Targa Miata
March 28, 2010 - Time for some more dyno testing!
One nice thing about the individual throttle body setups is that I can change out the air horns and alter the intake runner length. In theory, a short runner should trade off low rpm torque to gain high rpm power - and a long one should do the opposite. But if they're way off, then you just plain lose. Since I have a collection of horns, I'll simply do some back-to-back testing and see what happens. It's always interesting to simply install a pipe that's 1" longer and see a power bump.
I had the chance a while back to talk with Bill Schenker, a national-level CSP autocross competitor about his engine. It makes very good horsepower - similar peak power to my engine, but with less torque - and it's all come from hundreds of dyno runs, testing one slight change against another. One thing he told me was that the length of the intake tube running from the stock intake manifold to the filter had a big effect. Again, a 1" change made a notable difference. Of course, he was talking about naturally aspirated power so it wasn't a 15 hp difference, but if you can find 10 places to gain 1.5 hp, there's your 15 hp gain.
So, bring on the air horns!
entry 736 - tags: testing, intake, air horns, IRTB
March 28, 2010 - Here are the air horns I have to work with.
The silver one is what came with the throttle bodies, the others are some Titan units that I found in the shop. At least, I think that's where they're from. I have some TWM units around as well.
The first dyno runs were with the silver, "stock" horns. I followed that up with the longest of the black ones, just to see if they'd actually fit. The answer is yes, but the filters I was using won't fit over the end of them.
Dyno chart - the red trace is the medium-length silver horn, the black is the long one.
Overall, it looks like a big win for the long tube, with a solid gain from 4200 to redline and no real loss anywhere else. Unfortunately, it's not an apples-to-apples result. The biggest change is that the long tubes had no filters. Now, these are some pretty open filters with a large surface area, so I don't expect they have much effect. But I do need to test them back-to-back to confirm.
There's also a difference in the design of the bell mouth on the air horns. Note how the silver one has a simple horn shape, while the black ones have a more complete radius. This entry is fairly important, and it could be that the black ones have a better design.
The internal diameter of the horns is also a bit different. The black ones actually match the diameter of the throttles, while the silver one is a bit oversize. Interesting, given that it's the one supplied with the kit. The lip of the throttle bodies has a small chamfer in it that steps the diameter down, but basically there's a step change in the size.
Luckily, I have a black air horn that's almost exactly the same length as the silver one, so I can do comparative unfiltered tests between them to see which is the better design.
I only had the chance to do two different runner lengths today. I'll spend more time on the dyno this week and test all four options in the same session. Hopefully.
entry 737 - tags: dyno, IRTB, intake, engine, air horn
March 28, 2010 - Dyno run video.
It's not exciting, I know. Really, this was just an excuse to practice uploading video off the new camera and make the changes in the website code to use YouTube instead of the no-longer-accepting-uploads Google Video. But if you want to hear how the engine sounds with the new intake, well, it might be worth your time. Video
entry 738 - tags: video, dyno, IRTB, noise
March 30, 2010 - Results for the intake runner length testing.
This was interesting. Not because of what happened, but because of what didn't.
Each engine setup was dynoed three times in quick succession, because I found the first one tended to be erratic. The second and third would be almost exact copies of each other. When I was done, I went back to the beginning to test both the silver runners and the filtered option.
Here's the biggest difference: Short (blue) vs long (red). The shorties did indeed suffer in the midrange, with the biggest difference right around 4500. They didn't gain much up top though, which is a bit odd. Cam limitations? The medium and short runners were basically identical. The silver runners and the black ones of the same length were identical despite the difference in lip design.
But here's the really telling test: Filtered (blue) vs unfiltered (red). That's where my high-end gain came from last time. I'm a bit surprised by this, because the ITG filter I use on the Seven makes no difference at all. It's a big boy and apparently very free-flowing. Something will have to be done - read on for more.
So, the long runners were the winners. Everything else was the same. The short runners make the same power as the ones that came with the throttle bodies.
