MS6 Suspension Data & DIY Bilstein Coilovers

[phate]

We did quite a bit of work this weekend. Johanna was here and helped a bunch, as well as a couple nator guys on Saturday who knocked out several things.



I needed to triple check these ginormous tires because I'm still having trouble believing they fit. But, they still fit and there's no loss of steering angle or bump travel. There will still be some very minor fender trimming at the forward part of the upper section, still, but the flares are ready to go on.





Rear subframe bushings went in like they were measured and machined properly It's back in the car with the diff, but I didn't get to the rear suspension this weekend.






Steering wheel and quick release are in. Feels pretty good, the depth of the wheel position is near stock. I was hoping for at least that so I didn't need a spacer or move to a concave steering wheel.






The real highlight of the weekend was the diff install. I checked that all the splines mated nicely and they're great:









Next was to remove the stock diff - this ended up requiring a complete teardown of the trans. All the gear stacks and shifting hardware has to get removed to gain access to the diff.







I pulled the ring gear from the stock diff and bolted it to the new LSD (also a good fit):



I checked preload before reassembling by putting the diff in and bolting the case halves back together. Spec is for breakaway torque to be a 7-21 in-lb, and I took an educated guess that it felt like that



Assembly is the reverse of install:









And from there we put it all back into the car!




I have the radiator support back in and the engine wiring completed. For next weekend, that leaves the rear suspension install as the biggest project and then just a few smaller things like flares and a string alignment to get things close enough to pull it into the trailer.

Still shooting to hit the first event of the year on the 24th and 25th of this month. It's going to be tight, but it looks like we'll be able to make it.

[KevinK2]

Great work! In your hands, must be the fastest SCCA Solo MS6, all classes !

Do you know what Torque Bias Ratio the Torsen has?

[phate]

Originally Posted by KevinK2 Great work! In your hands, must be the fastest SCCA Solo MS6, all classes !

That's easy when you're the only one!

Originally Posted by KevinK2 Do you know what Torque Bias Ratio the Torsen has?

I'm unsure of the TBR, but I talked to the designer about this on a couple occasions. We went with a setup he was familiar with, but said if the diffs needed more/less torque bias, we could easily get new internal gears machined at a different helix angle.

[KevinK2]

As I noted before, based on my experience with the Rx7, you can also "tune" the diff to reduce the tendency to lock-up in low traction conditions. I found out that on wet roads, going from a stop exiting my development, and then accelerating while turning left to blend in with 40 mph traffic on a single lane road, the tail would hang out big time.

The equations for the Torsen lsd action start with a friction coefficient, so I added 1/2 bottle of a friction modifier to the diff and the car was much better in this move.

https://www.redlineoil.com/limited-s...ction-modifier

.

[phate]

Originally Posted by KevinK2 As I noted before, based on my experience with the Rx7, you can also "tune" the diff to reduce the tendency to lock-up in low traction conditions. I found out that on wet roads, going from a stop exiting my development, and then accelerating while turning left to blend in with 40 mph traffic on a single lane road, the tail would hang out big time. The equations for the Torsen lsd action start with a friction coefficient, so I added 1/2 bottle of a friction modifier to the diff and the car was much better in this move. https://www.redlineoil.com/limited-s...ction-modifier .

Funny, I just ordered trans fluid with a bottle of ford's friction modifier, Motorcraft XL-3

Sent from my SM-G935V using Tapatalk

[KevinK2]

I have sung that tune before, but you likely had another reason for using the Xl-3.

The Redline 75W90 gear oil I used said no modifier was usually needed, but it still worked as I described.

.

[phate]

Originally Posted by KevinK2 I have sung that tune before, but you likely had another reason for using the Xl-3. The Redline 75W90 gear oil I used said no modifier was usually needed, but it still worked as I described. .

I'm not familiar - what do you think about the XL3?

[KevinK2]

Originally Posted by KevinK2 The Redline 75W90 gear oil I used said no modifier was usually needed, but it still worked as I described.

