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Posted by: Cracker Nov 24 2015, 08:42 PM

The first video shows a couple laps running behind the 914/6/3.0 (SixAddict) of a good friend. The longer part shows a little more solo action...man these cars are fun!


Second Day after changes (1 lap only) - amazing balance in the car!
https://youtu.be/NhHMaa0_R5o

https://www.youtube.com/watch?v=NhHMaa0_R5o


https://youtu.be/LfFdP8GnXiQ (12+ minutes)

https://www.youtube.com/watch?v=LfFdP8GnXiQ


https://youtu.be/9Te6GScwxek (3 minutes)

https://www.youtube.com/watch?v=9Te6GScwxek


The GT3 Cup is faster everywhere but still allot of fun to (try) keep up with. I might be a smidgen faster down the straights - barely at best.

Tony

Posted by: ThePaintedMan Nov 24 2015, 08:49 PM

A lot of guys will run 1/16-1/8th toe in on the rear to keep the car from feeling so flighty when the hammer is down. Racer Chris will chime in and have the right direction for you though I'm sure.

Posted by: wndsrfr Nov 24 2015, 09:01 PM

I'm not an expert but am thinking it's not only front but rear to pay attention to....
Do you have good hard trailing arm bushings? If they're the stock rubber ones, the tail may be wagging the dog.
Kermee is set up with a smidge of toe-in in the rear as well as front--like 1/16 each side.
Twitchy at high speed is helped with the air dam/splitter, and good rear spoiler but I think you've got that covered on the front anyway.

Posted by: Cracker Nov 24 2015, 09:06 PM

John - I did fail to mention that the front and rear bushings are all new - poly. All very tight...thanks. I have thought about possibly bringing the toe in some in the rear too but the front is on the verge of scary - even at just 80-90! What Camber do you run?

It could be that I'm just rusty and being a wussy...but I don't believe so in this case.

Also. I'll be running Hoosier R7's, 650 lb rear springs and 23mm T bars up front.

T

Posted by: r_towle Nov 24 2015, 10:13 PM

My opinion only.

Your tub has some fixed limits.
You want as much negative camber as you can get up front.
So, push both sides in and find th one that goes the least amount, pull the other one out to match.
If you want more there are camber boxes that provide more adjustment, and they bolt in.
Toe in or almost zero up front
Toe out for slow speed autox for faster turn in.

Rear,
1/8 in toe in with that motor for sure.
When you drop the power, the rears toe out under torque.
Rear camber is in my opinion very track specific....if there is a lot of elevation change, it matters.

Search in the paddock forum, this has been discussed in quite a bit of depth over the years.

Rich

Posted by: Dave_Darling Nov 24 2015, 11:13 PM

How confident are you in your suspension pick-up points? In the suspension members themselves? Could anything be flexing overly?

--DD

Posted by: stownsen914 Nov 25 2015, 05:52 AM

I didn't see what tires you are running. Camber settings are very different for different tires (e.g. radials - slicks or DOT style - like more camber than bias ply tires). With that said, your settings seem in the ballpark, though you might want more camber for R compound radials.

What struck me is your toe settings. For a track car, I like toe out in front - about 1/16" total toe out. In the rear, for a 914 you need 1/4" total toe in as mentioned in the earlier post.

As for the dartiness you mention. you have 0 toe in the back. The rear is probably toeing out while you are driving, due to flex (and also the 914 rear suspension naturally toes out under compression). Rear toe-out will definitely make the car feel darty. You can also check for any looseness in your suspension, and make sure your rear suspension mounting point in particular are solid, since that is a weak area in 914s.

Scott

Posted by: Cracker Nov 25 2015, 06:37 AM

Scott, Rich & Dave - Thanks to you all. I did "search" the paddock for info but didn't find anything "right on" with what I was experiencing.

The entire rear suspension has been reinforced (Chris Foley's) along with Patrick M. arms. All the bushings are poly (noisy!) and new. Very tight.

I added the "tire" and "springs" in my second post - Hoosier R7 but I'm sorting on the street right now with 5-year old Victoracers. It sounds like the the culprit might be the rear toe since I'm experiencing the WORST while under heavier acceleration. If I'm going down the highway
at 75, at static speed, its not nearly as bad.

From what I've gathered, do you'all agree with having 1/4 MORE camber in the rear's than the fronts? If so, I'm well short currently in the rear...how will increasing my rear camber .75 degrees affect toe out (under acceleration)? More sensitive or less?

Thanks!

