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Author Topic: TFA Racing Lakester "tweak" diary  (Read 52629 times)
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RichFox
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« Reply #105 on: September 19, 2014, 10:06:51 AM »

I wonder if you could contact the Hondata guys for some thoughts on speed with FWD. They must know a lot about it.
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entropy
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« Reply #106 on: September 19, 2014, 10:31:45 AM »

I wonder if you could contact the Hondata guys for some thoughts on speed with FWD. They must know a lot about it.

Good idea!

Also, we were pitted next to Rex Svoboda (one of TFA's official Mentors) and he runs the FWD Saab, albeit with a bit more hp (his blower is as big as our motor). Rex didn't seem overly surprised at the handling, but said it can probably be improved by some of the things mentioned. 

As pointed out in this thread he suggested systematically test issues/settings.  I think that he agreed with confirming toe in at 1/8" as a test (Don talked with him about that item).    We came to the event with it set at approx 1/8" but wanted to make sure.  We just ran out of time.
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John Burk
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« Reply #107 on: September 19, 2014, 01:12:39 PM »

An easy way to see what wheel offset give zero scrub . Put a framing square against where the wheel bolts and clamp it to a couple of wheel studs with the 90* leg down and pointing out paralel to the axel axis . The bottom edge should be at the tire radius . When the hub is steered the point on the horizontal leg that revolves around one point is the zero scrub point . Clamps on the rotors on either side of the caliper only it rotates on the kingpin axis . Don't worry about the vertical leg being at an angle . The effect of caster and tire growth is small compared to the 3" or so of scrub built into the 4wd hubs we use . With 28"tires 10* of caster and 3/4" tire growth only adds .170" of scrub . I'd just check the scrub at bottom center and add .170"

I ordered my wheels with an extra 1/4" of negative offset so the wheels can be spaced in or out to dial in the handling .

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Rex Schimmer
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« Reply #108 on: September 19, 2014, 03:27:49 PM »

Rich Fox,
Neat pic of the Kurtis roadster, a neat car when it came out and still a neat car. You don't happen to know who owns the one in the picture do you? Notice the tube axle with trailing arm locators and probably a watts link for lateral location and I don't remember but I think that the the top trailing arm is connected to a cross torsion bar, just like his Indy cars. Neat car just like everything that Frank made.

One thing that I think we need to discuss is that positive or negative scrub radius(use whom ever's definition you want)  can be a very valuable handling tuning tool, it all depends on what kind of car you happen to be working on. I also think we all agree that minimizing the scrub radius on a front wheel drive Bonneville car is  beneficial for handling and from Sparky's previous experience with his first lakester minimizing scrub radius helped that cars handling. Big over the road trucks use close to zero scrub radius because it makes steering loads smaller, which is important when you may have 10,000 lbs on your front axle, but a sprint car may like lots of scrub radius as it can have a big cross weight jacking effect when you back it into a corner. Look at a fast go kart, they may have the wheel spaced out 3-4 inches with a huge scrub radius but they operate in the oversteer mode most of the time and this huge scrub radius helps them jack weight onto the inside tire, so there are places when scrub radius can be helpful.

Rex 
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gas pumper
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« Reply #109 on: September 19, 2014, 03:35:57 PM »

I agree with Rich on rollout.   More important than pressure. Set the largest tire to the pressure you want to run, than add more to the smaller one. We try for 1/2 inch difference. Less if we can get it. Sometimes we can be right on.
And always re check air at the starting line. The right side always gains from sunshine exposure.
Frank
Frank,
We set F tires pressure to 90psi in Houston (sea level+/-) before leaving:  both L&R circum were 91.25"
At WOS 9/5 L = 91.75 @ 74psi, R = 91.5 @ 73psi (tires free standing)
               9/7 L =  ?        76psi, R =  ?         77psi  (tires on salt), didn't re-measure cirum bc psi was so close

I thought the decrease in psi & increase in circum wrt sea level was an altitude effect, but i didn't cogitate on it very much.
Interesting thought on sunshine exposure, this never occurred to me.  Do you have any measurements which demonstrate this effect?  I don't doubt it, just wondering how much it affects the tire.
Karl

Karl:
2013 speed Week I remember it was consistently 10 psi higher on the right side in staging. I let the air out to what psi I marked on the hubcap in the pit but did not remeasure at the start line.
  
