Trebor69

Hello All

I have now finished my engine/ecu/turbo/suspension upgrades on my MY93 WRX and now feel its times I gave it some damn good braking power.

Currently running Subaru 4 pots at front with Blackdiamond grooved discs with tarox pads, and subaru two pots at back with tarox pads and standard discs.

My wheels are Kahn RSR's 5-spoke 17"

I have been looking at the AP racing or Tarox 6pot kit with grooved 330's dics for the front.

Will these fit under my wheels?
Will these get rid of my fading under heavy conditions?
What kind of braking performance will I get compared to what I have


For the rear I have considered either :-

Using same size dics but AP or Tarox ones with grooves, or going the whole hog and fittting a 330 size disc that uses the existing 2 pot caliper.

Has anyone done this upgrade and what was your feeling on it??

I am also wondering if I put the 330 6-pot kit on front and keep the rear discs standard size but grooved will this affect the braking balance of the car.

All info will be so greatly appreciated.

Cheers

Rob

MaDaSS

I would be interested in this too. I have a StopTech 330mm kit on the front of my MY03 WRX, but my rears are standard everything. I have often wondered if i have upset the braking balance or i need better on the rear too?
Any ideas oh wise folks?

Trebor69

Has no one out there ever put 6 pots on a scooby then LOL

Come on please

Cheers

Rob

Skippy1

ALCON do a really good kit ,as well as AP. It all depends on how big your budget is.....

dazc

I have a 330mm AP 4 pot conversion. I'm chuffed to bits with the stopping power and the confidence they give you at any speed. Sometimes find myself just pressing the brake for no reason just cos I like 'em so much.


Will these fit under my wheels? - Don't know, you need 17" wheels as a minimum

Will these get rid of my fading under heavy conditions? - Almost certainaly. I've never even got close to fading them.

What kind of braking performance will I get compared to what I have -

Big difference. They wipe speed off so quickly you dont even need to consider upgrading the rears, (unless they are knackered). Balance is fine, I wouldn't change the rear disc size either. Your current pads should be fine.

Can't imagine what a 6pot kit is like. Seems a bit like serious overkill to me!

Hope that helps you out a bit Rob. Daz

Matthew

If you want to check if the AP's will fit then go to their web site http://www.apracing.com/roadcar/brakekit/wheel.htm where they have templates you can print out and try against your wheels. I've got the 17" Subaru wheels on my MY95 and they fit fine over AP 4 pots.

Matthew

Trebor69

Cheers for the replies chaps

This gives me something to go on, I'd rather go from the horses mouth so to speak rather than someone trying to sell me it!!

I can get AP's 6 pots kit for about 1300 + V.A.T so this is my budget. Just spent X@+X!!! on New STI block, Gems ECU, Turbo, Exhaust and many other mods and running 340BHP with 340LB Torque so need some serious stopping power now....

DAZ, what brakes were you running on front before you went to the 4 - pot 330's?

Also considering just putting grooved/vented discs on rear with uprated pads...

Cheers

Rob

awd wrx

Godspeed are doing good deals on AP calipers kits at the mo , I seen them fitting a 335mm AP 6 pot kit to a Skoda Octavia Taxi TDi ( yes you did read that right ) last week , the kit cost the guy £1250 , this was using the Godspeed discs as they are slightly bigger at 335mm x 32mm which is about the biggest you can go under 17" wheels.

They also do a big disc kit for the back but I think its only the classic models with the single piston calipers fitted that the kit fits

dazc

Standard Impreza 4 pots. Also have Gems, FMIC ect similar spec to you and the brakes could cope with more. I would upgrade the fronts and see what you think before doing the rears as well.

In my opinion, the fronts seem to work so well at wiping off speed it seems that you are not braking for as long and the rears dont tend to heat up, but I could be wrong. Uprated pads at the back at the most I reckon.

