough surface area that at high boost it augments the ported signal going to the underside of the diaphram, and is overcoming the otherwise equalizing pressure on the top side of the valve. If the valve is flipped over, you can see a small opening which is ported to the underside of the diaphram. I'm wondering if a fix on high boost cars would be to place a restrictor in that port to reduce it's contribution wanting to unseat the valve. This isn't solely speculation, I have a valve in my hand and when the ported signal to the underside of the diaphram is eliminated, the closing force of the valve is definitely increased. What might be a better fix would be to plug the underside port altogether with a ballbearing, or a base gasket that occludes the port. A small hole should be drilled into the port column which runs along the side of the valve so that there's not an airtight compartment which would require force to compress its air. I think this modification might fix the unwanted pop-off of the BOV, but at the expense of some of the original function of the valve because it needs a stronger vacuum signal now to open as intended. Many turbo'd cars use electric vacuum pumps, solenoids, and/or reserve tanks for various signals; maybe a throttle switch to send a vacuum signal to the BOV between shifts would work. DAW

yeah, most turbo cars don't have a valve on the intake manifold that blows off if the motor is going to blow up. Maybe that should be called a BUV (blow-up valve). The reason I tried to make a distinction was because posts were coming in with questions like...will my stock BOV handle 18 lbs of boost... as if a CBV (aka BOV) were going to act as a safety valve and limit boost. That's not what it does. When operating at WOT and high boost, the valve is held closed by a spring and the diaphram is seeing the same pressure (boost level) on both sides because the signal is from the same big chamber (turbo outlet, intercooler, hoses, intake manifold) with the throttle plate open. If the throttle plate is slammed shut, then that signal (from intake) becomes a vacuum signal and helps the residual boost under the valve push against the spring and the boost is loose..zzzzingh! so that it makes a cool sound instead of worsenning turbo lag when the throttle is reopened. This is just a clarification. Better one long diatribe than scores of posts all using the same terminology but meaning completely different things. DAW