sgraber
|
| posted on 6/2/07 at 10:44 PM |
|
|
La Bala - First Track Day - Learned a lot
My first ever track event is over. The good news - the car didn't break and the engine didn't blow.
This is going to sound like I had a lot of issues (and actually, I did), but I think in general the day was a success. All you have to do is place
this event in the perspective that it's my first attempt at car building, I tried new things and am learning a lot in the process.
Since I am so inexperienced with driving I felt that an experience person would be the correct choice for the first seat. I enlisted the help of a
local driver named Glen, known to many at the tracks as a guy that can drive anything. Good choice.
Glen started out by noting the horrendous brake effort, pedal travel is good but the brakes just don't work. Press as hard as you want and the
car keeps going. I am going to swap out the pads first to some EBC greenstuffs and if that doesn't fix it I don't know what it could be. I
would expect the brakes to at least lock up....
Next he noted a slight miss in the engine while accelerating out of corners and this may be a fuel pickup issue. I'll have to maybe add a
swirlpot to solve this or a different tank. As the day wore on, the miss got worse. According to the megasquirt forums it's possible that the
ecu is resetting itself and I have to look into this.
Biggest issue IMHO The car oversteers. And it does so quickly without warning. Lowering tire pressures relieved some of this, but I think that the
issue is related to the springs and dampers. I need to drop the spring rate significantly and add an ARB. Also the dampers should be dyno'd and
the valving set for the car.
Also, the steering effort is too light and doesn't inspire confidence. This may be partially caused by the 60-40 weight bias, but my feeling is
that since I changed the wheel/tire size I think the scrub radius location is now outboard of the centerline of the wheel . To fix this I intend to
reduce the KPI from 16 to 12 degrees. Easily done with the upper balljoint I am using.
The steering itself lacks any self-centering. This should be fixed by adding more caster. I have around 4 degrees caster right now and will go to 6
degrees. Another simple change.
Basically I am not even in the ballpark yet.  However, my test driver noted that with these fixes we may be getting a lot closer into the ballpark,
and the car has a lot of potential. So you can see, I learned a lot about the car and what needs to be done before the next round of track driving.
BTW - I had a blast! Lots of people came by to see the car and everyone was very interested in it.
that's me in the grey shirt and floppy hat.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
|
|
|
|
|
ned
|
| posted on 6/2/07 at 10:48 PM |
|
|
congrats steve, car is looking good even if it does need a few tweeks under that gorgeous body 
beware, I've got yellow skin
|
|
|
JoelP
|
| posted on 6/2/07 at 10:50 PM |
|
|
rock on steve, its all part of the fun! Nothing too horendous there, just a bit of tweaking!
|
|
|
DIY Si
|
| posted on 6/2/07 at 10:54 PM |
|
|
Glad to hear that basically all went well. NO major problems, you still have an engine, didn't crash so overall a good day. Every car requires a
few tweeks to set up right and most have a manufacturer to ask. Only problem being you're that person this time round. General opinion for
7's seems to say that 7º or so of castor is about right, and spring settings take some sorting out.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
|
|
|
Volvorsport
|
| posted on 6/2/07 at 11:20 PM |
|
|
do you have wider tyres at the back ?
whats the toe in set at ?
can you swap springs back to front ?
generally need more castor for feel the lighter a car is .
www.dbsmotorsport.co.uk
getting dirty under a bus
|
|
|
tweek
|
| posted on 6/2/07 at 11:22 PM |
|
|
Considering the amount of money/resouces/people that the manufacturers throw at their cars and the amount of breakdowns they have I'd say thats
a great success.
Give yourself credit where it's due, you continue to do a superhuman/professional job on this project and I'm sure I'm not the only
one who is amazed you haven't been snapped up by a major manufacturer
best of luck with the modifications!
"oh dear..." said god,
"I hadn't thought of that"
and promptly vanishes in a puff of logic
|
|
|
sgraber
|
| posted on 6/2/07 at 11:36 PM |
|
|
Hey, thanks for the encouragement guys.
The rears are 235/45-17 and the fronts are 215/45-16.
Toe is 1/16"
Springs are same front and rear - I know... problem - this will be solved before next go-round.
More interesting news: SURPRISE! The car weighs more on the precision scales at the track than on my analogue ones at the shop. Total weight is
1,580Lbs with a full tank of gas (as seen in the photos above). Where did it all come from?! Bodywork, hinges, brackets, turbo, piping, rollbar,
windshield, they all add up ... 1,000lbs across the rear wheels for the 60-40 split. Dyno run confirms 145Hp and 111lb/ft torque on 5psi boost.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
|
|
|
MkIndy7
|
| posted on 6/2/07 at 11:37 PM |
|
|
Sounds quite a sucesss to me!.
