17 March 2018

Weather cleared up so an 80-mile drive broke in the new gears/synchros/LSD. Observations:

The ratios are noticeable closer, which isn’t a surprise but I kept catching myself pausing between gears, waiting to match gear speeds, a habit learned with the straight-cut gears, but when I let the clutch out with the new gear set, it’s clear I’m waiting too long. That’ll solve itself with time.

During the drive, 80 mph (GPS) was 4000 rpm, so back-calculating, the rolling diameter of the tires at speed is 25.1 inches (they compress about 0.5″ due to running ~15psi). That rpm is a bit high for cruising and will ironically serve to keep me more in line, read: driving slower on the freeway. Another reason to slow a bit is because boost is right there and ready to go by 4000 rpm, so it’s like riding a thoroughbred racehorse at a trot but who is ready to go right now. A third reason is that when in boost, fuel mileage takes a nosedive. That said, though the rpm is where MAP can reach maximum, since the throttle’s mostly closed, it’s only about 60 KPa (40 KPa below ambient). I read somewhere that a turbocharged engine can actually improve gas mileage somewhat by overcoming the pumping inefficiencies inherent in gasoline engines due to the throttle plate obstruction. Obviously not a big goal.

(Because of the rolling diameter of the rear tires, if I absolutely must reach 60mph in first gear, I either have to increase the rev limit to 8150 or put enough air in the rear tires to increase the OD to 25.6″, hah.)

After the drive, the OEM transmission fluid used for break-in was drained and replaced by magic oil supplied by the gear manufacture in unmarked bottles. Went for a short drive for gas and it “seems” to shift a bit easier, though it could also be my imagination. I assume it’s going to take several hundred miles for the carbon synchros to wear-in. Speaking of oil, I had an issue with the old transmission where the gear manufacturer, PPG, recommended brand X, while WaveTrac specifically recommended not using brand X. With the new transmission it’s similar, with Gear-X recommending their stuff (of course) and Giken recommending their stuff (of course) which, of course, wasn’t the same. I ended up getting both of them to hash it out on a group email and Giken finally said that Gear-X’s mystery oil would be fine.

There hasn’t been a peep out of the limited slip, or maybe I can’t hear it. Some people complain that Gikens makes noise, though others say it’s silent. Doesn’t matter either way, just a note.

If there was any question before, the test drive confirmed for sure that the engine mount has to be redone – way too much vibration.

 

4 Feb 2018

The wing material is on the way and until it arrives, it gives time to figure out something that’s been bouncing around a long time – my transmission. The current unit is a base-model RSX 5-speed converted to a 6-speed, gears 1-4 being straight-cut with dog engagement and 5-6 being OEM, and a stock Honda 4.39 final drive running a WaveTrac LSD. In short, another transmission’s going to be built. I can already hear it “why do you keep messing with stuff instead of driving it?”, and, “why didn’t you think this through the first time?” Easy answer to the latter: the gear sets weren’t available then. As for the former, well…

Anyway, the existing transmission works great on the street but isn’t optimum for the track on several points. As previously mentioned, 5th and 6th are OEM so they can’t be “used in anger” on the track with a turbo engine (I turn boost down to protect them). This isn’t a problem on the street because presumably you aren’t going >150 mph. The OEM gears can deal with ~160 ft-lbs from the stock engine but users report bad things happen when pushing high torque. Additionally, first gear also isn’t that useful on-track because it’s numerically than optimum, better suited for the street or drag racing. Lastly, the differential works perfectly on the street but like the gears, isn’t the best for on-track. All these issues came together into the idea of building a new transmission and selling the current one while it’s working perfectly. It’s worth decent money, versus practically nothing if I break it. The idea is that it can help pay for the new one, which will consist of:

1. Full Gear-X gear set, with lower numerical ratios and stronger 5th-6th
2. OS Giken LSD (reverse 1.5-way clutch type)
3. Carbon synchros

The final drive ratio will remain the same, 4.389.