Tony

Posted by: stownsen914 Nov 25 2015, 07:37 AM

Personally I run less camber in the rear since my rear tires are wider. This is a pretty typical setup from what I understand. What tires are you running?

Definitely fix the rear toe though. And for the front you could probably go with 0 toe rather than toe out if you're driving on the street.

Posted by: r_towle Nov 25 2015, 08:38 AM

Contact Chris.
He did a lot of great analysis on the rear trailing arm physics throughout the full range of motion.
The chassis has limits, so you will rub inside or outside depending on your camber in th rear, and your tire width.

Adding and removing shims is not too hard, Chris has those for sale.
Paint the inner edge of the rear tire with white shoe polish and check as you add more negative camber by removing shims.
Once it starts rubbing, add one shim back.
That will be the physical limitation of your tub, and mine will be different than yours.

Then make sure to match both sides.
Also, when you think you have as much negative as possible, take ten lbs of air out of the tires and go beat on it around all sorts of corners and up and over elevation changes...
Then check the shoe polish on the inside to make sure you are right.
The lower air pressure will allow the tire to flex more....to make it rub.

In the front, again, the tub will dictate what you can do with the stock setup.
If you don't car about stock, and the racing body won't add points for mods, using a die grinder you can oval out the three upper mounting holes and get more negative camber, but go slowly, once again the car will rub up front at the limit.

So, once again, get polish on the inner tire and look for rubbing at the rear.

Posted by: ThePaintedMan Nov 25 2015, 09:01 AM

Tony, good tips from Rich and the other folks here. As I said in my first post, and as Stowsen pointed out, rear toe out has a big tendency to make the ass end of the car point in random directions, especially under acceleration. Some folks (drifters), autocrossers, ralleyers and cars with inherent understeer may actually use rear toe out to help point the car, or free it up. But it comes with the trade off of being really, really touchy, bordering on unpredictable.

As said previously, your settings aren't far off, but the main difference is the rear toe. I would start there before making huge camber changes. Toe has the most immediate, noticeable effect on the way the car drives and turns into a corner. As Rich said, camber is *typically* adjusted based on tire temps/wear and eventually driver input on how the car feels at the center of the corner. Yes, some cars run more toe at the rear, depending on spring rates, tire loads and generally how the car is being driven.

I too like either a neutral front toe, or maybe a little toe out a the front (I HATE understeer). But the rear is always toe-in.

Posted by: andys Nov 25 2015, 10:50 AM

IMHO, There are street settings, and there are track settings. I don't believe in one size fits all. Aggressive camber and toe out (front) works well for the track, but will prematurely wear the tires on the street. If you plan on doing a track day, set it up accordingly, then re-set everything back to more street friendly settings.

As for the track, record all the data you can each time you pit; tire temp profiles, hot and cold tire pressures, shock settings, sway bar(s), springs, and what effect changes have on balance, etc. Without a tire temp probe and pressure gauge, you'll be shooting in the dark, though since you run a DSR, I suspect you already know this. Do you have a rear sway bar? 650# springs in the rear seems pretty stiff.

Andys

Posted by: JamesM Nov 25 2015, 11:34 AM

What sort of poly, Elephants multi piece poly bronze or are you talking a single piece of plastic? Single piece poly bushings, especially in the front, will bind and severely impact handling and ride quality. They can also wind up damaging your chassis and control arms. I have a thread somewhere on here with pictures of the damage caused by poly bushings. The harder ones can be made to work ok in the rear but absolutely must be machined to exact fit. Whatever you are running make sure they are allowing for smooth suspension movement.

My experience is autocross only, but i would agree with all the comments on rear toe, without a little toe in on the rear it can be lively and sometimes unpredictable.

Posted by: Andyrew Nov 25 2015, 11:41 AM

650lb springs??? I ran 275's in the rear with the SBC and thought that was a nice FIRM setup for the street... 21mm Tbars up front.. Do you have some 400's to try? That MIGHT help your darting issue...

Last I checked camber it was -1.7 front -1.2 rear towed 1/16 out front and 1/16 in rear.

Posted by: Cracker Nov 25 2015, 05:50 PM

Andys - I agree. Yes, I do have a tire temp probe gauge.

The poly bushing are from Patrick Motorsports however I'm installing Rebel racing's system in the rear next week - less noisy.

I have 550 lb springs on there now - quite comfortable to me but will be installing the 650's before the event. I'm running a wing which is wing tunnel tested and developed to have the "capacity to produce" up to 600 lbs of downforce. Due to airflow inefficiencies we'll be waaayy under that figure but still substantial (I hope). At a track like Roebling I'll have it down. Those spring rates are much lower than my two other and previous race cars - I don't see the big deal here.

