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Thread: Nova Kitcar Subaru flat-six PPC magazine project car or scoobynova.

  1. #581
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    I have taken my own advice and purchased some extended pushrods for the 3 master cylinders in my pedalbox.

    I calculated that I needed a pushrod length of 90-94mm to give me a good range of adjustment, sure enough I found a set of 5 pushrods @92mm on Ebay, they arrived today.

    However, what I thought was 92mm is in fact 88mm as the length quoted *includes* the head of the pushrod, so I have a 88mm pushrod with a 4mm head.

    What I am saying is the pushrods are a few mm short.
    What makes things worse is that I advised a Singapore-based member of forum royalty to purchase the same item...

    Anyway the pushrods still fit; I have >6 full turns into the Clevis mounts, so they are solid enough, you will see in the pic that mid-way down the pushrod I have locked 2 bolts together, used to turn the pushrod (or remove it) very handy to adjust the pedal position.


  2. #582
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    Quote Originally Posted by BlueNova View Post
    Must say I'm really pleased with Machine7's help during the current crisis (as I said before, other suppliers are available though!)

    Anyway, why not give them a call with your photo, and find out if the ones they sell could be engineered to fit your hubs and then find an engineering workshop, or perhaps a friendly Euro Nova Member (who has a few Nova bodies and a road going Avante) with lots of tools ... I'm sure you know who I mean! who could fine tune it to fit?

    Must be better than buying from the States when Trump is leading them into an even longer recession than Europe's likely to have!!

    (Sorry for the wee political outburst)

    Alistair
    I am already in discussion with a certain individual who may own multiple Nova bodies - amongst other Subaru-powered vehicles. It may even be the same person :-)

    Pinging Machine 7 is a good should as well - thanks.

  3. #583
    Quote Originally Posted by steve View Post

    What I am saying is the pushrods are a few mm short.
    What makes things worse is that I advised a Singapore-based member of forum royalty to purchase the same item...

    No worries Steve, they were cheap enough for mistakes not to matter. I'll be watching with interest to the final solution

  4. #584
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    I have been doing some research on how to set-up a brake balance (bar) system, and based on this article (https://www.joesracing.com/master-cylinder-math/) I plan on doing 2 things:

    First, the balance bar itself. In the pic below, you'll see that with the pedal at rest, the balance bar is not parallel to the front bulkhead, the top clevis mount is further away from the bulkhead than the bottom clevis mount.




    It is OK to see this with the pedal at rest, in fact, most set-ups should look like this. Why?

    When you press the brake pedal, both Master cylinder pushrods move forward together, and when they 'bite' (i.e. when the pedal stiffens and pads make contact with rotors) at that point, the balance bar should then be parallel to the bulkhead.

    The explanation is that the top Master Cylinder in the pic, feeds larger 44mm caliper Pots and the pushrod needs to move further (push more fluid) to move the pots/pads to the biting point.

    The bottom Master Cyl, which feeds a smaller 32mm caliper pot, does not need to push the same amount of fluid to move the pot/pads to its biting point. It does not need to travel as far.
    (Example assumes that both Master cylinders are the same size - same bore diameter)


    Ok moving on.
    Let’s assume that your balance bar is now parallel to the front bulkhead when the pads 'bite', and that you have the balance bar set in the mid-position: 50% of your 'pedal power' goes to the front Master cylinder, 50% to the 'rear' Master cyl.

    This even split of pedal power doesn't mean you have 50/50 balanced braking at the wheels however, that will depend on your Master cylinder bore size/diameter and caliper piston diameter (& quantity). This is where things get interesting:

    In my case,
    at the front, I have a 0.625 inch bore (15.9mm) Master Cyl, with twin-pot 44mm calipers.
    at the rear, I have a 0.7 inch bore (17.8mm) Master Cyl, with single pot 32mm calipers (EMPI Kit).


