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-   -   What the Mazda RX-8 should have been (new autocross car build) (http://forums.carmudgeons.com/showthread.php?t=143692)

Nick M3 09-16-2019 04:53 PM

Quote:

Originally Posted by John V (Post 552020)
Jerico makes transmissions (manuals). Bellhousings are engine specific.

Fortunately, Mazda made the automatic NC and it has a bolt-on bellhousing.

Well, that saves a lot of effort. You going 2 speed for minimum weight?

John V 09-16-2019 05:38 PM

I'm not really sure. I kind of feel like the answer is yes, although part of me thinks I should put a four speed in there just in case I ever want to take it to the track. But I haven't been to the track in over twenty years, and I'm not putting a cage in this car, so then I think I should just put the two speed in it.

John V 09-19-2019 07:01 AM

So, a two speed isn't an option. When I looked at the gearing charts for the two speed I realized that second gear is always 1:1, so that doesn't really work with any realistic rear-end ratio I would run.

I'm actually looking now at a G-Force GSR transmission. It's configured similarly to the Jerico, but the G-Force has internal shift rods which allow the shifter to be centered in the tunnel. The side shifter and external shift rods on the Jerico look like they're going to cause problems in the RX-8 tunnel.

https://www.gforcetransmissions.com/...e-page-pic.jpg

Biggins 09-19-2019 09:56 AM

Quote:

Originally Posted by John V (Post 552085)
So, a two speed isn't an option. When I looked at the gearing charts for the two speed I realized that second gear is always 1:1, so that doesn't really work with any realistic rear-end ratio I would run.

I'm actually looking now at a G-Force GSR transmission. It's configured similarly to the Jerico, but the G-Force has internal shift rods which allow the shifter to be centered in the tunnel. The side shifter and external shift rods on the Jerico look like they're going to cause problems in the RX-8 tunnel.

I'm sure it's a dumb question and not up on all the rules, but are transmissions basically completely open for whatever in Street Mod?

Your option looks pretty awesome, but I assume you can easily get the gearing where you want it for autocross?

John V 09-19-2019 04:22 PM

Drive train is almost completely open. It's a bonkers rule set.

ZBB 09-19-2019 05:12 PM

Just caught up on this thread. Wow on the piston destruction. Enjoy the rebuild!

John V 10-07-2019 05:50 PM

Moving slowly on all of this. I finally got the new (used) engine completely torn down, cleaned, honed and inspected. I'm happy that I got a good engine from the salvage yard, so now the buildup starts.

Cylinders honed with a ball hone, then the entire block was washed including every bolt hole, then blown dry with compressed air, then the cylinders oiled.

https://lh3.googleusercontent.com/ur...=w1036-h777-no

The new rods and pistons are just a little more beefy looking than the stock stuff.

https://lh3.googleusercontent.com/D2...=w1036-h777-no

Cylinder head was torn down to receive new valve springs, shims and retainers to allow a little more headroom on redline - 8,000 RPM vs 7,500.

https://lh3.googleusercontent.com/l_...=w1036-h777-no

Valve springs have more seat pressure than the stock ones.

https://lh3.googleusercontent.com/El...=w1036-h777-no

Cylinders were measured to be round within the tolerance of my dial bore gauge (0.0005"). The piston to bore clearance is 0.0055" which is above Wiseco's recommended minimum of 0.0035".

All crankshaft journals were in spec, and every bearing clearance is on the large end of the spec at 0.003". The spec is 0.0009" (!) to 0.0039" for both the rods and the mains.

The oil rings and 2nd compression rings all were within spec out of the box, but the top compression rings will need filing. The recommended ring gap for a boosted application is 0.0055" times the bore diameter which is 3.5", so about 0.019", and they came out of the box at 0.014" which is too tight. I'm borrowing a buddy's rotary ring file so when that arrives this week I should be able to finish that up. The bottom end gets new stock main bolts from Mazda which are inbound. The cylinder head is getting ARP studs. Probably not necessary at the boost levels I'm running but if I ever creep closer to 500hp they will be welcome insurance.

John V 11-30-2019 03:25 PM

Finally found some time to do things.

