AK260

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This was a box developed a few years ago by the racers in the uk’s Zclub.net before my time with Zs. I believe they did a lot of dyno testing and fine tuning - which proved that it added some significant ponies and eliminated some dead spots they had. It eventually became the “club airbox” offered at cost to paid up members. We recently did a couple of batch runs but not sure about plans for the future. The original design has a fibreglass back plate and clips to hold it on. I wasn’t a fan of having nyloc nuts where they “may” get sucked in. While this has never happened to anyone yet, I still set about making my own back plate for it. My interest in the inlet tract beyond the additional few small ponies (and detail OCD) is to reduce the carb standoff and reversion I get around 2.1-2.5 and 3.1-3.5 K rpm. My torque curve currently has 3 peaks. On the airbox, it has an 82mm ID / 86mm OD mouth. Most early S30 owners replace the air tube on the left of the car and reduce inlet pipes down to 76mm to get through the hole in the rad panel. On my ‘77, the hole on the left is 91mm in one direction and 110mm vertically. I’ve opted for 90mm ID 2ply flexible silicone ducting and an AP2 S2000 air filter. Why that filter? Well, the S2K head flows just north of 300cfm and at max revs it’s doing close to 290. My head at a theoretical 83% VE and current bhp output is doing a theoretical 277. The filter flows more than enough for my requirements, is very cheap compared to a K&N, filters better than a K&N, doesn’t need oiling, has a built in velocity stack and an 87mm OD / 83mm ID flange. The down side is that it’s a BIG old beast, puke green and has prosthetic limb coloured plastics (which will get a coat of black paint)!!!! On the upside, it will be hidden behind a front facing 190mm heat shield to protect it from water and stone chip damage, something like this in black. I don’t want anything visible through the grille! Well, I appear to have thread jacked myself!! ;)

Thanks dude. Not sure how I missed that in my googling hours! It’s one to read carefully - I just read the first 4 posts and it seems like a brilliant discussion with lots of good info! I was shocked to find my tapered 70mm ITG HS6 horns caused the car to feel flat EVERYWHERE and made the reversion at low revs even worse. Then I measured them to discover the throat went down to 40.5 on 44.5 mm carb openings reducing surface area by 17%!!!! Then I looked at the stock back plate on the air box to discover the opening is larger than the cab mouth so in effect a step causing frictional losses / vortices + an expansion wave all of it’s own! So I will be reaming out / tapering the carb mouths to match the exact dimensions of my home made aluminium back plate for my new plenum and the horns I finally go with. Here’s my new airbox / plenum with home made 4mm aluminium back plate.

Hello gang! My new bad obsession this year is the inlet side! Beyond planning on a new CAI and some David Vizaardry on the carbs, I have a new unhealthy obsession with inlet tract tuning. I have read many references to this not on a Z car, but I am keen to hear from you good fellas as to what we know of, that has been experimented with on a Z. For example, I regularly hear that the stock trumpets are actually very good. But what does that mean? They are no doubt very good for stock engines / cams / exhaust combo etc but what about modified engines with more overlap and duration? It’s common knowledge that long stacks give you better mid range and short ones are good for top end BHP + the end mouth shapes are also pretty important but has anyone done any real back to back fact based analysis on the Z and on a modified engine? And what were the findings for an ideal length for that spec of engine? I’m tempted but the fully radiused 50mm MSA ones but there are others out there including “12 second dual SU Nom’s” baby ring toss mod! https://www.classiczcars.com/forums/topic/60086-velocity-stacks/ Some links of interest below and some interesting results .... A geeky read ... https://core.ac.uk/download/pdf/82364512.pdf A great read ... https://www.emeraldm3d.com/articles/emr-adj-length-intake/ A good watch ... A mind boggling calculator ... https://www.classiczcars.com/forums/topic/60086-velocity-stacks/ Ps. I absolutely LOVE this thing machined but the UK MG guys from scratch!

To echo some of the comments above - on my modified L28 with north of 240 bhp, I run fidanza fly wheel on exedy clutch (240mm) rated for a 280zx 2+2 turbo. I wanted a relatively light pedal but a clutch that could take the additional power. The pedal feel is great - not too light or at all heavy. If you want or keep your existing pedal feel, then just replace the clutch disc. The pressure plate is what gives you that heavy / light feeling. As for the flywheel and drivability, it’s sooooo much happier revving now and a joy to drive. Sure, on the very slow stuff it can be a tiny bit jerkier than the stock set up but never any drivability issues in town or stop/start traffic. You do have to dial in 300-500 more rpm every now and then but that’s it! Oh and slightly quicker gear changes. I can still drive mine at 1200-1500 rpm without issues. I have never looked back since going lighter fly!!! Interestingly, I found my AP1 S2000 didn’t like pulling out of junctions below 2000rpm! But boy was it worth the 9krpm redline engine note!!!

