We saw drop-off in the RE71R during the GRM test, but not the Rival-S. That was on my CRX.

On the Miata with 225 Rival-S, I am cooking the rear tires after a few hard laps. Backing off brings them back, though. Saw the same thing at NCM on the west course (not full). These are both shorter courses with lots of turning Tracks with longer straights would likely provide more cooling. For example, I had no issues at COTA.

Getting back to this...big stuff coming soon, but here's a snippet that will helps others doing this same swap...

The K-series MAP sensor is designed to fit in a hole that is pretty deep, sealing against an o-ring. If the metal is thin, the o-ring does not seal perfectly. The metal in the GE intake is relatively thin.

I had a problem start to surface recently at COTA when the car began running super rich during the last session. I limped it home and eventually discovered MAP readings that were a little lower (less vacuum) than I had been seeing. I fixed it by installing a second o-ring around the base of the sensor “stub” and using a washer on the bolt to match the o-ring height. This did two things: 1) it set the standard o-ring depth shorter, and 2) what the standard o-ring does not seal, the second one does. I also put some sealer on the bolt threads since that penetrates the manifold as well.

https://www.miataturbo.net/attachmen...ine=1451568179

Happy New Year!! :party:

Remember this?

Solution => We are fitting 285/30-18 Bridgestone RE-71R's on 11's by tubbing the inner fenders and using a wide-body kit from DG Motorsports (AWR source).

This is a new size for that tire, due 3/1. In the meantime, we'll use 255/40-17 on 10's.

Proof of concept comes from the Wootton SSM autocrosser seen below in black using the same flare kit around 285 Hoosiers in front, and 315's on 12 in the rear. Rules disallow tubbing for that car, so he makes up for the 25" diameter by jacking up the perch height an inch. He's local, so I have studied it carefully.

The white car (Steve Garnjobst's XP autocrosser) is an example of a no-rules solution with tubbed inners. Not pretty, but very functional. Allows the suspension to have the same travel as with the typical 23" tall tire. You'd still have the other 1" higher ride height from chassis to ground, so Steve also moved all of the suspension pick-up points up an inch to get that back too. We will not be going that far...at least at this point.

While I could do this myself, it's being farmed out to someone who can make it pretty...since this car will see some more Optima event exposure in 2016. Apex Auto Works in Houston will do the fab. They do great race car construction, as well as paint and body...and vinyl is what they originally cut their teeth on. So we have many options on final finish. They have obtained a donor chassis (seen here in red) to cut out inner fenders that will then be blended onto mine about an inch or so up. Should make it look much more stock appearing.

Glass parts are built and enroute. Car goes under the knife in a week, with the goal to display it the end of January at the GRM tent at the Rolex 24 in Daytona.

PS: For non-200tw events, you can imagine the possibilities of slicks that we can run with so much room for activities.

Surprised the white car didnt move the shock pickup points as well. Or at least move their tubing most of the way to the shock top mounting holes, thats where the worst of the interference already is with fitting manly tires.

Project Big Wheel has begun.

https://www.miataturbo.net/attachmen...ine=1452576999

That moment when somebody takes a sawzall to your pride and joy...

https://www.miataturbo.net/attachmen...ine=1452576999

After the tubbing and flares are complete, we'll be converting to a 5x114.3 pattern using this method: MiataV8 Conversion: Five Lug Conversion

That gets a better bearing in the front, and a super easy five-bolt hub swap in the rear. I'm also investigating a couple of other front hubs to reduce the machining effort, but the FD RX7/Probe/MX6 hub with sleeve is a good known quantity.

That decision was made when we weighed Wootton'scustom 4x100 CCW wheel and discovered it was 26 lbs. Instead, we'll be using an off-the-shelf Enkei RPF1 18x10.5 ET15 5x114.3 that weighs 19 lbs for half the price, and available with no waiting.

Meanwhile back at the ranch...Andrew Keisler is working on a five-lug version of his front drop spindles for me.

This is just awesome. Can't wait to see the final product.

With the traction problem resolved, the next logical step is more power right? Love this build, I can't wait to see how it'll stack up at this years One Lap.

Nope...bigger brakes.

I suspect that the additional leverage of the 25" tall tire (vs 23) will overwhelm the 11.75 front rotor/Wilwood combo. Hope not, but it would not surprise me.

I have to do different hats anyway for the five-lug conversion...

:likecat:
https://www.miataturbo.net/attachmen...ine=1452623629

Richard does good work. I have had 3 cages built by him and all turned out well made. Based on the builds I have seen him and Ronnie do, the car is in good hands.

faeflora just got a random erection

God damn Honda kids finding out about Miatas and ruining them with their big rims and VTECs.

Ugh.

:giggle:

Serious question: Is this all about brakes? Why would you go up to a 17" wheel when there are 15X10s and such available at much lower weight?

Its about width and tire selection. Nobody makes anything bigger than a 225 in sticky street tires.

I see my guess was too close on the FB page?

It boggles my mind that a performance-oriented carmaker like Mazda (Zoom-Zoom) has not yet produced a dual-lobe cammed engine.

^^ This (clarified in bold).

One Lap uses a 200tw restriction as one of its few rules. You also have to finish the entire event on one set of tires...with 2/32nds remaining.

The fastest 200tw tires right now for a 3-lap time trial are the Rival-S and the RE-71R. The former comes in a 225/45-15, but not the latter. Further, the Rival-S is not good in deep water, whereas the RE-71R is amazing (see my GRM deep water testing sidebar in the track test article).

So ultimately, I wanted to find a way to run the RE-71R in sufficiently large enough size to put all the power down in 3rd, and with enough meat to not wear out during the week. 255/35-18 (or 255/40-17) would probably be enough, but with just a little more effort, I can also fit the new 285/30-18. Both are close to 25" tall and require massive fender work. I have the 255's on the way now and will compare them to the 285 once those are released. I'll run whichever is faster.

I mentioned it a bunch on mnet when everyone was whining about "y only 155hp! honda makes 200hp out of 2 litre!!", but it's worth repeating that Honda's the largest engine manufacturer in the world, had an F1 team and is getting back into developing F1 motors, and has a massive motorcycle business with the history to go with it, as well. Not to forget that Honda is one of the larger auto manufacturers and Mazda is comparatively quite small (and fragile when they keep betting the farm on the rotary).

They just have the R&D and history that Mazda doesn't. The MZR/L series is undeniably a good motor, especially the DISI; however, the K series motor is a contemporary equivalent, and it's just heads and shoulders above Mazda's powerplant efforts.

This project is awesome, and i'm sure the grip will be amazing. But damn, 18's look ugly as sin on a miata.

Personal preference.

I would still rock them for the grip :)

Also in for handling feedback, as historically heavier wheels means a worse ride/handling.

Toyota has also had dual-lobe cams for over a decade and a half. So there's two versions that Mazda could have copied.

Of course, the "right" answer is the infinitely variable BMW Valvetronic.

But we're getting a little off-topic now...