turbo time
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| posted on 7/12/04 at 10:40 PM |
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Brake proportioning
I was planning on using the distribution block from the donor car, with a proportioning valve for the fronts, but I honestly don't know how much
I will need to change the brake bias to compensate for the weight distribution difference, which I suspect could be nearly the oppositte of the donor.
The donor weight distribution was about 62% front, 38% rear, and my car will probably be nearly the oppositte of that, likely 42/58 with the gas tank
full. (maybe I'll just flip the distribution block around, haha). The Donor distribution block was off a FWD eclipse turbo, and is listed as
having a 597PSI split point and a 0.3 decompression ratio, so what does everyone think about using it with a prop valve for the fronts to lower the
pressure, should it work out ok? The other important part of this is that rather than having small rear brakes, this car has all four hubs/brakes off
the front of an eclipse, that means 10.5" vented discs at all corners, which makes me think that perhaps more pressure to the rear calipers is
better than less, especially because of the tendency the car will probably have to lock-up in front.
Oh yeah, I have never built a car before, so these questions will keep coming  .
[Edited on 7/12/04 by turbo time]
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sgraber
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| posted on 7/12/04 at 10:48 PM |
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Is it too late to suggest a dual master cylinder setup with an adjustable bias bar? 
Works really great for when you aren't certain what the bias should be. Esp. since you are using the same size brakes on all 4 corners.
Just a thought.
[Edited on 12/7/04 by sgraber]
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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turbo time
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| posted on 7/12/04 at 11:07 PM |
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I am just using all the stuff from the donor, including the whole power booster(yes, I'll have power brakes), pedal box, and clutch and brake
cyl's. Don't get me wrong though, I'd go your route if I could spend more than $2005 on this project.
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sgraber
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| posted on 7/12/04 at 11:18 PM |
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I hear ya.
BTW I have spent less than $1,500 on mine to get it to the point where it is...
What is your wheelbase and track on that neat machine you are building? and do you have a website for it where I can browse more photos? What did you
end up doing about the rear suspension? I saw in your photo archive how tall they are to your chassis...
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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Tralfaz
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| posted on 8/12/04 at 02:52 AM |
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quote:
Originally posted by turbo time
I am just using all the stuff from the donor, including the whole power booster(yes, I'll have power brakes), pedal box, and clutch and brake
cyl's. Don't get me wrong though, I'd go your route if I could spend more than $2005 on this project.
Oooo!!! Is it to be a GRM contest car?
Brian
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Ratman
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| posted on 8/12/04 at 06:50 AM |
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I have a few friends who have built cars with the same (ex FWD) brakes front and rear. Often, even with the extra weight of a midi at the rear, this
same-all-round system seems to work out just right. If it doesn't, it will be quite close, and you can just add a proportioning valve to the
stronger end. I used to think that the balance bar set-up was ideal, but they have their problems: if you get a failure in one circuit, they can jamb
hard over and you have no brakes. Also, even the name-brand bars have been known to snap. Its not good engineering to put a threaded rod into bending.
So.. my recommendation is to build it dead simple. Same brakes all round and a regular basic donor car tandem master cylinder. nothing more. Wait till
you see how it performs before going any more complicated. Cheers, Brian
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RallyHarry
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| posted on 8/12/04 at 03:22 PM |
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Steve, what pedalbox are you using ?
Cheers.
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derf
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| posted on 8/12/04 at 07:32 PM |
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Steve's pedal box is right, I have an extra tilton model similar to his setup that I'm ot using (for a single clutch and dual brake, does
not include brakes, bias bar or anything else, it's just the box). I think it might actually be the same one, only mine is silver. I'd be
willing to sell it, shoot me a u2u.
Along the lines of a proportioning brakes/biasing to the front or rear. You always want to have the front brakes do more of the work, no matter where
the majority of the weight is on the car. The front of the car dives, taking weight off the rear and will apply a different amount of weight to the
front wheels than it's originally setup with. That, plus while braking and cornering it could spin you slightly, making the car oversteer.
Proportioning more braking power to the front will give the car either a neutral feel or slight understeer.
All cars from the factory are setup this way, it is safer and more predictable, as well as it gives shorter stopping distances.
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sgraber
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| posted on 8/12/04 at 07:42 PM |
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quote:
Originally posted by RallyHarry
Steve, what pedalbox are you using ?
Cheers.
I use a wilwood pedalset purchased from an ebay store about 2 years ago. It included the bias bar. I can't say that it's still available.
I personally think that the spacing is a little tight for my big feet, but with the right shoes it's ok. The M/C's are CNC brand. 3/4 for
the brakes and 5/8 for the clutch.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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Aloupol
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| posted on 8/12/04 at 08:52 PM |
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I shouldn't use a pressure limiter at the front.
With that setup you will limit the front braking when weight transfer allows it to be the higher.
Even on a car with 60% weight on the rear end a 50/50 braking is close to the optimum because on hard braking conditions the weight transfer will
help.
[Edited on 8/12/04 by Aloupol]
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turbo time
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| posted on 9/12/04 at 03:20 AM |
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Steve:
Wow, only $1500, I would've figured that those seats alone would be a quarter of that, it'll be nice when you have a $75k-looking car for
just 2k .