Originally Posted by phate Funny, I just ordered trans fluid with a bottle of ford's friction modifier, Motorcraft XL-3

Originally Posted by KevinK2 I have sung that tune before, but you likely had another reason for using the Xl-3. The Redline 75W90 gear oil I used said no modifier was usually needed, but it still worked as I described.

Originally Posted by phate I'm not familiar - what do you think about the XL3?

I reposted the sequence, mostly for my benefit. "I'm not familiar ..." It's likely obvious, but I just don't know what this is relative to ? The Redline 75W90 ?

And I don't know anything about the XL3, but now there are many brands of this type of additive. When I selected the Redline version, there were only a couple others. Why did you decide to use it?

I think most friction modifiers were originally used to reduce chatter in LSD's with regular gear oil for open diff's, when making a low speed turn. The modifier is mostly the same slippery additives, in concentrated form, that are used to make gear oils rated for LSD use, like the Redline Synthetic that I used. (not to be confused with "friction modifiers" used in special manual trans gear oils that add friction to the oil for better, no clunk syncro action when shifting).

.

Originally Posted by KevinK2 The Redline 75W90 gear oil I used said no modifier was usually needed, but it still worked as I described.

[phate]

Originally Posted by KevinK2 I reposted the sequence, mostly for my benefit. "I'm not familiar ..." It's likely obvious, but I just don't know what this is relative to ? The Redline 75W90 ? And I don't know anything about the XL3, but now there are many brands of this type of additive. When I selected the Redline version, there were only a couple others. Why did you decide to use it? I think most friction modifiers were originally used to reduce chatter in LSD's with regular gear oil for open diff's, when making a low speed turn. The modifier is mostly the same slippery additives, in concentrated form, that are used to make gear oils rated for LSD use, like the Redline Synthetic that I used. (not to be confused with "friction modifiers" used in special manual trans gear oils that add friction to the oil for better, no clunk syncro action when shifting). .

It sounded like you had talked about the XL3 before and had an opinion of it, that's all.

I want it on hand because it can modify how quickly the diff reacts on top of reducing overall bias slightly. I'll start with just the trans fluid, then add friction modifier if it seems harsh or there's too much biasing

[KevinK2]

Originally Posted by phate It sounded like you had talked about the XL3 before and had an opinion of it, that's all. I want it on hand because it can modify how quickly the diff reacts on top of reducing overall bias slightly. I'll start with just the trans fluid, then add friction modifier if it seems harsh or there's too much biasing

Got it. Thanx. Now it makes sense. I was referring to my previous suggestions to add the friction modifier to the front Torsen diff, FORGETTING that the front diff does NOT have GL5 gear oil, as it shares lubricant with the transmission, as you knew.

The trans has a GL-4 gear oil spec, that's easy on brass synco parts. And there are several special versions of the GL-4 oil (manual transmission lubes) that include friction modifiers to make the syncros grab more ... ie make the oil less slippery. By adding the XL-3, designed to make the oil more slippery, you may make shifts notchy, fwiw.

.

[Crarrs]

Congrats!

https://www.scca.com/articles/200925...cipients-named

[KevinK2]

A great, accomplishment for Johanna, after finishing 3rd in last year's Nationals: “We are proud that Johanna, Youmna and Lexie are joining the ranks of many great autocrossers who earned the Wendi Allen Scholarship. ... "


.

[MS3johanna]

Originally Posted by Crarrs Congrats! https://www.scca.com/articles/200925...cipients-named

Awe shucks, you noticed!!! Thank you!
Of course, I wouldn't be in this position, if not for Clint's support, encouragement, dedication, engineering, etc, etc...

Sent from my VS988 using Tapatalk

[KevinK2]

Originally Posted by phate Got the new springs tested like I did my last ones. I went with 1100 lb/in for the front and 900 for the rear. That nets me about 30% more stiffness in pitch and about 15% more stiffness in roll compared to last year's 850/700 combo.....

Is the pitch reduction based on lower sprung wt and stiffer springs? Do you have a quantitative feel for how your anti-pitch Whiteline kit will help, especially in squat as you exit?


.