Also £1300+vat seems very good value for 6pots. Go for it. Daz

bighead

iTrader: (1)

Had Alcons on my P1...then upgrade them to AP 355mm 6 pots the APs about 50% better than the Prodrive Alcons

Hoppy

The disc is at the heart of any braking system. Calipers and pads matter, of course, but unless the disc can take the heat, it doesn't make any difference what's doing the squeezing.

First thing is be certain to get two-piece discs with alloy bells so they won't warp, and make sure they're as big as you can fit, ie 330mm APs under 17in wheels for maximum leverage. For preference get alloy calipers, also from AP, and make sure they have sealed pistons that won't get bunged up with road crap. Then choose your pads to suit your driving - most people go for Ferodo DS2500 as a great all-rounder. I prefer Pagid RS421 but wouldn't argue.

If you go the AP route, make sure you get an offical AP kit, and not a box of AP parts. You want their 330 x 28mm disc with 48 vanes (not 24 as on some cheaper kits). Godspeed also have a good reputation, and are good value. And give Alyn at AS Performace a call - always good advice, good prices and service. Posts as Stockcar on here.

If the rears are working ok, just uprate the pads. They don't do that much work, and the harder the fronts are stopping, so the less traction you've got for braking at the rear due to massive weight transfer. But the cooling is very poor at the rear and they do get hot. On second thoughts, I think the rears are solid on your car so upgrading to vented discs as fitted to later cars would be a good move. You'll need wider calipers then, I think.

Once you've had really good brakes, you'll never look back. Hard stopping is fun unless you're a passenger and brakes like these inspire great confidence.

I have AP 6-pots on a Classic and did some timed stops with my son on the stop watch. 100-zero in 3.2 secs, ABS on all the time, scarily violent I think that's 1.3g. Sorry for the lecture now, but don't try this unless you know exactly what you are doing, and the road is deserted, dry, and dead straight.

Richard.

MaDaSS

fukcing bollox, and i thought my StopTech kit was good
I still wish i had bought AP though, LOL.

Trebor69

Interesting read Richard, Cheers Mate

Keep it coming....

It looks like I will be going 6 Pot 330mm on Front the 48Vane AP kit, and uprate the rear discs to grooved and vented and change the pads to suit..

100 - 0 In under 4 seconds wow

Rob

Hoppy

Rob, you're welcome

Yes, big brakes do stop you quickly and my 100-0 time is quite impressive. It's absolutely true and we did it a few times, but you will find it very hard to replicate on public roads for reasons I'm not prepared to disclose

But you could get quite close to that even with OEM brakes. They are designed to do an emergency stop from motorway speeds at least. The real difference is they are not designed to do another emergency stop within a few seconds, which is why they give you such grief on a track day.

The biggest benefit of serious brakes is that they will stop you time and again, with absolute confidence. This is only possible because they can absorb the heat, and then disperse it again before the next corner. AP discs have turbo-venting which sucks air through the vents as the wheel turns.

Brakes are often overlooked as simple things that don't require much thought, but a mate did some calcs a while back and as I recall, the energy required to stop from 100mph in that time could boil three kettles of water in three seconds Looked at another way, how much horsepower would it take to launch a Scoob to 100mph in under 4 seconds? That's F1 fast and they kick out 900bhp for a car weighing only 600kg. A Scoob is double that and more, so maybe something close to 2,000bhp? Makes you think.

Richard.

dazc

100-zero in 3.2 secs

Holy ****. Thats impressed me. Daz

LoFi

Must agree with Hoppy on the rear brakes. I have 6 pots on 330 disks and thought it would upset the brake balance, but with the extra braking force the rears do very little work. In fact the back can go quite light through massive and quick weight transfer and needs to be kept under control on a bumpy road. You really need harnesses to use them properly. If Hoppy's 1.3G is right that it too much to just rely on the seatbelt and the wheel.

LoFi

stockcar

the fact the rear of your car goes light is because of the weight transfer caused by a brake imbalance not because the rears do anything........................

you will get a great benefit from upgrading the rears to re-balance the car and allow you to brake even harder whilst maintaining better control over the pitch of the car by keeping the car flatter under braking..................

alyn

Trebor69

Happy for all the feedback chaps...

