Dancing 818S

[Dave 53]

Just got my final engine tune on my 818S. The tuner got more, but dialed it back to 250hp at the wheels for reliability. I got 3,000 miles on the car before the tune (there's a long story as to why it took so long), so I'm use to how it feels. But now... holy ****! Under hard acceleration through 3rd gear, it wants to dance. She's pulling hard, but feels a bit twitchy and slippery and she's jumping around a bit like it never did before right up to 90mph (the fastest I went).

Is this normal? I'm thinking a LSD might settle it down? Or, could it be the alignment? Just read the post about the GTM dancing around while decelerating from 170 mph and many suggested an alignment. I've got 3,000 miles on the original alignment which has felt fine, but now I'm thinking things have settled in and its time for a realignment (and corner weights). I want an HPDE alignment, so alignment spec recommendations appreciated. Also, built with the original 19 year old, 110,000 mile donor car suspension bushings. Everything seemed fine with the pre-tune horse power, but could bushings be causing the hard acceleration dancing? Or is this just what an 1,800 pound car with 250 wheel hp feels like?

Update: Just called Roger Kraus Racing in Castro Valley, CA about an alignment. He can't find anyone to hire to do alignments and they are pretty much just selling tires.

[Jetfuel]

Tire pressure??
I have an LSD installed and at half throttle for the 300+ horses available it was fishtailing a good amount.
Playing with tire pressure made a big difference
For sure an LSD will make the blood rush out of your brain in a hurry

Jet

[fletch]

Tire pressure is a good suggestion. 22 psi or so seems to work well. I think I've heard the rule of thumb of ~1 psi/100 lbs. Also, a re-alignment would be wise. A few hours and some general-purpose tools can get it done reasonably. I encourage you to pay attention to caster. It makes a big difference in settling things down.

Here is a decent overview of the aspects of an alignment. https://www.tirerack.com/tires/tiret...e.jsp?techid=4
Forgive me if you know all this. Also, google "string alignment method" if you want to DIY it. Unfortunately most online DIY alignment guides don't mention caster. I have found a magnetic digital angle gauge does a decent job of measuring caster. Simply attach it to the part that is bolted to the upper part of the front knuckle and goes to the upper A-arm. The angle of that piece is a good approximation of caster.
https://www.amazon.com/Wixey-WR300-T...88151006&psc=1

[taco20]

Hey take it from someone that just finished the weekend at Summit Point with my car and saw 139 top speed going into turn one that the biggest help for the car dancing/moving around at higher speeds is CASTER. Get as much as you can. It settled my car right down. I ran my car at the drags on a bumpy track and I was all over the track. Put as much caster in the car as I could get and all the issues are gone. I have no problem changing lanes and passing cars at speed with no dancing or concern. It is a simple alignment fix that makes a huge difference to the way the car drives.

[Dave 53]

Hey take it from someone that just finished the weekend at Summit Point with my car and saw 139 top speed going into turn one that the biggest help for the car dancing/moving around at higher speeds is CASTER. Get as much as you can. It settled my car right down. I ran my car at the drags on a bumpy track and I was all over the track. Put as much caster in the car as I could get and all the issues are gone. I have no problem changing lanes and passing cars at speed with no dancing or concern. It is a simple alignment fix that makes a huge difference to the way the car drives.

Seems like on the 818, caster is less of an adjustment and more of an alteration to the suspension design. I see in the build manual there is a small blurb and a picture about increasing caster - "One more method to add Caster is to unbolt the two bolts that hold the control arm to the pivot stem and flip the stem 180 degrees and bolt it back to the arm. This will put the smaller flat surface against the control arm and the larger flat on the bolt head side."

Are you talking about an 818 specifically or just any car in general? If an 818, what methods did you use to increase castor?

[DSR-3]

Start by shortening the rearward link assembly as much as possible. I think you need cut at least 1 end.
Let's have lunch, and I will loan you this good reference and tools;
guide.jpg

[Dave 53]

Start by shortening the rearward link assembly as much as possible. I think you need cut at least 1 end.
Let's have lunch, and I will loan you this good reference and tools;
guide.jpg

PMed you. Anyone else interested in a Bay Area burger with a side of castor?

[Mechie3]

When you aligned the car did you make sure that the lateral links were parallel to each other? If one is higher than the other then you'll experience dynamic toe in/out when the rear compresses.

[lance corsi]

How much caster are you actually running?

[Dave 53]

Caster and tire pressure!

Brandon Kraus of Kraus Racing did the corner balance, alignment, and setup. After the first visit we were not able to get enough caster, so he sent me home to shorten the links and a few other things. Second visit got the caster up and finished the alignment. After this, the car was dramatically more stable.

my .02

Have a Baer bump steer kit.

Is Brandon Kraus Roger's son? I talked to Roger 2 weeks ago and he said they were pretty much just selling tires and weren't doing alignments anymore because they can't find a qualified alignment tech. He did mention if one wanted to throw a lot of money at it (he referenced the "rich Porsche owners") that his son could do it. How long ago did Brandon do your alignment and how much was it?

Can I buy you a coffee and check out your car?

[Dave 53]

It's all about who you know and (now) I know "bigger". Thanks to his relationship with Brandon Kraus, I've got an appointment. Let's hope he charges me built it myself prices and not rich Porsche owner prices.

This thread turned into meeting another 818 owner in the SF Bay Area. Any other 818's around? All I've got on my list is myself, "DSR-3" and "bigger".

Coffee and Cars in Danville (Cold Stone Creamery) Friday starting about 08:30.

[Dave 53]

Got a Brandon Kraus alignment. A proper alignment makes a huge difference! It's gotta be done at a race shop. No way a retail alignment shop could do what was needed.

Even though the car tracked straight and seemed fine before, the alignment and corner weights were a mess. Recall I started this thread because the car was dancing around under hard acceleration - not any more. Before when I cornered with some spirit, I could smell the tires (and my bumper is covered in tire dust) - not any more.

Ended up with:
Castor from 3.0 to 4.8 degrees
Front camber -1.1 -1.1
Front toe 0.06 0.05
Rear camber -1.5 -1.5
Rear toe 0.07 0.08

Weights with my 205 pounds and a full tank of gas
499 450
670 617

It took two hours and was pricy at $500, but it's dialed in and feels noticeably better! (think I got the Porsche pricing)

[Jetfuel]

If it is doing what you thought it could do…..priceless

Jet