Well chap, the best tuning tool I have EVER used is the AFR gauge - going down 1/6 or 1/3 at a time on the side of the road and hammering up and down the same piece of road is a good way to go. The car will feel more responsive and lively when you have it right. At 14ish AFR on WOT you’re definitely too lean for good power. I have found anything between 11.5-13.2 can work well but 12.2-13 is ideal.You will find that once you get it in this zone, your water temps drop too. Also you may aim for the higher end of that zone for better economy or a better compromise on idle AFR etc. I too was running SM needles that felt a little lean on my modified engine. The jets were very far down. Once they were modified by a tuner on the rolling road, the car absolutely came to life!!! I didn’t like their work so I set about experimenting and found MC needles with 2oz (stock) springs have superb throttle response and good all round AFRs. The tinkering was hampered by C19 and will pick up again this summer - but here is my thread on it so far in case you are bored .... https://zclub.net/community/index.php?threads/su-carbs-will-work-perfectly-on-my-modified-l28-and-give-dcoes-a-run-for-their-money.25839/ What is your engine spec?

Those AFRs are perfect for part throttle / cruising. You may wish to reconsider the mix if your definition of load is WOT. My idle is also pretty rich at about 12.5-12.8 - which makes for a cooler idling engine but boy does it smell ;) For comparison, my AFR on WOT dips to a crazy low 10.5 at 3.1krpm where there is a reversion torque hole and then sits doggedly between 12.5-12.8 from 3.5k to the red line.

I’m assuming you are familiar with electronics if you are building a speeduino. I which case if you use an Op-amp in follower mode, you should be able to take a signal from the existing thermostat housing sensor without affecting the impedance / voltage at the sensor. You can add an offset with something like the circuit below (obviously change resistor values) to get the required 5v input signal to your device if you ADC isn’t capable of taking 12v signals. Failing that, get the thermostat housing with two holes and either tap the thread or find a sensor with the thread pitch to fit a new / modern sensor. Or do what Jon has done. He too is a Speeduino user / expert.

That’s great to know, thank you for sharing. So we’re back on topic again then ;) and it’s going to be all about fan spacing!!

Now what you say makes a LOT of sense!!! Especially so if you consider the picture below where the additional auxiliary pulley is bolted in using those same bolts. I am going to call to ATi at some point to confirm. I guess for good practice you still should put something in those holes to make sure they don’t accumulate water etc. The only thing that comes to mind as I type is, I wonder if it would somehow off balance the damper if those bolts aren’t installed? I would absolutely love to get rid of them, they are a total nuisance!

Well you know, I did indeed consider that possibility, however, I discounted it as I thought I would probably weaken the fan blades and / or not get it accurately enough and off balance it. As it happens I still have some good safe clearance from the rad. But those bolts are indeed a pain! My engine builder kindly installed them as per instructions in the box. What bolts did you use?

Thanks for sharing! That is really interesting. I had to space mine out about 10mm. I plan to cut the end off an old water pump and use that to space out from behind - with a tiny bit of lathing of course. Much like you I wanted to keep the mech fan. I will likely install a pusher fan at the front for backup on a hot day. Especially as the new (as of 3 years ago) rockauto fan clutch doesn’t seem to want to engage when the engine is hot. I can make it stiffen up with a quick flash of the blow torch but it won’t engage at high engine temps for some reason.

You know, I had the same exact thought when I went back to look at it!! :o

I’m really interested to hear about what you found as I’ve had to use spacers on my fan to clear the ATi’s stickie outie bolts (forgive me if I’m using complex technical terms here)!!

Sorry to hear that dude! Good luck with the new one! I haven’t yet heard a totally silent one on any classic car but then I don’t have any real experience of them other than being an observer ;)

Just gone down to $2700 - the price too is starting to suffer with oxidisation. Seriously though - don’t we think it’s probably worth $1-2k to someone who is going to break it? Given it comes with a spare L28., there must be at least $2k of parts there, no? The glass, wings, roof, carbs, trans, diff, wiring loom, gauges, axles, steering rack, rear disc conversion etc etc etc and the L28 will surely fetch good money on eBay?

I totally get that and it’s very true. However even in the dry they had started to wheel spin out of junctions and feel vague. No other car in front or behind me travelling at the same gentle pace let go / understeered etc at that time. Either way tyres do go off over time and frankly they (and brakes) are keeping you safe and on the road. Relative to how much money we spend on our cars to keep them shiny, I just look at it as a cheap insurance policy not worth skimping on. They basically oxidise over time and go hard. Here’s a good article ... https://www.thetelegram.com/wheels/have-your-tires-reached-their-expiration-date-255224/

