Change to clutch pack LSD or not

[lutfy]

Originally Posted by Icecreamtruk

Working on it, should have something up with ECU + GPS logging and video to correlate, I should have it before the 6th july which is my next day out at the track. What should I be looking at appart from the classic throttle, brake and steering input? Individual wheel speeds? Is it possible to get that over OBDII?

Mike had shared the video link with me earlier and I was amazed at the wheel speed delta.

Anyways, there are multiple variables which can be addressed logically (with data - cause effect) but on topic of diff; I got custom OSG because I couldn’t put the power down in slow to mid speed corners especially with fresh Hoosiers (inside wheel spin).

The behavior of the car changed significantly not just at exits but also entry, braking and mid corner (throttle sensitivity). It was worth it but required adjustments to make it work as a whole (shock settings mostly).

Will it solve the described problem? Not sure. Does the diff help (changing characteristic of the car) for the better? It was worth it for me. Are there multiple variables (shocks, tire pressure etc) that needs to be correlated with the new clutch type diff? Yes.

Not a direct/linear answer but hope you get my gist.

Best of luck.

Lutfy



Sent from my iPhone using Tapatalk

[Icecreamtruk]

Thank you all for all of the answers, I figured it wouldnt be as dry cut as just slap on X part and be done with it, it never is really.

@CSG Mike, its similar to when you hit the kerbs in your video actually, it just does it for a longer period. Check in your video when you hit the kerb at 2:19 and the engines surges a bit (and wheel speed is aroudn 70 on one side, 80 on the other), but imagine it lasts longer for me, I dont know if the wheel speeds on my case are much farther appart than that or not, but possibly at least as much.

@lutfy Thanks for your input, its really nice since our cars arent that far off and I do plan to switch to hoosiers (As not Rs tho, time attack scenario calls for maximum grip for only 1 lap) and this is a problem that I think will get worse if I add more grip to the equation. Btw, how's your engine doing? have youdone any oil mods to keep it alive at those G forces?

To everyone else that talked about adjusting shocks, I can play with rebound only, so I assume softening the rear only would help there? I tried softer all around and the car felt worse and was slower, about half a second per lap consistently.

Originally Posted by soundman98

Why are you running such stiff springs? Are you trading off for not running a sway bar or something?

Springs are for aero mostly. The car has significant downforce and some of the tracks I run at have very high speed turns (think 110-120pmh turns uphill). I like those tracks the most so I try to set my car so it performs well there, which it does, but it is a shit show on bumpy tracks, as I noticed last weekend. I was previously running 6k/8k springs and I was on the bumpstops for most high to mid speed turns.


I will try to get as much data as possible, certainly wheel speed data at the very least on my next track day, I'll also see if I can setup a nice overlay to see it in action. That should be the 6th July so I'll update the post by then. If you have more ideas, keep them coming, I love a good conversation and I will keep it alive as long as there's interest.

Thanks!

[CSG Mike]

Originally Posted by Icecreamtruk

@CSG_Mike, its similar to when you hit the kerbs in your video actually, it just does it for a longer period. Check in your video when you hit the kerb at 2:19 and the engines surges a bit (and wheel speed is aroudn 70 on one side, 80 on the other), but imagine it lasts longer for me, I dont know if the wheel speeds on my case are much farther appart than that or not, but possibly at least as much.

Data will help determine, but you're definitely having a similar issue if the symptoms are similar.

Car in the video is on 7k/7k.

The LSD will 100% make power delivery more consistent and predictable.

[strat61caster]

Originally Posted by Icecreamtruk

To everyone else that talked about adjusting shocks, I can play with rebound only, so I assume softening the rear only would help there? I tried softer all around and the car felt worse and was slower, about half a second per lap consistently.

