balefire

FYI, I've successfully had my local Firestone mount 275/35/18 on 18x8 for several years. It is a little sloppy but is the absolute maximum tire avail for 8".
My buddy has used this method to win a variety of NTs and Pro Solos with my underdog cars (rx8, 996, and most recently 997 GT3) over the years

edfishjr

Good info, but I can't go to 18" and there's nothing wider in 17".

The optional 8"-wide rear wheel on these cars was 16" diameter, so the legal diameter range is 15" to 17"

But, if I decide to go to Nats with my Corvette in BS once again and get beat by the M2's I could do 275/315-18 Rivals on the 8.5 and 9.5 wheels. It's a possibility depending on what happens in the 944 at Bristol in a few weeks. It's not clear yet that this new wheel/tire combo is actually faster than the narrower tires on 15" wheels.

edfishjr

Got the head back from Memphis Motorwerks. Near mirror finish where it was surfaced, except for
dark spots that are areas of corrosion pitting. I plan to assemble with Permatex 51813 (Anaerobic gap filler) in these areas.

edfishjr

Got the engine reassembled and running fine. Had a test & tune on Sunday where I compared 245-17 on 7" (fronts) & 255-17 on 8" (rears) RE71Rs vs. 245-15 on 7" and 245-15 on 8" Rival-S.

Rivals faster by 1s on a 40s course even though had to shift up to 3rd and back down once. The 245 on the front gave awesome grip.

17" wheels/tires are almost exactly 2" diameter larger (gives me 56mph in 2nd but hurts acceleration and raises CG by 1") and 9lbs per corner heavier.

Lightness and lower CG win. Back into the Tiny Rivals club.

Edit: I also got runs in an SSR C7GS on Hoosiers (awesome), a turbo-Miata in SSM (don't like turbo lag), a CS S2000 (rolls too much without a front bar but they are great anyway) and a full-race old-school Camaro with who knows how much horsepower and a pneumatic paddle-shifter for the auto-trans and I couldn't hardly reach the pedals or the steering wheel with the fixed seat set for the very large driver and the harness wouldn't adjust enough to hold me in...(Yup. I spun it.)

Edit 2: Two of my ES competitors who drive a '99 Miata Sport each took a run in the Porsche. "You should never be able to beat me in my Miata with this car." was one conclusion. "That you have, in fact, beaten me tells me you're driving the crap out of this thing."

edfishjr

Goal achieved: Trophied in 3rd place in ES at the Bristol Match Tour last week.

burglar

Awesome! Great seeing you, unfortunately I didn't get to see you run, other than hearing you come through the finish as I was pulling up to the start line.

edfishjr

Man, you were killing it in GS. 1st place in the Match Tour and a trophy in the Champ Tour. Congrats.

My lack of downshifting skill & experience killed my chances in the Champ Tour. I think I've got it down now, so hopefully can do better at Peru.

edfishjr

Peru was tough. I think we (co-driver and I) were losing a lot in the longish transition section, plus we had to do a lot of shifting while the Miatas did not.

Day 2 there was a 5-cone slalom and then a set of offsets after coming out of a slow 180 turn-around. The winning Miata hit rev limit right at the 4th cone in the slalom, which is 58mph. We were only at 50mph at that point, just shifting into 3rd. I suspect that section alone was the difference between my co-driver (2018 CS Pro-Solo Finale winner) in 5th and 2nd. I was way down in 8th. I went to school on the data from my co-driver and think I learned something useful.

On to Nationals. The car really pulls high lateral-G's now, so hoping for lots of big sweepers. It also sounds good with a lightweight cat-back system using a Burns Stainless. Lost 17lbs. Goal is to finish in the top 50%.

edit: in a big push to get ABS working. Modulator was totally corroded. New (used) one going in now, but I had to cut one of the brake lines to get the old one out. Learning all about DIN bubble flares.

edit: ABS is fixed!

edfishjr

Time to bring this thread to a close.

