ProMAX Level 4

[pauljmcnulty]

Having been driven around Donnington in Paul Smith's 3.2 and John Sims' hose-blowing thingy.....and Darren Anderson's turbo at Bedford.

I can safely say that there is a great deal of satisfaction in actually keeping up with the GT3s and other slightly more expensive cars. Sort the tyres and suspension and a 350-400bhp 944 has everything you'd ever need either in a straight line or on a track.

 

[944Turbo]

keeping up? surely you mean passing

 

[Riverside]

ORIGINAL: Fen

I really like the idea of 1/4 miling, but I wouldn't do it in my 944. I'd want something with strong enough transmission.

One of your other cars maybe?

 

[Fen]

'Fraid not - the RS6's biggest weakness is its gearbox so already I tend not to deploy all the torques in 1st and 2nd and the diesels wouldn't really be much fun. I'm thinking more of a Monaro or something purposed modified with a big V8 once I get to NZ.

 

[333pg333]

That's it Fen, get a big Aussie Muscle car in place of the namby pamby i4 Kraut rubbish!![]
On another note as Riverside mentioned it, just what do we understand about sprung and unsprung weight? I am looking into some 6 pots with large rotors but of course many people bring up the 'unsprung' weight dilema or question. Just how much more are we likely to feel / suffer by adding say 20lbs unsprung to each corner than we would be carrying a 50lb package for example?

ORIGINAL: Fen

'Fraid not - the RS6's biggest weakness is its gearbox so already I tend not to deploy all the torques in 1st and 2nd and the diesels wouldn't really be much fun. I'm thinking more of a Monaro or something purposed modified with a big V8 once I get to NZ.

 

[Fen]

i4 as in inline 4? My Kraut rubbish already has a V8... (and an inline 6 that I hope not to have for much longer, the i4 isn't a car; it's an appliance to transport me to and from work).

On the subject of unspring weight my only back to back was in am MX5. I took off the awful wheels Mazda's UK importer fitted to my "Classic" special edition that weighed quote a lot and replaced them with some Rotas of the same size that weighed a lot less (I think I dropped from 12kg to 5.5kg per rim - plus tyres of course).

Instantly the car was much more nimble and willing to change direction. One caveat is that I went from a diffeerent brand tyre on each corner to a set of new GSD3s which would have made a difference in themselves, but the weight was the biggest difference I expect.

 

[DivineE]

No way on gods green earth would you get a fast time in a 944 at Santa Pod! (maybe on drag tires) my friends 220bhp 200sx which has a similar layout to the 944 would not get traction till the end of 3rd gear even when he was very light with the throttle! Its not a drag strip that works well with road tires! Its like accelarating on ice.

Regards,

Ben

p.s. I'm not putting drag tires on my 944 as it will destroy the gearbox! I'd be happy to use one of those 1/4 mile G-meters on the road though.. when my car is running.

 

[333pg333]

Well as I may have mentioned before(hey it's hard to remember everything when you're a forum junkie.)if GT3's and the like can have massive brakes and some of us will have more hp and a lot more tq in a similar weight car, why shouldn't we have similar sized brakes?

 

[DivineE]

Apart from the cost I suppose there is no reason why we shouldn't but I have to question whether the brakes on the GT3 are really necessary? I feel they have become more of a selling point of the car. I'm sure a set of big reds would give more than adequate braking force.

 

[Neil Haughey]

ORIGINAL: John Sims

ORIGINAL: Neil Haughey



..............I would like to see how quick all these turbo nutter 951's are up the 1/4 mile at Santa Pod.

You'd get more of an idea on a track day. 944's are about the whole package - power/handling/brakes. What is the point of going fast in a straight line? []

Slightly better control over all the variables, maybe, and a direct comparison with other cars on how effective the engine upgrades really are. Granted that a comparison of track times is more interesting to us lot but IMHO the tuners by and large would not be to keen on this because I suspect that they all know that a set of grippy tyres is probably worth more time then £10K worth of engine, and the best "engine" upgrades for track use are probably trans upgrades such as S2 ring and pinion and better / new LSD.

 

[333pg333]

Well the cost may not be quite as frightening as we all think, but I'm in the preliminary phases. The Monoblocks will have better heat dissipation and there's no way that Porsche would have put them on if they weren't superior IMHO. Maybe it will be overkill, I'm not sure at this stage, but I will have my current car back on the road in the next 10 days or so and then I will be able to start testing the BR's on the front, S4's on the rear. I'm confidant that the current engine will have 400hp comfortably so that should be a good test. I may be just dealing with quite a lot more hp than that later on this year that's why I'm making the enquiries re the 6 pots now. Will have to find a bigger Master Cylinder to go in too.

 

[MarkK]

The six pot brakes are amazing on the Gt3s,everyone swaps to solid discs now though either Alcon,Brembo or Performance friction as the standard porsche discs don't last long when driven hard,they tend to crack,the six pot upgrade was needed as the original GT3 mk1 4 pot settup tended to overheat(on a gt3) unless you were ginger with them or had ventilation upgrades.I have 964 cup car calipers on my tuned turbo and for me they are more than enough for regular trackdays,although some harder pads might be nice.Brakes and suspension were the first thing on my shopping list, if careful no real problems with laying the power down (in the dry anyway)[] and it stops really well.

 

[Hilux]

Unsprung weight.

My flabber is well and truly gasted at that one [&o][&o][&o]

No-one puts on smaller brakes to lose unsprung weight. Lighter (billet alloy) perhaps so as to uprate but keep a similar weight but you do need bigger brakes with more power. As I stated before greater momentum/speed requires a greater corresponding heat loss to lose the energy increase. Bigger brakes dissipate heat better.