With a single adjusted (mostly rebound) shock I'd guess stiffening the rear would help 'lock it down' and add some confidence, you might be skipping the tire off the pavement but it could still be more predictable than what you've got now allowing you to hammer through the rough patches, counter-intuitive but it's one of the few things I've figured out on my setup that's carried across to different cars with the same adjustment. It'd be a bandaid to either the diff or a spring/sway change but it sounds like you're headed out for at least one more day with the current setup so try a knob or two after you've replicated the problem.

[lutfy]

Originally Posted by Icecreamtruk

Thank you all for all of the answers, I figured it wouldnt be as dry cut as just slap on X part and be done with it, it never is really.


@lutfy Thanks for your input, its really nice since our cars arent that far off and I do plan to switch to hoosiers (As not Rs tho, time attack scenario calls for maximum grip for only 1 lap) and this is a problem that I think will get worse if I add more grip to the equation. Btw, how's your engine doing? have youdone any oil mods to keep it alive at those G forces?

To everyone else that talked about adjusting shocks, I can play with rebound only, so I assume softening the rear only would help there? I tried softer all around and the car felt worse and was slower, about half a second per lap consistently.


Thanks!

The car has been fine mate. No issues with oil issues (maybe I am not aware of potential issues So far running like a champ. Fingers crossed.

Regarding rebound, doubt that would do much other than fine tune. If you go down too much, the rear ends up dancing (un easy) at curbs and bumps hence unable to put power down effectively.

Try disconnecting the rear bar. That should help a bit with reduced spin coming out of turns but may give you a disconnected feel overall (which is what I found and didnt like it).

Keep us posted.

Cheers,

Lutfy

[Icecreamtruk]

Thanks for the extra info.

@strat61caster I tried stiffening and softening rebound and softer felt worse, but I only went 2 clicks in each direction. Counter intuitive as you said but stiffer produced better times and the rear was still lifting, maybe I needed a bigger change, like a full soft vs full stiff for comparisons' sake.

@CSG Mike I had planned doing the diff once the car had more power, in my head there was no need at NA power levels but it seems like a stiff enough suspension and bad enough track conditions might do it. Consistant power delivery is very much what I want. "Guessing" every time I hit the gas if the rear is going to slide, jump, hook or a mix of all those is getting old really quick. On a smooth and high speed track it was predictable and would slide always, that was probably a function of aero helping load the tires more.

@lutfy Thats great to hear man, gives me hope for next year trying the hoosiers, if the delta in time from entry level Rs and A7s is as big as I've read around, I will be in contention for the FTD overall, while being 3 classes down from the unlimited guys, it would be hilarious to see the look on their faces. Also, I tried disconnected the sway bars before (front, then rear), I did not like the feeling of the car at all and it did not produce better lap times, but it was a good experiment as it showed me what those actually do (aside from changing the balanced if you change their relative stiffness). A stiffer front sway might help, but that will introduce understeer on corner entry, and I hate understeer with a fiery passion.

[CSG Mike]

Just a FYI, you're not tagging me. I have no idea who @CSG_ is .

[Icecreamtruk]

Originally Posted by CSG Mike

Just a FYI, you're not tagging me. I have no idea who @CSG_ is .

I boy, I kept adding a _ thinking there was one. Going to correct the posts, so you'll have a bit of a spam on tags, sry

[rice_classic]

Agreed with Lufty. It's been my experience that on dry pavement and due to the way torsens work, their effectiveness as an LSD improves with the more traction you throw at them. Single adjustable shocks, as far as I'm aware, are only rebound so you can only adjust the rate at which the spring returns the spring to the ground (and the rate of body roll).

If too soft it won't properly dampen the shock and become bouncy but too stiff and during transition or rapid direction change, you can find you pick up the inside rear because the shock doesn't allow the spring to decompress fast enough. Therefore, once your in the window of rebound that neither of these two things occur - you need to address roll stiffness across the axle (sway bar) or droop. To Lutfy's point - I've raced with a sway bar removed on 1 end before (different car) and experienced a front and rear that simply didn't communicate with each other. In a few weeks I will be testing rear bar settings: Eibach rear bar stiff and soft, OEM bar and No bar. You may want to consider softening the rear bar or going to a softer rear bar if yours isn't adjustable.