Yea indeed sir, I was in my car with my brother in law who was monitoring / writing down cruising AFRs for me at part throttle - so we weren’t even pressing on really. I have a typo above - we were at 3.5k rpm, just at the point where the engine comes on cam. Thanks for asking - yes we were absolutely fine. But I’m pretty sure the driver behind needed a change of underwear, I was very lucky to have been able to hold it and avoid a spin into the barriers - oh and avoid hugging the trees to our left on the edge of the gravel area where we came to a stop. There was some minor damage / scuffing under the car and to the cill on the passenger side where the chunky lumps of sharp gravel got kicked up - but it was easy to surface fill, sand back and re-spray. We got VERY lucky. The video below shows the same corner in the dry (but gunning it). I love this corner and have been doing silly things on it in all weathers and cars for 30+ years! So I was shocked when the car suddenly and without warning lost traction. At the 13/14 seconds mark you can see the gravel on the left where we had all 4 wheels off the road - it ain’t very wide before you fall and hug the trees.

Ps. Just checked and it looks like Bridgestone have stopped making that size but these were a close 2nd when I was looking before ... https://www.blackcircles.com/tyres/brands/uniroyal/rainexpert-3

Allow me to be controversial - in my personal experience, tyre rubber really does start to go off it’s best around the 5 year mark. But then most of our cars are garaged / live indoors without UV and at a relatively constant temp. So shouldn’t the tyres last longer? Well, I thought so, until I fell off the road in 2019!! My 14” Michelins with 6.8mm tread on the rears were normally pretty OK. Then I got caught out in a rain shower after a dry spell and coming onto a dual carriageway, onto a long sweeping corner, in second @ 2.5k rpm, when I touched the throttle at no more than 30% there was that real WHOA moment when the rear lost traction and was fought back into line with three pendulums - but not before I went off the road onto a gravel drainage / trap on the side of the road!! I then switched to Bridgestone Turanza T005 tyres and found I could put more than 80% of the power down in the wet!! Hit the same corner several times again in the wet and with more power to prove the point and no issues. I even went to Silverstone the following week and drove around the muddy / wet country roads for the 50th anniversary Retro Run and the track in the pee-ing rain; all with supreme confidence! I guess it depends on how, where and in what conditions you drive. But that experience made me staunch in the belief that they do indeed go off. I just don’t want to go off with them!! Not sure if they are still available on this size but I would highly recommend !

I just posted this onto the other thread ... Not sure how good this is but it “looks” like a remake of the MSA / Pacesetter items ... https://www.ebay.co.uk/itm/1-5-Primary-Datsun-Z-Header-All-Square-Port-240Z-260Z-280Z-280ZX-/313386185058?_trksid=p2349624.m46890.l49292

Spotted this earlier - looks tasty but no real history I’m aware of, hopefully someone in the US can comment .... https://www.ebay.co.uk/itm/1-5-Primary-Datsun-Z-Header-All-Square-Port-240Z-260Z-280Z-280ZX-/313386185058?_trksid=p2349624.m46890.l49292

Hey big boy, apologies for the delayed response, I’ve been off planet for a while, but now that I’m back on earth ... I didn’t decide in the end but I am very tempted by the NISMO pump and a fuel regulator / filter like the one linked below which takes it down to 2.5-3.0 psi. Having said all that, we went from torrential rain to prong for one day and I took the Z out for the first time in months and no longer had the issue. So I really have to investigate what in the tank is causing the issue.

If at all helpful, mine is a VW colour, code:LD5Q Sits very well on the car but shows every small scratch / blemish. The up side is, it’s very easy to match! This is from when the PO first had it painted...

Excellent, you’re getting there!! Those open carb barbs would have caused no end of issues. You will of course have to retune your carbs once you have all this sorted out. I’ve never seen a vacuum feed off the carb insulator before (see my mark-up). That looks homemade. The vac advance I’m a big fan of. In short it’s a closed loop load sensing mechanism. But yes you can leave it disconnected at the distributor and plugged at the carb end. It’s good that you can’t suck air through the canister. I had two that were completely open to the atmosphere! When idling, off throttle or part throttle, the mix becomes lean. A lean mix takes longer to burn. Think of it as a line of gun powder - the more spaced apart the particles the longer it takes to burn all the way. So the manifold vac is used to drive a diaphragm inside the canister on your dizzy to add timing in low load / no load conditions. This ensures you get as full a burn as possible which has many subtle but positive outcomes: 1. better fuel economy 2. smoother transition from part to wide open throttle 3. The combustion completes inside the cylinder and not down the primary exhaust pipes, reducing under-bonnet temps directly below your carbs. 4. Cleaner plugs when idling in traffic 5. Lower emissions and less unburnt fuel smells. My old 280zx distributor used to add as much as 20 degrees @ 3.5k rpm! That is probably OK with stock engines having 8ish static compression but on my modified engine with 10.5:1, it made it difficult to go to sleep at night! ;) Here is a great table showing what advance which dizzy adds .... Keep at it, sounds like you are making great progress!! [emoji106]