[phate]

Originally Posted by KevinK2 Is the pitch reduction based on lower sprung wt and stiffer springs? Do you have a quantitative feel for how your anti-pitch Whiteline kit will help, especially in squat as you exit? .

I'm just basing that on the change in stiffness across each axle. The only dive and squat resistance I have in the car is springs, so that's the change in spring rate - 28-29%.

For the Whiteline LCA bushings - I'm not certain, but I think the rearward LCA pickup on the subframe is higher in the car than the forward LCA. I've only moved the rearward LCA's pickup point forward in the car, so it should increase the slope of the line between the LCA pickups, albeit a miniscule amount. That should increase anti-dive in braking, and anti-lift in accel. By how much, I don't have the measurements to say, but I suspect it's a very minor change.

Those bushings weren't really intended to change lift/dive characteristics, but more so to effect caster change (and give me tire clearance).

[phate]

So the last big update from 3/11, the car wasn't quite running and I was targeting the first autocross on the 24th and 25th. I did get it running the week after in time for the autocross, but the weather forecast kept getting worse and worse...so I decided to bail and postpone the corner balance and alignment in order to get a few more things accomplished before then.

We put the flares on the car. These are (I think) 90mm versions of the ones I had before. Not quite enough for the front end...




I started a low(ish) priority project of making a rear spoiler. I'm allowed a 10" spoiler, and plan to use every bit of that allowance. This was a first step, and I'll probably continue this next week. I was starting to get the trunk contour transferred to foam board as a first step in this pic:





I finally did make it to get corner balanced and aligned:





This is with a full tank of fuel and driver weight. I am looking into some things to reduce the necessity for a full fuel tank and reduce weight. I'd like to see it closer to 3300lb with driver.

And I just thought this was a great picture

[MS3johanna]

Originally Posted by phate I started a low(ish) priority project of making a rear spoiler. I'm allowed a 10" spoiler, and plan to use every bit of that allowance. This was a first step, and I'll probably continue this next week. I was starting to get the trunk contour transferred to foam board as a first step in this pic:

I can't even... At that spoiler mock-up...

Sent from my VS988 using Tapatalk

[turbskies]

Originally Posted by MS3johanna I can't even... At that spoiler mock-up... Sent from my VS988 using Tapatalk

Just keep it like that honestly jdm as fuk

Sent from my SM-N950U using Tapatalk

[KevinK2]

Originally Posted by phate .... I started a low(ish) priority project of making a rear spoiler. I'm allowed a 10" spoiler, and plan to use every bit of that allowance. This was a first step, and I'll probably continue this next week. I was starting to get the trunk contour transferred to foam board as a first step ......

Up to this point, about 99.9% of your very successful project was based on function. Are you sure a max rear spoiler will have a beneficial effect at autox speeds? Although it's not a spoiler, the aero rear wing of the Mitsu VR4 is activated (rises and tilts) at speeds exceeding 50 mph. Also, an air tunnel test of that car concluded the wing had no effect:
Active Aero In The Wind Tunnel - Mitsubishi 3000gt VR4 Rear Wing and Front Spoiler

Even the 3 spoke HED-3 CF bicycle wheel I structurally designed had no aero benefit until speeds approached 50 mph (30 mph road speed) at the 2/3 length of the spoke (with a nacca 3rd order profile).

Bottom line, where do you see getting a benefit from a 10" rear spoiler, and how much gain?

Edit: Just looked at some of the National SP top finishers (mustangs & camaros), and did not see tall spoilers .... that might actually add drag.


.

[KevinK2]

Originally Posted by phate .... And I just thought this was a great picture

Me too, great symmetry, and some mega tires! And I'm glad I gave you a little nudge to consider an alternate rear sway bar, like the 9/16" one I built for my 68 GT-6, SCCA D-Production prep'd by me, but kept a street car.

.