I need to quieten this car down for a 92 dB day at Laguna Seca in a bit less than two weeks. Ideally, I'd build a plenum to enclose those long runners and see what happens. But there's a way to cheat. A friend who runs a business selling parts for Titan race cars has a nice Pipercross 600 plenum I can use. I'll have to stick with the short runners to fit it, but it's a quick and easy way to quieten the car and bring in cold air. It should be here on Thursday and I'll fit it then.
entry 740 - tags: dyno, intake, IRTB, plenum
April 4, 2010 - No pictures of the new intake yet, but I have track videos!

Fastest lap
Smoother fast lap

The track day went pretty well. It was a fairly cold one and I only got about three sessions in the Targa car (along with the chance to drive a 350Z, a BMW M Coupe and a couple of FM Miatas), but my best time was a 1:04.959. That's about 0.2 seconds off my best in the car, nothing to be ashamed of. There was a time when simply dropping below 1:06 in any car was unusual!
The dual spring setup does allow for some body roll, but the lap times would indicate the car isn't suffering too badly. It absorbed the berms well and was very stable under braking. I'm trying to decide if I want to keep this setup for Laguna Seca or if I want to pull the secondary springs so the car corners flatter and has quicker reflexes. Tough call. If it can still hustle around our little autocross track here this quickly, I'm thinking the dual setup is working.
The engine felt good. For the first time, I noticed a lack of pick-up coming out of one of the hairpins at 4000 rpm - that's the dip in the torque curve. The heavier throttle pedal (due to a stiffer spring) took a little getting used to in order to be smooth, but I adapted pretty quickly. Nobody noticed that the car was particularly loud, so I'm hoping that's good for Laguna Seca sound levels. Hoping hoping hoping. I did have one person ask me if it was a V8 because it didn't sound like a four-cylinder!
Pictures of the intake are at work, I'll put them up tomorrow.
entry 742 - tags: video, GJMS, testing, track, IRTB
April 5, 2010 - Time for some pictures of the new plenum!
First, I had to drill a backing plate for my intake setup. In order to clear the fuel rail mounts, it has to sit a bit low.
entry 743 - tags: intake, plenum, IRTB
April 5, 2010 - The plenum clips on over the base plate.
I had to notch the edge of the plenum slightly to get clearance for the fuel rail, but here it is in place.
You can see the relocated IAC back by the fuel pressure regulator. It's a tight fit wiggling this on!
entry 744 - tags: intake, plenum, IRTB
April 5, 2010 - Now, I have to get cold filtered air into that plenum.
I have a conical filter that fits into the inlet, but I need to do some dyno testing to see how well that works. The ideal plumbing here would be to put the conical filter in, then run straight to a hole in the hood. But not today.
So instead, I used some flexible 4" hose and ran it down to the filter. It's a tight fit and I'm not excited about the tight radius bends from an airflow standpoint. But it's critical I get this car as quiet as possible.
entry 745 - tags: intake, plenum, IRTB
April 5, 2010 - The filter is a monster.
I needed one with a 4" inlet to match the inlet on the plenum, so I grabbed the same filter we use for our V8 Miatas. It's Honda sized! A 90 degree piece of silicone and a slightly-fudged adapter into a piece of 4" tube, and we're hooked up to the hose.
entry 746 - tags: plenum, IRTB, intake
April 5, 2010 - The filter is pretty exposed to road muck and goo thrown by the tire in this location.
And the weather forecast for the trackday on Saturday was looking sketchy. So I took this plastic cover from a 2005 Mazdaspeed and did a very quick and dirty installation. Very quick and dirty - note the use of tape! That's what happens when the track day is Saturday morning and you're still working on the car on Friday night. As it was, the day was dry so it wasn't a concern.
The first day at Laguna Seca has a 92 dB limit. I'm hoping to get past that. The next two days are 103 dB, so I might just pull the plenum off and stick the sock filters back on for maximum roar! Because I'm a child.
entry 747 - tags: intake, filter, IRTB