Looking at the budget, I spent most of my money on bolt-on engine parts, intercooler, stage 3 clutch, 255 lph fuel pump, etc..
I don't remember what the wheelbase was to the T, but when I measured it, it was about 105", even though the total length of the car will
only be 134", it'll have zero overhangs, hopefully it works out to a really small polar moment of inertia. The track is whatever the donor
was, I think 58" or so.
The rear suspension isn't doen yet, I just got all the parts I was waiting for. I was waiting for the seasons-end racing flea market.
(professional teams, purging their extras after the season). I got 28 aluminum rods, in various lengths, all with heim joints on both ends for $25, 6
Nascar-style control upper control arms for $15 (2 each in 3 different lenghts, no I don't like nascar, haha), a coffee can with about 30 heim
joints in it for $3, and an aluminum Appleton 9lb steering rack, 1.5 turns lock to lock for $20. So, I'm all set to start on the suspension
now.
About the GRM challenge....hopefully, if the car gets done in time, I'll run in '05, but it's up in the air right now.
Ratman and aloupol:
Good plan, I'll keep it simple and see how it works out. I think I'll simply get two of the "Tee" pipes and run them directly
split front and rear from the master cyl. Then if it needs to be changed up, I can always do it later, as mentioned, that method seems to make logical
sense.
-Thanks
[Edited on 9/12/04 by turbo time]
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krlthms
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| posted on 9/12/04 at 05:16 AM |
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quote:
Originally posted by turbo time
Steve:
Wow, only $1500, I would've figured that those seats alone would be a quarter of that, it'll be nice when you have a $75k-looking car for
just 2k .
Looking at the budget, I spent most of my money on bolt-on engine parts, intercooler, stage 3 clutch, 255 lph fuel pump, etc..
Hello TT,
I seem to recall reading somewhere about the "1.6 rule". I think it is to do with the ratio of wheelbase to track. Have you come across
this?
Also, where is a good place to look for Nascar flea market (I am in Chicago)?
Cheers
KT
I don't remember what the wheelbase was to the T, but when I measured it, it was about 105", even though the total length of the car will
only be 134", it'll have zero overhangs, hopefully it works out to a really small polar moment of inertia. The track is whatever the donor
was, I think 58" or so.
The rear suspension isn't doen yet, I just got all the parts I was waiting for. I was waiting for the seasons-end racing flea market.
(professional teams, purging their extras after the season). I got 28 aluminum rods, in various lengths, all with heim joints on both ends for $25, 6
Nascar-style control upper control arms for $15 (2 each in 3 different lenghts, no I don't like nascar, haha), a coffee can with about 30 heim
joints in it for $3, and an aluminum Appleton 9lb steering rack, 1.5 turns lock to lock for $20. So, I'm all set to start on the suspension
now.
About the GRM challenge....hopefully, if the car gets done in time, I'll run in '05, but it's up in the air right now.
Ratman and aloupol:
Good plan, I'll keep it simple and see how it works out. I think I'll simply get two of the "Tee" pipes and run them directly
split front and rear from the master cyl. Then if it needs to be changed up, I can always do it later, as mentioned, that method seems to make logical
sense.
-Thanks
[Edited on 9/12/04 by turbo time]
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turbo time
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| posted on 10/12/04 at 04:43 AM |
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quote:
Hello TT,
I seem to recall reading somewhere about the "1.6 rule". I think it is to do with the ratio of wheelbase to track. Have you come across
this?
Also, where is a good place to look for Nascar flea market (I am in Chicago)?
Cheers
KT
Nope, haven't heard of the 1.6 rule? Although I'm not certain on either one of those measuremnts I listed. I know wheelbase is front to
rear wheel hub center, but I'm looking for clarification of "Track". Is the track measurement from left hub bolt to right hub bolt?
(That's what I have been going by), The overall width of the bodywork? or the distance from tire sidewall to sidewall? I know the only
difference between my car and the donor, in terms of dimensions is height (obviously) and mine is about 6" longer in wheelbase, That's all
I wanted to mess with, and that was mainly because I thoguht it would be safer, as I'm not well versed in the handling of mid engine cars, so I
thought the extra wheelbase would probably save me from full rotation in some situations. I'll see how it works out in time I guess....
About the flea markets, the ones I went to were mostly dirt track/ sprint car teams...I went up to PA just to go to them. The only way I knew about
them was word of mouth....I reccomend going to local race shops and asking around, probably the best way to find out about ones in your area.
[Edited on 10/12/04 by turbo time]
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Rorty
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| posted on 10/12/04 at 05:53 AM |
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Ratman, I've grown up around cars with threaded bias bars and just took them for granted. I never thought of what a bad design the bar really
is! Mind you, I've never seen one break, only bend slightly (still made it impossible to use).
The 1:6 rule is highly debatable. Some of the world's best cars don't come anywhere near it. A lot depends on what you want to use the car
for. Higher ratios are good for high speed straight line stability, but smaller ratios are better for high manoeuverability like on a twisty race
circuit.
Track is measured from centre of tyre to centre of tyre at wheel centre height (to allow for camber).
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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