[phate]

Originally Posted by KevinK2 Up to this point, about 99.9% of your very successful project was based on function. Are you sure a max rear spoiler will have a beneficial effect at autox speeds? Although it's not a spoiler, the aero rear wing of the Mitsu VR4 is activated (rises and tilts) at speeds exceeding 50 mph. Also, an air tunnel test of that car concluded the wing had no effect: Active Aero In The Wind Tunnel - Mitsubishi 3000gt VR4 Rear Wing and Front Spoiler Even the 3 spoke HED-3 CF bicycle wheel I structurally designed had no aero benefit until speeds approached 50 mph (30 mph road speed) at the 2/3 length of the spoke (with a nacca 3rd order profile). Bottom line, where do you see getting a benefit from a 10" rear spoiler, and how much gain? Edit: Just looked at some of the National SP top finishers (mustangs & camaros), and did not see tall spoilers .... that might actually add drag. .

I'll pull up the info from RCVD this week.

Not sure what pics you were looking at, but the top 5 finishers in ESP all had 10" spoilers:

ESP
1) #57 - Yes spoiler - 2017 SCCA Solo National Championships » ESP » 3g7a7153.jpg: GotCone Autocross & Rallycross Photos
2) #197 - Yes spoiler - 2017 SCCA Solo National Championships » ESP » 3g7a7456.jpg: GotCone Autocross & Rallycross Photos
3) #18 - Yes spoiler - 2017 SCCA Solo National Championships » ESP » 3g7a7137.jpg: GotCone Autocross & Rallycross Photos
4) #87 - Yes spoiler - 2017 SCCA Solo National Championships » ESP » 3g7a7177.jpg: GotCone Autocross & Rallycross Photos
5) #191 - Yes spoiler - 2017 SCCA Solo National Championships » ESP » 3g7a7384.jpg: GotCone Autocross & Rallycross Photos


This is true of nearly every SP class.

[Fstrnyou]

I remember way back in my go-karting days, we would do something completely random that had zero effect on performance and would get a good laugh when everyone else copied it thinking that it must be the secret to going fast.

At autox speeds, a spoiler (even at 10") will be a negligible difference. Any down force and traction gained might be offset by an equally negligible amount of drag and additional weight.

Interesting read:
https://oppositelock.kinja.com/wings...ong-1665312667

[phate]

Originally Posted by KevinK2 Up to this point, about 99.9% of your very successful project was based on function. Are you sure a max rear spoiler will have a beneficial effect at autox speeds? Although it's not a spoiler, the aero rear wing of the Mitsu VR4 is activated (rises and tilts) at speeds exceeding 50 mph. Also, an air tunnel test of that car concluded the wing had no effect: Active Aero In The Wind Tunnel - Mitsubishi 3000gt VR4 Rear Wing and Front Spoiler Even the 3 spoke HED-3 CF bicycle wheel I structurally designed had no aero benefit until speeds approached 50 mph (30 mph road speed) at the 2/3 length of the spoke (with a nacca 3rd order profile). Bottom line, where do you see getting a benefit from a 10" rear spoiler, and how much gain? Edit: Just looked at some of the National SP top finishers (mustangs & camaros), and did not see tall spoilers .... that might actually add drag. .

Originally Posted by Fstrnyou I remember way back in my go-karting days, we would do something completely random that had zero effect on performance and would get a good laugh when everyone else copied it thinking that it must be the secret to going fast. At autox speeds, a spoiler (even at 10") will be a negligible difference. Any down force and traction gained might be offset by an equally negligible amount of drag and additional weight. Interesting read: https://oppositelock.kinja.com/wings...ong-1665312667

I remember being in my vehicle dynamics course and seeing the calculations for giant spoilers' effectiveness.


Just to throw some numbers out there:

Trunk lid area - 18x60" = 1080 in^2

Rear Window area - 30x60" = 1800 in^2 (@ ~30° from horizontal).

Even with an average reduction of 0.01psi across the two surfaces, that equates to a 25lb reduction in lift at the rear of the car. And, as your link shows, there's very little drag introduced with a spoiler. That seems like a worthwhile project to investigate.

The stock spoiler weighs approximately 10lbs, so I will likely save weight moving to a 3/16" lexan spoiler.

[KevinK2]

Originally Posted by phate I'll pull up the info from RCVD this week. Not sure what pics you were looking at, but the top 5 finishers in ESP all had 10" spoilers: ...... This is true of nearly every SP class.