So would upgrading the rear to 330 grooved vented discs using existing calipers be a good compromise or are you talking new calipers as well Alyn??

Cheers

Rob

stockcar

no need to go mad, depends on how far you go with the fronts!!

there aren't many proper upgrades fro the rear available (Tarox for one do a bigger rear disc conversion if needed)............as a min. a set of beter rear pads will help, after that it depends on model - something like the 2pot rear and type-R 290mm discs is a good set-up but can be a pain to adapt on std cars..........

Trebor69

LOL

Well i am deffo considering the AP 6 pot kit with 330 discs with 48 Vanes, a bloke local has got them on his classic with speedline 17" alloys, so going to meet up and put my wheel on his car to make sure they will fit ok with my Kahn 17x7 RSR's. If they do thats what I am having I reckon.... I need new rear discs any way, have been running Tarox rear pads allready. So would same size rear discs, but grooved/vented if posss with better pads be a good compromise in your opinion???

Cheers

Rob

dazc

If you upgrade the rears with bigger discs, wouldn't the extra power they give just cause them to lock up under hard braking?
The uprated fronts will still be trying to stand the car on its nose!

Trebor69

I did wonder this cos even with my standard size discs with subaru 4 pots, the discs are grooved/drilled/vented with Tarox pads. Under heavy braking the back end of car goes so light you feel it may swing round on you if that makes sense

Rob

Hoppy

Stockcar is taking the debate to a different level

I would contest that under very heavy braking, the rears contribute more to stability than stopping. But that is more of a guess than anything else. My car was a bit frisky when I had Ferodo DS2500 pads in the front and DS2000 in the rear, which is one of the reasons I moved to Pagid RS421 for the front. I know from experience that these pads require more pedal pressure so therefore that was an automatic change of brake bias in favour of working the rears harder. I moved this a stage further by fitting DS2500 pads in the rear as they have a higher friction coefficient over DS2000 and I reckoned this would work the rears a little bit harder still.

I'm quite happy with my car's brake bias now, and don't know of an easy way to push the bias further back to experiment a bit more. Fitting bigger discs or uprated calipers is very difficult, ie expensive, or impossible. To fit the Subaru 2-pot rears you have to fit new drive-shafts, I believe. I was told by AP that they were going to market a rear upgrade kit before Xmas but I've not yet heard anything. Alyn, have you?

There are also other considerations, such as the benefit of better modulated braking during slower stops that more powerful rears would give. But the last thing you want is the rears breaking away in the wet... Ideally, you want variable brake bias, which is what you often see Mr Schumacher twiddling with. At least we've got ABS which should get us out of the worst situations.

Taking this a bit further, I have a revised brake bias valve which was made up by a fellow ScoobNetter. He contends that significantly increased rear braking has great benefits. I have not fitted the new valve as I am happy with the ways things are and I am not convinced 100% that shifting the brake bias a lot more would be a good thing overall, ie in all driving situations, wet or dry, hard or gentle braking, track days and commuting. Also, if the worst should happen, I wonder what an insurance company would say if they found out you'd removed the factory's bias valve

Alyn, what's your take on this and how would you suggest we take it forward?

Thanks,

Richard.

PS My car is a UK00 with those nasty 1-pot sliding calipers in the rear. They are painted black so I can't see them, and what the eye doesn't see...

stockcar

have to dash so just a quickie (ooh err!!).................

basically the reason for the locking rears is because they have no weight over them and therefore you get to the edge of the envelope of the tyres grip (not braking ability!!), this is caused because of the extra forward weight transfer under extreme or uprated front braking (or both)...............

to help the car stop faster you need to keep more weight on the rear wheels, giving the front tyre an easier life and bringing it back from its locking limit.........and keeping the cars attitude "flatter"...............

to do this you upgrade the rears (pads/discs/etc) this 'pulls' the rear of the car down under heavy braking allowing you to brake harder as you share the load between the front and rear tyres............

hope this is a bit clearer
alyn

Matthew

Sorry, but upgrading the rear brakes won't do anything for the weight transfer. Take a look at the Physics of Racing http://www.miata.net/sport/Physics/ for a full explanation of what happens when you brake. If you want to reduce the transfer then you need to either lengthen the wheelbase, or lower the centre of gravity - neither of which is really practical without major work.

