JMortensen

Just don't get super anal about your compression ratio with the old valves. My valves had been cut and the seats had sank into the head a bit. I gained a lot of compression by installing the new intake seats and those valves without the dish that I mentioned. I can't recall the numbers anymore, but the volume shrank quite a bit.

BTW I got nearly all of this from the book "How to Modify Your Nissan/Datsun OHC Engine": https://www.amazon.com/Modify-Your-Nissan-Datsun-Engine-ebook/dp/B0092WMDCK/ref=sr_1_1?dchild=1&keywords=how+to+modify+your+nissan+datsun+ohc+engine&qid=1586372446&sr=8-1

I would do all your chamber work before you have the valves installed. If memory serves the exhaust is the same size and the intake is a bit larger. What you don't want to do is nick the seat, so you should leave the old exhaust valve in while you're working. I already had larger valves in my head, so I left both in. If you're replacing both seats then I think you're safe to leave them out. They do get in the way. What I did was to take a head gasket, set it on the dowels in the head, then shifted it left and scratched the head on the right side of the chamber with a pick to show the fire ring line, then shifted right and marked the left. You don't want to remove metal under the fire ring on the gasket, so I probably stayed .010 or so away from the line. I did the same on the block. Notched the block to a little above the piston ring mark in the cylinder, then removed the metal in the head and block out to the line. This should improve airflow on the cylinder side of the valve. Also smoothed the rings around the valves, mine had some fairly rough areas in the triangle areas between the valves. It's been 20 years, but I don't recall having to pick an area of the chamber to remove metal from to even out the volumes. I think all of it came from the areas described above. If you took a measurement of the cc's before you unshrouded the valves, then you could figure out which cylinders to be more aggressive with. Seems to me I had more quench than you appear to. Is than an L24 gasket? If the cylinder ring were bigger the quench pad would look bigger. I made an exaggerated drawing of what I tried to accomplish on mine. I did all the spots you marked in green, but most of the effort on mine was put in where I marked in red.

Might want to read this before you install them:

I cut the head just enough to make it flat, and replaced the valves with ones that didn't have any dish in the head. Stock gasket. It was just under 11, like 10.95:1 as I recall. I also ground out the extra spark plug threads, smoothed the chambers and cc's them, rounded the valve edge. It was pretty well optimized to not ping. The E31 has a better quench design than the E88 or N42, but not as good as the P heads. 2mm headgasket eliminates any benefit that you get from the better quench on the E31.

No change on cam recommendations. Again, that .490/280 cam worked really really well with SUs at 8.3:1 compression. It dwarfs all of those stock cams. If you look you'll probably see that I have hundreds of posts telling people to go bigger on the cam, no exaggeration. I am very biased, but it's because of my own experience. I've related this all before, but we're in quarantine, so what the hell... I built my L28 dished E31 combo and ran it, then added a small cam that my friend (a Nissan master tech and autocrosser) recommended. It was a high lift short duration cam, would make any of those stock cams look small. Aside from slightly changing the way it sounded at idle there was no noticeable change. Later I read online somewhere, probably on the old zhome.com mailing list, that people tended to use cams that are way too small. My friend had that .490/280 cam that he had accidentally ordered, and it was just sitting in his shop. He was afraid to install it. I bought it and he warned me how I was going to hate it, lose a bunch of bottom end, etc. but I went ahead and installed it anyway. It was probably worth 30 or 40hp, and there was no loss of bottom end at all, everywhere in the rpm range was so much better. I brought it by and let him drive it, and he immediately bought a .610/320 or some huge cam for his L18 with 44s in his race car. LOL. When I switched to the triples it was again probably 40 hp gain over the SUs, my wife was scared to drive it at first, but I really felt it could use more cam at that point. Then of course when I built the flat top bottom end it desperately needed more, but as I said, I gave up on it. 10:1 is pretty high compression for the crappy combustion chamber designs on the L heads. That's about what you get with an N42 and flat tops, and if you look, you'll see plenty of threads about pinging at that compression ratio with that combo. You can solve this with the cam, but it has to be big enough to compensate. That .540/310 cam would work great with triples and there are a lot of people running something around that size, so you don't have to take my speculation about it as your only guide. I don't know about SUs haven't tried them in a high compression build, but I suspect the same would be true. I think Greg Ira (gira) is selling a cam in about that same size range that was an old Don Potter grind. He would have more info on what to do with SUs if you're going that way, as he races EP and they are mandated. He is a member here, but I'm not sure how often he checks in anymore. You can also find him on FB.

Any stock cam is simply too small for a high compression NA build. WAY too small. WAAAAAAAAAY too small. Most people find the Schneider cams online. Their Stage 4 would be my minimum for a build with SUs, that's .490/290. I had a similar .490/280 regrind on my car with stock compression and SUs. Worked GREAT, but wasn't quite enough cam when I switched to 44s. Then I screwed up the crank (balancer came loose, broke the keyway, rounded the end of the crank) so I built a higher compression bottom end. Ended up 11:1 with E31. Pinged like a mofo, had to severely retard timing to prevent that and was way down on power. Was looking to upgrade the cam again, and then I gave up and went LS. There are a couple on the market from ISKY and Erson I believe that run about .540 lift and 310 duration, that would be the one to use for a hot street motor with triples based on my experience. In order to run a big enough cam to make it worth the effort to install it you will need springs and retainers and shorter valve stem seals. Despite not liking their cams, the Schneider springs and retainers work great, and you can use off the shelf Ford 2.9L valve stem seals and that will allow for ~.600 lift without any problems IIRC.

