Alfa Calipers Options

[rgalla9146]

What Alfa Romeo alloy caliper (from what model car) is suitable to replace 3"
front calipers ?
AND...is it suitable for use on the rear of a 914 with 911 vented rotors ? provided
911 emergency brakes are adapted.
TIA

[technicalninja]

Every proportioning valve I've messed with REDUCES pressure and flow to the rear.

The valves do not have the ability to increase pressure or flow to anything.

You could put a real proportioning valve in backwards and reduce pressure to the fronts but that sounds like a poor decision IMO.

Balancing the caliper piston sizes is the best way to gross balance a system and the 48mm pistons appear to be too large for application on the rear.

Found this in the classics forum and it's appropriate for this thread.

http://www.914world.com/bbs2/index.php?showtopic=55559


One nice thing regarding the original relief valve is that it doesn't care about balance at all. It just stops all pressures above 525 from reaching the rear calipers.

It's adjustable as well. Testing and adjusting it might be sketchy...

It's too bad PatMC is right.
Looked like a possible candidate for the rears.
Still looks like these could be used on the front, however.
They would be the same as the BMW calipers, just made out of aluminum.

Final thought. The ratio of front to rear that Porsche used is 42/33 4 cylinder and 48/38 on the six cylinders. On a 4 cylinder the size of the rears is 78.5% of the fronts and on the six it's 79.1%.

Staying close to this 80% ratio is the way to go in my book.
Most cars use a front to back ratio of 75-80% so Porsche was "normal" in how they set up brake bias.

Proper fronts for a 914 with 48mm rear pistons would be nearly 60mm on the fronts and you'd need a much larger master.

[PatMc]

It's too bad PatMC is right.
Looked like a possible candidate for the rears.
Still looks like these could be used on the front, however.
They would be the same as the BMW calipers, just made out of aluminum.

Final thought. The ratio of front to rear that Porsche used is 42/33 4 cylinder and 48/38 on the six cylinders. On a 4 cylinder the size of the rears is 78.5% of the fronts and on the six it's 79.1%.

Staying close to this 80% ratio is the way to go in my book.
Most cars use a front to back ratio of 75-80% so Porsche was "normal" in how they set up brake bias.

Proper fronts for a 914 with 48mm rear pistons would be nearly 60mm on the fronts and you'd need a much larger master.

You need to look at surface area, not diameter....

42mm = 2.14sq in
33mm = 1.32 sq in

48mm = 2.8 sq in
38mm = 1.75 sq in.

Boxster frt( 36/40mm pistons) = 3.53
Boxster rr (28/30 pistons) = 2.0


Now you can calc your ratios...but those are just hydraulic ratios.

Now you need to determine the effective radius in each of your examples (spindle centerline to centerpoint of brake pad friction puck) and take that into acct.

Very few vehicles have anywhere near as much rear brake as your 75-80% figure suggests.

I think you'll likely find that putting the stock brakes in excellent working order with quality pads will result in excellent performance and fewer headaches. The rear calipers don't weigh much...5 or 6lbs each. The fronts are a bit heavier but not much.