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

GTV6 I believe. You can usually find them on eBay. I don’t know it they will fit rear. Same mounting and spacing as an M caliper so if a front M caliper will fit in the rear then it should work but it doesn’t sound quite kosher to me.

Yes GTV6. I have a set on the back of my 914-6. They work quite well.

Matt

That's good to hear Matt.
Have you worked out the emergency brake yet ?
If so...do tell !

The Suby conversion car I just sold had a pair of tangerine racing e-brake adapters installed. They are used in conjunction with 911 e-brakes. It’s a super clean install that looks factory. I would do it again.

I also used the tangerine kit with early 911 emergency brake. It passed inspection but they could use some adjustment.
My front calipers are Boxster and the rear Alfa. Lets just say it stops fast...
Matt

A 48mm piston is way too much for the rear of a 914. Tge 4 cylinders used 33mm, the 914-6 a 38mm.

I was hoping to find a light weight caliper suitable for the rear but your point is well
taken.
I do intend to adapt 911 Ebrakes.
What caliper is suitable for the rear with vented rotors, a 19mm or 23mm master
and 911S alloy front calipers ?

911M caliper. S front & M rear were factory spec for the mid 70’s turbo. That was a heavy car.

48mm to big? How about with adjustable proportioning valve?

Matt

I imagine that would work but then you’re spending a couple hundred dollars extra just to loose a couple pounds. Not a bad thing but an expensive way to loose weight. It’s always nice to build around the bias that the Porsche engineers figured out.

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.

Good info. So what should I do? I have Boxster fronts and the Alfa rears? What would be the ideal front and brakes set up for a track/road car?
Matt

How big are the Boxster fronts or what size are Boxster rears. Figure out the ratios and see if you are in the ballpark. Ratio might be better than S front, Alfa rear.

I just bought a set of front and rear Boxster calipers. I figured it would make things easy(er)

I have base Boxster front calipers. I will look into the size of them. I have many other projects to do on the car first.
I have used the brakes very hard and never had the rear wheels lock.

Matt

Hey, if it works, it works. (IMG:style_emoticons/default/beerchug.gif)

@rgalla9146

They were used on 85-86 GTV-6 and the model that rep kn aced it in 87.

I installed SC's on the front with 48mm pistons and moved the old fronts to the rear 42mm. Works great. Four years no lock ups with auto cross and hard street driving also with a T replacing Proportioning valve. just no hand brake (OK with Me). Best, Mark

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.

The Alfa calipers on the front are a neat replacement for M’s because not only are they half the weight, they have a large pad. They mate up great with a 914-6 rear caliper.
If you already have M’s on the front, it’s just the cost of the calipers and some hardware.

If you are starting out from scratch, these big brake options are expensive. Remember, brakes really only see mass x velocity. Horsepower doesn’t really come into the equation.
That being said, my cars are big model toys to me so I built them the way that makes me happy. Cool looking brakes are one of those items that I just want what I want.