THANKS for the correction Phate, I'll have to look at my history file and see what I was looking at. Should be interesting, but I did spend some time researching 2017.

Thanks again! (I hate being wrong )

.

[KevinK2]

Originally Posted by phate I remember being in my vehicle dynamics course and seeing the calculations for giant spoilers' effectiveness.... Even with an average reduction of 0.01psi across the two surfaces, that equates to a 25lb reduction in lift at the rear of the car. And, as your link shows, there's very little drag introduced with a spoiler. That seems like a worthwhile project to investigate.

25 lbs at what speed? I only studied Fluid Mechanics and Experimentation at WPI, no vehicle dynamics available back then in that Engineering school. But I recall the frontal drag force was proportional to the velocity squared. We did test a VW bus model in a small wind tunnel, and established terminal speed was only ~60 mph. .

But I'm now sure there is merit in your project, based on the examples.


.

[phate]

Originally Posted by KevinK2 25 lbs at what speed? I only studied Fluid Mechanics and Experimentation at WPI, no vehicle dynamics available back then in that Engineering school. But I recall the frontal drag force was proportional to the velocity squared. We did test a VW bus model in a small wind tunnel, and established terminal speed was only ~60 mph. . But I'm now sure there is merit in your project, based on the examples. .

I'm assuming it will only be applicable to near-max autocross speeds. That's ~65mph for my car in 2nd gear with the 335's. We did get pretty far into 3rd gear at nats on the east course, the majority being in a huge sweeper and a very, very fast slalom into the finish. I'd estimate some SP cars were nearing 80mph in those sections.

[GroceryGtr]

clint what performance aspect are you attempting to solve/improve with the spoiler? I generally only see spoilers on rwd vehicles for auto-x setups. I'd be amazed if you were having significant traction issues at 50+mph. I would think with awd, a lsd, and slicks you wouldnt see that much of a gain with the additional downforce generated.

The spoiler will indeed create a noticeable downforce increase(above 50-60mph), but my question would be are there any benefits in an awd setup that generally wouldnt have the same traction issues as a rwd.

[turbskies]

Why tf not have a spolier if anything it looks good lol

Sent from my SM-N950U using Tapatalk

[phate]

Originally Posted by GroceryGtr clint what performance aspect are you attempting to solve/improve with the spoiler? I generally only see spoilers on rwd vehicles for auto-x setups. I'd be amazed if you were having significant traction issues at 50+mph. I would think with awd, a lsd, and slicks you wouldnt see that much of a gain with the additional downforce generated. The spoiler will indeed create a noticeable downforce increase(above 50-60mph), but my question would be are there any benefits in an awd setup that generally wouldnt have the same traction issues as a rwd.

Actually, I'd like a little more high speed stability for quick transitions. I suspect we'll be seeing higher average speeds because of the improvements over the winter and any more rear stick I can get is welcome. I've gotten the car to a point where I can tailor overall under/oversteer behavior and overall transient behavior, but none of that differentiates between high and low speed.

Just the fact that everything happens in a shorter time period at higher speeds mean we have to react that much quicker to whatever is going on. I'd like to think this will let me set the car up for low speed desired touchiness, while still being easy to drive at the limit at higher speeds.




Check out the AWD cars in ASP - they all have rear spoilers like what I'm talking about.

[GroceryGtr]

well it certainly helps for high speed bus stops and 'Ss' in roadracing(even in spec Bs), so I gotta believe it would accomplish your goals even at lower speeds.

It allows me to really stiffen up the rear for low speed rotation and then plant it at high speeds for the same stability you're looking for in both my abarth setups and my higher hp track cars. My question was more to understand the auto-x environment for the spoilers, not necessarily implying(incorrectly) it wouldnt be effective.

[phate]

Originally Posted by GroceryGtr well it certainly helps for high speed bus stops and 'Ss' in roadracing(even in spec Bs), so I gotta believe it would accomplish your goals even at lower speeds. It allows me to really stiffen up the rear for low speed rotation and then plant it at high speeds for the same stability you're looking for in both my abarth setups and my higher hp track cars. My question was more to understand the auto-x environment for the spoilers, not necessarily implying(incorrectly) it wouldnt be effective.