No rear swar bar but I might fabricate one eventually - probably a T-bar actually.

Spoke with Chris F. this morning...I believe the feedback regarding rear toe seems to be
accurate and the next step. Thanks to all!

Tony

Posted by: r_towle Nov 25 2015, 07:19 PM

You have some unique setup requirements for that car.

Might be worth mounting a go pro underneath to watch what is going on to make y adjustments.

Posted by: andys Nov 25 2015, 07:43 PM

Tony,

Careful with the aero balance at those kinds of speeds (150MPH). Can you post photos of your car with the wing and spoiler? With regard to the springs, keep in mind the rear trailing arm motion ratio; think it's 1.17:1, so your wheel rate will be higher. On Terry Stewart's SBC/914, we ran 450# springs with a big wing.

Forgot to ask. Open diff or LSD?

Andys

Posted by: Cracker Nov 25 2015, 08:52 PM

Andys: Guard LSD 40/60

Posted by: r_towle Nov 25 2015, 09:13 PM

I think the rear wing is too small....

Posted by: messix Nov 25 2015, 09:15 PM

whats the caster at?

Posted by: Cracker Nov 26 2015, 07:23 AM

We don't know where caster is set...easy to overlook I know (I stated that in the first post). I'll change the rear toe today - if I can sneak into the garage for a bit.

Rich - Thanks for the "paint/shoe pollish" suggestion - good idea. This car had run with the same suspension setup, tire/wheel sizes, etc and had no problems. Another friend, however, did have a little issue with the new R7's having a more squared off shoulder - a little rubbing ensued (and adjustments made). Could be the case here too.

Tony

Posted by: stugray Nov 26 2015, 11:37 AM

I just had my head in my wheel well looking at what mods I need to do to get more camber up front.
It looks like the limiting factor with the stock setup (if you hog out the holes and cut the sides off of the hats where the bushings are) is that the top of the shock will hit the body on the inside.
There is no way the tire will rub at the top on the inside as the shock will hit the body first.

I am considering using the offset ball joints to get a little more camber without hitting.

Posted by: brant Nov 26 2015, 12:29 PM

Stu. Check in with me at some point. There are a few mods that will give you a little more

Posted by: messix Nov 26 2015, 03:30 PM

find what the caster is set at. i bet its pretty low and more would give you a better on center feel and reduce the "twitchy" feel at speed.

some a/x set ups dont use much caster to reduce steering effort.

Posted by: Cracker Nov 26 2015, 03:47 PM

Thanks for the tip. Please define, in your words "low caster and more caster" please? I understand caster as positive and negative. Please advise. Chris Foley was telling me the same thing yesterday. I'll try that too.

Argh! Just found I busted a rear shock! Ain't race cars full of fun...

Tony

Posted by: r_towle Nov 26 2015, 06:06 PM

That could explain the squirrelly behavior you described.

Stu, front tire rubs at lower rear against inner fender at the bottom.
Lock to lock...with fat tires.

Posted by: Cracker Nov 26 2015, 06:14 PM

LOL. It felt better today WITH the blown shock. I did take it out for about 20 minute spirited drive this morning. Later in the day, for the first time, I found a small puddle of oil directly under the shock. I must have some binding on the raised shock mounts. Will fix...will be at track in 8 days!!!

Tony

Posted by: r_towle Nov 26 2015, 06:18 PM

The wing is too small....that will fix it.

Posted by: Cracker Nov 26 2015, 06:38 PM

You do have a thing with my wing...

T

Posted by: Dave_Darling Nov 26 2015, 08:46 PM

Put as much caster in as you can get. That means shock towers all the way aft; should be 6 degrees of caster or more. I think that's positive caster.

--DD

Posted by: Cracker Nov 26 2015, 09:12 PM

Thank you Dave...I know what that is but was curious as to how he was defining what he was suggesting.

Tony

Posted by: mgp4591 Nov 26 2015, 11:52 PM

Think of negative caster as what the grocery cart has on the front- the pivot point is forward of the wheel axle and the cart follows bumps and slopes in the floor but is very easy to steer. Translates into high speed instability on a car. Actually ANY speed instability on a car. Positive caster is what your bicycle has- you can take your hands off the bars and it will travel in a straight line. The pivot point is behind the wheel axle and you have more high speed stability on a car but more effort to the steering wheel at low speeds. BMW and Mercedes (and I'm sure others too) have around 7 degrees positive caster to promote high speed stability on the fast roads.
Clear as mud?