Unsprung weight is more critical in outboard wheels on light cars a la westy`s and F1 cars, less so when inboard like ours.

 

[Riverside]

ORIGINAL: Hilux
Unsprung weight is more critical in outboard wheels on light cars a la westy`s and F1 cars, less so when inboard like ours.

I don't know where you're coming from with the outboard vs inboard wheels bit, but I certainly agree that the proportion of sprung to unsprung weight is a factor in how much effect increasing unsprung weight has on the car's behaviour. The lighter the car the more difference increasing unsprung weight by a given amount makes.

ORIGINAL: Hilux
Why have brakes that are on their limits when you could (SHOULD) have brakes that are well within their performance parameters for the additional massive kinetic energy increase that can only be lost via heat dissipation.

To answer more fully, one of the reasons for not having the biggest available brakes is to avoid increasing unsprung weight (another is cost). It's a compromise, not win-win situation. I'm sure most here would argue that the benefit of BBs outweighs any downside, but to imply that it's a no-brainer is foolish imo.

The benefit of bigger brakes & more consistent stopping power needs to be balanced against the detrimental effect to the roadholding (keeping the tyre in contact with the road) of increasing the unsprung weight. The same problem applies to big wheels, which of course would be needed to fit over BBs.

Add big wheels & big brakes to a car without altering the springs & shocks to suit could be problematic, the suspension needs to be tuned to work with the masses at both ends of the spring/shock, not just the body. The effect is quite noticeable as Fen describes of his MX-5, I had the same issue with my old lux when I replaced the original 15" wheels, I just put the original wheels back on to solve the problem rather than changing the suspension though, it was cheaper []

It's been a reccuring theme throughout this thread, one needs to consider what effect a change will have on the rest of the car.

I hope your Flabber is feeling better []

 

[sawood12]

You've got to look at more modern Porsches and compare weights and power output when sizing brakes. The GT3m2 is hardly a shabby handler, and in any case I doubt the 6-pot calipers weigh much more than the big black/reds if any more at all. And similarly I doubt the 350mm dia disks are much heavier than the 330mm disks - unless they are much thicker. In anycase I think unsprung weight becomes more of an issue on lighter cars e.g. Lotus Elises, Westfields etc as they have less body weight to handle the unsprung wieght and keep it under control. At the weight of a 944 a couple of extra pounds at each corner is not going to make much of a difference at all assuming your suspension is in good nick.

 

[nick_968]

I am pretty sure the bigger brakes will be considerably heavier, but if anyone has the figures I would be interested to know for sure. Question is when do the tyres become the limiting factor to how much extra braking power can acutally be put down to the ground?

 

[sawood12]

Well strangly enough too much rubber can actually impede braking performance as the weight of the car is spread over a larger area. Narrower tyres have more pressure exerted on them and as long as you don't overexert them you will get more grip (i.e. similar to F1 cars improving braking due to more aerodynamic downforce).

I think you'd be surprised about the weights though. The Big Blacks are considerably bulkier than the 6-pots which are quite slim really, and being a one piece casting rather than four seperate castings bolted together with four huge steel bolts the weight difference will be less than you think. Don't know the numbers but i'd be willing to bet there isn't alot in it. The piston sizes are much smaller also on the 6 pots also.

 

[Riverside]

ORIGINAL: nick_968

I am pretty sure the bigger brakes will be considerably heavier, but if anyone has the figures I would be interested to know for sure. Question is when do the tyres become the limiting factor to how much extra braking power can acutally be put down to the ground?

Provided you can push the pedal hard enough to lock the wheels at your initial speed (ie so you can limit brake all the way) the tyres are the only factor (ignoring aerodynamics). Better brakes just mean you can do it more before they cook (or that they never cook).

To stop sooner on a given surface you need stickier tyres. Oddly I don't think weight or tyre width come into it, or at least maybe they aren't significant. I don't fully understand why though.

 

[Riverside]

ORIGINAL: sawood12

Well strangly enough too much rubber can actually impede braking performance as the weight of the car is spread over a larger area. Narrower tyres have more pressure exerted on them and as long as you don't overexert them you will get more grip (i.e. similar to F1 cars improving braking due to more aerodynamic downforce).

I think you'd be surprised about the weights though. The Big Blacks are considerably bulkier than the 6-pots which are quite slim really, and being a one piece casting rather than four seperate castings bolted together with four huge steel bolts the weight difference will be less than you think. Don't know the numbers but i'd be willing to bet there isn't alot in it. The piston sizes are much smaller also on the 6 pots also.

I think we're talking about the same thing Sawood, your explanation about pressure makes more sense than mine.

It's the total surface area of the pots that's important, the number of pots just allows the pressure to be more evenly distributed (important, but less important than total leverage).

 

[333pg333]

Well this is what I could come up with at short notice. These are all just fronts:

S4: 304x32mm @14lbs (rotor wieght). Pad area 112.5 cm2
BB: 322x32mm @18lbs (rw) Pad area 151 cm2
GT2: 330x34 @27lbs Pad area 153cm2

So you can see that the BR/BB's are the best single upgrade v's extra rw conceded and I don't have the weight of the larger 350 rotors either. So there are significant increases in unsprung weight to be considered. However let us also assume that I will have lightweight wheels and they will be probably 10" f and 12" r with an engine power output of approx 600hp crank, at least that in tq, and a lighter body, but adding a cage. Surely I can justify running these brakes no?