What you're describing is pretty much exactly what I'm looking for. Make the low speed as tail happy as I want, then let the spoiler calm it down a bit at higher speed.

Sent from my SM-G960U using Tapatalk

[phate]

I've attached several pages from the aerodynamics section of the vehicle dynamics course I took a few years ago. I thought these two pages were especially important, but please grab all 10 pages if you are interested. If the resolution is too poor, let me know and I'll upload the high res versions of the pictures - these were all done in digital notes software, and the conversions from pdf to notes and back to pdf made them pretty grainy.

[Tomas]

Have you thought about one these Duraflex spoilers? Not going to be super effective but at least is sort of easy to instal.
I've been think about one meself but I still need to overcome some of my internal rice aprehensions.

2006 Mazda Mazda6 Wings Spoilers - page-1 : Duraflex Body Kits

[phate]

Originally Posted by Tomas Have you thought about one these Duraflex spoilers? Not going to be super effective but at least is sort of easy to instal. I've been think about one meself but I still need to overcome some of my internal rice aprehensions. 2006 Mazda Mazda6 Wings Spoilers - page-1 : Duraflex Body Kits

Too small!



I think there's pretty good data in the attached to show going as big as my rules allow will be the most beneficial.

The piece that I was missing from my last post was spoiler angle of attack. I found the book that several figures were taken from, and there was an example showing effects from altering angle of attack:



It looks like, if you extrapolate the points out for angle of attack, the lift will continue to decrease and and the coefficient of drag levels off a bit. So, max height (10") at an angle of or very near vertical will give the most dramatic change in rear lift.

[phate]

Adding this article, because it talks about a couple things I've been questioning with spoiler design.

https://grassrootsmotorsports.com/ar...-spoiler-tips/


Curved (following the trunk edge) or straight spoiler. This article indicates a curved spoiler will be beneficial in yaw (what I was planning on, but now I have at least some opinion on it).




The article touches on angle of attack, also. In particular, it talks about spoiler angle in relation to extending beyond bodywork - and that's exactly how the rules are worded for my class.

It is a non-production rear spoiler which is mounted to the rearmost portion of the rear hatch, deck, or trunk lid. The spoiler may extend no more than 10” (254 mm) from the original bodywork in any direction. Alternatively, in a hatchback, the spoiler may be mounted to the rear hatch lid at or near the top of the hatch; in such a configuration the spoiler may extend no more than 4” (101.6 mm) from the original bodywork in any direction. The spoiler shall not protrude beyond the perimeter of the original bodywork as viewed from above. The use of endplates is prohibited. Angle of attack is free. The spoiler may not function as a wing.

The article says to extend it to the absolute max of body work, maximizing area for downforce to be applied. I'm a little skeptical, since I'm not sure this is going to actually create positive pressure. If there was positive pressure back there, I'd agree. If there's net lift, it's going to negate some of the effects further forward of the spoiler.

[KevinK2]

Originally Posted by phate Adding this article, because it talks about a couple things I've been questioning with spoiler design.....

I have a lot of reading to do!

But if it's not too late, PLEASE do this mod after a couple of races so you will see the effect of just it. Putting the oem rear spoiler on should be easy. You have already made a bunch of changes that should make a big improvement in lap times.

BTW, are the course layouts "standardized" so you can compare lap times with previous events? I had always kept a list of times in my class for the year, so I could compare my deltas vs routine competition's times. Not many if any mods during each year, but I'd see improvements vs competition every time I spent a day at the 2 mile road course at Summit Point, W Va, mostly due to extreme braking for "tight" road course corners.


.

[phate]

Originally Posted by KevinK2 I have a lot of reading to do! But if it's not too late, PLEASE do this mod after a couple of races so you will see the effect of just it. Putting the oem rear spoiler on should be easy. You have already made a bunch of changes that should make a big improvement in lap times. BTW, are the course layouts "standardized" so you can compare lap times with previous events? I had always kept a list of times in my class for the year, so I could compare my deltas vs routine competition's times. Not many if any mods during each year, but I'd see improvements vs competition every time I spent a day at the 2 mile road course at Summit Point, W Va, mostly due to extreme braking for "tight" road course corners. .

