|October 21, 2009 - I just finished writing a new book, and it's been a hard slog for the past few months.|
I actually took the initial call from my editor proposing this book on the way home from Targa last year. More details later, but if you enjoy the content of this website I think you'll really dig the book.
Anyhow, now that I have time to play with cars, I'm going to do some testing with fuel pressure. Will a higher, fixed pressure as found in the NB (1999-05) Miata work better with my NB injectors? First step is to fit an adjustable regulator such as this one from AEM.
entry 707 - tags: fuel pressure
|October 21, 2009 - If I'm going to be messing around with fuel pressure, I don't want the stock unit in the loop.|
This means I need a different outlet from my fuel rail. Just for fun, I decided to cut a junk regulator open. They're not complicated! Taking the spring out means there's no pressure regulation, but I do wonder about the strength of that rubber diaphragm with 60+ psi of pressure and no spring to support it. So I won't be using this.
entry 708 - tags: fuel pressure
|October 23, 2009 - Of course, the final solution to the fuel rail outlet was simple.|
Tap the hole for a 1/4 NPT and screw in a hose barb. However, I was lucky. The 1999-00 fuel rail I'm using has a fairly beefy casting where the damper/regulator plugs in. It's a damper on the returnless 1999-00 fuel system, but for my 1994 system with a return line I had a regulator in place. That's a damper right beside the rail. Anyhow...
All the other rails such as the 2001-05 one above have a much thinner flange design. Would it be enough to tap to 1/4 NPT? Probably. But I'm more comfortable with all that extra metal around mine. With the 2001 version, I might have left the damper in place and drilled/tapped the end of the rail for 1/8 NPT. Not a lot of meat, but it's been done.
entry 709 - tags: fuel pressure
|October 23, 2009 - While pulling the top half of the intake manifold to change the rail, I discovered the actuator for the VICS butterflies was disconnected.|
The butterflies were stuck in the high rpm position. Interesting, I wonder how long this has been the case. There's supposed to be a c-clip retaining this. So I used safety wire instead and now the problem is solved.
entry 710 - tags: fuel pressure, VICS
|October 24, 2009 - While I had the fuel rail off, I decided to swap injectors.|
I had been using stock 1999-00 injectors (the red one) and I had a set of 2001-05 injectors (purple) on the shelf. The reds are 240cc and the purples are 265.
Why? Because I've come to realize that I simply may not have had enough injector in the car and that might have been causing the car to run lean at sea level. When I drop down to sea level from 5000', the engine makes 20% more power because of the thicker air. Could this be why the car was wanting to detonate at Laguna Seca, or why it started to misfire on the last day of the Targa? I don't know, but quite possibly. It should have been a fairly easy thing to do and Jeremy at FM mentioned it to me once a couple of years back. Between one thing and another, it just never got done.
I'll be more comfortable with the larger injectors. Also, I'll get more fuel from the higher pressure. Will these 270s be enough? Not if I start to get close to 200 hp, that's about where they peak. In that case, I have a set of 550cc injectors I can swap in. But they'd require new connectors for the injectors so I didn't bother to do that. I'm about to embark on a series of tests and I'd like to leave the wiring as unmolested as possible for the time being.
entry 711 - tags: fuel pressure, injectors
|October 26, 2009 - With the fuel system all buttoned up, I was seeing odd numbers on the gauge built into the FPR.|
I'd been a bit concerned about the fuel pump (of unknown history, I'm really not sure where it's from) dealing with sustained 60 psi fuel pressure, so I decided to swap it out for a Walbro I had sitting around the garage. It's pretty easy when your car has no interior! I also plumbed in a second fuel pressure gauge to confirm the readings.
Good thing, the cool little built-in one was pretty fictional most of the time. I set the pressure to a fixed 60 psi and went out for a run to let the ECU auto tune. It's definitely not feeling perky right now, probably far too rich. I'll put it on the dyno in the next couple of days and see what I can do with it. Since it's so simple to adjust the pressure now and I have some existing tuned maps, I can easily do back-to-back dyno runs with the 1994 fuel pressure and the 1999 fixed amount.
entry 712 - tags: fuel pressure
|October 28, 2009 - Time to see if the fuel pressure changes did anything!|
Background: there's a big dip in the car's torque curve between 3500 and 4500 rpm. Massive, actually. It's about a 10% drop. The theory was presented to me that the B (1999-05) injectors are designed to run at a higher pressure, so they weren't atomizing properly. Thus my work of late to raise the pressure.
Unfortunately, it did nothing. Nothing at all. After a bit of tuning to deal with the different fuel curve that's a result of the fixed fuel pressure, the car didn't change a bit. I spent some time playing with timing and fuel, just to prove that naturally aspirated cars have a pretty big sweet spot. Adding an extra 3 degrees of ignition advance didn't do anything, so I took it out again.
Okay, so that didn't do anything. While the car was on the dyno, I decided to mess with the intake cam timing because that's quick and easy. I advanced the cam by 5°. This should theoretically help the bottom end while hurting the top. And it did. Kinda. The bottom end got stronger and there was a bit of a taper above 6700 rpm. Pretty good tradeoff. The weird thing is that the dip was unaffected. All the gains were on each side of it. It's obvious that there's something that's just not working in that rpm range, but what is it?
Next, I retarded the intake cam 5° from my original setting. More overlap, should be a bad idle, a weaker low end and more up top. These are fairly big changes, but I was trying to see trends. Oddly, the car purred at idle. It's always had a very grouchy idle, lumpy and a bit tricky to launch. Not any more. But the car really didn't like the cam settings, losing a huge amount of power down low and only gaining a little bit way up top.
So, not a terribly successful day really. Although it was educational. The cams in the car are Stage 2 cams from Integral Camshafts, and they say that for some reason their 1.8 hydraulic lifter cams just don't work well. The 1.6 ones do, as do the 1.8 solid lifter cams. Just not these. So the next step is to play with a few different cams. It's the second set I've tried, but I have at least three other options to stick in there and see what happens. Once that's done, I'm going to play with a couple of intake manifold options that are available to me. What I'd really like is a VVT head, as I've seen a very similar engine to mine make big torque right where I have my dip. That engine is in the FM shop, not far from where the Targa car is parked. And the boss is going on vacation...
But still, the engine's getting stronger. Here's a comparison between what it looked like when it first hit the dyno and now. Since then, I've altered the intake pre-throttle, built the header and changed cams.
entry 714 - tags: dyno, fuel pressure, cams