On the self Centering issue, was it causing a problem or was it just because you were looking for it?.
Our MkIndy didn't self centre at all the first few times we took it out and we never even noticed!
We only set our car to self centre for the SVA and then retuned it to a neutral position because the tyres were on the verge of scrubbing to get it to
self centre.
|
|
|
sgraber
|
| posted on 6/2/07 at 11:43 PM |
|
|
I can't say it was a problem, but my personal preference is that it have some tendency to return to straight line running. Why does SVA require
it?
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
|
|
|
MkIndy7
|
| posted on 7/2/07 at 12:00 AM |
|
|
Don't know really, just does over here.
Maybe incase you take your hands off the wheel, collapse slip, or helps in case of a blow out are the kind of things I can think of.
Or to scrub and wear your tyres out quickly lol, because thats all ours was doing!
|
|
|
RazMan
|
| posted on 7/2/07 at 12:41 AM |
|
|
Steve, I had EXACTLY the same problem with my brakes - two feet on the pedal and still not enough braking 
All solved with a change of master cylinder bore size. I went down to 0.65" front and 0.7" rear and now it does what its supposed to.  I
was sent a little spreadsheet that works out the right sizes for everything and it really worked for me.
Good to hear that you are getting to grips with it now 
[Edited on 7-2-07 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
|
|
|
alister667
|
| posted on 7/2/07 at 12:50 AM |
|
|
quote:
Originally posted by RazMan
Steve, I had EXACTLY the same problem with my brakes - two feet on the pedal and still not enough braking
All solved with a change of master cylinder bore size. I went down to 0.65" front and 0.7" rear and now it does what its supposed to. I
was sent a little spreadsheet that works out the right sizes for everything and it really worked for me.
Good to hear that you are getting to grips with it now
[Edited on 7-2-07 by RazMan]
Yep I was about to reply but Razman beat me to it, when I was doing my build I used a brand new master cylinder a friend of my dad's gave me -
but it gave exactly the same symptoms you have. I changed it for a re-con'd part of the correct bore and lo and behold she stops on a dime!
The rest sounds like minor fettling. The car looks stunning by the way.
Well done and the best of luck
Ali
http://members.lycos.co.uk/alister667/
|
|
|
sgraber
|
| posted on 7/2/07 at 02:38 AM |
|
|
quote:
Originally posted by RazMan
Steve, I had EXACTLY the same problem with my brakes - two feet on the pedal and still not enough braking
All solved with a change of master cylinder bore size. I went down to 0.65" front and 0.7" rear and now it does what its supposed to. I
was sent a little spreadsheet that works out the right sizes for everything and it really worked for me.
Good to hear that you are getting to grips with it now
[Edited on 7-2-07 by RazMan]
getting to GRIPS with it. That's funny!
Seriously though. I did go through the process of determining the correct master cylinder. I was using .75" units prior and at that size there
was virtually no pedal travel (and no grip) either. So I went to a racecar shop specializing in vintage to pre-90's cars. He ran the numbers
through a spreadsheet to come up with the .625" units I am currently using. The pedal travel is sufficient, just no grip.
So any other thoughts? Don't the pads sound suspect?
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
|
|
|
Ivan
|
| posted on 7/2/07 at 06:12 AM |
|
|
Unless you have extremely hard racing pads that haven't had a chance to heat up I doubt if a pad change would make much difference. I would tend
to look at the hydraulics i.e. is the pressure getting to the calipers - are the brakes properly bled and, are the flexible hoses not bulging, are
there no blockages and is your brake balance right. I ask this because it sounds strange that you are getting the pedal travel but not the clamping
force.
Congrats on the project - I think its an impressive looking car that puts many of the commercial kit car designs to shame.
|
|
|
Doug68
|
| posted on 7/2/07 at 07:21 AM |
|
|
First of all HUGE respect for getting to this stage.
The difference between EBC Greens pads and regular pads is noticeable but definitely not going to cure the described problem.
Looking at your gallery it looks like you're using slidey pin calipers, to me the order to search in would be (Not wishing to sound
remedial):
1. Is it bled properly
2. Is the system developing sufficient pressure?
3. Are the calipers working right? i.e.
i Could the pads jam?
ii Are the pistons free?
iii Are the slidey pins free?
