SCCA ESP Thread

[Simmons-Racing]

That a motorcycle battery?

Yes it is. Lithium ion....it weighs 1.5lbs


Simmons

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[boardkat]

thought i'd give a quick recap of my west coast national event swing; what a long month it was! can't ever remember doing this many high profile events so early in the season before.

ESP didn't make a class at any of the events (san diego match tour, el toro pro, crows landing tour, crows landing pro), so i bolted on a set of 18x11/315 rival-s and had some "fun" running in CAM-C. a relative term to be sure, at least for the socal events, as i ran into a monster of a car belonging to SD-local brett madsen. '99 roush 'stang right at 3200lbs (he had to meltdown 500lbs of lead into the subframe to make weight, as it was a former CP car), 315/335s, an engine making not much less than mine (and revving to 9500!), real aero, heim jointed suspension bits, etc etc etc. i got my clock cleaned on the loose SD surface, but at least kept him honest at the el toro pro. 2nd both weekends, not even within 2 seconds on the first, but within 8/10ths at the pro.

my car was a basket case for the first half of the month, as i failed to add back the camber/toe-in that i took out to test fit the 18x12/335 combo earlier this spring. end result was an oversteering beast that tried it's best to live up to the C&C memes of late, lol. once i dialed everything back in, the car was much more compliant, and i could start focusing on throwing it around again.

the higher grip concrete surface of crows landing was the first time i could start using the extra 70 horses i added over the winter, and boy, did it expose some weaknesses in my setup. i was fuel starving on any sustained-g left handers that had me high in the revs, which meant pretty much all of them. quick note: if you ever get a chance to run at crows landing, do it! i was in 3rd gear 4 times, pushing almost 90mph through some sections. haven't felt like cones were coming at warp speed since i campaigned in a CM FF, and it was definitely a task staying ahead of things.

back on topic, i quickly discovered the starving wasn't a tank capacity issue (i ran it close to full on day 2), but rather the fuel pump failing to keep up with the demands of E85 over 8k RPMs (i already have 47lbs/hr injectors). i even ended up going agricultural at the tour, as i took the finishing left hand complex @ WOT near the limiter - luckily the only damage was to my pride! needless to say, i've already ordered a BAP to combat this, and am thinking long and hard about putting the 3.31 gearset in, to alleviate any gearing issues on high speed national courses. with only 430whp, it didn't make much sense, but with 500whp and no loss of torque, i'm thinking it won't be as much an issue sacrificing low-RPM digs any longer. blew the class away by over 10 seconds (yes, i felt bad), and put my car near the top of PAX overall. PAX sucks, btw

picked up a co-driver for the pro to fill the class, and managed to take both the class win and the top qualifier position into the super challenge, even as my tires are nearing cords. had kiesel and his green monster on the ropes by 3/4 of a second in the 2nd rd, until i found out i'd hit a cone. went for a hero run to try and make the time back up, hit another cone, and that was the end of it. co-driver ran out of talent and put my car into the field for the second week in a row, but this time some damage resulted - bumper clips broke off (again) on both sides. if nothing else, this has strengthened my resolve to make a permanent fix - by pulling the bumper out and bolting it down, cutting and flaring my fenders, and going 18x12/335 square. it's going to be a whirlwind trying to figure out the right setup in time for lincoln, but i don't want to wait for next season any longer.

no pics this time around, but i'll be sure to post up my progress as i tear back into the car in the coming weeks.

 

[SteveW]

Thanks for showing the way to fast times on street tires beyond FS!

 

[daltron]

Yes it is. Lithium ion....it weighs 1.5lbs


Simmons

Thanks, which model?

 

[Simmons-Racing]

Thanks, which model?

Click on the link for my build thread under my signature.
There is a picture of it.

Simmons

 

[SteveW]

You guys that have experience with OS Giken diffs please help me understand how they would help the Mustang put power down.

