DAW

Since your temps are going up at freeway driving more than around town, I'd bet on a scaled up core in the radiator, restricting coolant flow, or the splash pan factor. BTW the LD28 incorporates a water/oil cooler which runs the heater hose through the oil filter base housing. It's a bolt-on, and you could still run your aftermarket oil cooler base sandwiched under the filter. Measure the actual temp that the thermostat is opening and initiating the cross flow of coolant across the top tank of the radiator (180 is good), and remember that ethylene glycol has a higher specific heat than plain water so run at least 50/50 mix. DAW

One case where "seeing the light" is not a good thing. I'm wearing sunglasses when I go to look at mine. DAW

26 degrees base would be to test the knock sensor to see if it can save your engine. That sounds more like total advance that the dist/cas and ecu can put in, in addition to the base (static) advance. If all connections are clean, on a stock engine the hesitation (poor throttle response) is probably due to a lean condition or inadequate timing advance, or both. I'd recommend some simple tuning tricks which are reversible but should help overall performance regardless. First, check your thermostat (with the meat thermometer borrowed from the kitchen so that you can test instead of actually pulling the thermostat to see the number stamped on it: actual function is better anyway than what it's supposed to be). You want 180, not 195 or 190. If it's not 180, don't go further without making it 180 because that's what signal you want to go to the ecu. Next, try advancing the timing just a little, maybe 2 to 4 degrees over stock specs. Next, splice a RadioShack #271-1117 680 ohm resistor in one of either wire to the cylinder head temp sensor (use Posi-Twist connectors from auto parts store). This will fool the computer into richenning the mixture just a bit. If improved by these measures (it will be) but still needs a little more, then tackle the AFM. I wouldn't recommend going there first because it's a bit more involved and if you should loose track of how much you modified the AFM spring tension, it can become a mess. All these measures will help higher end performance too. DAW

For those who haven't seen a Maxima N47 head flip side, it looks like a P79 peanut-shaped chamber but the roof of the combustion chamber is much lower and so uses the std L28 length valves rather than the shorter valves as found on the F54 ZX car engines. Would make a lot of compression on a F54 shortblock but may be better tolerated than e.g. an E31 because of the high quench design of the Maxima head. DAW Are we there yet?...Are we there yet?...

Who wants to be working a flap valve manually while driving? Besides, that is not really the same re the dynamic function I'm referring to; it's just a dump or diverter valve. The concept of the sliding tubes is closer to what I'm describing because of the change in resonance. It could work well if it weren't for the carbon jamming things up. Another potential means of regulating a staged exhaust system would be to incorporate a flow regulator design that resembles very much a large SU carb with the throttle plate removed. This device goes up close to the engine at a "Y" pipe connector. One side of the Y is a small dia. full exhaust system (a very restrictive stock system will do fine) and the other side of the Y is a larger dia. pipe with the device in it, close to the Y. As exhaust flow increases off idle it flows only through the small system because there is not pressure enough to raise the "SU" piston due to it's weight and opposing damper spring tension. This is good because the high gas velocity associated with flow through the small cross-section pipe creates backpressure and has a scavenging effect both. The small dia. system will begin to build pressure when the gas volume increases and this occurs at mid-range. (Calibration of the primary (small dia.) system is done by pipe dia. according to how much low-end back pressure is optimal for that engine before it needs relief). Backpressure then becomes sufficient to lift the SU piston which allows flow directly in proportion to further increases in gas volume. Once the device is in operation, the primary system still has flow but essentially becomes a fixed "orfice" or bleed jet and is not really involved in the advanced secondary system operation per se. The secondary device then meters the flow of gas from the rpm which exceeds what the primary can deal with, on up. A little bit of high-end back pressure is maintained and tuned in or out by changes in piston weight, with transitional smoothness by damper spring choice. OK, so in operation, let's say you're coming full bore down a straightaway towards a hairpin turn which is at the base of a hill: Full flow @WOT/high rpm with what can get through the stuffy primary system and the bulk flowing out the SU side, pegging the piston full open. Hard on the brakes and vehicle speed is way down at apex of hairpin, lots of low-end torque is needed there and is available because the device has let the shunt lapse closed and good throttle response is enhanced by the backpressure/scavenging properties of the primary exhaust. Heading up the hill is a steady midrange pull and the shunt device can smoothly transistion as rpm rises or falls even though the throttle is full open (just as a SU carb does for induction). It's a nice concept because it is not just a pop-off valve but a smooth, fully automatic, exhaust flow tuner. Problem? Carbon would foul up the operation and the device could be expensive to make with the proper materials. Constructive comments welcome. DAW

