Chassis Tuning 3170

Cobra #3170 · #1 (**permalink**) 07-21-2014, 11:27 AM

Thought I would post an update because we have made more changes. We raised the front and rear spring rates by 50 and 100 pounds respectively. This allowed us to lower the front by .2 and the rear by .3" with out having tire to body contact. We installed a GPS data system to start gathering data because the car is right in a good adjustment window now. We can change rake angle by .1" and get a measurable difference in handling. Next week new tires these tires have a jillion heat cycles on them so things should get better but you never know. Measured G loads are consistently in the 1.2 G range now and we were actually in the 1.4 range around a 75 mph sweeper. Still cannot get anything over 1/2 throttle or so even at high rpm. It actually got side ways in second gear even though the engine was at 7000 when I tried more throttle.
1.7 to 1 second 3:31 rear end and 25.5 tire. This is a video of my first run we did not have a camera on my last run but it was better.
Who says big blocks won't RPM!

http://youtu.be/Pba5Tf46v6I

xlr8tr · #2 (**permalink**) 07-21-2014, 12:01 PM

looks like a blast! What is it about the rake angle that changes handling so much?

Cobra #3170 · #3 (**permalink**) 07-21-2014, 12:20 PM

Quote:

Originally Posted by xlr8tr

looks like a blast! What is it about the rake angle that changes handling so much?

It influences how much weight is transferred across the front and rear wheels
or the distribution of that transfer. The amount of transfer is unchanged just how much goes to each pair of wheels. It is similar to what can be done with spring rates but this is more of a fine tune. A few weeks ago is was under steering like a pig and we raised the rear .2 and that brought back the balance. The understeer was because of the surface we were on, it had less grip than this weekend so we lowered the rear .1 and it was perfect.

DMXF · #4 (**permalink**) 07-23-2014, 09:30 AM

So any plan to determine setup parameters with CR6 ZZ Avons, which is what many original car owners have fitted today?

RallySnake · #5 (**permalink**) 07-25-2014, 12:50 AM

That reminded me of how much fun Solo2 is. You need to work on a wider approaches to the turns. You missed the apexes in the first half of the course and that adds a lot of time. Your car accelerates and brakes really well! If you approach from the outside of the turn, you can get the power on earlier and be faster all the way down the straight.

RS (A Former SCCA Solo2 Regional Champ)

Cobra #3170 · #6 (**permalink**) 07-25-2014, 06:20 AM

Quote:

Originally Posted by RallySnake

That reminded me of how much fun Solo2 is. You need to work on a wider approaches to the turns. You missed the apexes in the first half of the course and that adds a lot of time. Your car accelerates and brakes really well! If you approach from the outside of the turn, you can get the power on earlier and be faster all the way down the straight.

RS (A Former SCCA Solo2 Regional Champ)

Shortest distance trumps wider lines almost every time according to data acquisition system, spoken as a former solo II National champion.

Jamo · #7 (**permalink**) 07-25-2014, 12:31 PM

Having walked backwards on many courses and laying out cones for many layouts I drew up in the 90s (damn difficult to get folks out the night before at Castle to help put out cones...chapter prez is simply the title given to the designated slave), I gotta say I go with Bruce on that one. Really depends on the track and the next 3-4 corners rather than apexes. Won a few regionals with the Vette and Butler myownself.

Also...top award for cone killer for a couple of seasons when I took the wife's 96 Impala out a few times with three riders. I mean really truly dead cones.

Bobcat · #8 (**permalink**) 07-25-2014, 01:26 PM

especially since he has the hard data , and experience , to back it up !

Jamo · #9 (**permalink**) 07-25-2014, 01:28 PM

Assolutely...there is that!

Jamo · #10 (**permalink**) 07-26-2014, 04:33 PM

We had an extremely unique feature at some of our Fresno autocrosses in the 90s...a moving cone.

Cheryl, a little person, a damn good autocrosser in a Camaro, and one blessed with the ability to out cuss any man (and a great perspective on farts in elevators), would wear an orange safety vest and basically run like hell when we steered towards her.

fordracing65 · #11 (**permalink**) 07-15-2015, 11:46 PM

How big of a tire do you run on the front now, do you run the new big size always no matter what course, do you have a front and rear sway bar when you autocross...

Cobra #3170 · #12 (**permalink**) 07-16-2015, 11:21 AM

Quote:

Originally Posted by fordracing65

How big of a tire do you run on the front now, do you run the new big size always no matter what course, do you have a front and rear sway bar when you autocross...

fordracing65,

I was surprised to see this up again but assume it is recent.
Front tires: trying, 315x30x18 and 275x35x18 still have not made a decision on brand or size. We run both front and rear bars and both are set full soft
front bar is 1.25 D with .125 wall and blade adjustment, rear is .562 D the car is so low now that to run 315, ride height or camber has to be compromised to avoid body contact. Rear can run either 315 or 335 but we have not evaluated 335 yet. Small tight tracks that have low grip seem to like the narrower tires because they get to temperature quicker. We are running more tests this weekend at a location that is lower grip than airports but better than Goodguys surface. I have installed an idler pulley on the alternator belt to try and keep it in place at 8000. I also changed some seals on the front wheel bearings and installed a 10 psi check valve to try and cure knockback.
If I can solve those two problems we can get on to fine tuning the chassis.

xlr8tr · #13 (**permalink**) 07-16-2015, 01:48 PM

what exactly is brake knockback? Sounds like it affects braking quite severely.

fordracing65 · #14 (**permalink**) 07-16-2015, 03:31 PM

Quote:

Originally Posted by xlr8tr

what exactly is brake knockback? Sounds like it affects braking quite severely.

When you race with turns stuff bends, as the wheel hub and wheel bearine deflect during cornering, the rotor hat is sandwiched in between and forced to go along for the ride, the caliper is attached to a more rigid suspension component, the upright, when these are not in parallel the deflection of the rotor relative to the brake pads forces them away form eachother, there is not springback in the piston seal to push everything back together, the pads are then pushed off the rotor until the brakes are applied again...

DanEC · #15 (**permalink**) 07-16-2015, 04:09 PM

Jeeez - still can't imagine what 8000 (+) rpm from an FE running in first or second gear on an autocross track must be like.

Cobra #3170 · #16 (**permalink**) 07-16-2015, 09:10 PM

Quote:

Originally Posted by DanEC

Jeeez - still can't imagine what 8000 (+) rpm from an FE running in first or second gear on an autocross track must be like.

last time we ran one of the guys watching was sure it was a small block.
The rpm gives it a broad running range in gears so no shifting is required.
the car will go over 75 mph in first with a 3.73 first gear and 95 in second so it will cover 99.9% of all autox with 1 or 2 gears. Both intake and exhaust valves are titanium plus it has some very good valve springs along with Carrillo rods, a light Moldex crank and a dry sump.