For sure, I'll be doing several events with the stock spoiler (it's back on right now). I haven't gotten back to the new one at all, recently.

Layouts are not standard, so it can be tough to compare. I do have the accelerometer and a couple 'measuring sticks' to compare against (consistently fast people). Overall, at larger events, my PAX/RTP position compared to the entire field is a pretty good indicator if I'm doing things right. I need to be in the top handful at local events to be competitive at the national level.



No autocross last weekend - I had a few things to finish up and ran out of time. Took it out for a drive Saturday morning and it puked coolant all over the place and got to 230-240°, so I didn't want to risk anything until I had time to figure that all out. But, all is well and I'm thinking it was a huge bubble in the cooling system. I've refilled and done several pulls with it since, and no issues at all.


Edit: Autocross is scheduled for this weekend, but with a 100% chance of rain, currently.

[KevinK2]

Originally Posted by phate For sure, I'll be doing several events with the stock spoiler (it's back on right now). I haven't gotten back to the new one at all, recently. ....... Took it out for a drive Saturday morning and it puked coolant all over the place and got to 230-240°, so I didn't want to risk anything until I had time to figure that all out. But, all is well and I'm thinking it was a huge bubble in the cooling system. I've refilled and done several pulls with it since, and no issues at all ....

Good news about the spoiler !

Looking at the FSM for the V6 and 4 cyl M6's, your cooling system likely has a vented overflow (like my Rx7), vs the pressurized overflow tank on the V6 that maintains near cap pressure in the system. The manual describes an elaborate process for filling the system, including a slow rate to avoid trapping air. On the Rx7, I slowly fill until it tops out, then start the engine with cap off and add more coolant as level drops. Usually done before coolant gets warm and starts expanding. My fill is on the suction side of the pump, and this method with running the engine, would probably not work if fill is on the discharge side of the pump.


.

[KevinK2]

Speaking of coolant .... I think the MS6 has a vented exp tank, like the M6 I4 engine and also my HPDE tracked Rx7.

I quickly learned of overheating issues with my stock Rx7, at the track. This lead to testing of coolant pressure with my vented overflow tank, that applies to the MS6 too. I found that cap pressure was maintained under load, but as soon as I lifted, sys pressure dropped to zero as coolant temp dropped slightly at speed. Roughly, this lowered the BP from 265F to 225F , increasing the chance of excessive local boiling (nucleate) when first back on the gas, and related knock.

The pressurized exp tank found on GM & VW cars for ~decades, and in my M6S, includes an air space above the coolant level. IF designed right, coolant expansion at design temperature will provide full cap pressure in the system, with little change when lifting due to the air cushion, reducing the chance of excessive local boiling. The advantage of the vented tank is assuring full cap pressure will be maintained, most of the time.

.

[phate]

I had the car out yesterday for its first autocross of the season - it was cold (~35°) and very, very wet. I'm not drawing any conclusions or making any changes based on yesterday's behavior.

My Hoosier wets, in hindsight, should have been driven a little bit to get the release goo off of them. They were awful the first couple runs. The car spins all 4 in a straight line if you get into boost too quickly.

So, ultra low grip day, to say the least. The car ran well, and feels a lot stiffer than last year. The smaller diameter steering wheel feels good and seems to quicken the steering just a bit. The LSD seems to pull the front end into the corner when powering out, and it was extreme oversteer when powering out hard. Again, I'm not drawing any conclusions from this since the overall behavior will likely be different when the grip goes way up.

My driving could have been much better, I felt pretty rusty and was not smooth with my inputs. I'm headed to the dragon later this week, then it's a weekend off. The weekend of May 6th looks like it will be with Indy SCCA for their first points event.

5/6 - Indy Points #1
5/13 - Chicago SCCA (maybe)
5/19-5/20 - Indy test and tune
5/27 - Spring nationals in Lincoln, NE.