FWIW I had a weird combo of a 3/4" master and a hydraulic throwout and dual disk button clutch. There were no instructions on what size master worked and it wouldn't have been for a Datsun clutch pedal assembly anyway, but there were warnings on not overextending the pressure plate springs. I modded the pedal stop to allow it to engage much farther out, then moved it one turn at a time until the clutch just disengaged and then I think went another 1/2 turn past that. You could do something similar if you're worried about it.

If he's going dual master cylinder the weight transfer issue can be adjusted out with a bias adjuster, or at worst a master cylinder swap.

Agree with Ironhead. If you're trying to figure out master cylinder sizes and that sort of thing, both Tilton and Wilwood can help with that. In the meantime you're asking an extremely open ended question: "I don't know what suspension I'm going to use, but what brakes are going to work with it?" is an impossible question. There are several spreadsheets that you can find online which will allow you to plug in a pedal pressure, rotor diameter, pad size, number of pistons, etc and figure out the resultant brake bias, but last time I looked, about 10 years ago, they were all wrong. Every one of them that I looked at. As to the single vs two piece rotor thing, a two piece rotor is more likely to have issues with pad knockback, although I'm currently having issues with that on one piece rotors. Haven't figured it out yet, my guess is that it's a result of axle shaft movement in the rear in my case. I have anti-knockback springs, but need to disassemble all of the calipers to install them, which I'm not looking forward to.

Viscous has one really long shaft, so they look like CLSD to me.

Don't remember Ron's pic exactly, but that is definitely the same idea.

I believe Ron Tyler did this on his Z. There used to be pics here, but they're long gone I'm sure. What was done was to set the battery at frame level, cut the (rotten) battery tray and that part of the fenderwell out, then rebuild. The battery is already fairly well positioned in the car fore/aft and offsets some driver weight, but moving it down does have a little benefit. 10 ft reduction in stopping distance sounds optimistic to me, but I'm no engineer. In addition to moving weight in the car, reducing it also serves the same function. Fenderwells are gone in my car, and I have side pipes, so I had to put it into the cabin. I tried a 3 lb lithium battery, and was going to install behind the driver's seat but then realized that the cabling would add weight, so I stuck it on the trans tunnel. At 3 lb, wasn't so worried about the height of the weight, and it was still lower than the stock position. After I bricked 2 of them, went back to a PC680 and stuck that behind the pass seat and dealt with the extra 15 lbs of battery and cables.

The flip side of taking the wheels off is that you can get to the tie rods and whatever other adjustments you have a lot easier. When I have done string alignments getting at the adjusters is really difficult, and one time I tried putting the car up on a couple of piece of wood stacked up with greased floor tiles for slip plates. When I was making adjustments the car wanted to slide off of the plates. Only would have fallen 3", but still not a good feeling when you're laying on the shop floor with your head stuck under there.

Cracked right in the corner as I recall.

I searched here and Google and couldn't find pics, but I have seen it several times. Just for fun I googled "240z cracked front differential crossmember" and that has been posted probably 10 or more times and didn't come up in the images either.

There have been multiple ITS cars over the years that have posted cracked uprights. Usually crack right up at the top.

Load sensors is interesting, especially with a set of scales being ~$1000.

Main thing is a flat surface to set them on. Can do most of the rest with digital level and tape measure. I find measuring caster to be a real PITA. That would be easier with turn plates, but then you'd need 4 or at least platforms in the back to get back to level again.

I cheated. Bolted one mount to the plates, tacked them in. Then bolted the rest of the seat in, tacked in the other side.

LOL. Looking at my pic, I remembered that I used 2x2 on the pass side. 1x1 on driver's side. Pass side seat is 20 degree layback, driver's is 10 degree. Sorry for misinfo.

No, I cut holes in the tubes, welded nuts to plates, and welded them to the tubes, so that the bolts screw straight into the tubing.

This is incorrect. I was under the same assumption and blueovalz fixed me up about 15 years ago. The way it works is that the negative camber increases (very linearly) until the spindle is perpendicular to the control arm, then you would see camber go more positive. I think this is practically impossible to do in a Z, so for all intents and purposes it's not going to be an issue. The real issues are having the roll center underground, and bumpsteer. Roll center might not be underground at this particular car's ride height, but if it does end up underground it will require more spring to get the same amount of body roll. Basically gives you some "pro roll" in the suspension geometry. The bumpsteer is bad on a Z, but if you get low enough it gets really wacky. I had a situation where I was running really low without fixing bumpsteer and there was a sharp rise in the track, and when I'd hit it my car would jerk hard to the right, like an emergency avoidance maneuver that it just decided to do on its own. Fixed bumpsteer by raising the inner LCA pivot about 7/16 and that was gone.

Cutting those stupid seat brackets out is the friggin worst. I'd rather do 10 spindle pins. BTW, I use 1x1 for the mounts.