So Tee Zee, if one bank is 10.0:1 c.r. and the other bank is 8.0:1 are you running a 9.0:1 engine? DAW

Simple is best, and a device that changes the path length of the gas flow while regulating back pressure would be more dynamic than just lowering the back pressure, i.e. like a variable runner intake manifold (except for the exhaust gases). Longer path with a scavenging effect for low-end torque and responsiveness, then transitioning to a shorter, direct path for high rpm. A simple split system (dual exhaust: one big/short, one little/long) would accomplish more than just effectively removes a restrictor. DAW

More info needed, especially re too much fuel or too little. If too much, you should have black smoke and fuel-fouled plugs. When you are "giving it a lot of gas" you may actually be going into the "clear-flood" mode because it is dumping gas on it's own. See if you can get it to start with the cold-start valve disconnected. DAW

Pete, I've been fooling around with an exhaust pressure staged system which has a fairly small dia. full length primary system with some backpressure inherently that is good for low-end torque and responsiveness, and is quiet. When throttle is increased the pressure builds up quickly, but instead of restricting performance, the pressure forces open a relief-valve which is at a "Y" with the smaller system. I'm thinking the valve would open typically at highway speeds during normal driving, earlier when driving harder, never at idle; and so could be relavively unmuffled since a portion of the flow is always fully muffled. I've chosen a brass sump-pump relief valve 1 1/4" dia. as the prototype relief valve and it has adjustable spring pressure. The valve has a stem, head and seat not unlike an external wastegate. This is an idea that seems worth a look but I haven't gotten to it in earnest...the I pick up a new issue of Auto Week and page through to the newest Ferrari road car and...doh! There's a shot of the twin exhaust outlets and one of them has a throttle plate! Same concept, different method. DAW

By the way, there is no modification necessary to the hood re clearance with the LD28 block/L28ET top-end set up, it fits fine even though the LD28 block height is 19.6mm taller than the L24 block. As to the internals of the LD28: 140mm rods, beefy pistons with floating 23mm pins. I was concerned re the generous compression ht of the pistons (46.5mm) for performance use but they seem to work fine. BMW 3.0L inline 6's have 42mm and the stock L24/26/28's have 38.1. DAW

You're '82 Maxima isn't a 4-door Zcar chassis; it's a ZX. You have one major difference in that your L6 oilpan is front sump whereas the Z & ZX L6s are rear sump. This could make for interesting swap possibilities including some 4 and 6cyl turbo engines. My favorite Maxima hybrid is to take a Diesel Maxima (LD28), leave the shortblock as is, and modify a P90 head with its turbo and all ECI fuel and ignition components, intercool, and you're set. The LD28 pan even has a sump oil drain from the diesel engine's alternator-driven vacuum pump that can be now used for the turbo oil drain. Front & rear sway bars from '82-'83 280ZXT bolt-on directly. Makes a great grocery getter (especially if you're in a hurry). DAW

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Arch, Look here for the solid buckets @ $65 ea. DAW