Right now I feel that the biggest thing holding my times back is the ability to put power down on corner exit. This wasn't as noticeable on the tiny lots at home until recently because of the low speeds and damp conditions. Damp surface + Mustang V8 is an obvious situation of hardly being able to use the gas. But as the weather has gotten better and I've gotten on fast courses I can see that this something to work on.

From what I've been able to gather from researching Torsen vs OS Giken in this phase is a Torsen goes open when the inside tire is unloaded where a clutch type diff like OS Giken is still able to transfer torque to the outside tire. When a Torsen rwd car unloads the inside rear and the diff goes open you get one wheel peel (if I understand that right).

I'm not feeling a one wheel peel. I'm feeling the rear break loose and go sideways instead of push the car forward. Maybe that's the same thing...So, I'm trying to work out in my head if that's a diff problem or something else. I feel like it is two other things: too stiff a rear sway bar and driver induced but want to better understand the way the different diffs handle power.

Thanks!

 

[Competition Orange]

Usually 1 wheel peels do NOT incite a fishtail/oversteer.

Its the function of the differential spinning both wheels/tires that allows for the car to fishtail/oversteer.

The comparison though, I can't help with.

 

[OppositeLock]

. i even ended up going agricultural at the tour, as i took the finishing left hand complex @ WOT near the limiter - luckily the only damage was to my pride!

I was watching that from station 2....that was quite the off! Between the white stp 2013 mustang after you and Mark Scroggs in the eb earlier in the day, all losing it in that corner, id say we lived up to our mustang meme reputation a bit

Anyways, nice to meet you! Would love to get a ride in that thing on course some time...looked badass through the fast stuff. :cheers:

 

[Gearz]

A Torsen diff works by using the friction in the differential gears to "lock up" the diff. It works on the principle that some gear mechanisms work well in one direction but not the other from a driving/driven context. Think of a worm gear, easy to turn the worm forward but difficult to drive it backwards by turning the spur gear.

When the inside tire gets totally unloaded, the friction bind in the gearset goes to zero and the diff unlocks completely. A Mustang doesn't unload the inside rear enough for that to really ever be a problem so the amount of diff lockup is going to be based on the amount of torque going into it pretty much all of the time.

The OS Giken diff is a conventional clutch type diff except that the clutch pack is compressed by ramps on the spider rod supports. So, the more torque going into the diff, the more it locks up. The ramps are set so that on forward acceleration they work to lock up the clutches and therefore lock the diff.

However, the difference between the diffs is the way they work in reverse acceleration, or engine braking. The Torsen will still want to lock up under engine braking since the same mechanism that locks it up under fwd acceleration (gear bind) also works in deceleration. The OS Giken has ramps on the forward side but flats on the reverse/decel side so it works like an open diff on deceleration.

The difference in driving dynamics will be noticeable on corner entry, the OS Giken diff can turn in better since the front tires don't have to fight a diff that is trying to keep the car going straight by keeping the rear tires at the same speed.

My opinion is the difference between the two is small and probably not terribly noticeable on these heavy cars, but there are some who swear by the merits of the OS Giken style diff. It is "tuneable" by changing the clutch pack static preload, and the ramp angles for fwd/rev torque.

For the problem of power-on oversteer, I don't think either one will make much difference. Probably soften the rear sway bar, add more front bar, soften the rebound on the rear shocks and fiddle with alignment (more toe-in) would help more. Also, roll in the throttle a little slower (easy to suggest, difficult to do).

Now the magic E-diff that's coming in the new Camaro 1LE has a computer control the amount of lockup in the diff all the time and if they get it right (for autox - that's a big if) it could make a BIG difference in how well that car digs out of a turn.

-B Meyer

 

[dontlifttoshift]

Good post but I have a question.

Probably soften the rear sway bar, add more front bar, soften the rebound on the rear shocks and fiddle with alignment (more toe-in) would help more. Also, roll in the throttle a little slower (easy to suggest, difficult to do).

How would less rebound help corner exit oversteer? Less rear bar and more toe in all make sense but I can't see less rebound helping the situation.

 

[SteveW]

Good post but I have a question.



