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 Post subject: What year donor Miata?
PostPosted: June 26, 2019, 6:43 pm 
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Joined: December 19, 2018, 11:16 pm
Posts: 3
Location: Bonney Lake, WA
I'm planning to build a Caterham copy, specifically a copy of the CSR frame and suspension with a G7 roll cage. There's a new group of Caterham G7's that run in my run group in ICSCC (we call it conference) road racing here in the Northwest. I've been driving a Formula Vee for the past five years, I built a new Vee in 2016. Now I want to race a Caterham-like Locost as that group is growing and they can be fast. One of them has 300hp, it's a CSR, the others are G7's with what looks like a catfish mouth and lower hp motors, but still plenty quick.

I'm no stranger to building things as I've been an aircraft mechanic all my life, currently also in the process of building a Tailwind and have done a few other restoration jobs over the years.

My sister has a body shop in Missoula and she can find wrecking yard miatas very easily, so now I need to know what year is suitable, I know I would like at least a 95 to get the 1.8 diff, hopefully Torsen, but she sees a lot of much later model years available for wholesale body shop prices because they're totaled, so I could find something as new as a 2019 that is destroyed except for the drivetrain parts that I want.

How new is too new to rob for a Locost? Any newer years to avoid for whatever reason? Should I simply buy the newest I can get that has a torsen diff and the rest will be workable?

Any guidance appreciated.

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PostPosted: June 27, 2019, 5:36 pm 
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Joined: May 27, 2006, 9:46 pm
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Location: BC, Canada. eh?
Personally, I'd recommend a '99 or '00. They are a bit simpler design, and run on regular, 87 octane pump gas - the '01 & up models require premium fuel. Here in Canada, that adds another $1 or so per gallon, so it means something!

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PostPosted: June 27, 2019, 8:28 pm 
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Joined: December 19, 2018, 11:16 pm
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Location: Bonney Lake, WA
Thanks Zetec, good info. I found a 99 close by, what's the best way to determine torsen or not?

I know about fuel proces in Canada, just spent a weekend at Mission Raceway, gas is crazy expensive up there.

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PostPosted: June 28, 2019, 10:27 am 
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Joined: April 22, 2010, 4:43 pm
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Location: Livermore, Calif.
This link may help you. Scroll down past the photos for the description.

https://www.miata.net/garage/diffguide/index.html

Cheers,
Roy

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PostPosted: June 28, 2019, 10:54 am 
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Joined: May 27, 2006, 9:46 pm
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Location: BC, Canada. eh?
Gas prices here have just started to make their way back down week or two from $6.50 Canadian per US gallon (regular gas) down to its current $5.10 level ($6.12 for premium), but every time there's an oil refinery issue somewhere in North America (or an oil company exec gets the sniffles), our prices shoot up immediately. It's crazy! A few weeks ago, premium was close to $8.50 per US gallon - that's why I suggested the "regular fuel only" 99-00 Miata engines!

I had a '00 Miata, and absolutely loved it.

There is ONE little thing to watch out for on the '99-'00 engines. Check the crankshaft endplay. Easy to do, no tools required - just grab onto the crankshaft main pulley (the bottom one) and try pulling & pushing it, forward into the engine and back towards the grill. You will, without doubt, get a tiny amount of travel, and that's fine (IIRC, somewhere in the neighborhood of .015" or so is normal). SOME of these engines were manufactured with improper-thickness thrust bearings, and came from the factory with endplay on the order of 1/4" or more, which quickly destroyed those engines.

The vast majority were replaced under warranty, and those that didn't pretty much all failed by 10K-12K miles, so any that are much beyond that mileage (pretty much any you'll find, now) were obviously fine. My engine had .017" endplay, which was absolutely fine....although it was disconcerting, to say the least, to discover I could push the crankshaft forward & back (in the engine of my running & driving daily driver) with an audible "click-clack-click-clack"). I panicked, got out my dial gauge, and measured it....whew!

There's a list of the serial number ranges affected, and here's a website that explains the issue: https://www.miata.net/solo/99miatathrus ... ilure.html

Just be aware that if you found, for example, a '99 engine with 3,000 miles on it, you definitely want to check for that. If it has 30,000 miles on it, buy it & have fun!

:cheers:

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PostPosted: June 28, 2019, 12:31 pm 
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Thanks for the info and links guys, much appreciated.

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PostPosted: March 3, 2021, 12:30 am 
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Joined: January 5, 2011, 11:09 pm
Posts: 33
Location: Easley, SC
I started down the path of using the third gen MIATA or RX8 rear components, the connections on the rear uprights and their suspension controlling arms get really complicated fast, unless you use the entire rear subframe. That gets really heavy fast. I backed off after buying and returning ( expensive choice) and went successfully forward with a second gen NB diff, axles, and drive shaft which work with my NA uprights. I’m sure with NB uprights would be about the same. Was able to source the Torsten II limited slip diff. I think it’s a good choice

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PostPosted: March 3, 2021, 2:44 pm 
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Joined: November 6, 2020, 6:29 pm
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I seem to recall the 01+ Miata engines with VVT having a clearance issue with the Locost hood, as the VVT actuator is on top of (or higher than) the valve cover.


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PostPosted: March 3, 2021, 6:37 pm 
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Joined: April 26, 2008, 6:06 pm
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Location: Under the weather. (Seattle)
Welcome! Nice to see another local. There are a handful of us locally, that (in non-COVID times) like to get together from time to time.

Mazda should be able to tell you by VIN what options it had, but here's a list to help you determine by year and option packages whether it had LSD or not.
https://www.miata.net/faq/america/index.html

Up through 2005 have easier to use upright designs for conventional double wishbone suspension geometry. From 1994 through 2002 have a true Torsen brand differential. From 2001-2002 larger brakes were available on the Hard S suspension (should be listed on door passenger door jamb sticker) and became standard in 2003. So factory equipment wise, perhaps the 2001-2002 with Hard S suspension would check the most boxes.

However, it's hard to provide a detailed answer on the engine side without knowing what are the limitations of your class and budget, and what are your goals for power and competitiveness? If <150whp is fine and every hp doesn't count, any stock Miata engine will do. If turbo is an option, stock Miata engine is good into the 225-250whp range. Alternatively, there are numerous swap options intended to work in a Miata, so presumably *might* be on the easier side to get up and running. These include at least the GM Ecotec, GM LFX, GM LSX, Honda K-Series, and Honda J-Series. Beyond that, any Ford/Mazda Duratec/MZR I4 (2.0, 2.3, or 2.5) will bolt up to a NC Miata flywheel, clutch, and transmission... Which are the engines used in the Caterhams. Or, go nuts with whatever else your imagination can come up with a way to mount and control.

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