Babalouie

Maybe you're just a lucky guy, Tony

http://japanesenostalgiccar.com/blog/2009/11/05/sema-2009-os-giken-tc24-b1-twin-cam-l-series-head/ OS Giken displayed a TC-24 head at SEMA last yr, and the word from OS Giken USA is: "If anyone is serious about acquiring one of the proposed new units, OS Japan is willing to manufacture them if enough people are ready to put down a deposit. The manufacturing chief mentioned that they need about 25 people lined up to get the ball rolling, and there are already several people ready to pull the trigger on it! At approximately $30-35K it’s definitely not for the meek. Regarding the original production numbers, only 9 of the TC-24′s were produced, including the one displayed at SEMA. There were over 20 of the TC-16 heads made, though."

Yeah, this part became pretty clear with the wideband results. I was experimenting with 50, 55 and 60 idle jets, and you could clearly see the effects on part throttle AFRs, as high as 4000rpm on 1/2 throttle. I'm using 36mm chokes tho. Agree. But I think I've taken it as far as it can go with the jetting, and ended up with similar conclusions to yours. 60F9 on the idles has a little stumble but not a lot. Downside is very rich smelling running and lazy response. But a recent discovery is that what helps eradicate the stumbles even more, is ignition advance. As little as 3 degs more static advance made a massive difference to overcoming the stumbles (and the AFRs went richer at 3000rpm too!...not sure about the theoretical reason behind it, but it did...). As an experiment, I cranked in 6 degs more static advance (18degs static) which meant that it pinged at high revs and so that was off limits, but the 3000rpm stumble point was smooth as silk. So the next step is to recurve the distributor to something more like 10 degrees mech advance, so I can run 18 degs static.

Thought I'dd add my recent experiences to this thread Here's my motor: L28 bored to 2950cc 11:1 flat tops N42 head with lots of big/nasty headwork 252 (@50 thou) degree cam/505 thou lift 40DCOEs For a long time, I ran 32mm chokes, and life was good I could pretty much just floor it at 2000rpm and the car would just...go. Then one day I got greedy, and fitted 36mm chokes. Went to the dyno with this setup: Choke 36 Mains 140 Airs 200 Idles 60F8 Tubes F11 Pump 45 Aux vent 3.5 Result was an aborted dyno run when it got really lean in the midrange. At that point I figured it would make sense to install a wideband o2 sensor: It wasn't difficult to install (although I couldn't get the rpm readout working) and hooked up to my laptop, where I could record runs and chart the results in Excel later. Take 2 The chart starts at 2500rpm and goes to 6500rpm. It was a little too rich in the midrange and the response was a bit lazy. But more of a concern for me was that the cruise AFRs were really rich and hovered at the high 10s and low 11s most of the time on light loand and part throttle. It also smelled rich and blackened the plugs a bit. But overall, very smooth response with only a small hiccup at 2800rpm. But I felt like I was backed into a bit of a corner here, I experimented with going down a size in the idles, but it start getting a bad hesitation at 2700rpm, and since it was already too rich in the midrange, I felt that going up a size in mains to compensate wasn't the answer. Take 3 I tried a richer F16 tube next, in conjunction with leaner mains and idles, but I think I went too far on the idles. It ran very poorly below 3000rpm, and even with a small throttle opening, would start to hiccup with a light load. This is not a power run, but just the AFRs on cruise, with part throttle from 2500-3500rpm, which suggested things were too lean. Take 4 Bumped up the idle jet size to 55F9 and driveability got a lot better but not great. This is the AFR curve on a full-power run, and you can see the big lean spike at 2500rpm (where it did a big fat hiccup!). But then after that the AFRs are pretty flat. Cruise AFRs are more or less in the ballpark, 13-14 on part throttle and light load. Take 5 Decided to ignore the low rpm for now and fix the midrange and top end. Went leaner on mains to 140, but the airs look to be too lean. Take 6 Didn't get a chance to record the run (it's hard to do by yourself!) but everything was the same as Take 5, but with airs reduced to 185. Now it's at the high 12s just before redline, so I think that's probably sorted. ...and that's where I am at the moment. It's very nice and crisp above 3500rpm, and below 3000rpm, pulls quite cleanly with small throttle openings. Give it as much as half throttle though, and you can feel it do a bit of a hiccup at 2700rpm and the AFRs will momentarily go very lean (16-18:1). Next thing to try is go back to a 60F9 idle, which I think will address most of the hiccup, but at the expense of somewhat rich part throttle fuelling and perhaps lazier response. Will post back with results... Some interesting observations though...increasing the size of the mains does very little to fix the 2700rpm stumbles (even going up 3 sizes doesn't seem to make much difference). Going richer on the 'tube helps a little but not a lot. What really seems to fix the stumbles is jacking up the idle jet size, but according to the wideband, the idle jet has a pretty wide ranging effect, and still seems to affect light throttle fuelling even as high as 4000rpm.

Speaking of wideband, I just bought one of these guys: http://www.wbo2.com/2j/default.htm AU$256 (which works out to US$235 I spose) plus postage. You can choose to buy the wideband with a display screen for real-time AFR, but if you want to use a laptop, the software that it uses is pretty simple. Just click one button to start recording AFRs before a run. It saves the result in a .txt file, which you can then cut and paste into MS Excel and have a chart against RPM. I haven't installed it yet though, but plan to use to to fine tune my triples

Cheers Alan

Sorry to go off topic, but Alan, are there any significant differences between the Sport Option N42 block and the regular production edition?

