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Old 01-07-2018, 01:07 PM   #8
John V
No more BMWs
 
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Join Date: Apr 2005
Carmudgeonly Ride: Ram, MS3, CX-5, RX-8
Location: Glenwood, MD
Posts: 14,753
So... I mentioned an MX-5. Interestingly, the third-generation MX-5, the NC chassis, is almost identical to the RX-8 from the firewall forward and from the rear glass backwards. The NC's front and rear subrames will bolt directly into the RX-8, and vice versa. The inboard suspension mounting locations are in exactly the same location between the two cars - the only differences are the engine mounts and the steering rack mounts. The two cars use different uprights, hubs, brakes, and control arms, as the Miata has a narrower wheelbase and less weight.

I figured I'd use this to my advantage. I know that the RX-8's firewall is a different shape than the MX-5 as it's designed for a rotary and not the taller piston engine. The MX-5's 2.0L engine is very similar to the 2.3L and 2.5L versions that were offered in various other Ford and Mazda products, but with far less robust internals. I don't want to use the 2.0L as it's not remotely strong enough to handle the power I'll be throwing at it, but given that it's the only engine in the MZR family that's installed in a rear-wheel drive chassis (excluding the Ford Ranger which used a 2.5L version of the MZR, but with truck-oriented manifolds and tuning) I thought it'd be very handy to have an NC around for parts scavenging.

So I bought one.



And that's where we are now. Today, the goal is to lower the engine, transmission and subframe out of the NC as one unit and start taking measurements. I can already tell that it won't directly bolt into the RX-8 because the engine setback is so extreme on the MX-5. The top of the 2.0L will hit the top of the RX-8's firewall. The even-taller 2.5L that I'll eventually pick up will be even worse. But as a starting point, it'll be helpful to have everything out of a running NC to get going on converting wiring, which will be far from plug 'n play.

To convert a 2.5L engine (out of one of a million Fusion, Mazda 6, Mazda 3 or similar cars) to a rear wheel drive configuration requires many parts off of an NC Miata, so this 2.0L will donate a lot of good stuff. Looking at how it's installed in the MX-5, I think I can easily lower it 2-3 inches and move it 4-5 inches forward to make it fit in the RX-8. Obviously moving the engine forward isn't ideal for handling, and perhaps a rotary would have upset the balance of the chassis less. But I'm not allowed to hack up the firewall, and I really do think this will be the best long-term solution to making this car fast and reliable. So I'm committed to blasphemy... and ending my long love affair with the rotary.
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