August 27, 2008 - Dyno run!
The car spent some time on the dyno yesterday, making sure that it was safe and ready to go. Jeremy at Flyin' Miata managed to pick up a bit of top-end power but more importantly he was able to confirm that everything was in good shape and ready to go.
The chart is interesting. There's a big dip in the curve at around 4000 rpm. I don't feel it when driving, but the car would be faster without it of course! Jeremy spent some time trying to tune it out but didn't have much luck. If I was building the car now, I'd probably use a VVT head from a 2001-05 Miata instead of the 1999-00 one I used. They have much better torque curves down low. But if you don't learn something over the course of a project, you're not trying hard enough.
I waffled a little bit about whether I should put this chart online as it will invariably get held up on various forums for ridicule and taken out of context, but what the heck. Here goes.
This is Janel's little blue car vs the race car. She has a Flyin' Miata Voodoo II turbo installed on a stock 110,000 mile 1.6 engine. The turbocharger itself is the smaller 2554 unit, chosen for response instead of ultimate power. Since her power level is limited by the injectors in the car regardless of altitude, I used an uncorrected chart for her. Since I'll be able to make more power at sea level (close to 20% more), I used the SAE standard correction. This chart should be accurate for the relative behaviors of the two cars at sea level. The biggest change will be that the turbo will spool up a bit quicker.
What's interesting about the chart is how similar the power curves are, once you hit 3700 rpm. Two very different ways of making power but with surprisingly consistent results. Below 3700, the big displacement of the naturally aspirated car really helps. It's no wonder people comment on how quickly it squirts out of corners, with almost full torque available at 3200 rpm. That's more important than some sort of headline horsepower number. The dip that bothers me (intellectually, I've never noticed it driving) in the race car is there in the turbo car as well, but it's not as noticeable because it doesn't have the big torque swell earlier in the range.
I've always known that I chose a more difficult way of making power. If I was using that little turbo 1.6 in the Targa, I'd be running in the Unlimited class and would have to drive much faster to avoid penalties. But really, it was an excuse to build a cool engine. I love the response of a good naturally aspirated motor. I'll do more development on the engine when I return from the race, trying to open up the breathing on the intake side and maybe swapping a VVT head on. For the race, reliability and tractability are more important and I didn't want to have to babysit a fussy mill. Focusing on the handling and suspension of the car will pay greater dividends, so that's why I spent my time there.
I'm looking forward to feeling how the race engine feels at sea level with a 20% power boost. I think it's going to be a very good tool for the job at hand - dealing with unknown roads as expeditiously as possible.
Dyno chart
tags: engine, dyno |
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