Cut a hole in the transmission tunnel to accommodate the shifter housing and enable the driveline angles to work out correctly. I'll fill this in later.

https://lh3.googleusercontent.com/e0...=w1036-h777-no

Made a new crossmember for the gearbox.

https://lh3.googleusercontent.com/qr...=w1036-h777-no

Modified the driver's side engine mount. I had originally tilted the motor a little bit to the passenger's side to clear the steering rack. I fixed that issue so I wanted to level the engine so the gearbox was level. It also gave me a little more clearance between the top of the gearbox and the tunnel. I just sliced the bottom off of the mount, then cut a couple new pieces of metal to fill in what was missing. This mount also was always a little close to the oil cooler lines coming off of the engine, and I had notched it in a really ugly way. So I cleaned that up and made it look nicer.

https://lh3.googleusercontent.com/nq...=w1036-h777-no

https://lh3.googleusercontent.com/2c...=w1036-h777-no

https://lh3.googleusercontent.com/ne...=w1036-h777-no

John V 10-13-2020 03:08 PM

I guess when I took a Carmudgeons hiatus I stopped updating this. I'm on vacation this week and relaxing after a hike and a gym workout, so I guess I'll update it for the two people still following along.

This year did not turn out like any of us expected, and even taking CV-19 out of the equation, RX-8 V2.0 did not turn out as expected. I had massive problems with my fresh engine (caused by my new gearbox, which I'll get into) and only just a month ago got everything sorted out.

I'll go in kind of reverse order. This was a month ago down in Virginia Beach at my favorite rolling road with my favorite tuner at the wheel.



It makes 350whp at minimum boost (i.e. on the 7lb wastegate spring) and around 420 at 14psi. We didn't take it higher mostly because I don't think I'll ever need more power than that and more power equals harder to drive. The torque curve is basically flat from 3,000 RPM to redline (it does drop a little bit) and the engine can easily do 550whp, at the expense of longevity. It also makes sweet, sweet noises from the straight cut gears in the NASCAR dog box. Those dog-style engagement rings were the bane of my existence for much of the summer months.

Mazda, in designing the MZR, did what most manufacturers do and went away from keyed timing components. That means the only thing holding the engine in time is friction. That works great when every car is sold with an automatic transmission, or even a synchronized manual. But with dogs, the "gear" engagement is so abrupt it shocks the engine and can throw it out of time. Back in May when I hit the dyno the first time with my fresh engine, that happened pretty much right away. Fortunately, nothing internal was damaged, but the engine and cams being 20 degrees out of time makes for a very poor-running engine. So my freshly-built engine came all the way apart so the crankshaft and timing gear could be sent out to have keyways milled and broached.

https://lh3.googleusercontent.com/pw...-no?authuser=0

Super happy this only took 5 hours, on jack stands even, because at the time the Mazdaspeed3 was on the lift getting all the VVT components replaced and the valves adjusted.

https://lh3.googleusercontent.com/pw...-no?authuser=0

https://lh3.googleusercontent.com/pw...-no?authuser=0

This, combined with the factory friction washers and a crank bolt torqued to around 350ft-lbs should do the trick, and in fact the car ran flawlessly on the dyno.

I also got sick of guessing what my oil pressure and temperature were during competition, so when I found a very inexpensive, used digital dashboard I jumped at it. I think I'll probably 3D print a nicer-looking plate for mounting it at some point, but I needed something quick for the dyno session and so I whipped this up. Including a little circuit to send the fuel level to the ECU. Kinda junky.

https://lh3.googleusercontent.com/pw...-no?authuser=0

Looks okay installed though.

https://lh3.googleusercontent.com/pw...-no?authuser=0




I also put line locks on the car, to make for easier burnouts at ProSolos. Pump the brakes, push and hold the DSC button and release the brakes and voila! The front brakes are locked but the rears are open. Build some revs, engage the clutch, instant burnout.

I've driven the car on the road a bit and think I've found a way to get tags on it. The season was kind of a bust but I'm going to try to get into a semi-local event here before the snow flies.

equ 10-13-2020 04:52 PM

Very cool; thanks for sharing your world.


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