How would less rebound help corner exit oversteer? Less rear bar and more toe in all make sense but I can't see less rebound helping the situation.

Great reply Gearz, thank you! I'm confused too by the rebound...Did you mean rear compression instead?

I have more comments but will further hijack this thread later when I'm on a real keyboard. )

 

[Gearz]

Really stiff rebound (like excessively stiff) will "hold" the inside wheel up as the chassis rotates, lifting the inside rear wheel and throwing more weight on the outside rear. I don't mean to suggest it's holding the wheel up off the ground, but it's reducing the dynamic load transfer on the rears. Reducing the rebound will allow the inside wheel to "fall" faster with chassis roll.

Of course now that I'm thinking more about it, both rears should be loading up on corner exit and the shocks should be seeing compression, not rebound... so... never mind. I am wrong.

-B Meyer

 

[dontlifttoshift]

Thanks!

 

[Conedodger]

You guys that have experience with OS Giken diffs please help me understand how they would help the Mustang put power down.

Right now I feel that the biggest thing holding my times back is the ability to put power down on corner exit. This wasn't as noticeable on the tiny lots at home until recently because of the low speeds and damp conditions. Damp surface + Mustang V8 is an obvious situation of hardly being able to use the gas. But as the weather has gotten better and I've gotten on fast courses I can see that this something to work on.

From what I've been able to gather from researching Torsen vs OS Giken in this phase is a Torsen goes open when the inside tire is unloaded where a clutch type diff like OS Giken is still able to transfer torque to the outside tire. When a Torsen rwd car unloads the inside rear and the diff goes open you get one wheel peel (if I understand that right).

I'm not feeling a one wheel peel. I'm feeling the rear break loose and go sideways instead of push the car forward. Maybe that's the same thing...So, I'm trying to work out in my head if that's a diff problem or something else. I feel like it is two other things: too stiff a rear sway bar and driver induced but want to better understand the way the different diffs handle power.

Thanks!

I just put the OS Giken in my car so I have a little insight for you.
I totally understand what you are saying as to corner exit dynamics of the car. As you apply power on corner exit with the Torsen the car gives you the feeling that it is under control. It feels like I got this, I got this, I got this and then suddenly you don't. It just breaks away with no warning and goes into yaw spinning both tires.
When you install the OS the car looses that sudden break away and becomes more linear and predictable.

Another improvement over the Torsen is the middle to late middle corner push you get when you role on the throttle. I have noticed a big decrease in this with the diff change.

Launching the car at the Pro was much easier than last year as well. I don't know why this is but it seems to go much straighter on launch with zero wheel hop.

There is one other big change I have noticed. Every Torsen car tucks the nose of the car to the left on decel. Go drive your car on a flat surface in second gear to the rev limiter. Quickly lift off the throttle and do not touch the brakes. When you do you will notice the nose of the car tucking left. With the OS Giken the nose tuck goes away.

I strongly suggest you make the upgrade. BTW I have a Torsen for sale :-)

 

[jhols]

I just put the OS Giken in my car so I have a little insight for you.
I totally understand what you are saying as to corner exit dynamics of the car. As you apply power on corner exit with the Torsen the car gives you the feeling that it is under control. It feels like I got this, I got this, I got this and then suddenly you don't. It just breaks away with no warning and goes into yaw spinning both tires.
When you install the OS the car looses that sudden break away and becomes more linear and predictable.

Another improvement over the Torsen is the middle to late middle corner push you get when you role on the throttle. I have noticed a big decrease in this with the diff change.

Launching the car at the Pro was much easier than last year as well. I don't know why this is but it seems to go much straighter on launch with zero wheel hop.

There is one other big change I have noticed. Every Torsen car tucks the nose of the car to the left on decel. Go drive your car on a flat surface in second gear to the rev limiter. Quickly lift off the throttle and do not touch the brakes. When you do you will notice the nose of the car tucking left. With the OS Giken the nose tuck goes away.

I strongly suggest you make the upgrade. BTW I have a Torsen for sale :-)

Where did you buy your OS Giken diff?

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