ITB's
I'm waiting on a quote to get a few flanges watercut, then I'll decide if I want to go that route or plasma cut the basic shapes and machine them clean. The tooling I have available isn't really capable of being able to chop this manifold (soft aluminum gums cutting tools up really easily), so it looks like I'm actually going to go at it with a sawzall, angle grinder with a big wheel, or possibly just a hacksaw.
dsldubn wrote:what kind of gains are expected from the itbs?
If I get it REALLY right (which is asking a lot), I'll get slightly better throttle response. These injectors are quite a bit better (12-hole 300cc/min) than the stock (4-hole 230cc) Miata injectors, but that advantage would be much easier/cheaper to achieve just by replacing these injectors or increasing my fuel pressure. There are four
real reasons I'm considering this:
- They're extremely simple, which eases my idle-tuning process.
- Dual-stage injection should provide me with more fine-tuned idle control. The primary injectors (300cc/min) come on under heavy load, but the idle injectors (~120cc/min, if I remember correctly) control idle/cruise fuel delivery. Megasquirt2 isn't necessarily the best way to handle this system, and I may not be able to fit the stock airbox (which hold the idle injectors) under the hood so it may be a moot point anyway.
- By building my own flange/runners, I can choose whatever runner length I want. There's a bunch of math to do, but runner length can be tuned such that the positive-pressure wave generated when an intake valve closes can be timed such that that pressure wave rebounds back against the head just as the intake valves open again. It may be possible for me to beef up the 3750rpm power-hole I have right now. That power lull has a pretty big impact on my corner exit speeds in low-2nd, so it could make a substantial difference for me.
- They sound really cool.
In short, if you're considering ITB's for logical reasons, stop now. It's extremely difficult to get a meaningful return on investment out of them, and there are much better places to spend your time/money. My idle issues put me in a unique position where I already want to replace the stock plenum anyway, and that's what tipped me far enough to put these parts together.
dsldubn wrote:does is change your class?
I assume installing these means I add the 'non-stock induction' modification, but even with that modifier I'm firmly planted in SP6. Effectively, no. I couldn't find a clear definition of what the 'non-stock induction' rule actually means though, so I may not even be subject to it ('non-stock induction' may mean natural aspiration vs forced induction, or it might mean a different air filter, since that's part of the induction system).
If I had some sensible modifications (anti-roll bars, sticky/wider wheels, etc) and this qualifies as 'non-stock induction' this could be the straw that bumps me up to SP5, but I'm apparently starting off with the non-sensible stuff. If I end up in SP5 next seasons, I think a roll cage and turbocharger/intercooler are going to happen instead of ITB's.
In other news...
I finally isolated the rattle/clunk noise to one of the exhaust heat shields, after I removed the rear anti-roll bar (they're comically small on the Miata). I may replace this exhaust as a winter project, but for now I'll just accept that it's noisy over bumps. My driver's door hardtop seals aren't doing their job any more, so after Okemo II I'll have to replace them. Getting rained on every time I turn left isn't fun.
I removed a little more dead weight while I had the car up on the lift, which meant the dead antenna (that motor is surprisingly heavy):
and finally cleaning up the nastiness left over from the 'fender vents' that a PO put on.
At some point, I should probably weld up those holes or replace the fenders with something that actually vents ... but that's not even on the to-do list right now. At best, I may spray some paint over the bare metal ... maybe.
I ordered some parts from Flyin' Miata, which should show up on Friday. Unfortunately, I'm heading out directly from work, with a caravan of workers so I think I'm going to have to accept hot air blowing up through my shifter hole all weekend. I was always surprised by how hot my shifter got, and found that my shift boots were pretty much non-existent. Now they're literally non-existent, and I may have to cut some cloth/leather to cover the opening as a temporary solution for Okemo.
Finally, I took some time to
REALLY mount the ECU (I had taped it down with some sturdy 3M tape previously, but I didn't trust that 100%). I cut some bolts to length and cleaned up the threads on them, machined the Megasquirt housing a little to accept them, and tacked some nuts to the inside of the fenderwell so I could easily mount and unmount the ECU. I'm finding that Serial->USB cables are very failure-prone, and that's what prevented me from dialing in a decent ignition tune at Burke I. I finally got a new one, but I'm starting to think it's worth investing in a few backups to have on-hand.