Posted by: messix Nov 27 2015, 12:37 AM

a low number would be 0 to +3, higher number would be +3 to what ever the chassis i capable of.

i wouldn't even imagine that any suspension tech would set any car up with neg caster.


keep in mind that the more + caster the more steering effort you will have but more "on center" feel at speed. you can dial back some camber with more caster.

imagine a bicycle or motor cycle when you turn the handle bars....... and what the front tire does.

Posted by: messix Nov 27 2015, 12:39 AM

cliff notes or front set up for dummies http://www.vikingspeedshop.com/suspension-101-camber-caster-and-toe/

Posted by: Cracker Nov 27 2015, 07:08 AM

Thanks fella's. I understood "caster" from the get go but was just asking messix to explain his use of terminology. Clear as mud?

Tony

Posted by: Dave_Darling Nov 27 2015, 10:38 AM

I don't think you can set a 914 up with negative caster, unless you do some Sawz-All work! So any mention of caster in our cars has to be positive caster.

--DD

Posted by: r_towle Nov 27 2015, 10:48 AM

Push the top of the strut back towards the windshield as far as it will go.
Measure both sides, one side will be more than the other
Pull one side back forward to match the extreme of the other side.

Unless you cut sheet metal, or install different ball joints, that will be the limit of your chassis.

Clear as mud?

Posted by: Cracker Nov 27 2015, 05:12 PM

Yes'm... ;-)

T

Posted by: r_towle Nov 27 2015, 08:18 PM

Cracker, rear this

http://www.cassidy-online.com/porsche914/aerodynamic_aids/index.html

Posted by: Cracker Nov 27 2015, 08:47 PM

Thanks. I remember seeing that years ago...very interesting.

T

Posted by: messix Nov 27 2015, 10:38 PM

wow clear as mud?

low caster angle.......

high caster angle......

measured in degrees..... you are unable to garner any idea of info from my posts?

i don't think my knowledge and experience in chassis set up and dynamics is that far advanced to confuse most moderately competent shade tree mechanics.

good luck with your car.

Posted by: Cracker Nov 28 2015, 06:47 AM

I certainly didn't mean to hurt feelings...thanks for your insight. The "clear as mud" was brought out by "someone else", simply poking fun at me, nothing more - I just returned the favor. Again, nothing nasty intended. Everyone should be good (I hope).

BTW: My family used to live in University Place growing up - I sure do miss your part of the country! Have a wonderful day Messix!

Tony

Posted by: jimkelly Nov 28 2015, 07:03 AM

do I have this right for front?


Attached image(s)

Posted by: Cracker Nov 28 2015, 07:08 AM

Just don't max out your "toe-in" (adjusted at tie-rods) - it has to be measured. Your Inward facing arrows will adjust for negative camber. From what I've been told you want anything between 1/8" OUT for AX and zero to 1/8" IN for street and road racing applications. Regarding the caster...you're correct.

Jim: Regarding your radiator problem...for what its worth - I'm using a STEEL radiator in lieu of the aluminum. Very strong and cools just fine. Just a thought...

Tony

Posted by: r_towle Nov 28 2015, 09:59 AM

Yes, you have it right.

The key is one side will go less than the other.
You need to match them, so pull one side back to however far you can get the other side.

Move tower, set car on suspension, roll car back and forth about 3 feet, and bounce it up and down, then measure.

It takes a bit of time, but it's all fairly simple.

Rich

Posted by: stugray Nov 28 2015, 02:23 PM

Since this racing front suspension oriented thread is getting a lot of attention:

Has anyone ever considered cutting the front A-arms, moving the ball joint mount out by ~1/2" and welding it back together? (with 1/2" spacers of course).

That should give an equivalent of ~1 degree additional camber (negative) and 1 inch additional track.
Then we could pull the camber adjustment a little back from "all the way" and give us a little adjustment to play with for various track setups.

If we wanted to be extreme, we could even make the length of the control arm adjustable as well....

Posted by: Dave_Darling Nov 28 2015, 06:39 PM

Lengthening the A-arms is somewhat common in the 911 racing world. They do it with some frequency, since they are as camber-challenged as we are. The preferred solution for them seems to be to go a to 935-style front end, though that requires going with coil-overs, and therefore reinforcing the shock towers and so forth.

--DD

Posted by: Cracker Nov 28 2015, 06:59 PM

Dave - I've thought about doing that conversion but have chosen not to at this point. I've seen these cars do very, very well without it. I for one, will wait and see how good or how bad the car performs.