4. Did your driver have chicken legs?
Having said all that I doubt all 4 calipers a not right so at least one wheel should have locked assuming thats there's not air in both the
front and rear systems so my votes on the wrong size MC's
Here's a fugly test: swap the MC's front to rear to see if you can improve the rear with the smaller diam front unit (i assume) if that
works the the MC's are the wrong size.
The other way to reduce the oversteer is stick wider wheels on the back.
Flares and 315's would upset the lines of the body a bit though.
Or narrower ones on the front could you do that with the rims available?
My other recommendation is do one thing at a time and make big adjustments so you know definately what the effect of the change was.
For example if its over-steering now then try and do enough that it'll under-steer then at least you'll have book-ended the problem and
know the range of settings you need to work in.
[Edited on 7/2/07 by Doug68]
|
|
|
Fred W B
|
| posted on 7/2/07 at 08:13 AM |
|
|
Looking awesome Steve, congrats on getting some laps on the car.
You are showing admirable self restraint, letting someone else do the pedalling.
Have sent you the brake spread sheet Raz revers to, as well as one I put together on suspension travel and rate calculation, as per Staniforths
books.
Cheers
Fred W B
[Edited on 7/2/07 by Fred W B]
|
|
|
RazMan
|
| posted on 7/2/07 at 08:20 AM |
|
|
quote:
Originally posted by sgraber
So any other thoughts? Don't the pads sound suspect?
It depends on the compound you are presently using - I am using Greenstuff and suspect they need to be a softer compound for road use although they
seem about right for track use (still a bit 'wooden' though).
I have heard that guys with lighter cars get better results with the budget pads and sometimes even standard calipers so that might be worth a
look.
Another option is to move the calipers outward from the hubs on bigger discs, therefore increasing the leverage factor.
[Edited on 7-2-07 by RazMan]
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
|
|
|
chockymonster
|
| posted on 7/2/07 at 09:11 AM |
|
|
oh, and EBC pads suck!
PLEASE NOTE - Responses on Forum Threads may contain Sarcasm and may not be suitable for the hard of Thinking.
|
|
|
monopoot
|
| posted on 7/2/07 at 10:22 AM |
|
|
I heard of rear midengined cars running 165 wide (narrow) tires at the front to overcome the oversteer!
|
|
|
Dantheman
|
| posted on 7/2/07 at 10:32 AM |
|
|
Would a rear spoiler get rid of some of the oversteer?
Well done, btw. Reading about your project is really inspiring me to get a move on with mine. I'm hoping to start building this year.
[Edited on 7/2/07 by Dantheman]
|
|
|
ned
|
| posted on 7/2/07 at 10:40 AM |
|
|
quote:
Originally posted by Dantheman
Would a rear spoiler get rid of some of the oversteer?
I'd severly doubt it, I'd be guessing that at the speeds involved the aero factor isn't all that great (most production cars with
auto rising spoilers eg porsche, vw corrado storm etc only rise properly at 60-70mph+and doubtful make much difference below 100mph) most likely to be
mechanical grip and hence the spring rates which Steve is already going to change.
Ned.
[Edited on 7/2/07 by ned]
beware, I've got yellow skin
|
|
|
monopoot
|
| posted on 7/2/07 at 10:55 AM |
|
|
Could there be a little roll steer? You could, as a last resort, change the position of the steering rack to have it counter steer a little. The book
"competition car suspension" from Allan Staniforth could be a great help in understanding and wisely changing the set up of your car.
It's a highly recommended read!
|
|
|
suparuss
|
| posted on 7/2/07 at 01:43 PM |
|
|
congratulations on your first proper run! you ve got this far so im sure youll sort it. good luck!
|
|
|
kb58
|
| posted on 7/2/07 at 02:05 PM |
|
|
It sounds like the pads and brake disks haven't be properly bedded in. Have they?
About the oversteer, it sounds like rear toe-out in bump (bumpsteer). Check using a string and floor jack. While you're at it, check the front
too.
Is the wheel rate roughly 1/2 the sprung weight at each corner of the car? Not spring rate, wheel rate? Very stiff rear springs could cause the
oversteer, and an ARB will only make it worse, if installed at the rear.
[Edited on 2/7/07 by kb58]
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
|
|
|
sgraber
|
| posted on 7/2/07 at 02:09 PM |
|
|
Wow, thanks for the responses gentlemen. The brake system has been gone over several times to make certain there are no issues. BUT - I'll do it
again. Maybe I need someone ELSE to do it.... 2 pair of eyes and all that.
Fred, I got your spreadsheets and am going to use them today! I am very excited to get those, so thank you!!!!
I'll keep you updated with my findings.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
|
|
|
