The Breakup (Miata build)

Re: The Breakup (Miata build)

Postby sdwarf36 » Sat Aug 01, 2015 10:37 am

Looking at the head, I bet you can't cut it very much before you hit the intake seats. I used to have to figure out compression ratios on a daily basis. Just pulling numbers out of my butt, I'm guessing thats about a 50cc chamber. Also guessing-i'd say that it would work out to probably about .005 per cc removed. So if you cut .025 off the head, you'd drop to a 45 cc chamber. MAYBE a .5 change in comp ratio. (8.0 to 8.5 cr) Not enough of a change to matter much. Maybe 3 or 4 hp with no other changes.
Translating road racing to hillclimbing:
Proper tire selection== nothing hooks up on moss or wet leaves.
Staying on the racing line==anything paved is considered good.
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Re: The Breakup (Miata build)

Postby drummingpariah » Sat Aug 01, 2015 6:14 pm

sdwarf36 wrote:Looking at the head, I bet you can't cut it very much before you hit the intake seats. I used to have to figure out compression ratios on a daily basis. Just pulling numbers out of my butt, I'm guessing thats about a 50cc chamber. Also guessing-i'd say that it would work out to probably about .005 per cc removed. So if you cut .025 off the head, you'd drop to a 45 cc chamber. MAYBE a .5 change in comp ratio. (8.0 to 8.5 cr) Not enough of a change to matter much. Maybe 3 or 4 hp with no other changes.


Got it, thanks for catching me before this got expensive Sherm. It's pretty straight right now (within .003") so I'll leave that alone, and just clean up the ports, lap the valves, and call the head done. If I can find 1.6 high compression pistons, I'll start thinking about the bottom end, but it's likely that this will just end up as an effort to get back up to OEM power levels, hopefully with a few minor gains from the ITB rack (really, any gains would be from removing the current heat/restriction in the OEM intake system). I imagine cams would make a big difference, but it seems I'm already into modifications that would be 'illegal' in spec Miata, and that means their data isn't as useful. I have a lot more freedom in available modifications than spec Miata, but a lot less freedom in budget.
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Re: The Breakup (Miata build)

Postby drummingpariah » Fri Aug 07, 2015 12:15 pm

A little more cleaning, and it's starting to look pretty good. I've felt like crap this week, and have been sleeping a lot so I haven't made anywhere near as much progress as I'd like. I was planning to have this ported and polished by tonight, but that's not going to happen. Instead, I think I'll just reassemble it and swap the heads so I have a 'clean, healthy oem spec' head on the current engine. Based on my compression test, that should reduce my fuel consumption and give me a bit more power. Three cylinders on my currently running have at least one valve that isn't closing completely, and that could certainly be a factor on why I'm only making 87whp right now. With a healthy head, I believe I should be closer to 105whp. A good port and polish could potentially get me closer to 110whp, after another tuning session.
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Re: The Breakup (Miata build)

Postby sdwarf36 » Fri Aug 07, 2015 6:20 pm

To give you a metric to measure by, A good tuned Spec Miata is 115hp. Read up on what they do-or can't do ;) . That should give you an idea how to get there.
Translating road racing to hillclimbing:
Proper tire selection== nothing hooks up on moss or wet leaves.
Staying on the racing line==anything paved is considered good.
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Re: The Breakup (Miata build)

Postby drummingpariah » Sat Aug 08, 2015 6:45 am

sdwarf36 wrote:To give you a metric to measure by, A good tuned Spec Miata is 115hp. Read up on what they do-or can't do ;) . That should give you an idea how to get there.


I've been doing a ton of research on it, but they sound pretty limited. Everything needs to be within factory spec, which means a lot of extra work for a modest power gain. It seems like ignition timing and AFM spring tension are where the 'big gains' are, but converting to Megasquirt has already eliminated that. I'm going to try to get the "new" transmission swapped in today, and hopefully it doesn't make quite as many awful noises as the one I've been running.
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Re: The Breakup (Miata build)

Postby drummingpariah » Sun Aug 09, 2015 4:32 pm

Yesterday as Okemo Prep day (transmission swap from 'known bad' to 'unknown'). I got the transmission out
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... but then I realized that I hadn't drained it beforehand.
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During reinstall, nothing was lining up right, and I couldn't quite figure out why. Eventually I pulled the trans back out and put it side-by-side with the old one. I realized that the PO had left one of the locating dowel pins in the transmission, and I still had that pin in the block. It took two hours to work that thing out of the transmission. Then everything went together like it was designed to.
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I'm happy to say that the straight-cut whining sound is gone now, but the shifter has a lot of slop in this transmission. Total cost, including a few bearings, a new slave cylinder, 5 cans of brake cleaner, fresh hydraulic fluid, DEI transmission tunnel insulation, and 5 qt of gear oil: $217.97 and almost 12 hours (lots of cleaning went into this, even though it doesn't show).

The plan is to rebuild the whining one (it's most likely a bad bearing somewhere in it) and swap that back in a little later. Then I can rebuild this one while using the rebuilt original, and have it sitting around as a spare.
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Re: The Breakup (Miata build)

Postby sachilles » Mon Aug 10, 2015 9:16 am

You are not accounting for the laundry detergent needed to save the shirt :lol:
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Re: The Breakup (Miata build)

Postby drummingpariah » Mon Aug 10, 2015 10:35 pm

sachilles wrote:You are not accounting for the laundry detergent needed to save the shirt :lol:


There's no saving that shirt. It's long gone, at this point. Instead, I bought a pack of $8 tshirts at walmart (because I was 45 minutes away from home, working at the makerspace).

Today is just a minor update, since I have a race coming up this weekend. I'm at 'code freeze' now, where I'm not starting any high-risk projects on the Miata.
The ecu location wasn't ideal, so I fabricated a few mounting tabs
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And bent up some aluminum to make a standoff on the firewall.
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I'll have to do some creative ducting to get heat/defrost with a fan again, but I'm not afraid of a bit of fabrication. This work took very little time, about $30 worth of tools, and left the car just as ready to daily/race as before.
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Re: The Breakup (Miata build)

Postby walterclark » Tue Aug 11, 2015 6:35 am

Electronics like cool.

I take it your Megasquirt doesnt have an SD card for data logging or handy USB/Serial ports that you like to connect to frequently for programming...

Mine has both so I end up mounting it on the face of the "dash" where the glove box used to be so I can easily get to them.

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The older I get the better I was.
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Re: The Breakup (Miata build)

Postby drummingpariah » Tue Aug 11, 2015 9:30 am

This one's only MS2, so it really doesn't have any of the nice features. Just after my first tuning session with it, the serial port (which is really the only port) stopped providing a connection. At some point, I'll open it up and check for cold solder joints ... but I've had higher priority projects to deal with. I did cut an access port for that serial port though, so I can just pop it through this small aluminum cover. The MS3 unit in the Datsun is a different story altogether, but I'm not sure if I'm going to keep that now that I have the 302's (EFI is worth considering, but carbs are so much simpler to get to running).
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