Brake upgrade isn't enough

[rolls 912]

Hi folks.
I have a 912 running a 3.2.

I upgraded the stock brake system to M calipers with gas slotted rotors. This is sufficient but not conducive to spirited driving. I also notice the m calipers wear marks on the rotor don't utilize the entire disk.

My questions for those in the know please are:
What's the next step up caliper option?
Would I need to replace the rotors or would they work with larger specified calipers?
Is it a bolt on application or will I need captor plates etc?

Thanks to those that reply....

I don't want to offend you, but a 3.2 in a 912 body and you just want to improve your braking system? What about suspension, specifically the rear, is not build for 200+ hp. "Spirited driving" without front and rear stabilizers? Upgrading to a chassis suitable for safe driving with that torque and hp would need a late '70's suspension. Well you better could have spent your money on a nice 911 SC and you would have had power brakes for free.

Otto

[Jaems]

The problem with putting a larger engine in one of these older 901 bodies. The suspension contact point are not strong enough to continually to take the kind of forces and the weight of this bigger engine. They will need to be reenforced to handle it.

These cars were design for the engines and tires of their day. Putting more weight and torque on the rear will continue to stress the suspension contacts until they will tear out , especially with the wider sticky tires of today. Beside the suspension contact points you will need to watch the area under the rear of the door longitudinal's, for stress cracks. The body twists at these points.

You should to go to the brakes for the 85-89 911. You will be over 500kg lighter than a 85-89 car. So you need to be careful with applying too much brake and locking them up; also there will be a lot more oversteer that will need to be addressed. Depending if you have a SWB or LWB car.

I hoped that you have gone to a newer type transaxle like a G50. The 901 series will not take the torque for very long.

The difference between the US and the Europeans, in general, is that the US is very good at putting large cubic inch engines in smaller, lighter, and older cars and the Europeans are very good at getting more HP out of very small cc engines. We learned this the hard way during the muscle car era.


Have fun

[rolls 912]

The car handles beautifully - quite surprising actually. Much better than my 356! i was sick and tired of the spitting solexs etc. EFI - get in and go rain hail or shine. its a hoot to drive.

The 50 / 50 split is only 3 kilos out. externally its 100% stock. G50 is in with custom axles etc. I absolutely love this car and to me, that's what matters.

I'm keen to get back to the brake question please. John kindly pinged pmb calipers... Could anyone that has installed these please comment?

[Jaems]

You might get a better response on the 911 forum. They're more into doing these kind of upgrades that the 912 group.

[JT912]

How can this car be only 3 kilos (6.6 lbs) out from being 50/50 weight distribution? The 912 engine weighed 200 lbs less than the early 2.0L and was still tail heavy. A 3.2L has to weigh more than a 2.0L. What am I missing?

Logic is only the beginning of wisdom ...

[Jaems]

Right on ---Otto

[Matt Monson]

Did you just upgrade the fronts or did you do both front and rear?

When you say that the brakes aren't enough, please describe what that means to you and how it exhibits itself in practice?

[chris_seven]

Originally Posted by Jaems

The problem with putting a larger engine in one of these older 901 bodies. The suspension contact point are not strong enough to continually to take the kind of forces and the weight of this bigger engine. They will need to be reinforced to handle it.

These cars were design for the engines and tires of their day. Putting more weight and torque on the rear will continue to stress the suspension contacts until they will tear out , especially with the wider sticky tires of today. Beside the suspension contact points you will need to watch the area under the rear of the door longitudinal's, for stress cracks. The body twists at these points.

You should to go to the brakes for the 85-89 911. You will be over 500kg lighter than a 85-89 car. So you need to be careful with applying too much brake and locking them up; also there will be a lot more oversteer that will need to be addressed. Depending if you have a SWB or LWB car.

I hoped that you have gone to a newer type transaxle like a G50. The 901 series will not take the torque for very long.

The difference between the US and the Europeans, in general, is that the US is very good at putting large cubic inch engines in smaller, lighter, and older cars and the Europeans are very good at getting more HP out of very small cc engines. We learned this the hard way during the muscle car era.


