JoeMag

Putting brake lines on the new race car. What size should I run?

...what factors influence what size I should run?

Noel

Hey Joe, How have you been?

You might want to post this question in the regular forum or on Pelican and look for a guy named Bill Vernberg. He is an expert with such questions. However, from what I know, the main thing that influences the size of lines is the size of your master cylinder. You need a big enough MC to engage the brakes in one pump without the pedel going to the floor and conversly one that is not too big that you loose feel. Non-standard stuff may require some mixing and matching.

How is the old Nelson Ledges track? I was at Mid-Ohio this Spring Driving a friends Sc with a 3.6L. I just love that track. But other than that, I don't get back to Ohio much anymore.

Noel

A930Rocket

I think -3 is the usual size.

Greg A

Noel,

It's Bill Verburg

Greg A

Noel

You are correct sir. Thanks.

Matt Romanowski

For soft lines you want -3, -4 generally has too much volume. For the hard lines, I'd run 3/16. If there are no lines in the car, I'd do it all with SAE fittings so the adapters are easier and cheaper. Plus, I'd use the generic premade braded lines that are available.

BC

I was just trying to figure this out myself, as I have to replumb a whole race car, but I have to use the originally speced Master and slaves, as there are no real options. I was going to use -4, which is 1/4 inch. -3 is 3/16.

If you look at it, there is quite a bit of difference between the two sizes, so its a big question. More fluid mass means less more temp resistance.

Matt Romanowski

-4 Doesn't tend to work well on brake lines. You end up with too much volume to move in the lines. Almost everyone uses -3.

Professor Helmüt Tester

Maybe I'm missing something here (but I don't think so...) -

Isn't it simply the amount of volume required by the piston to move that defines the fluid flow ? The size of the line should have nothing to do with it. The size of the line MAY have some influence on how fast that fluid will flow, but at the pressures and volumes extant in brake systems, it probably is minimal. Also, the difference in line diameter may have some 'elastic' influence...but somebody else can calculate that.

This I know for sure: Keep the length of 'flexible' lines in any braking system to an absolute minimum. Flex lines are a WHOLE LOT more elastic than hard line, and you will notice a 2-3' difference in flex line length (total system length) in brake pedal feel. About 10 years ago I ended up re-plumbing a race car for somebody who thought it would be 'easier' to just run flex lines every place that it would be 'inconvenient' to bend/flare/install hard lines. Har....brake pedal was like stepping on a wet sponge.

chris walrod

You'll never build enough pressure with -4 line. -3 is typical, -2 for long runs such as from the rear master cylinder (in a dual setup) to the rear splitter tee, then -3 out to the rear calipers from there.

And of course, there are many factors that play into line sizing like m/c diameter, pedal ratio and caliper pistion diameters.

BC

Then I will too.

kurt M

I am with the good Dr. on this one. Keep it simple and use as much hard line as you can. A larger bore hard line will have more fluid in it but as it is part of a linear hydraulic system the pedal movement is 100% based on the flow of fluid at the other end along with any system component expansion. Within reason the bore of the tubing has nothing to do with pedal movement from resting to full piston movement. (I guess you could make a tube a foot in diameter and possibly get some fluid compression #s to be large enough to be factored) As the system is resting the tubing is filled with fluid already. The pedal and MC movement from resting to full compression is equal to the amount of fluid needed to move the pistons in the calipers and to make up any pressure based expansion of components. Pedal movement is from the movement of the stuff at the other end not the amount of fluid in the system. (again this is sizing within reason, you could make a stupid out of ratio system that introduced unwanted variables)

You might be able to calculate the slightly increased inertia of the larger fluid mass in the lines but I bet it would be largely offset by reduced flow resistance if all the fittings and fluid movement device bores were sized up as well. Not the MC and caliper pistion size the equipment between them. Built right you might end up with a faster reacting, sharper feeling system but I bet that overall it would be not much.
As to an added thermal capacity from a larger fluid mass. This will not add much if any as the fluid in the system and calipers is not circulating. The fluid in the calipers largely just sits there and a small % is added and released each time you cycle the brakes. The fluid moved into and out of the binders is very small overall to the total amount in the system. As it is released it only moves a short distance in the line on the caliper and is the same fluid shoved back in the next time you brake.
There are some very complex looped systems in use in some exotic equipment. It keeps the fluid moving and has coolers in the loop to cool the fluid and calipers between cycles.
Larger diameter hard line tubing will not hurt not is likely not needed. You might have problems getting fittings to translate from the larger than standard tubing to existing devices so this looks like a good time to go with the flow and keep it standard.

I think Bill VerNberg is Bill Verburg’s redneck ½ brother from down South.

924RACR

I presume the good Doctor means 2-3", not 2-3' difference in flex hose length?

I know we look at line size in Modulation/Chassis Controls, when trying to pump fluid to those calipers - going to an 8mm line vs. a 6mm line, trying to fill big truck calipers when the fluid's cold and sluggish... it can help a little, we're talking on the order of less than half a second to lock pressure... but none of that really matters here!

I am surprised to hear that, with such large calipers, which no doubt consume quite a bit of fluid, there's no great appreciation of the larger lines (8mm/-4)?

JoeMag

Interesting info... I forgot to mention that i was looking at using bigger calipers (gt3r 4piston front and 993rs rear).

I didn't mention this in beginning to steer conversation.

-- pegasus recomments using -3 lines for hardest pedal over -4 for the braided lines to caliper. maybe it has something to do with -4 line expanding more than -3.
-- i asked tilton and they said to use -4 brake lines. ...that just didn't seem right.

I did ask over on pelican and bill recommended the 3/16" (~4.5mm) or the 6mm which he said was standard 993.

I was think'n along the same lines that I thought tubing size (disregarding tube expansion) would make a difference in amount pedal travel, but makes sense to me it doesn't now.

BC

For going from the Porsche sized 1.0x10 fittings on the master and slaves (I have to plumb the clutch too), you have the choice on -3 or -4.

http://www.pegasusautoracing.com/gro...=BRAKEADAPTMET