After a little hiatus...the engine is beig worked on again It's at my friend Nathan's workshop. I figured since the head was full of custom stuff, the bottom end might be too, and so I better let a pro take a look at it. The headline? It's a stock crank, so it's not a 3.1L stroker but only 2950cc. But there's some interesting stuff. As expected, it's very fresh, and hasn't done more than maybe a thousand kms. It's also not very standard, but in line with the rest of the car, it's a weird mix of hi-end work and some very shocking shortcuts and laziness. The pistons are a brand called ART, and are racing items, which very thin compression rings. Nathan says that as a result it'll have a somewhat shorter lifespan than normal, and also that we have less margin for error when tuning, as those thin rings will be more easily damaged than usual. It means that I might only have 100,000kms between rebuilds, but for a Sunday car this isn't a big problem. Brass button clutch... Balanced flywheel... And a balanced crank. There's been quite a bit of material taken off it, so it's been lightened quite a bit, and is probably a new item since there's no wear on it. I think it's an N42 crank. Here's a short cut though....after balancing, they didn't clean up the edges of the lightening holes....there are little curly bits of metal hanging off the edges, waiting to fall into the oil supply... ...which is undoubtedly what happened here. The bearings are all pretty new looking but two of them show that some metal has passed thru and scored the surfaces. Interestingly the Japanese builder built the bottom end with two sets of bearings. Both the upper and lower bearing have that groove in the middle, so they've used two top bearing shells on each journal (the other side is meant to be plain). By using two top/grooved halves, you reduce surface area and friction and hence make more power at the cost of a somewhat reduced lifespan. But it's not quite a "grenade" engine though and the clearances checked out perfectly with no wear on the crank journals. But when Nathan puts it back together, the engine will be rebuilt with conventional bearings for longer life. Another short cut is balancing. Even though the crank and flywheel are balanced, there was a 10gram difference between the heaviest and lightest piston/rod! The whole set will be balanced before reassembly, but it's weird that you'd go to the trouble of preparing the crank and flywheel, and then undo all that good work with a very unbalanced set of pistons. More dodginess awaits on the block... As you can see here, the hole for the oil pickup is in the middle of the block. This is correct for a Z-car, which has the bowl of the sump at the back.... ...but for a Skyline the sump bowl is in the front, so they modified the oil pickup tube to extend to the front bowl! Not exactly top notch workmanship... The extended oil pickup tube also meant that they had to cut away the baffle in the sump to allow the pickup tube to pass thru. See that missing section from that plate in the middle of the sump? That plate is to stop oil from sloshing to the back of the sump under acceleration, where it will be frothed up by the crank, where it will not only cost power but also compromise the lubrication if the oil supply is full of bubbles. Nathan will redrill the block to resite a new oil pickup tube at the front, where it can go straight down into the sump bowl. The old hole will be blocked up, and the sump baffle repaired. The bores are in great shape so they'll just be treated to a light hone. The next step is for the block to be drilled, the welch plugs removed, and then it'll be tank cleaned and repainted before reassembly.

$700 is a lot. I had a set of triples rebuilt for $450 (Australian dollars) and that included bead blasting the castings to make em look nice again. Before After

Latest Update:

Here's more updates from testing the completed head today:

No...still too lazy to have done that

We have interesting new pictures! Here's the latest reports from Tony the builder: First the head is disassembled: ...where it is discovered that the valve seats are only 1/2mm (ie the valve seat only "seals" to the valve thru a thin contact patch 1/2mm wide). Tony said that was way too thin for longevity on the road, and is more evidence that this was a purpose built race head. The head is bead blasted to clean it up. Inpet ports are reshaped, you can see the valve guide boss has been trimmed down in size and made into a more streamlined shape. Also the surface finish of the inlet ports was deemed too smooth by Tony, and hence he roughed up the surface a bit to prevent fuel pooling on the port walls. One of the inlet ports had broken thru to water jacket by the head porter in Japan, and the hole was filled with 2 pack metal putty. It was holding ok, but Tony blasted it out, drilled out the hole and filled it properly with Devcon. He also said that the short turns (whatever they are!) were lumpy and ridged, so they're now smoothed and reshaped for better low-rpm flow. Exhaust ports refinished too. Almost the finished product.... ...combustion chambers were opened up a little bit to unshroud and expose the valves, the valve were also not concentric in the seats, so he's recut them to be central, and also remachined them to widen the valve seat from the thin 1/2mm to more like 1mm. The finished ports. The head will be assembled, and then sent off for flow testing to see how much hp it will support...should be interesting. He said that if he were to start again, he wouldn't have the ports quite so big and the bowls would be smaller too, for better low-rpm flow, but just the same he's pretty happy with how it turned out.

My cam was machined much more than that I saw an article in a japanese mag of a 510 engine and the cam in that had the same amount machined off it. I've been meaning to ask someone japanese to read it to see if we can id the source of these cams.

AFAIK, it's not-uncommon in Japan to sand off the engine and head numbers, to hide the fact that you have up-engined your car. The road-tax over there is capacity-based you see, so admitting to 2800cc would have made the registration more expensive. The block clearly has N42 and L28 markings on it, so I guess it might just have been the shop practice of the place that did the cylinder head to machine off the head casting id. The guy who's doing my head probably doesn't realise that there's a reason why ppl in Japan de-tag their engines and heads, so he's assumed that it's some sort of mystery-head.