Matthew

Trebor69

Wahoo !! , This is all getting technical, Just what I wanted, Cheers Chaps.. Keep it coming.......

I do want to make the right decision here as It will mean spending mega bucks on my Scoob again!!!!!

Rob

Hoppy

Alyn, are you out of the toilet yet?

I understand what you're saying, but in practical terms, how can we get more braking to the rear of a Scoob? ie, what new bits can you sell me

Mathew, that's one hell of a link I'll try and read it sometime. But in practise, if you've got more braking in the rear the car will stop flatter. Until I'm proved wrong, I still say that the biggest advantage provided by a bit more bite from the rear brakes is in stability, not stopping, but there must be a useful contribution to stopping also, if that makes sense.

Imagine for a moment that instead of a rear brake you throw a parachute out of the back. That would hold the rear down, and also raise the nose, wouldn't it? Isn't that what the rear brakes are doing?

Richard.

PS Calling Harvey!

PPS And Mike Wood will have something interesting to say on this.

Matthew

Hoppy

Given fixed CofG stopping flatter is more to do with suspension geometry - anti dive/squat. Maximum retardation is achieved when all the wheels are just on the point of locking. That's why you see the F1 drivers fiddling with the balance. As the fuel load in the car changes and the brakes wear, the optimum braking force to each end of the car also changes.

The last thing you want is the rears locking before the fronts which is why some cars (I don't know about Imprezas) adjust the bias depending on how hard you are braking - my old Gordini Turbo had a link from the rear suspension to a bias adjuster, which basically moved the bias forward as the rear of the car lifted.

I'd agree under heavy braking the rears contribute more to stability than stopping. Coming from a motorcycling background it somehow feels better to have some rear brake even when the back wheel is 6" off the ground

The main reason I'd see for upgrading the rears is if they overheat (probably only applicable on track), in which case going to vented disks would be a definite advantage.

On the parachute - it depends where it is attached. If you imagine it on a long pole on top of the car then it will tend to pull down on the back and lift the front, if attached nearly at ground level then it will pull the back higher, and if in line with the CofG then it should be almost neutral.

Matthew

Hoppy

Bu99er! Just written a long and fascinating reply about how Mike Hailwood and Valentino Rossi defy the laws of physics, and my internet connection went down.

More relevant is how big the rear brakes are on a 911, which I'm sure has got more to do with keeping the front ahead of the back, but it also happens to slow the car very well (and Porkers do stop very well), and keeps the car level.

So, getting back on topic, what benefits are to be had by putting more braking effort through the rear wheels of a Scoob, in all driving situations, and how can they be realistically achieved? (All Scoobs since 1999 have vented rears.)

Richard.

dazc

More relevant is how big the rear brakes are on a 911...


....Not forgetting where the engine is on one of those, behind the rear wheels no less. A parachute in itself.

More braking effort to the rear wheels on an Impreza would just lock them up (theoretically). The abs pump would compensate for this by just reducing the pressure to them. Ie, less braking but more control.

To get more braking from the rear, you would need to keep the car flatter and hence put more weight over the rear.

Cue stiffer suspension components. All well and good up to a point, but how stiff will your car need to be to keep it virtually flat under maximum braking.
Rally cars run massive rear brakes as do touring cars. But I shouldn't imagine either would make a pleasant daily driver..Stop well enough though..

Vented discs probably wont give better braking at the rear either, but will give more consistant braking, as they will naturally handle the heat better of a few consecutive hard stops. If they are not vented I would change them Rob, and put some pads in that can handle a bit of heat. Should sit just nicely with your shiny new AP's.
You will have good stopping power.

Upgrading the rear disc size on a road car seems pointless to me.
Read this, it's not too bad...

http://www.stoptech.com/whitepapers/...tter120601.htm

Daz