With all that being said - once rebound, roll stiffness and droop are addressed then at THAT point would I be looking to address things with a shiny new clutch diff. In my previous race car I switched from torsen to clutch and guess what - I didn't "just go faster", in fact, I went slower. The diff bound up the power in some circumstances so I had to learn to drive differently to get back to my original pace. The clutch diff outperformed the torsen when I applied too much throttle out of a hairpin or was in a low tractive environment like rain.

[Icecreamtruk]

Updates for those interested:

I went to the track last weekend and had 2 drivers (me and the local Alien) on the car the whole day, chasing time with what little we could adjust on the setup. Sadly, I couldnt get the datalogger I had borrow for testing to work, its supposed to pair with the phone and send the data from the OBDII port to its phone app but it kept unpairing non stop every 15 seconds, will have to try again.

Anyways, the second driver on the car is a much better driver than myself and could tell things about my setup that I didnt feel. First, the setup had no rear grip on exit, according to him, this was not a diff problem, but rather a suspension problem. Secondly, the ABS intervenes too much during trail braking, so much so that he had to reduce pressure during trail to the bare minimum for the car to turn properly. His thoughs overall on the car are that it is easy to drive just at or before the limit of grip and fairly fast, but that past that limit it is too twitchy and unpredictable, he found the window of grip at the limit was just too narrow. He also hates how little power the engine has at lower RPM. (like 5-5.5 low, not like 4k low). He did not personally found the diff to be obstrusive to lap times, not more than the car's twitchyness at least. He recommended bigger and ajustables sway bars to have more tools to fine tune the car with.

Here's a video of a side by side comparison of him and me driving (him on top, me on the bottom) after we dialed the setup a bit more:

[ame="https://www.youtube.com/watch?v=hj-E4Zvmnpg"]https://www.youtube.com/watch?v=hj-E4Zvmnpg[/ame]

[oinojo]

i would check to see if you are sitting on the bumpstops

[CSG Mike]

Is he pedal danced? What pads/tires are you on?

[soundman98]

Originally Posted by Icecreamtruk

First, the setup had no rear grip on exit, according to him, this was not a diff problem, but rather a suspension problem. Secondly, the ABS intervenes too much during trail braking, so much so that he had to reduce pressure during trail to the bare minimum for the car to turn properly.

His thoughs overall on the car are that it is easy to drive just at or before the limit of grip and fairly fast, but that past that limit it is too twitchy and unpredictable, he found the window of grip at the limit was just too narrow. He also hates how little power the engine has at lower RPM. (like 5-5.5 low, not like 4k low). He did not personally found the diff to be obstrusive to lap times, not more than the car's twitchyness at least. He recommended bigger and ajustables sway bars to have more tools to fine tune the car with

*note: i have no clue what i'm talking about, here to learn just as much as everyone else.*

so the the car is twitchy. my pickup truck is twitchy when not loaded down too. both are what i would consider problems with running too heavy of springs. i don't see how getting bigger sway bars could improve this situation in any way because you're already getting odd wheel speeds and numb handling, both something i would attribute to rigidly connecting either sides of the axles... what it seems is missing is low speed reaction times.

which brings to mind, how lowered are you and how much sag is in the suspension when the car is at rest?

i'm also curious what drive mode the other driver was using that ABS was active.

my first thought was to run 5k/12k double-rate stacked springs like they do in the offroad world



running a small softer spring should make the contact patch a little more predictable and able to react faster, which should make track imperfections less obvious, but would increase spring sag under aero load.

at least that's the reasoning bouncing around in my head.

[Racecomp Engineering]

Springs that stiff, real aero, sticky tires, and a bumpy track will really show the weakness of suboptimal damping (which is one thing I see in your video). I don't think a diff change alone will solve your issue.

- Andrew