    Using the calculation method explained in the above Joesracing link my current set-up results in a 71-29% Front-Rear brake bias, not great for a Nova.
    (Calculation assumes the balance bar in the mid-position and similar sized rotors/discs front and rear - which mine are)

    This imbalance is caused by a greater mechanical advantage in the front vs rear set-ups,
    My front brake system has a smaller Master Cyl and larger caliper pots, giving it a big mechanical advantage over the rear.

    The fix is to increase the bore size of the front Master cylinder, e.g.
    with a 0.7 inch bore Master cylinder, I get 66-34% front-rear,
    with an 0.8 bore, I get 60-40% front-rear


    My current plan is to go for a ~0.8 Master Cyl to give me 60/40 front-rear braking and use the balance bar to fine tune the system when the car is on the road.

    Any thoughts?
    Last edited by steve; 31-03-2020 at 11:22 PM.

  5. #585
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    Blimey
    I never realised my initial problem and thoughts could create such a topic! I knew the theory but not the maths, so glad I was going in the right direction. My friend told me to use a .75 on the front !
    Will now add this.
    The theory is for an even weighted car? Looking at the difference in front to rear weights of a nova would a .8 be too excessive?

  6. #586
    Played with my bias for ages and ended up fitting a cable adjuster. Made my own from the old speedo cable after I went digital and just bought a nice knob to fit.
    Off setting the push-rods using the bias makes quite a difference but of course getting it close in the first place. I am sure I will have to use a bigger master on the 4 pot Wilwoods and the current 3/8" on the rear discs.
    I had to modify the throttle pedal of course to clear the cable.
    IMG453.jpg



    The opinions expressed in my posts may not be made in a sound mind and should be taken in the spirit intended, Jack Daniels is fine.
    Some people see things as they are and ask why? I dream things that never were and ask, why not?” JFK

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  7. #587
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    Quote Originally Posted by Buffy View Post
    Blimey
    I never realised my initial problem and thoughts could create such a topic! I knew the theory but not the maths, so glad I was going in the right direction. My friend told me to use a .75 on the front !
    Will now add this.
    The theory is for an even weighted car? Looking at the difference in front to rear weights of a nova would a .8 be too excessive?
    Hi Mark, Yeah when you mentioned you were changing your Master Cyl after the Dirk Mod, it prompted me to research this, and I now see that my set-up is miles out for the weight distribution of the Nova (40/60), my brakes are massively front-biased.

    The numbers quoted in my post above, e.g. 71-29% Front-Rear is the clamping force of the calipers, i.e. if you press the pedal with 100% force, 71% goes to the front calipers.

    If your disk rotors are the same size front vs rear (mine are) then the clamping force (71-29%) is the brake bias of your car.

    Weight distribution does come into it of course, if I was running an AC Cobra, 71-29% Front/Rear would probably work well.


    But for a vehicle with 60% of its weight at the rear, and very little weight transfer under braking, I am thinking that 45-55% would be the right bias (in my case that would need a Master Cyl of around 0.9!)
    and then fine-tune with the balance bar from there.

    Can you tell me what Master Cyl you are using at the rear of your car please? and the caliper pot size (if you have the EMPI kit then it's a 32mm single).

  8. #588
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    Steve
    I have the empi kit on the back and a .7 master cylinder.
    It’s interesting ( and now frustrating ) for when I took the car for mot ( want to at the moment but difficult to class as essential ! ) I always struggled with the rear brake test. Others have also mentioned this with their empi set up.
    So are you thinking, .9 on the front and .8 on the rear ?

  9. #589
    Don't forget, the bigger the master the more effort needed. a smaller master may mean more travel but more effective.



    The opinions expressed in my posts may not be made in a sound mind and should be taken in the spirit intended, Jack Daniels is fine.
    Some people see things as they are and ask why? I dream things that never were and ask, why not?” JFK

    http://ukhozi.page.tl

  10. #590
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    Quote Originally Posted by Peter View Post
    Don't forget, the bigger the master the more effort needed. a smaller master may mean more travel but more effective.

    You have got a point mate, you lose mechanical advantage with bigger Master cyls...

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