Gear-X offers two gearset ratios, identical other than 5-6 which vary slightly depending upon application. Assuming a self-imposed redline of 8000 rpm, the more long-legged set tops out at a theoretical 170 mph, while the very slightly shorter set tops out at 162 mph. The fastest Midlana might ever see is about 160 mph at AutoClub Speedway, but wings are planned, so expected top speed will drop to something less, so the slightly shorter gearset appears best. Back in the practical world, with this gearset, 70 mph on the freeway results in  an engine speed of around 3400 rpm, so that works.

I asked an Arial Atom owner what gear ratios he uses because this particular Atom has as much or more power than I do. The reason I asked is because the Gear-X first gear is really low numerically (2.313) compared to 2.615 of the current PPG first, which is lower than the OEM ratio – it’s a pretty big difference. Because of this, there’s a lot of complaints that such a low first gear ratio makes it all but impossible to take off fast and is “obviously just for road racing, not the street.” The Atom owner correctly pointed out though, that when those ratios are put in a car weighing half as much as OEM, it changes everything and is downright perfect.

Regarding the differential, everything I read indicates that the OS Giken LSD is good for somewhere between 0.4-3 seconds a lap. Granted the numbers are anecdotal with little basis in hard fact, but what was telling was how virtually everyone who switched to it said they went faster. It’s supposedly also able to make the car easier to control in turns. Again, what “easier” means, who knows, but it’s promising that all the comments are positive. BTW, the “reverse 1.5” configuration of the LSD was recommended by the manufacturer specifically for the mid-engine Midlana and would not be a good choice for a FWD engine placement.

Because the above gear set is rated for 500 hp and is also helical, I’m somewhat taking a step backwards. The reason is that for street driving, it’s the right choice for me. On the other hand, for someone who’s built a turbo car for drag racing and wants to be a badass on the street, the dog-box will serve them well.

Lastly, adding the carbon synchros should prevent the dreaded Honda 2nd-gear grind that tends to happen if shifted too energetically for too long. There’s still some logistics to work out but it looks like it’ll happen. When it’ll be done and when it gets installed, who knows.

Okay, there might be one more perk of the above gear ratios. Between the new first gear ratio, the existing final drive, tire diameter, and the engine’s red-line, I can reach 60 mph in first gear – I’ve always wanted at least once to own a car that can do that. The reality is that it’s totally pointless, good only for setting a rather awesome 0-60 time :)

I’d love to try out a sequential gearbox but can’t justify the ~$10,000+ entry fee. There’s the cost, but there’s also the suspicion that it might be a pain to live with in traffic, given how shifts aren’t buffered by clutch engagement, going “bang” every single time, up or down, unless you perfectly match gear speeds. Also, users report that the sequential unit should be considered a wear item (caused by imperfect shifting) that requires periodic teardowns. I think I’ll pass.

1 Nov 2016

Something I’ve wondered about for a long time is transmission longevity when running a turbocharged engine. The stock gearbox handles about 170 ft-lbs torques (as Clarkson calls it), but add a turbo and torque can be double that. 1st-4th isn’t an concern since they were upgraded to PPG straight-cut gears; the concern is about 5th and 6th which are still OEM helical parts. Certain tracks like Autoclub Speedway are set up for NASCAR and track day events run half the oval, a billiard-table smooth freeway where you go flat-out. Fast cars can easily do 150-165 down the front straight and with fourth gear at 0.909, it results in 139 mph at 7500 rpm. 8000 rpm is 149 mph but I’d rather not (regardless of what my engine builder says) since the K24 has a piston-rod geometry that isn’t as friendly to high rpm like the K20 is. Okay, part of my reluctance has to do with popping the first engine and wanting this one to last*.

Anyway, I asked on a Honda forum what the guys with turbocharged cars had found and unsurprisingly, several had stripped the teeth off 5th and 6th. The gears will still be used for cruising, but for longevity, boost will be reduced on those gears. I don’t want to spend $$$$ on a very nice sequential Quaife transmission because I have to draw the line somewhere on cost.

Somewhat related, the new engine is noticeably smoother, even with the stiffer engine mount. Just yesterday I wound it out in second gear and got surprised by the rev-limiter. Normally I can tell what rpm it’s at by feel but not so with this engine. It’s more “Swiss watch like” over the old one. I guess that’s a good thing!