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Hi , I am considering fitting the BMW 750 M/C that has been mentioned in past threads and was looking from feedback from anyone that has fitted it . My understanding is that as the front and rear brake cylinders are equal size it can cause issues with rear brakes locking . Is an adjustable brake bias the way round this or will the 5/18 bias valve work as this supplies 50% less brake pressure to the rear above 18 bar ?
I am running some F50 calipers with piston sizes of 40/44mm compared to 993tt 36/44 so although brakes work well the pedal is longer than I would like .
Thanks .
Err... No I am in the right place but thank you ,it's nice to have a reply .
This has been done before , I was just looking for some feedback .
I have gone ahead and purchased the bmw m/c and a small bias valve I will place into the rear brake line within the front scuttle area as I have no need on a road car to be adjusting the balance on the hoof .
I have attached a photo of the bmw m/c next to the one on the car and as can be seen, they are phsically the same size , bolt patterns are good , just the need to tee the front brake pipes together . Also a shot of the front S8 calipers with porsche cayanne discs . These are 330mm but you could run the larger 350mmcayanne or the audi 345mm disc if needed .
Just waiting on some brake pipe. bmw m/c S8 caliper with cayanne disc
In the end, it's critically important to get your F/R bias right. You can do it on jack stands and the procedure is in some past posts, or consult Mr. Google. Just be sure to do it.
MM
PS: Be sure to double flare all your new brake lines!
PSS: Interesting intake plenum! Share some more pics?
Thank you for the reply Michael , I have had a quick google search for setting up the bias as you suggest , if there is any tips you could add from your experience it would be much appreciated .
I have attached a couple of photos of my intakes .
The yellow one is a 3.2 offset 16v , RS2 TB with two aston martin plenum's spliced together which is in the car at the moment .
The black one is a 3L 16v nicosil wet liners , Jenvey TB and a modified 1JZ /968 intake .
And the red is a 3L 16v supra/S2 intake in my other car .
Regards simon
Hello Simon,
Here are several cut and paste descriptions of the method I used for many years on my race cars. It's a simple process and it will serve you well. With your alternate calipers, rotors, and master cylinders you need to start with this method and determine if the adjustable bias will get you there. The Porsche 5/18 pressure limiting valve may lead to issues since this method (below) won't require the >18bar line pressure. Once you're in range, I'm confident this method will allow you to be delighted with your brake investment and their performance.
PS: I really like your intake manifolds and your engine(s) overall. I'd like to discuss them further but perhaps best to start another thread. How about sharing some of your engine details. Happy to comment further on this if you like.
MM
Another method you can use is to put the car up on jack stands and manually check the bias. Have someone sit in the car to use the brakes (or reach and pull the brake pedal by hand). Have them push down on the brake pedal gradually and slowly as you turn/rotate the front tire. As soon as you can’t turn the wheel any more, have the driver hold that pressure on the pedal. Go to the rear and turn the wheel – you should be able to just barely turn it. This will mean the fronts have a little more bias than the rears. This technique might take a few times to get it right, and it’s something that you get a feel for, but it’s surprisingly effective. Again, then turn on the data and take reading right then as to what the numbers are and compare that to past readings. Over time you’ll learn what you and your car likes best.
Brake bias can make a big difference!
The test and check on jack stands will “rough” it in to the right bias, but with experience can be surprisingly accurate. As I wrote in my answer, you want the fronts to lock with a certain pedal pressure, and at that same pressure have the rears turn just slightly. That means there is slightly more bias to the fronts. And that bias to the front is what addresses the load transfer. If there was no load transfer, you’d want the bias to be equal, 50-50, front to rear. But because the fronts do more work when braking, due to the load transfer to the front, they need more “bite” from the brakes. If you follow the procedure in my answer, you’ll find the ideal for the specific car, in those specific conditions. But it will change, as I mentioned in regard to rain. And every car is different. Some could be very close to 50-50 (a rear engine Porsche, because the rears are doing more work due to all the weight at the rear of the car), some closer to 60-40. If you find what works on the track, then test/check it on jack stands by hand and make note of the way it feels, you can tear the entire brake system apart, put it back together, and then set it on jack stands and know you’ll be very close to the ideal bias – to start. And be prepared to adjust as you drive to suit the conditions, and fine-tune it.