We have ran as much as 15 psi different across the rear, drive tires to get the stagger out. But that was a few years ago running a set of mismatched used tires.
 
We run the 18" M/T's. And have found when you buy a new pair right from the source they match up nice and grow with pressure evenly.

I have never put any thought into altitude effects either. I think leaving them at high pressure stretched them. And I leave the air high on them too when stored and transporting. I see no ill effect. Some say to let them down to low pressure for transport and storage.

BTW, this years set was marked 92 as delivered and when mounted and aired to 110 they went to 96. I wonder how big they will be when we get them to WF?

Frank
 
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SPARKY
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« Reply #110 on: September 19, 2014, 03:52:11 PM »

I sure hope you guys get it done this meet "old what's his name"  has waited long enough to put two runs together
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« Reply #111 on: September 19, 2014, 03:52:48 PM »

The Kurtis belongs to Peter Hendrickson. Leader of the Montana Dodge Boys. He just bought it. Appears to be branching out.
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entropy
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« Reply #112 on: September 20, 2014, 05:07:59 AM »

Guys,
     Thank you all soooooo much for your input, GREAT discussion.   cheers
Be assured Don & I will review/use it as we attack the handling issue over the winter. Note that I obsessively copy & paste all comments into one of my many excel spreadsheets, tabbed in a way that I can reliably find the info.  Don (and our Mentors) will attest to my addiction to spreadsheets  grin.
An interesting associated comment...
     Yesterday I talked to Allied Wheel Component's Greg Mulkey; the guy in LA who made our cool 2 7/16" offset Al wheels. I was giving him a summary about tech inspection of his wheels,  other racers comments, how they performed at WOS, etc. 
     He was particularly interested in my comments on "hunting", said he knew nothing about salt, but that his Baja-type race truck did the same thing on dirt/sand at speed.  Greg mentioned that it took him "hours" of racing the truck until he got comfortable with it.  Said a light touch on the steering wheel, minimize changes, know it will mostly re-orient itself after it's "hunting expeditions", mostly... 
     Like you guys, Rex & Tom, he advised us to check all set-up factors & then make single changes at the track, but noted "there may be nothing wrong with your set up, you may simply need to learn to drive it..."
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SPARKY
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« Reply #113 on: September 20, 2014, 05:43:38 AM »

Sounds like he drives a roadster  huh
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Miss LIBERTY,  changing TKI  to noise, dust and RUST!!!

The # 1 issue is: TO KEEP THE REPUBLIC      
   Center for Self Governance            tncsg.org     mrspowell.org

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller
entropy
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« Reply #114 on: September 20, 2014, 06:36:14 AM »

Oh, i almost forgot this...

One item on our list hasn't been kicked around and maybe it shouldn't he on that list at all = ballast. 
If anyone has thoughts, we'd love to hear them.

As the car sits now with driver & fluids the F/R weight distribution is about 50/50,
The question is: "should we add ballast over the front axle?".

current F/R:       51/49% 
add 250# to F:   55.5/44.5%
add 400# to F:   58/42% 

associated info:
1. approx 350hp on Dynojet dyno
2. With Tom's help, we found a silver lining in the dark clouds over the recent SW.
     Took #5448 to Darko's wind tunnel:  Cd = 0.325, F lift = 239#
3. Cp approx 42" aft of Cg
4. 1st & 2nd gears:  must carefully modulate throttle to minimize wheel spin.
    3rd gear: WOT = very little if any wheel spin
5. car weight 2360# w/suited driver & fluids, no ballast

At this point,  I am interested in the impact of ballast on handling/stability.
     (I am obsessed with small end acceleration and its impact on big end mph, but that's another discussion)

It wouldn't be horribly difficult to add say 250# ballast (easy for me to say, Don does the fabrication...)
     - 250# would counter the 237# lift? So what?
     - 250# would add 6"(guessing) to Cp/Cg separation; So what?

Q:  would adding F ballast be likely to improve stability?
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Peter Jack
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« Reply #115 on: September 20, 2014, 07:18:32 AM »

Can the ballast be set up such that it can be bolted in relatively easily? That could then become another of the incremental changes that you make. It would also allow you to try various weights and try them with a variety of front end alignment settings.

Pete
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« Reply #116 on: September 20, 2014, 09:19:31 AM »

....At this point,  I am interested in the impact of ballast on handling/stability.
     (I am obsessed with small end acceleration and its impact on big end mph, but that's another discussion)....