Now I really like the rear conversion (996?) by one of our members...I have my eye on how that develops. Super sweet!

Tony

Posted by: Cracker Dec 4 2015, 11:05 AM

UPDATE: So thanks to everyone for your input...I added rear toe as suggested and maxed-out to positive caster. I also loosened the sway bar to max-soft. All of the above
has contributed to a much, much, much more pleasant vehicle. Thanks again!!!


Rich - So you think I need a bigger wing - huh? LOL!

Heading to Roebling today!

Tony

Posted by: andys Dec 4 2015, 12:37 PM

Tony,

Looks like you're all set to go. When you say "much more pleasant", did you track it already, or just run it around town?

When I took my 914/LS! to Willow Springs (Streets), I quickly discovered my right rear shock (Koni DA) was blown out. Did only two sessions before deciding what's the use; too unstable on right handers (especially when running CW direction), and packed it up. Got to say that it otherwise behaved very well right out of the box with the suspension settings I used. Tire temp profiles were nearly perfect.

Andys

Posted by: Cracker Dec 4 2015, 10:38 PM

Sorry Andy for the late reply...just got to the hotel. My "unpleasant" experience was on public roads as were the testing with the changes. I've been duped before because its impossible to duplicate driving at track limits on the street. However, my biggest gripe was with straight line acceleration stability - I believe I'm good/comfortable. I have no basis for how this car will handle when pushed through the corners. Tomorrow will be quite an eye opener - I hope for the better. I have TWO back up shocks (rear) in the hauler and one brand new on on the RR. I wasn't taking chances blowing the trip over a shock. I'll let you know how it turns out and if I have time to focus on Video - some footage. Thanks for the tips and feedback!

Tony

Posted by: Cracker Dec 5 2015, 09:14 PM

UPDATE:

Okay. I had a good day. Still running after a full day of tracking (YAY!) - no mechanicals! The car I'm chasing is an ex-IMSA 997 Cup Car (sequential)- AMAZING car actually. It is owned by a former Brumos racing team member - quick car and driver. Anyway, he put 2 seconds a lap on me. This was only my (and the cars) second session...who says a LS 914 is too heavy?

PS: I hit 154 down the front straight - braking way, way early - I'll fix that!

Tony/Cracker

https://youtu.be/9Te6GScwxek

Posted by: andys Dec 6 2015, 11:32 AM

Tony,

Looks like a fun drive! Anything to report on how the car behaved, and the data you recorded (track data sheets)?

Andys

Posted by: Andyrew Dec 6 2015, 12:10 PM

Awesome! Looks like the chassis is really stable! In some spots I thought the back might come around it just stayed planted. Good job!

Posted by: wndsrfr Dec 6 2015, 03:02 PM

Wow Tony.....sweet driving....what transmission & linkage are you using...nice positive shifts.

Posted by: Cracker Dec 6 2015, 08:07 PM

My good buddy, Terry O'Toole (SixAddict)" was also here this weekend. He did a great job piloting his "massaged" 3.0 914 around! Herman (Porter?) - it was also good to see you again!

Andy - I don't have telemetry...I have "seat of the pants" feedback - low tech I guess. The car felt amazingly stable but once I pushed it a little harder the rear was getting loose. It was occurring too easily though. Today, before the second session, I changed four things (at once), I know that's not suggested but fortunately it worked. We took 1" off the front bar (tighter), lowered the rear by 3/8", lowered tire temps to 25 psi (from 27), and set the rear shocks to full-stiff. This made an amazing difference - totally settled the rear when pushed and stayed that way throughout the entire session.

Andyrew - Thanks. Yes it is very stable.

John/Wndsrfer - Thank you. The trans is an early Boxster S (iirc a 2003) with a Guard LSD and the shifter is made by CAE with motorsports cables. I couldn't imagine an H-pattern shifter/trans being any better (for performance). It took a little time tweaking and adjusting but once we got it dialed in - oh baby! How was Daytona? Video you can share?

BTW: You might have noticed an ignition stumble several times..I am not doing this of course. A flaw in my intake design has the MAF sensor at a convergence point where as it needs to be fed within a 4" tube and with a straight feed 6" prior. We are having to use a speed density tune which isn't perfect. Parts to correct this are on the way but not in time for this weekend. In the future this stumble will (should) a thing of the past. It caused the back end to come around on lap 2 in the video - I just kept my foot in it, steered towards it and pulled the next gear. A little unnerving at times...
Tony

Posted by: Justinp71 Dec 7 2015, 07:02 PM

Nice Car! Awesome video chasing the GT3