Vintage and going strong , still keeping my tools off the floor.
Thank you again Michael , very helpful information . And thank you on the engine comments , the worry is I have two more built 16v turbo engines on stands in the shed just in case.
If I list the engines please feel free to pass comment but the last one might possibly be of most interest .
3L S2 Block , flanged westwood steel liners , Je 8v pistons with valve reliefs cut for stock16v head and k27/ turbo , supra 2jz modified intake , Augment automotive ecu , 6 puck turbo sprung clutch, turbo bellhousing and sensors .
3.28L S2 Block ,flanged westwood steel liners , Ford V8 pistons , Eagle rods, 94mm offset ground crank , stock 16v head , Holset hx35 with t3 .82 exhaust housing , large front mount intercooler , 6 puck turbo sprung 6 puck clutch, vems ecu . The ford pistons sit low in the bore 2.5mm , not ideal squish but saved having to machine the piston reliefs and does not seem to have much effect on performance .
3L S2 Block , flanged westwood steel liners , Je pistons with valve reliefs machined for stock 16v head
2.7L S2 Block, straight steel liners, Arias 968 pistons with the dish machined out for correct CR, this was going to be a 3L but the two cranks I had both had cracks in them so used the 2.5 crank and had some con rods made to the correct length.
3L 2.5L Block , 968 crank , modified with a physical baffle to separate the water flow around the block ( top and bottom ) from the two water pump inlets , nicosil coated mid liners , wills sealing rings , o ringed head , head and block machined for 9/16 head studs , carrillo rods , sodium filled exhaust valves , ground piper cams , wossner pistons , 968 head with variocam ,billet crank pulley with a super damper , billet water pump housing to allow electric water pump to be fitted , Holset hy35 with hx35 wheels , crossover increased in size after wastegate tie in .
The first two are in my cars with the other three engines are waiting for the first sign of a problem.
I can not claim any credit for the last engine as I purchased the parts from Baz at Hartech who was doing this engine as a pet project . His original intention was to use the two separate water outlets on the 968 head for the two flows around the block , ideally going to two radiators as in a boxster . But I intend to have this in my road car as I like the tighter tolerances of the nicosil , so have fitted a billet pump housing to allow an electric water pump which may help the flow.
I have attached a couple of photos , the first shows the ford pistons in the block and how they sat down in the bore , 2 and 3 is the modified 2.5 block and the last shows how I cut and welded the intake .
A hobby that gets out of control !
Hi Simon,
great motors. Did you consider going dual cam pulleys on any of these given that the sprockets on the production cams were a valve train weak point?
Hi Tim , I have never come across a head with a broken sprocket , although I have seen our German friend on you tube fixing his .
I did buy some toyota sprockets once to look at doing this but decided to keep things simple.
When swapping M/C's on a 951, be aware that Porsche used two different manufacturers for the 'stock' M/Cs for a 951. The little known fact is that the M/Cs from Porsche for the 951 are not completely interchangeable, but need to be paired with the correct OEM brake booster (two different boosters). The reason is because the ATE M/C has a shorter shaft (~12mm) and needs to be paired with the ATE booster. I had similar soft pedal issues with my 951 when I was trying different M/Cs with my Big Black calipers. Once I matched the shaft length to the correct booster the soft pedal problem disappeared. By the way, I also tried the BMW M/C, but felt that the stock 951 M/C paired with the 5/33 brake valve work best with my BB calipers.
01-01-2022, 07:15 AM
BMW M/C