Have fun

How did you fit the G50?, did you cut out the torsion bar tube and fit 935 Type spring plates which would need to be custom made for a SWB car or did you replace the entire torsion bar tube to one suitable for the G50? I guess the alternative is to shorten the G50 by around 20mm - I have done this once but it is quite tricky. Did you also change out all of the gear shift and gear shift console as the 901 parts would be incompatible with a G50? We fitted a 3.6 and a G50 to a 1969 car which was quite exciting and not quite as much work as would be needed to fit into into a SWB car.

We are just fitting a Carrera 3 motor (3.0 litre) Twin plug and 915 to a 1967 912 and have cut down some steel LWB trailing arms as part of the conversion and this has helped with braking mods. We also made a custom rear sway bar to suit his new arrangement and some investment cast sway bar mounting consoles to prevent damage to the flimsy standard parts.

I assume you have fitted with 911 engine mounts in the back corners and then there really isn't much difference in the hull to any other 911 shell.

The kidney bowl structure didn't change until (apart from late model Targas) until the 964

The torsion bar tubes are virtually identical apart from the trailing arm bracket position and the later brackets are actually a lighter gauge steel than those fitted to the early cars.

The rear seat pans are a little narrower on the early shells but I would be surprised if this made a significant difference to the strength/stiffness of the structure.

The weight of a 1965 911 is typically 1070kg and the 3.2 Carrera isn't a great deal different at 1210kg with about another 10kg when the 915 was replaced by the G50.

The 2.0 litre aluminium engine and the 3.2 unit have about the same weight. The 1969 - 1974 magnesium engines were around 20kg lighter than the 2.0 and 3.0 Aluminium motors.

I am surprised that you weight distribution isn't more like 45/55.

I would agree with comments about sway bars but these are easy to retrofit and a 24mm rear torsion bar from an SC would be a bit better than a 23mm but this size bar was fitted to early Aluminium engine cased 2.0 litre cars and they seemed to be OK.

The brakes could be an issue but shouldn't be too difficult to improve, but having said that we run our 200BHP FIA race car on standard 1965 calipers and solid discs without huge problems.

If you still have the early strut and have used a Front M type Caliper with 3" spacing then you will have a small pad. This Caliper should have a 48mm dia piston.

If you have fitted a vented rotor from this generation of car then you shouldn't have a swept area problem as the disc should be interchangeable with the solid 912 rotor. There could be an issue of you have a 3.2 rotor for the A Type Caliper.

If you still have the separate caliper mounting plate you can remake this to suit a 3.5" SC type caliper with the larger pad. This pad would then be the same size as that used in the Aluminium Calipers fitted to the 1969 911S, 2.7 Carrera RS and 3.0 litre Turbos and should be OK.

If you have retained the early SWB L type Rear caliper you may have 35mm dia pistons and these won't help.

Later SWB cars upgraded this caliper to 38mm pistons but still used the very small pad.

To fit a later caliper is quite tricky and you would need to cut the mounting lugs off the trailing arm and weld on a suitable mounting lug.

You could then fit a Rear M type caliper - again with a 3" lug and a larger pad then the L type unit. This caliper would have a 38mm piston and when used with a 19mm dia tandem Master cylinder would give you a nominally stock 911 brake balance if you fit the SC Front caliper.

If you use a 911T rear M type caliper you could still use a solid rear disc.

If you use a vented caliper and have SWB trailing arms then the only disc you can buy is an early 911S part - I think this is Porsche Only and are about $350 each.

You can modify a late 924S/ early 944 rotor without too much difficulty.

If you have a LWB 911 then you already have the correct rear caliper and can just add a spacer kit and a vented rotor. You would need to change the struts to fit the SC caliper with 3.5" mountings.

I have recently seen a 1965 912 that was imported from the USA and someone had fitted vented front discs and 3" M Type Calipers.

The only problem being that they had fitted M Type rear calipers (38mm pistons) on the front and left the solid L Type on the rear.

Surprisingly the braking was good enough for it to pass in annual MOT Inspection but it was a bit lacking in bite!