I took the car to Nats and it drove great. Power was good, even better with Miller's Nano racing oil in it. Handling was best it's ever been, thanks to some tweaks suggested by my co-driver. Pulled peaks of 1.25g's all over the place. OH, and the car sounds great with the Burns Stainless 2-stage muffler. A 3" cat-back system saved 17lbs.

One of the front bump stops was found to be ripped out on the morning of Day 2 as I was stiffening the front sway bar, but trapped within the spring coils. This seems to have hurt max lateral G on that side just a little. My co-driver was within striking distance of the trophies after Day 1 on the corn side. I sucked.

Day 2 on the plane side I think we both drove quite well (except for my co-driver coning his fast run) but all the shifting killed our chances. 4 upshifts to 3rd and 4 downshifts. I didn't miss a shift in 3 runs, but I think it was just too much on a speed-maintenance course.

I'll be removing the extra bump stops and doing a few other things to prepare it for sale.

Big congrats to PedalFaster and Burglar on their trophies!

burglar

This was an EPIC odyssey to follow, thanks so much for sharing the journey with us.

So, uh, what's next?

PedalFaster

I vote Porsche 968 for C Street!

edfishjr

I'm set to co-drive a friend's BSP MazdaSpeed Miata next year. The owner just done blowed up the motor, however, so I'm taking the downtime to figure out what his shock valving out to be based on the Dennis Grant calculator. His Penskes apparently leaked enough fluid that the dyno showed they weren't doing much of anything.

BTW, I have curves for three different sets of Penskes that were speced for 3 different Street-class Corvettes by a well-known supplier. The shock valving is different for each (one GS and two C6Z06's) but there is one common denominator: the shock valving is insane in rebound, as in 200% or more critically damped. (One of them may have enough adjustment that set soft they will be okay.) I had co-driven the GS before and kept losing the rear when accelerating during an increasing radius sweeper. On concrete. Now I know why.

I did the calcs for my B-Street Corvette and have just enough adjustment to reset the Ohlins to get close for 90% critical damping in both compression and rebound with the soft stock springs. Driving it around it seems very different, but in a good way. I have an event to test at this weekend.

edfishjr

One last thing:



As I was readjusting the front sway bar softer for street duty I found this. These two pieces form a triangulated mount that comes with the Tarett 944 adjustable sway bar. I remember hearing a loud metallic ping during one of my runs on day 1 at Nats. Now I know what it was.

So, the FSB was unable to develop much if any force in either direction after being completely disconnected from the body on one side.

edfishjr

I'm getting kind of wound up about maybe doing a 986 Boxster S in CS next year. (I have a co-drive in a BSP Miata (that never happened this year) so this would be a backup.)
I faced-off the ND2 and the 03/04 Boxster S in the latest version of my autocross spreadsheet. Results below. I was kinda shocked. Assumes 8"/10" wheels for the Boxster as run by the winner of the last trophy in CS at 2018 Nats. Probably 255/35-18 on the front and 285/30-18 rear. Front could also be a 255/40-17 for maybe less weight.
Of course, intangibles like the lack of front camber are not included. But, even if that knocks 1 or 2 points off the Boxster S, it's still in the competitive range.
The wide range of tire sizes now available, especially the RT660, makes this appealing, along with the ability to stiffen it with bump stops, as I did the 944 and as is being done by all the fast ND2s, as well. But the stock Porsche bump stops are even longer than the Mazda.
Opinions?

edfishjr

About the ND2 vs. Boxster S: I did a thrust chart for the two which makes the ND2 look a lot better than just using peak torque as I usually do, especially with the new 215/35-17 Falken tire which is only 23.8" in diameter. I'm assuming the ND2s will switch to that tire from the 225 they've been running which is 25.0" in diameter. As a result, I factored the Boxster S thrust rating down to where it was a little below the ND2. This is a course-dependency where if the Mazda doesn't have to use 3rd it's in the gravy. If it does, the advantage goes to the Porsche. The resulting ratings have the two cars dead even and are shown below.






If the ND2 has the 225/45-17 on it then the Boxster S looks better. I'd probably call it a wash.