I'd put the 400# in the car in an instant.  You could always take it out.  This could improve your 'small end acceleration' as you aren't using much throttle in 1st and 2nd now because of wheel spin.  On the big end where you might be only picking up say 20 mph in the last mile the weight isn't hurting you as almost all the HP is going into overcoming aero drag.  How much HP does it take to accelerate 400# of weight 20 mph in one mile?  Not much so you aren't giving up much by adding it and if your acceleration gets you to a higher speed by say the 2 1/4 then you have more track at the higher speeds where you need it.

The weight is going to help the CP/CG also which is a good thing.  Your car is light now and with more HP down the road you are going to need even more traction.  Think what 1st/2nd will be like then.  On that thought I'd also explore a different transmission option (one with a closer ratio).  I think 1st will become even more useless with more HP.  Hooley runs a 1.90 first with 2.47 gears and we can never run more than 50% throttle in first and with the 1.30's second still no 100% throttle and the car weighs over 5000 lbs..   

You have one big advantage over most of us and that is any weight you add is all beneficial as it is over the drive tires and also in the right place for improved CP/CG.  With a rear-wheel driven car when you add weight at the back for traction you also need to add weight to the front to keep the CP/CG reasonable.  The added frontal weight in this case impacts acceleration and doesn't help with traction.

Sum
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Rex Schimmer
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« Reply #117 on: September 20, 2014, 08:11:50 PM »

Entropy,
The item that I find interesting is that the Cd is .325 which show how the wheels and tires and almost anything else sticking out in the air really spoil what is a very nice shape. My bet is that the body by its self probably has a Cd of .1 or even less. The bain of running a lakester! After you drop the "big" motor in your next project is to do something with that horrible looking front axle to make it better looking to the air. Also doing some stream lining on the rear will help. We added fairing to the rear axle on Steve Nelson's lakester this year and with not to many other additional changes and with the exact same engine that Steve set the record at 196+ two years ago we went 6 mph faster and since I did the axle fairing I will claim that it was all due to the fairing!!!

You guys are destine to have lots of fun!

Rex


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« Reply #118 on: September 21, 2014, 05:24:43 AM »

SPARKY
- I am clueless how a roadster handles but have read about the spins they sometimes experience… YIKES!!!!  Thinking about my roadster cluelessness emphasizes my need to roam around, go to other pits, yak with many people. For whatever reason, I tend to not roam around; gotta change that.

Peter Jack
- Don & I have kicked around ballast mounting possibilities. Moving the fuel pump & filter would free up space in front of the quick change.  Would need to remove the nose to get at it which is doable.

Sumner
- Your post reminds me that I haven't yet "treated" you to my motorcycle-based interminable (largely dismissed) rant on the impact of small end "balls to the wall - show no mercy - take no prisioners" type acceleration Cheesy.  But you also make me think again about the possibilty of some of the hunting/jinking being generated as our locked rear end momentarily loses traction on one wheel. This was mentioned earlier in this thread.  Would 400# significantly subdue that lopsided traction loss?

Rex
- Fairing the front & rear axles has been on my Partner's list from the beginning of this project. Not only is he an ace-fabricator but also a career pilot so all the aero stuff makes him smile & plan.  He mocked up front fairings at Darko and Cd dropped from .325 to .320, but only decreased F lift from .234# to 227#.  Don is cogitating... 

Notes:
1. At our current config, on WOS pass #8, the car gained 1mph (208.5 to 209.5) over the last 12.3sec leading up to the 5.  Is the aero drag close to stalling more mph gains? Maybe the type of aero improvements Rex mentions is our key?

2. Our 2.19 gearing delivered 209.2mph at 5650rpm. 
The Patriot motor spec shows max hp is 501 @ at 6100rpm = 226mph estimated max speed. 
It seems that we have room to test aero improvements at the current gearing.
I LOVE this stuff!!!
karl
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« Reply #119 on: September 21, 2014, 06:32:44 AM »

You mentioned a locked rear (front) end in the above post. Is it a spool or a locker or something else? At this point I might be tempted to follow one of Sparky's favourite suggestions and look at a true track type differential. They tend to have a softer action than some of the other locker types and give you a differential rather than a spool. Just another suggestion to add to the confusion.  rolleyes rolleyes grin

Pete
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