It would be a lot better to find a JY head with a valve cover on it, or looks to be just recently removed, but it's the cam that's going to suffer most from exposure to rain & dirt if the hood has been left open and you could transfer your cam/rockers/lash pads directly to the JY head. A couple of things you mention don't really mesh, i.e., thinking about porting and polishing the head but running strictly 87 octane gas. They just don't go together. Increasing c.r. over stock will require higher octane gas but could improve mpg and will increase power, whereas the time & money into porting and polishing a stock lower compression head would not offset the savings of using low octane gas. Money would be better spent on higher octane gas using more c.r. The Maxima head I'm referring to, used on an L26 will be higher compression than your L24/E31 combination and you'd have to use at least 89 octane gas. If you insist on using the lowest octane gas then you'd probably be best by using an N42 head off a '75-'76 280Z. It won't increase compression, has hardenned valve seats, and square exhaust ports to match your manifold. DAW

I have a set of brand new factory option Nissan headlight covers with the chrome rings but I'm saving them. Meanwhile, I use the MSA/Victoria British type clear covers and I instead of the rubber trim ring that comes with them I use a thin chrome/plastic U-channel trim with self-adhesive that I push onto the edge of the plexiglass covers. It looks great! I'd say look up the OEM specs on a 240Z re headlight projection distances, etc., put on clear covers and a set of H4s and request a test by the State Highway Patrol if your're cited, so that you can demonstrate that your car exceeds the required specs. DAW

You are not limited to the Maxima head and any L24, L26 or L28 head will bolt on. However, they will vary in how much compression ratio they will yield on your engine. Higher compression is a plus re performance, mpg and efficiency but if too high it will cut short the life of the engine and/or require special racing ga$oline to operate it even for daily driving. Your engine is relatively smaller displacement so you don't really have worries about getting too high a c.r.; just too low. It's all about selecting a head that gives the best combination of factors, including access, time consumed, $$, performance, longevity, and most important, fun factor. The L28 heads all should have hardened valve seats for unleaded gas as do the Maxima L24 heads. The main difference, other than intake valve size (which doesn't matter for your displacement and intended use) is the volume and configuration of the combustion chambers. The Maxima head would be better for higher quench design/less ping than the L28 for a given c.r. Running a Maxima head on a 280Z would produce a very high c.r. but on a 240Z it would be great because of the lower cylinder swept volume. I'd recommend that you not hesitate to substitute a head that makes sense and represents an evolution in technology over a dozen years. Which is better, points ignition or electronic? Finally, you're likely going to pay less for a Maxima head at a JY than when you say "for a 280Z." DAW

You're going to be pulling the head so plan in advance to avoid problems that will make a lot more work. You want to bring the timing mark up to TDC on the compression stroke of #1 cyl, i.e., the dist rotor pointing at #1 cap terminal, the #1 valve lobes angled upwards (not holding valves partially open). Break the cam sprocket bolt loose by whacking the end of a 19mm box-end with a hammer, but leave it on once loose. Then you need to insert a wooden or plastic block between the strands of the timing chain down in the timing cover so it won't move (get loose and force you to pull the cover, radiator, fan, maybe drop the oilpan some, double the time invested). There are two bolts with 10mm heads at the front of the head/top of timing cover. Remove them first. Look up the head bolt tightenning sequence and follow it in reverse to loosen head bolts. Breaker bar into an exhaust port, lift gently, and work along the head until it lets loose. Maybe it was too much info re the head swap but think ahead, the Maxima head also has hardenned valve seats for use with unleaded gas, your E88 probably does not (you can tell on inspection once the head's off). DAW

This is a great thread! I'm going to have to dust off some old analytical geometry, trig and calculus books to follow it all but it's a great discussion. DAW

