The Targa Miata

I'm not done with the intake yet, but first I need to play with some springs.

Mon, 01 Mar 2010 23:26:28 -0700

Why? Because the 750 lb springs on the car are borrowed, and they have to go on to a V8 Miata instead. And just today, I got a package from AFCO with my dual spring setup!
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That was worthwhile.

Sat, 27 Feb 2010 22:33:42 -0700

Overall the throttle body setup shows gains over most of the range with no real losses anywhere. The peak gain is probably around 15 hp at 6000 rpm. Based on some post-dyno tuning, I know I'll be able to pick up a bit more in the 3500-4000 range as well.
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That's starting to look like a race engine.

Fri, 26 Feb 2010 17:58:35 -0700

It took a fair bit of work to get to this point - I spent all day Wednesday as well as a couple of hours on Thursday and Friday - but I've added at least 50 visual horsepower.
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The new intake moves the injectors into the cylinder runners.

Fri, 26 Feb 2010 17:20:41 -0700

The factory ones are in the head. So the holes need to be plugged. When I discovered this, I spent some time looking at various options to solve the problem. I'd honed in on the creative misuse of a specific oil pump plug. I just needed to drill a hole in the top so I could screw something in to yank them out in case I needed to relocate the injectors to their rightful home.
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Time for a new intake test!

Fri, 26 Feb 2010 17:17:00 -0700

This particular one is designed for a 1994-97 head. Well, I have a 1999-05 head. The ports are the same shape, but they're higher in the head on my setup. Usually this involves cutting and welding the manifold to move stud holes.
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We made the cover of Forever MX-5 magazine!

Sat, 13 Feb 2010 11:19:59 -0700

Along with the cover is an 8-page article about the race. They've kindly given me permission to post it here.
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There's a huge change in the factors for 2010.

Fri, 29 Jan 2010 12:52:33 -0700

I've discussed this with the event organizers and it appears it's become public now so I can talk about it. You might remember the discussion of last year's factors. Basically, a base time is set for Class 9 Modified Large. This time is multiplied by the factor for other classes to provide the handicapping. The point is to try to make it an even race so the best team can win, regardless of car.
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There hasn't been an update in some time - because I haven't worked on the car in some time.

Mon, 11 Jan 2010 16:11:49 -0700

The combination of a very, very cold December, a bunch of snow and other projects such as Janel's MG have kept me from working on the Targa car. I have a set of rebuilt shocks ready to install and some plans to try something different on the intake.
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No dyno charts yet, but the new hollow intake did nothing.

Mon, 30 Nov 2009 17:35:32 -0700

Nothing at all. This matches up with what a couple of other good engine builders have seen. There are some indications this modification is beneficial for boosted cars, but not naturally aspirated.
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Ta daaaah!

Tue, 17 Nov 2009 18:18:26 -0700

Okay, it doesn't look like anything. But that's the hollowed out intake manifold. I'll take the car to work tomorrow and hopefully get the chance to put it on the dyno and see what difference it makes, if any.
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I'm proud of this one.

Mon, 16 Nov 2009 19:09:02 -0700

Grassroots Motorsports (GRM) magazine just celebrated their 25th anniversary, and as part of their big issue they named "Our 25 favorite cars from the last quarter century". It should be no surprise to GRM readers that the Miata topped the list. They also highlighted 10 milestone Miatas, "The most important examples of a very important car". And guess what one of them was?
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Based on some things I've read, I've cut out the wall between the plenum and the resonance chamber.

Wed, 04 Nov 2009 20:28:00 -0700

With this setup, the plenum is effectively much larger - but more importantly I now have variable length intake runners. With the butterflies closed, the air will follow the same route as before. But when they open, a short intake path will become available which should benefit high-rpm operation. I also removed the EGR ducting because I don't run an EGR system, and this cleans up the flow near the throttle body. While cutting out the EGR ducting, I did manage to break through into one of the bolt holes, but that was patched up with some good two-part epoxy (ie, not JB Weld). I also modified the gasket that sits between the two halves to match my modified manifold.
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Time for some intake manifold testing.

Wed, 04 Nov 2009 20:06:31 -0700

Since the big torque dip wasn't affected at all by the cam change or the fuel pressure change, I'm thinking it's something with the intake manifold.
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Temptation.

Wed, 04 Nov 2009 19:57:47 -0700

Okay, I was really just doing some suspension work on the car and the plastic V8 mockup happened to be used for something else. But wouldn't these two work well together?

Track day time!

Mon, 02 Nov 2009 11:55:26 -0700

The new 750/450 springs worked quite well, pretty much eliminating body movement but allowing the suspension to still soak up those berms in the chicane. The car was fairly quick as well, allowing me to match my best-ever time of 1:04.7 despite a cold day and slow times for most people. Janel also liked it, posting a personal best and getting down into the 1:10 range. She's not a big fan of the feel of cold race tires on the warmup lap. There was actually ice on the start/finish line when we arrived in the morning, I'm not exaggerating about the cold!
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A quick engine comparison.

Thu, 29 Oct 2009 09:11:30 -0600

Before Elvis - a 2002 Miata at Flyin' Miata that should be fitted with velcro motor mounts - was fitted with a V8, it had a naturally aspirated motor that was broadly similar to mine. The car had a set of roller barrel throttle bodies and a Racing Beat header but more importantly, it had a VVT head. The dip is missing!
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Time to see if the fuel pressure changes did anything!

Wed, 28 Oct 2009 21:29:17 -0600

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.
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I've been doing some testing on the suspension of the car.

Mon, 26 Oct 2009 21:35:52 -0600

As usual! This time, I'm running some very stiff 750 lb front springs with 450 lbs in the rear. Usually I'd run a higher rear spring rate with that much in the front, but it was a matter of what was on hand. The car works surprisingly well on the road, even though that front rate is exactly double what we ran in the race. It's going to be a lot of fun on the track this weekend for sure, with some very quick reflexes right now. In fact, the rear rate seems to be working pretty well. Well enough to make me wonder what I should run in the next Targa. I'd been leaning towards 450/375.
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With the fuel system all buttoned up, I was seeing odd numbers on the gauge built into the FPR.

Mon, 26 Oct 2009 21:32:25 -0600

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.
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While I had the fuel rail off, I decided to swap injectors.

Sat, 24 Oct 2009 10:49:02 -0600

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.
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