I think KD Tools sells spark plug hole adapters to put a compressed air hose to each cylinder in turn. You want the piston at TDC on compression stroke (so that both valves are closed). If you've got air coming out of the carbs or intake port of the head: intake valve leaking; exhaust, that valve; oil cap hole of valve cover: rings or piston hole; radiator cap: head gasket or crack in block or head. If you've got no compression on two cylinders though, the problem may be visible to you without a test. On another note, it's time to consider the economics and logistics of performance. The pic of your car looks like it's a '72. If so, it will have an E88 head with combustion chamber volume to yield about 8.5:1. There are some rare E88 heads which have a smaller chamber volume like the '70-'71 E31 (but shaped different) which yield about 9.0:1. Regardless, they have 33mm exhaust valves and 42mm intakes. L28s have 35mm and 45mm respectively. The L24 exhaust valve is somewhat limiting to breathing and performance and Nissan put in a 35mm valve on L26s and later L24s. If you're doing a valve job on an early L24 it would benefit from installation of L28 exhaust valves. These can be installed on the L24 seats with machining (intakes need new seats). What I suggest you do is to go to your favorite JY and pull a head off the lowest mileage '81-'84 Maxima L24 you can find and if the chambers look uniform in color and no oily deposits, bolt it on. The head will be a P79 but it is very different from the 280ZX P79. The Maxima has small chambers for 9.0:1 compression on your car, better quench design than your E88 or the E31 (less pinging tendency), already has 35mm exhaust valves (has 42mm intakes), and has notches in the intake ports so that you can install f.i. in the future. You will want to transfer your cam & rockers to this head. Exhaust manifold? Use the Maxima or 280ZX with an O2 sensor for future use. Forget about the square exhaust port vs round port issue between the head choices, it's completely meaningless in the street engine you're building and the round port exhaust liners accomplish the same thing that those air supply tubes on your original manifold do, i.e. promote burning of all hydrocarbons in the exhaust gases. Look at the pros and cons and bang for the buck. There's a good chance you can pick up a Maxima head that needs nothing and with the money you saved from not doing your valve job you might be able to pick up the distributor with IC module and the entire fuel injection set up from the Maxima. DAW

It's not your rings. There would be a lot of oil and there isn't. I think Tony may be right re the back carb being lean. Was the engine pinging? DAW

I've devised a way to eliminate the SU choke cables but it's a bit advanced and possibly more than the average wrench would want to tackle. However, it does work great compared to the sometimes finicky SU chokes. One big problem is that one or both chokes can hang up at the jet nozzle and not release fully which disrupts the mixture and kills performance. Anyway, the device I made is based on an old aircraft design which is similar to a marine carb device and is a primer system. It is for carbs without accelerator pumps like planes, boats and SUs. I set mine up with a small electric pump but a manual primer pump or a squeeze valve could be used instead. I ran a small diameter copper tube from the pump to a fitting on the intake between the two carbs and pinched the tip a bit so it would spray a small amount of fuel before cranking. Once running, the intake vacuum can draw a small amount of extra fuel through the copper tube. I used a GM water temp/vacuum valve into the heater hose off the engine to allow this draw of fuel until the temp reaches 100 degrees. This has worked flawlessly through two winters but lately it's taken more time on the primer button to fire it up so I think I need to use some fuel system cleaner. Fuel system experience is a requirement for this mod; otherwise just repair the choke cables and make sure the nozzles are clean (carb cleaner) and move freely. DAW

Head gasket/warped head between those two cylinders. White is from steam from water leaching out of water jacket passage in gasket. Another possibility, though remote, would be that the intake manifold gasket was leaking for those two cyls, leaning them way out and you burned holes in the pistons. It's the head gasket. DAW

Red hot is good. Get all of your sockets and extensions, etc., set up beforehand so that you can go for it right away once it's hot. If you're going to reassemble it try to find 8mm brass high nuts to use as these aren't prone to seizing. DAW

How are you "resetting" the SUs? Are you adjusting the jet height (knurled ring adjuster) to affect the mixture across the entire rpm range? DAW

Whoa Trigger! Unbolt, then get out the chisel. There are three, count them, three bolts to undo; then unleash the brutane. DAW